Attachment 3.A_ Technical Studies - Air Quality and Greenhouse Gas Assessment 03.07.24 — Atherton City Council, September 18, 2024

ATHERTON HOUSING ELEMENT

UPDATE AND ZONING CODE

AMENDMENTS AIR QUALITY &

GREENHOSE GAS ASSESSMENT
Atherton, California
January 25, 2024
Prepared for:

Adam Petersen
Principal Planner
M-Group
1475 S. Bascom Ave, Suite 210
Campbell, CA 95008t
Prepared by:

James A. Reyff
Casey Divine
Jordyn Bauer
429 East Cotati Avenue
Cotati, CA 94931
(707) 794-0400
I&R Project: #23-116
Revised March 7, 2024
1 INTRODUCTION
The purpose of this report is to address air quality, health risk, and greenhouse gas (GHG) impacts associated with buildout of the proposed Housing Element Update and resulting zoning code amendments located in Atherton, California. The air quality and GHG impacts from the Housing Element Update would be associated with construction of the new buildings and infrastructure and operation of the project. Air pollutants associated with construction and operation are addressed qualitatively since construction and operational details are not known at the level necessary to predict meaningful quantitative impacts. All analyses were conducted following guidance provided by the Bay Area Air Quality Management District (BAAQMD).1

BACKGROUND
The Town of Atherton has an area of approximately 3,600 acres or 5.6 square miles, comprised of 89% residential, 5% parks and open space, and 6% public and private schools and municipal facilities. The Town has been primarily developed with lower density residential uses, with no commercial or industrial uses. The 2023-2031 Housing Element was passed in January 2023.

PROJECT DESCRIPTION
The Project is the proposed update to the Town of Atherton’s Housing Element 2023-2031 and the resulting amendment of Title 17 of the Town of Atherton Municipal Code that would apply overlays zones to specific properties located within the Town of Atherton, California. The proposed Project would allow for housing to be constructed on these properties, helping meet the Town’s future housing needs at all economic levels. As a policy document, the Housing Element Update and amended municipal code does not result in direct physical changes to the environment but would indirectly lead to physical environmental changes by enabling the potential development of additional housing units within the Town’s jurisdiction. Additional housing leads to additional air pollutant and GHG emissions as well as potential localized air quality impacts.

Regional Housing Needs Allocation (RHNA)
In accordance with Government Code § 65584, projected housing needs for each city and county in the San Francisco Bay area region are prepared by the Association of Bay Area Governments (ABAG) and the Metropolitan Transportation Commission (MTC) under a process known as the Regional Housing Needs Assessment (RHNA). The RHNA allocates regional housing needs by income level among member jurisdictions.

California law established the planning period for the current RHNA from 2023 to 2031. ABAG’s RHNA allocation for Atherton during this period is 348 units. The 348 units for Atherton are out of the anticipated construction need of 441,176 additional housing units in the ABAG region.

Atherton’s 348 units are distributed into Very Low Income, Low Income, Moderate Income, and Above Moderate-Income categories. Each category is defined by households falling into a certain percentage of the Area Median Income (AMI) as shown in Table 1. 1 Bay Area Air Quality Management District, 2022 CEQA Guidelines, April 2023 2 Table 1. RHNA Allocation
Income Category 6th Cycle
RHNA
10% Buffer Units Total Units Percent
Extremely Low / Very Low 94 9 103 26%
Low 54 5 59 16%
Moderate 56 6 62 18%
Above Moderate 144 14 158 40%
Total 348 34 382 100%
Comparison of Site Inventory and RHNA
In addition to the proposed goals, objectives, policies, and programs to meet the RHNA, Atherton factored in programs including, but not limited to, a Residential Medium (RM) 10 overlay zone at 23 Oakwood, overlay zones on developed portions of open space sites, including the California Water Service site, the Circus Club, and the Gilmore House and Knox Playschool sites, vacant sites, lot splits (under the 2022 state law for urban lot splits; SB 9), private school sites, and accessory dwelling units (ADUs). The total new housing units needed to achieve the 6th Cycle RHNA are summarized in Table 2.

Table 2. Net RHNA – Projected Dwelling Units
Very Low
& Low Moderate Above Moderate Total New
0-80% Housing Units
AMI
81-120%
AMI
>120%
AMI
Projected Dwelling Units
ADUs 112 56 112 280
Lot Splits (SB 9) 0 0 48 48
Vacant Sites 0 0 9 9
RM 10 (23 Oakwood) 4 0 12 16
PFS (Private Schools) 96 95 0 191
Multi-Family Residential
Opportunity Sites 17 34 34 85
Dwelling Unit Total 229 185 215 629
Total Net New Units Above or
below RHNA +81 +129 +71 +281
Anticipated Accessory Dwelling Units (ADUs)
The 2016 through 2020 updates to State law – Assembly Bill (AB) 2299 (2016), Senate Bill (SB) 1069 (2016), AB 494 (2017), SB 229 (2017), AB 68 (2019), AB 881 (2019), AB 587 (2019), SB 13 (2019), AB 670 (2019), AB 671 (2019), and AB 3182 (2020) – included changes pertaining to the allowed size of accessory, permitting ADUs by right in at least some areas of a jurisdiction, and limits on parking requirements related to ADUs. More recent bills reduce the time to review and approve ADU applications to 60 days, remove lot size and replacement parking space requirements, and require local jurisdictions to permit junior ADUs (JADUs). 3 In 2021 and 2022, the Town of Atherton experienced the construction of 44 new ADUs, three (3) JADUs, and seven (7) ADU conversions. Based on this trend, the Town projects an average of 35 new ADUs per year over the next eight (8) years. The Housing Element includes programs to amend the zoning code to facilitate ADU and JADU construction.

SB 9
Senate Bill 9 or SB 9 waives discretionary review and public hearings for building two homes on a parcel in a single-family zone and subdividing a lot into two that can be smaller than the previously required minimum size. In early 2022, the Town adopted an implementing ordinance consistent with state law to provide property owners clarity for the development opportunities under SB 9. The ordinance allows new lots to be created under the provisions of SB 9 to utilize the existing development standards for the base zoning district. A new residence built on a lot created through an SB 9 lot split can use the same setbacks, floor area ratio, building heights and other standards as provided for any existing lot in the same zoning district.

It is projected that approximately 48 new above moderate-income housing units will result from lot splits and new housing development facilitated by the 2021 SB 9 State law (GC section 65852.21) during the 2023-2031 Planning Period. There are 606 lots of an acre or greater in size, and Atherton received six (6) applications in 2022 and an additional six (6) inquiries that would result in a total of 23 new dwelling units.

Vacant Sites
The Town of Atherton surveyed all Town parcels to determine adequate sites for housing. There is little vacant developable land in the Town, and most of the Town's land acreage is developed at existing General Plan densities. However, the Town did identify eight (8) undeveloped sites that it expects would provide single-family housing at the above-moderate income level. These sites are listed in Table 3.
4 Table 3. Vacant Sites
Site
ID
Lot
Acres APN Address Current Zoning
Max. Primary
Units under
current
Zoning
Potential Net
New Primary
Units under
SB-9
Reason not
selected as
Opportunity
Site
V1 1.42 070-
343-100
97 Santiago
Ave. R-1A 1 4
SB-9 application
filed. City Council
decision on
7/19/23.

V2 2.12 070-
012-270
Polhemus
Ave. R1-A 2 4
City Council
decision on
7/19/23. Discussed
as part of 290
Polhemus Ave.

V3 1.13 070-
180-400
95 Faxon
Road R1-A 1 4
Not fully vacant.

Improved with
tennis court,
landscaping &
walkways. Serves
as extended rear
yard of adjacent
property.

V4 0.95 070-
180-340
12 Faxon
Forest
Road
R1-A 1 4
Not located on
major road or near
public & private
services.

V5 0.85 070-
180-350
16 Faxon
Forest
Road
R1-A 1 4
Not located on
major road or near
public & private
services.

V6 1.00 070-
180-290
No Address
(Located
between 7
& 11
Faxon
Forest Rd.)
R1-A 1 4
Not located on
major road or near
public & private
services.

V7 1.78 070-
131-010
15 Monte
Vista Ave. R1-A 1 4
Not fully vacant.

Portion occupied
by existing house.

Part of a larger
estate, approx. 12.6
acres.

V8 0.98 070-
180-020
25 Monte
Vista Ave. R1-A 1 4
Not fully vacant.

Portion occupied
by existing house.

Part of a larger
estate, approx. 12.6
acres.

TOTAL PRIMARY HOUSING UNITS 9 32
5 Residential Sites Inventory
An important component of the Town of Atherton Housing Element is the identification of sites for future housing development, and an evaluation of the adequacy of those sites in fulfilling the Town’s share of regional housing needs. To accomplish this, all town parcels were surveyed to determine their development capacity. Due to limited vacant and underutilized sites in Atherton, the Town has selected candidate sites for rezoning. Each site was analyzed in light of the development standards for its proposed zoning designation. All parcels in Atherton were evaluated through a process of elimination based on required criteria set by the State (HCD).

Multi-Family Residential Opportunity Sites
The Town has identified seven (7) sites as multi-family residential opportunity sites, in addition to the ADU, SB 9, and vacant sites identified above. The Town is proposing to either rezone or adopt an overlay zone on these properties to facilitate multi-family housing at a density of up to 10 dwelling units per acre (du/ac). The Housing Element does not institute the rezoning or zoning overlay, but rather these are recommended legislative actions that would be implemented separately and after adoption and certification of the Housing Element. A list of sites for multifamily residential opportunities is identified in Table 4.

The rezoning or zoning overlay allows residential units to be built at a density of 10 dwelling units per acre. Potential units were calculated would yield a total of 68 units on approximately 6.89 acres of land.

Table 4. Multi-Family Residential Opportunity Sites
Site ID Address Lot Acres Existing
Zoning
Proposed Zoning
Overlay
Proposed Net
Residential Units from
Zoning Overlay
MFO-1 999 Ringwood Ave. 0.90 R-1A R-10 9
MFO-2 352 Bay Rd. 0.92 R-1A R-10 9
MFO-3 318 Bay Rd. 0.94 R-1A R-10 9
MFO-4 296 Bay Rd. 0.93 R-1A R-10 9
MFO-5 175 Ravenswood 1.1 R-1A R-10 11
MFO-6 185 Ravenswood 1.1 R-1A R-10 11
MFO-7 197 Ravenswood 1 R-1A R-10 10
TOTALS 6.89 68
Municipal Code Changes
Implementation of the Housing Element would effectuate the following zoning changes to the Atherton Municipal Code:
• RM-10 Overlay Zone – Public Open Space Sites: The project proposes an amendment to the Town’s Municipal Code of an RM-10 overlay to permit multifamily residential uses by right in the developed areas of properties in the Public Open Space zone. This includes the following: approximately 0.9 acres of Holbrook Palmer Park, occupied by the Gilmore 6 House; approximately 0.5 acres of developed portions of the Circus Club; and approximately 0.25 acres of portions of the California Water Service site at Bear Gulch Reservoir that are currently developed with offices or an ancillary off-street parking area. • RM-10 Overlay Zone – 23 Oakwood: The project proposes an amendment to the Town’s Municipal Code of an RM-10 overlay zone to permit multifamily residential uses by right.

Included in the amendment request is a maximum density of 10 dwelling units per acre, building height standards of 40 feet, setbacks to accommodate the density, parking, and objective design standards. The site would yield 16 dwelling units. • Menlo College Overlay Zone – 1000 El Camino Real: Implementation of the Housing Element would institute an overlay zone on three locations of the Menlo College site as described:
o Site 1: The existing O’Brien surface parking lot at the southwest corner of El Camino Real and Alejandra Avenue is approximately 75,000 square feet (1.7 acres) in area. The site is level and currently contains a paved parking lot. The lot is surrounded by mature vegetation. Construction of a multi-family housing building is feasible at this location with podium parking at ground level and three-stories of housing above, or below grade parking. The Town does not have on-site parking requirements. Parking would be replaced to meet the needs of the college. The Town will amend the PFS zone, implementing an overlay zone on this site that permits 40 units per acre by right with objective design standards. The College has expressed interest in developing 60 dwelling units at this site. o Site 2: There are four residences located on the campus in World War II era houses that are currently utilized for faculty housing. Demolition of these residences would accommodate 30 apartment units, resulting in a net increase of 26 multifamily housing units. The Town will amend the PFS zone, implementing an overlay zone on this site that permits a density of 20 units per acre by right with objective design standards.
o Site 3: The College has identified a site that is viable for a multi-story multi-family development of approximately 40 units. The site, near the Administration Building, is currently used as parking. Additional parking can be developed near the entry to the College off El Camino Real. The Town will amend the PFS zone, implementing an overlay zone on this site that permits 40 units per acre by right with objective design standards.

Additional actions for all three sites include reducing the minimum front yard setback to 30 feet, amending the height limit to allow up to four-stories or 48 feet, permitting multifamily housing by right with objective design standards. • Menlo School Overlay Zone – 50 Valparaiso Avenue: Implementation of the Housing Element would implement an overlay zone at two locations on the Menlo School as described below:
7 o Site 1: A surface parking located at the southwest corner of the campus with frontage on Valparaiso Avenue and the school entry drive, approximately 56,000 square feet (sf.) would have an overlay zone that permits 20 dwelling units per acre by right with objective design standards. This site would yield 25 dwelling units. o Site 2: An approximately 44,000 sf. surface parking lot located at the southeast corner of the campus, with a frontage on Valparaiso Avenue and the school entry drive. With an overlay zone that permits 20 dwelling units per acre by right with objective design standards, this site could yield approximately 20 dwelling units.

To accommodate the new housing development, the zoning will be amended as follows:
o Reduce the minimum front yard setback to 30 feet (along Valparaiso Road). o Amend the height limit to allow four-stories or 48 feet. o Permit multifamily housing by right with objective design standards. • Sacred Heart Overlay Zone – 150 Valparaiso Avenue: There are currently five (5) apartment units on the campus and housing for retired Nuns at Oakwood. The school anticipates this facility being renovated in the future to accommodate faculty housing which would be allowed under the PFS Zoning with an amendment for a density of 20 units per acre. The site would yield approximately 20 units. • Implementation of the Housing Element would amend the ADU provisions of the Atherton Municipal Code, permitting the following:
o Second story ADUs above detached garages, increasing the allowable height to 18 feet.
o Two ADUs to be constructed on properties two-acres or greater in area; the first ADU is exempt from floor area limitations and the second ADU will be included in the ADU floor area.
o Allow pool housing and guest houses to be rented as ADUs. o Waiving fees for all new ADUs.
o Eliminating the owner occupancy limitation on ADUs, including guest and pool houses.

Further, implementation of the Housing Element would result in the following amendments to the Atherton Municipal Code:
8 • Allowing Permanent Supportive Housing by-right in use zones where multi-family and mixed-uses are permitted; and a by-right allowance for 100% affordable housing that has 25%, or 12 units, of permanent supportive housing where multi-family or mixed-use housing is permitted.
• Permitting Low Barrier Navigation Centers in zones where multi-family and mixed uses are permitted.
• Permitting mobile homes and manufactured housing on a permanent foundation under the same manner as single-family homes.
• Allowing group homes for seven (7) or more residents in any district where residential uses are permitted.
• Permitting shelters, and amending their parking requirements, without discretionary action. • Amending the minimum lot size in the R-1B and subdivision ordinance allowing one-third (0.33) acre lots for the subject zone.

REGULATORY FRAMEWORK
Air pollutants are governed by multiple federal and state standards to regulate and mitigate health impacts. The pollutants regulated by the US EPA include” criteria” pollutants and 188 air toxics referred to as hazardous air pollutants (HAPs). Considering all the HAPs, the EPA has identified nine compounds with significant contributions from mobile sources that are among the national and regional-scale cancer risk drivers or contributors and non-hazard contributors. These are 1,3- butadiene, acetaldehyde, acrolein, benzene, diesel particulate matter (DPM), ethylbenzene, formaldehyde, naphthalene, and polycyclic organic matter.

The State of California also regulates criteria pollutants, which include the federal list but also adds pollutants specific to certain industries, such as hydrogen sulfide and vinyl chloride. The State also regulates HAPs, which are referred to as TACs. The common pollutants, their potential sources, and effects are summarized in Table 5.
9 Table 5. Health Effects of Air Pollutants
Pollutants Sources Primary Effects
Carbon
Monoxide (CO)
• Incomplete combustion of fuels
and other carbon-containing
substances, such as motor exhaust.
• Natural events, such as
decomposition of organic matter.
• Reduced tolerance for exercise.
• Impairment of mental function.
• Impairment of fetal development.
• Death at high levels of exposure.
• Aggravation of some heart diseases (angina).

Nitrogen
Dioxide (NO2)
• Motor vehicle exhaust.
• High temperature stationary
combustion.
• Atmospheric reactions.
• Aggravation of respiratory illness.
• Reduced visibility.
• Reduced plant growth.
• Formation of acid rain.

Ozone
(O3)
• Atmospheric reaction of organic
gases with nitrogen oxides in
sunlight.
• Aggravation of respiratory and cardiovascular
diseases.
• Irritation of eyes.
• Impairment of cardiopulmonary function.
• Plant leaf injury.

Lead
(Pb)
• Contaminated soil. • Impairment of blood functions and nerve construction. • Behavioral and hearing problems in children.

Suspended
Particulate
Matter
(PM2.5 and
PM10)
• Stationary combustion of solid
fuels.
• Construction activities.
• Industrial processes.
• Atmospheric chemical reactions.
• Reduced lung function.
• Aggravation of the effects of gaseous pollutants.
• Aggravation of respiratory and cardiorespiratory
diseases.
• Increased cough and chest discomfort.
• Soiling.
• Reduced visibility.

Sulfur Dioxide
(SO2)
• Combustion of sulfur-containing
fossil fuels.
• Smelting of sulfur-bearing metal
ores.
• Industrial processes.
• Aggravation of respiratory diseases (asthma,
emphysema).
• Reduced lung function.
• Irritation of eyes.
• Reduced visibility.
• Plant injury.
• Deterioration of metals, textiles, leather, finishes, coatings, etc.

Toxic Air
Contaminants
• Cars and trucks, especially diesel
engines.
• Industrial sources such as chrome
platers.
• Neighborhood businesses such as
dry cleaners and service stations.
• Building materials and product.
• Cancer.
• Chronic eye, lung, or skin irritation.
• Neurological and reproductive disorders.

Source: CARB, 2009. ARB Fact Sheet: Air Pollution and Health, see:
https://www.arb.ca.gov/research/health/fs/fs1/fs1.htm
Federal Air Quality Regulations
At the federal level, the EPA has been charged with implementing national air quality programs.

EPA’s air quality mandates are drawn primarily from the Federal Clean Air Act (FCAA), which was enacted in 1963. The FCAA was amended in 1970, 1977, and 1990. Pursuant to the FCAA of 1970, the EPA established National Ambient Air Quality Standards (NAAQS) for the following criteria pollutants:
10 Ozone (O3) -Ozone is a secondary air pollutant produced in the atmosphere through a complex series of photochemical reactions involving reactive organic gases (ROG) and oxides of nitrogen (NOX). The main sources of ROG and NOX, often referred to as ozone precursors, are combustion processes (including combustion in motor vehicle engines) and the evaporation of solvents, paints, and fuels. In the Bay Area, automobiles are the single largest source of ozone precursors. Ozone is referred to as a regional air pollutant because its precursors are transported and diffused by wind concurrently with ozone production through the photochemical reaction process. Ozone is a powerful oxidant that is harmful to public health at high concentrations.

Ozone, at high levels, can damage the tissues of the lungs and respiratory tract. High concentrations of ozone irritate the nose, throat, and respiratory system and constrict the airways.2 Ozone also can aggravate other respiratory conditions such as asthma, bronchitis, and emphysema, causing increased hospital admissions. Repeated exposure to high ozone levels can make people more susceptible to respiratory infection and lung inflammation and permanently damage lung tissue. Ozone can also have negative cardiovascular impacts, including chronic hardening of the arteries and acute triggering of heart attacks.

Carbon Monoxide - Carbon monoxide (CO) is an odorless, colorless gas usually formed as the result of the incomplete combustion of fuels. The single largest source of CO is motor vehicles.

While CO transport is limited, it disperses with distance from the source under normal meteorological conditions. However, under certain extreme meteorological conditions, CO concentrations near congested roadways or intersections may reach unhealthful levels that adversely affect local sensitive receptors (e.g., residents, schoolchildren, the elderly, hospital patients, etc.). Typically, high CO concentrations are associated with roadways or intersections operating at unacceptable levels of service (LOS) or with extremely high traffic volumes.

Exposure to high concentrations of CO reduces the oxygen-carrying capacity of the blood and can cause headaches, nausea, dizziness, fatigue, impair central nervous system function, and induce angina (chest pain) in persons with serious heart disease. Very high levels of CO can be fatal.

Nitrogen Dioxide - Nitrogen Dioxide (NO2) is a reddish-brown gas that is a byproduct of combustion processes. Automobiles and industrial operations are the main sources of NO2.

Aside from its contribution to ozone formation, NO2 also contributes to other pollution problems, including a high concentration of fine particulate matter, poor visibility, and acid deposition. NO2 may be visible as a coloring component on high pollution days, especially in conjunction with high ozone levels. NO2 decreases lung function and may reduce resistance to infection.

Sulfur Dioxide - Sulfur dioxide (SO2) is a colorless, irritating gas formed primarily from incomplete combustion of fuels containing sulfur. Industrial facilities also contribute to gaseous SO2 levels in the region. SO2 irritates the respiratory tract, can injure lung tissue when combined with fine particulate matter, and reduces visibility and the level of sunlight. 2 See: California Air Resource Board, Web: https://ww2.arb.ca.gov/resources/ozone-and-health 11 Particulate Matter - Particulate matter is the term used for a mixture of solid particles and liquid droplets found in the air. Coarse particles are those that are larger than 2.5 microns but smaller than 10 microns (PM10). PM2.5 refers to fine suspended particulate matter with an aerodynamic diameter of 2.5 microns or less that is not readily filtered out by the lungs. Nitrates, sulfates, dust, and combustion particulates are major components of PM10 and PM2.5. These small particles can be directly emitted into the atmosphere as by-products of fuel combustion, through abrasion, such as tire or brake lining wear, or through fugitive dust (wind or mechanical erosion of soil). They can also be formed in the atmosphere through chemical reactions. Particulates may transport carcinogens and other toxic compounds that adhere to the particle surfaces and can enter the human body through the lungs.

Lead - Lead is a metal found naturally in the environment as well as in manufactured products.

The major sources of lead emissions have historically been mobile and industrial sources. As a result of the phase-out of leaded gasoline in the 1990’s, metal processing is currently the primary source of lead emissions. The highest levels of lead emissions are generally found near lead smelters. Other stationary sources are waste incinerators, utilities, and lead-acid battery manufactures.

NAAQS include both primary and secondary standards. Primary standards set limits to protect public health, including the health of sensitive populations such as asthmatics, children, and the elderly. Secondary standards set limits to protect public welfare, including protection against decreased visibility, damage to animals, crops, vegetation, and buildings.3 Areas (i.e., air basins) that do not meet the NAAQS, or nonattainment areas, are required to develop State Implementation Plans (SIPs) that are designed to bring them into attainment of the NAAQS by specific dates.

The FCAA Amendments of 1990 changed deadlines for attaining NAAQS as well as the remedial actions required of areas of the nation that exceed the standards. Conformity with an area’s SIP requirements satisfy the FCAA requirements for a given project.

State Air Quality Regulations
California Clean Air Act
In 1988, the CCAA established its own, more stringent ambient air quality standards, known as California Ambient Air Quality Standards (CAAQS). The CCAA requires that all air basins in the state endeavor to achieve and maintain CAAQS for CO, O3, SO2, and NO2 by the earliest practical date. The CCAA establishes local air districts and provides them with authority to regulate indirect sources and mandates that air quality districts focus particular attention on reducing emissions from transportation and area-wide emission sources. Each nonattainment area in the State is required to adopt a plan to achieve a 5 percent annual reduction, averaged over consecutive 3-year periods, for each nonattainment pollutant or its precursors. A Clean Air Plan is a SIP that shows how a district would reduce emissions to achieve air quality standards. 3 See: U.S. Environmental Protection Agency, Web: https://www.epa.gov/criteria-air-pollutants/naaqs-table, Accessed 13 August 2020
12 California Air Resources Board
The California Air Resources Board (CARB) is the agency responsible for coordination with the EPA and developing SIPs to achieve and maintain both the NAAQS and CAAQS. As a result, it has oversight of the state’s air pollution control programs. Other CARB duties include monitoring air quality (in conjunction with air monitoring networks maintained by air pollution control and air quality management districts), determining and updating area designations and maps, and setting emissions standards for new mobile sources, consumer products, small utility engines, and off-road vehicles.

California Air Resources Board Handbook
In 1998, CARB identified particulate matter from diesel-fueled engines (i.e., DPM) as a toxic air contaminant. CARB has completed a risk management process that identified potential cancer risks for a range of activities using diesel-fueled engines.4 CARB subsequently developed an Air Quality and Land Use Handbook5 (Handbook) in 2005 that is intended to serve as a general reference guide for evaluating and reducing air pollution impacts associated with new projects that go through the land use decision-making process. The 2005 CARB Handbook recommends that planning agencies consider proximity to air pollution sources when considering new locations for “sensitive” land uses, such as residences, medical facilities, daycare centers, schools, and playgrounds.

Air pollution sources of concern include freeways, rail yards, ports, refineries, distribution centers, chrome plating facilities, dry cleaners, and large gasoline service stations. Key recommendations in the Handbook relative to the Plan Area include taking steps to consider or avoid siting new, sensitive land uses:
• Within 500 feet of a freeway, urban roads with 100,000 vehicles/day or rural roads with 50,000 vehicles/day.
• Within 300 feet of gasoline fueling stations (note that new fueling stations utilize enhanced vapor recovery systems that substantially reduce emissions). • Within 300 feet of dry-cleaning operations (note that dry cleaning with TACs is being phased out and will be prohibited in 2023).

Advanced Clean Cars
The Advanced Clean Cars Program, adopted by CARB in 2012, was designed to bring together CARB’s traditional passenger vehicle requirements to meet federal air quality standards and also support California’s AB 32 goals to develop and implement programs to reduce GHG emissions back down to 1990 levels by 2020, a goal achieved in 2016 as a result of numerous emissions reduction programs.
4 California Air Resources Board, 2000. Risk Reduction Plan to Reduce Particulate Matter Emissions from Diesel-Fueled Engines and Vehicles. October. 5 California Air Resources Board, 2005. Air Quality and Land Use Handbook: A Community Health Perspective.

April.
13 This recent rule, Advanced Clean Cars II (ACC II) is phase two of the original rule. ACC II establishes a year-by-year process, starting in 2026, to have all new cars and light trucks sold in California be zero emission vehicles (ZEVs) by 2035. The regulation codifies the light-duty vehicle goals set out in Governor Newsom’s Executive Order N-79-20. Currently, 16 percent of new light-duty vehicles sold in California are zero emissions or plug-in hybrids. By 2030, 68 percent of new vehicles sold in California would be zero emissions and 100 percent by 2035.

On-road Heavy-Duty Diesel Vehicle Regulations
CARB is actively enforcing on-road heavy-duty diesel vehicle regulations that require fleets to replace or retrofit older heavy-duty diesel vehicles. As of January 1, 2020, the DMV cannot register any vehicle that does not meet the diesel engine replace/retrofit requirements. Other CARB diesel programs affecting heavy-duty diesel vehicles include:
• Idling limits of no more than 5 minutes with special exceptions. • Emission Control Labels must be affixed to engines of all commercial heavy-duty diesel vehicles, and must be legible as proof the engine, at minimum, meets U.S. federal emissions standards for the engine model year.
• The Periodic Smoke Inspection Program requires owners of California-based fleets of two or more diesel vehicles to perform annual smoke opacity tests and to keep records for at least two years for each vehicle.
• The Heavy-Duty Vehicle Inspection Program uses random roadside inspections to verify that diesel engines do not smoke excessively and are tamper-free.

Advanced Clean Trucks (ACT)
California’s Advanced Clean Trucks (ACT) rule increases the percentage of medium and heavyduty trucks sold as ZEVs beginning in 2024. By 2035, 40 to 75 percent of new trucks sold, depending on size, would have to meet ZEV requirements. In addition, large employers including retailers, manufacturers, brokers, and others are required to report about their existing fleet operations and report information about shipments and shuttle services with 50 or more trucks,.

Off-Road Vehicle and Equipment Regulations
CARB has adopted and implemented regulations to reduce DPM and nitrogen oxides (NOx) emissions from in-use (existing) and new off-road heavy-duty diesel vehicles (e.g., loaders, tractors, bulldozers, backhoes, off-highway trucks, etc.). The regulations apply to diesel-powered off-road vehicles with engines 25 horsepower (hp) or greater. The regulations are intended to reduce particulate matter and NOx exhaust emissions by requiring owners to turn over their fleet (replace older equipment with newer equipment) or retrofit existing equipment in order to achieve specified fleet-averaged emission rates. Implementation of this regulation, in conjunction with stringent Federal off-road equipment engine emission limits for new vehicles, is expected to substantially reduce emissions of DPM and NOx.

Fleet owners must report the vehicle and engine information for all vehicles within their fleets operating in California. Fleet owners must also report owner information using DOORS, which is 14 CARB’s online reporting tool. CARB issues a unique Equipment Identification Number (EIN) that is assigned to each vehicle. The fleet owner must label their vehicles with the EIN.

Other CARB diesel programs affecting off-road vehicles and equipment include:
• Idling limits of no more than 5 minutes with special exceptions. • Portable engines 50 hp or greater may require a permit or registration to legally operate.

Bay Area Air Quality Management District
The BAAQMD is the local air quality management authority charged with attainment of the NAAQS/CAAQS and maintenance of air quality in the San Francisco Bay Area Air Basin (SFBAAB). They do this through a comprehensive program of planning, regulation, enforcement, technical innovation, and education. The BAAQMD also inspects stationary sources and responds to citizen complaints, monitors ambient air quality and meteorological conditions, and implements programs and regulations required by law.

Clean Air Plan
The BAAQMD is responsible for developing a Clean Air Plan which guides the region’s air quality planning efforts to attain the NAAQS and CAAQS. The BAAQMD’s 2017 Clean Air Plan is the latest air quality plan which contains district-wide control measures to reduce ozone precursor emissions (i.e., ROG and NOX), particulate matter, and greenhouse gas (GHG) emissions. The 2017 Clean Air Plan, which was adopted on April 19, 2017 by the BAAQMD’s board of directors:
• Updates the Bay Area 2010 Clean Air Plan in accordance with the requirements of the CCAA to implement “all feasible measures” to reduce ozone; • Provides a control strategy to reduce ozone, particulate matter, air toxics, and GHGs in a single, integrated plan;
• Reviews progress in improving air quality in recent years; and • Continues and updates emission control measures.

Planning Healthy Places
BAAQMD developed a guidebook that provides air quality and public health information intended to assist local governments in addressing potential air quality issues related to exposure of sensitive receptors to exposure of emissions from local sources of air pollutants. The guidance provides tools and recommends best practices that can be implemented to reduce exposures. The information is provided as recommendations to develop policies and measures in city or county General Plans, neighborhood or specific plans, land use development ordinances, or into projects. 15 BAAQMD California Environmental Quality Act Air Quality Guidelines The BAAQMD California Environmental Quality Act (CEQA) Air Quality Guidelines6 were prepared to assist in the evaluation of air quality impacts of projects and plans proposed within the Bay Area. The guidelines provide recommended procedures for evaluating potential air impacts during the environmental review process consistent with CEQA requirements including thresholds of significance, mitigation measures, and background air quality information. They also include assessment methodologies for TACs, odors, and GHG emissions. In June 2010, the BAAQMD’s Board of Directors adopted CEQA thresholds of significance and an update of their CEQA Guidelines. In May 2011, the updated BAAQMD CEQA Air Quality Guidelines were amended to include a health risk and hazards threshold for new receptors and modify procedures for assessing impacts related to TAC impacts. The Guidelines were then updated in May 2017 and again in April 2023, and this version serves as the Air District’s most recent CEQA guidance. The updated guidelines provide recommended procedures for evaluating potential air impacts during the environmental review process consistent with CEQA requirements including thresholds of significance, mitigation measures, and background air quality information. They include assessment methodologies for air toxins, odors, and GHG emissions.

Per Appendix G of the CEQA Guidelines, air quality and GHG impacts are considered significant if implementation of the General Plan (or specific area plan) would:
1) Conflict with or obstruct implementation of an applicable air quality plan. 2) Result in a cumulatively considerable net increase of any criteria pollutant for which the project region is nonattainment 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.
5) Generate greenhouse gas emissions, either directly or indirectly, that may have a significant impact on the environment.
6) Conflict with an applicable plan, policy, or regulation adopted for the purpose of reducing the emissions of greenhouse gases.

Additionally, specific projects within a planning area that have TAC emissions that could adversely affect sensitive receptors must prepare a health risk assessment to quantify the potential risks to the community and, if appropriate, identify mitigation measures to reduce impacts.

The BAAQMD’s current significance thresholds are listed in Table 6 and Table 7. Though not necessarily a CEQA issue, the effect of existing TAC sources on future sensitive receptors (e.g., residences) is requested by BAAQMD to comply with the 2017 Clean Air Plan’s key goal of reducing population TAC exposure and protecting public health in the Bay Area. 6 Bay Area Air Quality Management District, 2022 CEQA Guidelines, April 2023 16 Table 6. BAAQMD Plan-Level Air Quality Significance Thresholds Pollutant/
Contaminant Construction Operational
Criteria Air
Pollutants and
Precursors
None

1. Consistency with Current Air Quality Plan control measures.

2. Projected vehicle miles traveled (VMT) or vehicle trip increase is less than or equal to projected population increase.

Risks and Hazards None

1. Overlay zones around existing and planned sources of TACs (including adopted Risk Reduction Plan areas).

2. Overlay zones of at least 500 feet from all freeways and highvolume roadways.

For this analysis – overlay zones are based on potential for sources to result in the following impacts:

1. Excess cancer risk >10.0 chances per million 2. Annual PM2.5 Concentration > 0.3 µg/m3

3. Hazard Index >1.0
Odors None Identify the location, and include policies to reduce the impacts, of existing or planned sources of odors
Greenhouse gases None

1. Meet State’s goals to reduce emissions to 40% below 1990 levels by 2030 and carbon neutrality by 2045; OR

2. Be consistent with a local GHG reduction strategy that meets the criteria under State CEQA Guidelines Section 15183.5(b) 17 Table 7. BAAQMD Project-Level Air Quality Significance Thresholds Criteria Air
Pollutant
Construction Thresholds Operational Thresholds
Average Daily Emissions
(lbs./day)
Average Daily
Emissions (lbs./day)
Annual Average
Emissions (tons/year)
ROG 54 54 10
NOX 54 54 10
PM10 82 (Exhaust) 82 15
PM2.5 54 (Exhaust) 54 10
CO Not Applicable 9.0 ppm (8-hour average) or 20.0 ppm (1-hour average)
Fugitive Dust Construction Dust Ordinance or other
Best Management Practices (BMPs)* Not Applicable
Health Risks
and Hazards
Single Sources/
Individual Project
Combined Sources (Cumulative from all
sources within 1000-foot zone of influence)
Excess Cancer
Risk
>10 in a
million
OR
Compliance with
Qualified
Community
Risk Reduction Plan
>100 in a million OR
Compliance with
Qualified Community
Risk Reduction Plan
Hazard Index >1.0 >10.0
Incremental
annual PM2.5
>0.3 µg/m3 >0.8 µg/m3
Greenhouse Gas Emissions
Land Use Projects
– (Must Include A
or B)
A. Projects must include, at a minimum, the following project design elements:

1. Buildings
a. The project will not include natural gas appliances or natural gas plumbing (in both residential and nonresidential development).
b. The project will not result in any wasteful, inefficient, or unnecessary energy usage as determined by the analysis required under CEQA Section 21100(b)(3) and Section 15126.2(b) of the State CEQA Guidelines.

2. Transportation
a. Achieve a reduction in project-generated VMT below the regional average consistent with the current version of the California Climate Change Scoping Plan (currently 15 percent) or meet a locally adopted Senate Bill 743 VMT target, reflecting the recommendations provided in the Governor’s Office of Planning and Research’s Technical Advisory on Evaluating Transportation Impacts in CEQA:
i. Residential projects: 15 percent below the existing VMT per capita ii. Office projects: 15 percent below the existing VMT per employee iii. Retail projects: no net increase in existing VMT
b. Achieve compliance with off-street electric vehicle requirements in the most recently adopted version of CALGreen Tier 2.

B. Be consistent with a local GHG reduction strategy that meets the criteria under State CEQA Guidelines Section 15183.5(b).

Note: ROG = reactive organic gases, NOX = nitrogen oxides, PM10 = course particulate matter or particulates with an aerodynamic diameter of 10 micrometers (µm) or less, PM2.5 = fine particulate matter or particulates with an aerodynamic diameter of 2.5µm or less. GHG = greenhouse gases.
* BAAQMD strongly recommends implementing all feasible fugitive dust management practices especially when construction projects are located near sensitive communities, including schools, residential areas, or other sensitive land uses.

Source: Bay Area Air Quality Management District, 2022
The BAAQMD recommends all projects include a “basic” set of best management practices (BMPs) to manage fugitive dust and consider impacts from dust (i.e., fugitive PM10 and PM2.5) to be less than significant if BMPs are implemented.
18 Basic Best Management Practices: Include measures to control dust and exhaust during construction.

During any construction period ground disturbance, the applicant shall ensure that the project contractor implement measures to control dust and exhaust. Implementation of the measures recommended by BAAQMD and listed below would reduce the air quality impacts associated with grading and new construction to a less-than-significant level. The contractor shall implement the following BMPs that are required of all projects:

1. All exposed surfaces (e.g., parking areas, staging areas, soil piles, graded areas, and unpaved access roads) shall be watered two times per day.

2. All haul trucks transporting soil, sand, or other loose material off-site shall be covered.

3. All visible mud or dirt track-out 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.

4. All vehicle speeds on unpaved roads shall be limited to 15 miles per hour (mph).

5. 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.

6. All excavation, grading, and/or demolition activities shall be suspended when average wind speeds exceed 20 mph.

7. All trucks and equipment, including their tires, shall be washed off prior to leaving the site.

8. 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.

9. 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.

BAAQMD strongly encourages enhanced BMPs for construction sites near schools, residential areas, or other sensitive land uses. Enhanced measures include:
• Limit the simultaneous occurrence of excavation, grading, and ground-disturbing construction activities.
• Install wind breaks (e.g., trees, fences) on the windward side(s) of actively disturbed areas of construction. Wind breaks should have at maximum 50 percent air porosity. 19 • Plant vegetative ground cover (e.g., fast-germinating native grass seed) in disturbed areas as soon as possible and watered appropriately until vegetation is established. • Install sandbags or other erosion control measures to prevent silt runoff to public roadways from sites with a slope greater than one percent.
• Minimize the amount of excavated material or waste materials stored at the site. • Hydroseed or apply non-toxic soil stabilizers to construction areas, including previously graded areas, that are inactive for at least 10 calendar days.

CARE Program
The BAAQMD’s Community Air Risk Evaluation (CARE) program was initiated in 2004 to evaluate and reduce health risks associated with exposures to outdoor TACs in the Bay Area.7 The program examines TAC emissions from point sources, area sources, and on-road and off-road mobile sources with an emphasis on diesel exhaust, which is a major contributor to airborne health risk in California. The CARE program is an on-going program that encourages community involvement and input. The technical analysis portion of the CARE program has been implemented in three phases that includes an assessment of the sources of TAC emissions, modeling and measurement programs to estimate concentrations of TAC, and an assessment of exposures and health risks. Throughout the program, information derived from the technical analyses has been used to focus emission reduction measures in areas with high TAC exposures and high density of sensitive populations. Risk reduction activities associated with the CARE program are focused on the most at-risk communities in the Bay Area. The BAAQMD has identified six communities as impacted: Concord, Richmond/San Pablo, Western Alameda County, San José, Redwood City/East Palo Alto, and Eastern San Francisco.

Overburdened Communities Program
To address localized health impacts in Bay Area communities, BAAQMD staff met with community advocacy organizations to develop concepts and recommendations on how the air district could be more health protective. Through a series of public workshops and a public comment period, BAAQMD amended Rule 2 (i.e., Regulation 2-1-24) in 2021. It identifies an overburdened community as an area located (i) within a census tract identified by the California Office of Environmental Health Hazard Assessment's (OEHHA’s) Communities Environmental Health Screening Tool (CalEnviroScreen), Version 4.0, as having an overall score at or above the 70th percentile, or (ii) within 1,000 feet of any such census tract. Projects in overburdened communities must conduct specific public involvement activities and stationary sources are subject to specific permitting requirements. The entire Town of Atherton fall under the 10th percentile in CalEnviroScreen.
7 See BAAQMD: https://www.baaqmd.gov/community-health/community-health-protection-program/communityair-risk-evaluation-care-program. 20 Atherton General Plan
The Atherton General Plan, adopted in November 2002 and updated in 2019, includes goals, objectives, policies, and actions to reduce exposure of the Town’s sensitive population to exposure of air pollution and toxic air contaminants or TACs. The following objectives, goals, policies, and actions relevant to air quality are contained in the Land Use, Circulation, and Open Space & Conservation Elements.

Land Use.

Goal LU-1 To preserve the Town’s character as a scenic, semi-rural, thickly-wooded residential area with abundant open space.

Policies:

LU-1.5: Proposed residential subdivisions as well as proposals to replace existing homes, shall adhere to the following design criteria:
a. Maintenance of existing neighborhood environments shall be promoted by the design of the subdivision and subdivision improvements. Designs shall be visually harmonious and compatible with neighborhood character.
b. Adequate drainage and off-street parking shall be provided. Street lighting shall be kept to a minimum. Temporary or guest on-street parking areas shall be minimized, c. Uniformity of lot design should be avoided by using such techniques as meandering streets.
d. Trees shall be preserved to the maximum extent feasible while allowing for construction within established parameters for setbacks and lot coverage in accordance with the Municipal Code chapter regulating removal of and damage to heritage trees.
e. Residential land uses shall be designed in accordance with the density, floor area ratio, height, bulk, and other standards established by the Town. f. All utilities installed in conjunction with new subdivisions shall be placed underground.
g. Residential land uses shall be consistent with the goals, objectives, and policies of the Atherton General Plan Housing Element.
h. Accessory dwelling units are permitted when consistent with adopted standards. i. Privacy is a factor which shall be incorporated into subdivision, subdivision improvements and home design.
j. The Town allows minimum lot size subdivisions only where such minimum lot sizes do not significantly degrade established levels of privacy, wooded areas, and/or the open space environment.
k. Residential improvements shall follow the model policies developed for the San Mateo Countrywide Stormwater Pollution Prevention program and the Town’s Green Infrastructure Plan to minimize the discharge of pollutants into the waterways.
21 LU-1.7: Land uses which diminish the open space character of the Town, such as commercial and high-density residential uses, shall be prohibited.

LU-1.8: Maximize preservation of heritage trees and existing trees within a development site to the greatest degree feasible, consistent with the Heritage Tree Ordinance and Tree Preservation Standards and Specifications. Require new development to comply with the Town’s requirements for tree protection, removal, and replacement.

Circulation.

Goal CIR-1 To develop a circulation system that is compatible with the needs of various land uses planned within the Town of Atherton.

Policies:

CIR-1.7: Paving for temporary on-street parking within the roadway right-of-way will be prohibited.

CIR-1.13: On-street and visible off-street parking shall be preserved to the extent consistent with traffic safety.

Goal CIR-4 To achieve a balanced, multi-modal transportation network that meets the needs of all users of Atheron streets and highways for safe and convenient travel in a manner that is suitable to the semi-rural context of the general plan.

Policies:

CIR-4.1: To incorporate, over time and where feasible, the principles of Complete Streets in future roadway projects. Complete Streets are streets and facilities that accommodate all users including bicyclists, children, persons with disabilities, motorists, movers of commercial goods, pedestrians, users of public transportation, and seniors.

CIR-4.2: Bicycle paths separating bicycles from vehicular traffic are considered desirable.

Goal CIR-5 To achieve a high quality of roadway operation on all Atherton streets.

Policies:

CIR-5.6: The Town shall support the continued operation and upgrading of passenger rail service operated over the Joint Powers Board right-of-way between Gilroy and San Francsico.

Open Space and Conservation.

Goal OSC-1 Protect both publicly and privately held open space lands from deterioration of their semi-rural charm, scenic value and environmental equilibrium. 22 Action
OSC-1.1: Minimum lot sizes, setback restrictions, height limitations, tree protection and preservation, and sign regulations shall be employed to accomplish open space and conversation objections.

Goal OSC-2 Protect and enhance the existing Coastal Oak Woodland character of the Town.

Policies
OSC-2.1: Trees shall be preserved where practical. This policy shall be explicitly considered during the development and subdivision process.

OSC-2.2: Wherever possible, drought tolerant native species trees shall be used for new and replacement planting and be tolerant of seasonal water inundation where used in or adjacent to green infrastructure facilities.

OSC-2.3: Enforce the Heritage Tree Ordinance and Tree Preservation Guidelines and Standards, or equal document.

Goal OSC-3 Minimize the impacts of flooding on health, safety, and property damage.

Actions
OSC-3.2: The Town will encourage property owners to incorporate water conservation techniques into their landscaping to reduce water usage and use green infrastructure techniques to capture and/or treat rainfall and stormwater runoff at its source, as feasible.

Goal OSC-5 Implement the GHG programs in the Atheron Climate Action Plan related to energy efficiency, community waste generation, and reduced water consumption.

SETTING AND EXISTING AIR QUALITY CONDITIONS
The project is located in San Mateo County, which is part of the San Francisco Bay Area Air Basin.

The Air Basin includes the counties of San Francisco, Santa Clara, San Mateo, Marin, Napa, Contra Costa, and Alameda, along with the southeast portion of Sonoma County and the southwest portion of Solano County.

This Project is within the jurisdiction of the BAAQMD. Air quality conditions in the San Francisco Bay Area have improved significantly since the BAAQMD was created in 1955. Ambient concentrations of air pollutants, and the number of days during which the region exceeds air quality standards, have fallen dramatically. Exceedances of air quality standards occur primarily during meteorological conditions conducive to high pollution levels, such as cold, windless winter nights or hot, sunny summer afternoons.
23 Air quality is a function of both local climate and local sources of air pollution. Air quality is the balance of the natural dispersal capacity of the atmosphere and emissions of air pollutants from human uses of the environment. Climate and topography are major influences on air quality.

Climate and Meteorology
During the summer, mostly clear skies result in warm daytime temperatures and cool nights in the Santa Clara Valley. Winter temperatures are mild, except for very cool but generally frost-less mornings. Further inland where the moderating effect of the bay is not as strong, temperature extremes are greater. Rainfall amounts are modest, ranging from 13 inches in the lowlands to 20 inches in the hills. Wind patterns are influenced by local terrain, with a northwesterly breeze in response to the sea breeze infiltrating San Francisco Bay typically developing during the daytime.

Winds are usually stronger in the spring and summer. The southerly winds experienced are more common in late fall and winter. The wind rose shown in Figure 1 describes the patterns and frequency of winds at the San Carlos Airport near the Town. Wind data was collected from 2011 through 2015.

Figure 1. Windrose for San Carlos Airport Years 2011-2015 Notes: Based on data provided by BAAQMD
24 NAAQS and CAAQS Status
Both the US EPA and CARB designate air basins as attainment, nonattainment, or unclassified based on ambient monitoring data. An “attainment” designation for an area signifies that pollutant concentrations did not violate the standard for that pollutant in that area. A “nonattainment” designation indicates that a pollutant concentration violated the standard at least once, excluding those occasions when a violation was caused by an exceptional event, as defined in the criteria.

An “unclassified” designation signifies that data does not support either an attainment or nonattainment status, or that monitoring data were not available. Table 8 shows the state and federal standards for criteria pollutants and provides a summary of the attainment status for the San Francisco Bay Area.

Table 8. NAAQS and CAAQS and Air Basin Attainment Status Pollutant Averaging
Time
State Federal
Standard Status Standard Status
Carbon
Monoxide (CO)
8-Hour 9 ppm
(10 mg/m3) Attainment 9 ppm(10 mg/m3) Attainment
1-Hour 20 ppm
(23 mg/m3) Attainment 35 ppm(40 mg/m3) Attainment
Nitrogen
Dioxide (NO2)
Annual
Mean

0.030 ppm
(57 mg/m3) Attainment 0.053 ppm(100 µg/m3) Attainment
1-Hour 0.18 ppm
(338 µg/m3) Attainment 0.100 ppm Unclassified
Ozone
(O3)
8-Hour 0.07 ppm
(137 µg/m3) Nonattainment 0.070 ppm Nonattainment
1-Hour 0.09 ppm
(180 µg/m3) Nonattainment Not Applicable Not Applicable Suspended
Particulate
Matter (PM10)
Annual
Mean 20 µg/m3 Nonattainment Not Applicable Not Applicable 24-Hour 50 µg/m3 Nonattainment 150 µg/m3 Unclassified
Suspended
Particulate
Matter (PM2.5)
Annual
Mean 12 µg/m3 Nonattainment 12 µg/m3 Attainment
24-Hour Not Applicable Not Applicable 35 µg/m3 Nonattainment Sulfur Dioxide
(SO2)
Annual
Mean Not Applicable Not Applicable 80 µg/m3(0.03 ppm) Attainment 24-Hour 0.04 ppm
(105 µg/m3) Attainment 365 µg/m3(0.14 ppm) Attainment
1-Hour 0.25 ppm
(655 µg/m3) Attainment 0.075 ppm(196 µg/m3) Attainment
Lead (Pb) is not listed in the above table because it has attained the NAAQS/CAAQS since the 1980s. ppm = parts per million, mg/m3 = milligrams per cubic meter, µg/m3 = micrograms per cubic meter Source: Bay Area Air Quality Management District, 2017. Air Quality Standards and Attainment Status. January 5.

Criteria Pollutant Concentrations
BAAQMD monitors air pollution at various sites within the airshed. The closest air monitoring station is approximately 2 miles northwest of the Town in the City of Redwood City (897 Barron 25 Ave). This station monitors O3, CO, NO2, and PM2.5 over the past 5 years (2018 through 2022).

The data shows over the past few years, the general plan area has exceeded the state and/or federal O3 and PM2.5 ambient air quality standards. Table 9 lists air quality trends in data collected for the past 5 years and published by the BAAQMD and CARB for the Redwood City monitoring location, which is the most recent time-period available. Note that some of these concentrations were influenced by smoke from wildfires.

Table 9. Ambient Air Quality Concentrations for Redwood City from 2018-2022 Pollutant Standard 2018 2019 2020 2021 2022
O3, Ozone
Max 1-hr concentration 67 ppb 83 ppb 98 ppb 85 ppb 79 ppb No. days exceeded: CAAQS 90 ppb 0 0 1 0 0
Max 8-hr concentration 49 ppb 77 ppb 78 ppb 64 ppb 62 ppb No. days exceeded: CAAQS
NAAQS
70 ppb
70 ppb
0 0
2 2
1 1
0 0
0 0
CO, Carbon Monoxide
Max 1-hr concentration 2.5 ppm 2.0 ppm -- -- --
No. days exceeded: CAAQS
NAAQS
0 0
0 0
0 0
--
--
--
--
--
--
Max 8-hr concentration 1.7 ppm 1.1 ppm -- -- --
No. days exceeded: CAAQS
NAAQS
0 0
0 0
0 0
--
--
--
--
--
--
PM2.5
Max 24-hr concentration 120.9µg/m3 29.5 µg/m3 124.1 µg/m3 30.1 µg/m3 27.4 µg/m3 No. days exceeded: NAAQS >35 µg/m3 13 0 9 0 0
Annual Concentration 10.3µg/m3 7.0µg/m3 9.8µg/m3 6.0µg/m3 6.8µg/m3 No. days exceeded: CAAQS
NAAQS
>12 µg/m3
>12 µg/m3
-
-
-
-
-
-
-
-
-
-
NO2, Nitrogen Dioxide
Max 1-hr concentration 77 ppb 55 ppb -- -- --
No. days exceeded: CAAQS
NAAQS

0.18 ppm

0.100 ppm
0 0
0 0
--
--
--
--
--
--
Note: Monitoring of CO and NO2 discontinued in 2020.

Source: Bay Area Air Quality Management District, Web: https://www.baaqmd.gov/about-air-quality/air-qualitymeasurement/air-quality-summaries.

California Air Resource Board, Web: https://arb.ca.gov/adam/select8/sc8start.php Ozone and PM2.5, are the major regional air pollutants of concern in the San Francisco Bay Area.

Elevated concentrations of PM10 and PM2.5 are the result of both region-wide (or cumulative) emissions and localized emissions. Understanding and controlling ozone and PM2.5 pollution is described in BAAQMD’s most recent Clean Air Plan.
8 These descriptions are summarized below.

High ozone levels are caused by the cumulative emissions of ROG and NOX. Controlling the emissions of these precursor pollutants is the focus of BAAQMD’s attempts to reduce ozone levels. The highest ozone levels in the Bay Area occur in the eastern and southern inland valleys that are downwind of air pollutant sources. Ozone frequently forms on hot summer days when the prevailing seasonal northerly winds carry ozone precursors southward across the county. 8 Bay Area Air Quality Management District, 2017. Spare the Air Cool the Climate Final 2017 Clean Air Plan.

April. Web: https://www.baaqmd.gov/~/media/files/planning-and-research/plans/2017-clean-air-plan/attachment-a_- proposed-final-cap-vol-1-pdf.pdf?la=en
26 Because emissions in one part of the region can impact air quality miles downwind, efforts to reduce ozone levels focus on reducing emissions of ROG and NOx throughout the region. The relationship between ROG and NOx in ozone formation is complex; the ratio between the precursor pollutants influences how ozone forms. BAAQMD’s ozone modeling indicates that the Bay Area is “ROG‐limited” for ozone formation. This means that reducing ROG emissions in the Bay Area will be more productive in reducing ozone, at least in the near term. However, modeling also suggests that large reductions in NOx emissions will be needed to achieve the ozone reductions required to attain the current health-based ozone standards. A certain amount of ozone formation occurs naturally, even in the absence of anthropogenic emissions of ROG and NOx.

PM2.5 concentrations are from direct and indirect emissions. Fossil fuel combustion and wood burning are the primary contributors of directly-emitted PM2.5. Formation of PM2.5 occurs in the atmosphere by complex chemical processes with precursors such as NOx, ammonia, and sulfur dioxide. According to BAAQMD, particulate matter concentrations vary considerably in composition and in spatial distribution both on a daily basis and on a seasonal basis in response to changes in weather and emissions. The Bay Area generally experiences its highest PM2.5 concentrations in the winter, with exceedances of the 24-hour standard mostly between November and February. High and very high PM2.5 episodes from wildfire smoke are typically regional in scale, affecting the area mostly in late summer and fall. On an annual average basis, PM2.5 levels in the Bay Area are relatively low.

With the exception of smoke from wildfires, the Bay Area currently meets PM2.5 standards, but has yet to attain the state annual and 24-hour standards for PM10. BAAQMD efforts to reduce PM2.5 and PM10 concentrations are focused on reducing woodburning, cooking emissions, and NOx emissions. BAAQMD, along with CARB and U.S. EPA have efforts to reduce particulate matter emissions from combustion engines associated with stationary and mobile sources.

Existing Sources of TACs and Sensitive Receptors
Atherton is primarily a residential area with no industries or substantial sources of air pollution.

Primary emission sources are traffic and diesel-powered locomotives using the CalTrain rail line.

The primary substantial roadway within the Town is El Camino Real. The CalTrain line services diesel-powered commuter trains and some freight trains. CalTrain is currently being modernized and will mostly serve electric-powered trains in the future; although some commuter trains and freight trains will still be powered by diesel.

There are groups of people more affected by air pollution than others. CARB has identified the following people who are most likely to be affected by air pollution: children under 16, the elderly over 65, athletes, 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. For cancer risk assessments, children are the most sensitive receptors, since they are more susceptible to cancer causing TACs. Residential locations are assumed to include infants and small children. Sensitive receptors in Atherton include residences, 27 schools and daycare facilities. The proposed Housing Element Update and resulting zoning code amendments would include new residential dwellings that are considered sensitive receptors.

The proposed lots and surrounding community are not considered to be in an overburdened community. According to CalEnviroScreen, the census tracts representative of the project sites and environs within 1,000 feet of the project have an overall percentile scores of 10th or less. Note that Oakwood Boulevard portion adjacent to Redwood City would be near the 40th percentile.

AIR QUALITY IMPACTS AND PROPOSED ZONE CODE AMENDMENT

POLICIES
Air pollutant emissions and associated health risks were predicted using emissions and dispersion models. The methodology for computing health risks impacts is contained in Appendix E of the BAAQMD CEQA Guidelines.9 The latest version of the California Emissions Estimator Model (CalEEMod) Version 2022 was used to compute annual emissions. The model output from CalEEMod along with inputs are included as Attachment 1.

Impact AIR-1: Conflict with or obstruct implementation of an applicable air quality plan?
BAAQMD, with assistance from Association of Bay Area Governments (ABAG) and the Metropolitan Transportation Commission (MTC), has prepared and implements specific plans to meet the applicable laws, regulations, and programs. The most recent and comprehensive of which is the Bay Area 2017 Clean Air Plan.
10 The BAAQMD has also developed CEQA guidelines to
assist lead agencies in evaluating the significance of air quality impacts. In formulating compliance strategies, BAAQMD relies on planned land uses established by local general plans. Land use planning affects vehicle travel, which in turn affects region-wide emissions of air pollutants and GHGs.

Consistency of the proposed Project with Clean Air Plan control measures is demonstrated by assessing whether the proposed zoning implements the applicable Clean Air Plan control measures. The 2017 Clean Air Plan includes control measures that are intended to reduce air pollutant emissions in the Bay Area either directly or indirectly. The control measures are divided into five categories that include:
• 40 measures to reduce stationary and area sources;
• 8 mobile source measures;
• 23 transportation control measures (including land use strategies); • 4 building sector measures;
• 2 energy sector measures;
• 4 agriculture sector measures;
• 3 natural and working lands measures;
• 4 waste sector measures;
9 BAAQMD, 2022. Appendix E of the BAAQMD CEQA Guidelines. April 2023. 10 Bay Area Air Quality Management District (BAAQMD), 2017. Final 2017 Clean Air Plan. 28 • 2 water sector measures; and
• 3 super-GHG pollutants measures.

In developing the control measures, BAAQMD identified the full range of tools and resources available, both regulatory and non-regulatory, to develop each one. This approach relies upon lead agencies to assist in implementing some of the control measures. A key tool for local agency implementation is the development of land use policies and implementing measures that address new development or redevelopment in local communities. To address this impact, the proposed Project’s effect on implementing the Clean Air Plan is evaluated based on consistency with Clean Air Planning projections (i.e., rate of increase in population versus vehicle travel).

Consistency with Clean Air Plan Projections
The BAAQMD, with assistance from ABAG and MTC, has prepared and implemented the Clean Air Plan to meet the applicable laws, regulations, and programs. The primary goals of the Clean Air Plan are to attain air quality standards, reduce population exposure and protect public health, and reduce GHG emissions and protect the climate. The BAAQMD has also developed CEQA guidelines to assist lead agencies in evaluating the significance of air quality impacts. In formulating compliance strategies, BAAQMD relies on planned land uses established by local general plans. Land use planning affects vehicle travel, which in turn affects region-wide emissions of air pollutants and GHG.

The BAAQMD CEQA Guidelines recommend comparing the increase in the rate of population compared to the rate of traffic increase that is based on vehicle miles travelled (VMT) or trips.

Table 10 provides population and traffic conditions for existing and future build out conditions with the Housing Element Update developed. The Housing Element Update identified 332 potential new single-family and 292 multi-family housing opportunities that could be developed.

This could increase the population by 2,048 people or 31 percent over existing conditions. Daily vehicle trips for this build out in housing were provided by the project traffic consultant. Using “Existing” as a baseline condition (estimated at 17,644 trips), daily trips attributable to the Project are anticipated to increase 29 percent at build-out with the Housing Element Update (22,750 trips).

The VMT per population is anticipated to decrease from 18.35 miles per capita to 17.99 miles with the Project. In summary, the Project increases population and traffic. The rate of increase in traffic, measured as the rate of trips or VMT, would be less than increase in population.

Table 10. Atherton Housing Element Update Traffic and Population Projections Scenario Population Dwelling Units Daily Trips
VMT per
Population
Existing Conditions
(Dept. of Finance 2023) 6,678 2,547 17,644 18.35
Year 2031 Additional 2,048 Single fam. 337
Multi Fam. 292 5,106 --
2031 Conditions 8,726 22,750 17.99
2031 Project - Exist +31% +29% -2%
Source: Project Description and Hexagon Transportation Consultants, per email from Adam Peterson (M Group), dated Nov. 20, 2023.
29 Consistency with Clean Air Plan Control Measures
The BAAQMD CEQA Air Quality Guidelines establish criteria for determining consistency with the Clean Air Plan control measures. In general, a plan is considered consistent if a) the plan supports the primary goals of the Clean Air Plan; b) includes control measures; and c) does not interfere with implementation of the Clean Air Plan measures. Growth under the Housing Element Update changes is considered sustainable since it is a plan for infill development. Atherton is served by local and regional transit and is located near a mix of uses that include employment and services located in adjacent jurisdictions. The Town of Atherton relies on strategies in its adopted Climate Action Plan to guide new development to meet GHG reduction goals. These goals are also in line with Clean Air Plan control measures. The development in the Town under the proposed Amendment changes is consistent with the Town’s General Plan and would generally be consistent with Clean Air Plan measures intended to reduce automobile and energy use. Table 11 lists those Clean Air Plan measures relevant to the Amendment changes and indicates consistency between the Town’s General Plan, Climate Action Plan, and the Clean Air Plan.

Table 11. BAAQMD Control Strategy Measures from the Clean Air Plan Applicable BAAQMD Control Strategy
Measures Consistency
Transportation Control Measures
TR1: Clean Air Teleworking Initiative Consistent
Supported by CAP Goal 3.2.1 Measure TRM2.

TR2: Trip Reduction Programs Consistent
Supported by CAP Goal 3.2.1 Measure TRM3.

TR 5: Transit Efficiency and Use Consistent
Supported by Circulation Element Goal CIR-5
Policy CIR-5.6 and Goal CIR-6 Objective CIR6.2.

TR7: Safe Routes to Schools and Safe Routes to
Transit
Consistent
Supported by Cap Goal 3.2.1 Measure TRC2.

TR8: Ridesharing, Last-Mile Connection Consistent
Supported by CAP Goal 3.2.1 Measure TRM3.

TR9: Bicycle and Pedestrian Access and Facilities Consistent Supported by General Plan Circulation Element
Goal CIR-4 Objectives CIR-4.1 and 4.2.

Also supported by CAP Goal 3.2.1 Measure
TRC1.

TR10: Land Use Strategies Consistent
Supported by General Plan Land Use Element
Goal LU-1 Policies LU-1.5 and 1.7.

Also supported by Cap Goal 3.2.1 Measure
TRC1.

TR13: Parking Policies Consistent
Supported by General Plan Circulation Element
Goal CIR-1 Policies CIR-1.7 and 1.13 as well as
Land Use Element Goal LU-1 Policy LU-1.5.

Building Control Measures
30 Applicable BAAQMD Control Strategy
Measures Consistency
BL1: Green Buildings Consistent
Supported by General Plan Open Space and
Conservation Element Goal OSC-5.

Also supported by CAP Goal 3.1.1 Measures
EC1, EC2, EC4, EC5, EC6, EM2, EM3, EM4.

BL2: Decarbonize Buildings Consistent
Supported by General Plan Open Space and
Conservation Element Goal OSC-5.

Also supported by CAP Goal 3.1.1 Measures
EC1, EC2, EC4, EC5, EC6, EM2, EM3, EM4.

BL4: Urban Heat Island Mitigation Consistent
Supported by CAP Goal 3.1.1 Measure EC3.

Natural and Working Lands Control Measures
NW2: Urban Tree Planting Consistent
Supported by General Plan Land Use Element
Goal LU-1 Policies LU 1.5 and 1.8, Open Space
and Conservation Element Goal OSC-1 Policy
OSC-1.1 and Goal OSC-2 Policies 2.1, 2.2, and

2.3. Also supported by CAP Goal 3.1.1 Measure EC3.

Waste Management Control Measures
WA4: Recycling and Waste Reduction Consistent
Supported by General Plan Open Space and
Conservation Element Goal OSC-5.

Also supported by CAP Goal 3.3.1 Measures
WC1, WC2, WC3, WM1, WM2, and WM3.

Water Control Measures
WR2: Support Water Conservation Consistent
Supported by General Plan Open Space and
Conservation Element Goal OSC-3 Action OSC3.2 and Goal OSC-5.

Also supported by CAP Goal 3.1.1 Measures
WTRC1, WTRC2, and WTRC3.

As indicated in Table 11, the Town’s General Plan and CAP includes implementing policies and measures that are consistent with the applicable Clean Air Plan control measures. As a result, this impact is less-than-significant.

Impact AIR-2: Result in a cumulatively considerable net increase of any criteria pollutant for which the project region is nonattainment under an applicable federal or state ambient air quality standard? The Bay Area is considered a nonattainment area for ozone and PM2.5 under both the NAAQS and the CAAQS and nonattainment for PM10 under the CAAQS only. The area has attained the NAAQS and CAAQS for CO. As part of an effort to attain and maintain the NAAQS/CAAQS for ozone and PM10, the BAAQMD has established CEQA thresholds of significance for these air pollutants and their precursors (ROG, NOX, PM10, and PM2.5). These thresholds apply to both 31 construction period and operational period impacts. The quantified thresholds identified by BAAQMD apply only to projects.

Construction Emissions
Build-out of the proposed Project housing sites would result in temporary emissions from construction activities associated with subsequent development, including site grading, asphalt paving, building construction, and architectural coating. Emissions commonly associated with construction activities include fugitive dust from soil disturbance, fuel combustion from mobile heavy-duty diesel- and gasoline-powered equipment, portable auxiliary equipment, and worker commute trips.

Fugitive dust, the dominant source of PM10 and PM2.5 emissions during construction, is generated through the ground disturbances by equipment and vehicles. Sources of fugitive dust include disturbed soils at the construction site and trucks carrying uncovered loads of soils. Unless properly controlled, vehicles leaving the site would deposit mud on local streets, which could be an additional source of airborne dust after it dries. Uncontrolled dust from construction activities can become a nuisance and potential health hazard to those living and working nearby.

Exhaust emissions include those from construction equipment (i.e., off-road) and traffic (on-road vehicles and trucks). Off-road construction equipment is often diesel-powered and can be a substantial source of NOX emissions, in addition to PM10 and PM2.5 emissions. Architectural coatings and application of asphalt pavement are dominant sources of ROG emissions. The potential health risk impacts from construction are addressed under Impact 3.

Emissions associated with all of the projects that would be constructed under the proposed zoning amendments may have levels that exceed the significance thresholds. However, the pollutant emissions thresholds for construction activities contained in BAAQMD’s CEQA Air Quality Guidelines would apply to specific housing projects and not this action of adopting zoning code amendments. Buildout would consist of numerous construction projects that would occur at various times over many years.

The BAAQMD CEQA Air Quality Guidelines include project size screening levels to determine if there is a potential for projects to exceed the emission-based significance thresholds. Projects constructed would range from a single ADU up to about 60 multi-family units. The project-level screening size ranges from 254 single-family homes to 416 apartment units. Construction of individual residential projects affected by the proposed Project would not exceed these screening levels.

However, the BAAQMD’s CEQA Air Quality Guidelines The BAAQMD recommends all projects include a “basic” set of best management practices (BMPs) to manage fugitive dust and considers impacts from dust (i.e., fugitive PM10 and PM2.5) to be less-than-significant if BMPs are implemented to reduce these emissions. Mitigation Measure AQ-1 would implement BAAQMD’s basic BMPs.
32 Mitigation Measure AQ-1: Include measures to control dust and exhaust during construction.

During any construction period ground disturbance, the project contractor shall implement measures to control dust and exhaust. Implementation of the measures listed below would reduce the air quality impacts associated with grading and new construction to a less-than-significant level. The contractor shall implement the following BMPs that are required of all projects: