Los Altos City Council
June 23, 2026

CITY COUNCIL SPECIAL

MEETING
AGENDA
June 23, 2026 - 5:00 PM
In Person
Members of the public may participate by being present at the Los Altos Council Chamber at Los Altos City Hall located at 1 N. San Antonio Rd, Los Altos, CA during the meeting. Public comment is accepted in person at the physical meeting location, or via email to [email protected].

RULES FOR CONDUCT: Pursuant to Los Altos Municipal Code, Section 2.05.010 "Interruptions and rules for conduct": Understanding that the purpose of the city council meetings is to conduct the people's business for the benefit of all the people, in the event that any meeting of the city council is willfully interrupted by a person or group of persons so as to render the orderly conduct of the meeting impossible, the mayor, mayor pro-tem, or any other member of the city council acting as the chair may order the removal of the person or persons responsible for the disruption and bar them from further attendance at the council meeting, or otherwise proceed pursuant to Government Code Section 54957.0 or any applicable penal statute or city ordinance.

REMOTE MEETING OBSERVATION: Members of the public may view the meeting via the link below, but will not be permitted to provide public comment via Zoom or telephone. Public comments will be accepted in person, and members of the public may submit written comments by following the instructions below. https://losaltosca-gov.zoom.us/j/99500114824?pwd=jMgxOG4mx6S6nub4hmkaTlxqBvpkji.1 Telephone: 1-669-444-9171 / Webinar ID: 995 0011 4824 / Passcode: 327692 SUBMIT WRITTEN COMMENTS: Prior to the meeting, comments on matters listed on the agenda may be emailed to [email protected]. Emails sent to this email address are sent to/received immediately by the City Council. Emails sent directly to the City Council as a whole or individually, and not sent to [email protected] will not be included as a public comment in the Council packet.

Please note: Personal information, such as e-mail addresses, telephone numbers, home addresses, and other contact information are not required to be included with your comments. If this information is included in your written comments, they will become part of the public record. Redactions and/or edits will not be made to public comments, and the comments will be posted as they are submitted. Please do not include any information in your communication that you do not want to be made public. The Mayor will open public comment and will announce the length of time provided for comments during each item.

AGENDA

CALL MEETING TO ORDER

ESTABLISH QUORUM

STUDY SESSION

1. Halsey House Project Draft Environmental Impact Report (EIR) Study Session Direct staff to work with David J. Powers & Associates, Inc. (Consultant) to prepare Final EIR (FEIR). If the FEIR is certified and the project is approved, the City shall file a Notice of

Determination

ADJOURNMENT

SPECIAL NOTICES TO THE PUBLIC
In compliance with the Americans with Disabilities Act, the City of Los Altos will make reasonable arrangements to ensure accessibility to this meeting. If you need special assistance to participate in this meeting, please contact the City Clerk 72 hours prior to the meeting at (650) 947-2610.

City Council Staff Report
Meeting Date: June 23, 2026
Prepared By: Harun Musaefendic
Approved By: Gabe Engeland
Subject: Halsey House Project Draft Environmental Impact Report (EIR) Study Session

COUNCIL PRIORITY AREA
General Government

RECOMMENDATION
Direct staff to work with David J. Powers & Associates, Inc. (Consultant) to prepare Final EIR (FEIR). If the FEIR is certified and the project is approved, the City shall file a Notice of Determination

ENVIRONMENTAL IMPACT
The City Council’s action in holding a study session and providing staff direction is statutorily exempt from review under California Environmental Quality Act (CEQA) pursuant to CEQA Guidelines Section 15262 (Feasibility and Planning Studies), in that any direction from Council will be tentative pending further analysis by City officials and final action by the City Council.

FISCAL IMPACT
Future fiscal impact associated with the Halsey House project will be determined by the treatment method for the existing structure and future use.

PREVIOUS COUNCIL CONSIDERATION
May 9, 2023; April 25, 2023; November 30, 2021; September 21, 2021; May 25, 2021; March 23, 2021; January 12, 2021; December 15, 2020; January 28, 2018; November 15, 2016; June 14, 2016; December 8, 2015; April 23, 2013.

BACKGROUND
Funding for the Halsey House CEQA Analysis was appropriated at the Council Meeting held on May 9, 2023. Authorizing the City Manager to execute an agreement not to exceed $200,000 with an environmental consultant to perform the CEQA analysis was granted at the same Council Meeting. On October 13, 2023, City of Los Altos entered into a professional services agreement with the Consultant for the preparation of an Environmental Impact Report (EIR) for Halsey House. Environmental Impact Report is an information document that assesses potential environmental impacts of a proposed project, as well as identifies mitigation measures and alternatives to the proposed project that could reduce or avoid adverse environmental impacts.

ANALYSIS
Consultant and City Staff have worked on the CEQA analysis since the agreement was executed

in October 2023. Notice of Preparation (NOP) of a Draft Environmental Impact Report (EIR) was circulated on February 12, 2025, with a review period of thirty (30) days concluding on March 14, 2025. Consultant and City Staff gathered comments during the NOP circulation period and have included them in the Draft EIR. Draft EIR was circulated on June 11, 2026, with a review period of forty-five (45) days concluding on July 27, 2026. Consultant and City Staff will gather comments during the Draft EIR circulation period and will include them in the Final Environmental Impact Report.

DISCUSSION
The proposed project evaluated in the Draft EIR is the demolition of the Halsey House and restoration of the site with native landscaping. The Draft EIR summarizes significant environmental impacts, and the mitigation measures proposed to avoid or reduce those impacts.

The Draft EIR also identifies five (5) alternatives to the proposed project that could reduce or avoid adverse environmental impacts. The five alternatives are:

No Project Alternative (retain the existing Halsey House as-is), Preservation Alternative 1 – Relocation of Historic Resource Off-Site, Preservation Alternative 2 – Full Rehabilitation of Historic Resource, Preservation Alternative 3 – Partial Rehabilitation/Partial Demolition, Preservation Alternative 4 – Mothballing.

The proposed project was selected as this option represents the broadest range of potential impacts among the alternatives currently under consideration. By evaluating that scenario, and then studying multiple alternatives against it, the Draft EIR provides the City Council and the public with the most comprehensive information possible regarding the environmental consequences, benefits, and tradeoffs associated with each option. The City Council is required to consider the information in the Draft EIR in deciding whether to approve the project, but the Draft EIR does not recommend either approval or denial of a project.

ATTACHMENTS

1. Attachment 1 - Halsey House Draft EIR

2. Attachment 2 - Appendix A Notice of Preparation and Comments

3. Attachment 3 - Appendix B CalEEMod Halsey House Demolition Project Detailed Report

4. Attachment 4 - Appendix C Biological Resources Report

5. Attachment 5 - Appendix D Historic Resources Evaluation

6. Attachment 6 - Appendix E Geotechnical Investigation

7. Attachment 7 - Appendix F Hydrologic Evaluation

8. Attachment 8 - Appendix G Relocation Feasibility Study

9. 06-23-2026 Written Public Comment

DraŌ EIR
SCH #: 2025020308
Halsey House Project
June 2026
In ConsultaƟon with
Prepared by
Attachment 1 - Halsey House Draft EIR

Halsey House Project, SCH# 2025020308 i Draft Environmental Impact Report City of Los Altos June 2026
Table of Contents
Section 1.0 Introduction and Purpose ............................................................................................ iii Section 2.0 Summary ....................................................................................................................... v Section 3.0 Project Information and Description ............................................................................1 Section 4.0 Environmental Setting, Impacts, and Mitigation..........................................................6

4.1 Aesthetics ...............................................................................................................................9

4.2 Agriculture and Forestry Resources .....................................................................................17

4.3 Air Quality .............................................................................................................................21

4.4 Biological Resources.............................................................................................................34

4.5 Cultural Resources................................................................................................................46

4.6 Energy ...................................................................................................................................59

4.7 Geology and Soils..................................................................................................................62

4.8 Greenhouse Gas Emissions...................................................................................................70

4.9 Hazards and Hazardous Materials........................................................................................74

4.10 Hydrology and Water Quality ...............................................................................................83

4.11 Land Use and Planning..........................................................................................................90

4.12 Mineral Resources................................................................................................................93

4.13 Noise .....................................................................................................................................95

4.14 Population and Housing......................................................................................................102

4.15 Public Services ....................................................................................................................104

4.16 Recreation...........................................................................................................................109

4.17 Transportation....................................................................................................................111

4.18 Tribal Cultural Resources....................................................................................................115

4.19 Utilities and Service Systems..............................................................................................118

4.20 Wildfire ...............................................................................................................................123 Section 5.0 Growth-Inducing Impacts .........................................................................................125 Section 6.0 Significant and Irreversible Environmental Changes................................................126 Section 7.0 Significant and Unavoidable Impacts........................................................................127 Section 8.0 Alternatives...............................................................................................................128 Section 9.0 References ................................................................................................................141 Section 10.0 Lead Agency and Consultants...................................................................................146 Section 11.0 Acronyms and Abbreviations....................................................................................147

Halsey House Project, SCH# 2025020308 ii Draft Environmental Impact Report City of Los Altos June 2026
Figures
Figure 3.1-1: Regional Map....................................................................................................................2 Figure 3.1-2: Vicinity Map......................................................................................................................3 Figure 3.1-3: Aerial Photograph, Project Boundary, and Surrounding Land Uses.................................4 Photos
Photo 1: Photo of existing building......................................................................................................11 Photo 2: Photo of existing building and pathway................................................................................11 Photo 3: Photo of Adobe Creek. ..........................................................................................................12 Photo 4: Photo of redwood trees and pathways in the surrounding area..........................................12 Photo 5: Photo of pedestrian bridge. ..................................................................................................13 Photo 6: Photo of entrance to Redwood Grove Nature Preserve.......................................................13 Tables
Table 4.0-1: Cumulative Projects List.....................................................................................................7 Table 4.0-2: Geographic Considerations in Cumulative Analysis...........................................................8 Table 4.3-1: Sources and Health Effects of Criteria Air Pollutants and Toxic Air Contaminants.........22 Table 4.3-2: Bay Area Air District Air Quality Significance Thresholds................................................27 Table 4.3-3: Bay Area Air District Health Risks and Hazards Thresholds.............................................27 Table 4.3-4: Average Daily Emissions Demolition Criteria Pollutant Emissions ..................................29 Table 4.13-1: Groundborne Vibration Impact Criteria ........................................................................96 Table 4.13-2: Exterior Noise Limits......................................................................................................97 Table 4.13-3: Vibration Levels for Typical Construction Equipment .................................................100 Table 8.2-1: Comparison of Impacts from Alternatives to the Proposed Project .............................140 Appendices
Appendix A: Notice of Preparation and Comments Received Appendix B: California Emissions Estimator Model Report Appendix C: Biological Resources Report
Appendix D: Historic Resources Evaluation
Appendix E: Geotechnical Investigation
Appendix F: Hydrologic Evaluation
Appendix G: Relocation Feasibility Study

Halsey House Project, SCH# 2025020308 iii Draft Environmental Impact Report City of Los Altos June 2026
Section 1.0 Introduction and Purpose

1.1 Purpose of the Environmental Impact Report
An Environmental Impact Report (EIR) is an informational document that assesses potential environmental impacts of a proposed project, as well as identifies mitigation measures and alternatives to the proposed project that could reduce or avoid adverse environmental impacts (CEQA Guidelines 15121(a)). As the CEQA Lead Agency for this project, the City of Los Altos is required to consider the information in the EIR along with any other available information in deciding whether to approve the project. The basic requirements for an EIR include discussions of the environmental setting, significant environmental impacts including growth-inducing impacts, cumulative impacts, mitigation measures, and alternatives. It is not the intent of an EIR to recommend either approval or denial of a project.

1.2 EIR Process

1.2.1 Notice of Preparation and Scoping
In accordance with Section 15082 of the CEQA Guidelines, the City of Los Altos prepared a Notice of Preparation (NOP) for this EIR. The NOP was circulated to local, state, and federal agencies on February 12, 2025. The standard 30-day comment period concluded on March 14, 2025. The NOP provided a general description of the proposed project and identified possible environmental impacts that could result from implementation of the project. Appendix A of this EIR includes the NOP and comments received on the NOP.

1.2.2 Draft EIR Public Review and Comment Period
Publication of this Draft EIR will mark the beginning of a 45-day public review period. During this period, the Draft EIR will be available to the public and local, state, and federal agencies for review and comment. Notice of the availability and completion of this Draft EIR will be sent directly to every agency, person, and organization that commented on the NOP, as well as the Governor’s Office of Planning and Research (OPR). Written comments concerning the environmental review contained in this Draft EIR during the 45-day public review period should be sent to:

Harun Musaefendic
Public Works Department
City of Los Altos
1 N. San Antonio Road
Los Altos, CA 94022
[email protected]

Halsey House Project, SCH# 2025020308 iv Draft Environmental Impact Report City of Los Altos June 2026

1.3 Final EIR/Responses to Comments
Following the conclusion of the 45-day public review period, the City of Los Altos will prepare a Final EIR in conformance with CEQA Guidelines Section 15132. The Final EIR will consist of:
• Revisions to the Draft EIR text, as necessary;
• List of individuals and agencies commenting on the Draft EIR; • Responses to comments received on the Draft EIR, in accordance with CEQA Guidelines (Section 15088);
• Copies of letters received on the Draft EIR.

Section 15091(a) of the CEQA Guidelines stipulates that no public agency shall approve or carry out a project for which an EIR has been certified which identifies one or more significant environmental effects of the project unless the public agency makes one or more written findings. If the lead agency approves a project despite it resulting in significant adverse environmental impacts that cannot be mitigated to a less than significant level, the agency must state the reasons for its action in writing. This Statement of Overriding Considerations must be included in the record of project approval.

1.3.1 Notice of Determination
If the project is approved and the EIR is adopted, the City of Los Altos will file a Notice of Determination (NOD), which will be available for public inspection and posted at the County Clerk’s Office and the State Clearinghouse for public review for 30 days. The filing of the NOD starts a 30- day statute of limitations on court challenges to the approval under CEQA (CEQA Guidelines Section 15094(g)).

Halsey House Project, SCH# 2025020308 v Draft Environmental Impact Report City of Los Altos June 2026
Section 2.0 Summary

2.1 Summary of Project
The project site is located at 482 University Avenue in Los Altos within the six-acre Redwood Grove Nature Preserve (Preserve). The Preserve is surrounded by single-family residences. The Halsey House, built in 1923, is a local Historic Landmark and is eligible for the California Register of Historic Resources (CRHR). The Halsey House is currently boarded up, and a locked fence surrounds the building to secure the site and prevent intruders. The project proposes to demolish the Halsey House building.

2.2 Summary of Significant Impacts
The following Table 2.2-1 is a summary of the significant environmental impacts identified and discussed in the EIR, and the mitigation measures proposed to avoid or reduce those impacts. The project description and full discussion of the impacts and mitigation measures can be found in Section 3.0 Project Information and Description and Section 4.0 Environmental Setting, Impacts, and Mitigation of this EIR. Alternatives to the proposed project are summarized at the end of this section and described in more detail in Section 8.0 Alternatives.

Table 2.2-1: Summary of Significant Impacts and Mitigation Measures Significant Impacts Mitigation Measures
Biological Resources
Impact BIO-1: Disturbance of the existing
woodrat nests on-site could result in the
destruction of nests and injury or mortality of
individual woodrats. (Less than Significant
Impact with Mitigation Incorporated)
MM BIO-1.1: Pre-Activity Survey. A qualified biologist shall conduct a pre-activity survey for San Francisco dusky-footed woodrat nests within 30 days of the start of work activities. If active woodrat nests are determined to be present in, or within 10 feet of, the impact areas, MM BIO-1.2 and MM BIO1.3 below shall be implemented, as appropriate.

MM BIO-1.2: Avoidance Buffers. Active woodrat nests that are detected in, or within 10 feet of, the impact areas shall be avoided. A minimum 10-foot buffer shall be maintained
between project activities and woodrat nests to avoid
disturbance. In some situations, a smaller buffer may be allowed if, in the opinion of a qualified biologist, nest relocation (MM BIO-1.3 below) would represent a greater disturbance to the woodrats than the adjacent work activities.

MM BIO-1.3: Nest Relocation. If avoidance of active woodrat nests within and immediately adjacent to the work impact is not feasible (e.g., because it would preclude implementation of the project), then nest materials shall be relocated to suitable habitat as close to the project area as possible, as determined and implemented by a qualified biologist (ideally,

Halsey House Project, SCH# 2025020308 vi Draft Environmental Impact Report City of Los Altos June 2026
Significant Impacts Mitigation Measures
within or immediately adjacent to the project site). Relocation efforts shall avoid the peak nesting season (February to July).

Prior to the start of work activities, a qualified biologist shall disturb the woodrat nest to the degree that all woodrats leave the nest and seek refuge outside of the impact area.

Disturbance of the woodrat nest shall be initiated no earlier than one hour before dusk to prevent the exposure of
woodrats to diurnal predators. Subsequently, the biologist shall dismantle and relocate the nest material by hand. During the deconstruction process, the biologist shall assess if there are juveniles in the nest. If immobile juveniles are observed, the dismantling process shall be discontinued until a time when the biologist believes the juveniles will be capable of independent survival (typically after two to three weeks). A no-disturbance buffer shall be established around the nest until the juveniles are mobile. The nest may be dismantled once the biologist has determined that adverse impacts on the juveniles would not occur.

Impact BIO-2: Demolition of the structure onsite would disturb Townsend’s big-eared bats roosting within the structure. (Less than
Significant Impact with Mitigation
Incorporated)
MM BIO-2.1: Bat Exclusion from Halsey House. Prior to the start of any project-related activities on the exterior or interior of the Halsey House building, a qualified bat biologist shall guide and supervise the installation of appropriate exclusion devices to allow any roosting Townsend’s big-eared bats (and other bat species, if present) to vacate the roost and prevent bats from reoccupying these features before
construction activities are initiated. Bird exclusion netting shall not be used because bats may become entangled in it, potentially leading to mortality. Exclusion materials shall be inspected by a qualified biologist once per month between their installation and initiation of building demolition, to ensure that the materials are in good working order. If exclusion materials become compromised, the City shall
perform maintenance on these devices, as directed by the qualified biologist.

Cultural Resources
Impact CUL-1: Implementation of the
proposed project would result in the
demolition of the Halsey House, which is a
historic resource. (Significant and Unavoidable
Impact)
MM CUL-1.1: Historic Resources Mitigation Action Plan. Prior to issuance of any demolition permits, the City shall retain a qualified historian to prepare and submit a Historic Resources Mitigation Action Plan (Action Plan) to the Director of Development Services or the Director’s designee for review and approval. The Action Plan shall include the following elements:

Documentation. The structure and associated features on the project site shall be documented in accordance with the guidelines established for the Level III Historic American Building Survey (HABS) consistent with the Secretary of the Interior’s Standards for Architectural and Engineering
Documentation. The documentation shall be funded by the City and undertaken by a qualified historian who meets the

Halsey House Project, SCH# 2025020308 vii Draft Environmental Impact Report City of Los Altos June 2026
Significant Impacts Mitigation Measures
Secretary of the Interior’s Professional Qualification Standards for history, architectural history, or historic architecture (Code of Federal Regulations, Title 36, Part 61, Appendix A). The documentation shall consist of the following components:

A. Drawings – Original architectural drawings or as-built measured drawings of the building shall be submitted as part of the documentation package. Reasonable efforts
shall be made to locate original drawings of the historic building. If located, selected representative drawings
(such as site plans, elevations, sections, and relevant key details) shall be photographed or scanned at high
resolution, reproduced, and included in the dataset. If original architectural or construction drawings cannot be located, then measured drawings shall be prepared
according to HABS guidelines by a professional who
meets the Secretary of the Interior’s Professional
Qualification Standards for Architecture or Historic
Architecture. The measured drawings shall be reviewed
by the historian retained to prepare the written historical report.

B. Photographs – Digital photographs shall be taken of the historic building, associated landscaping, and the overall character and setting of the property. All digital
photography shall be conducted according to current
National Park Service (NPS) standards as specified in the National Register of Historic Places and National Historic Landmarks Program Consolidated and Updated
Photograph Policy 2024. The photography shall be
undertaken by a qualified professional with
demonstrated experience in documentation
photography. Large format negatives are not required. All photographs shall be referenced on a photographic key
map or site plan. The photographic key shall show the
photograph number with an arrow to indicate the
direction of the view. Digital photographs shall be taken in uncompressed RAW file format and saved as TIFF files.

The size of each image shall be a minimum of 1600x1200
pixels at 300 pixels per inch or larger and in color format.

The file name for each electronic image shall correspond with the index of photographs and photograph label.

C. Written Data – A written historical narrative and report that meets the HABS Historical Report Guidelines shall be produced for the property by a qualified historian. The HABS-Style Historical Report shall follow the outline
format with a statement of significance of the property.

The documentation shall be submitted to the Director of Development Services or the Director’s designee for review and approval. After approval, the required documentation shall be filed with the Northwest Information Center at Sonoma State University (the repository for the California

Halsey House Project, SCH# 2025020308 viii Draft Environmental Impact Report City of Los Altos June 2026
Significant Impacts Mitigation Measures
Historical Resources Information System) and the Los Altos History Museum.

Interpretive Display. Prior to issuance of any demolition permits, the City, in consultation with a qualified historian or architectural historian who meets the Secretary of the
Interior’s Professional Qualification Standards, shall provide plans for interpretive signage for the property to provide historical context and education about the history of the property. The plans shall include the proposed display type(s) and location(s) of the content, as well as high-quality graphics and written narratives that will be incorporated. In addition to narrative text, the interpretive display(s) may include, but are not limited to, a display of photographs, news articles, and drawings. The permanent, high-quality interpretive display(s) shall be installed within the project site boundaries, made of durable all-weather materials, and positioned to allow for high public visibility and interactivity. The signage plan shall be reviewed and approved by the Director of Development Services or the Director’s designee prior to issuance of any demolition permits.

MM CUL-1.2: Salvage. The structure shall be made available for salvage to companies facilitating the reuse of historic building materials prior to the issuance of any demolition permits. The time frame available for salvage shall be
established by the Director of Development Services or the Director’s designee in accordance with the Action Plan. The City must provide evidence to the Director of Development Services or the Director’s designee that this condition has been met prior to the issuance of any demolition permits.

Impact HAZ-1: Demolition of the existing
building could expose construction workers or
residents in the vicinity of the project site to
harmful levels of asbestos-containing materials
or lead-based paint. (Less than Significant
Impact with Mitigation Incorporated)
MM HAZ-1.1: Pre-Demolition Survey. In conformance with
State and local laws, a visual inspection/pre-demolition survey, and possible sampling, shall be conducted prior to the demolition of on-site buildings to determine the presence of asbestos-containing materials and/or lead-based paint.

MM HAZ-1.2: Removal of Asbestos-Containing Materials. All potentially friable asbestos-containing materials shall be removed in accordance with National Emission Standards for Hazardous Air Pollutants (NESHAP) guidelines prior to any building demolition or renovation that may disturb the
materials. All demolition activities will be undertaken in accordance with Cal/OSHA standards contained in Title 8 of California Code of Regulations (CCR), Section 1529, to protect workers from exposure to asbestos. A registered asbestos abatement contractor shall be retained to remove and
dispose of asbestos-containing materials identified in the asbestos survey performed for the site in accordance with the aforementioned standards. Materials containing more than one percent asbestos are also subject to Bay Area Air District (Air District) regulations. Removal of materials containing

Halsey House Project, SCH# 2025020308 ix Draft Environmental Impact Report City of Los Altos June 2026
Significant Impacts Mitigation Measures
more than one percent asbestos shall be completed in
accordance with Air District requirements.

MM HAZ-1.3: Removal of Lead-Based Paint. Prior to
demolition activities, all building materials containing leadbased paint shall be removed in accordance with Cal/OSHA Lead in Construction Standard, Title 8, CCR 1523.1, including employee training, employee air monitoring, and dust control.

Any debris or soil containing lead-based paint or coatings would be disposed of at landfills that meet acceptance criteria for the waste being disposed.

2.3 Significant Unavoidable Impacts
This EIR includes a detailed discussion of the existing setting, impacts, and mitigation measures proposed to protect environmental resources and avoid and/or reduce impacts. The analysis concluded that the proposed project would result in a significant and unavoidable impact to a historic resource. The impact is identified in the EIR as follows:
• Impact CUL-1: Implementation of the proposed project would result in the demolition of the Halsey House, which is a historic resource. (Significant and Unavoidable Impact)

2.4 Summary of Alternatives to the Proposed Project
CEQA requires that an EIR identify alternatives to the project as proposed. CEQA Guidelines Section 15126.6 specifies that an EIR must identify alternatives that would feasibly attain the most basic objectives of the project but avoid or substantially lessen the project’s significant environmental effects or would further reduce impacts that are considered less than significant with the incorporation of identified mitigation. A summary of the alternatives follows. A full analysis of project alternatives is provided in Section 8.0 Alternatives.

The EIR analyzed the following alternatives to the proposed project:
• No Project Alternative
• Preservation Alternative 1 – Relocation of Historic Resource Off-Site • Preservation Alternative 2 – Full Rehabilitation of Historic Resource • Preservation Alternative 3 – Partial Rehabilitation/Partial Demolition • Preservation Alternative 4 – Mothballing

Halsey House Project, SCH# 2025020308 x Draft Environmental Impact Report City of Los Altos June 2026

2.5 Areas of Public Controversy
Areas of public concern identified during the Notice of Preparation (NOP) scoping process include:
• Request for a public scoping meeting
• Reconsider feasibility of equipment access because the eight-ton bridge has potentially deteriorated
• Potential existing creekbank soil contamination from septic tank • Potential existing lead contamination from water pipes • Consultation with Native American tribes that are traditionally and culturally affiliated with the geographic area of the project
• Whether proposed “native plant landscaping” aims to meet aesthetic or ecological restoration needs
• Project should not impact Valley Water’s native plant mitigation site on Adobe Creek at the Jesuit Retreat
• Potential project impact to redwood forest and riparian woodlands, in addition to wetlands

Halsey House Project, SCH# 2025020308 1 Draft Environmental Impact Report City of Los Altos June 2026
Section 3.0 Project Information and Description

3.1 Project Location
The project site is located at 482 University Avenue in Los Altos (Assessor Parcel Number [APN] 175- 30-021). The site is situated within the six-acre Preserve, which is surrounded by single-family residences. Refer to Figures 3.1-1 and Figure 3.1-2 for regional and vicinity maps of the project site.

An aerial photograph showing the project boundary and surrounding land uses is shown on Figure

3.1-3.

3.2 Background
The Halsey House was built in 1923 and was used as a private residence until the property was purchased by the City of Los Altos in 1974 to serve as a park. The building was then converted into a nature center for educational and recreational programming. In 2008, the building was closed to the public. Since 2008, the Halsey House has remained vacant and unused. The building is currently boarded up and surrounded by a locked fence to secure the site and prevent intruders. The Halsey House is a local Historic Landmark and is eligible for the CRHR. As a result, it is considered a historic resource under CEQA.

Since its closure in 2008, the City has explored various treatments for the Halsey House, including full rehabilitation, adaptive reuse, mothballing, and full demolition. This EIR analyzes the impacts associated with full demolition of the building.

3.3 Project Description

3.3.1 Demolition Details
The project proposes to demolish the Halsey House. Demolition activities would occur within an approximately 15,000 square foot (or 0.3 acre) area of disturbance surrounding the building (also referred to as the project boundary) and would last roughly three months. Equipment and workers would access the site via the Preserve entrance on University Avenue. Equipment staging would occur within the proposed area of disturbance. Refer to Figure 3.1.3 for the area of disturbance.

Demolition equipment, such as an excavator and a compact track loader, would be utilized throughout the demolition period. Due to the weight capacity and width (approximately eight tons and 10 feet, respectively) of the pedestrian bridge that crosses Adobe Creek and provides access to the Halsey House, the equipment used for demolition would be small and lightweight. For example, the compact track loader would weigh seven tons and the excavator would weigh six tons.

Base Map: ESRI, ArcGIS.

Saratoga
CuperƟno
Sunnyvale
Palo Alto
Menlo Park
East Palo Alto
Redwood City
Saratoga
CuperƟno
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Los Altos
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East Palo Alto
Redwood City San
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Bay
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280
280
101
101
Project Site
04 .5 6 Miles 3
Pacific Ocean
Monterey Bay
San José Sunnyvale
San Mateo Fremont
Redwood City
Livermore
Oakland
San Francisco
Santa Cruz
Mountain View
Morgan Hill
Project Site
San Francisco Bay
CuperƟno
Los Altos
REGIONAL MAP FIGURE 3.1-1

Lennox Way Fremont Road
Burke Road
Chapin Road
Darling Lane
Burke Lane
East
Sunset
Drive
West Sunset Drive
Manresa Lane
Manresa
Way
Manresa Way
University Avenue
Adobe
Creek Way
Sherman Street
Orange Avenue
Palm Avenue
Sheridan Street
Lee Street Lincoln Avenue
Lincoln Avenue
Foothill Expressway
1st Street Lyell Street
Lennox Way Fremont Road
Burke Road
Chapin Road
Darling
Lane
Burke Lane
E
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Orange Avenue
Palm Avenue
Sheridan Street
Lee Street Lincoln Avenue
Lincoln Avenue
Foothill Expressway
1st Street Lyell Street
Base Map: ESRI, ArcGIS
0 50 300 400 600 Feet
Project Boundary
Halsey House
VICINITY MAP FIGURE 3.1-2

ResidenƟal
ResidenƟal
ResidenƟal
ResidenƟal
ResidenƟal
ResidenƟal
Redwood Grove
Nature Preserve
Fremont Road
Lennox Way
Lennox Way
Manresa Lane
Sheridan Street
University Avenue
Sherman Street
Orange Avenue
Adobe Creek Way
Fremont Road
Lennox Way
Lennox Way
Manresa Lane
Sheridan Street
University Avenue Sherman Street
Orange Avenue
Adobe Creek Way Photo Date: Apr. 2022
0 25 150 200 300 Feet
Project Boundary
Halsey House
Aerial Source: Google Earth Pro, Apr. 19, 2024.

AERIAL PHOTOGRAPH AND SURROUNDING LAND USES FIGURE 3.1-3

Halsey House Project, SCH# 2025020308 5 Draft Environmental Impact Report City of Los Altos June 2026
Service utility trucks weighing approximately four tons would be used for hauling. The service trucks would be able to hold a maximum of three tons. When hauling materials off-site, the service utility trucks would weigh seven tons total.

During demolition, construction equipment and manual labor would be used to tear down the Halsey House. Some of the demolition would be completed manually with hand tools due to the weight and width constraints of the pedestrian bridge. After demolition of the building, the site would be cleared and replanted with native plant vegetation that matches the existing vegetation in the Preserve. Building materials would be hauled to an appropriate off-site disposal location.

The proposed project would remove two trees, neither of which qualify as protected trees under the City’s Tree Protection Ordinance.

3.4 Project Objectives
Pursuant to CEQA Guidelines Section 15124, the EIR must include a statement of the objectives sought by the proposed project. Project objectives as proposed by the City include:
• Protect the health, safety, and welfare of the surrounding community by eliminating safety hazards associated with the Halsey House building, which is currently vacant and in a state of disrepair.
• Maintain and improve public open space at the project site through restoration of landscaped areas and enhanced open space accessibility and visibility. • Reduce or eliminate ongoing maintenance costs associated with an unused public facility. • Reduce or eliminate the cost to rehabilitate the existing structure to a usable condition. • Comply with the Secretary of the Interior’s Standards as necessary.

3.5 Uses of the EIR
This Draft EIR is intended to provide the City of Los Altos, other public agencies, and the general public with the relevant environmental information needed in considering the proposed project.

The City of Los Altos anticipates the following permit approvals by the City will be required to implement the project addressed in this Draft EIR:
• Demolition Permit
• Historic Alteration Permit
• Tree Removal Permit
• Watercourse Protection Permit

Halsey House Project, SCH# 2025020308 6 Draft Environmental Impact Report City of Los Altos June 2026
Section 4.0 Environmental Setting, Impacts, and
Mitigation
This section presents the discussion of impacts related to the following environmental subjects in their respective subsections:

4.1 Aesthetics

4.2 Agriculture and Forestry Resources

4.3 Air Quality

4.4 Biological Resources

4.5 Cultural Resources

4.6 Energy

4.7 Geology and Soils

4.8 Greenhouse Gas Emissions

4.9 Hazards and Hazardous Materials

4.10 Hydrology and Water Quality

4.11 Land Use and Planning

4.12 Mineral Resources

4.13 Noise

4.14 Population and Housing

4.15 Public Services

4.16 Recreation

4.17 Transportation

4.18 Tribal Cultural Resources

4.19 Utilities and Service Systems

4.20 Wildfire
The discussion for each environmental subject includes the following subsections:

Environmental Setting – This subsection 1) provides a brief overview of relevant plans, policies, and regulations that compose the regulatory framework for the project and 2) describes the existing, physical environmental conditions at the project site and in the surrounding area, as relevant.

Impact Discussion – This subsection includes the recommended checklist questions from Appendix G of the CEQA Guidelines to assess impacts.
• Project Impacts – This subsection discusses the project’s impact on the environmental subject as related to the checklist questions. For significant impacts, feasible mitigation measures are identified. “Mitigation measures” are measures that will minimize, avoid, or eliminate a significant impact (CEQA Guidelines Section 15370). Mitigation measures are numbered to correspond to the impact they address. For example, MM BIO-1.3 refers to the third mitigation measure for the first impact in the Biological Resources section. • Cumulative Impacts – This subsection discusses the project’s cumulative impact on the environmental subject. Cumulative impacts, as defined by CEQA, refer to two or more individual effects, which when combined, compound or increase other environmental impacts. Cumulative impacts may result from individually minor, but collectively significant effects taking place over a period of time. CEQA Guideline Section 15130 states that an EIR should discuss cumulative impacts “when the project’s incremental effect is cumulatively considerable.” The discussion does not need to be in as great detail as is necessary for project impacts, but is to be “guided by the standards of practicality and reasonableness.”

Halsey House Project, SCH# 2025020308 7 Draft Environmental Impact Report City of Los Altos June 2026
The purpose of the cumulative analysis is to allow decision makers to better understand the impacts that might result from approval of past, present, and reasonably foreseeable future projects, in conjunction with the proposed project addressed in this EIR.

The CEQA Guidelines advise that a discussion of cumulative impacts should reflect both their severity and the likelihood of their occurrence (CEQA Guidelines Section 15130(b)). To accomplish these two objectives, the analysis should include either a list of past, present, and probable future projects or a summary of projections from an adopted general plan or similar document (CEQA Guidelines Section 15130(b)(1)). This EIR uses the list of projects approach.

The analysis must determine whether the project’s contribution to any cumulatively significant impact is cumulatively considerable, as defined by CEQA Guideline Section 15065(a)(3). The cumulative impacts discussion for each environmental issue accordingly addresses the following issues: 1) would the effects of all of past, present, and probable future (pending) development result in a significant cumulative impact on the resource in question; and, if that cumulative impact is likely to be significant, 2) would the contribution from the proposed project to that significant cumulative impact be cumulatively considerable?
Table 4.0-1 identifies the approved (but not yet constructed or occupied) and pending projects in the project vicinity that are evaluated in the cumulative analysis.

Table 4.0-1: Cumulative Projects List
Name and
Location
Description
Distance to
Proposed
Project
Estimated Schedule
Start Finish
Los Altos Library
Courtyard Project
The project includes the
construction of a courtyard
on the northern part of the
existing City library.
3,380 feet
northeast

N/A N/A
Adobe Sewer
Replacement
Project
The project would replace
the Adobe Creek Sewer Main
which includes 53 sewer lines
in the City.

Adjacent to
the south
2026 2029
For each resource area, cumulative impacts may occur over different geographic areas. For example, the project effects on air quality would combine with the effects of projects in the entire air basin, whereas noise impacts would primarily be localized to the surrounding area. The geographic area that could be affected by the proposed project varies depending upon the type of environmental issue being considered. Section 15130(b)(3) of the CEQA Guidelines states that lead agencies should define the geographic scope of the area affected by the cumulative effect. Table 4.0-2 provides a summary of the different geographic areas used to evaluate cumulative impacts.

Halsey House Project, SCH# 2025020308 8 Draft Environmental Impact Report City of Los Altos June 2026
Table 4.0-2: Geographic Considerations in Cumulative Analysis Resource Area Geographic Area
Aesthetics Project site and adjacent parcels
Agriculture and Forestry Resources Countywide
Air Quality San Francisco Bay Area Air Basin
Biological Resources Project site and adjacent parcels
Cultural Resources Project site and adjacent parcels
Energy Energy provider’s territory
Geology and Soils Project site and adjacent parcels
GHGs Planet-wide
Hazards and Hazardous Materials Project site and adjacent parcels Hydrology and Water Quality Lower Peninsula watershed
Land Use and Planning/Population and
Housing
Citywide
Minerals Identified mineral recovery or resource area
Noise and Vibration Project site and adjacent parcels
Public Services and Recreation Citywide
Transportation/Traffic Citywide
Tribal Cultural Resources Project site and adjacent parcels Utilities and Service Systems Citywide
Wildfire Within or adjacent to the wildfire hazard zone

Halsey House Project, SCH# 2025020308 9 Draft Environmental Impact Report City of Los Altos June 2026

4.1 Aesthetics

4.1.1 Environmental Setting
Regulatory Framework
State
Streets and Highway Code Sections 260 through 263
The California Scenic Highway Program (Streets and Highway Code, Sections 260 through 263) is managed by the California Department of Transportation (Caltrans). The program is intended to protect and enhance the natural scenic beauty of California highways and adjacent corridors through special conservation treatment.

Local
Los Altos General Plan
The City of Los Altos General Plan (General Plan) was adopted in November 2002 and serves as the primary source of long-range planning and policy direction used to guide growth and preserve the quality of life within the City. Implementation of the General Plan ensures future development is consistent with the community’s goals and that adequate urban services are available to meet the needs of new development. The General Plan is divided into eight different elements, each of which describe issues, goals, and policies related to the element topic. The eight elements include Community Design and Historic Resources, Land Use, Housing, Economic Development, Open Space, Conservation and Community Facilities, Circulation, Natural Environment and Hazards, and Infrastructure and Waste Disposal.

The following policies in the General Plan have been adopted for the purpose of reducing or avoiding impacts related to aesthetic resources and are applicable to the project.

Policy Description
OSCC 4.1 Provide adequate level of maintenance for City parks, open space, and public property to ensure safety, aesthetics, and recreational enjoyment for Los Altos residents.

Los Altos Municipal Code
The City of Los Altos Municipal Code (LAMC) contains provisions and laws adopted by the City Council to maintain a healthy and safe community and to preserve the quality of life in Los Altos.

Title 14 (Zoning) of the LAMC provides development standards and regulations that are meant to enhance the visual quality of new development through building height limits, building density, building design and landscaping standards, setback requirements, sign regulations, open space requirements, and lighting requirements. These standards and regulations are provided for each individual zoning district. Title 14 also outlines the design review process for new projects within

Halsey House Project, SCH# 2025020308 10 Draft Environmental Impact Report City of Los Altos June 2026
the City, in addition to the required design review findings that projects must meet.

Existing Conditions
Project Site
The Halsey House is one-story building characterized by stucco cladding and a hipped1clay tile roof.

The structure is generally U-shaped and is arranged around a private courtyard with bench seating and a fountain. The structure is currently vacant, boarded up, and encircled by chain link fencing.

Views of the project site are shown in Photos 1 and 2.

Surrounding Area
The project site is within the Preserve, a local park. The park is characterized by mature redwood and oak trees with walking paths around the perimeter and along Adobe Creek, which runs through the park. Surrounding development consists primarily of one- to two-story single-family residences.

Views of the surrounding area are shown in Photos 3 through 6.

Scenic Vistas and Resources
There are no designated scenic vistas in Los Altos.2 The project site is located in a suburban area developed with single-family residences. The project area is relatively flat land parkland situated at a lower elevation than surrounding development. The Preserve consists of stands of mature Redwood trees, which limits the number of expansive views from the project site.

Scenic Corridors and Highways
State-designated scenic highways include State Route (SR) 9 from the Santa Cruz County line to the Los Gatos City Limit, and Interstate 280 (I-280) from the San Mateo County line to Santa Clara County line. Eligible State Scenic Highways (not officially designated) include SR 17 from the Santa Cruz County line to SR 9, SR 35 from Santa Cruz County line to SR 9, I-280 from the San Mateo County line to SR 17, and the entire length of SR 152 within the County.

There are no state-designated scenic highways in Los Altos.3 The project site is located approximately five miles east of the nearest officially designated state scenic highway segment along I-280.
1 A hipped roof is a roof where all four sides of the roof slope downwards from the peak. 2 City of Los Altos. Initial Study/Mitigated Negative Declaration for the Los Altos General Plan Update. November 2002. Page 12.
3 California Department of Transportation. “Scenic Highways.” Accessed December 19, 2025. https://dot.ca.gov/programs/design/lap-landscape-architecture-and-community-livability/lap-liv-i-scenichighways.

Photo 1: Photo of exisƟng building.

Photo 2: Photo of exisƟng building and pathway.

PHOTOS 1 & 2

Photo 3: Photo of Adobe Creek.

Photo 4: Photo of redwood trees and pathways in surrounding area.

PHOTOS 3 & 4

Photo 5: Photo of pedestrian bridge.

Photo 6: Photo of entrance to Redwood Grove Nature Preserve.

PHOTOS 5 & 6

Halsey House Project, SCH# 2025020308 14 Draft Environmental Impact Report City of Los Altos June 2026

4.1.2 Impact Discussion
For the purpose of determining the significance of the project’s impact on aesthetics, except as provided in Public Resources Code Section 21099, would the project:
1) Have a substantial adverse effect on a scenic vista? 2) Substantially damage scenic resources, including, but not limited to, trees, rock outcroppings, and historic buildings within a state scenic highway? 3) In non-urbanized areas, substantially degrade the existing visual character or quality of public views of the site and its surroundings?4If the project is in an urbanized area, would the project conflict with applicable zoning and other regulations governing scenic quality? 4) Create a new source of substantial light or glare which would adversely affect day or nighttime views in the area?
Project Impacts
a) Would the project have a substantial adverse effect on a scenic vista? As discussed in Section 4.1.1.2 Existing Conditions, the project site is located within the Preserve and surrounded by existing residences. The project site and surrounding area are relatively flat and there are no scenic vistas visible on or through the site. For these reasons, the project would not have a substantial adverse effect on a scenic vista. (No Impact) b) Would the project substantially damage scenic resources, including, but not limited to, trees, rock outcroppings, and historic buildings within a state scenic highway? The project site is not located within a state-designated scenic highway. As discussed in Section

4.1.1.2 Existing Conditions, the nearest state-designated scenic highways to the project site are I280 and SR 9. The project site is approximately five miles southeast of I-280 and approximately eight miles north of SR 9. Because the project site is not located within a state-designated scenic highway, implementation of the project would not damage scenic resources within a statedesignated scenic highway. (No Impact) 4 Public views are those that are experienced from publicly accessible vantage points.

Halsey House Project, SCH# 2025020308 15 Draft Environmental Impact Report City of Los Altos June 2026
c) In non-urbanized areas, would the project substantially degrade the existing visual character or quality of public views of the site and its surroundings? If the project is in an urbanized area, would the project conflict with applicable zoning and other regulations governing scenic quality?
The project consists solely of the demolition of the Halsey House and would not include the construction of a new building. The removal of the structure and revegetation of the site would leave the project site consistent with the surrounding undeveloped parkland within the Preserve.

Therefore, there would be no change or degradation to the scenic quality or conflict with scenic quality zoning regulations. (No Impact)
d) Would the project create a new source of substantial light or glare which would adversely affect day or nighttime views in the area?
The project consists solely of the demolition of the Halsey House and would not include the construction of a new building or installation of new lighting. Therefore, there would be no new sources of substantial light or glare. (No Impact)
Cumulative Impacts
Would the project result in a cumulatively considerable contribution to a significant cumulative aesthetics impact?
The geographic area for cumulative aesthetics impacts is limited to the project site and adjacent development from which the project site would be visible. The Adobe Creek Sewer Project identified in Table 4.0-1 is adjacent to the site; however, it would consist of improvements to underground infrastructure and would not have any aesthetic impacts.

Scenic Vistas
The project site and surrounding area have minimal to no scenic views due to the existing built environment with no designated scenic resources. Therefore, the project would not contribute to a cumulatively significant impact to scenic vistas. (No Cumulative Impact) Scenic Resources within a State Scenic Highway
The project would have no impact on scenic resources within a state scenic highway and, therefore, would not contribute to a cumulatively significant impact to those resources. (No Cumulative Impact)

Halsey House Project, SCH# 2025020308 16 Draft Environmental Impact Report City of Los Altos June 2026
Scenic Quality
The project would not contribute to a cumulatively significant conflict with zoning and other regulations governing scenic quality since no development is proposed. (No Cumulative Impact) Lighting or Glare
The project would not contribute to any lighting or glare because no development or the installation of any lighting is proposed. Therefore, the project would not contribute to a cumulatively significant light and glare impact. (No Cumulative Impact) For the reasons described above, the project would have no cumulative aesthetic impacts. (No Cumulative Impact)

Halsey House Project, SCH# 2025020308 17 Draft Environmental Impact Report City of Los Altos June 2026

4.2 Agriculture and Forestry Resources

4.2.1 Environmental Setting
Regulatory Framework
Farmland Mapping and Monitoring Program
The California Department of Conservation’s Farmland Mapping and Monitoring Program (FMMP) assesses the location, quality, and quantity of agricultural land and conversion of these lands over time. Agricultural land is rated according to soil quality and irrigation status. The best quality land is identified as Prime Farmland. In CEQA analyses, the FMMP classifications and published county maps are used, in part, to identify whether agricultural resources that could be affected are present on-site or in the project area.5
California Land Conservation Act
The California Land Conservation Act (Williamson Act) enables local governments to enter into contracts with private landowners to restrict parcels of land to agricultural or related open space uses. In return, landowners receive lower property tax assessments. In CEQA analyses, identification of properties that are under a Williamson Act contract is used to also identify sites that may contain agricultural resources or are zoned for agricultural uses.6 Fire and Resource Assessment Program
The California Department of Forestry and Fire Protection (CAL FIRE) identifies forest land, timberland, and lands zoned for timberland production that can (or do) support forestry resources.7 Programs such as CAL FIRE’s Fire and Resource Assessment Program and are used to identify whether forest land, timberland, or timberland production areas that could be affected are located on or adjacent to a project site.8
5 California Department of Conservation. “Farmland Mapping and Monitoring Program.” Accessed December 19, 2025. http://www.conservation.ca.gov/dlrp/fmmp/Pages/Index.aspx. 6 California Department of Conservation. “Williamson Act.” Accessed December 19, 2025. http://www.conservation.ca.gov/dlrp/lca.
7 Forest Land is land that can support 10 percent native tree cover and allows for management of forest resources (California Public Resources Code Section 12220(g)); Timberland is land not owned by the federal government or designated as experimental forest land that is available for, and capable of, growing trees to produce lumber and other products, including Christmas trees (California Public Resources Code Section 4526); and Timberland Production is land used for growing and harvesting timber and compatible uses (Government Code Section 51104(g)).
8 California Department of Forestry and Fire Protection. “Fire and Resource Assessment Program.” Accessed December 19, 2025. http://frap.fire.ca.gov/.

Halsey House Project, SCH# 2025020308 18 Draft Environmental Impact Report City of Los Altos June 2026
Existing Conditions
The project site is designated as Urban Built-Up Land which is defined as land with at least six structures per 10 acres.9 Common examples of Urban Built-Up Land are residential, institutional, industrial, commercial, landfill, gold course, airports, and other utility uses.

The project site has a General Plan designation of Parks and is within the Public and Community Facilities zoning district. The project site and surrounding sites are not used for agricultural, forestry, or timberland uses, nor are they subject to a Williamson Act contract.10

4.2.2 Impact Discussion
For the purpose of determining the significance of the project’s impact on agriculture and forestry resources, would the project:
1) Convert Prime Farmland, Unique Farmland, or Farmland of Statewide Importance (Farmland), as shown on the maps prepared pursuant to the Farmland Mapping and Monitoring Program of the California Resources Agency, to non-agricultural use? 2) Conflict with existing zoning for agricultural use, or a Williamson Act contract? 3) Conflict with existing zoning for, or cause rezoning of, forest land (as defined in Public Resources Code Section 12220(g)), timberland (as defined by Public Resources Code Section 4526), or timberland zoned Timberland Production (as defined by Government Code Section 51104(g))?
4) Result in a loss of forest land or conversion of forest land to non-forest use? 5) Involve other changes in the existing environment which, due to their location or nature, could result in conversion of Farmland, to non-agricultural use or conversion of forest land to non-forest use?
Project Impacts
a) Would the project convert Prime Farmland, Unique Farmland, or Farmland of Statewide Importance, as shown on the maps prepared pursuant to the Farmland Mapping and Monitoring Program of the California Resources Agency, to non-agricultural use? As discussed in Section 4.2.1.2 Existing Conditions, the project site is not designated for agricultural use. Therefore, the project would not result in the conversion of designated farmland to nonagricultural use. (No Impact) 9 California Department of Conservation. “California Important Farmland Finder.” Accessed December 19, 2025. https://maps.conservation.ca.gov/DLRP/CIFF/.
10 County of Santa Clara. “Williamson Act Properties Map,” Accessed December 19, 2025. https://experience.arcgis.com/experience/034e46f2f4bc44d1ada505dd92940ff7.

Halsey House Project, SCH# 2025020308 19 Draft Environmental Impact Report City of Los Altos June 2026
b) Would the project conflict with existing zoning for agricultural use, or a Williamson Act contract?
As discussed in Section 4.2.1.2 Existing Conditions, the project site is within the Public and Community Facilities zoning district and is not zoned for agricultural use. Therefore, the project would not conflict with existing zoning for an agricultural use or a Williamson Act contract. (No Impact)
c) Would the project conflict with existing zoning for, or cause rezoning of, forest land, timberland, or timberland zoned Timberland Production?
The project site is not zoned, or adjacent to land zoned, for forest land, timberland, or Timberland Production. Therefore, the project would not conflict with existing zoning or cause rezoning of forest land or timberland uses. (No Impact)
d) Would the project result in a loss of forest land or conversion of forest land to non-forest use?
Section 12220(g) of the California Public Resources Code defines forest land as “land that can support ten percent native tree cover of any species, including hardwoods, under natural conditions, and that allows for management of one or more forest resources, including timber, aesthetics, fish and wildlife, biodiversity, water quality, recreation, and other public benefits.” The Halsey House is located within the Preserve, which could meet the definition of forest land.

However, the proposed project consists solely of the demolition of the Halsey House. After demolition of the building, the site would be cleared and replanted with native plant vegetation that matches the existing vegetation in the Preserve. Therefore, no forest land would be lost as a result of the project, nor would the project result in the conversion of existing forest land to nonforest uses. (Less than Significant Impact) e) Would the project involve other changes in the existing environment which, due to their location or nature, could result in conversion of Farmland, to non-agricultural use or conversion of forest land to non-forest use?
As mentioned under checklist questions a) and d) above, the project site and adjacent properties are not designated or used as farmland or forest land. Therefore, development of the project would not cause the conversion of farmland to non-agricultural use or forest land to non-forest use. (No Impact)

Halsey House Project, SCH# 2025020308 20 Draft Environmental Impact Report City of Los Altos June 2026
Cumulative Impacts
Would the project result in a cumulatively considerable contribution to a cumulatively significant agricultural and forestry resources impact?
The geographic area for cumulative agricultural and forestry resource impacts is Santa Clara County, since agricultural and forestry resources are mapped and managed at the county level. As discussed above, the project would not result in the conversion of farmland to non-agricultural use, loss of farmland or forestland, conversion of forestland to non-forest use, or the conversion of forest land to non-forest use. Therefore, the project would not contribute to a cumulatively significant agricultural and forestry resources impact. (No Cumulative Impact)

Halsey House Project, SCH# 2025020308 21 Draft Environmental Impact Report City of Los Altos June 2026

4.3 Air Quality
The following discussion is based, in part, on a California Emissions Estimator Model (CalEEMod) prepared internally by DJP&A. The report is attached to this EIR as Appendix B.

4.3.1 Environmental Setting
Background Information
Criteria Pollutants
Criteria air pollutants are pollutants that have established federal or State standards for outdoor concentrations to protect public health. Pursuant with the federal and State Clean Air Acts, the United States Environmental Protection Agency (EPA) and the California Air Resources Board (CARB) have established and enforced the National Ambient Air Quality Standards (NAAQS) and California Ambient Air Quality Standards (CAAQS), respectively. The NAAQS and CAAQS address the following criteria air pollutants: ozone (O3), nitrogen dioxide (NO2), carbon monoxide (CO), particulate matter with a diameter of 10 microns or less (PM10), particulate matter with a diameter of 2.5 micros or less (PM2.5), sulfur dioxide (SO2), and lead. The CAAQS also includes visibility reducing particles, sulfates, hydrogen sulfide, and vinyl chloride.

Toxic Air Contaminants
Toxic air contaminants (TACs) include airborne chemicals that are known to have short- and longterm adverse health effects. TACs are found in ambient air, especially in urban areas, and are caused by industry, agriculture, diesel fuel combustion, and commercial operations (e.g., dry cleaners). TACs are typically found in low concentrations, even near their source (e.g., diesel particulate matter [DPM] near a freeway). Unlike criteria air pollutants, which have a regional impact, TACs are highly localized and regulated at the individual emissions source level.

DPM is the predominant TAC in urban air and is estimated to represent about three-quarters of the cancer risk from TACs. DPM is comprised of diesel exhaust which is a complex mixture of gases, vapors, and fine particles. Medium- and heavy-duty diesel trucks represent the bulk of DPM emissions from California highways. The majority of DPM is small enough to be inhaled into the lungs. Most inhaled particles are subsequently exhaled, but some deposit on the lung surface or are deposited in the deepest regions of the lungs (i.e., areas most susceptible to injury).11 Chemicals in diesel exhaust, such as benzene and formaldehyde, are also TACs identified by the CARB.

An overview of the sources of criteria pollutants and TACs, as well as their associated health effects, is provided in Table 4.3-1.
11 California Air Resources Board. “Overview: Diesel Exhaust and Health.” Accessed December 19, 2025. https://ww2.arb.ca.gov/resources/overview-diesel-exhaust-and-health.

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Table 4.3-1: Sources and Health Effects of Criteria Air Pollutants and Toxic Air Contaminants Pollutants Description and Sources Primary Effects
Ozone (O3) O3 is a secondary criteria air pollutant that is the result of a photochemical (sunlight) reaction between reactive
organic gases (ROG) and nitrogen oxides (NOx). Pollutants emitted by motor vehicles, power plants, industrial
boilers, refineries, and chemical plants are the common source for this reaction. High O3 levels are caused by the cumulative emissions of ROG and NOX. These precursor or primary pollutants react under certain meteorological
conditions to form high O3 levels. Common sources of
ROG and NOx are vehicles, industrial plants, and consumer products.
• Aggravation of respiratory
and cardiovascular diseases
• Irritation of eyes
• Cardiopulmonary function
impairment
Nitrogen
Dioxide (NO2)
NO2 is a reactive gas that combines with nitric oxide (NO) to form NOx. NO2 is the byproduct of fuel combustion with common sources of NO2 being emissions from cars, trucks, buses, power plants, and off-road equipment. Sources of NO2 include motor vehicle exhaust, high temperature
stationary combustion, and atmospheric reactions.
• Aggravation of respiratory
illness
• Reduced visibility
Carbon
Monoxide (CO)
CO is a colorless, odorless, and toxic gas that is the
product of incomplete combustion of carbon-containing
substances (e.g., when something is burned). Common
outdoor sources of CO include mobile vehicles (passenger cars and trucks) and machinery that burn fossil fuels.
• Interferes with oxygen
delivery to the body’s organ
due to binding with the
hemoglobin in the blood
• Fatigue, headaches,
confusion, and dizziness
Fine
Particulate
Matter (PM2.5)
and Coarse
Particulate
Matter (PM10)
Particulate Matter (PM) is any material that is emitted as liquid or solid particles or a gaseous material, such as dust, soot, aerosols, and fumes. PM10 and PM2.5 are both small enough particulates to be inhaled into the human lungs, and PM2.5 is small enough to deposit into the lungs, which poses an increased health risk compared to PM10. Typical sources of PM include stationary combustion of solid
fuels, construction activities, vehicles, industrial processes, and atmospheric chemical reactions.
• Reduced lung function,
especially in children
• Aggravation of respiratory
and cardiorespiratory
diseases
• Increased cough and chest
discomfort
• Reduced visibility
Sulfur Dioxide
(SO2)
SO2 is a pungent and colorless gaseous pollutant that is part of the sulfur oxides (SOx) group and is the pollutant of greatest concern in the SOx group. SOx can react with
other compounds in the atmosphere to form small
particles. These particles contribute to pollution. SO2 is primarily formed from fossil fuel combustion at power
plants and other industrial facilities. Sources of SO2
include motor vehicles, locomotives, ships, and off-road diesel equipment that are operated with fuels that contain high levels of sulfur. Industrial processes, such as natural gas and petroleum extraction, oil refining, and metal
processing.
• Aggravation of respiratory
illness
• Respiratory irritation such
as wheezing, shortness of
breath and chest tightness
• Increased incidence of
pulmonary symptoms and
disease, decreased
pulmonary function

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Pollutants Description and Sources Primary Effects
Lead Lead is a naturally occurring element that can be found in all parts of the environment including the air, soil, and water. As an air pollutant, lead is present in small
particles. The most common historic source of lead
exposure was the past use of leaded gasoline in motor
vehicles. The exhaust resulting from use of leaded
gasoline would release lead emissions into the air. Now, major sources of lead in the air are from ore and metals processing plants and piston-engine aircraft operating on leaded aviation fuel. Other sources are waste incinerators, utilities, and lead-acid battery manufacturers. The highest air concentrations of lead are usually found near lead
smelters.
• Adversely affect the
nervous system, kidney
function, immune system,
reproductive and
developmental systems and
the cardiovascular system
Toxic Air
Contaminants
(TACs)
TACs include certain air pollutants known to increase the risk of cancer and/or a range of other serious health
effects. Sources of TAC include, but are not limited to, cars and trucks, especially diesel-fueled; industrial sources, such as chrome platers; dry cleaners and service stations; and building materials and products.
• Cancer
• Chronic eye, lung, or
skin irritation
• Neurological and
reproductive disorders
Sensitive Receptors
Some groups of people are more affected by air pollution than others. CARB has identified the following groups who are most likely to be affected by air pollution: children under 16, the elderly over 65, and people with cardiovascular and chronic respiratory diseases. These groups are classified as sensitive receptors. Locations that may contain a high concentration of these sensitive population groups include residential areas, hospitals, daycare facilities, elder care facilities, and elementary schools.

Regulatory Framework
Federal and State
Clean Air Act
At the federal level, the EPA is responsible for overseeing implementation of the Clean Air Act and its subsequent amendments. The federal Clean Air Act requires the EPA to set national ambient air quality standards for the six common criteria pollutants, discussed previously; PM, O3, CO, SO2, NO2, and lead.12
CARB is the state agency that regulates mobile sources throughout the state and oversees implementation of the state air quality laws and regulations, including the California Clean Air Act. 12 NOx is the group of nitrogen compounds (NO2 and nitric oxide [NO]) that typically represents NO2 emissions because NO2 emissions contribute the majority of NOx exhaust emissions emitted from fuel combustion.

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The EPA and the CARB have adopted ambient air quality standards establishing permissible levels of these pollutants to protect public health and the climate. Violations of ambient air quality standards are based on air pollutant monitoring data and are determined for each air pollutant. Attainment status for a pollutant means that a given air district meets the standard set by the EPA and/or CARB.

Diesel Risk Reduction Plan
To address the issue of diesel emissions in the state, CARB developed the Risk Reduction Plan to Reduce Particulate Matter Emissions from Diesel-Fueled Engines and Vehicles. In addition to requiring more stringent emission standards for new on-road and off-road mobile sources and stationary diesel-fueled engines to reduce particulate matter emissions by 90 percent, this plan involves the application of emission control strategies to existing diesel vehicles and equipment to reduce DPM and other pollutants. Implementation of this plan, in conjunction with stringent federal and CARB-adopted emission limits for diesel fueled vehicles and equipment, including off-road equipment, will significantly reduce emissions of DPM and NOX.

Regional
2017 Clean Air Plan
The Bay Area Air District (Air District) is the agency primarily responsible for assuring that the federal and state ambient air quality standards are maintained in the San Francisco Bay Area (Bay Area), which includes the project area. Regional air quality management districts, such as the Air District, must prepare air quality plans specifying how federal and state air quality standards will be met. The Air District’s most recently adopted plan is the Bay Area 2017 Clean Air Plan (CAP). The 2017 CAP focuses on the following two related Air District goals and how to achieve them:
• Protect air quality and health at the regional and local scale by attaining all state and national air quality standards and eliminating disparities among Bay Area communities in cancer health risk from TAC; and
• Protect the climate by reducing Bay Area greenhouse gas (GHG) emissions 40 percent below 1990 levels by 2040 and 80 percent below 1990 levels by 2050.13 CEQA Air Quality Guidelines
The Air District’s CEQA Air Quality Guidelines are intended to serve as a guide for those who prepare or evaluate air quality impact analyses for projects and plans in the Bay Area. Jurisdictions in the Bay Area Air Basin utilize the thresholds and methodology for assessing air quality impacts developed by Air District within their CEQA Air Quality Guidelines. The guidelines include information on legal requirements, Air District rules, methods of analyzing impacts, and recommended mitigation measures. The latest CEQA Air Quality Guidelines are the 2022 CEQA Air Quality Guidelines adopted on April 20, 2023 by the Air District’s Board of Directors. 13 Bay Area Air District. Final 2017 Clean Air Plan. April 19, 2017. Page 12.

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Local
Los Altos General Plan
The following policies in the City’s General Plan have been adopted for the purposes of reducing or avoiding impacts related to air quality, and are applicable to the project.

Policy Description
LU 8.3 Interpret and implement the General Plan to be consistent with the regional Bay Area Air Quality Management Plan, as periodically updated.

LU 8.4 Ensure location and design of development projects so as to conserve air quality and minimize direct and indirect emissions of air contaminants.

Existing Conditions
Attainment Status
The Bay Area Air Basin is designated a non-attainment area for the federal O3 and PM2.5 standards and for the state O3, and PM10 standards.
14,15 The area has attained both NAAQS and CAAQS for CO, SO2, and NO2. As the regional air district, the Air District is responsible for attaining the NAAQS and CAAQS for these pollutants. As part of an effort to attain and maintain ambient air quality standards for O3, PM10, and PM2.5, the Air District has established thresholds of significance for these air pollutants and their precursors that apply to both construction period and operational period impacts. Controlling the emissions of these precursor pollutants is the focus of the Bay Area’s attempts to reduce O3 levels. The highest O3 levels in the Bay Area occur in the eastern and southern inland valleys where temperatures are higher, there is less wind circulation, and sources of the precursor pollutants (ROG and NOx) are prominent. In the Bay Area, most particulate matter is generated from the following activities: combustion, factories, construction, grading, demolition, agriculture, and motor vehicles. Elevated concentrations of PM10 and PM2.5 are the result of both region-wide emissions and localized emissions.

Sensitive Receptors
There are single-family residences surrounding the Preserve where the Halsey House is located. The nearest residence is approximately 140 feet southwest of the Halsey House. 14 Bay Area Air Quality Management District. “Air Quality Standards and Attainment Status.” Last Updated December 15, 2025. Accessed December 19, 2025. https://www.baaqmd.gov/about-air-quality/research-anddata/air-quality-standards-and-attainment-status. 15 The area has attained both state and federal ambient air quality standards for CO. The project does not include substantial new emissions of SO2 or lead. These criteria pollutants are not discussed further.

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4.3.2 Impact Discussion
For the purpose of determining the significance of the project’s impact on air quality, would the project:
1) Conflict with or obstruct implementation of the applicable air quality plan? 2) Result in a cumulatively considerable net increase of any criteria pollutant for which the project region is non-attainment under an applicable federal or state ambient air quality standard?
3) Expose sensitive receptors to substantial pollutant concentrations? 4) Result in other emissions (such as those leading to odors) adversely affecting a substantial number of people?
Note: Where available, the significance criteria established by the applicable air quality management district or air pollution control district may be relied upon to make the determinations.

Thresholds of Significance
As discussed in CEQA Guidelines Section 15064(b), the determination of whether a project may have a significant effect on the environment calls for judgment on the part of the lead agency and must be based to the extent possible on scientific and factual data. The City of Los Altos has considered the air quality thresholds updated by the Air District in April 2023 and regards these thresholds to be based on the best information available for the Bay Area Air Basin and conservative in terms of the assessment of health effects associated with TACs and PM2.5. The Air District CEQA Air Quality thresholds for criteria air pollutants and fugitive dust used in this analysis are identified in Table 4.3-2. Table 4.3-3 below lists the Air District health risk and hazards thresholds for single-source and cumulative sources.

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Table 4.3-2: Bay Area Air District Air Quality Significance Thresholds Criteria Air
Pollutant
Construction Thresholds* Operation Thresholds Operation Thresholds Average Daily Emissions
(pounds/day)
Average Daily Emissions
(pounds/day)
Annual Average
Emissions (tons/year)
ROG and NOx 54 54 10
PM10 82 (exhaust) 82 15
PM2.5 54 (exhaust) 54 10
CO Not Applicable 9.0 ppm (eight-hour) or 20.0 ppm (one-hour) Fugitive Dust
Dust Control Measures/Best
Management Practices
Not Applicable
Notes: ROG = reactive organic gases; NOX = oxides of nitrogen; PM10 = respirable particulate matter with an aerodynamic resistance diameter of 10 micrometers or less; PM2.5= fine particulate matter with an aerodynamic resistance diameter of 2.5 micrometers or less; CO = carbon monoxide * The Air District recommends that for construction projects that require less than one year to complete, lead agencies should annualize impacts over the scope of actual days that peak impacts would occur rather than over the full year. Additionally, for phased projects that results in concurrent construction and operational emissions. Construction-related exhaust emissions should be combined with operational emissions for all phases where construction and operations overlap.

Source: Bay Area Air District. 2022 California Environmental Quality Act Air Quality Guidelines. April 2023. Pages 3-5 and 3-6.

Table 4.3-3: Bay Area Air District Health Risks and Hazards Thresholds Health Risk Single Source Combined Cumulative Sources
Cancer Risk 10 per one million 100 per one million
Non-Cancer Hazard Index 1.0 10.0
Annual PM2.5 Concentration 0.3 µg/m3 0.8 μg/m3(average) Notes: µg/m3 = micrograms per cubic meter; PM2.5= fine particulate matter with an aerodynamic resistance diameter of 2.5 micrometers or less
Thresholds are applicable to construction and operational activities.

Source: Bay Area Air District. 2022 California Environmental Quality Act Air Quality Guidelines. April 2023. Pages 3-5 and 3-6.

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Project Impacts
a) Would the project conflict with or obstruct implementation of the applicable air quality plan?
2017 Clean Air Plan
As described in Section 4.3.1.2 Regulatory Framework, the most current air quality plan from the Air District is the 2017 CAP. The Air District Air Quality Guidelines state that a determination of consistency with the 2017 CAP should demonstrate that the project supports the primary goals of the 2017 CAP, includes applicable control measures from the 2017 CAP, and does not disrupt or hinder implementation of any 2017 CAP control measures.

The project would not disrupt or hinder the 2017 CAP control measures for stationary sources, transportation, energy, buildings, agriculture, natural and working lands, waste management, and water because no new buildings are proposed post-demolition activities. During demolition, the project would generate temporary construction criteria air pollutant emissions due to use of diesel construction equipment and trucks. As described in further detail below, the project would not exceed the Air District significance thresholds for criteria air pollutant emissions (refer to Table

4.3-4); therefore, the project would not hinder the 2017 CAP’s goal of attaining the NAAQS and CAAQS. (Less than Significant Impact)
Demolition Criteria Air Pollutant Emissions
CalEEMod Version 2022.1.0 was used to estimate emissions from demolition activity and demolition vehicle trips. The model provides emission estimates for both on-site and off-site construction activities. On-site activities primarily consist of construction equipment operation, while off-site activity includes worker, hauling, and vendor traffic.

A three-month demolition period was entered into CalEEMod, assuming demolition would be active five days per week. The model default construction equipment and emission standards for a project of this size (approximately 0.3 acres) were used with the addition of one excavator (conservatively assumed to operate for eight hours per day). Refer to Appendix B for details about the CalEEMod construction inputs and model output.

Average daily emissions were calculated for demolition by dividing the annual construction emissions by the number of active construction workdays that year. Table 4.3-4 shows the average daily demolition emissions of ROG, NOX, PM10 exhaust, and PM2.5 exhaust.

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Table 4.3-4: Average Daily Emissions Demolition Criteria Pollutant Emissions Year ROG NOx PM10 Exhaust PM2.5 Exhaust
2025 Annual Emissions (tons per year) 0.02 0.17 0.01 0.01 2025 Average Daily Emissions (pounds per day) 0.63 5.31 0.31 0.31 Significance Threshold (pounds per day) 54 54 82 54
Significant? No No No No
Note: Average daily emissions are calculated by dividing the construction emissions by the number of construction workdays. A total of 64 construction workdays were assumed. A rate of 2,000 pounds per ton was used to convert annual emissions.

Source: Appendix B
As shown in Table 4.3-4, predicted average daily project demolition emissions would not exceed the Air District significance thresholds. Therefore, project demolition would have a less than significant criteria pollutant emissions impact and would not conflict with or obstruct implementation of the 2017 Clean Air Plan. (Less than Significant Impact)
Operational Criteria Pollutant Emissions
The project consists of the demolition of the Halsey House and would not include the construction and operation of a new building. The project site would be undeveloped post-demolition.

Therefore, the project would not generate any operational criteria pollutant emissions. (No Impact) As described above, the project would not conflict with or obstruct implementation of the applicable air quality plan. The demolition proposed would not hinder the goals of the 2017 Clean Air Plan, and project criteria air pollutant emissions (including both construction and operation emissions) would not exceed Air District significance thresholds. Therefore, impacts would be less than significant. (Less than Significant Impact)
b) Would the project result in a cumulatively considerable net increase of any criteria pollutant for which the project region is non-attainment under an applicable federal or state ambient air quality standard?
The Bay Area is designated a non-attainment area for the federal O3 and PM2.5 standards and for the State O3, PM10, and PM2.5 standards. As described in the Air District CEQA Air Quality Guidelines, air pollution by its nature is largely a cumulative impact. No single project is sufficient in size, by itself, to result in non-attainment of ambient air quality standards. If a project exceeds the identified significance thresholds, its emissions would be cumulatively considerable, resulting in significant adverse air quality impacts to the region’s existing air quality conditions.

While the project would temporarily increase criteria pollutants in the Bay Area due to demolition activities, which would contribute to existing violations of O3 and particulate matter standards, the

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project would not result in any air pollutant emissions that would exceed the Air District’s significance thresholds (see discussion under checklist question a) above). As a result, the proposed project would not result in a cumulatively considerable net increase of any criteria pollutant for which the region is in non-attainment. (Less than Significant Impact) c) Would the project expose sensitive receptors to substantial pollutant concentrations? Criteria Air Pollutants
In a 2018 decision (Sierra Club v. County of Fresno), the state Supreme Court determined CEQA requires that when a project’s criteria air pollutant emissions would exceed applicable thresholds and have a cumulatively considerable contribution to a significant cumulative regional criteria pollutant impact, the potential for the project’s emissions to affect human health in the air basin must be disclosed. State and federal ambient air quality standards are health-based standards, and exceedances of those standards result in continued unhealthy levels of air pollutants. In developing thresholds of significance for air pollutants, the Air District considered the emission levels for which a project’s individual emissions would be cumulatively considerable. If a project has a less than significant impact for criteria pollutants, it is assumed to have no adverse health effect.

As described under checklist question a), the project would generate construction criteria air pollutant emissions below the Air District significance thresholds and no operational air pollutant emissions would be generated. Therefore, the project would not expose sensitive receptors to substantial criteria air pollutant concentrations that would result in adverse health effects.

Fugitive Dust
Construction demolition activities associated with the project would temporarily generate fugitive dust in the form of PM10 and PM2.5. Sources of fugitive dust would include disturbed soils at the construction site and trucks carrying uncovered loads of soils. Unless properly controlled, vehicles leaving the site could deposit mud on local streets, which could be an additional source of airborne dust after it dries. The Air District CEQA Air Quality Guidelines consider these impacts to be less than significant if best management practices (BMPs) are implemented to reduce the emissions.

The project would be required to implement the following Standard Conditions of Approval that incorporate the Air District’s BMPs to reduce fugitive dust impacts.

Standard Condition of Approval: Basic Air Quality Construction Measures: All construction contractors shall implement the basic construction BMPs recommended by the Bay Area Air District (Air District) to reduce fugitive dust emissions. Emission reductions BMPs will include the following measures:
• All exposed surfaces (e.g., staging areas, soil piles, and graded areas) shall be watered two times per day.
• All haul trucks transporting soil, sand, or other loose material off-site shall be covered.

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• All visible mud or dirt trackout onto adjacent public roads shall be removed using wet power vacuum street sweepers at least once per day. The use of dry power sweeping is prohibited. • All roadways, driveways, and sidewalks to be paved shall be completed as soon as possible.

Building pads shall be laid as soon as possible after grading unless seeding or soil binders are used.
• Idling times shall be minimized either by shutting equipment off when not in use or reducing the maximum idling time to five minutes. Clear signage shall be provided for construction workers at all access points.
• All excavation, grading, and/or demolition activities shall be suspended when average wind speeds exceed 20 mph.
• All trucks and equipment, including their tires, shall be washed off prior to leaving the site. • All construction equipment shall be maintained and properly tuned in accordance with manufacturer’s specifications. All equipment shall be checked by a certified mechanic and determined to be running in proper condition prior to operation. • Unpaved roads providing access to sites located 100 feet or further from a paved road shall be treated with a 6- to 12-inch layer of compacted layer of wood chips, mulch, or gravel. • Publicly visible signs shall be posted with the telephone number and name of the person to contact at the lead agency regarding dust complaints. This person shall respond and take corrective action within 48 hours. The Air District’s General Air Pollution Complaints number shall also be visible to ensure compliance with applicable regulations.

The BMPs listed above shall be printed on all construction documents, contracts, and project plans.

The City and/or contractor shall submit the construction documents, contracts, and project plans to the Development Services Director or the Director’s designee for review and approval prior to the issuance of a demolition or grading permit, whichever occurs earliest.

Implementation of the Standard Condition of Approval above would minimize and reduce fugitive dust emissions to less than significant levels. (Less than Significant Impact) Toxic Air Contaminants
Construction
Construction equipment and associated heavy-duty truck traffic emits DPM, which is a known TAC.

Demolition of the Halsey House would take approximately three months, but construction equipment and trucks would not be operating continuously during the entire three-month period.

There would be periods of no activity where no DPM would be emitted. Due to the short duration of construction, the limited use of heavy equipment, and the small project footprint, emissions of pollutants during construction would be minimal and below relevant Air District thresholds.

Therefore, the project would not result in significant TAC impacts during construction. (Less than Significant Impact)

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Operation
There would be no sources of operational TAC post-demolition as the area would be undeveloped and landscaped with vegetation. Therefore, the project would not result in TAC impacts during operation. (No Impact)
Based on the above discussion, impacts to sensitive receptors would be less than significant. (Less than Significant Impact)
d) Would the project result in other emissions (such as those leading to odors) adversely affecting a substantial number of people?
According to the Air District CEQA Guidelines, an odor source with five or more confirmed complaints per year averaged over three years is considered to have a significant impact.

Demolition of the Halsey House would generate localized emissions of diesel exhaust from the use of heavy-duty equipment and vehicles and when equipment is idling. The odors from these emissions may be noticeable from time to time by nearby receptors; however, these odors would be intermittent and would disperse with distance. All demolition-related odors would cease upon completion of demolition. The project would not site any potential sources of odor post-demolition (such as landfills, food manufacturing, compositing facilities, or chemical plants) that would result in complaints from surrounding uses. Therefore, the proposed demolition activities would not result in odor emissions that would adversely affect a substantial number of people. (Less than Significant Impact)
Cumulative Impacts
Would the project result in a cumulatively considerable contribution to a significant cumulative air quality impact?
The geographic area for cumulative air quality impacts is the Bay Area Air Basin. Past, present, and future development projects contribute to the region’s adverse air quality impacts on a cumulative basis. By its very nature, air pollution is largely a cumulative impact. In developing thresholds of significance for air pollution, the Air District considered the emission levels for which a project’s individual emissions would be cumulatively considerable. If a project exceeds the identified significance thresholds, its emissions would be cumulatively considerable, resulting in significant adverse air quality impacts to the region’s air quality conditions.

Implementation of the 2017 Clean Air Plan
As described above under checklist question a), the project would be consistent with the 2017 CAP.

The project, therefore, would not result in a cumulatively considerable impact to the implementation of the 2017 CAP. (Less than Significant Cumulative Impact)

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Increase in Criteria Pollutants
As discussed under checklist questions a) and b), the construction and operational emissions generated by the project would not exceed the Air District thresholds for criteria air pollutant emissions. Therefore, the project would not result in a cumulatively considerable contribution to criteria pollutant emissions. (Less than Significant Cumulative Impact) Exposure Sensitive Receptors to Substantial Pollutant Concentrations The geographic area for cumulative impacts to sensitive receptors is 1,000 feet from the project site. The Library Courtyard project is over a half mile away and is outside of the geographic area for this impact. The Adobe Sewer Main Replacement project was adopted in 2020 and estimated to be completed in 2029. The project would potentially overlap with the proposed demolition. As discussed under checklist question c), the project would not expose sensitive receptors to substantial criteria air pollutant emissions and fugitive dust emissions would be reduced with incorporation of City Standard Conditions of Approval. The Adobe Sewer Main Replacement project would also be required to implement fugitive dust control measures.

A screening level cumulative community health risk assessment was prepared and considered all substantial sources of TACs (such as permitted stationary sources and/or roadways with average daily trips exceeding 10,000 vehicles) that could affect sensitive receptors located within 1,000 feet of the project site. No permitted stationary sources and no roadways with average daily trips exceeding 10,000 vehicles are within 1,000 feet.16 Based on the lack of cumulative community risk sources within 1,000 feet of the project site and the temporary health risk impacts the project would generate during demolition, the project would not expose sensitive receptors to substantial pollutant concentrations from cumulative sources of TAC. (Less than Significant Cumulative Impact)
Odors
On its own, demolition activities would not result in other emissions, such as odors, that would adversely affect a substantial number of people. As mentioned above, the Adobe Sewer Main Replacement project would potentially overlap with the demolition proposed. Due to the fact that construction odors are both localized and temporary, the cumulative odor impact from the construction of the project and the nearest cumulative project would be less than significant. (Less than Significant Cumulative Impact)
Overall, as discussed above, the project would have less than significant cumulative air quality impacts. (Less than Significant Cumulative Impact)
16 Bay Area Air District. “Permitted Stationary Sources Screening Report.” Accessed December 19, 2025. Available at https://baaqmd.maps.arcgis.com/apps/webappviewer/index.html?id=845658c19eae4594b9f4b805fb9d89a3.

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4.4 Biological Resources
The following discussion is based, in part, on a Biological Resources Report prepared by H.T. Harvey & Associates in August 2024. The report is attached to this EIR as Appendix C.

4.4.1 Environmental Setting
Regulatory Framework
Federal and State
Endangered Species Act
Individual plant and animal species listed as rare, threatened, or endangered under state and federal Endangered Species Acts are considered special-status species. Federal and state endangered species legislation has provided the United States Fish and Wildlife Service (USFWS) and the California Department of Fish and Wildlife (CDFW) with a mechanism for conserving and protecting plant and animal species of limited distribution and/or low or declining populations.

Permits may be required from both the USFWS and CDFW if activities associated with a proposed project would result in the take of a species listed as threatened or endangered. To “take” a listed species, as defined by the State of California, is “to hunt, pursue, catch, capture, or kill, or attempt to hunt, pursue, catch, capture, or kill” these species. Take is more broadly defined by the federal Endangered Species Act to include harm of a listed species.

In addition to species listed under state and federal Endangered Species Acts, Sections 15380(b) and (c) of the CEQA Guidelines provide that all potential rare or sensitive species, or habitats capable of supporting rare species, must be considered as part of the environmental review process. These may include plant species listed by the California Native Plant Society and CDFW-listed Species of Special Concern.

Migratory Bird Treaty Act
The federal Migratory Bird Treaty Act (MBTA) prohibits killing, capture, possession, or trade of migratory birds except in accordance with regulations prescribed by the Secretary of the Interior.

Hunting and poaching are also prohibited. This includes direct and indirect acts, except for harassment and habitat modification, which are not included unless they result in direct loss of birds, nests, or eggs. The CDFW also protects migratory and nesting birds under California Fish and Game Code Sections 3503, 3503.5, and 3800. The CDFW defines taking as causing abandonment and/or loss of reproductive efforts through disturbance.

Sensitive Habitat Regulations
Wetland and riparian habitats are considered sensitive habitats under CEQA. They are also afforded protection under applicable federal, state, and local regulations, and are generally subject to regulation by the United States Army Corps of Engineers (USACE), Regional Water Quality Control

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Board (RWQCB), CDFW, and/or the USFWS under provisions of the federal Clean Water Act (e.g., Sections 303, 304, 404) and State of California Porter-Cologne Water Quality Control Act.

Fish and Game Code Section 1602
Streambeds and banks, as well as associated riparian habitat, are regulated by the CDFW per Section 1602 of the Fish and Game Code. Work within the bed or banks of a stream or the adjacent riparian habitat requires a Streambed Alteration Agreement from the CDFW.

Local
Los Altos General Plan
The following policies in the City’s General Plan have been adopted for the purpose of reducing or avoiding impacts related to biological resources and are applicable to the project.

Policy Description
CDHR 1.1 Preserve trees, especially heritage and landmark trees that protect privacy in residential neighborhoods.

OSCC 2.3 Protect creeks, creekside areas and riparian habitat in their natural state while ensuring public safety and preserving a valuable natural resource.

OSCC 2.5 Enforce local, state, and federal regulations addressing water quality and stormwater quality management.

OSCC 4.1 Provide adequate level of maintenance for City parks, open space, and public property to ensure safety, aesthetics, and recreational enjoyment for Los Altos residents.

Los Altos Municipal Code
The LAMC contains provisions and laws adopted by the City Council to maintain a healthy and safe community and to preserve the quality of life in Los Altos. Chapter 11.08 of the LAMC is the City’s Tree Protection Ordinance, which prescribes measures for removal and replacement of trees in the City, and protective actions to be taken to avoid damage to existing trees. The Tree Protection Ordinance defines a “protected tree” as:
• Any tree that is 38 inches in circumference (12 inches in diameter measured at 48 inches above grade;
• Any tree of a native species that is 10 inches in diameter or greater measured at 48 inches above grade;
• Any tree designated by the Historical Commission as a heritage tree or any tree under official consideration by the Historical Commission for heritage tree designation;17 or 17 Trees may be designated as “heritage trees” upon application by the owner of the property on which the tree is located, a study of the proposed tree by the Historical Commission, and a determination of designation based on the criteria outlined in Section 11.08.060 of the Municipal Code.

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• Any tree which was required by the City to be either saved or planted in conjunction with a development review application.

All protected trees require a Tree Removal Permit before they can be removed based on the criteria described in LAMC Subsection 11.08.100.

Chapter 6.32 of the LAMC outlines the City’s watercourse protection regulations which detail required protection measures for waterways in the City, establish setbacks for development near Adobe Creek, and list permitted and prohibited activities within the setback areas adjacent to Adobe Creek.

Existing Conditions
As discussed in Section 3.0 Project Information and Description, the project site is located within the six-acre Preserve which is surrounded by single-family residences. The project site currently contains the Halsey House building that was originally used as a private residence but was subsequently converted to a nature center until it was vacated in 2008. It has remained vacant since 2008 and is no longer in use by staff or visitors. The area surrounding the structure contains seating areas, pathways, an ornamental garden, and an equipment shed. The remainder of the site consists of wooded areas that are dominated primarily by redwood trees and coast live oaks, interspersed with several other tree species including native California bay, California buckeye, and valley oak as well as some non-native tree species. Adobe Creek, which is an intermittent stream, is located approximately 50 feet northeast of the project site. The riparian habitat associated with Adobe Creek does not extend on to the project site.

Special-Status Species
Special-Status Plant Species
There are 89 special-status plant species that could potentially occur in the project region; however, 85 of those 89 species were determined to be absent from the project site for at least one of the following reasons: (1) absence of suitable habitat types, (2) lack of specific microhabitat or soil requirements, (3) the elevation range of the species is outside of the range of the project site, and/or (4) the project site is outside the species’ known geographic range and/or there are no nearby existing records.

Suitable habitat, soil conditions, and elevation range are present on the project site for four remaining special-status plant species. These species include Dudley’s lousewort, bent-flowered fiddleneck, California bottlebrush, and arcuate bush-mallow. To confirm whether these four species are present on-site, a focused survey was completed on May 7, 2024 during the blooming season for all four species. This survey determined that all four species are absent from the project site.

Because no special-status plant species were detected during appropriately timed, focused surveys, special-status plants are determined to be absent from the project site.

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Special-Status Animal Species
The coast live oak trees on the project site provide suitable roosting habitat for common bat species such as the Yuma myotis, California myotis, and big brown bat, and for three California species of special concern: the western red bat, Townsend’s big-eared bat, and pallid bat.

During a survey on May 7, 2024, a Townsend’s big-eared bat was observed roosting in the structure on-site. To further evaluate the presence of these bats, a follow-up dusk emergence survey was completed on-site on May 16, 2024. This survey utilized an acoustic detector which recorded bat calls both outside and inside the structure. Two California myotis and one Townsend’s big-eared bat were recorded flying overhead. Further, an acoustic detector was also left inside the Halsey House building for five nights. Based on an analysis of the recorded calls, it was determined that the Townsend’s big-eared bats using the building are most likely a non-maternity roost of a small number of individuals since the calls were only recorded in the late evening and early morning, when the bats exited and returned to the roost, as opposed to numerous call detections throughout the night, which is typical when adults are feeding young. Therefore, this roost likely consists of one or a few individual male bats, which is typical of this species.

Biologists conducting the May 7, 2024 survey also observed four active nests being utilized by the San Francisco dusky-footed woodrat, which is a California special species of concern. Suitable habitat areas for this species are located throughout the project site.

The California giant salamander (a California species of special concern), Vaux’s swift (a California species of special concern while nesting), yellow warbler (a California species of special concern), and white-tailed kite (a California fully protected species) could be present as foragers based on the suitable site conditions and habitat; however, none were noted during the survey on-site.

Other species including the mountain lion (a candidate for listing under the California Endangered Species Act, monarch butterfly (a candidate for listing under the Federal Endangered Species Act, western red bat, and pallid bat (both are California species of special concern) may also forage on the project site. The focused surveys did not determine suitable locations or detect the species.

Therefore, these species are not expected to den, roost, or breed on or immediately adjacent to the project site. The olive-sided flycatcher (a California species of special concern only when nesting) may occasionally occur on or over the project site as nonbreeding transients, foragers, or migrants, but no suitable nesting habitat for this species occurs on the project site. No aquatic habitats capable of supporting special-status fish species are present on the project site; however, Adobe Creek could potentially support the southern coastal roach and riffle sculpin which are California species of special concern.

Sensitive Natural Communities and Vegetation Alliances
The CDFW categorizes and ranks natural communities of vegetation based on the condition (rarity and endangerment) of a habitat throughout California. There are no sensitive natural communities or sensitive vegetation alliances present on-site.

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Riparian Habitat and Waters of the State/United States
As noted above, Adobe Creek is approximately 50 feet northeast of the project site. Riparian habitat associated with Adobe Creek does not extend onto the project site, and no wetlands or other waters of the United States/California occur on the project site.

4.4.2 Impact Discussion
For the purpose of determining the significance of the project’s impact on biological resources, would the project:
1) Have a substantial adverse effect, either directly or through habitat modifications, on any species identified as a candidate, sensitive, or special status species in local or regional plans, policies, or regulations, or by the California Department of Fish and Wildlife (CDFW) or United States Fish and Wildlife Service (USFWS)?
2) Have a substantial adverse effect on any riparian habitat or other sensitive natural community identified in local or regional plans, policies, regulations or by the CDFW or USFWS?
3) Have a substantial adverse effect on state or federally protected wetlands (including, but not limited to, marsh, vernal pool, coastal, etc.) through direct removal, filling, hydrological interruption, or other means?
4) Interfere substantially with the movement of any native resident or migratory fish or wildlife species or with established native resident or migratory wildlife corridors, or impede the use of native wildlife nursery sites?
5) Conflict with any local policies or ordinances protecting biological resources, such as a tree preservation policy or ordinance?
6) Conflict with the provisions of an adopted Habitat Conservation Plan, Natural Community Conservation Plan, or other approved local, regional, or state habitat conservation plan? Project Impacts
a) Would the project have a substantial adverse effect, either directly or through habitat modifications, on any species identified as a candidate, sensitive, or special status species in local or regional plans, policies, or regulations, or by the CDFW or USFWS? Special-Status Plant Species
The project’s demolition activities would result in the disturbance of approximately 15,000 square feet (or 0.3 acres) on the project site, which would include the footprint of the existing structure and vegetated areas containing trees and shrubs immediately adjacent to the building. As discussed in Section 4.4.1.2 Existing Conditions above, there are no special-status plant species present onsite. There are a variety of regionally common habitats and associated plant species that would be

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disturbed; however, these habitats do not provide regionally rare or especially high-value habitat for native vegetation, wildlife, or special-status species. Following the demolition of the structure on-site and removal of the demolished materials, the site would be replanted with native vegetation, which would provide some habitat value. Therefore, impacts to special-status plant species would be less than significant. (Less than Significant Impact) Special-Status Animal Species
As discussed in Section 4.4.1.2 Existing Conditions above, several special-status animal species have been identified on-site, and the site has habitat areas that could potentially be utilized by additional special-status animal species for shelter, travelling, foraging, and/or breeding.

Special-Status Aquatic Species
The project would not include any direct impacts to Adobe Creek or the surrounding riparian habitat; however, indirect impacts on water quality in the creek could potentially occur as a result of demolition activities. These activities could potentially impact the southern coastal roach and riffle sculpin in Adobe Creek due to a temporary increase in erosion, sedimentation, and turbidity in aquatic habitats located downstream of the work area. As discussed in further detail in Section 4.10 Hydrology and Water Quality, the project would implement Standard Conditions of Approval during demolition activities which would include BMPs to control erosion of exposed soil surfaces, which would prevent the discharge of stormwater pollutants into Adobe Creek. Additionally, the project would comply with the City’s permanent stormwater control measures (LAMC Section 10.16). With implementation of these BMPs, potential impacts to aquatic species adjacent to the site would be reduced to a less than significant level.

In addition, there is a low potential for individual California giant salamander to be present on-site due to the proximity of Adobe Creek. Although demolition activities could result in direct impacts to individuals who are foraging or traveling on-site, this would likely only impact one or two individuals, which would represent a very small proportion of the regional population. Therefore, this impact would be less than significant. (Less than Significant Impact) Non-breeding Special-Status Invertebrates, Birds, and Mammals As discussed in Section 4.4.1.2 Existing Conditions, the monarch butterfly, olive-sided flycatcher, mountain lion, and western red bat may occur on the project site as non-breeding migrants, transients, or foragers. Construction activities might result in a temporary direct impact through the alteration of foraging patterns (e.g., avoidance of work sites because of increased noise) but they would not result in the loss of individuals, as individuals of these species would move away from any construction areas or equipment before they could be injured or killed. In addition, the project site does not provide foraging habitat for large numbers of individuals of these species; therefore, impacts resulting from the project would be less than significant. (Less than Significant Impact)

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Special-Status Bird Species
Three special-status bird species have the potential to nest on or adjacent to the site. The whitetailed kite could nest in oak woodland habitat or landscape trees on and adjacent to the project site. The Vaux’s swift could nest in the existing structure’s chimney or in hollow snags in surrounding areas. The yellow warbler could nest adjacent to the project site in riparian trees along Adobe Creek. Demolition activities associated with the project would not result in the permanent loss of suitable nesting habitat for the yellow warbler, as no activities are proposed within the adjacent riparian habitat along Adobe Creek. However, the project would result in the permanent loss of suitable nesting and foraging habitat for the white-tailed kite and Vaux’s swift, as well as suitable foraging habitat for the yellow warbler.

Based on site observations, the amount of suitable habitat areas within and adjacent to the site, and known nesting densities of these species, it is unlikely that more than one or two pairs of these species would inhabit the project area at the same time. This would represent a very small fraction of the regional population of these species. Therefore, any potential impacts from the project would not constitute a significant impact on these species or their habitat. To protect individuals of these species and any other nesting birds or raptors that may utilize habitat on-site, the project would implement the following Standard Conditions of Approval.

Standard Conditions of Approval: Preconstruction Nesting Bird Survey: To the extent practicable, vegetation removal and construction activities shall be performed from September 1 through January 31 to avoid the general nesting period for birds. If construction or vegetation removal cannot be performed during this period, preconstruction surveys will be performed no more than two days prior to construction activities to locate any active nests as follows:
• The applicant shall be responsible for the retention of a qualified biologist to conduct a survey of the project site and surrounding 500 feet for active nests – with particular emphasis on nests of migratory birds – if construction (including site preparation) will begin during the bird nesting season, from February 1 through August 31. • If active nests are observed on either the project site or the surrounding area, the applicant, in coordination with the appropriate City staff, shall establish no-disturbance buffer zones around the nests, with the size to be determined in consultation with the California Department of Fish and Wildlife (CDFW) (usually 100 feet for perching birds and 300 feet for raptors). The no-disturbance buffer will remain in place until the biologist determines the nest is no longer active or the nesting season ends. If construction ceases for two days or more and then resumes during the nesting season, an additional survey will be necessary to avoid impacts on active bird nests that may be present.

Implementation of the Standard Conditions of Approval above would ensure that either project activities would take place outside of the nesting season, or that pre-construction surveys are completed and appropriate buffers are established, to reduce any impacts to nesting birds and raptors on or near the project site to a less than significant level. (Less than Significant Impact)

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San Francisco Dusky-Footed Woodrat
As discussed in Section 4.4.1.2 Existing Conditions, four nests of San Francisco dusky-footed woodrats were observed in the coast live oak woodland habitat on-site. Woodrats from this community would also likely forage in the oak woodland habitats throughout the site. Vegetation clearing and operation of equipment during demolition activities could result in the injury or mortality of individual woodrats and the disturbance or destruction of nests which could lead to increased predation risk for these individuals. Although woodrats are abundant in the surrounding region, impacts to these woodrat nests would be a significant impact due to their ecological importance as a prey source for other predatory species.

Impact BIO-1: Disturbance of the existing woodrat nests on-site could result in the destruction of nests and injury or mortality of individual woodrats.

Mitigation Measures:

MM BIO-1.1: Pre-Activity Survey. A qualified biologist shall conduct a pre-activity survey for San Francisco dusky-footed woodrat nests within 30 days of the start of work activities. If active woodrat nests are determined to be present in, or within 10 feet of, the impact areas, MM BIO-1.2 and MM BIO-1.3 below shall be implemented, as appropriate.

MM BIO-1.2: Avoidance Buffers. Active woodrat nests that are detected in, or within 10 feet of, the impact areas shall be avoided. A minimum 10-foot buffer shall be maintained between project activities and woodrat nests to avoid disturbance.

In some situations, a smaller buffer may be allowed if, in the opinion of a qualified biologist, nest relocation (MM BIO-1.3 below) would represent a greater disturbance to the woodrats than the adjacent work activities.

MM BIO-1.3: Nest Relocation. If avoidance of active woodrat nests within and immediately adjacent to the work impact is not feasible (e.g., because it would preclude implementation of the project), then nest materials shall be relocated to suitable habitat as close to the project area as possible, as determined and implemented by a qualified biologist (ideally, within or immediately adjacent to the project site). Relocation efforts shall avoid the peak nesting season (February to July).

Prior to the start of work activities, a qualified biologist shall disturb the woodrat nest to the degree that all woodrats leave the nest and seek refuge outside of the impact area. Disturbance of the woodrat nest shall be initiated no earlier than one hour before dusk to prevent the exposure of woodrats to diurnal predators. Subsequently, the biologist shall dismantle and relocate the nest material by hand. During the deconstruction process, the biologist shall assess if there are juveniles in the nest. If immobile juveniles are observed, the

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dismantling process shall be discontinued until a time when the biologist believes the juveniles will be capable of independent survival (typically after two to three weeks). A no-disturbance buffer shall be established around the nest until the juveniles are mobile. The nest may be dismantled once the biologist has determined that adverse impacts on the juveniles would not occur.

With implementation of mitigation measures MM BIO-1.1 through BIO-1.3 above, impacts of the project on the San Francisco dusky-footed woodrat would be reduced to a less than significant level. (Less than Significant Impact with Mitigation Incorporated) Common and Special-Status Roosting Bats
As discussed in Section 4.4.1.2 Existing Conditions, one or several Townsend’s big-eared bats are roosting in the structure on-site. In addition, the large coast live oak trees on the project site provide suitable roosting habitat for the western red bat, pallid bat, and common bat species, such as the Yuma myotis, California myotis, and big brown bat. Although the trees on the site provide suitable roosting habitat, no evidence of a colony of roosting bats was detected in trees on-site during the May 7, 2024 survey, indicating that bats are not roosting in these trees currently, and no maternity colony is present. However, the proposed demolition of the structure on-site could result in direct impacts to the Townsend’s big-eared bats, as individuals could be physically injured or killed, subjected to physiological stress, or face increased predation because of exposure during daylight. Direct impacts to the Townsend’s big-eared bats would be considered significant.

Impact BIO-2: Demolition of the structure on-site would disturb Townsend’s big-eared bats roosting within the structure.

Mitigation Measures:

MM BIO-2.1: Bat Exclusion from Halsey House. Prior to the start of any project-related activities on the exterior or interior of the Halsey House building, a qualified bat biologist shall guide and supervise the installation of appropriate exclusion devices to allow any roosting Townsend’s big-eared bats (and other bat species, if present) to vacate the roost and prevent bats from reoccupying these features before construction activities are initiated. Bird exclusion netting shall not be used because bats may become entangled in it, potentially leading to mortality.

Exclusion materials shall be inspected by a qualified biologist once per month between their installation and initiation of building demolition, to ensure that the materials are in good working order. If exclusion materials become compromised, the City shall perform maintenance on these devices, as directed by the qualified biologist.

With implementation of mitigation measure MM BIO-2.1, the project would reduce potential impacts to the Townsend’s big-eared bat to a less than significant level. (Less than Significant Impact with Mitigation Incorporated)

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Based on this discussion, implementation of mitigation measures MM BIO-1.1 through BIO-1.3, and MM BIO-2.1 would reduce project impacts to special-status animal species to a less than significant level. (Less than Significant Impact with Mitigation Incorporated) b) Would the project have a substantial adverse effect on any riparian habitat or other sensitive natural community identified in local or regional plans, policies, regulations, or by the CDFW or USFWS?
As discussed in Section 4.4.1.2 Existing Conditions, there are no sensitive natural communities or sensitive vegetation alliances present on-site. Adobe Creek and its associated riparian habitat is adjacent to the project site; however, there is no riparian habitat on-site and there would not be any direct impacts to riparian habitat resulting from the project. As discussed under checklist question a) above, demolition activities on-site could result in indirect impacts to Adobe Creek and the associated riparian habitat if these activities generate contaminated stormwater runoff that drains into Adobe Creek. To reduce those potential indirect impacts, the project would implement Standard Conditions of Approval (as discussed in Section 4.3 Air Quality) during demolition activities and utilize BMPs to control erosion of exposed soil surfaces. Additionally, the project would comply with the City’s permanent stormwater control standards (LAMC Section 10.16). Therefore, discharge of stormwater pollutants into Adobe Creek would be prevented, and potential impacts to the riparian habitat areas adjacent to the site would be reduced to a less than significant level. (Less than Significant Impact)
c) Would the project have a substantial adverse effect on state or federally protected wetlands through direct removal, filling, hydrological interruption, or other means? There are no wetland areas present on-site. As discussed under checklist questions a) and b) above, Adobe Creek is approximately 50 feet northeast of the project site, and there is some potential for indirect impacts to the creek that could occur if contaminated stormwater runoff drains to the creek. The project would implement Standard Conditions of Approval (as discussed in Section 4.3 Air Quality) during demolition activities and utilize BMPs to control erosion of exposed soil surfaces.

With implementation of these Standard Conditions of Approval, potential impacts to wetland areas along Adobe Creek would be reduced to a less than significant level. (Less than Significant Impact) d) Would the project interfere substantially with the movement of any native resident or migratory fish or wildlife species or with established native resident or migratory wildlife corridors, or impede the use of native wildlife nursery sites? There are no established native resident or migratory wildlife corridors on-site; however, Adobe Creek and the associated riparian corridor adjacent to the project site are utilized by various aquatic and terrestrial wildlife species as a movement corridor. Migrating songbirds also utilize the creek corridor during their migration. The project would not result in any loss of aquatic, wetland, or

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riparian habitat along Adobe Creek or in any substantial reduction in the value of the Adobe Creek corridor for wildlife movement. In addition, the removal of the existing structure on-site could result in a net benefit to foraging or migrating individuals utilizing the creek corridor as there would be fewer physical barriers adjacent to the creek. Aquatic and terrestrial species would continue to be able to move north to south along Adobe Creek following completion of the project.

As discussed under checklist question a), the primary structure on-site is not currently utilized as a nursery site by the Townsend’s big-eared bats roosting in the structure. The project would implement MM BIO-2.1 prior to demolition activities to prevent any common or special-status bat species from roosting in the building and/or establishing a maternity roost. In addition, Standard Conditions of Approval would be implemented to reduce potential impacts to nesting birds on-site.

Based on this discussion, the project would not interfere substantially with the movement of any native resident or migratory fish or wildlife species, with established native resident or migratory wildlife corridors, or impede the use of native wildlife nursery sites. Therefore, the project would result in a less than significant impact with mitigation incorporated. (Less than Significant Impact with Mitigation Incorporated)
e) Would the project conflict with any local policies or ordinances protecting biological resources, such as a tree preservation policy or ordinance? Los Altos Tree Protection Ordinance
Demolition activities on-site could potentially include the removal of two existing trees located directly adjacent to the structure, a small oak tree and a mature cypress tree, neither of which would be considered protected trees under the City’s Tree Protection Ordinance. The project would comply with Section 11.08.120 of the LAMC requiring a one-to-one replacement ratio and tree replacement plan. In addition, the project would implement tree protection measures outlined in Section 11.08.140 of the LAMC which would include installing protective fencing around remaining trees, maintaining the existing grade out to the dripline of existing, adjacent trees, repairing trees that are damaged by project activities, and avoiding attachment of signs, wires, or other objects to existing trees. As a result, the proposed project would not conflict with the City’s Tree Protection Ordinance. (Less than Significant Impact)
Los Altos Watercourse Protection Regulations
Per Section 6.32.040 of the LAMC, an 80-foot setback from the top of bank of Adobe Creek would be required based on the location and size of the project site. This buffer area is required to protect Adobe Creek, any associated riparian habitat, and species that may utilize the habitat and foraging space. The northern portion of the structure on-site and several walkways are currently within this established setback area. In addition, there are approximately 243 square feet of coast live oak woodland on-site that fall within the setback area. The project would demolish the Halsey House and may also require the pruning of existing trees to accommodate construction equipment. Some of these activities would occur within the established setback area.

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Consistent Section 6.32.060 of the LAMC, an exception would be required to perform demolition activities (e.g., removal of vegetation, demolition, grading) within the setback area. The project would be required to obtain this exception prior to initiating demolition activities on-site; therefore, it would comply with the City’s Watercourse Protection Regulations. In addition, the removal of all structures and existing improvements on-site would result in a minor improvement to the area within the 80-foot setback as there would no longer be physical barriers for wildlife on-site and the area that previously contained built structures would return to a ruderal habitat that would provide some habitat value (e.g., foraging habitat) for animals associated with the creek corridor. Based on this discussion, the proposed project would not conflict with the City’s Watercourse Protection Regulations. (Less than Significant Impact)
f) Would the project conflict with the provisions of an adopted Habitat Conservation Plan, Natural Community Conservation Plan, or other approved local, regional, or state habitat conservation plan?
The City of Los Altos has not established a habitat conservation plan or a natural community conservation plan, nor is it located within the boundaries of an approved local, regional, or state habitat conservation plan. Therefore, the project would not conflict with an adopted local, regional, or state habitat conservation plan. (No Impact)
Cumulative Impacts
Would the project result in a cumulatively considerable contribution to a significant cumulative biological resources impact?
The geographic area for cumulative impacts to biological resources includes the project site and surrounding area because it is assumed any impacts on-site would affect similar biological resources in the surrounding area. The cumulative impact on biological resources resulting from the project in combination with other cumulative projects in the vicinity would be dependent on the relative magnitude of adverse effects of these projects on biological resources compared to the relative benefit of impact avoidance and minimization efforts prescribed by planning documents, CEQA mitigation measures, and permit requirements for each project. Any cumulative projects in the vicinity would undergo separate environmental review and implement appropriate measures to reduce impacts to biological resources to a less than significant level.

The project would not have a significant impact on biological resources as it would implement the mitigation measures described in checklist questions a) through f) above to reduce potential impacts. With implementation of these measures, the project would avoid or reduce impacts to biological resources. Any impacts would be made to a small fraction of regional populations of the affected species. Therefore, the project would not result in a cumulatively considerable contribution to a significant cumulative biological resources impact. (Less than Significant Cumulative Impact with Mitigation Incorporated)

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4.5 Cultural Resources
The following discussion is based, in part, on a Historic Resources Evaluation prepared by Page & Turnbull in July 2021. The report is attached to this EIR as Appendix D.

4.5.1 Environmental Setting
Regulatory Framework
Federal and State
National Historic Preservation Act
Federal protection is legislated by the National Historic Preservation Act of 1966 (NHPA) and the Archaeological Resource Protection Act of 1979. These laws maintain processes for determination of the effects on historical properties eligible for listing in the National Register of Historic Places (NRHP). Section 106 of the NHPA and related regulations (36 Code of Federal Regulations [CFR] Part 800) constitute the primary federal regulatory framework guiding cultural resources investigations and require consideration of effects on properties that are listed or eligible for listing in the NRHP.

Impacts to properties listed in the NRHP must be evaluated under CEQA.

California Register of Historical Resources
The CRHR is administered by the State Office of Historic Preservation and encourages protection of resources of architectural, historical, archeological, and cultural significance. The CRHR identifies historic resources for state and local planning purposes and affords protections under CEQA. Under Public Resources Code Section 5024.1(c), a resource may be eligible for listing in the CRHR if it meets any of the NRHP criteria.18
Historical resources eligible for listing in the CRHR must meet the significance criteria described previously and retain enough of their historic character or appearance to be recognizable as historical resources and to convey the reasons for their significance. A resource that has lost its historic character or appearance may still have sufficient integrity for the CRHR if it maintains the potential to yield significant scientific or historical information or specific data.

The concept of integrity is essential to identifying the important physical characteristics of historical resources and, therefore, in evaluating adverse changes to them. Integrity is defined as “the authenticity of a historical resource’s physical identity evidenced by the survival of characteristics that existed during the resource's period of significance.” The processes of determining integrity are similar for both the CRHR and NRHP and use the same seven variables or aspects to define integrity 18 California Office of Historic Preservation. “California Office of Historic Preservation Technical Assistance Series #6.” Accessed August December 19, 2025.
https://ohp.parks.ca.gov/pages/1069/files/technical%20assistance%20bulletin%206%202011%20update.pdf.

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that are used to evaluate a resource's eligibility for listing. These seven characteristics include 1) location, 2) design, 3) setting, 4) materials, 5) workmanship, 6) feeling, and 7) association.

California Native American Historical, Cultural, and Sacred Sites Act The California Native American Historical, Cultural, and Sacred Sites Act applies to both state and private lands. The act requires that upon discovery of human remains, construction or excavation activity must cease and the county coroner be notified.

Public Resources Code Sections 5097 and 5097.98
Section 15064.5 of the CEQA Guidelines specifies procedures to be used in the event of an unexpected discovery of Native American human remains on non-federal land. These procedures are outlined in Public Resources Code Sections 5097 and 5097.98. These codes protect such remains from disturbance, vandalism, and inadvertent destruction, establish procedures to be implemented if Native American skeletal remains are discovered during construction of a project, and establish the Native American Heritage Commission (NAHC) as the authority to resolve disputes regarding disposition of such remains.

Pursuant to Public Resources Code Section 5097.98, in the event of human remains discovery, no further disturbance is allowed until the county coroner has made the necessary findings regarding the origin and disposition of the remains. If the remains are of a Native American, the county coroner must notify the NAHC. The NAHC then notifies those persons most likely to be related to the Native American remains. The code section also stipulates the procedures that the descendants may follow for treating or disposing of the remains and associated grave goods.

Local
Los Altos General Plan
The following policies in the City’s General Plan have been adopted for the purpose of reducing or avoiding impacts related to cultural resources and are applicable to the project.

Policy Description
CDHR 6.1 Ensure that the integrity of historic structures and the parcels on which they are located are preserved through the implementation of applicable design, building, and fire codes.

CDHR 6.2 The City shall regard demolition of landmark and historic resources, listed in the Historic Resources Inventory as a last resort. Demolition would be permitted only after the City determines that the resource has lost its physical integrity, retains no reasonable economic use, that demolition is necessary to protect health, safety, and welfare, or that demolition is necessary to proceed with a new project where the benefits of the new project outweigh the loss of the historic resource.

CDHR 6.4 Preserve archaeological artifacts and sites found in Los Altos or mitigate disturbance to them, consistent with their intrinsic value.

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Policy Description
CDHR-6.5 Require an archaeological survey prior to the approval of significant development projects near creeksides or identified archaeological sites.

Los Altos Municipal Code
Chapter 12.44 of the LAMC establishes the criteria and processes for the designation of historic resources in the City, outlines the responsibilities of the City’s Historical Commission, and describes the permit requirements for proposed alterations to historic resources. The primary purposes of Chapter 12.44 are to ensure protection of irreplaceable historic resources, enhance visual character through architectural compatibility, and encourage appreciation of the City’s past. The criteria for local designation are:

1. Age. A structure or property should be more than 50 years in age.

2. Determination of Integrity. A structure or property should retain sufficient historic integrity in most of the following areas: design, setting, materials, workmanship, and feeling.

3. Historic Significance. A structure or property should be clearly associated with one or more of the following areas of significance: event, person/people, architecture/design, and archaeology.

Los Altos Historic Resources Inventory
The City maintains a Historic Resources Inventory (HRI) which contains historic landmark properties, historic resource properties, and designated heritage trees of local importance.19 There are two main types of protected structures in Los Altos: historic resources and historic landmarks. A historic resource is a property or structure that has been determined to be over 50 years old; retains its physical integrity; has historical, architectural, cultural, and/or aesthetic value; and is listed on the HRI. A historic landmark is a building, improvement, structure, natural feature, site, or area of land that has significant historical, architectural, cultural, and/or aesthetic interest or value, and is officially designated as a landmark by the City Council. Structures are deemed historic resources or landmarks through an evaluation of consistency with Chapter 12.44.

Existing Conditions
Archaeological Resources
Native Americans occupied Santa Clara Valley and the greater Bay Area for more than 5,000 years.

The exact time period of the Ohlone (originally referred to as Costanoan) migration into the Bay Area is debated by scholars. Dates of the migration range from between 3,000 B.C. and 500 A.D.

Regardless of the actual time frame of their initial occupation of the Bay Area and, in particular, Santa Clara Valley, it is known that the Ohlone had a well-established population of approximately 7,000 to 11,000 people with a territory that ranged from the San Francisco Peninsula and the East 19 City of Los Altos. “Historic Resources Inventory.” Accessed December 19, 2025. https://www.losaltosca.gov/535/Historic-Inventory.

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Bay, south through Santa Clara Valley and down to Monterey and San Juan Bautista. The Ohlone people were hunter/gatherers focused on hunting, fishing, and collecting seasonal plant and animal resources, including tidal and marine resources from San Francisco Bay. The customary way of living, or lifeway, of the Ohlone people disappeared by about 1810 due to disruption by introduced diseases, a declining birth rate, and the impact of the California mission system established by the Spanish in the area beginning in 1777.

A Sacred Lands File inventory request was submitted to the NAHC on March 1, 2024. The NAHC responded on March 5, 2024 with information that the Sacred Lands File search was negative for the presence of sacred sites. However, the negative Sacred Lands File results do not preclude the project area from having unknown subsurface cultural resources (including tribal cultural resources). Historically, the Ohlone and Muwekma Indian tribes have made their homes along creeks.20 Adobe Creek is approximately 50 feet northeast of the Halsey House. Therefore, the project site may be sensitive for archaeological resources.

Historic Resources
The Halsey House is located on-site. The Spanish Colonial Revival style21 house was historically the single-family residence of Theodore Vail Halsey and Emma Wright Halsey from 1923 through 1945.

Prior the construction of the Halsey House, the surrounding land, which now consists of the Preserve, was owned by the parents of Emma Wright Halsey, who bought the property in 1912 to construct a summer cottage to be used seasonally as a getaway from San Francisco. The land was gifted to Emma Wright Halsey when she wed Theodore Vail Halsey in 1915. The couple decided to make Los Altos their permanent residence in 1923, which led to the construction of the Halsey House. Additions were made to the residence in 1928 to provide an apartment for Emma Wright Halsey’s mother, Myra Wright, and in the 1930s to add living quarters for a servant. During her occupancy of the Halsey House, Emma Wright Halsey with the help of Mori and Yoshio Hongo, her gardeners, changed the landscape of the property by planting redwoods, fruit trees (including apple, pear, apricot, cherry, almond, persimmon, and walnut trees), and flowering gardens. Other improvements to the property included several small wood bridges that crossed over Adobe Creek, the construction of benches, the lining of planting areas with stone borders, the construction of a croquet court, and the construction of other small buildings (e.g., caretaker’s cottage, guest cottage, and garage).

From 1945 to 1970, the Halsey House was owned by Edward C. Bessey and Rachel M. S. Bessey (Bessey Family). While the Bessey Family owned the property, there are no records indicating the family lived in the Halsey House because their residences were identified in San José, Palo Alto, 20 City of Los Altos. Los Altos General Plan Initial Study/Mitigated Negative Declaration. November 2002. Page 20. 21 The Halsey House illustrates some of the common features of the Spanish Colonial Revival style through its material palette of clay tile roofing, lightly colored stucco cladding, and multi-lite windows and doors with wood sash. The Halsey House also integrated interior and exterior spaces through the use of French doors and courtyards, which is an element of this particular style. Source: Page & Turnbull. Halsey House Historic Resource Evaluation. July 28, 2021. Pages 36 and 37.

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Mountain View, Los Altos, and Los Altos Hills. Instead, the Halsey House was subdivided into two units and a range of six to ten cottages were constructed for rent.

In 1970, Meredith Pearson bought the six-acre property to save the area from development and establish a communal living space for family and friends. During her ownership the Halsey House and cottages constructed by the Bessey Family were occupied by friends and renters, respectively.

The City of Los Altos bought the six-acre property in 1974 to be a park, using the Halsey House as an educational center and small museum for the public until 2008 when it was closed. Since 2008, the Halsey House has been vacant.

National Register of Historic Places
The Halsey House is not currently listed on the NRHP.

California Register of Historical Resources Evaluation
The Halsey House is not currently listed on the CRHR. The residence was evaluated for eligibility for the CRHR.

In order for a property to be eligible for listing in the CRHR, it must be found significant under one or more of the following criteria.
• Criterion 1 (Events): Resources that are associated with events that have made a significant contribution to the broad patterns of local or regional history, or the cultural heritage of California or the United States.
• Criterion 2 (Persons): Resources that are associated with the lives of persons important to local, California, or national history.
• Criterion 3 (Design/Architecture): Resources that embody the distinctive characteristics of a type, period, region, or method of construction, or represent the work of a master, or possess high artistic values.
• Criterion 4 (Information Potential): Resources or sites that have yielded or have the potential to yield information important to the prehistory or history of the local area, California, or the nation.

Criterion 1 (Events)
The Halsey House and Preserve are an example of the residential patterns of Los Altos. As mentioned above, the six-acre property was originally owned by the parents of Emma Wright Halsey as a summer retreat from San Francisco. Middle- to upper middle-class residents of San Francisco typically owned a second residential property in Los Altos and along the Peninsula to escape the fog and cooler weather of San Francisco during the summer. As businesses, schools, and public transit options (e.g., railway systems) became more common along the Peninsula, more families migrated out of San Francisco to establish homes in Los Altos and the surrounding area.

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The Halsey family’s decision to permanently reside at Halsey House in 1923 coincided with the boom of year-round residential properties being constructed in Los Altos along the University Avenue and Orange Avenue area. Unlike the other residential residences that were developed as freestanding single-family residences on small parcels facing the street, the Halsey House was constructed in a manner that complimented the rural setting of its location. Emma Wright Halsey, Mori, and Yoshio kept the rural setting of the area by planting redwoods, fruit trees, and gardens.

While most of the landscaping done by Emma Wright Halsey and her gardeners no longer exists, their work helped establish the area known today as the Preserve and the area is still able to convey the historic setting of the Halsey House. Since both the residence and surrounding area made a significant contribution to the broad patterns of local and regional history of California, the Halsey House and the Preserve are individually eligible for the CRHR under Criterion 1 (Events).

Criterion 2 (Persons)
As mentioned above, the Halsey House was owned by Emma Wright Halsey and her husband Theodore Vail Halsey, the Bessey Family, and Meredith Pearson. While Theodore Vail Halsey had a successful career in the telephone industry, his personal achievements were not tied specifically to the Halsey House because no research indicates he used the home for professional reasons. While Emma Wright Halsey and her gardeners are tied to the development of Halsey House and the creation of what would be the Preserve, they themselves are not considered historically significant people. Their contributions do not rise to the level of importance where they, as individual persons, would be considered significant contributors to local, state, or national history. Emma Wright Halsey’s, Mori’s, and Yoshio’s work on the Halsey House and surrounding area are better tied to CRHR Criterion 1. The Bessey Family and Meredith Pearson were individuals that owned the residence from 1945 and 1974. They are largely unknown individuals with no significant personal achievements tied to the Halsey House. For these reasons, the property is not eligible for listing on the CRHR under Criterion 2 (Persons).

Criterion 3 (Design/Architecture)
The Halsey House was constructed in 1923 and was designed by an unknown architect. The building was designed in a modest Spanish Colonial Revival style, demonstrated through its stucco cladding, hipped clay tile roof, low one-story massing arranged around a private courtyard with bench seating and a fountain, and extensive use of multi-lite windows and doors. Two additions were added in 1928 and in the early 1930s in the same existing style and design to match the original architecture of the Halsey House. While the Halsey House is an example of Spanish Colonial Revival Style, it does not have decorative plasterwork, tile, or exposed wood elements that are indicative of this style. It is neither a modest nor high-style example of Spanish Colonial Revival Style but a simple interpretation. The Halsey House is also not the only residence representative of this style in Los Altos or the greater Bay Area (Palo Alto, Mountain View, Hillsborough, and San José). It does not represent distinctive methods of construction or craftsmanship. As the architect or builder of the residence remains unidentified, the Halsey House is also not considered significant for its association with a master architect or builder. The landscaping of Halsey House is also not considered individually significant under Criterion 3 because the majority of the original landscaping

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has been removed. Therefore, the Halsey House is not eligible for the CRHR under Criterion 3 (Design/Architecture).

Criterion 4 (Information Potential)
The “potential to yield information important to the prehistory or history of California” typically relates to archaeological resources rather than built resources. When Criterion 4 does relate to built resources, it is relevant for cases when the buildings themselves are the principal source of important construction-related information. The property is not eligible for the CRHR under Criterion 4 (Information Potential).

Aspects of Integrity
To qualify for listing in the CRHR, a property must possess significance under one or more of the above-listed criteria and have historic integrity. Historic integrity is based on location, design, setting, materials, workmanship, feeling, and association.

Location and Setting
The building retains integrity of location and setting since it has not been moved and the surrounding area has retained its wooded and natural setting. The redwood saplings that were planted by Emma Wright Halsey and Mori are now mature trees.

Design
The integrity of design has not been diminished since the Halsey House still retains its overall form, massing, and materials as a modest example of a 1920s Spanish Colonial Revival despite several alterations. While lacking the more ornate features of the style including decorative plasterwork, tile, and exposed wood elements, the building features a large number of multi-lite windows and French doors that illustrate the porous relationship between the interior and exterior spaces of the building. Also, the alterations to the massing and footprint of the building were undertaken during the ownership of the Halsey family and are considered historic. Overall, the original design of the building remains intact, and the materials, decoration, craftsmanship, and massing of the building have remained largely unchanged since 1945 with the exception of some replacement windows and doors. Therefore, the structure retains integrity of design.

Workmanship
The Halsey House retains its wood-frame building with stucco cladding and a clay title hipped roof.

The residence also retains the scored and tinted concrete patios and metal features throughout the building. These details convey the workmanship of the Halsey House. Therefore, the structure retains integrity of workmanship.

Feeling
The Halsey House is still within the Preserve and set within the wooded landscape around Adobe Creek. The feeling of a 1920s year-round home has not been diminished since the residence retains

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a semi-rural feeling and the architecture has not been altered. Therefore, the residence retains integrity of feeling.

Association
The Halsey House is still significant for its residential and development history. The Preserve is evidence of the landscaping started by Emma Wright Halsey and Mori and Yoshio Hongo. The Halsey House still remains intact with its 1920s architectural characteristics and represents Emma Wright Halsey’s period of residence. Therefore, the structure retains integrity of association.

Based on the above, the Halsey House and the Preserve retain all seven aspects of their integrity.

Since the residence and the Preserve are individually eligible for listing on the CRHR under Criterion 1 for their contribution to the broad patterns of local history and retain their integrity, the structure is considered a historical resource under CEQA.

City of Los Altos Historic Resources Inventory
The residence and the Preserve have been designated as City Historic Landmarks since May 1981.

The Historic Resources Evaluation (Appendix D) included an analysis of the Halsey House against the City’s local criteria. For a property to be a historic resource on the City of Los Altos HRI, it must be over fifty years of age, retain its physical integrity, and have historical significance related to historic events, persons, architecture and design, or archaeological significance. These criteria reflect the NRHP and CRHR but prioritize the evaluation of a structure’s integrity first in evaluation of its historic significance as opposed to evaluating integrity only after historic significance is determined as is the case under the NRHP and CRHR criteria. For listing as a Historic Landmark, the City requires that the resource is a rare or unique property type.

The Halsey House is over a century old and meets the age threshold as a historic resource. In addition, while the condition of the building is poor due to environmental damage and vandalism, the building retains over 50 percent of its original materials, form, and character-defining features, which is the threshold for physical integrity as established in the City’s Historic Resource Inventory criteria. As described above, the Halsey House property has all seven aspects of integrity (location, design, setting, materials, workmanship, feeling, and association). The residence is also representative of residential development patterns in Los Altos and for the establishment of the Redwood Grove. For these reasons, the Halsey House property continues to meet the criteria for inclusion on the HRI and as a City Historic Landmark.

4.5.2 Impact Discussion
For the purpose of determining the significance of the project’s impact on cultural resources, would the project:
1) Cause a substantial adverse change in the significance of a historical resource pursuant to CEQA Guidelines Section 15064.5?

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2) Cause a substantial adverse change in the significance of an archaeological resource pursuant to CEQA Guidelines Section 15064.5?
3) Disturb any human remains, including those interred outside of dedicated cemeteries? Project Impacts
a) Would the project cause a substantial adverse change in the significance of a historical resource pursuant to CEQA Guidelines Section 15064.5?
As discussed above in Section 4.5.1.2 Existing Conditions, the Halsey House is on the HRI and was determined to be eligible for listing on the CRHR under Criterion 1 as an example of residential development patterns in Los Altos and the development of the Preserve. The residence retains all seven aspects of integrity. Therefore, Halsey House is considered a historical resource. The demolition of Halsey House would permanently remove the resource, resulting in a substantial adverse change to a significant historical resource pursuant to CEQA Guidelines Section 15064.5.

Impact CUL-1: Implementation of the proposed project would result in the demolition of the Halsey House, which is a historic resource.

Mitigation Measures:

MM CUL-1.1: Historic Resources Mitigation Action Plan. Prior to issuance of any demolition permits, the City shall retain a qualified historian to prepare and submit a Historic Resources Mitigation Action Plan (Action Plan) to the Director of Development Services or the Director’s designee for review and approval. The Action Plan shall include the following elements:

Documentation. The structure and associated features on the project site shall be documented in accordance with the guidelines established for the Level III Historic American Building Survey (HABS) consistent with the Secretary of the Interior’s Standards for Architectural and Engineering Documentation. The documentation shall be funded by the City and undertaken by a qualified historian who meets the Secretary of the Interior’s Professional Qualification Standards for history, architectural history, or historic architecture (Code of Federal Regulations, Title 36, Part 61, Appendix A). The documentation shall consist of the following components:

A. Drawings – Original architectural drawings or as-built measured drawings of the building shall be submitted as part of the documentation package. Reasonable efforts shall be made to locate original drawings of the historic building. If located, selected representative drawings (such as site plans, elevations, sections, and relevant key details) shall be photographed or scanned at high resolution, reproduced, and included

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in the dataset. If original architectural or construction drawings cannot be located, then measured drawings shall be prepared according to HABS guidelines by a professional who meets the Secretary of the Interior’s Professional Qualification Standards for Architecture or Historic Architecture. The measured drawings shall be reviewed by the historian retained to prepare the written historical report.

B. Photographs – Digital photographs shall be taken of the historic building, associated landscaping, and the overall character and setting of the property. All digital photography shall be conducted according to current National Park Service (NPS) standards as specified in the National Register of Historic Places and National Historic Landmarks Program Consolidated and Updated Photograph Policy 2024. The photography shall be undertaken by a qualified professional with demonstrated experience in documentation photography. Large format negatives are not required. All photographs shall be referenced on a photographic key map or site plan. The photographic key shall show the photograph number with an arrow to indicate the direction of the view. Digital photographs shall be taken in uncompressed RAW file format and saved as TIFF files. The size of each image shall be a minimum of 1600x1200 pixels at 300 pixels per inch or larger and in color format. The file name for each electronic image shall correspond with the index of photographs and photograph label.

C. Written Data – A written historical narrative and report that meets the HABS Historical Report Guidelines shall be produced for the property by a qualified historian. The HABS-Style Historical Report shall follow the outline format with a statement of significance of the property.

The documentation shall be submitted to the Director of Development Services or the Director’s designee for review and approval. After approval, the required documentation shall be filed with the Northwest Information Center at Sonoma State University (the repository for the California Historical Resources Information System) and the Los Altos History Museum.

Interpretive Display. Prior to issuance of any demolition permits, the City, in consultation with a qualified historian or architectural historian who meets the Secretary of the Interior’s Professional Qualification Standards, shall provide plans for interpretative signage for the property to provide historical context and education about the history of the property. The plans shall include the proposed display type(s) and location(s) of the content, as well as high-quality graphics and written narratives that will be incorporated. In addition to narrative text, the interpretative display(s) may include, but are not limited to, a display of photographs, news articles, and drawings. The permanent, high-quality interpretive display(s) shall be installed within the

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project site boundaries, made of durable all-weather materials, and positioned to allow for high public visibility and interactivity. The signage plan shall be reviewed and approved by the Director of Development Services or the Director’s designee prior to issuance of any demolition permits.

MM CUL-1.2: Salvage. The structure shall be made available for salvage to companies facilitating the reuse of historic building materials prior to the issuance of any demolition permits. The time frame available for salvage shall be established by the Director of Development Services or the Director’s designee in accordance with the Action Plan. The City must provide evidence to the Director of Development Services or the Director’s designee that this condition has been met prior to the issuance of any demolition permits.

Even with implementation of mitigation measures MM CUL-1.1 and MM CUL-1.2, the proposed project would result in the demolition of a CRHR eligible property and a City Historic Landmark. As a result, the proposed project would result in a significant unavoidable impact to a historic resource. (Significant and Unavoidable Impact with Mitigation Incorporated) b) Would the project cause a substantial adverse change in the significance of an archaeological resource pursuant to CEQA Guidelines Section 15064.5? It is possible that unrecorded archaeological resources could be encountered during project demolition. The project would be required to implement the following Standard Condition of Approval to avoid impacts to unrecorded archaeological resources (if discovered on-site).

Standard Condition of Approval:
• Discovery of Archaeological Resources: If prehistoric or historic-period cultural materials are unearthed during ground-disturbing activities, all work within 100 feet of the find shall be halted until a qualified archaeologist and Native American representative can assess the significance of the find. Prehistoric materials might include obsidian and chert-flaked stone tools (e.g., projectile points, knives, scrapers) or tool-making debris; culturally darkened soil (“midden”) containing heat-affected rocks and artifacts; stone milling equipment (e.g., mortars, pestles, handstones, or milling slabs); and battered-stone tools, such as hammerstones and pitted stones. Historic-period materials might include stone, concrete, or adobe footings and walls; filled wells or privies; and deposits of metal, glass, and/or ceramic refuse. If the find is determined to be significant, the archaeologist, in consultation with the Native American representative, will develop a treatment plan that could include site avoidance, capping, or data recovery.

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Implementation of the above Standard Condition of Approval would reduce impacts to unrecorded archaeological resources to a less than significant level. (Less than Significant Impact) c) Would the project disturb any human remains, including those interred outside of dedicated cemeteries?
Human graves are most often associated with prehistoric occupation sites. Although unlikely, it is possible that project demolition activities could disturb unrecorded human remains. The project would be required to implement the following Standard Condition of Approval to avoid impacts to human remains (if discovered on-site).

Standard Condition of Approval:
• Discovery of Human Remains: In the event of the discovery of human remains during construction or demolition, there shall be no further excavation or disturbance of the site within a 50-foot radius of the location of such discovery, or any nearby area reasonably suspected to overlie adjacent remains. The Santa Clara County Coroner shall be notified and shall make a determination as to whether the remains are Native American. If the Coroner determines that the remains are not subject to their authority, the Coroner shall notify the Native American Heritage Commission, which shall attempt to identify descendants of the deceased Native American. If no satisfactory agreement can be reached as to the disposition of the remains, then the City shall reinter the human remains and associated burial items on the property in a location not subject to further subsurface disturbance. A final report shall be submitted to the City’s Development Services Director. This report shall contain a description of the mitigation programs and its results, including a description of the monitoring and testing resources analysis methodology and conclusions, and a description of the disposition/curation of the resources. The report shall verify completion of the mitigation program to the satisfaction of the City’s Development Services Director.

The above Standard Condition of Approval would reduce impacts to human remains to a less than significant level. (Less than Significant Impact)
Cumulative Impacts
a) Would the project result in a cumulatively considerable contribution to a significant cumulative cultural resources impact?
The geographic area for cumulative impacts to cultural resources includes the project site and surrounding area because it is assumed disturbance in the project area would affect similar cultural resources.

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Historic Structures
Implementation of the proposed project would result in the loss of a City of Los Altos Historic Landmark and a structure eligible to be listed on the CRHR due to its contribution to residential patterns of local history. However, as discussed in Section 4.5.1.2 Existing Conditions, the Halsey House lacks the decorative features typical of both modest and high-style examples of the Spanish Colonial Revival Style. Further, it is not the only example of the Spanish Colonial Revival style in Los Altos or the Bay Area such that it would be considered a rare example, nor is it associated with a well-known architect. Since the Halsey House would not be considered rare, the loss of this building would not be cumulatively considerable. (Less than Significant Cumulative Impact) Archaeological Resources
The cumulative projects (refer to the list in Table 4.0-1) may require excavation and grading or other activities that may affect unknown prehistoric cultural resources and/or historic resources. As a result, the City’s Standard Condition of Approval is requires of all projects to reduce impacts to subsurface cultural resources to a less than significant level. In addition, project-level analyses for sites located in archaeologically sensitive areas would determine the necessity of additional mitigation measures to reduce localized and site-specific impacts to these resources. All projects would also be subject to federal, state, and local regulations pertaining to the protection of cultural resources. As a result, the project would not result in a cumulatively considerable impact to subsurface archaeological resources. (Less than Significant Cumulative Impact) Human Remains
All cumulative projects (including the project) are required to comply with existing regulations, including California Health and Safety Code Sections 7054 and 7050.5 and Public Resources Code Sections 5097.9 through 5097.99, and the City’s Standard Condition of Approval to reduce impacts to human remains to a less than significant level. For these reasons, the cumulative projects (including the project) would not result in significant cumulative impacts on human remains. (Less than Significant Cumulative Impact)

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4.6 Energy

4.6.1 Environmental Setting
Regulatory Framework
Local
Los Altos Municipal Code
Chapter 6.14 – Collection, Recycling and Disposal of Waste Generated from Deconstruction, Demolition, Construction and Renovation Projects, in the LAMC, seeks to divert at least 65 percent of construction and demolition debris unless the applicant is granted an infeasibility exemption.

Existing Conditions
The existing building has been vacant since 2008 and does not currently consume electricity or natural gas.

4.6.2 Impact Discussion
For the purpose of determining the significance of the project’s impact on energy, would the project:
1) Result in a potentially significant environmental impact due to wasteful, inefficient, or unnecessary consumption of energy resources, during project construction or operation? 2) Conflict with or obstruct a state or local plan for renewable energy or energy efficiency? 3) Result in a substantial increase in demand upon energy resources in relation to projected supplies?
Project Impacts
a) Would the project result in a potentially significant environmental impact due to wasteful, inefficient, or unnecessary consumption of energy resources, during project construction or operation?
Demolition
Demolition of the project would require energy for the operation of equipment and trucks (e.g., diesel and gasoline fuel). Demolition processes are generally designed to be efficient in order to avoid excess monetary costs. Furthermore, the proposed demolition would occur in an urbanized area in proximity to roadways, construction supplies, and workers, making it more efficient than construction occurring in outlying, undeveloped areas. For these reasons, the proposed demolition would not use energy in a wasteful manner. (Less than Significant Impact)

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Operation
The project site would be vacant and undeveloped after demolition; therefore, no net increase in energy use would occur and the project would not result in wasteful, inefficient, or unnecessary consumption of energy resources during project operation. (No Impact) b) Would the project conflict with or obstruct a state or local plan for renewable energy or energy efficiency?
The project is a demolition project that would use energy temporarily during demolition but not require permanent energy use as no operational activities are proposed. Therefore, the project would not conflict with or obstruct a state or local plan for renewable energy or energy efficiency. (Less than Significant Impact)
c) Would the project result in a substantial increase in demand upon energy resources in relation to projected supplies?
Electricity
The project proposes only demolition, which is a temporary activity (about three months) that would not result in a permanent increase in electricity consumption. Any electricity use would cease upon completion of the demolition. As a result, the project’s electricity use would not result in a significant increase in demand on electrical energy resources in relation to projected supplies statewide. (No Impact)
Natural Gas
The project would not result in any substantial increase in natural gas demand relative to projected supply because it would not use any natural gas. (No Impact) Fuel Usage
During demolition, diesel and gasoline would be consumed to fuel the equipment used on-site and trucks traveling to and from the site. This fuel consumption would be temporary and cease upon completion of the demolition. As a result, the project would not result in a significant increase in gasoline demand relative to projected supply. (Less than Significant Impact)

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Cumulative Impacts
a) Would the project result in a cumulatively considerable contribution to a significant cumulative energy impact?
By its nature, energy is a cumulative resource. The geographic area for cumulative energy impacts is the state. Past, present, and future development projects contribute to the state’s energy impacts.

If the project is determined to have a significant energy impact, it is concluded that the impact is cumulatively considerable. As discussed under checklist questions a) through c) above, the project would not result in significant energy impacts. Therefore, the project would not result in a cumulatively considerable contribution to a significant cumulative energy impact. (Less than Significant Cumulative Impact)

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4.7 Geology and Soils
The following discussion is based, in part, on a geological hazard evaluation and geotechnical investigation prepared for the project by Cornerstone Earth Group in February 2024. The report is attached to this EIR as Appendix E.

4.7.1 Environmental Setting
Regulatory Framework
State
Alquist-Priolo Earthquake Fault Zoning Act
The Alquist-Priolo Earthquake Fault Zoning Act regulates development in California near known active faults due to hazards associated with surface fault ruptures. Alquist-Priolo maps are distributed to affected cities, counties, and state agencies for their use in planning and controlling new construction. Areas within an Alquist-Priolo Earthquake Fault Zone require special studies to evaluate the potential for surface rupture to ensure that no structures intended for human occupancy are constructed across an active fault.

Seismic Hazards Mapping Act
The Seismic Hazards Mapping Act (SHMA) directs the California Geological Survey (CGS) to identify and map areas prone to liquefaction, earthquake-induced landslides, and amplified ground shaking.

CGS has completed seismic hazard mapping for the portions of California most susceptible to liquefaction, landslides, and ground shaking, including the central Bay Area. The SHMA requires that agencies only approve projects in seismic hazard zones following site-specific geotechnical investigations to determine if the seismic hazard is present and identify measures to reduce earthquake-related hazards.

California Green Building Code
CALGreen Code Section 5.106.1 requires projects that disturb less than one acre of land prevent the pollution of stormwater runoff from demolition and construction activities through compliance with a lawfully enacted stormwater management and/or erosion control ordinance, or through implementation of CALGreen BMPs. CALGreen BMPs include the following:
• Soil loss BMP’s that should be considered for implementation as appropriate for each project include, but are not limited to, the following:
o Scheduling construction activity during dry weather, when possible; o Preservation of natural features, vegetation, soil, and buffers around surface waters; o Drainage swales or lined ditches to control stormwater flow; o Mulching or hydroseeding to stabilize disturbed soils; o Erosion control to protect slopes;

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o Protection of storm drain inlets (gravel bags or catch basin inserts); o Perimeter sediment control (perimeter silt fence, fiber rolls); o Sediment trap or sediment basin to retain sediment on site; o Stabilized construction exits;
o Wind erosion control;
o Other soil loss BMPs acceptable to the enforcing agency • Good housekeeping BMP’s to manage construction equipment, materials, non-stormwater discharges, and wastes that should be considered for implementation as appropriate for each project include, but are not limited to, the following:
o Dewatering activities;
o Material handling and waste management;
o Building materials stockpile management;
o Management of washout areas (concrete, paints, stucco, etc.); o Control of vehicle/equipment fueling to contractor’s staging area; o Vehicle and equipment cleaning performed off site;
o Spill prevention and control;
o Other housekeeping BMPs acceptable to the enforcing agency.

California Division of Occupational Safety and Health Regulations Excavation, shoring, and trenching activities during construction are subject to occupational safety standards for stabilization by the California Department of Industrial Relations, Division of Occupational Safety and Health (Cal/OSHA) under Title 8 of the California Code of Regulations and Excavation Rules. These regulations minimize the potential for instability and collapse that could injure construction workers on the site.

Public Resources Code Section 5097.5
Paleontological resources are the fossilized remains of organisms from prehistoric environments found in geologic strata. They range from mammoth and dinosaur bones to impressions of ancient animals and plants, trace remains, and microfossils. These materials are valued for the information they yield about the history of the earth and its past ecological settings. Under the CEQA Guidelines, a project would have a significant impact on paleontological resources if it would disturb or destroy a unique paleontological resource or site or unique geologic feature.

Regional
Municipal Regional Permit Provision C.6
Provision C.6 of the MRP requires permittees to implement a construction site inspection and control program at all construction sites to prevent construction site discharges of pollutants and impacts to beneficial uses of receiving waters. All construction sites are required to have site specific and seasonally and phase-appropriate BMPs pertaining to erosion control, run-on and runoff control, sediment control, active treatment systems, good site management, and stormwater management.

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Existing Conditions
Regional Geology
The City of Los Altos is located in the northern portion of the Coast Ranges Geomorphic Province in California. The mountain ranges in this Geomorphic Province are generally northwest trending and were formed tens of millions of years ago by intense folding and faulting caused by tectonic activity between the Pacific Oceanic Plate and the North American Continental Plate.

On-site Geological Conditions
Soils and Topography
The topography of the site is relatively flat with the site being approximately 210 feet above mean sea level (amsl). Soils on-site were found to be a mixture of undocumented fill, native stiff to hard sandy lean clay, and clay (dense and very stiff). Undocumented fill was found to a depth of one foot below ground surface (bgs). Native stiff to hard sandy lean clay was found one foot to 14.5 feet bgs and medium dense to dense clay sand was identified approximately 21.5 feet bgs. Very stiff lean clay was found approximately 23.5 feet bgs.22 On-site soils are classified as having low expansion potential.23
Seismicity and Seismic Hazards
As the Bay Area contains numerous active and potentially active faults, there is a high potential for seismic events such as fault surface ruptures and ground shaking, which can cause ground failure (landslides), settlement, erosion, liquefaction, lateral spreading, and soil expansion. Faults in the region are capable of generating earthquakes of magnitude 6.7 or higher, and strong-to very- strong ground shaking would be expected to occur at the project site during a major earthquake on one of the nearby faults. The nearest active fault to the project site is the Monte Vista-Shannon fault approximately 2.7 miles west of the project site. The San Andreas fault line is approximately 4.3 miles west of the project site and the Hayward fault line is approximately 13.7 miles northeast of the project site.24 The project site is not located within a State of California Earthquake Fault Zone or a Fault-Rupture Hazard Zone.25
During a major earthquake on a segment of one of the nearby faults, strong to severe ground shaking is expected to occur at the project site. The ground shaking intensity felt at the project site would depend on the size of the earthquake (magnitude), the distance from the site to the fault source, the directivity (focusing of earthquake energy along the fault in the direction of the rupture), and the site-specific soil conditions.
22 Cornerstone Earth Group. Geotechnical Investigation Halsey House. February 2024. Page 4. 23 County of Santa Clara. “Soils of Santa Clara County” Accessed December 19, 2025. https://hub.arcgis.com/datasets/sccplanning::soils-of-santa-clara-county/explore. 24 Cornerstone Earth Group. Geotechnical Investigation Halsey House. February 2024. Page 3. 25 California Department of Conservation. “Earthquake Zones of Required Investigation.” Accessed December 19, 2025. https://maps.conservation.ca.gov/cgs/EQZApp/.

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Liquefaction and Lateral Spreading
Soil liquefaction can be defined as a complete loss of strength that causes otherwise solid soil to take on the characteristics of a liquid. The types of soil most susceptible to this hazard are loose, saturated, uniformly graded, fine-grain sands. Liquefaction most frequently occurs under vibratory conditions, such as those created by seismic events. The project area is located in a designated liquefaction hazard zone.26
Lateral spreading typically occurs as a form of horizontal displacement of relatively flat-lying soil toward an open or “free” face such as an open body of water, channel, or excavation. This movement is often associated with liquefaction and commonly occurs on gentle slopes in seismically active regions. Lateral spread presents a significant hazard to the integrity of buildings and other structures. The nearest waterbody to the project site where lateral spreading may occur is Adobe Creek, approximately 50 feet north of the project site. Based on historical ground failure mapping for the project area, no occurrences of lateral spreading were identified.27 Landslides
The project site is relatively flat and is not mapped within a state-designated Landslide Hazard Zone.28
Groundwater
Groundwater was encountered at depths ranging from 10 to 15 feet bgs.29 Water levels on-site may vary depending on seasonal precipitation, irrigation practices, and other climate conditions.

Paleontological Resources and Geological Features
Most of the City, including the project site, is situated on alluvial fan deposits of Holocene age that have a low potential to contain paleontological resources.30 There are no unique geological features (e.g., serpentine rock outcrops) on the project site.

4.7.2 Impact Discussion
For the purpose of determining the significance of the project’s impact on geology and soils, would the project:
1) Directly or indirectly cause potential substantial adverse effects, including the risk of loss, injury, or death involving:
26 Cornerstone Earth Group. Geotechnical Investigation Halsey House. February 2024. Page 5. 27 Ibid.
28 Ibid., page 6.
29 Ibid., page 4.
30 City of Los Altos. Los Altos General Plan Initial Study/Mitigated Negative Declaration. November 2002. Page 20.

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- Rupture of a known earthquake fault, as delineated on the most recent AlquistPriolo Earthquake Fault Zoning Map issued by the State Geologist for the area or based on other substantial evidence of a known fault (refer to Division of Mines and Geology Special Publication 42)?
- Strong seismic ground shaking?
- Seismic-related ground failure, including liquefaction? - Landslides?
2) Result in substantial soil erosion or the loss of topsoil? 3) Be located on a geologic unit or soil that is unstable, or that would become unstable as a result of the project, and potentially result in on- or off-site landslide, lateral spreading, subsidence, liquefaction, or collapse?
4) Be located on expansive soil, as defined in the current California Building Code, creating substantial direct or indirect risks to life or property? 5) Have soils incapable of adequately supporting the use of septic tanks or alternative wastewater disposal systems where sewers are not available for the disposal of wastewater?
6) Directly or indirectly destroy a unique paleontological resource or site or unique geological feature?
Project Impacts
a) Would the project directly or indirectly cause potential substantial adverse effects, including the risk of loss, injury, or death involving rupture of a known earthquake fault, as delineated on the most recent Alquist-Priolo Earthquake Fault Zoning Map issued by the State Geologist for the area or based on other substantial evidence of a known fault; strong seismic ground shaking; seismic-related ground failure, including liquefaction; or landslides? Fault Rupture
As discussed in Section 4.7.1.2 Existing Conditions, the project site is not located in an Alquist-Priolo Earthquake Fault Zone, has no known faults. The site would be vacant after demolition of the Halsey House. Therefore, there would be no impacts related to fault rupture. (No Impact) Seismic Ground Shaking
There are several major fault lines within 30 miles of the project site that have the potential to produce earthquakes with a magnitude of 6.0 or higher. During a major earthquake on a segment of one of the nearby faults, strong to severe ground shaking is expected to occur at the project site.

However, there would be no damage to structures or safety threats to occupants since no development is proposed. As such, the existing seismic hazards on the project would not be exacerbated by the project such that it would impact (or worsen) off-site conditions. For these reasons, there would be no impacts related to seismic ground shaking. (No Impact)

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Liquefaction and Lateral Spreading
As described in Section 4.7.1.2 Existing Conditions, the project site is not located in a lateral spreading zone but is within a designated liquefaction hazard zone. No new development is proposed by the project; therefore, risks of liquefaction would have no impact on the project. Since the existing liquefaction hazard on the project site would not be exacerbated by the project, there would be no impact related to liquefaction and lateral spreading. (No Impact) Landslides
As discussed in Section 4.7.1.2 Existing Conditions, the project site is not located in a designated landslide hazard zone. Demolition activities would not include substantial earthwork that would create unstable slopes that would exacerbate any existing landslide risks, and there are no risks of landslides impacting the project. For these reasons, there would be no impact related to landslides. (No Impact)
b) Would the project result in substantial soil erosion or the loss of topsoil? The demolition of the Halsey House would result in soil disturbance. The project would disturb approximately 0.3 acres, which is below the one-acre threshold requiring compliance with the NPDES Construction General Permit. During demolition, the project would implement Standard Conditions of Approval requiring BMPs to control erosion of exposed soil surfaces, which would minimize soil erosion and loss of topsoil. The project would be subject to the CALGreen requirements to implement stormwater control measures during construction, such as wind erosion control, dewatering activities, material handling and waste management, and control of vehicle/equipment fueling to the staging area, and spill prevention and control. By implementing erosion control BMPs and stormwater control measures, consistent with City Standard Conditions of approval and CALGreen requirements, erosion and sedimentation impacts would be less than significant. (Less than Significant Impact)
c) Would the project be located on a geologic unit or soil that is unstable, or that would become unstable as a result of the project, and potentially result in on- or off-site landslide, lateral spreading, subsidence, liquefaction, or collapse? As discussed under checklist question a), the project site is within a liquefaction hazard zone but the project would not site any new building or infrastructure on the project site. Therefore, the project would have no impact related to on- or off-site landslide, lateral spreading, subsidence, liquefaction, or collapse. (No Impact)

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d) Would the project be located on expansive soil, as defined in the current California Building Code, creating substantial direct or indirect risks to life or property? The proposed project is the demolition of the Halsey House and would not construct any new buildings or structures on the project site. Therefore, there would be no direct or indirect risk to life or property due to expansive soils. (No Impact)
e) Would the project have soils incapable of adequately supporting the use of septic tanks or alternative wastewater disposal systems where sewers are not available for the disposal of wastewater?
The project would not require any septic tanks or connect to the City’s existing sanitary sewer systems because the project would not generate wastewater. (No Impact) f) Would the project directly or indirectly destroy a unique paleontological resource or site or unique geological feature?
As described in Section 4.7.1.2 Existing Conditions, the project site has low potential to contain paleontological resources and there are no unique geological features (e.g., serpentine rock outcrops) at the project site . While it is unlikely that paleontological resources would be encountered on-site, the project would implement the following Standard Condition of Approval to reduce potential impacts to paleontological resources.

Standard Condition of Approval:
• Discovery of Paleontological Resources. In the event that a fossil is discovered during construction of the project, excavations within 50 feet of the find shall be temporarily halted or delayed until the discovery is examined by a qualified paleontologist, in accordance with Society of Vertebrate Paleontology standards. The City shall include a standard inadvertent discovery clause in every construction contract to inform contractors of this requirement. If the find is determined to be significant and if avoidance is not feasible, the paleontologist shall design and carry out a data recovery plan consistent with the Society of Vertebrate Paleontology standards.

The above Standard Condition of Approval would reduce impacts to paleontological resources to a less than significant level. (Less than Significant Impact)

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Cumulative Impacts
Would the project result in a cumulatively considerable contribution to a cumulatively significant geology and soils impact?
The geographic area for cumulative geology and soils impacts includes the project site and adjacent parcels. All other projects within the vicinity would be subject to similar geology, soils, and seismicity impacts as the project. All projects occurring within the City are required to prepare a design-level geotechnical investigation and would be constructed consistent with the latest CBC to avoid and/or reduce impacts related to geologic hazards. Adherence to the Standard Conditions of Approval discussed in checklist question f) would reduce potential impacts to paleontological resources. Therefore, the project would not result in a cumulatively considerable contribution to a significant geology and soils impact. (Less than Significant Cumulative Impact)

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4.8 Greenhouse Gas Emissions

4.8.1 Environmental Setting
Regulatory Framework
State
Assembly Bill 32 and State Bill 32
Under the California Global Warming Solutions Act, also known as AB 32, CARB established a statewide GHG emissions cap for 2020, adopted mandatory reporting rules for significant sources of GHGs, and adopted a comprehensive plan, known as the Climate Change Scoping Plan, identifying how emission reductions would be achieved from significant GHG sources. The first Scoping Plan was approved by CARB in 2008 and must be updated at least every five years. Since 2008, there have been two updates to the Scoping Plan.

In 2016, SB 32 was signed into law, amending the California Global Warming Solution Act. SB 32, and accompanying Executive Order B-30-15, requires CARB to ensure that statewide GHG emissions are reduced to 40 percent below the 1990 level by 2030. CARB updated its Climate Change Scoping Plan in December of 2017 to express the 2030 statewide target in terms of million metric tons of CO2e (MMTCO2e). Based on the emissions reductions directed by SB 32, the annual 2030 statewide target emissions level for California is 260 MMTCO2e.
2022 Scoping Plan
On December 15, 2022, CARB approved the 2022 Scoping Plan. The 2022 Scoping Plan provides a sector-by-sector guide on how to reduce man-made (i.e., anthropogenic) GHG emissions by 85 percent below 1990 levels and achieve carbon neutrality by 2045 over a 25-year horizon.31 The primary focus of the 2022 Scoping Plan is to reduce the usage of fossil fuels by electricizing the transportation sector, procuring electricity from renewable resources, phasing out natural gas in land use developments, and building transit-oriented communities that encourage multi-modal transportation. If implemented successfully, the 2022 Scoping Plan would not only reduce GHG emissions but also reduce smog-forming air pollution (NOx) by 71 percent and reduce fossil fuel demand by 94 percent. The 2022 Scoping Plan also details natural carbon capture and storage process along with mechanical carbon capture programs to address the remaining 15 of anthropogenic GHG emissions that will remain post-2045. To meet these goals, CARB also includes a revised goal of reducing state GHG emissions 48 percent below 1990 levels by 2030. 31 CARB. 2022 Scoping Plan for Achieving Carbon Neutrality. November 16, 2022. Page 5.

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Executive Order B-55-18 and Assembly Bill 1279
Executive Order B-55-18 was issued in September 2018. It ordered a new statewide goal of achieving carbon neutrality no later than 2045 and to maintain net negative emissions thereafter.

Assembly Bill 1279, also known as the California Climate Crisis Act, was approved on September 16, 2022 and codifies the statewide goal set by Executive Order B-55-18 of achieving net zero GHG emissions no later than the year 2045 and maintaining net negative emissions thereafter. In addition, this bill has a statewide goal of reducing anthropogenic GHG emissions by 85 percent below the 1990 levels by the year 2045. The bill requires CARB to work with relevant state agencies to ensure that updates to the scoping plan identify and recommend measures to achieve these policy goals, and implement strategies that enable CO2 removal solutions and carbon capture, utilization, and storage technologies in California. The bill requires CARB to submit an annual report.

Regional
2017 Clean Air Plan
To protect the climate, the 2017 Clean Air Plan prepared by the Air District includes control measures designed to reduce emissions of methane and other super-GHGs that are potent climate pollutants in the near-term, and to decrease emissions of carbon dioxide by reducing fossil fuel combustion.

BAAD CEQA Thresholds for Evaluating Climate Impacts from Land Use Projects and Plans In April 2022, the Air District Board of Directors adopted the Justification Report: CEQA Thresholds for Evaluating the Significance of Climate Impacts from Land Use Projects and Plans. The report includes the Air District’s thresholds of significance for use in determining whether a proposed project or plan will have a significant impact on climate change and provides substantial evidence to support these thresholds. The April 2022 GHG thresholds replace the GHG thresholds set forth in the May 2017 Air District CEQA Air Quality Guidelines and represent what is required of new land use development projects and plans to achieve California’s long-term climate goal of carbon neutrality by 2045.

Existing Conditions
Unlike emissions of criteria and toxic air pollutants, which have regional and local impacts, emissions of GHGs have a broader, global impact. Global warming is a process whereby GHGs accumulating in the upper atmosphere contribute to an increase in the temperature of the earth and changes in weather patterns.

The Halsey House is vacant and does not generate GHG emissions.

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4.8.2 Impact Discussion
For the purpose of determining the significance of the project’s impact on greenhouse gas emissions, would the project:
1) Generate GHG emissions, either directly or indirectly, that may have a significant impact on the environment?
2) Conflict with an applicable plan, policy, or regulation adopted for the purpose of reducing the emissions of GHGs?
Project Impacts
a) Would the project generate GHG emissions, either directly or indirectly, that may have a significant impact on the environment?
The project would only generate temporary GHG emissions during demolition. Sources of GHG emissions would be demolition equipment, trucks traveling to and from the site, and worker trips.

There would be no sources of operational GHG emissions post-demolition. Neither the City of Los Altos nor the Air District have an adopted threshold of significance for demolition-related GHG emissions. Since demolition would be temporary (approximately three months) and would not result in a permanent increase in emissions, the project would not result in a significant GHG impact from demolition emissions. (Less than Significant Impact) b) Would the project conflict with an applicable plan, policy, or regulation adopted for the purpose of reducing the emissions of GHGs?
The project would not conflict with any applicable plan, policy, or regulations adopted for the purpose of reducing GHG emissions because the project does not propose to construct a building or infrastructure that would generate GHG emissions. The GHG emissions associated with the demolition of the Halsey House would be temporary and cease upon completion of demolition activities. Since the project would not create a new source of GHG emissions, it would not interfere with the overall goals under SB 32 or as outlined in the 2022 Scoping Plan. (Less than Significant Impact)
Cumulative Impacts
Would the project result in a cumulatively considerable contribution to a cumulatively significant GHG emissions impact?
As discussed above, GHG emissions have a broader, global impact. No single land use project could generate sufficient GHG emissions on its own to noticeably change the global average temperature.

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The combination of GHG emissions from past, present, and future projects in Los Altos, the entire state of California, and across the nation and around the world, contribute cumulatively to the phenomenon of global climate change and its associated environmental impacts. The above analysis of the project’s GHG emissions impacts is, therefore, also an analysis of the project’s contribution to cumulative GHG emissions impacts. The project would only generate temporary GHG emissions not permanent operational sources of GHG emissions. Therefore, the project would not result in a cumulatively considerable contribution to a cumulatively significant GHG impact. (Less than Significant Cumulative Impact)

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4.9 Hazards and Hazardous Materials

4.9.1 Environmental Setting
Regulatory Framework
Overview
The storage, use, generation, transport, and disposal of hazardous materials and waste are highly regulated under federal and state laws. In California, the EPA has granted enforcement authority over federal hazardous materials regulations to the California Environmental Protection Agency (CalEPA). In turn, local agencies have been granted responsibility for implementation and enforcement of many hazardous materials regulations under the Certified Unified Program Agency (CUPA) program.

Worker health and safety and public safety are key issues when dealing with hazardous materials.

Proper handling and disposal of hazardous material is vital if it is disturbed during project construction. Cal/OSHA enforces state worker health and safety regulations related to construction activities. Regulations include exposure limits, requirements for protective clothing, and training requirements to prevent exposure to hazardous materials. Cal/OSHA also enforces occupational health and safety regulations specific to lead and asbestos investigations and abatement.

Federal and State
Comprehensive Environmental Response, Compensation, and Liability Act The Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA), commonly known as Superfund, was enacted by Congress on December 11, 1980. This law created a tax on the chemical and petroleum industries and provided broad federal authority to respond directly to releases or threatened releases of hazardous substances that may endanger public health or the environment. Over five years, $1.6 billion was collected and the tax went to a trust fund for cleaning up abandoned or uncontrolled hazardous waste sites. CERCLA accomplished the following objectives:
• Established prohibitions and requirements concerning closed and abandoned hazardous waste sites;
• Provided for liability of persons responsible for releases of hazardous waste at these sites; and
• Established a trust fund to provide for cleanup when no responsible party could be identified.

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The law authorizes two kinds of response actions:
• Short-term removals, where actions may be taken to address releases or threatened releases requiring prompt response; and
• Long-term remedial response actions that permanently and significantly reduce the dangers associated with releases or threats of releases of hazardous substances that are serious, but not immediately life-threatening. These actions can be completed only at sites listed on the EPA’s National Priorities List.

CERCLA also enabled the revision of the National Contingency Plan (NCP). The NCP provided the guidelines and procedures needed to respond to releases and threatened releases of hazardous substances, pollutants, or contaminants. The NCP also established the National Priorities List.

CERCLA was amended by the Superfund Amendments and Reauthorization Act on October 17, 1986.32
Resource Conservation and Recovery Act
The Resource Conservation and Recovery Act (RCRA), enacted in 1976, is the principal federal law in the United States governing the disposal of solid waste and hazardous waste. RCRA gives the EPA the authority to control hazardous waste from the "cradle to the grave." This includes the generation, transportation, treatment, storage, and disposal of hazardous waste. RCRA also sets forth a framework for the management of non-hazardous solid wastes.

The Federal Hazardous and Solid Waste Amendments (HSWA) are the 1984 amendments to RCRA that focused on waste minimization, phasing out land disposal of hazardous waste, and corrective action for releases. Some of the other mandates of this law include increased enforcement authority for the EPA, more stringent hazardous waste management standards, and a comprehensive underground storage tank program.33
Government Code Section 65962.5
Section 65962.5 of the Government Code requires CalEPA to develop and update a list of hazardous waste and substances sites, known as the Cortese List. The Cortese List is used by state and local agencies and developers to comply with CEQA requirements. The Cortese List includes hazardous substance release sites identified by the Department of Toxic Substances Control (DTSC) and State Water Resources Control Board (SWRCB).
34 32 United States Environmental Protection Agency. “Superfund: CERCLA Overview.” Accessed December 19, 2025. https://www.epa.gov/superfund/superfund-cercla-overview. 33 United States Environmental Protection Agency. “Summary of the Resource Conservation and Recovery Act.” Accessed December 19, 2025. https://www.epa.gov/laws-regulations/summary-resource-conservation-andrecovery-act. 34 California Environmental Protection Agency. “Cortese List Data Resources.” Accessed December 19, 2025. https://calepa.ca.gov/sitecleanup/corteselist/.

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Toxic Substances Control Act
The Toxic Substances Control Act (TSCA) of 1976 provides the EPA with authority to require reporting, record-keeping and testing requirements, and restrictions relating to chemical substances and/or mixtures. Certain substances are generally excluded from TSCA, including, among others, food, drugs, cosmetics, and pesticides. The TSCA addresses the production, importation, use, and disposal of specific chemicals including polychlorinated biphenyls (PCBs), asbestos, radon, and lead-based paint.

Asbestos-Containing Materials
Friable asbestos is any asbestos-containing material (ACM) that, when dry, can easily be crumbled or pulverized to a powder by hand, allowing the asbestos particles to become airborne. Common examples of products that have been found to contain friable asbestos include acoustical ceilings, plaster, wallboard, and thermal insulation for water heaters and pipes. Common examples of nonfriable ACMs are asphalt roofing shingles, vinyl floor tiles, and transite siding made with cement.

The EPA began phasing out use of friable asbestos products in 1973 and issued a ban in 1978 on manufacture, import, processing, and distribution of some asbestos-containing products and new uses of asbestos products.
35 The EPA is currently considering a proposed ban on on-going use of asbestos.36 National Emission Standards for Hazardous Air Pollutants (NESHAP) guidelines require that potentially friable ACMs be removed prior to building demolition or remodeling that may disturb the ACMs.

CCR Title 8, Section 1532.1
The United States Consumer Product Safety Commission banned the use of lead-based paint in 1978. Removal of older structures with lead-based paint is subject to requirements outlined by the Cal/OSHA Lead in Construction Standard, CCR Title 8, Section 1532.1 during demolition activities.

Requirements include employee training, employee air monitoring, and dust control. If lead-based paint is peeling, flaking, or blistered, it is required to be removed prior to demolition.

Fire Hazard Severity Zones
CAL FIRE is required by law to map areas of significant fire hazards based on fuels, terrain, weather, and other relevant factors. Referred to as Fire Hazard Severity Zones (FHSZs), these maps influence how people construct buildings and protect property to reduce risk associated with wildland fires.

FHSZs are divided into areas where the state has financial responsibility for wildland fire protection, known as state responsibility areas (SRAs), and areas where local governments have financial responsibility for wildland fire protection, known as local responsibility areas (LRAs). Homeowners living in an SRA are responsible for ensuring that their property is in compliance with California’s building and fire codes. Only lands zoned for very high fire hazard are identified within LRAs. 35 United States Environmental Protection Agency. “EPA Actions to Protect the Public from Exposure to Asbestos.” Accessed December 19, 2025. https://www.epa.gov/asbestos/epa-actions-protect-public-exposure-asbestos 36Ibid.

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Local
Los Altos General Plan
The following policies in the City’s General Plan have been adopted for the purpose of reducing or avoiding impacts related to hazards and hazardous materials and are applicable to the project.

Policy Description
NEH 3.1 Cooperate with and participate in development of the policies and future programs of the Santa Clara County Health Department and the California Legislature.

NEH 3.2 Support the management of hazardous materials contamination and abatement by public and private agencies.

NEH 6.1 Maintain an updated Emergency Preparedness Plan. The plan should increase public awareness of natural hazards and hazards associated with human activity and of methods to avoid or mitigated the effects of these hazards and should ensure that critical facilities will function during and after a disaster.

Los Altos Municipal Code
Chapter 10.08 of the LAMC seeks to protect the citizens of Los Altos through prevention and control of unauthorized discharges of hazardous materials. Chapter 10.08 includes several hazardous materials regulations, such as requiring construction sites to maintain a spill response plan, prohibiting the storage of materials next to storm drains, and prohibiting the disposal of hazardous materials in an area that may eventually lead to pollution reaching the sewer system.

City of Los Altos Emergency Operations Plan
The City of Los Altos updated its Emergency Operations Plan (EOP) in October 2018. The City of Los Altos EOP outlines the City’s framework for managing a variety of hazards such as natural disasters and human-caused events. The EOP describes organizational structures, roles and responsibilities, policies, and protocols for providing emergency support. The EOP details the City’s mitigation strategies, preparedness planning, short and long-term recovery strategies, and the operating procedures for the Emergency Operations Center (EOC). It also details the jurisdictional structure for responding to emergencies when the response may require regional, state, or federal coordination.

Existing Conditions
Site History
As discussed in Section 4.5 Cultural Resources, the site was undeveloped until the Halsey House was constructed in 1923. Starting in 1974, the property and Halsey House served as a public educational center and museum. Since 2008, the Halsey House has been vacant.

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Potential On- and Off-Site Sources of Contamination
Asbestos Containing Materials and Lead-Based Paint
Due to the age of the existing building, ACMs and lead-based paint may be present on-site.

Cortese List
The project site is not on a list of hazardous materials sites compiled pursuant to Government Code Section 65962.5.37, 38, 39
Wildland Fires
The project site is in an urban area surrounded by existing development. The project site is not located near wildlands that could present a fire hazard. The site is not located within an identified Very High Fire Hazard Severity Zone in an SRA or LRA.40 Proximity to an Airport
The project site is not located within an airport land use plan area. Moffett Federal Airfield, a joint civil military airport, located approximately 4.5 miles northeast of the project site, is the nearest airport.

4.9.2 Impact Discussion
For the purpose of determining the significance of the project’s impact on hazards and hazardous materials, would the project:
1) Create a significant hazard to the public or the environment through the routine transport, use, or disposal of hazardous materials?
2) Create a significant hazard to the public or the environment through reasonably foreseeable upset and accident conditions involving the release of hazardous materials into the environment?
3) Emit hazardous emissions or handle hazardous or acutely hazardous materials, substances, or waste within one-quarter mile of an existing or proposed school? 37 Department of Toxic Substances Control. “EnviroStor database.” Accessed December 19, 2025. https://www.envirostor.dtsc.ca.gov/public.
38 State Water Resources Control Board. “GeoTracker.” Accessed December 19, 2025. https://geotracker.waterboards.ca.gov.
39 California Environmental Protection Agency. “Cortese List Data Resources.” Accessed November December 19, 2025. https://calepa.ca.gov/sitecleanup/corteselist/.
40 California Department of Forestry and Fire Protection. “Fire Hazard Severity Zones.” Accessed December 19, 2025. https://osfm.fire.ca.gov/what-we-do/community-wildfire-preparedness-and-mitigation/fire-hazard-severityzones.

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4) Be located on a site which is included on a list of hazardous materials sites compiled pursuant to Government Code Section 65962.5 and, as a result, would it create a significant hazard to the public or the environment?
5) For a project located within an airport land use plan or, where such a plan has not been adopted, within two miles of a public airport or public use airport, result in a safety hazard or excessive noise for people residing or working in the project area? 6) Impair implementation of or physically interfere with an adopted emergency response plan or emergency evacuation plan?
7) Expose people or structures, either directly or indirectly, to a significant risk of loss, injury, or death involving wildland fires?
Project Impacts
a) Would the project create a significant hazard to the public or the environment through the routine transport, use, or disposal of hazardous materials? The proposed project would demolish the Halsey House building. Demolition would involve the use of fuels, oils, and fluids for vehicles and equipment. All hazardous materials would be transported, contained, stored, used, and disposed of in accordance with manufacturers’ instructions and would be handled in compliance with all applicable standards and regulations. Demolition-related hazardous materials use would be temporary, and does not constitute routine transport, use, or disposal. The project does not propose to use or store any hazardous materials on-site after demolition. The project does not propose construction of any buildings or structures on-site.

Therefore, the project would not create a significant hazard to the public or the environment through the routine transport, use, or disposal of hazardous materials. (Less than Significant Impact)
b) Would the project create a significant hazard to the public or the environment through reasonably foreseeable upset and accident conditions involving the release of hazardous materials into the environment?
Demolition
As discussed in Section 4.9.1.2 Existing Conditions, ACMs and lead-based paint may be present onsite due to the age of the existing building (pre-1980 construction). Demolition of the existing building could expose construction workers or residents in the vicinity of the project site to harmful levels of ACMs or lead. The project is required to conform to regulatory programs for the presence of ACMs and/or lead-based paint.

Impact HAZ-1: Demolition of the existing building could expose construction workers or residents in the vicinity of the project site to harmful levels of asbestoscontaining materials or lead-based paints.

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Mitigation Measures:

MM HAZ-1.1: Pre-Demolition Survey. In conformance with State and local laws, a visual inspection/pre-demolition survey, and possible sampling, shall be conducted prior to the demolition of on-site buildings to determine the presence of asbestos-containing materials and/or lead-based paint.

MM HAZ-1.2: Removal of Asbestos-Containing Materials. All potentially friable asbestoscontaining materials shall be removed in accordance with National Emission Standards for Hazardous Air Pollutants (NESHAP) guidelines prior to any building demolition or renovation that may disturb the materials. All demolition activities will be undertaken in accordance with Cal/OSHA standards contained in Title 8 of California Code of Regulations (CCR), Section 1529, to protect workers from exposure to asbestos. A registered asbestos abatement contractor shall be retained to remove and dispose of asbestos-containing materials identified in the asbestos survey performed for the site in accordance with the aforementioned standards. Materials containing more than one percent asbestos are also subject to Bay Area Air District (Air District) regulations.

Removal of materials containing more than one percent asbestos shall be completed in accordance with Air District requirements.

MM HAZ-1.3: Removal of Lead-Based Paint. Prior to demolition activities, all building materials containing lead-based paint shall be removed in accordance with Cal/OSHA Lead in Construction Standard, Title 8, CCR 1523.1, including employee training, employee air monitoring, and dust control. Any debris or soil containing lead-based paint or coatings would be disposed of at landfills that meet acceptance criteria for the waste being disposed.

Conformance with MM HAZ-1.1 through MM HAZ-1.3 would result in a less than significant impact from ACMs and lead by determining the presence and ensuring proper removal and disposal of both materials. The project would not create a significant hazard to the public or the environment through reasonably foreseeable upset and accident conditions involving the release of hazardous materials into the environment during demolition. There would be no operational impacts. (Less than Significant Impact with Mitigation Incorporated)
c) Would the project emit hazardous emissions or handle hazardous or acutely hazardous materials, substances, or waste within one-quarter mile of an existing or proposed school? The nearest schools are the Los Altos Chinese school, approximately 0.6 mile east of the site, and Covington Elementary School, approximately 0.6 mile southeast of the site. There are no known proposed schools within one-quarter mile of the project site. Therefore, the project would not emit hazardous emissions within one-quarter mile of an existing school or proposed school. (No Impact)

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d) Would the project be located on a site which is included on a list of hazardous materials sites compiled pursuant to Government Code Section 65962.5 and, as a result, would it create a significant hazard to the public or the environment? As discussed in Section 4.9.1.2 Existing Conditions, the project site is not included on a list of hazardous materials sites compiled pursuant to Government Code Section 65962.5. (No Impact) e) If located within an airport land use plan or, where such a plan has not been adopted, within two miles of a public airport or public use airport, would the project result in a safety hazard or excessive noise for people residing or working in the project area? As discussed in Section 4.9.1.2 Existing Conditions, the project site is not located within an airport land use plan or within two miles of an airport. Therefore, the proposed project would not result in safety hazard or noise impacts due to airport activities. (No Impact) f) Would the project impair implementation of or physically interfere with an adopted emergency response plan or emergency evacuation plan?
As discussed in Section 4.9.1.1 Regulatory Framework, the City of Los Altos has an EOP that outlines the City’s framework for managing a variety of hazards such as natural disasters and human-caused events. Demolition would occur within the project site and would not block access to roadways.

There would be no structures on-site post-demolition. Therefore, the project would not impair implementation of or physically interfere with the EOP, including its operating procedures. (No Impact)
g) Would the project expose people or structures, either directly or indirectly, to a significant risk of loss, injury, or death involving wildland fires? As discussed in Section 4.9.1.1 Regulatory Framework, the project site is not located in or near SRAs or lands classified as very high FHSZs. Therefore, the project would not result in wildfire impacts. (No Impact)
Cumulative Impacts
Would the project result in a cumulatively considerable contribution to a cumulatively significant hazards and hazardous materials impact?
The geographic area for cumulative hazards and hazardous materials impacts is the project site and immediate vicinity. There are no other proposed projects within the immediate vicinity of the site.

As discussed above, the project would not create a significant hazard to the public or the

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environment through the routine transport, use, or disposal of hazardous materials, or impair implementation of the City’s EOP. Additionally, the project site is not located within one-quarter mile of an existing or proposed school, within two miles of an airport, or in or near SRAs or very high FHSZs. As discussed under checklist question b), the project would implement Standard Conditions of Approval to reduce the presence of ACMs and/or lead-based paint. For these reasons, the proposed project would not result in a cumulatively considerable contribution to cumulatively significant hazards and hazardous materials impact. (Less than Significant Cumulative Impact)

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4.10 Hydrology and Water Quality
The following discussion is based, in part, on a hydrology memorandum prepared for the project by Schaaf & Wheeler in March 2024. The report is attached to this EIR as Appendix F.

4.10.1 Environmental Setting
Regulatory Framework
Federal and State
The federal Clean Water Act and California’s Porter-Cologne Water Quality Control Act are the primary laws related to water quality in California. Regulations set forth by the EPA and the SWRCB have been developed to fulfill the requirements of this legislation. EPA regulations include the NPDES permit program, which controls sources that discharge pollutants into the waters of the United States (e.g., streams, lakes, bays, etc.). These regulations are implemented at the regional level by the RWQCBs. The project site is within the jurisdiction of the San Francisco Bay RWQCB.

Under Section 303(d) of the federal Clean Water Act, the SWRCB and RWQCBs are required to identify impaired surface water bodies that do not meet water quality standards and develop total maximum daily loads for contaminants of concern. The list of the state’s identified impaired surface water bodies, known as the “303(d) list” can be found on the on the SWRCB’s website.41 National Flood Insurance Program
The Federal Emergency Management Agency (FEMA) established the National Flood Insurance Program to reduce impacts of flooding on private and public properties. The program provides subsidized flood insurance to communities that comply with FEMA regulations protecting development in floodplains. As part of the program, FEMA publishes Flood Insurance Rate Maps that identify Special Flood Hazard Areas (SFHAs). An SFHA is an area that would be inundated by the one-percent annual chance flood, which is also referred to as the base flood or 100-year flood.

Statewide Construction General Permit
The SWRCB has implemented an NPDES General Construction Permit for the State of California (Construction General Permit). For projects disturbing one acre or more of soil, a Notice of Intent (NOI) must be filed with the RWQCB by the project sponsor, and a Storm Water Pollution Prevention Plan (SWPPP) must be prepared by a qualified professional prior to commencement of construction and filed with the RWQCB by the project sponsor. The Construction General Permit includes requirements for training, inspections, record keeping, and, for projects of certain risk 41 California State Water Resources Control Board. “2020-2022 California Integrated Report (Clean Water Act Section 303(d) List and 305(b) Report).” May 11, 2022. Accessed December 19, 2025. https://www.waterboards.ca.gov/water_issues/programs/water_quality_assessment/2020_2022_integrated_rep ort.html.

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levels, monitoring. The general purpose of the requirements is to minimize the discharge of pollutants and to protect beneficial uses and receiving waters from the adverse effects of construction-related storm water discharges.

Regional
San Francisco Bay Basin Plan
The San Francisco Bay RWQCB regulates water quality in accordance with the Water Quality Control Plan for the San Francisco Bay Basin (Basin Plan). The Basin Plan lists the beneficial uses that the San Francisco Bay RWQCB has identified for local aquifers, streams, marshes, rivers, and the San Francisco Bay, as well as the water quality objectives and criteria that must be met to protect these uses. The San Francisco Bay RWQCB implements the Basin Plan by issuing and enforcing waste discharge requirements, including permits for nonpoint sources such as the urban runoff discharged by a City’s stormwater drainage system. The Basin Plan also describes watershed management programs and water quality attainment strategies.

Municipal Regional Permit Provision C.6
Provision C.6 of the MRP requires permittees to implement a construction site inspection and control program at all construction sites to prevent construction site discharges of pollutants and impacts to beneficial uses of receiving waters. All construction sites are required to have site specific and seasonally and phase-appropriate BMPs pertaining to erosion control, run-on and runoff control, sediment control, active treatment systems, good site management, and stormwater management.

Water Resources Protection Ordinance and District Well Ordinance Valley Water operates as the flood control agency for Santa Clara County. Valley Water also provides stream stewardship and is the wholesale water supplier throughout the county, which includes the groundwater recharge program. Well construction and deconstruction permits, including borings 45 feet or deeper, are required under Valley Water’s Well Ordinance 90-1. Under Valley Water’s Water Resources Protection Ordinance, projects within Valley Water property or easements are required to obtain encroachment permits.
2021 Groundwater Management Plan
The 2021 Groundwater Management Plan (GWMP) describes Valley Water’s comprehensive groundwater management framework, including existing and potential actions to achieve basin sustainability goals and ensure continued sustainable groundwater management. The GWMP covers the Santa Clara and Llagas subbasins, which are located entirely in Santa Clara County. Valley Water manages a diverse water supply portfolio, with sources including groundwater, local surface water, imported water, and recycled water. About half of the county’s water supply comes from local sources and the other half comes from imported sources. Imported water includes the District’s State Water Project and Central Valley contract supplies and supplies delivered by the San

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Francisco Public Utilities Commission (SFPUC) to cities in northern Santa Clara County. Local sources include natural groundwater recharge and surface water supplies. A small portion of the county’s water supply is recycled water.

Local groundwater resources make up the foundation of the county’s water supply, but they need to be augmented by the District’s comprehensive water supply management activities to reliably meet the county’s needs. These include the managed recharge of imported and local surface water and in‐lieu groundwater recharge through the provision of treated surface water and raw water, acquisition of supplemental water supplies, and water conservation and recycling.42 Local
Los Altos General Plan
The following policies in the City’s General Plan have been adopted for the purpose of avoiding or mitigating impacts on hydrology and water quality and are applicable to the project:

Policy Description
IWD 3.1 Control surface runoff discharges into the stormwater system to comply with the National Pollution Discharge Elimination System Permit and the receiving water limitations assigned by the California Regional Water Quality Control Board.

IWD 3.3 Minimize the amount of impervious surfaces and directly connected impervious surfaces in areas of new development and redevelopment and where feasible maximize on-site infiltration of stormwater runoff.

IWD 3.4 Implement pollution prevention methods supplemented by pollutant source controls and treatment. Use small collection strategies located at, or as close as possible to the source (i.e., the point where water initially meets the ground) to minimize the transport of urban runoff and pollutants offsite.

Los Altos Municipal Code
Section 10.16 of the LAMC requires new development to implement permanent stormwater pollution measures, including source control requirements, site design and treatment requirements and prevention consistent with the requirements of the RWQCB.

Existing Conditions
Hydrology and Drainage
Los Altos is in the Lower Peninsula Watershed, a 98-square-mile area whose creeks feed into the San Francisco Bay. There are four creeks located within the City of Los Altos, including Adobe Creek, Stevens Creek, Permanente Creek, and Hale Creek.43 The nearest creek to the project site is Adobe 42 Valley Water. 2021 Groundwater Management Plan, Santa Clara and Llagas Subbasins. November 2021. 43 City of Los Altos. “Local Creeks.” Accessed December 19, 2025. https://www.losaltosca.gov/461/Local-Creeks.

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Creek, which is approximately 50 feet north of the project site. 44 The project site is located in the
Adobe drainage basin which drains to Adobe Creek via a network of connecting stormwater pipes.45 Groundwater
The project site is located in the Santa Clara Plain groundwater subbasin.46 Groundwater on-site was encountered at depths ranging from 10 to 15 feet bgs.47 Water levels on-site may vary depending on seasonal precipitation, irrigation practices, and other climate conditions.

Flooding
The effective FEMA map shows the project site within the Regulatory Floodway and a Special Flood Hazard Area (SFHA) for the 100-year floodplain (Zone AE) of Adobe Creek. A Regulatory Floodway is the area reserved for watercourse and the adjacent land that must be reserved in order to discharge the base flood without cumulatively increasing water surface elevation more than a certain height. Zone AE has a defined base flood elevation.48 An analysis of Adobe Creek in the vicinity of the site completed by Schaaf & Wheeler determined that the alignment of the creek in the County’s 2020 Light Detection and Ranging (LIDAR) dataset differs from the alignment shown in the FEMA map. Schaaf & Wheeler completed a site visit in January 2024 and, utilizing GPS points, determined that the creek currently aligns with the LIDAR data and not the FEMA map. If the FEMA map were to be revised to match the LIDAR and GPS data, the Halsey House would not be located within a Regulatory Floodway or 100-year floodplain. It should be noted that, unless and until the FEMA map is revised through FEMA’s Letter or Map Revision (LOMR) process, which requires an application to FEMA and hydrologic modeling to support the change, the Halsey House will remain mapped within a Regulatory Floodway and 100- year floodplain.

Seiches and Tsunamis
A seiche is defined as a standing wave generated by rapid displacement of water within an enclosed body of water (such as a reservoir, lake, or bay) due to an earthquake that triggers land movement within the water body or land sliding into or beneath the water body. There are no landlocked bodies of water near the project site that would affect the site in the event of a seiche.

A tsunami is a large tidal wave caused by an underwater earthquake or volcanic eruption. Tsunamis affecting the Bay Area can result from offshore earthquakes within the Bay Area. Los Altos is located five to six miles from the San Francisco Bay with an elevation of 150 feet or more above sea 44 Valley Water. “Map of District Creeks.” Accessed December 19, 2025. https://valleywater.maps.arcgis.com/apps/instant/nearby/index.html?appid=3f6d541471544eea8bf27a3259ec03 84&sliderDistance=1
45 City of Los Altos. Stormwater Master Plan Appendix A: Drainage Basins. April 2016. 46 Valley Water. 2021 Groundwater Management Plan, Santa Clara and Llagas Subbasins. November 2021.Figure

1.2 Topography of the Santa Clara and Llagas Subbasins. 47 Cornerstone Earth Group. Geotechnical Investigation Halsey House. February 2024. Page 4. 48 Schaaf & Wheeler. Halsey House CEQA Hydrology Memorandum. March 2024. Page 3.

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level. Tsunami water waves hazards are not likely due to the distance of the city from the San Francisco Bay.49

4.10.2 Impact Discussion
For the purpose of determining the significance of the project’s impact on hydrology and water quality, would the project:
1) Violate any water quality standards or waste discharge requirements or otherwise substantially degrade surface or ground water quality?
2) Substantially decrease groundwater supplies or interfere substantially with groundwater recharge such that the project may impede sustainable groundwater management of the basin?
3) Substantially alter the existing drainage pattern of the site or area, including through the alteration of the course of a stream or river or through the addition of impervious surfaces, in a manner which would:
- result in substantial erosion or siltation on- or off-site; - substantially increase the rate or amount of surface runoff in a manner which would result in flooding on- or off-site;
- create or contribute runoff water which would exceed the capacity of existing or planned stormwater drainage systems or provide substantial additional sources of polluted runoff; or
- impede or redirect flood flows?
4) In flood hazard, tsunami, or seiche zones, risk release of pollutants due to project inundation?
5) Conflict with or obstruct implementation of a water quality control plan or sustainable groundwater management plan?
Project Impacts
a) Would the project violate any water quality standards or waste discharge requirements or otherwise substantially degrade surface or ground water quality? Demolition activities have the potential to result in temporary impacts to surface water quality in adjacent waterways. When soil disturbance occurs, sediments may be dislodged and discharged into the storm drainage system when surface runoff flows across the site. The proposed project would disturb approximately 0.3 acres, which is below the one-acre threshold requiring compliance with the NPDES Construction General Permit. During demolition, the project would implement Standard Conditions of Approval requiring BMPs to control erosion of exposed soil surfaces, which 49 City of Los Altos. Initial Study/Mitigated Negative Declaration for the Los Altos General Plan Update. November 2002. Page 30.

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would prevent the discharge of stormwater pollutants. Post-demolition, there would be no increase in impervious surface area that would require stormwater runoff treatment controls. For these reasons, the project would not violate any water quality standards or waste discharge requirements. (Less than Significant Impact)
b) Would the project substantially decrease groundwater supplies or interfere substantially with groundwater recharge such that the project may impede sustainable groundwater management of the basin?
As described in Section 4.10.1.2 Existing Conditions, groundwater is present at 10 to 15 feet bgs.

The project would only include demolition and would not introduce new development on the site.

There would not be any ground-disturbing activities, such as excavation or trenching, extending to depths where groundwater could be encountered. Therefore, the project would not substantially decrease groundwater supplies or interfere substantially with groundwater recharge such that the project may impede sustainable groundwater management of the basin. (Less than Significant Impact)
c) Would the project substantially alter the existing drainage pattern of the site or area, including through the alteration of the course of a stream or river or through the addition of impervious surfaces, in a manner which would result in substantial erosion or siltation onor off-site; substantially increase the rate or amount of surface runoff in a manner which would result in flooding on- or off-site; create or contribute runoff water which would exceed the capacity of existing or planned stormwater drainage systems or provide substantial additional sources of polluted runoff; or impede or redirect flood flows? As discussed in Section 4.10.1.2 Existing Conditions, the site is currently mapped in a regulatory floodway and in Zone AE.

The project involves the demolition of the existing Halsey House, which would remove impervious surfaces and increase the pervious surface area on-site. This would result in a reduction in runoff volumes compared to existing conditions. The project, therefore, would not substantially alter the drainage pattern of the site or result in off-site flooding and the existing public storm drain system would continue to have capacity to treat runoff from the site, regardless of whether the site is considered to be located in a floodway or floodplain based on FEMA mapping or LIDAR/GPS data. (Less than Significant Impact)

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d) Would the project risk release of pollutants due to project inundation in flood hazard, tsunami, or seiche zones?
As discussed in Section 4.10.1.2 Existing Conditions and Appendix F, the project site is currently mapped in a regulatory floodway and in Zone AE. Due to the project site’s inland location and distance from large bodies of water (i.e., the Bay), it is not subject to seiche or tsunami hazards. No hazardous materials or other pollutants would be stored on-site post-demolition. Therefore, the project would not risk the release of pollutants due to project inundation in flood hazard, tsunami, or seiche zones. (No Impact)
e) Would the project conflict with or obstruct implementation of a water quality control plan or sustainable groundwater management plan?
As described in Section 4.10.1.2 Existing Conditions, the project site is within the Santa Clara groundwater subbasin, and this subbasin has not been identified in the GMP as being overdrafted.

Implementation of the project would not interfere with any actions set forth by Valley Water in its GMP in regard to groundwater recharge, transport of groundwater, and/or groundwater quality. In addition, as discussed under checklist question b), the project would not substantially decrease groundwater supplies or substantially interfere with groundwater recharge. For these reasons, the project would not conflict with or obstruct implementation of a water quality control plan or sustainable groundwater management plan. (Less than Significant Impact) Cumulative Impacts
Would the project result in a cumulatively considerable contribution to a cumulatively significant hydrology and water quality impact?
The cumulative geographic area for hydrology is considered the Adobe drainage basin. The project would not involve redevelopment of existing developed and vacant sites with substantial impervious surfaces. The proposed project would increase pervious surfaces, therefore decreasing the amount of stormwater runoff from the project site and would implement Standard Conditions of Approval to reduce potential surface and groundwater quality impacts during demolition.

However, any future projects in the City of Los Altos may result in the construction of new developments and impervious area. These cumulative projects in the City and within the Adobe drainage basin would be required to conform to applicable General Plan policies (e.g., Policy 3.1, Policy 3.3, and Policy 3.4), as well as all other applicable laws and regulations (e.g., NPDES and MRP) regarding stormwater runoff, infrastructure and flooding to ensure hydrology and water quality impacts are avoided or minimized. The existing policies and regulations would reduce the hydrology and water quality impacts of the proposed project and cumulative projects in the area. Therefore, the project would not result in a cumulatively considerable contribution to a cumulatively significant hydrology and water quality impact. (Less than Significant Cumulative Impact)

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4.11 Land Use and Planning

4.11.1 Environmental Setting
Regulatory Framework
Local
Los Altos General Plan
The following policies in the City’s General Plan have been adopted for the purpose of avoiding or mitigating land use impacts and are applicable to the proposed project:

Policy Description
LU4.6 Continue to review development proposals to ensure a balance between development rights and impacts on surrounding residential neighborhoods.

Los Altos Municipal Code
Title 14 of the LAMC contains the Zoning Code, where standards for growth and development in the City are codified. The Zoning Code is the primary tool for implementing the policies of the General Plan and addressing physical development standards and criteria for the City. Government Code Section 65860 requires municipalities to maintain consistency between their zoning ordinance and their adopted General Plan. One of the purposes of zoning is to implement the land use designations set forth in the General Plan. Although the two are distinct documents, the General Plan and Zoning Code are closely related, and state law mandates that zoning regulations be consistent with the General Plan maps and policies.

Existing Conditions
The project site has a General Plan land use designation of Parks and is within the Public and Community Facilities zoning district.

The Parks designation provides for publicly owned and dedicated parkland. Activities that may be developed include areas for active sports play, large multipurpose fields for community events, informal recreation, tot lots, picnic areas, multipurpose sports fields and courts, concessions, community event space, outdoor amphitheaters, maintenance/support facilities, and caretaker facilities. The maximum intensity of development is a floor area ratio (FAR) of 0.4:1. The anticipated development intensity for this land use designation is a FAR of 0.1:1.

The Public and Community Facilities zoning district is reserved for the construction, use, and occupancy of governmental, public utility, and educational buildings and facilities and other uses compatible with the semipublic character of the district. The following uses are permitted in this zoning district: all facilities owned, leased, or operated by the city, the county, the state, or the

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United States of America; open space conservation areas; public schools; recycling facilities (small collection facilities and reverse vending machines); and uses which are determined by the city planner to be of the same general character. The district also allows for low-intensity, non-retail uses such as childcare facilities, educational uses, and recreational activities. For sites within this zoning district, the minimum site area shall be one acre for each of the conditional uses and no structure shall exceed two stories or 30 feet in height, whichever is lesser.

4.11.2 Impact Discussion
For the purpose of determining the significance of the project’s impact on land use and planning, would the project:
1) Physically divide an established community?
2) Cause a significant environmental impact due to a conflict with any land use plan, policy, or regulation adopted for the purpose of avoiding or mitigating an environmental effect? Project Impacts
a) Would the project physically divide an established community? A physical division of an established community typically refers to the construction of a physical feature (such as a wall, roadway, or railroad tracks) or the removal of a means of access (such as a local roadway or bridge) that would impair mobility within an existing community or between communities.

The project site is located in a suburban neighborhood surrounded by single-family residences and the Preserve. The project would demolish the Halsey House and leave the site vacant. The project would not construct physical features or close an existing street that would impair mobility. The project, therefore, would not physically divide an established community. (No Impact) b) Would the project cause a significant environmental impact due to a conflict with any land use plan, policy, or regulation adopted for the purpose of avoiding or mitigating an environmental effect?
The project consists of the demolition of the Halsey House. The project would not construct any buildings or structures, nor would it change the existing General Plan designation or zoning district.

General Plan policies CDHR 6.1 and 6.2 (listed in Section 4.5 Cultural Resources) require preservation of historic structures and require the City to regard demolition as a last resort. Per General Plan policy CDHR 6.2, demolition of a historic structure can only be permitted after the City determines that the resource has lost its physical integrity, retains no reasonable economic use, that demolition is necessary to protect health, safety, and welfare, or that demolition is necessary

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to proceed with a new project where the benefits of the new project outweigh the loss of the historic resource.

As discussed in Section 4.5 Cultural Resources and throughout this EIR, the proposed project would result in a significant unavoidable impact through demolition of a CRHR eligible property and City Historic Landmark. However, the project would be consistent with General Plan policies CDHR 6.1 and 6.2 because the primary objective of the project is to protect the health, safety, and welfare of the surrounding community by eliminating safety hazards associated with the Halsey House building, which is currently vacant and in a state of disrepair. Therefore, the project would not conflict with any land use plan, policy, or regulation adopted for the purpose of avoiding or mitigating an environmental effect. (No Impact)
Cumulative Impacts
Would the project result in a cumulatively considerable contribution to a cumulatively significant land use and planning impact?
The geographic area for cumulative land use impacts is Los Altos. The Library Courtyard project and Adobe Sewer Replacement Project would be subject to the same Standard Conditions of Approval as the proposed project to reduce impacts. The project does not propose any development and would not result in any land use impacts. Therefore, the proposed project would not result in a cumulatively considerable contribution to a cumulatively significant land use and planning impact. (No Cumulative Impact)

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4.12 Mineral Resources

4.12.1 Environmental Setting
Regulatory Framework
State
Surface Mining and Reclamation Act
The Surface Mining and Reclamation Act (SMARA) was enacted by the California legislature in 1975 to address the need for a continuing supply of mineral resources, and to prevent or minimize the negative impacts of surface mining to public health, property, and the environment. As mandated under SMARA, the State Geologist has designated mineral land classifications in order to help identify and protect mineral resources in areas within the state subject to urban expansion or other irreversible land uses which would preclude mineral extraction. SMARA also allowed the State Mining and Geology Board, after receiving classification information from the State Geologist, to designate lands containing mineral deposits of regional or statewide significance.

Existing Conditions
The City of Los Altos exists on the very deep alluvial soils in the Santa Clara Valley formed from erosion of the nearby Santa Cruz Mountains to the west. As a result of this process, the topography of the project area is relatively flat and there are no significant mineral resources within the City of Los Altos.50

4.12.2 Impact Discussion
For the purpose of determining the significance of the project’s impact on mineral resources, would the project:
1) Result in the loss of availability of a known mineral resource that would be of value to the region and residents of the state?
2) Result in the loss of availability of a locally important mineral resource recovery site delineated on a local general plan, specific plan, or other land use plan? 50 City of Los Altos. Los Alto General Plan 2020 Initial/Mitigated Negative Declaration. November 2002. Page 32.

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Project Impacts
a) Would the project result in the loss of availability of a known mineral resource that would be of value to the region and residents of the state?
b) Would the project result in the loss of availability of a locally important mineral resource recovery site delineated on a local general plan, specific plan, or other land use plan? There are no identified mineral resources or mineral resources recovery sites located on-site.

Therefore, the project would not result in the loss of availability of a mineral resource or the loss of a locally important mineral resource recovery site. (No Impact) Cumulative Impacts
Would the project result in a cumulatively considerable contribution to a cumulatively significant mineral resources impact?
As mentioned previously, the project site is not located within an area containing known mineral resources, and no mineral resources are located in the City of Los Altos. Therefore, the project would not result in a cumulatively considerable contribution to a cumulatively significant mineral resources impact. (No Cumulative Impact)

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4.13 Noise

4.13.1 Environmental Setting
Regulatory Framework
Background Information
Noise
Factors that influence sound as it is perceived by the human ear, include the actual level of sound, period of exposure, frequencies involved, and fluctuation in the noise level during exposure. Noise is measured on a decibel scale, which serves as an index of loudness. The zero on the decibel scale is based on the lowest sound level that the healthy, unimpaired human ear can detect. Each 10 decibel increase in sound level is perceived as approximately a doubling of loudness. Because the human ear cannot hear all pitches or frequencies, sound levels are frequently adjusted or weighted to correspond to human hearing. This adjusted unit is known as the A-weighted decibel, or dBA.

Since excessive noise levels can adversely affect human activities and human health, federal, state, and local governmental agencies have set forth criteria or planning goals to minimize or avoid these effects. Noise guidelines are generally expressed using one of several noise averaging methods, including Leq, DNL, or CNEL.51 These descriptors are used to measure a location’s overall noise exposure, given that there are times when noise levels are higher (e.g., when a jet is taking off from an airport or when a leaf blower is operating) and times when noise levels are lower (e.g., during lulls in traffic flows on freeways or in the middle of the night). Lmax is the maximum A-weighted noise level during a measurement period.

Vibration
Ground vibration consists of rapidly fluctuating motions or waves with an average motion of zero.

Vibration amplitude can be quantified using Peak Particle Velocity (PPV), which is defined as the maximum instantaneous positive or negative peak of the vibration wave. PPV has been routinely used to measure and assess ground-borne construction vibration. Studies have shown that the threshold of perception for average persons is in the range of 0.008 to 0.012 inches/second (in/sec) PPV.
51 Leq is a measurement of average energy level intensity of noise over a given period of time. Day-Night Level (DNL) is a 24-hour average of noise levels, with a 10 dB penalty applied to noise occurring between 10:00 PM and 7:00 AM. Community Noise Equivalent Level (CNEL) includes an additional five dB applied to noise occurring between 7:00 PM and 10:00 PM. Where traffic noise predominates, the CNEL and DNL are typically within two dBA of the peak-hour Leq.

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Regulatory Framework
Federal
Federal Transit Administration Vibration Limits
The Federal Transit Administration (FTA) has developed vibration impact assessment criteria for evaluating vibration impacts associated with transit projects. The FTA has proposed vibration impact criteria based on maximum overall levels for a single event. The impact criteria for groundborne vibration are shown in Table 4.13-1 below. These criteria can be applied to development projects in jurisdictions that lack vibration impact standards.

Table 4.13-1: Groundborne Vibration Impact Criteria
Land Use Category
Groundborne Vibration Impact Levels
(VdB inch/sec)
Frequent
Event
Occasional
Events
Infrequent
Events
Category 1: Buildings where vibration would interfere with interior operations
65 65 65
Category 2: Residences and buildings where people normally sleep 72 75 80
Category 3: Institutional land uses with primarily daytime use 75 78 83 Source: Federal Transit Administration. Transit Noise and Vibration Assessment Manual. September 2018.

State and Local
Los Altos General Plan
The following policies in the City’s General Plan have been adopted for the purpose of reducing or avoiding impacts related to noise, and are applicable to the project:

Policy Description
NEH 7.9 Minimize stationary noise sources and noise emanating from construction activities.

Los Altos Municipal Code
Chapter 6.16 of the LAMC contains standards and regulations to control unnecessary, excessive, and annoying noise and vibration within the City. Specifically, Section 6.16.50 of the LAMC establishes exterior noise limits for various zoning districts as shown in Table 4.13-2.

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Table 4.13-2: Exterior Noise Limits
Receiving Land Use Category Time Period Noise Level (dBA)1 All R1 Zoning Districts 10:00 PM – 7:00 AM
7:00 AM – 10:00 PM
45 55
All R3 Zoning Districts 10:00 PM – 7:00 AM
7:00 AM – 10:00 PM
50 55
All R3 Zoning Districts 10:00 PM – 7:00 AM
7:00 AM – 10:00 PM
55 60
All OA Zoning Districts 10:00 PM – 7:00 AM
7:00 AM – 10:00 PM
60 65
1 Levels not to be exceeded more than 30 minutes in any hour.

The LAMC prohibits the production of noise on one property that would (i) exceed the noise standard on any other property for a cumulative period of more than thirty minutes in any hour; (ii) exceed the noise standard plus five dB on any other property for a cumulative period of more than fifteen minutes in any hour; (iii) exceed the noise standard plus 10 dB on any other property for a cumulative period of more than five minutes in any hour; (iv) exceed the noise standard plus 15 dB on any other property for a cumulative period of more than one minute in any hour; or (vi) exceed the noise standard plus 20 dB or the maximum measured ambient on any other property for any period of time.

The City’s LAMC states that if the measured ambient level exceeds the maximum permissible noise level within any of the first four noise limit categories, the allowable noise exposure standard shall be increased in five dB increments in each category as appropriate to encompass or reflect such ambient noise level. In the event the ambient noise level exceeds the fifth noise limit category, the maximum allowable noise level under said category shall be increased to reflect the maximum ambient noise level. If the noise measurement occurs on a property adjacent to a zone boundary, the noise level limit applicable to the lower noise zone, plus five dB is the applicable noise limit.

To ensure that unnecessary or excessive noise disturbances from specific activities and equipment are avoided, the Noise Control Ordinance sets noise thresholds for musical instruments, loudspeakers, loading and unloading, construction and demolition, and air-conditioning equipment (Section 6.16.070 of the LAMC). Exceeding those thresholds is considered a prohibited act and would constitute a violation of the Ordinance.

Existing Conditions
The project site is currently developed with the Halsey House, which is vacant and does not generate any noise. Surrounding land uses include single-family residences to the north, south, and east. The nearest residence is approximately 140 feet southwest of the Halsey House. The primary noise sources in the project vicinity include vehicular traffic along University Avenue and occasional aircraft flyovers.

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4.13.2 Impact Discussion
For the purpose of determining the significance of the project’s impact on noise, would the project result in:
1) Generation of a substantial temporary or permanent increase in ambient noise levels in the vicinity of the project in excess of standards established in the local general plan or noise ordinance, or applicable standards of other agencies?
2) Generation of excessive groundborne vibration or groundborne noise levels? 3) For a project located within the vicinity of a private airstrip or an airport land use plan or, where such a plan has not been adopted, within two miles of a public airport or public use airport, would the project expose people residing or working in the project area to excessive noise levels?
Thresholds of Significance
A significant impact would be identified if project construction would result in a substantial temporary increase in ambient noise levels at sensitive receivers in excess of the local noise standards contained in the Los Altos General Plan or LAMC, as follows:
• Temporary Noise Increase. A significant temporary noise impact would be identified if construction would occur outside of the hours specified in the LAMC or if construction noise levels were to exceed the City’s construction noise limits at adjacent noise sensitive land uses. Construction occurring during allowable hours is limited to 75 dBA in single-family residential areas (all R1 Zoning Districts), 80 dBA in multi-family residential areas (all R3 Zoning Districts), and 85 dBA in commercial areas (all OA and C Zoning Districts).

The City of Los Altos does not specify a construction vibration limit. For structural damage, Caltrans recommends a vibration limit of 0.5 in/sec PPV for new residential and modern commercial/industrial structures, 0.3 in/sec PPV for older residential structures, and a limit of 0.25 in/sec PPV for historic and some old buildings. The nearest residence, 140 feet southwest of the Halsey House, was constructed in 1949.52 The 0.3 in/sec PPV vibration limit would be applicable to properties in the vicinity of the project site.
52 Zillow. “13390 Lennox Way, Los Altos Hills, CA 94022.” Accessed December 19, 2025. https://www.zillow.com/homedetails/13390-Lennox-Way-Los-Altos-Hills-CA-94022/19527413_zpid/.

Halsey House Project, SCH# 2025020308 99 Draft Environmental Impact Report City of Los Altos June 2026
Project Impacts
a) Would the project result in generation of a substantial temporary or permanent increase in ambient noise levels in the vicinity of the project in excess of standards established in the local general plan or noise ordinance, or applicable standards of other agencies? The project would result in a temporary noise increase during demolition. There would be no sources of permanent noise because there would be no operational activities or sources postdemolition. The demolition activities would last three months and include a limited amount of equipment (excavator, bulldozer, and track loader). All noise would cease upon completion of the demolition. During demolition, the project would implement the following construction-related measures as Standard Conditions of Approval to reduce temporary demolition noise.

Standard Conditions of Approval:
• Work Hours/Construction Site Signage: No work shall commence on the job site prior to 7:00 a.m. nor continue later than 5:30 p.m., Monday through Friday, from 9 a.m. to 3 p.m.

Saturday, and no work is permitted on Sunday or any City observed holiday. • Disturbance Coordinator: Designate a “disturbance coordinator” who shall be responsible for responding to any local complaints regarding construction noise. The coordinator (who may be an employee of the general contractor) will determine the cause of the complaint and will require reasonable measures warranted to correct the problem be implemented. A telephone number of the noise disturbance coordinator shall be conspicuously posted at the construction site fence and on the notification sent to neighbors adjacent to the site.

The sign must also list an emergency after-hours contact number for emergency personnel. • Construction Noise Reduction: The following noise reduction measures shall be incorporated into construction plans and contractor specifications to reduce the impact of temporary construction-related noise on nearby properties:
o Comply with manufacturer’s muffler requirements on all construction equipment engines;
o Turn off construction equipment when not in use, where applicable; o Locate stationary equipment as far as practical from receiving properties; o Shroud or shield impact tools and use electric-powered rather than diesel-powered construction equipment.

The above Standard Conditions of Approval would reduce temporary demolition noise levels to less than significant. (Less than Significant Impact)

Halsey House Project, SCH# 2025020308 100 Draft Environmental Impact Report City of Los Altos June 2026
b) Would the project result in generation of excessive groundborne vibration or groundborne noise levels?
As mentioned in Section 4.13.1.4 Existing Conditions, the nearest structure is a single-family residence approximately 140 feet southwest of the disturbance area. The residence was constructed in 1949 and is, therefore, subject to the 0.3 in/sec PPV threshold for older residential structures. Demolition activities may generate perceptible vibration when heavy equipment or impact tools (e.g., jackhammers, hoe rams) are used in the vicinity of nearby sensitive land uses.

Table 4.13-3 shows the vibration levels generated by typical construction and demolition equipment at 25 and 50 feet.

Table 4.13-3: Vibration Levels for Typical Construction Equipment Equipment PPV at 25 feet (in/sec) PPV at 50 feet (in/sec) Clam shovel drop 0.202 0.094
Hydromill (slurry wall) in soil
in rock

0.008

0.017

0.001

0.002
Vibratory roller 0.210 0.099
Hoe Ram 0.089 0.004
Large bulldozer 0.089 0.004
Caisson drilling 0.089 0.004
Loaded trucks 0.076 0.036
Jackhammer 0.035 0.016
Small bulldozer 0.003 0.001
Source: Federal Transit Administration, Office of Planning and Environment, U.S. Department of Transportation.

Transit Noise and Vibration Impact Assessment Manual. September 2018.

Based on the type of equipment to be used (e.g., excavator, bulldozer, track loader, and trucks) and the distance of the nearest structure, the project would not generate vibration levels that would exceed the recommended Caltrans vibration limit of 0.3 in/sec PPV. Therefore, the project would not result in the generation of excessive groundbourne vibrations or groundbourne noise levels. (Less than Significant Impact)

Halsey House Project, SCH# 2025020308 101 Draft Environmental Impact Report City of Los Altos June 2026
c) For a project located within the vicinity of a private airstrip or an airport land use plan or, where such a plan has not been adopted, within two miles of a public airport or public use airport, would the project expose people residing or working in the project area to excessive noise levels?
The project site is not located within two miles of a public airport or in the vicinity of a private airstrip. Therefore, the project would not expose people residing or working in the project area to excessive aircraft noise levels. (No Impact)
Cumulative Impacts
Would the project result in a cumulatively considerable contribution to a cumulatively significant noise impact?
The geographic area for cumulative noise and vibration impacts is the project site and immediate vicinity. Cumulative projects within 1,000 feet of the project site could contribute to the same noise impacts as the proposed projects. The Library Courtyard project is over a half mile away and is outside of the geographic area for this impact. Construction of the Adobe Creek Sewer project may occur at the same time as demolition of the Halsey House, such that construction-related noise impacts could occur simultaneously. However, all projects are required to incorporate noise and vibration reduction measures as identified in the City’s General Plan (Policy 7.1 through 7.10) and LAMC. For these reasons, the project would not result in a cumulatively considerable contribution to cumulatively significant noise or vibration impacts. (Less than Significant Cumulative Impact)

Halsey House Project, SCH# 2025020308 102 Draft Environmental Impact Report City of Los Altos June 2026

4.14 Population and Housing

4.14.1 Environmental Setting
Regulatory Framework
Housing-Element Law
State requirements mandating that housing be included as an element of each jurisdiction’s general plan is known as housing-element law. The Regional Housing Need Allocation (RHNA) is the statemandated process to identify the total number of housing units (by affordability level) that each jurisdiction must accommodate in its housing element. California housing-element law requires cities to: 1) zone adequate lands to accommodate its RHNA; 2) produce an inventory of sites that can accommodate its share of the RHNA; 3) identify governmental and non-governmental constraints to residential development; 4) develop strategies and a work plan to mitigate or eliminate those constraints; and 5) adopt a housing element and update it on a regular basis.53 The City of Los Altos Housing Element and related land use policies were last updated in August 2023.54 Regional and Local
Existing Conditions
As of May 2025, the City of Los Altos had a total population of approximately 31,553 residents.55 The project site is developed with the Halsey House, which has been vacant since 2008 and has not been utilized as a residence since 1974.

4.14.2 Impact Discussion
For the purpose of determining the significance of the project’s impact on population and housing, would the project:
1) Induce substantial unplanned population growth in an area, either directly (for example, by proposing new homes and businesses) or indirectly (for example, through extension of roads or other infrastructure)?
2) Displace substantial numbers of existing people or housing, necessitating the construction of replacement housing elsewhere?
53 California Department of Housing and Community Development. “Regional Housing Needs Allocation and Housing Elements” Accessed December 19, 2025. https://www.hcd.ca.gov/planning-and-communitydevelopment/housing-elements 54 City of Los Altos. 6th Cycle Housing Element 2023-2031. Adopted January 2023, revised August 2023. https://www.losaltosca.gov/DocumentCenter/View/286/6th-Cycle-Los-Altos-Housing-Element-2023-to-2031-PDF. 55 State of California Department of Finance. “E-5 Population and Housing Estimates for Cities, Counties and the State — January 1, 2021-2025.” May 2025. Accessed December 19, 2025. https://dof.ca.gov/forecasting/demographics/estimates/e-5-population-and-housing-estimates-for-cities-countiesand-the-state-2020-2025/

Halsey House Project, SCH# 2025020308 103 Draft Environmental Impact Report City of Los Altos June 2026
Project Impacts
a) Would the project induce substantial unplanned population growth in an area, either directly (for example, by proposing new homes and businesses) or indirectly (for example, through extension of roads or other infrastructure)?
The proposed project is the demolition of the vacant Halsey House. The project would not include any housing units or extend any roadways or other infrastructure. Therefore, the project would not induce any substantial unplanned population growth in the area. (No Impact) b) Would the project displace substantial numbers of existing people or housing, necessitating the construction of replacement housing elsewhere?
The Halsey House is vacant and does not house any residents. Therefore, implementation of the project would not displace existing residents from the project site that would necessitate construction of replacement housing elsewhere. (No Impact) Cumulative Impacts
Would the project result in a cumulatively considerable contribution to a cumulatively significant population and housing impact?
The geographic area for cumulative population and housing impacts is the City of Los Altos. The project would not be a residential or employment-generating use. For this reason, the project would not result in a cumulatively considerable contribution to a cumulatively considerable significant population and housing impact. (No Cumulative Impact)

Halsey House Project, SCH# 2025020308 104 Draft Environmental Impact Report City of Los Altos June 2026

4.15 Public Services

4.15.1 Environmental Setting
Regulatory Framework
City of Los Altos General Plan
The following policies in the City’s General Plan have been adopted for the purpose of avoiding or reducing public services impacts and are applicable to the project:

Policy Description
OSCCF 1.4 Require park dedication, public open space, or require fees in lieu thereof, for all new subdivisions and multi-family residential development in Los Altos.

OSCCF 6.1 Promote community order by preventing criminal activity, enforcing laws, and meeting the community service demands.

OSCCF 6.3 Promote response times for police and fire protection services emergencies that are comparable to similar jurisdictions in Santa Clara County.

OSCCF 6.4 Continue cooperative mutual aid agreements with nearby jurisdictions to ensure rapid and sufficient response to emergency situations.

OSCCF 9.2 Work with private developers to offer cultural activities within the community, such as a community theater and cinema.

Los Altos Parks Plan
The Los Altos Parks Plan, adopted in May of 2012, is intended to create a clear set of goals, policies, and objectives that will provide direction to the City Council and City staff for the development, improvement, and enhancement of the City’s park system for the next twenty to thirty years. The Parks Plan was designed to parallel the General Plan’s Open Space, Conservation, and Facilities Element by providing specific direction and recommendations related to parks in Los Altos.

Existing Conditions
Fire and Police Protection Services
The City of Los Altos contracts with the Santa Clara County Fire District for fire and emergency medical services.56 There are two fire stations in Los Altos: Almond Fire Station located at 10 Almond Avenue and Loyola Fire Station located at 765 Fremont Avenue. The nearest station to the project site is the Almond Fire Station, located approximately 1.2 miles northeast. 56 City of Los Altos. “Fire.” Accessed December 19, 2025. https://www.losaltosca.gov/358/Fire.

Halsey House Project, SCH# 2025020308 105 Draft Environmental Impact Report City of Los Altos June 2026
Police protection services for the project site are provided by the Los Altos Police Department, headquartered at 1 North San Antonio Road, approximately one mile northeast of the project site.

The Department has 32 sworn officers and 14 professional support staff.57 Schools
Residents in Los Altos could attend school in the following districts: Los Altos School District, Cupertino Union School District, Santa Clara County Office of Education, Mountain View Los Altos High School District, and Fremont Union High School District.58 The project site is located in the Los Altos School District and the Mountain View-Los Altos High School District. Elementary school students in the project area attend Gardner Bullis School, located approximately one mile northwest of the project site. Middle school students in the project area attend Egan Junior High School located approximately two miles north of the project site. High School students in the project area attend Los Altos High School, located approximately 1.5 miles northeast of the project site.

Parks
The City provides and maintains developed parkland and open space to serve its residents.

Residents of Los Altos are served by community park facilities, neighborhood parks, playing fields, and community centers. The City’s Parks and Recreation Department is responsible for development, operation, and maintenance of all City park facilities. The City has 18 different park and recreational facilities available for public use.59 The project site is located within the Preserve. The Halsey House was most recently used as a nature center where educational and recreational programs were conducted for children. The Halsey House has been closed since 2008 due to health and safety code concerns. Shoup Park is approximately 400 feet north of the project site.

Libraries
The City of Los Altos is served by the Santa Clara County Library District. The nearest library to the project site is located at 13 South San Antonio Road, approximately one mile northeast of the project site.
57 City of Los Altos. “About Us.” Accessed December 19, 2025 https://www.losaltosca.gov/262/About-Us. 58 City of Los Altos. “School Districts.” Accessed December 19, 2025. https://www.losaltosca.gov/462/SchoolDistricts. 59 City of Los Altos. “Map of Parks.” Accessed December 19, 2025. https://www.losaltosca.gov/documentcenter/view/1950.

Halsey House Project, SCH# 2025020308 106 Draft Environmental Impact Report City of Los Altos June 2026
Community Centers
There are two community centers located in Los Altos: Grant Park Community Center located at 1575 Holt Avenue, approximately four miles southeast of the project site, and Los Altos Community Center located at 97 Hillview Avenue, approximately one mile northeast of the project site.

4.15.2 Impact Discussion
For the purpose of determining the significance of the project’s impact on public services, would the project result in substantial adverse physical impacts associated with the provision of new or physically altered governmental facilities, need for new or physically altered governmental facilities, the construction of which could cause significant environmental impacts, in order to maintain acceptable service ratios, response times, or other performance objectives for any of the public services:
1) Fire protection?
2) Police protection?
3) Schools?
4) Parks?
5) Other public facilities?
Project Impacts
a) Would the project result in substantial adverse physical impacts associated with the provision of new or physically altered governmental facilities, need for new or physically altered governmental facilities, the construction of which could cause significant environmental impacts, in order to maintain acceptable service ratios, response times, or other performance objectives for fire protection services? b) Would the project result in substantial adverse physical impacts associated with the provision of new or physically altered governmental facilities, need for new or physically altered governmental facilities, the construction of which could cause significant environmental impacts, in order to maintain acceptable service ratios, response times, or other performance objectives for police protection services? The project proposes to demolish the Halsey House. The project does not propose the construction or operation of a new building that would require increased fire or police protection services, construction of new fire or police protection facilities, or expansion of existing fire or police protection facilities. No new residents or employees would be generated by the project. Therefore, there would be no change to the acceptable service ratios, response times, or other performance objectives for fire and police protection services. The project would have no impact on fire or police protection services. (No Impact)

Halsey House Project, SCH# 2025020308 107 Draft Environmental Impact Report City of Los Altos June 2026
c) Would the project result in substantial adverse physical impacts associated with the provision of new or physically altered governmental facilities, need for new or physically altered governmental facilities, the construction of which could cause significant environmental impacts, in order to maintain acceptable service ratios, response times, or other performance objectives for schools?
The project proposes to demolish the Halsey House. The project would not result in population growth because the project would not generate new residents. Therefore, no new students would be generated. Project implementation would not impact existing school services or result in the need for new or physically altered schools in the project area. (No Impact) d) Would the project result in substantial adverse physical impacts associated with the provision of new or physically altered governmental facilities, need for new or physically altered governmental facilities, the construction of which could cause significant environmental impacts, in order to maintain acceptable service ratios, response times, or other performance objectives for parks?
The project proposes to demolish the Halsey House. The project would not result in population growth because the project would not generate new residents. Demolition of the Halsey House would not change or hinder access to the Preserve. As discussed in Section 4.15.1.2 Existing Conditions, the Halsey House was used as an educational nature center until it closed in 2008. Since the Halsey House has not been an active public facility in 17 years, and there are other public facilities provided throughout the City, the proposed project would not constitute a significant loss of a public facility. Therefore, the project would not overburden existing park facilities or create the need for any new park facilities or adversely impact the physical condition of existing park facilities. (No Impact)
e) Would the project result in substantial adverse physical impacts associated with the provision of new or physically altered governmental facilities, need for new or physically altered governmental facilities, the construction of which could cause significant environmental impacts, in order to maintain acceptable service ratios, response times, or other performance objectives for other public facilities? The project proposes to demolish the Halsey House. The project would not result in population growth or result in the increased use of local libraries or community centers. The project would not generate new residents or employees. The project would not create the need for or adversely impact the physical condition of existing library or community center facilities. (No Impact)