Diamond Bar City Council
March 17, 2026

Diamond Bar Objective Design Standards Addendum No. 2 to the EIR February 2026 Sapphos Environmental, Inc.

3.5 ENERGY
This section evaluates the effects on energy from the proposed project. This Addendum relies on and incorporates by reference the project setting and regulatory setting as described in Section

3.5, Energy, Climate Change, and Greenhouse Gases, of the Certified EIR. Potential impacts to energy from the proposed project are discussed relative to conclusions in the Certified EIR. The Certified EIR determined that the implementation of the General Plan 2040 would result in less than significant energy impacts, with no mitigation measures required. Consistent with the Certified EIR, energy for the proposed project was evaluated with regard to the General Plan 2040, Title 24 of the California Green Building Standards (CalGreen), SCAG’s Connect SoCal, and the City’s Climate Action Plan (CAP).

3.5.1 Setting
The project setting for energy is the same as that considered in the Certified EIR. A review of available records and literature determined that new energy information has become available since the certification of the EIR, including (1) an update to Connect SoCal, which includes goals to improve energy efficiency in the region to facilitate sustainable development;12 and (2) required compliance with the California Code of Regulations, including Title 20 Division 2, Chapter 4 (Energy Conservation), and Title 24, Part 6 of the California Energy Code (CEC). These regional plan updates include more stringent energy efficiency goals and regulations, when compared to the regional plans discussed in the Certified EIR. However, the proposed project does not include changes or reductions in energy efficiency or compliance with energy or sustainable development standards that would conflict with applicable energy plans.

3.5.2 Impact Analysis
Project Impact Analysis
The potential for the proposed project to result in a new significant impact or a substantial increase in the severity of previously identified significant impacts to energy was evaluated in relation to the following questions as stated in Appendix G of the State CEQA Guidelines. (a) Would the proposed project result in potentially significant environmental impact due to wasteful, inefficient, or unnecessary consumption of energy resources, during project construction or operations?
The proposed project would not exceed General Plan 2040 assumptions, and it would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts in relation to resulting in wasteful, inefficient, or unnecessary consumption of energy resources during project construction or operations. The expenditure of non-renewable resources would be incurred as a result of future design modifications from the proposed project, including electricity, natural gas, propane, diesel, and gasoline. The application of the proposed project to future multifamily and mixed-use development would be subject to project-specific development review requirements and compliance with existing energy-based regulations.

Moreover, the proposed project includes functional architectural elements, such as room to accommodate shade structures for townhouses, flex/loft buildings, walk-up flat parking; courtyard 12 Southern California Association of Governments. 2024. Connect SoCal: A Plan for Navigating to a Brighter Future. https://scag.ca.gov/sites/default/files/2024-05/23-2987-connect-socal-2024-final-complete-040424.pdf (accessed October 30, 2025).

Diamond Bar Objective Design Standards Addendum No. 2 to the EIR February 2026 Sapphos Environmental, Inc.

multi-family buildings, wrap building, urban blocks; and photovoltaic panels for buildings (Appendix A), which would decrease electricity consumption and other non-renewable energy expenditures. Furthermore, there would be no increase in VMT as a result of the proposed project (see Section 3.13, Transportation). Therefore, no additional energy expenditures for vehicular travel would result from the proposed project.

The proposed project would not result in additional development or induce growth beyond what was considered in the Certified EIR. As such, the proposed project would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts related to resulting in wasteful, inefficient, or unnecessary consumption of energy resources during project construction or operations.
(b) Would the proposed project conflict with or obstruct a state or local plan for renewable energy or energy efficiency?
The proposed project would not exceed General Plan 2040 assumptions, and it would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts related to a conflict with or obstruction of a state or local plan for renewable energy or energy efficiency. As with the Certified EIR, the proposed project would result in less than significant impacts in relation to a conflict with or obstruction of a state or local plan for renewable energy or energy efficiency. The application of the proposed project to future multifamily and mixed-use development would be subject to project-specific development review requirements. In addition, the proposed project would be required to comply with existing energybased regulations, including the General Plan 2040, Title 24 of the California Green Building Standards, SCAG’s Connect SoCal, and the City’s CAP. Future multifamily and mixed-use development also would be required to comply with energy conservation regulations embedded in California Code of Regulations Title 20, Division 2, Chapter 4; and CCR Title 6. The updates to Connect SoCal and the California Code of Regulations since adoption of the Certified EIR include more stringent energy efficiency goals and regulations, when compared to the regional plans discussed in the Certified EIR, and future development in the City would continue to be subject to these most recent versions. Further, the proposed project does not include changes or reductions in energy efficiency that would conflict with energy or sustainable development standards and, therefore, would not change the findings in the Certified EIR. Additionally, as previously discussed, the proposed project includes functional architectural elements for a variety of building types that would decrease electricity consumption and other non-renewable energy expenditures.

The proposed project would not result in additional development beyond what was previously evaluated in the Certified EIR. As such, the proposed project would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts that would conflict with or obstruct a state or local plan for renewable energy or energy efficiency.

Mitigation Measures
As with the Certified EIR, no mitigation measures have been identified related to energy. No further mitigation measures are required for the proposed project.

Cumulative Impact Analysis
The implementation of the proposed project would not result in or contribute to a cumulative energy impact. This proposed project is a design overlay that works within the regulatory framework and cumulative growth assumptions of the Certified EIR and is consistent with the

Diamond Bar Objective Design Standards Addendum No. 2 to the EIR February 2026 Sapphos Environmental, Inc.

analysis of cumulative impacts under the development evaluated in the General Plan 2040. The Certified EIR concluded that the environmental impact due to wasteful, inefficient, or unnecessary consumption of energy resources, during project construction or operations, conflict with or obstruct a state or local plan for renewable energy or energy efficiency would not be cumulatively considerable. Consistent with the Certified EIR, implementation of the proposed project would not result in cumulatively considerable impacts in relation to energy. The proposed project would not result in a new significant cumulative impact or a substantial increase in the severity of previously identified significant cumulative impacts related to energy.

Diamond Bar Objective Design Standards Addendum No. 2 to the EIR February 2026 Sapphos Environmental, Inc.

3.6 GEOLOGY, SOILS, AND SEISMICITY
This section evaluates the effects on geology and soils impacts from the proposed project. This Addendum relies on and incorporates by reference the project setting and regulatory setting as described in Section 3.6, Geology, Soils, and Seismicity, of the Certified EIR. Potential impacts to geology and soils from the proposed project are discussed relative to conclusions in the Certified EIR. The Certified EIR concluded that the General Plan 2040 would result in less than significant impacts to geology and soils. Consistent with the Certified EIR, geology and soils for the proposed project were evaluated with regard to the Los Angeles County General Plan Safety element; County of Los Angeles All-Hazard Mitigation Plan, the USGS 7.5-minute series topographic quadrangle; California Division of Mines and Geology (CDMG) publications; the most recent Alquist-Priolo Earthquake Fault Zone (APEFZ) Map; the City of Diamond Bar Natural Hazards Mitigation Plan; published maps; and technical studies. Review of available records and literature determined that no new information has become available since the certification of the Certified EIR.

3.6.1 Setting
The project setting for geology and soils remains consistent with the setting considered in the Certified EIR.

3.6.2 Impact Analysis
Project Impact Analysis
The potential for the proposed project to result in a new significant impact or a substantial increase in the severity of previously identified significant impacts to hydrology and water quality was evaluated in relation to the following questions in Appendix G of the State CEQA Guidelines. (a) Would the proposed project directly or indirectly cause potential substantial adverse effects, including the risk of loss, injury, or death involving:
i. 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.

The proposed project would not exceed General Plan 2040 assumptions, and it would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts in relation to the rupture of a known earthquake fault. The Certified EIR established that the project area is not within an Alquist-Priolo Earthquake Fault Zone, and no known active faults transect the area. Therefore, the risk of surface fault rupture is consistently considered very low. Since the proposed project is limited to the design and articulation of the building envelope, the ODS exerts no influence on regional tectonic hazards or the potential for surface rupture. The proposed project would not increase the degree of exposure to this hazard beyond the existing baseline and the General Plan’s projections. Therefore, the proposed project would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts regarding rupture of a known earthquake fault.

Diamond Bar Objective Design Standards Addendum No. 2 to the EIR February 2026 Sapphos Environmental, Inc.

ii. Strong seismic ground shaking?
The proposed project would not exceed General Plan 2040 assumptions, and it would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts in relation to strong seismic ground shaking. The Certified EIR concluded that impacts from strong seismic ground shaking are less than significant because all new buildings must be constructed in compliance with the California Building Code (CBC), Section 1613, which requires structures to be designed and constructed to resist seismic forces in accordance with the Minimum Design Loads for Buildings and Other Structures (ASCE standards). The proposed project comprises a set of aesthetic, functional, and form-based requirements (e.g., facade articulation, frontage types) that are subordinate to the CBC. Further, structural integrity and seismic design are governed by mandatory project-specific engineering and the CBC and required for all development within the General Plan 2040 inclusive of the proposed project. The proposed project would not compromise the seismic integrity of future development. Therefore, the proposed project would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts regarding strong seismic ground shaking. iii. Seismic-related ground failure, including liquefaction? The proposed project would not exceed General Plan 2040 assumptions, and would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts in relation to seismic-related ground failure, including liquefaction. The Certified EIR identified a risk of liquefaction and lateral spreading in areas underlain with loose saturated cohesionless soils, notably within valley basins and along major highway corridors. The proposed project is intended to regulate visual design and has no effect on subsurface hydrogeologic conditions or soil mechanics. All future development subject to the proposed project, particularly those within identified liquefaction hazard zones, are mandatorily required to undergo site-specific geotechnical investigations as part of the permitting process. These investigations, in conjunction with the CBC, prescribe specific foundation design, soil stabilization, and ground improvement techniques necessary to mitigate liquefaction risk. The proposed project does not override these critical regulatory requirements. Therefore, the proposed project would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts regarding strong seismic ground shaking.
iv. Landslides?
The proposed project would not exceed General Plan 2040 assumptions, and it would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts in relation to landslides. The Certified EIR acknowledged that steep hills (30 percent slope or greater) in the Planning Area are subject to a high risk of seismically induced landslides. However, the impact was determined to be less than significant because all development must address these hazards through site-specific geotechnical studies and conform to the current design provisions of the CBC and General Plan 2040 policies protecting hillside development. The proposed project applies primarily to urbanized and infill areas designated for multifamily and mixed-use development, which are generally located outside the most sensitive steep hillsides. Future development subject to the proposed project that occurs on or adjacent to slopes, the proposed project architectural requirements will not supersede the need for comprehensive geotechnical reporting and the implementation of slope stability measures required by the City Engineer and the CBC. Therefore, the proposed project would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts regarding landslides.

Diamond Bar Objective Design Standards Addendum No. 2 to the EIR February 2026 Sapphos Environmental, Inc.

(b) Would the proposed project result in substantial soil erosion or the loss of topsoil? The proposed project would not exceed General Plan 2040 assumptions, and it would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts in relation to substantial soil erosion or the loss of topsoil. The Certified EIR concluded that development under the General Plan 2040 could expose soils to erosion during earthwork activities. However, the impact was found to be less than significant due to mandatory compliance with the National Pollutant Discharge Elimination System (NPDES) permit requirements for projects disturbing over one acre, which includes the implementation of a Storm Water Pollution Prevention Plan (SWPPP) and Best Management Practices (BMPs). Additionally, General Plan 2040 policies RC-P-24 and RC-P-26 specifically require these measures to control erosion and sedimentation during and after construction.

The proposed project would not expand the total area of land disturbance; nor would it increase the overall development capacity of the City beyond the levels analyzed in the Certified EIR.

Future development (new multifamily and mixed-use buildings) subject to the proposed project remain fully subject to all mandatory federal, state, and local regulations related to water quality and soil protection, including the requirements for NPDES permits, SWPPPs, and BMPs. While the proposed project influences exterior elements like landscaping and courtyards, the critical engineering aspects of site preparation, grading, and permanent drainage control are governed by the City Engineer and mandatory grading permits, which prioritize erosion control. The proposed project will not compromise the mandatory regulatory framework that prevents substantial soil erosion and loss of topsoil. Therefore, the proposed project would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts regarding substantial soil erosion or the loss of topsoil. (c) Would the proposed 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? The proposed project would not exceed General Plan 2040 assumptions, and it would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts in relation to unstable geologic units or soils. The Certified EIR concluded that areas with unstable underlying materials (undocumented fills, soft compressible deposits, expansive soils) exist within the proposed project area, particularly in areas of hilly terrain and near valley basins. However, the EIR determined that the potential for adverse impacts from geologic hazards (landslide, lateral spreading, subsidence, liquefaction, or collapse) was less than significant for the General Plan 2040 buildout due to the integration of geotechnical requirements into the planning and design process. Since all future development remains fully subject to the strict regulatory framework and policies designed to eliminate risks associated with unstable soils and geologic units, the proposed project does not introduce any new mechanism that would destabilize soils or increase exposure to these hazards. Therefore, the proposed project would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts regarding unstable geologic units or soils resulting in landslide, lateral spreading, subsidence, liquefaction or collapse.

Diamond Bar Objective Design Standards Addendum No. 2 to the EIR February 2026 Sapphos Environmental, Inc.

(d) Would the proposed project be located on expansive soil, as defined in Table 18-1-B of the Uniform Building Code (1994), creating substantial direct or indirect risks to life or property?
The proposed project would not exceed General Plan 2040 assumptions, and it would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts in relation to expansive soils. The Certified EIR acknowledged that areas within the Planning Area contain soils with expansive properties, which swell and shrink with changes in moisture content, potentially causing damage to foundations, pavements, and utility lines, thereby creating risks to life or property. However, the Certified EIR concluded this impact was less than significant. The proposed project comprises a set of architectural and aesthetic design criteria and is entirely unrelated to subsurface soil mechanics, geotechnical engineering, or structural foundation design. The proposed project would not authorize any development that would be exempt from the mandatory requirements for site-specific geotechnical investigation and mitigation measures enforced by the City Engineer and the CBC. Therefore, the proposed project would not introduce any new risks to life or property in areas of the City that may contain expansive soils. Therefore, the proposed project would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts to expansive soil hazards.
(e) Would the proposed project have soils incapable of adequately supporting the use of septic tanks or alternative waste water disposal systems where sewers are not available for disposal of waste water?
The proposed project would not exceed General Plan 2040 assumptions, and it would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts in relation to the capability of soils to support septic systems. The Certified EIR indicated that the General Plan 2040 and the overall project area are already served by extensive public sewer infrastructure, provided by various agencies including the Sanitation Districts of Los Angeles County. The General Plan 2040’s anticipated growth, which is the maximum potential growth accommodated by the proposed project, is based on the assumption that all new development will connect to and utilize the existing and planned public wastewater conveyance and treatment facilities. The proposed project applies to multifamily and mixed-use infill development within the urbanized areas of the City, which are already fully serviced by public sewers. There are no anticipated instances where future development subject to the proposed project would rely on septic tanks or alternative on-site wastewater disposal systems.

Furthermore, the proposed project is a design standard and has no bearing on the presence, functionality, or capacity of public sewer systems or the use of private disposal systems.

Therefore, the proposed project would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts as it relates to the capacity of soils to support septic or alternative wastewater disposal systems. (f) Would the proposed project directly or indirectly destroy a unique paleontological resource or site or unique geologic feature?
The proposed project would not exceed General Plan 2040 assumptions, and it would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts in relation to the destruction of unique paleontological or geologic resources.

The Certified EIR concluded that, while the Planning Area contains underlying geologic formations (such as the Fernando Formation) known to contain paleontological resources and includes potentially unique geologic features (like steep hillsides), the potential for destruction was

Diamond Bar Objective Design Standards Addendum No. 2 to the EIR February 2026 Sapphos Environmental, Inc.

determined to be less than significant due to mandatory regulatory compliance and mitigation measures MM-GEO-1 and MM-GEO-2. The proposed project does not determine the extent of ground disturbance or excavation depth, which are the primary factors leading to the destruction of these resources. The amount of earthwork is dictated by the maximum density and intensity of the General Plan 2040. Furthermore, all future development subject to the proposed project is required to abide by the appropriate regulatory requirements, including the cessation of earthmoving activity if potential resources are discovered, and the mandatory recovery and preservation of any unique paleontological resources in accordance with the Los Angeles County Paleontological Resource Assessment and Guidelines. Since the proposed project must adhere to existing General Plan policies and protocols for resource discovery and preservation, the proposed project does not introduce any new significant risks that would destroy a unique resource. However, consistent with the Certified EIR, all development subject to the proposed project would continue to implement mitigation measures MM-GEO-1 and MM-GEO-2 to ensure that impacts to paleontological resources would be less than significant. Therefore, the proposed project would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts that would directly or indirectly cause the destruction of a unique paleontological resource or site or unique geologic feature.

Mitigation Measures
As with the Certified EIR, mitigation measures MM-GEO-1 and MM-GEO-2 are required for implementation in order to lessen and/or alleviate the impacts related to paleontological resources expected to result from implementation of the proposed project (Appendix B).

No further mitigation measures are required.

Cumulative Impact Analysis
There are no new circumstances involving new impacts to geology and soils for the proposed project that were not previously analyzed in the Certified EIR. As evaluated in the Certified EIR, cumulative increases in population and development that would result from the implementation of the full buildout of the General Plan 2040 would increase the number of residents and employees exposed to the region's known seismic hazards; however, conformance with the CBC and proposed General Plan 2040 policies would preserve building integrity during a seismic event, and other regulatory measures would reduce geohazards impacts to below the level of significance. As a result, cumulative impacts would be minimized and less than significant.

Consistent with the Certified EIR, the proposed project would not result in a significant adverse cumulative impact to geology and soils as the proposed project is strictly an architectural and functional design overlay. In addition, the proposed project does not increase underlying development capacity, nor does it override mandatory safety regulations. All future development, regardless of ODS requirements, is obligated to follow the CBC and requires site-specific geotechnical investigations to mitigate risks from seismic shaking, liquefaction, landslides, and expansive soils. Therefore, the proposed project would not result in a new significant cumulative impact or a substantial increase in the severity of previously identified significant cumulative impacts related to geology and soils.

Diamond Bar Objective Design Standards Addendum No. 2 to the EIR February 2026 Sapphos Environmental, Inc.

3.7 GREENHOUSE GAS EMISSIONS
This section evaluates the effects on greenhouse gas (GHG) emissions from the proposed project. This Addendum relies on and incorporates by reference the physical setting and regulatory setting as described in Section 3.5, Energy, Climate Change, and Greenhouse Gases, of the Certified EIR. Potential impacts to GHG emissions from the proposed project are discussed relative to the conclusions in the Certified EIR. The Certified EIR determined that the implementation of the General Plan 2040 would result in less than significant GHG emissions impacts, with no mitigation measures required. Consistent with the Certified EIR, the proposed project was evaluated with regard to the General Plan 2040, the CARB Scoping Plan Update, Executive Orders S-3-05 and B-48-18, SCAG’s Connect SoCal, and the City’s CAP.

3.7.1 Setting
The project setting for GHG emissions is the same as that considered in the Certified EIR. A review of available records and literature determined that new GHG emissions information has become available since the Certified EIR, including (1) a 2024 update to Connect SoCal, which includes a revision from CARB to set more stringent GHG reduction targets for the SCAG region at 8 percent below 2005 per capita emissions levels by 2020 and 19 percent below 2005 per capita emissions levels by 2035,13 and (2) a 2022 update to the CARB Scoping Plan,14 which includes more stringent GHG reduction goals compared to the 2017 Scoping Plan update analyzed in the Certified EIR. While these regional plan updates are reviewed for consistency, the updates to SCAG’s Connect SoCal and the CARB Scoping Plan would not result in substantial changes to the regional framework analyzed in the Certified EIR with respect to GHG emissions and, thus, would not result in changes to the findings made in the Certified EIR.

3.7.2 Impact Analysis
Project Impact Analysis
The potential for the proposed project to result in a new significant impact or a substantial increase in the severity of previously identified significant impacts to GHG emissions was evaluated in relation to the following questions as stated in Appendix G of the 2025 CEQA Guidelines. (a) Would the proposed project generate greenhouse gas emissions, either directly or indirectly, that may have a significant impact on the environment? The proposed project would not exceed General Plan 2040 assumptions, and it would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts in relation to generating direct or indirect GHG emissions that may have a significant impact on the environment. The Certified EIR determined that the General Plan 2040 would result in less than significant impacts. According to AB 32, GHG emissions are defined as emissions of the following gases: carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF6). While SCAG’s Connect SoCal and the CARB Scoping Plan have been updated since adoption of the 13 Southern California Association of Governments. 2024. Connect SoCal: A Plan for Navigating to a Brighter Future. https://scag.ca.gov/sites/default/files/2024-05/23-2987-connect-socal-2024-final-complete-040424.pdf (accessed November 5, 2025).
14 California Air Resources Board. December 2022. 2022 Scoping Plan for Achieving Carbon Neutrality. https://ww2.arb.ca.gov/sites/default/files/2023-04/2022-sp.pdf (accessed November 3, 2025).

Diamond Bar Objective Design Standards Addendum No. 2 to the EIR February 2026 Sapphos Environmental, Inc.

Certified EIR to set more stringent GHG reduction targets, these updates would not change the conclusions of the Certified EIR, and the proposed project would not conflict with the reduction targets. Future development in the City that would be subject to the proposed project would continue to be subject to the most recent versions of SCAG’s Connect SoCal and the CARB Scoping Plan to meet the most recent reduction targets. The proposed project is a set of design standards and does not increase development capacity; as such, it would not result in unplanned development in the City beyond the development that was evaluated for GHG emissions in the Certified EIR. As found in the Certified EIR, future multifamily residential and mixed-use development subject to the proposed project would have the potential to emit these GHG emissions from area, energy, and mobile sources. However, there would be no additional development that would increase VMT as a result of the proposed project compared to the Certified EIR (see Section 3.13, Transportation). Thus, no additional GHG emissions from vehicular travel, as measured by VMT, would result from the proposed project. Similarly, the proposed project would not involve area or energy sources that would result in an exceedance in GHG emissions, and no additional development would occur that was not planned in the General Plan 2040 and considered in the Certified EIR. Furthermore, the application of the proposed project to future multifamily and mixed-use development would be subject to project-specific development review requirements and compliance with existing GHG emissions regulations. The proposed project includes a requirement for at least 25 percent of outdoor space to be dedicated to landscaping (e.g., shrubs, cover, and/or trees) for walk-up flats, courtyard multifamily buildings, wrap buildings, and urban blocks, which could provide for an increase in available carbon storage opportunities within the City.

Therefore, the proposed project would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts related to generating direct or indirect GHG emissions that may have a significant impact on the environment. (b) Would the proposed project conflict with an applicable plan, policy, or regulation adopted for the purpose of reducing the emissions of greenhouse gases? The proposed project would not exceed General Plan 2040 assumptions, and it would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts in relation to any conflicts with an applicable plan, policy, or regulation adopted for the purpose of reducing the emissions of greenhouse gases. As with the Certified EIR, the proposed project would result in less than significant impacts. The proposed project would comply with existing energy regulations, including the most recent versions of the General Plan 2040, the CARB Scoping Plan Update, Executive Orders S-3-05 and B-48-18, SCAG’s Connect SoCal, and the City’s CAP. While SCAG’s Connect SoCal and the CARB Scoping Plan have been updated since adoption of the Certified EIR to set more stringent GHG reduction targets, these updates would not change the conclusions of the Certified EIR, and the proposed project would not conflict with the reduction targets. Future development in the City that would be subject to the proposed project would continue to be subject to the most recent versions of SCAG’s Connect SoCal and the CARB Scoping Plan to meet the most recent reduction targets. The proposed project is a set of design standards and does not increase development capacity; as such, it would not result in unplanned development in the City beyond the development that was evaluated for GHG emissions in the Certified EIR. The application of the proposed project to future multifamily and mixed-use development would be subject to project-specific development review requirements.

The proposed project includes landscaping design standards for a variety of building types which could provide for an increase in available carbon storage opportunities within the City.

Diamond Bar Objective Design Standards Addendum No. 2 to the EIR February 2026 Sapphos Environmental, Inc.

The proposed project does not propose new development and would not alter the growth projections analyzed in the Certified EIR. The proposed project also does not increase the overall development capacity or change the level of intensity that was the basis for the Certified EIR analysis. As such, the proposed project would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts related to conflict with applicable plan, policy, or regulation adopted for the purpose of reducing GHG emissions.

Mitigation Measures
As with the Certified EIR, no mitigation measures have been identified related to GHG emissions.

No further mitigation measures are required.

Cumulative Impact Analysis
There are no new circumstances involving new impacts to GHG emissions for the proposed project not previously evaluated in the Certified EIR. The Certified EIR found that the General Plan 2040 would not result in cumulatively considerable impact to the generation of direct or indirect GHG emissions and regarding conflict with goals, policies, and regulations established for reducing GHG emissions. Consistent with the findings of the Certified EIR, implementation of the proposed project would not result in a cumulatively considerable impact on GHG emissions.

The proposed project would not result in a new significant cumulative impact or a substantial increase in the severity of previously identified significant cumulative impacts to GHG emissions.

Diamond Bar Objective Design Standards Addendum No. 2 to the EIR February 2026 Sapphos Environmental, Inc.

3.8 HAZARDS AND HAZARDOUS MATERIALS
This section evaluates the potential impacts associated with hazards and hazardous materials resulting from the proposed project. This Addendum relies on and incorporates by reference the physical setting and regulatory setting as described in Section 3.7, Hazards, Hazardous Materials, and Wildfire, of the Certified EIR. This analysis assesses the potential impacts associated with the use, transport, or disposal of hazardous materials, hazardous materials sites, airport hazards, emergency response planning, and wildfire hazards. Potential impacts are discussed relative to the conclusions in the Certified EIR.

3.8.1 Setting
The project setting for hazards and hazardous materials is consistent with that considered in the Certified EIR. The proposed project would not alter the physical or regulatory conditions described in the Certified EIR.

3.8.2 Impact Analysis
Project Impact Analysis
The potential for the proposed project to result in a new significant impact or a substantial increase in the severity of previously identified significant impacts to hazards and hazardous materials was evaluated in relation to the following questions as stated in Appendix G of the State CEQA Guidelines.
(a) Would the proposed 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 not exceed General Plan 2040 assumptions, and it would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts in relation to the routine transport, use, or disposal of hazardous materials.

The Certified EIR analyzed the potential for hazardous materials generation from the construction activities associated with the General Plan 2040. The construction and operation of new multifamily and mixed-use buildings includes the routine use of common hazardous materials such as cleaning agents, landscaping chemicals, vehicle fluids, fuels, oils, and construction related materials. The Certified EIR concluded that the implementation of applicable federal, state, and local regulations and policies would be sufficient to lessen the risk of death, injury, and property loss.

The routine use of hazardous materials by the proposed project is limited to materials commonly found in residential and low-intensity commercial settings, such as paints, cleaning agents, and landscape chemicals. Since the proposed project is limited to aesthetic details and architectural goals that require specific exterior finishes or color schemes, the proposed project would not increase the volume of construction, operational hazardous materials, or waste generated beyond what was anticipated and deemed less than significant in the Certified EIR. All handling, storage, and transport of hazardous materials and waste associated with future development remain subject to a robust regulatory framework, including federal, state, and local regulations (e.g., Resource Conservation and Recovery Act, Emergency Planning and Community Right-to-Know Act, Hazardous Materials Transportation Act, California Health and Safety Code, and the Consolidated Fire Code). Compliance with the Hazardous Materials Business Plan (HMBP) for threshold quantities and regulations specifying storage areas designed to prevent accidental

Diamond Bar Objective Design Standards Addendum No. 2 to the EIR February 2026 Sapphos Environmental, Inc.

release and protect against fire or health hazards remains mandatory. Since there are currently no permitted hazardous waste facilities in the City, disposal practices are governed strictly by state and local standards. Furthermore, the Certified EIR noted that the General Plan 2040 includes policies that seek to lessen the risk from transport by minimizing truck traffic through residential areas and promoting safe goods distribution. The transport of hazardous materials is primarily related to General Plan 2040 construction development (fuel deliveries), and the movement of household/commercial hazardous waste would not be affected by the proposed project. Since the proposed project would not result in land use changes or increase traffic volumes beyond the Certified EIR, the proposed project would not increase the number of vehicles transporting materials on highways (SR-57 and SR-60) or local roads. Existing regulations and policies manage the safety risks associated with transport. The proposed project does not introduce new types of hazards, increase the scale of hazardous materials used beyond the General Plan's projections, or override any mandatory federal, state, and local regulations that promote safe handling, storage, and emergency response.

The proposed project would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts related to routine transport, use, or disposal of hazardous materials.
(b) Would the proposed project create a significant hazard to the public or the environment through reasonably foreseeable upset and accidental conditions involving the release of hazardous materials into the environment?
The proposed project would not exceed General Plan 2040 assumptions, and it would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts related to the accidental release of hazardous materials. The Certified EIR concluded that, given the existing regulations and programs and the General Plan 2040 policies that address the potential for hazardous materials upsets and promote the ability of emergency services to respond to incidents, impacts associated with the release of hazardous materials into the environment would be less than significant.

The potential releases of hazardous materials associated with the proposed project are the same as described in the Certified EIR. The Certified EIR describes new development (housing and mixed-use) could increase the risk of the potential upset of routinely used hazardous materials, such as household cleaners and landscaping chemicals, but these would not be present in sufficient quantities to pose a significant risk to the public and must be used in accordance with all applicable laws and regulations. The implementation of the proposed project does not alter site grading, construction methods, or safety protocols. Therefore, the same potential impacts associated with site contamination that were described in the Certified EIR could occur with the proposed project. Grading, drilling, or excavation at a future development site have the potential to mobilize hazardous materials (if currently present in the soil), which could result in exposure of personnel and other sensitive receptors, such as plants and wildlife, to contaminant levels that could result in short- and long-term health effects. Accidental release from operational and construction activities would be addressed through mandatory regulatory compliance. All future development remains subject to existing regulations regarding storage, transport, and safety protocols designed to prevent accidental releases, and facilities handling hazardous materials are subject to routine inspections by the Los Angeles County Fire Department. Furthermore, construction activities for future development must also adhere to strict protocols regarding the handling and storage of construction related hazardous materials, as well as Occupational Safety and Health Administration (OSHA) worker safety standards. The proposed project is an architectural design guide and has no role in regulating the use, storage, or handling of hazardous

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materials or the remediation of contaminated sites. As such, the proposed project would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts related to the reasonably foreseeable upset and accidental conditions involving the release of hazardous materials into the environment. (c) Would the proposed 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 proposed project would not exceed General Plan 2040 assumptions, and it would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts in relation to the emission of hazardous emissions or the handling of hazardous or acutely hazardous materials, substances, or waste within one-quarter mile of an existing or proposed school. The Certified EIR concluded that the General Plan 2040 would result in less than significant impacts regarding hazardous emissions and materials within one-quarter mile of a school. The Certified EIR conclusion noted that the most intense uses likely to handle acutely hazardous materials (e.g., Light Industrial) are confined to specific areas, with only one school, Walnut Elementary, falling within a quarter mile of such designation. The proposed project would only apply to multifamily and mixed-use projects, meaning it would not increase exposure of students to industrial hazardous materials beyond what was identified in the Certified EIR. The proposed project would not change the type of land uses allowed or intensity the manufacture, use, transport, or disposal of hazardous materials, within one-quarter mile of any of the 14 existing schools identified in the Certified EIR. The allowed land uses remain limited to residential, commercial, or mixed-use, which are generally not substantial emitters or handlers of acutely hazardous waste. The General Plan 2040 has policies in place (e.g., PS-P-26) that prohibit the development of projects anticipated to emit hazardous air emissions or handle extremely hazardous substances within one-quarter mile of a school. The proposed project would not interfere with the Local Hazard Mitigation Plan and Emergency Operations Plan’s (EOP) (PS-G8) ability to respond to local hazards, including hazardous materials incidents, and to plan for the protection of critical facilities (i.e., schools). Furthermore, the small quantities of routine hazardous materials (household cleaners, paints, etc.) associated with the proposed project would be the same as those considered in the Certified EIR analysis; these types of hazardous materials are not present in sufficient quantities to pose a significant risk to the public or schools and are subject to mandatory state regulations. Therefore, the proposed project would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts related to emission of hazardous emissions or handling of hazardous or acutely hazardous materials, substances, or waste within one-quarter mile of an existing or proposed school.
(d) Would the proposed project be located on a site which is included on a list of hazardous materials site compiled pursuant to Government Code § 65962.5 and, as a result, would it create a significant hazard to the public or the environment? The proposed project would not exceed General Plan 2040 assumptions, and it would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts in relation to development on designated hazardous materials sites. The Certified EIR acknowledges the existence of numerous sites in the City that are included on the “Cortese List” (Government Code No. 65962.5) or require further investigation (as depicted in Figure 3.7-1 and Table 3.7-1 of the Certified EIR). These sites, often located along major local roadways (e.g., Diamond Bar Boulevard, Grand Avenue, Golden Springs Drive), have experienced releases resulting in soil and groundwater contamination. The Certified EIR

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concluded that, while redevelopment of these sites could potentially pose a hazard, the impact would be less than significant because these sites are strictly regulated by existing federal and state policies and are in various stages of the mandatory cleanup process. The proposed project, which guides architectural and site design elements (e.g., building placement, facade articulation) for future multifamily and mixed-use development, has no influence, jurisdiction, or impact over the environmental cleanup, remediation, or regulatory compliance required for contaminated sites. The proposed project would not change the underlying zone or increase the maximum density or intensity of development allowed on these specific sites. Therefore, the proposed project would not increase the degree of intrusion into contaminated soil or groundwater beyond the scope already anticipated and analyzed by the Certified EIR. Compliance with the established regulatory framework will continue to ensure that impacts related to development on designated hazardous material sites are appropriately addressed. The proposed project is a design standard that would not modify the regulatory or remedial requirements governing Cortese List sites.

Therefore, the proposed project would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts in relation to development on designated hazardous materials sites.
(e) For a proposed 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, would the project result in a safety hazard or excessive noise for people residing or working in the project area?
The proposed project would not exceed General Plan 2040 assumptions, and it would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts in relation to airport-related safety hazards or excessive noise for people residing or working in the proposed project area. The Certified EIR concluded that the implementation of the General Plan 2040 would have no impact on an airport-related safety hazard because there is no public airport located within two miles of the City. The closest facility, Brackett Field, is located over six miles away, and its Air Impact Assessment (AIA) area does not overlap with the City. The proposed project would apply to the entire City, which is not located within two miles of a public airport or public use airport. Since the proposed project is entirely outside the relevant airport safety and noise influence zones, the proposed project would not result in a safety hazard or excessive noise for people residing or working in the project area related to airport operations. Consistent with the findings of the Certified EIR, the project would have no impact related to an airport-related safety hazard or excessive noise. Thus, the proposed project would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts related to airport noise. (f) Would the proposed project impair implementation of or physically interfere with an adopted emergency response plan or emergency evacuation plan? The proposed project would not exceed General Plan 2040 assumptions, and it would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts in relation to interference with an adopted emergency response plan or emergency evacuation plan. The Certified EIR established that the overall buildout of the General Plan 2040 would result in less than significant impacts to emergency response due to the enforcement of existing regulations and specific General Plan 2040 policies. Compliance with the General Plan 2040’s policies regarding emergency access, evacuation route development, and roadway development would ensure that emergency vehicle movement could efficiently access all parts of the planning area. The proposed project is a design guide and would not authorize new infrastructure, change the function of existing roadways, or affect the protocols established

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in the City’s adopted emergency plans. The proposed project includes requirements for building placement and parking (e.g., Principle 8: Parking and Vehicle Areas) that seek to place parking at the rear of buildings and prioritize street frontage. These requirements are intended to improve pedestrian experience and visual quality, and they do not supersede the requirements of the Fire Code or the City’s Engineering Division. Future multifamily and mixed-use development must still undergo development review to ensure compliance with the Los Angeles County Fire Code and the Diamond Bar Emergency Operations Plan (EOP). This mandatory review dictates minimum driveway widths, turning radii, and fire department access routes necessary for the movement of emergency vehicles. Aesthetic or site design standards in the proposed project cannot be approved if they conflict with minimum fire and emergency access requirements. Future development projects, to which the ODS applies, would still be required to be reviewed by the Los Angeles County Fire Department and other relevant emergency service providers to ensure compliance with all mandatory access, water flow, and life safety standards. The ODS does not modify or interfere with these regulatory mechanisms. The proposed project would not introduce any elements or changes to primary circulation that would physically interfere with designated emergency evacuation routes. Since the ODS is subordinate and works in tandem with the mandatory Fire Code and the City’s EOP (General Plan Policy PS-G-8), the proposed project would have no potential to physically interfere with an adopted emergency response or evacuation plans. Therefore, the proposed project would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts in relation to interference with an adopted emergency response plan or emergency evacuation plan. (g) Would the proposed project expose people or structures, either directly or indirectly, to a significant risk of loss, injury or death involving wildland fires? The proposed project would not exceed General Plan 2040 assumptions, and it would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts in relation to wildland fire risk. The Certified EIR assessed wildfire risk for the General Plan 2040 buildout and determined impacts would be less than significant with adherence to regulatory requirements. The proposed project does not include new development or increase the intensity of development beyond the buildout already analyzed in the Certified EIR. The proposed project would likewise not expand the development footprint into areas adjacent to wildlands or Wildland-Urban Interface (WUI) zones. All developments in or near a Very High Fire Hazard Severity Zone (VHFHSZ) must comply with the California Public Resources Code and the Los Angeles County Fire Code, including defensible space, fire-resistant building materials, and fuel modification zones. The ODS has an emphasis on durable, high-quality, and non-combustible exterior materials that provide incidental support for fire-safe building practices, which are mandatory under the California Building Code and Fire Code. The proposed project is limited to urbanized areas; therefore, the proposed project would not expose people or structures to a new or increased risk related to wildland fires beyond the analysis already contained in the Certified EIR. The proposed project would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts related to wildland fire risk.

Mitigation Measures
As with the Certified EIR, no mitigation measures have been identified related to hazards and hazardous materials. No further mitigation measures are required.

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Cumulative Impact Analysis
There are no new circumstances involving new impacts to hazards and hazardous materials for the proposed project that were not previously analyzed in the Certified EIR. The proposed project would result in no new significant cumulative impacts related to hazards and hazardous materials than those disclosed in the Certified EIR. Due to rigorous state and federal regulatory frameworks covering hazardous material handling, site cleanup, and mandatory fire safety compliance, cumulative impacts would be less than significant. Implementation of the proposed project does not conflict with or otherwise negate any existing mandatory hazard reduction policies.

Furthermore, the proposed project would not add new physical development or increase the severity of any underlying hazard exposure beyond the baseline established in the Certified EIR.

Therefore, the proposed project would not introduce any new types of hazardous activities, result in any additional development, or undermine the protective regulatory environment.. The cumulative impact related to hazards and hazardous materials remains less than significant, consistent with the findings of the Certified EIR. The proposed project would not result in a new significant cumulative impact or a substantial increase in the severity of previously identified significant cumulative impacts related to hazards and hazardous materials.

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3.9 HYDROLOGY AND WATER QUALITY
This section discusses the effects on hydrology and water quality from the proposed project. This Addendum relies on and incorporates by reference the project setting and regulatory setting as described in Section 3.8, Hydrology and Water Quality, of the Certified EIR. Potential impacts to hydrology and water quality from the proposed project are discussed relative to conclusions in the Certified EIR. The Certified EIR determined that the implementation of the General Plan 2040 would result in less than significant impacts to hydrology and water quality, with no mitigation measures required. Consistent with the Certified EIR, hydrology and water quality impacts were evaluated in relation to the General Plan 2040, groundwater basin data from the California Department of Water Resources,15 and National Flood Insurance Program Flood Insurance Rate Maps for Los Angeles County.16

3.9.1 Setting
The environmental and regulatory setting for Hydrology and Water Quality remains unchanged from that described in the Certified EIR. A review of available records and literature confirms that no new information of importance has been identified since the Certified EIR, including changes to regulations or permitting requirements regulated by the Federal Clean Water Act (CWA), the State Water Resources Control Board, the Construction General Permit (CGP), the Greater Los Angeles County Region Integrated Regional Water Management Plan (GLACR IRWM), or the City of Diamond Bar Water Pollution Control Regulations including the Stormwater and Urban Runoff Pollution Control Ordinance.

3.9.2 Impact Analysis
Project Impact Analysis
The potential for the proposed project to result in a new significant impact or a substantial increase in the severity of previously identified significant impacts to hydrology and water quality was evaluated in relation to the following questions in Appendix G of the State CEQA Guidelines. (a) Would the proposed project violate any water quality standards or waste discharge requirements or otherwise substantially degrade surface or ground water quality? The proposed project would not exceed General Plan 2040 assumptions, and it would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts in relation to the potential violation of water quality standards. The proposed project primarily dictates aesthetic and functional design components (e.g., sense of place, style, details) for specific types of development and substantial improvements, and does not require new construction, operation, or maintenance activities that would deviate from the types of activities, or the associated impacts, already analyzed and addressed in the Certified EIR.

As discussed in the Certified EIR, the General Plan 2040 may result in local and temporary impacts related to water quality during construction, but such impacts would be less than significant due to compliance with federal, state, and local water quality regulations and General Plan 2040 policies. The proposed project would not alter the fundamental construction scenario, 15 California Department of Water Resources. 2003. California’s Groundwater. Bulletin 118 – Update 2003. 16 Federal Emergency Management Agency. 2008. National Flood Insurance Program Flood Insurance Rate Map for Los Angeles County and Incorporated Areas.

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scale, or duration of future development; the proposed project establishes ODS for projects that already fall under the scope of the Certified EIR. Consistent with the Certified EIR, to minimize impacts to surface and ground water quality, measures to minimize and contain erosion and sedimentation would be implemented in accordance with the Los Angeles County Grading Code, and a grading permit would be submitted to the County for approval prior to commencement of any construction activities. Furthermore, for projects that disturb more than one acre, compliance with the NPDES General Construction Permit would be required. As required by this permit, future development would develop a SWPPP and comply with any regional requirements to meet State water quality objectives. To prevent hazardous materials from entering drainages and affecting water quality, future development would be required to implement a Hazardous Materials Business Plan and submit it to the Los Angeles County Environmental Health Services Department for review and approval. Though local and temporary water quality impacts are possible during the construction of developments that would be subject to the proposed project, any future development would implement NPDES compliance, which is designed to minimize and mitigate potential impacts, as specified in the Certified EIR.

The proposed project would not require construction, operation, or maintenance efforts that were not previously addressed in the Certified EIR. Impacts related to water quality standards or waste discharge requirements are expected to be less than significant as described in the Certified EIR.

The City's existing development review process, which would incorporate the proposed ODS checklist, and the mandatory regulatory framework (e.g., NPDES, SWPPP, Grading Code) require future development demonstrate compliance with all required water quality permits prior to commencement of construction activities. Therefore, the proposed project would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts to water quality standards or waste discharge requirements. (b) Would the proposed project substantially decrease groundwater supplies or interfere substantially with groundwater recharge such that the project may impede sustainable groundwater management of the basin?
The proposed project would not exceed General Plan 2040 assumptions, and it would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts in relation to groundwater supplies or groundwater recharge. The Certified EIR concluded that the General Plan 2040 would not substantially decrease groundwater supplies or interfere substantially with groundwater recharge, and impacts would be less than significant. The General Plan 2040 contains policies that are specifically designed to support groundwater recharge and conserve groundwater. These policies include the goal of preserving permeable surfaces, ridgelines, and hillsides, which directly aids in maintaining the natural filtration and recharge capabilities of the land. The City’s Water Pollution Ordinance and General Plan 2040 policies also aim to protect groundwater from potential sources of contamination, thereby ensuring the quality of the resource. In addition, the Certified EIR noted that groundwater-supplied recycled water could be a potential source for landscape irrigation, reducing potential impacts on imported and surface potable water supplies.

The proposed project does not increase the maximum number of dwelling units, building square footage, or site coverage allowed by the existing zoning. Therefore, the proposed project does not increase the City’s overall water demand or impervious surface area beyond what was already analyzed in the Certified EIR, nor does it override the City’s existing conservation policies. Any increase in new impervious surface would be localized and distributed, constituting a small fraction of the City’s overall permeable surface area. The proposed project would not have a measurable effect on groundwater recharge at the basin level. Any small, localized increase in

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runoff would be managed by existing stormwater regulations and Low Impact Design (LID) standards (as discussed in the Certified EIR) and would not result in a significant impact to the overall volume of groundwater recharge. The proposed project would not fundamentally alter the scale of development or the regulatory environment pertaining to water conservation and stormwater management established by the Certified EIR. The proposed project would not introduce new or greater impacts related to groundwater demand or interfere with groundwater recharge beyond the levels previously determined to be less than significant in the Certified EIR.

Accordingly, the proposed project would not impede on sustainable groundwater management of the basin, and impacts related to groundwater supplies and recharge remain less than significant.

Accordingly, the proposed project would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts to groundwater supplies or recharge.
(c) Would the proposed 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:
i. Result in a substantial erosion or siltation on- or off-site? The proposed project would not exceed General Plan 2040 assumptions, and it would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts in relation to substantially altering the existing drainage patterns. The Certified EIR determined that development or redevelopment anticipated by the General Plan 2040 could increase impervious surfaces, such as roofs, patios, driveways, and parking areas and lead to increased stormwater flow, but impacts would be less than significant. The Certified EIR states the majority of development that could occur in the City would be redevelopment of areas with already impervious surfaces and would comply with City ordinances and General Plan 2040 policies that reduce erosion. The proposed project would not change the requirements for all future development disturbing over one acre to develop and implement a SWPPP and comply with the NPDES Construction General Permit. The proposed project does not override any water quality regulatory requirements or alter standard construction practices that are already subject to the Los Angeles County Grading Code. As such, the proposed project would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts from erosion or siltation.
ii. Substantially increase the rate or amount of surface runoff in a manner which would result in flooding on- or off-site?
The proposed project would not exceed General Plan 2040 assumptions, and it would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts in relation to surface runoff. The Certified EIR already analyzed the maximum potential increase in impervious surfaces and runoff. The Certified EIR determined that development or redevelopment anticipated by the General Plan 2040 could increase impervious surfaces, such as roofs, patios, driveways, and parking areas and lead to increased stormwater flow, but impacts would be less than significant. The Certified EIR states the majority of development that may occur in the City is redevelopment of areas with already impervious surfaces and would comply with City ordinances and General Plan 2040 policies that reduce runoff. The proposed project applies to development already considered in the Certified EIR; it would not increase the maximum impervious area beyond what was previously considered.

Furthermore, post-development runoff is regulated by the MS4 Permit (Order No. R4-2012-0175) and local ordinances, which mandate the incorporation of LID practices to detain, retain, or treat

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runoff and prevent an increase in post-development flow rates that could cause flooding. These practices are designed to manage runoff rate and volume to prevent new flooding, regardless of the architectural style required by the proposed project. For these reasons, impacts associated with the proposed project would be less than significant and the proposed project would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts from surface runoff that could result in flooding. iii. 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?
The proposed project would not exceed General Plan 2040 assumptions, and it would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts in relation to runoff in excess of stormwater drainage systems. The Certified EIR determined that development or redevelopment anticipated by the General Plan 2040 could increase impervious surfaces, such as roofs, patios, driveways, and parking areas and lead to increased stormwater flow, but impacts would be less than significant. The Certified EIR states the majority of development that may occur in the City is redevelopment of areas with already impervious surfaces and would comply with City ordinances and General Plan 2040 policies that reduce runoff and pollution. Stormwater drainage capacity is managed through adherence to the MS4 Permit’s Hydromodification Management requirements which include engineering controls and detention/retention features to ensure that the post-development hydrograph does not substantially exceed the pre-development hydrograph. Polluted runoff is strictly controlled by BMPs required by the MS4 Permit. The ODS requirements in the proposed project, such as providing off-street parking in surface lots or garages at the rear of buildings (Principle 8) or orienting building façades (Principle 5), relate to site layout but do not introduce new or substantial sources of pollution not previously addressed in the Certified EIR. Therefore, the proposed project would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts in relation to existing or planned stormwater draining systems or providing additional sources of polluted runoff.
iv. Impede or redirect flood flows?
The proposed project would not exceed General Plan 2040 assumptions, and it would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts in relation to impeding or redirecting flood flows. The Certified EIR determined that development or redevelopment anticipated by the General Plan 2040 could change site layouts, but impacts would be less than significant. The Certified EIR states the majority of development that may occur in the City is redevelopment of areas with already impervious surfaces and would comply with City ordinances and General Plan 2040 policies that reduce flood flows. The proposed project does not contain specific mandates for grading or filling that would inherently impede flood flows. Future development in the City must comply with the City’s Floodplain Management Ordinance and all required permits, which ensures flood flows are not redirected in a manner that causes off-site impacts. Therefore, the proposed project would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts regarding flood flows.

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(d) In flood hazard, tsunami, or seiche zones, would the proposed project risk release of pollutants due to project inundation?
The proposed project would not exceed General Plan 2040 assumptions, and it would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts in relation to the potential release of pollutants in flood hazard, tsunami, or seiche zones. The Certified EIR found that impacts would be less than significant because the City is located sufficiently inland to be out of what would be considered a potential hazard area for seiches, tsunamis, and sea level rise. The proposed project would not require or encourage the placement of development or new significant sources of pollutants within high-risk inundation zones that were not already anticipated by the Certified EIR. Any future development subject to the proposed project must comply with state and local regulations for the storage and management of hazardous materials and waste, which minimizes the risk of pollutant release during an inundation event. Future development must comply with all federal, state, and local safety codes, including the preparation and implementation of a Hazardous Materials Business Plan (if required), which ensures that materials are stored to minimize the risk of release during an inundation event. Therefore, the proposed project would result in less than significant impacts regarding the risk of pollutant release due to inundation in flood hazard, tsunami, or seiche zones, and it would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts regarding the risk of pollutant release due to such inundation.
(e) Would the proposed project conflict with or obstruct implementation of a water quality control plan or sustainable groundwater management plan? The proposed project would not exceed General Plan 2040 assumptions, and it would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts in relation to a conflict with a water quality control plan or sustainable groundwater management plan. The Certified EIR found that impacts would be less than significant because development would be subject to the RWQCB requirements, the Diamond Bar City Code, and General Plan 2040 policies. Consistent with the Certified EIR, development subject to the proposed project would continue to be subject to those requirements. Future development associated with the proposed project would not conflict with the MS4 Permit (NPDES Permit CAS004001) or the City's Stormwater and Urban Runoff Pollution Control Ordinances. The proposed project must adhere to these mandatory regulatory requirements, including the use of source control, treatment, and LID BMPs. The proposed project would not affect the water demand projections in the General Plan 2040 and would not override the General Plan's policies that are designed to preserve permeable surfaces, reduce impervious areas, and support groundwater recharge. The Certified EIR states the General Plan 2040’s goals and policies ensure that water quality is protected to the maximum extent practicable. Thus, the proposed project would not substantially degrade water quality or impede sustainable groundwater management and impacts would be less than significant. Therefore, the proposed project would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts that would conflict with or obstruct the implementation of a water quality control plan or sustainable groundwater management plan.

Mitigation Measures
As with the Certified EIR, no mitigation measures have been identified related to hydrology and water quality. No further mitigation measures are required.

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Cumulative Impact Analysis
There are no new circumstances involving new impacts to hydrology and water quality for the proposed project that were not previously analyzed in the Certified EIR. The Certified EIR analyzed the cumulative impacts of full buildout under the General Plan 2040, which includes the maximum potential for new impervious surfaces, increased runoff, and associated water quality degradation from anticipated future development and redevelopment in the City. The Certified EIR concluded that the impacts to hydrology and water quality were less than significant because the General Plan 2040 mandates rigorous regulatory compliance. Consistent with the Certified EIR, development subject to the proposed project would continue to be subject to the RWQCB requirements, the Diamond Bar City Code, and General Plan 2040 policies, ensuring that cumulative impacts to hydrology and water quality would remain less than significant with implementation of the proposed project. This conclusion is based on the function of the proposed project as a design overlay that works within the regulatory framework and cumulative growth assumptions of the Certified EIR. Therefore, the proposed project would not result in a new significant cumulative impact or a substantial increase in the severity of previously identified significant cumulative impacts related to hydrology and water quality.

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3.10 LAND USE AND HOUSING
This section evaluates the effects on land use and housing from the proposed project. This Addendum relies on and incorporates by reference a project setting and regulatory setting as described in Section 3.9, Land Use, Population, and Housing, of the Certified EIR. Potential impacts to land use and housing from the proposed project are discussed relative to conclusions in the Certified EIR. The Certified EIR determined that impacts related to the physical division of an established community; conflict with any land use plan, policy, or regulation adopted for the purpose of avoiding or mitigating an environmental effect; and displacement of substantial numbers of existing people or housing, necessitating the construction or replacement of housing elsewhere, would be less than significant with no mitigation measures required. Consistent with the Certified EIR, land use and housing impacts from the proposed project were evaluated with regard to the General Plan 2040 and Title 22 (Development Code) of the Diamond Bar City Code.

3.10.1 Setting
The project setting for land use and housing is the same as that considered in the Certified EIR.

However, while the Certified EIR considered the entire City, the study area for the proposed project is established as areas where the General Plan 2040 land use designations allow for multifamily residential and mixed-use development (Figure 1). A review of available records and literature determined that new housing information has become available since certification of the EIR, including the City’s adoption of the 2021-2029 Housing Element Update. The 2021-2029 Housing Element Update conducted an analysis of the City’s demographic and housing characteristics and subsequently projected housing needs based on the 2021-2029 RHNA. The RHNA is a key requirement for local governments to plan for anticipated growth. The RHNA quantifies the anticipated need for housing within each jurisdiction for the 6th Housing Element cycle extending from July 2021 to October 2029. The RHNA for the 6th cycle was adopted by SCAG in March 2021. The total housing growth need for the City during the 2021–2029 planning period is 2,521 units, distributed by income category (Table 2, 2021–2029 Regional Housing Needs Assessment).

TABLE 3.10-1
2021–2029 Regional Housing Needs Assessment
Very Low Low Moderate Above Moderate Total
844 434 437 806 2,521
Source: City of Diamond Bar. 2022. 2021-2029 Housing Element Update to the Diamond Bar General Plan 2040.

3.10.2 Impact Analysis
Project Impact Analysis
The potential for the proposed project to result in a new significant impact or a substantial increase in the severity of previously identified significant impacts to land use and housing was evaluated in relation to the following questions as stated in Appendix G of the 2025 CEQA Guidelines. (a) Would the proposed project physically divide an established community? The proposed project would not exceed General Plan 2040 assumptions, and it would not result in a new significant impact or a substantial increase in the severity of previously identified

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significant impacts in relation to physically dividing an established community. The Certified EIR determined that the General Plan 2040 would result in less than significant impacts and would not physically divide any established community. The proposed project would not physically divide the community in the City since the proposed project would only apply toward the design of future multifamily and mixed-use development that is already planned in the General Plan 2040 and considered in the Certified EIR. Furthermore, Principle 4 of the ODS aims to “animate building edges on the ground floor to create an inviting Public Realm and pedestrian friendly environment and to support multi-modal development and mobility,” which would make it easier for the community to travel locally within the City. All future development projects subject to the ODS would also be subject to project-specific development review requirements and compliance with existing land use-based regulations that focus on improving land use.

The proposed project would not result in additional development or induce growth greater than what was considered in the Certified EIR. Rather, the proposed project would inform the design of future multifamily and mixed-use development that is already planned for within the City. As such, the proposed project would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts related to physically dividing an established community.
(b) Would the proposed project cause a significant environmental impact due to conflict with any land use plan, policy, or regulation adopted for the purpose of avoiding or mitigating an environmental effect?
The proposed project would not exceed General Plan 2040 assumptions, and it would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts in relation to conflict with a land use plan, policy, or regulation adopted for the purpose of avoiding or mitigating an environmental effect. The Certified EIR found that the General Plan 2040 does not conflict with an applicable land use plan, policy, or regulation adopted for the purpose of avoiding or mitigating an environmental effect; and amendments to the Diamond Bar City Code were required for consistency with the General Plan 2040. The Certified EIR concluded that impacts would be less than significant. As discussed in Section 2, Project Description, implementation of the proposed project would require amendments to Title 22 (Development Code) of the Diamond Bar City Code. All future development projects subject to the ODS would also be subject to project-specific development review requirements and compliance with existing land use-based regulations that focus on improving land use.

As the proposed project would not result in additional development or induce growth greater than what was considered in the Certified EIR, the project would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts that would conflict with any land use plan, policy, or regulation adopted for the purpose of avoiding or mitigating an environmental effect.
(c) Would the proposed 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 would not exceed General Plan 2040 assumptions, and it would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts in relation to inducing substantial unplanned population growth. The Certified EIR determined that the City would undergo planned population growth through 2040 that was analyzed throughout the Certified EIR, particularly concentrated in four focus areas, including a

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new Town Center and mixed-use neighborhood. The Certified EIR determined that housing growth under the General Plan 2040 would be sufficient to accommodate the associated increase in population. The proposed project would not induce substantial unplanned growth in an area, either directly or indirectly. The proposed project would only apply toward the design of future multifamily and mixed-use development that has been planned for in the General Plan 2040 and considered in the Certified EIR. The proposed project does not propose new development and would not alter the land use designations and growth projections analyzed in the Certified EIR.

The proposed project does not increase the overall development capacity, modify the General Plan land use boundaries, or change the level of intensity that was the basis for the Certified EIR’s analysis. Additionally, the proposed project would not extend utility infrastructure or extend roads that would support additional housing in new areas of the City. Finally, the proposed project does not include provisions for new businesses or other commercial development that could require a new workforce that would lead to population growth or demand for housing.

As the proposed project would not result in additional development or induce growth greater than what was considered in Certified EIR, the project would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts related to the inducement of 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).
(d) Would the proposed project displace substantial numbers of existing people or housing, necessitating the construction of replacement housing elsewhere? The proposed project would not exceed General Plan 2040 assumptions, and it would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts in relation to displacing people or housing. The Certified EIR found that the General Plan 2040 would result in less than significant impacts and would not displace substantial numbers of people or housing, as it would increase the overall number of dwelling units and incentivize housing development. As with the Certified EIR, the proposed project would result in less than significant impacts in relation to displacing substantial numbers of existing people or housing. The proposed project does not contain any provisions for removal of housing; rather, adoption of ODS would allow the City to utilize existing State legislation options for streamlining housing development. As described in Section 2, Project Description, adoption of ODS encourages streamlined housing production through SB 35, SB 6, and AB 2011. As such, the proposed project would not displace substantial numbers of existing people or housing but, rather, provide a benefit to housing in the community. Therefore, the proposed project would not result in new significant impacts or a substantial increase in the severity of previously identified significant impacts related to displacing substantial numbers of existing people or housing, necessitating the construction or replacement housing elsewhere.

Mitigation Measures
As with the Certified EIR, no mitigation measures have been identified related to land use or housing. No further mitigation measures are required.

Cumulative Impact Analysis
There are no new circumstances involving new impacts to land use or housing for the proposed project that were not previously analyzed in the Certified EIR. As evaluated in the Certified EIR, impacts from the physical division of an established community and from conflict with existing

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plans are not cumulative in nature; however, population growth and housing impacts can be cumulative in nature through direct and indirect effects. The Certified EIR determined that the General Plan 2040 would have a less than cumulatively considerable contribution to impacts on land use and housing. As discussed above, there would be no additional development or induce growth greater than what was considered in Certified EIR, and the proposed project would only apply toward the design of future multifamily and mixed-use development that has been planned in the General Plan 2040 and considered in the Certified EIR. Consistent with the findings of the Certified EIR, cumulative impacts to land use and housing would remain less than significant with implementation of the proposed project, when compared to the General Plan 2040. The proposed project would not result in a new significant cumulative impact or a substantial increase in the severity of previously identified significant cumulative impacts related to land use and housing.

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3.11 NOISE
This section evaluates the potential noise effects from the proposed project. This Addendum relies on and incorporates by reference the project setting and regulatory setting as described in Section

3.10, Noise, of the Certified EIR. Potential impacts are discussed relative to conclusions in the Certified EIR. The Certified EIR determined that implementation of the General Plan 2040 would result in less than significant impacts regarding the 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; and the generation of excessive groundborne vibration or groundborne noise levels.

The Certified EIR determined that there would be no impact regarding excessive noise level exposure due to public or private airport proximity. Consistent with the Certified EIR, noise generated from the proposed project was evaluated with regard to the City’s General Plan 2040 Noise Element; and Diamond Bar City Code Sections 8.12.530, 8.12.540, 8.12.720, and 8.12.840.

Based on a review of established local general plan or noise ordinance, or applicable standards of other agencies covering the project area, the regulatory framework for noise remains consistent with the Certified EIR.

3.11.1 Setting
The project setting for noise remains consistent with the setting considered in the Certified EIR.

3.11.2 Impact Analysis
Project Impact Analysis
The potential for the proposed project to result in a new significant impact or a substantial increase in the severity of previously identified significant impacts from noise was evaluated in relation to the following questions as stated in Appendix G of the State CEQA Guidelines. (a) Would the proposed 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 proposed project would not exceed General Plan 2040 assumptions, and it would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts in relation to the 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 Certified EIR found that impacts from traffic, construction, railway noise would be less than significant, and that stationary noise would be less than significant with adherence to General Plan 2040 policies. The application of the proposed project to future multifamily housing and mixed-use development would be subject to development review requirements and compliance with existing regulations that focus on improving noise, such as those in the City’s General Plan 2040 Noise Element; and Diamond Bar City Code Sections 8.12.530, 8.12.540, 8.12.720, and 8.12.840.

The proposed project does not propose new development and would not alter the land use designations and growth projections analyzed in the Certified EIR. The proposed project would not increase the overall development capacity or change the level of intensity that was the basis for the Certified EIR's analysis. Therefore, the proposed project would not result in a new significant

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impact or a substantial increase in the severity of previously identified significant impacts related to the 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.
(b) Would the proposed project result in generation of excessive groundborne vibration or groundborne noise levels?
The proposed project would not exceed General Plan 2040 assumptions, and it would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts in relation to the generation of excessive groundborne vibration or groundborne noise levels. The application of the ODS to future multifamily and mixed-use development within the City would be consistent with the construction phases, activities, and anticipated construction equipment outlined in the Certified EIR. Any change in construction noise from future multifamily housing and mixed-use development would be, therefore, negligible.

Compared to the Certified EIR, there would be no new groundborne vibration and noise during operations as the proposed project would not result in additional development beyond what is analyzed in the Certified EIR. The application of the proposed project to future multifamily housing and mixed-use development would be subject to development review requirements and compliance with existing regulations that focus on reducing noise and vibration.

The proposed project does not propose new development and would not alter the land use designations and growth projections analyzed in the Certified EIR. The proposed project would not increase the overall development capacity or change the level of intensity that was the basis for the Certified EIR's analysis. Therefore, the proposed project would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts related to an excessive generation of groundborne vibration or groundborne noise levels. (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 proposed project would not exceed General Plan 2040 assumptions, and it would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts in relation to a project located within an airport land use plan or within two miles of a public use airport or private airstrip. The Certified EIR confirmed that the City is not located within an airport land use plan or within two miles of a public use airport or private airstrip.

The City of La Verne hosts the closest airport, Brackett Field Airport, located approximately 3.5 miles from the northernmost boundary of the City.

As the proposed project would not result in additional development beyond the Certified EIR, or result in any new or additional growth within or near an airport land plan or within two miles of a public use airport or private airstrip area, the proposed project would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts related to excessive noise level exposure due to public or private airport proximity.

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Mitigation Measures
As with the Certified EIR, no mitigation measures have been identified related to noise. No further mitigation measures are required.

Cumulative Impact Analysis
There are no new circumstances involving new impacts to noise for the proposed project that were not previously analyzed in the Certified EIR. The Certified EIR determined that General Plan 2040 would result in less than significant cumulative impacts regarding the 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; and an excessive generation of groundborne vibration or groundborne noise levels.

Consistent with the findings of the Certified EIR, cumulative impacts to noise would remain less than significant with the implementation of the proposed project, as it is a set of design standards that does not contain provisions for additional development beyond what was evaluated in the Certified EIR. Therefore, the proposed project would not result in a new significant cumulative impact or a substantial increase in the severity of previously identified significant cumulative impacts in relation to noise.

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3.12 PUBLIC FACILITIES AND RECREATION
This section evaluates the potential impacts on public facilities and recreation from the proposed project. This Addendum relies on and incorporates by reference the project setting and regulatory setting as described in Section, 3.11, Public Facilities and Recreation, of the Certified EIR.

Potential impacts to public services from the proposed project are discussed relative to the conclusions in the Certified EIR. The Certified EIR for the General Plan 2040 concluded that impacts on fire protection, police protection, schools, parks, and other public facilities would be less than significant due to compliance with existing regulations, General Plan policies, and the concentration of growth in areas already served by infrastructure. Consistent with the Certified EIR, public services for the proposed project were evaluated based on a review of the Los Angeles County General Plan, the Los Angeles County Code of Ordinances, and the Los Angeles County Fire Department Fuel Modification Plans and Wildlife Action Plan, the City of Diamond Bar Sheriff’s Office, and the websites for the Pomona Unified School District (PUSD) and the Walnut Valley Unified School District (WVUSD). Review of available records and literature determined that no new information of substantial importance was identified that was not known at the time of the certification of the Certified EIR.

3.12.1 Setting
The project setting for public services and recreation remain consistent with those considered in the Certified EIR.

3.12.2 Impact Analysis
Project Impact Analysis
The potential for the proposed project to result in a new significant impact or a substantial increase in the severity of previously identified significant impacts to public facilities and recreation was evaluated in relation to the following questions as stated in Appendix G of the 2025 CEQA Guidelines.
(a) Would the proposed project result in substantial adverse physical impacts associated with the provision of new or physically altered government facilities, need for new or physically altered government 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:
i. Fire protection?
The proposed project would not exceed General Plan 2040 assumptions, and it would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts in relation to substantial adverse physical impacts associated with the provision of, or need for, new or physically altered fire protection facilities. The Certified EIR determined that the anticipated population increase associated with the General Plan 2040 would not necessitate the construction of new fire stations, as new development anticipated by the General Plan 2040 would be efficiently located within three miles of existing stations, and new policies would reduce the need for new facilities. As stated in Section 3.10, Land Use and Housing, the proposed project does not propose new development, increase development capacity, change land use designations, extend utility infrastructure or roads, nor include provisions for new businesses. As such, the proposed project would not increase the projected

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population or housing units that generate service demand. The proposed project, which sets ODS that regulate building design and site layout (e.g., parking, frontage), is subordinate to the Los Angeles County Fire Code and the City’s emergency response protocols. The proposed project must satisfy mandatory requirements regarding building materials, fire flow, and minimum dimensions for emergency vehicle access and turning radius. The proposed project would not compromise the Fire Department’s ability to maintain acceptable response times or service ratios.

Therefore, the proposed project would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts related to substantial adverse physical impacts associated with the provision of, or need for, new or physically altered fire protection facilities.
ii. Police protection?
The proposed project would not exceed General Plan 2040 assumptions, and it would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts in relation to substantial adverse physical impacts associated with the provision of, or need for, new or physically altered police protection facilities. The Certified EIR determined that the anticipated population increase associated with the General Plan 2040 would not necessitate the construction of new police stations, as new development anticipated by the General Plan 2040 would be efficiently located within three miles of existing stations, and new policies would reduce the need for new facilities. As stated in Section 3.10, Land Use and Housing, the proposed project does not propose new development, increase development capacity, change land use designations, extend utility infrastructure or roads, nor include provisions for new businesses. As such, the proposed project would not increase the projected population or housing units that generate service demand. Therefore, implementation of the proposed project would not result in the need to construct new, or to physically alter existing, police protection facilities to maintain acceptable services. The design elements of the proposed project, such as requirements for enhanced pedestrian visibility, active frontages, and parking placement (Principle 8), could potentially improve Crime Prevention Through Environmental Design (CPTED) principles, which may reduce calls for service in new developments. The proposed project is expected to result in better-designed, safer environments without increasing the demand placed upon the Los Angeles County Sheriff’s Department beyond the levels previously determined to be acceptable. Therefore, the proposed project would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts related to substantial adverse physical impacts associated with the provision of, or need for, new or physically altered police protection facilities. iii. Schools?
The proposed project would not exceed General Plan 2040 assumptions, and it would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts in relation to substantial adverse physical impacts associated with the provision of, or need for, new or physically altered school facilities. The Certified EIR’s analysis of the Diamond Bar public school system projected a net decline in student enrollment rates between 2017 and 2040, despite the addition of up to 3,264 new housing units. No new school facilities were required. The proposed project applies to multi-family residential and mixed-use units, but it does not increase the total number of units beyond the General Plan's scope. As stated in Section 3.10, Land Use and Housing, the proposed project does not propose new development, increase development capacity, change land use designations, extend utility infrastructure or roads, nor include provisions for new businesses. As such, the proposed project would not increase the projected population or housing units that generate service demand. Thus,

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the demographic trends in the General Plan 2040 and the resulting determination that no new school facilities would be required remain valid. The proposed project would not affect the number of students generated or the service standards of the school district. Therefore, the proposed project would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts related to substantial adverse physical impacts associated with the provision of, or need for, new or physically altered school facilities. iv. Parks?
The proposed project would not exceed General Plan 2040 assumptions, and it would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts in relation to substantial adverse physical impacts associated with the provision of, or need for, new or physically altered park facilities. The Certified EIR concluded that impacts to parks would be less than significant because the General Plan 2040 would improve the citywide parkland ratio (to 2.77 acres per 1,000 residents) and would utilize existing park dedication and fee ordinances. As stated in Section 3.10, Land Use and Housing, the proposed project does not propose new development, increase development capacity, change land use designations, extend utility infrastructure or roads, nor include provisions for new businesses. As such, the proposed project would not increase the projected population or housing units that generate service demand. The proposed project would not affect the number of residents or the park service standards of the City. Additionally, the proposed project establishes ODS that would require new multifamily and mixed-use projects to incorporate various forms of on-site private recreational open space (e.g., courtyards, common areas). The proposed project would minimize the demand placed on public parks by requiring high-quality, private recreational amenities within the new development projects. Specifically, the proposed project contains standards that are designed to encourage architectural diversity and ensure all buildings contribute to an active public realm while providing private outdoor amenities such as gardens, courtyards, and porches, where appropriate. The provision of these functional, on-site, private recreational spaces would lessen the demand on existing public neighborhoods and regional parks generated by residents, thereby protecting the service ratios and physical integrity of the public park system. Therefore, the proposed project would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts related to substantial adverse physical impacts associated with the provision of, or need for, new or physically altered park facilities. v. Other public facilities?
The proposed project would not exceed General Plan 2040 assumptions, and it would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts on other public facilities. As stated in Section 3.10, Land Use and Housing, the proposed project does not propose new development, increase development capacity, change land use designations, extend utility infrastructure or roads, nor include provisions for new businesses. As such, the proposed project would not increase the projected population or housing units that generate service demand. The proposed project would not affect the number of residents or the service standards of the City. The proposed project would not influence the operational needs, staffing levels, or physical requirements of other public facilities, such as administrative or library facilities. The proposed project does not increase the projected growth, therefore, the demand for other public facilities remains consistent with the assumptions in the Certified EIR. Therefore, the proposed project would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts related to substantial adverse physical impacts associated with the provision of, or need for, new or physically altered public facilities.

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(b) Would the proposed project increase the use of existing neighborhood and regional parks or other recreational facilities such that substantial physical deterioration of the facility would occur or be accelerated?
The proposed project would not exceed General Plan 2040 assumptions, and it would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts in relation to the substantial physical deterioration of recreational facilities. The Certified EIR determined that impacts related to substantial physical deterioration of recreational facilities would be significant and unavoidable, as the potential increase in population anticipated by the General Plan 2040 could place additional physical demands on existing parks. The potential increase in population has the potential to increase the use of vital park elements such as vegetation, built structures, paths, and sport facilities, resulting in increased wear and tear and a shortened lifespan.

However, the implementation of the proposed project would not accelerate the physical deterioration of recreational facilities because the proposed project would not increase the City’s population or growth rate beyond the levels analyzed in the Certified EIR (please see Section

3.10, Land Use and Housing). Moreover, the proposed project establishes ODS that would require new multifamily and mixed-use projects to incorporate various forms of high-quality, on-site, private outdoor amenities such as gardens, courtyards, and porches, where appropriate. This would ensure that new residents have immediate and attractive recreational options within their own development. By providing functional, well-designed private recreational space, the proposed project would disperse and absorb recreational usage that might otherwise fall onto public parks, supporting the longevity of existing neighborhood and regional parks and decreasing the severity of the significant impact identified in the Certified EIR. Therefore, the proposed project would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts related to the substantial physical deterioration of recreational facilities.
(c) Does the proposed project include recreational facilities or require the construction or expansion of recreational facilities which might have an adverse physical effect on the environment?
The proposed project would not exceed General Plan 2040 assumptions, and it would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts in relation to the construction or expansion of recreational facilities. The Certified EIR found that new park developments required to serve the General Plan’s anticipated growth could result in adverse physical effects, including conversion of habitat, water pollution during construction, increased noise levels, and an increase in impermeable surfaces. However, the Certified EIR determined that with compliance with existing regulations and General Plan 2040 policies, the overall impact would be less than significant. The proposed project does not include or require the construction or expansion of any public recreational facilities (e.g., new public parks, public sports fields). The proposed project is a set of ODS that would include the incorporation of private recreational facilities (e.g., internal courtyards, communal plazas, and gardens) as features of new multifamily residential and mixed-use developments. Consistent with the Certified EIR, impacts associated with new recreation facilities would be less than significant with implementation of existing regulations and proposed General Plan policies. Additionally, new developments and associated private recreational spaces would be subject to project-specific CEQA requirements for environmental assessment. Therefore, the proposed project would not

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result in a new significant impact or a substantial increase in the severity of previously identified significant impacts related to construction or expansion of recreational facilities.

Mitigation Measures
As with the Certified EIR, no mitigation measures have been identified related to public facilities and recreation. No further mitigation measures are required.

Cumulative Impact Analysis
There are no new circumstances involving new impacts to public facilities or recreation for the proposed project that were not previously analyzed in the Certified EIR. The Certified EIR determined that the General Plan 2040 would not result in cumulatively considerable adverse impacts to fire stations, police stations, schools, or other public facilities. However, the Certified EIR determined that the project population growth may result in a cumulatively considerable impact on parkland due to the overuse and degradation of existing park facilities, as the General Plan 2040 would not provide sufficient park access to all residents. Elements of the proposed General Plan 2040 were designed to minimize potentially cumulatively considerable environmental impacts of new development, including developing sustainable park and recreational facility design and planning standards. The proposed project is an architectural and functional design overlay that regulates the visual quality and on-site amenities of new development. As stated in Section 3.10, Land Use and Housing, the proposed project does not propose new development, increase development capacity, change land use designations, extend utility infrastructure or roads, nor include provisions for new businesses. As such, the proposed project would not increase the projected population or housing units that generate service demand. The proposed project would also not affect the number of residents or the service standards of the City, and it does not introduce any new demand for public services that was not already accounted for in the Certified EIR. The proposed project is an implementing tool that regulates the design of development already assessed in the Certified EIR. Further, the proposed project contains provisions that functionally reduce stress on public park resources due to the provision of private on-site amenities such as courtyards, plazas, and gardens. The proposed project thereby would reduce the overuse and degradation of existing public park facilities that was found in the Certified EIR. Therefore, the proposed project would not result in a new significant cumulative impact or a substantial increase in the severity of previously identified significant cumulative impacts to fire stations, police stations, schools, parks, or other public facilities.

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3.13 TRANSPORTATION
This section evaluates the effects on transportation from the proposed project. This Addendum relies on and incorporates by reference a project setting and regulatory setting as described in Section 3.12, Transportation, of the Certified EIR. Potential impacts to transportation from the proposed project are discussed relative to conclusions in the Certified EIR. The Certified EIR determined that impacts related to conflict or inconsistency with State CEQA Guidelines Section 15064.3(b) would be significant and unavoidable, with no feasible mitigation available to reduce these impacts to a less than significant level. The Certified EIR determined that impacts related to conflicts with applicable plans, substantial increases in hazards due to a geometric design feature, and inadequate emergency access would be less than significant. Consistent with the Certified EIR, transportation impacts from the proposed project were evaluated with regard to the General Plan 2040.

3.13.1 Setting
A review of available records and literature determined that no new information of substantial importance was identified that was not known at the time of the certification of the Certified EIR.

Thus, the project setting for transportation is consistent with the setting considered in the Certified EIR.

3.13.2 Impact Analysis
Project Impact Analysis
The potential for the proposed project to result in a new significant impact or a substantial increase in the severity of previously identified significant impacts to transportation was evaluated in relation to the following questions as stated in Appendix G of the State CEQA Guidelines:
(a) Would the proposed project conflict with a program, plan, ordinance or policy addressing the circulation system, including transit, roadway, bicycle and pedestrian facilities? The proposed project would not exceed General Plan 2040 assumptions, and it would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts in relation to a conflict with a program, plan, ordinance, or policy addressing the circulation system, including transit, roadway, bicycle, and pedestrian facilities. The proposed project would set new minimum design standards for future multifamily and mixed-use development throughout the City (see Section 2.2). These new minimum design standards would work in tandem with City regulations related to transportation and traffic, including Title 22 of the City’s Development Code and General Plan 2040. Application of the proposed project to future multifamily and mixed-use development would be subject to project-specific development review requirements and compliance with existing regulations that focus on improving transportation and traffic.

As the proposed project would not result in additional development beyond what was considered in the Certified EIR, the proposed project would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts related to any conflicts with a program, plan, ordinance or policy addressing the circulation system, including transit, roadway, bicycle, and pedestrian facilities.

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(b) Would the proposed project conflict or be inconsistent with CEQA Guidelines § 15064.3, subdivision (b)?
The proposed project would not exceed General Plan 2040 assumptions, and it would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts in relation to a conflict or inconsistency with State CEQA Guidelines Section 15064.3(b). The Certified EIR found that the implementation of the General Plan 2040 would increase both resident and employee VMT per capita on a citywide basis, even with the City’s goals and policies to reduce potential impacts. State CEQA Guidelines Section 15064.3(b) denotes criteria for the analysis of transportation impacts; specifically, the change in VMT as a result of a project. According to State CEQA Guidelines Section 15064.3(a), VMT refers to “the amount and distance of automobile travel attributable to a project.”17 The proposed project is a design overlay that works within the regulatory framework and cumulative growth assumptions of the Certified EIR and would not add more vehicles compared to the Certified EIR; thus, there would be no increase in VMT as a result of the proposed project. According to Principle 4, the ODS aim to “support multi-modal development and mobility.” Multi-modal development and mobility rely on expanding travel mode choice, which “will help to promote business, provide access to opportunity, and improve the quality of life across our state.”18 Expanding travel mode choices helps to decrease overall VMT because of the availability of greater travel options (e.g., bicycles, ride-hailing services). Section 5.12 of the ODS (Appendix A) provides short-term guidelines regarding bicycle parking standards for site and open space standards. Therefore, there would be no conflict with State CEQA Guidelines Section 15064.3(b). As mentioned in Section 3.13, the application of the proposed project to future multifamily housing and mixed-use development would be subject to development review requirements and compliance with existing regulations that focus on improving transportation and traffic.

As there would be no increase in VMT from the application of the proposed project to future multifamily and mixed-use development, the proposed project would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts previously identified in the Certified EIR as it relates to CEQA Guideline Section 15064.3, Subdivision (b).
(c) Would the proposed project substantially increase hazards due to a geometric design feature (e.g., sharp curves or dangerous intersections) or incompatible uses (e.g., farm equipment)?
The proposed project would not exceed General Plan 2040 assumptions, and it would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts in relation to substantial increase in hazards due to a geometric design feature or incompatible uses. The Certified EIR found that impacts regarding an increase in hazards due to a design feature or incompatible uses would be less than significant with adherence to General Plan 2040 policies. As discussed in Section 3.13, the proposed project would set new minimum design standards for future multifamily and mixed-use development throughout the City (see Section 2.2) and would work in tandem with City regulations related to transportation and traffic, including Title 22 of the City’s Development Code and General Plan 2040. The application of the 17 California Association of Environmental Professionals. January 2025. 2025 California Environmental Quality Act (CEQA) Statute and Guidelines. https://www.califaep.org/docs/CEQA_Handbook_2025combined.pdf (accessed October 29, 2025).
18 State of California: Governor’s Office of Land Use and Planning. 2025. CEQA: Transportation Impacts (SB 743). https://lci.ca.gov/ceqa/sb-743/ (accessed October 29, 2025).

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proposed project to future multifamily housing and mixed-use development would be subject to development review requirements and compliance with existing regulations that focus on improving transportation and traffic.

Specifically, Principle 8 of the ODS would “provide off-street parking in surface lots or garages at the rear of buildings so that parking does not dominate the built environment,” thereby, reducing incompatible land uses in the City. In addition, Principle 2 of the ODS would “ensure that streets and spaces with high volumes of pedestrian traffic are comfortable ... and physically engaging at the ground level.” Furthermore, no sharp curves or dangerous intersections would be included as part of the proposed project.

As the proposed project would not result in additional development beyond what was considered in the Certified EIR, the proposed project would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts related to an increase in hazards due to a design feature or incompatible uses. (d) Would the project result in inadequate emergency access? The proposed project would not exceed General Plan 2040 assumptions, and it would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts in relation to inadequate emergency access. The Certified EIR found that impacts would be less than significant, as inadequate emergency access would not occur with adherence to General Plan 2040 policies. The proposed project would not add more vehicles compared to the Certified EIR. As such, the proposed project would not contribute to congestion and, therefore, not inhibit emergency access to future multifamily housing and mixed-use developments in the case of an emergency. In addition, the proposed project would not result in greater multifamily housing and mixed-use density and would not result in a greater need for emergency response, compared to the Certified EIR. While the proposed project would not adversely affect the emergency access system, all future multifamily housing and mixed-use development subject to the proposed project would continue to be subject to development review requirements and compliance with existing regulations that focus on improving transportation and traffic, including Title 22 of the City’s Development Code and the General Plan 2040. The proposed project would not result in additional development beyond what was considered in the Certified EIR. As there would be no additional development, there would be no additional vehicles added as a result of the proposed project. Therefore, the proposed project would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts related to inadequate emergency access.

Mitigation Measures
As with the Certified EIR, no mitigation measures have been identified related to transportation.

No further mitigation measures are required.

Cumulative Impact Analysis
There are no new circumstances involving new impacts to transportation for the proposed project that were not previously analyzed in the Certified EIR. The Certified EIR found that, as a result of the amount of development anticipated by the General Plan 2040, the travel demand and VMT was the cumulative condition for CEQA purposes. Under the General Plan 2040 cumulative scenario, VMT was expected to increase compared to existing conditions. Per CEQA Guidelines Section 15064.3, this constitutes a considerable contribution to the significant impact regarding

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VMT. However, the General Plan 2040 would result in a less than cumulatively considerable contribution towards conflicts with programs and plans that address the circulation system given that the proposed General Plan includes multiple policies that improve multi-modal mobility and would expand the existing bicycle and pedestrian facilities while accommodating vehicle traffic.

Additionally, the proposed General Plan 2040 would have a less than cumulatively considerable impact on hazards and emergency access. The proposed project would not create new or substantially more adverse significant impacts related to the cumulative transportation impacts from those previously disclosed in the Certified EIR. The proposed project would not increase population, change land uses, or otherwise add more vehicles to the road; therefore, it would not increase VMT beyond levels previously analyzed in the Certified EIR. With respect to conflict with adopted policies, plans, ordinances, or programs; hazardous design features; and inadequate emergency access, the proposed project’s impacts would be negligible. Therefore, the proposed project would not result in a new significant cumulative impact or a substantial increase in the severity of previously identified significant cumulative impacts related to transportation.

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3.14 TRIBAL CULTURAL RESOURCES
This section evaluates the potential environmental effects on tribal cultural resources from the proposed project. This Addendum relies on and incorporates by reference the project setting and regulatory setting as described in Section 3.4, Cultural, Historic, and Tribal Cultural Resources, of the Certified EIR. Potential impacts to tribal cultural resources from the proposed project are discussed relative to the conclusions in the Certified EIR. The Certified EIR determined that the implementation of the General Plan 2040 would result in less than significant impacts to tribal cultural resources.

3.14.1 Setting
The environmental setting for tribal cultural resources is consistent with what was described in the Certified EIR. As discussed in the Certified EIR, no tribal cultural resources have yet been recorded within the City. The regulatory setting applicable to tribal cultural resources presented in the Certified EIR, including the California Register of Historic Resources, AB 52, SB 18, and all applicable state and local regulations are the same and apply to the proposed project.

3.14.2 Impact Analysis
Project Impact Analysis
The potential for the proposed project to result in a new significant impact or a substantial increase in the severity of previously identified significant impacts on tribal cultural resources was evaluated in relation to the following questions as stated in Appendix G of the 2025 CEQA Guidelines.
(a) Would the proposed project cause a substantial adverse change in the significance of a tribal cultural resource, defined in Public Resources Code § 21074 as either a site, feature, place, cultural landscape that is geographically defined in terms of the size and scope of the landscape, sacred place, or object with cultural value to a California Native American tribe, and that is:
i. Listed or eligible for listing in the California Register of Historical Resources, or in a local register of historical resources as defined in Public Resources Code section 5020.1(k), or
ii. A resource determined by the lead agency, in its discretion and supported by substantial evidence, to be significant pursuant to criteria set forth in subdivision (c) of Public Resources Code § 5024.1. In applying the criteria set forth in subdivision (c) of Public Resource Code § 5024.1, the lead agency shall consider the significance of the resource to a California Native American tribe.

The proposed project would not exceed General Plan 2040 assumptions, and it would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts in relation to tribal cultural resources. The Certified EIR determined that impacts would be less than significant. As discussed in the Certified EIR, no tribal cultural resources have been recorded within the City. However, it is possible that future development could result in discovery of yet unrecorded tribal cultural resources. Implementation of state and local regulatory guidelines pertaining to tribal cultural resources, such as AB 52 that would require Native American consultation to identify and mitigate potential adverse effects to tribal cultural resources, would reduce potential adverse effects to less than significant. The proposed project

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is intended to regulate visual design and would have no effect on tribal cultural resources beyond those effects previously evaluated in the Certified EIR. Further, consistent with the Certified EIR, regulatory compliance with state and local regulatory guidelines would ensure that impacts would be less than significant for the proposed project. Therefore, the proposed project would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts related to tribal cultural resources.

Mitigation Measures
As with the Certified EIR, no mitigation measures have been identified related to tribal cultural resources. No further mitigation measures are required.

Cumulative Impact Analysis
There are no new circumstances involving new impacts to land use or housing for the proposed project that were not previously analyzed in the Certified EIR. As evaluated in the Certified EIR, cumulative impacts to tribal cultural resources would not be cumulatively considerable with implementation of AB 52 involving consultation with Native American tribes to establish development processes that avoid or mitigate adverse impacts to tribal cultural resources.

Therefore, the proposed project’s contribution to cumulative impacts of tribal cultural resources is not cumulatively considerable. The proposed project would not result in a new significant cumulative impact or a substantial increase in the severity of previously identified significant cumulative impacts related to tribal cultural resources.

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3.15 UTILITIES AND SERVICE SYSTEMS
This section evaluates the effects on utilities and service systems from the proposed project. This Addendum relies on and incorporates by reference the project setting and regulatory setting as described in Section 3.13, Utilities and Service Systems, of the Certified EIR. Consistent with the Certified EIR, utilities and service systems for the proposed project were evaluated with regard to the Los Angeles County General Plan, Los Angeles County Code, the GLACR IRWM, the Walnut Valley Water District UMWP and the Diamond Bar City Code.

3.15.1 Setting
The physical and regulatory environmental setting for utilities and service systems is the same as described in the Certified EIR. The proposed project does not alter the physical or regulatory conditions described in the Certified EIR.

3.15.2 Impact Analysis
Project Impact Analysis
The potential for the proposed project to result in a new significant impact or a substantial increase in the severity of previously identified significant impacts to utilities and service systems was evaluated in relation to the following questions as stated in Appendix G of the State CEQA Guidelines.
(a) Would the proposed project require or result in the relocation or construction of new or expanded water, wastewater treatment or storm water drainage, electric power, natural gas, or telecommunications facilities, the construction or relocation of which could cause significant environmental effects?
The proposed project would not exceed General Plan 2040 assumptions, and it would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts in relation to the relocation or construction of new or expanded utilities and service systems. Implementation of the ODS would not increase demand for utilities or service systems because it would not increase the number of residences or commercial development in the City. All future multifamily and mixed-use development that would be subject to the ODS are already anticipated under the General Plan 2040 and analyzed in the Certified EIR. As such, the proposed project would not require the expansion of utilities or service systems as it would not increase overall service demand beyond the General Plan’s projections. Therefore, the proposed project would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts in relation to the construction of new or expanded utilities and service systems.
(b) Would the proposed project have sufficient water supplies available to serve the project and reasonably foreseeable future development during normal, dry and multiple dry years?
The proposed project would not exceed General Plan 2040 assumptions, and it would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts in relation to sufficient water supplies. The Certified EIR determined that the Walnut Valley Water District, which serves the Planning Area, has sufficient water supply (per its

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UWMP) to meet the projected demand from the full buildout of the General Plan 2040 during normal, dry, and multiple dry years, resulting in a less than significant impact.

As the proposed project would not increase the number of housing units or commercial development beyond that which was analyzed in the Certified EIR, the proposed project would not add any new, unanalyzed demand on water supplies. Therefore, the proposed project would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts in relation to water supplies. (c) Would the proposed project result in a determination by the wastewater treatment provider, which serves or may serve the project that it has adequate capacity to serve the project’s projected demand in addition to the provider’s existing commitments? The proposed project would not exceed General Plan 2040 assumptions, and it would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts in relation to wastewater treatment capacity. The Certified EIR concluded that the wastewater treatment provider, the Los Angeles County Sanitation Districts, has adequate capacity to serve the projected increase in demand resulting from the full buildout of the General Plan 2040. The proposed project would not generate new wastewater flow beyond the amount projected in the General Plan 2040 and Certified EIR. Therefore, the proposed project would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts in relation to wastewater treatment capacity. (d) Would the proposed project generate solid waste in excess of state or local standards, or in excess of the capacity of local infrastructure, or otherwise impair the attainment of solid waste reduction goals?
The proposed project would not exceed General Plan 2040 assumptions, and it would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts in relation to the generation of solid waste. The Certified EIR determined that the projected increase in solid waste generation from the General Plan 2040 buildout would not exceed local infrastructure capacity or impair reduction goals, due to mandatory compliance with state laws (e.g., AB 341, AB 1826, SB 1383) that require source reduction and recycling.

As the proposed project would not increase the number of housing units or commercial development beyond the that which was analyzed in the Certified EIR, the proposed project would not generate any additional solid waste. Therefore, the proposed project would not result in a new significant impactor a substantial increase in the severity of previously identified significant impacts in relation to the generation of solid waste.
(e) Would the proposed project comply with federal, state, and local management and reduction statutes and regulations related to solid waste? The proposed project would not exceed General Plan 2040 assumptions, and it would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts in relation to compliance with solid waste statutes and regulations. The proposed project does not contain any provision that contradicts or overrides mandatory federal, state, or local statutes governing solid waste management (such as SB 1383). Therefore, the proposed project would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts in relation to compliance with solid waste statutes and regulations.

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Mitigation Measures
As with the Certified EIR, no mitigation measures have been identified related to utilities and service systems. No further mitigation measures are required.

Cumulative Impact Analysis
The implementation of the proposed project would not result in or contribute to a cumulative utilities and service systems impact. This conclusion is based on the function of the ODS as a design overlay that works within the regulatory framework and cumulative growth assumptions of the Certified EIR. The Certified EIR analyzed the cumulative impacts of full buildout under the General Plan 2040, which includes the maximum demand for utilities and service systems in the City. The Certified EIR concluded that the cumulative impacts to utilities and service systems would not be cumulatively considerable. Therefore, the proposed project would not result in a new significant cumulative impact or a substantial increase in the severity of previously identified significant cumulative impacts in relation to utilities and service systems.

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3.16 WILDFIRE
This section discusses the effects on wildfire from the proposed project. This Addendum relies on and incorporates by reference the project setting and regulatory setting as described in Section

3.7, Hazards, Hazardous Materials, and Wildfire, of the Certified EIR. Potential impacts to wildfire from the proposed project are discussed relative to conclusions in the Certified EIR. The Certified EIR determined that the implementation of the General Plan 2040 would result in less than significant wildfire impacts, with no mitigation measures required. Consistent with the Certified EIR, wildfire for the proposed project was evaluated with regard to the General Plan 2040 and the California Department of Forestry and Fire Protection (Cal FIRE) Fire Hazard Severity Zone (FHSZ) maps.

3.16.1 Setting
As previously described, the project setting for wildfire is the same as that considered in the Certified EIR. A review of available records and literature determined that new wildfire information has become available since the certification of the EIR, including: (1) a March 2025 update to Cal FIRE’s FHSZ maps based on revised wildfire modeling and climate data, and updated risk assessments; and (2) development standards ingrained under Title 32 – the County of Los Angeles Fire Code, which incorporates the California Fire Code. The Certified EIR found that FHSZs are present in several locations throughout the City but are confined exclusively to those areas that the General Plan 2040 designates for open and rural residential land uses. However, based on review of the March 2025 CAL FIRE FHSZ maps, the study area contains lands classified as Very High FHSZ (VHFHSZ) and a Local Responsibility Area (LRA).19

3.16.2 Impact Analysis
Project Impact Analysis
The potential for the proposed project to result in a new significant impact or a substantial increase in the severity of previously identified significant impacts to wildfire was evaluated in relation to the following questions as stated in Appendix G of the 2025 CEQA Guidelines.

If located in or near state responsibility areas (SRAs) or lands classified as VHFHSZs, would the proposed project:
(a) Substantially impair an adopted emergency response plan or emergency evacuation plan?
The proposed project would not exceed General Plan 2040 assumptions, and it would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts in relation to substantially impairing an adopted emergency response plan or emergency evacuation plan. The Certified EIR found that the General Plan 2040 would result in less than significant impacts in relation to applicable adopted emergency response plans or emergency evacuation plans through compliance with existing local programs, regulations, and 19 California Department of Forestry and Fire Protection (Cal FIRE) Office of the State Marshall. 2025. Find Your Fire Hazard Severity Zone (FHSZ). https://osfm.fire.ca.gov/what-we-do/community-wildfire-preparedness-andmitigation/fire-hazard-severity-zones (accessed November 5, 2025).

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General Plan 2040 policies. The City is located within lands classified as VH FHSZ and an LRA.20 The future multifamily and mixed-use developments that would be subject to the proposed project would also be subject to project-specific development review requirements and compliance with existing wildfire-based regulations, including Title 32 of the County Fire Code, Cal FIRE’s FHSZ maps, and the General Plan 2040 (e.g., policies PS-P-16 and PS-P-23 to ensure minimal development intensification within or around VHFHSZs). Future multifamily and mixed-use development would also need to assess, as part of development review requirements, consistency with the County’s disaster routes21 and the Diamond Bar Local Hazard Mitigation Plan.22 The proposed project does not introduce any elements or changes to primary circulation that would physically interfere with designated emergency evacuation routes. As discussed in Section 3.13, Transportation, the proposed project would not result in greater multifamily housing and mixed-use density and would not result in a greater need for emergency response nor increase congestion, compared to the Certified EIR. Therefore, the proposed project would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts related to substantial impairment of an adopted emergency response plan or emergency evacuation plan.
(b) Due to slope, prevailing winds, and other factors, exacerbate wildfire risks, and thereby expose project occupants to pollutant concentrations from a wildfire or the uncontrolled spread of a wildfire?
The proposed project would not exceed General Plan 2040 assumptions, and it would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts in relation to exacerbating wildfire risks and exposing occupants to wildfire hazards. The Certified EIR found that the General Plan 2040 would result in less than significant impacts, as intensive development is not expected to occur in or around SRAs or VHFSZs, and compliance with existing local programs, regulations, and General Plan 2040 policies would ensure that impacts would be less than significant. The proposed project would set new minimum design standards for future multifamily and mixed-use development throughout the City (see Section 2, Project Description) and would not change the land uses established in the General Plan 2040 and considered in the Certified EIR. Differing from the Certified EIR, multifamily and mixed-use development may occur in or around SRAs or VHFSZs. However, consistent with the Certified EIR, the future multifamily and mixed-use development subject to the proposed project would continue to be subject to project-specific development review requirements and compliance with existing regulations, which would reduce impacts associated with wildfire risks from slope, prevailing winds, and other factors to be below the level of significance.

Accordingly, the proposed project would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts related to slope, prevailing winds, and other factors, exacerbating wildfire risk.

20 California Department of Forestry and Fire Protection (Cal FIRE) Office of the State Marshall. 2025. Find Your Fire Hazard Severity Zone (FHSZ). https://osfm.fire.ca.gov/what-we-do/community-wildfire-preparedness-andmitigation/fire-hazard-severity-zones (accessed November 5, 2025). 21 County of Los Angeles. N.d. Disaster Route Maps (by City): Area D – Diamond Bar. https://dpw.lacounty.gov/dsg/DisasterRoutes/city.cfm (accessed November 5, 2025) 22 City of Diamond Bar. 2022. 2022 Hazard Mitigation Plan. https://www.diamondbarca.gov/DocumentCenter/View/10286/Diamond-Bar-Local-Hazard-Mitigation-Plan2022?bidId= (accessed November 20, 2025).

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(c) Require the installation or maintenance of associated infrastructure (such as roads, fuel breaks, emergency water sources, power lines or other utilities) that may exacerbate fire risk or that may result in temporary or ongoing impacts to the environment? The proposed project would not exceed General Plan 2040 assumptions, and it would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts in relation to the installation or maintenance of infrastructure that may exacerbate fire risk. The Certified EIR found that the General Plan 2040 would result in less than significant impacts, as infrastructure development of the General Plan 2040 would be located away from SRAs and VHFSZs, and General Plan 2040 policies serve to mitigate wildfire risk. The City contains lands classified as VHFHSZs and an LRA, and the proposed project has the potential to apply to development in these areas. However, consistent with the Certified EIR, “should development occur in or around State Responsibility Areas or VHFSZs, components of the [General Plan 2040] serve to mitigate wildfire risk, and would thus keep the construction of additional infrastructure needed to combat fire to a minimum.”23 Specifically, the Certified EIR found that the following General Plan 2040 policies would address risks associated with wildfire exposure: Policies PS-G-3, PS-P-14, PS-P-16, PS-P-17, PS-P-18, PS-P-19, PS-P-20, PS-P-22, PS-P-23, PS-P-32, PS-P-33, LU-G-2, LU-G-4, LU-P-2, LU-G-28, and LU-P-56.24 The future multifamily and mixed-use development subject to the proposed project would also be subject to project-specific development review requirements and compliance with existing regulations.

Furthermore, the proposed project is a set of design standards and would not include new roads, fuel breaks, emergency water sources, power lines, or other utilities compared to the Certified EIR.

Therefore, the proposed project would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts related to requiring the installation or maintenance of associated infrastructure (such as roads, fuel breaks, emergency water sources, power lines or other utilities) that may exacerbate fire risk or that may result in temporary or ongoing impacts to the environment.
(d) Expose people or structures to significant risks, including downslope or downstream flooding or landslides, as a result of runoff, post-fire slope instability, or drainage changes? The proposed project would not exceed General Plan 2040 assumptions, and it would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts in relation to exposing people or structures to significant risks as a result of runoff, postfire slope instability, or drainage changes. The Certified EIR determined that the General Plan 2040 would result in less than significant impacts through compliance with existing local programs, regulations, and General Plan 2040 policies. The future multifamily and mixeduse development that would be subject to the proposed project would continue to be subject to project-specific development review requirements and compliance with existing regulations. As discussed in Section 3.9, Hydrology and Water Quality, LID development practices as regulated by local ordinances and MS4 Permit (Order No. R4-2012-0175) would help manage the runoff rate and volume to prevent new flooding, regardless of the architectural style required by the proposed project. All future development would be subject to the provisions of CEQA inclusive of 23 City of Diamond Bar. 2019. Diamond Bar Comprehensive General Plan Update and Climate Action Plan Draft Environmental Impact Report. P. 3.7-5. https://ceqanet.opr.ca.gov/2018051066/2 24 City of Diamond Bar. 2019. Diamond Bar General Plan 2040. https://www.diamondbarca.gov/DocumentCenter/View/7072/Diamond-Bar-General-Plan-2040?bidId= (accessed November 5, 2025).

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additional survey, design, and engineering and would be required to abide by city, state, and federal regulations. As discussed in Section 3.6, Geology, Soils, and Seismicity, future development subject to the proposed project would not expose people or structures to landslides since these future developments would not be located within steep hillsides in the City, which are areas that can produce landslides. Additionally, comprehensive geotechnical reporting and compliance with the design provisions of the CBC and General Plan 2040 policies for hillside development would be required for all future development subject to the proposed project. As such, consistent with the Certified EIR, future development subject to the proposed project would comply with existing local programs, regulations, and General Plan 2040 policies such that people or structures would not be exposed to significant risks.

Therefore, the proposed project would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts related to exposing people or structures to significant risks as a result of runoff, post-fire slope instability, or drainage changes.

Mitigation Measures
As with the Certified EIR, no mitigation measures have been identified related to wildfire. No further mitigation measures are required.

Cumulative Impact Analysis
There are no new circumstances involving new impacts to wildfire for the proposed project that were not previously analyzed in the Certified EIR. As evaluated in the Certified EIR, the General Plan 2040 would result in a less than cumulatively considerable impact on the implementation of emergency response plans, fire risk, and associated effects on soil and water movement due to compliance with existing local programs, regulations, and General Plan 2040 policies. As discussed, the proposed project would not result in additional development that was not considered in the Certified EIR. The proposed project would not change the conclusions stated in the Certified EIR. Consistent with the Certified EIR, implementation of the proposed project would not result in a cumulatively considerable impact on wildfire, as all development would continue to comply with existing local programs, regulations, and General Plan 2040 policies that reduce fire risk. The proposed project would not result in a new significant cumulative impact or a substantial increase in the severity of previously identified significant cumulative impacts related to wildfire.

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4.0. LIST OF PREPARERS
The following individuals contributed to the preparation of this document.

4.1 LEAD AGENCY
City of Diamond Bar
21810 Copley Drive
Diamond Bar, CA 91765
Contributor Title Area of Responsibility
Greg Gubman Community Development Director Document Review Grace S. Lee Planning Manager Document Review
Mayuko Nakajima Senior Planner Document Review
Ricia Hager Director – Woodruff & Smart Document Review Dan Cruz Associate – Woodruff & Smart Document Review

4.2 CONSULTANT
Sapphos Environmental, Inc.
430 North Halstead St.

Pasadena, CA 91107
Contributor Title Area of Responsibility
Marie C. Campbell President Principal-in-Charge
Aimee Frappied Environmental Compliance Director EIR review / EIR author / Quality control
Paulette Franco Environmental Compliance Specialist EIR review / Quality control Rory Baker Environmental Compliance
Coordinator
Project Manager / EIR author
/ Quality Control
Andy Dunlap Sustainability Coordinator EIR author
Candace Rojas QSP/QSD Specialist EIR author
Diana Dyste Cultural Resources Manager EIR review
Jonathan Cain Sustainability Director EIR review
Laura Razo CEQA Team Supervisor Quality control
Matthew Adams Senior Technical Editor Document production Morgan Thomas Cultural Resources Coordinator EIR author Stefanie Paz GIS Team Lead GIS analysis

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5.0. REFERENCES
California Air Resources Board. 2022. Area Designations Maps / State Ambient Air Quality Standards. http://www.arb.ca.gov/desig/adm/adm.htm (accessed October 24, 2025).

California Air Resources Board. December 2022. 2022 Scoping Plan for Achieving Carbon Neutrality. https://ww2.arb.ca.gov/sites/default/files/2023-04/2022-sp.pdf (accessed November 3, 2025).

California Association of Environmental Professionals. January 2025. 2025 California Environmental Quality Act (CEQA) Statute and Guidelines. https://www.califaep.org/docs/CEQA_Handbook_2025combined.pdf (accessed October 29, 2025).

California Department of Forestry and Fire Protection (Cal FIRE) Office of the State Marshall. 2025. Find Your Fire Hazard Severity Zone (FHSZ). https://osfm.fire.ca.gov/what-wedo/community-wildfire-preparedness-and-mitigation/fire-hazard-severity-zones (accessed November 5, 2025).

California Department of Water Resources. 2003. California’s Groundwater. Bulletin 118 – Update 2003.

City of Diamond Bar. 2019. Diamond Bar Comprehensive General Plan Update and Climate Action Plan Draft Environmental Impact Report.
https://ceqanet.opr.ca.gov/2018051066/2
City of Diamond Bar. 2019. Diamond Bar General Plan 2040. https://www.diamondbarca.gov/961/General-Plan-2040
City of Diamond Bar. 2019. Diamond Bar General Plan 2040: Chapter 2. Land Use and Economic Development. https://www.diamondbarca.gov/DocumentCenter/View/7089/2- Land-Use-Econ-Devr?bidId= (accessed September 29, 2025).

City of Diamond Bar. 2022. 2022 Hazard Mitigation Plan. https://www.diamondbarca.gov/DocumentCenter/View/10286/Diamond-Bar-LocalHazard-Mitigation-Plan-2022?bidId= (accessed November 20, 2025).

City of Diamond Bar. 2022. Diamond Bar General Plan 2040 Housing Element Update 2021- 2029.

City of Diamond Bar. November 2019. Mitigation Monitoring & Reporting Program for the City Of Diamond Bar General Plan 2040 And Climate Action Plan 2040 Environmental Impact Report. SCH No. 2018051066.

County of Los Angeles. N.d. Disaster Route Maps (by City): Area D – Diamond Bar. https://dpw.lacounty.gov/dsg/DisasterRoutes/city.cfm (accessed November 5, 2025) Federal Emergency Management Agency. 2008. National Flood Insurance Program Flood Insurance Rate Map for Los Angeles County and Incorporated Areas.

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Southern California Association of Governments. 2024. Connect SoCal: A Plan for Navigating to a Brighter Future. https://scag.ca.gov/sites/default/files/2024-05/23-2987-connect-socal2024-final-complete-040424.pdf (accessed October 30, 2025).

State of California: Governor’s Office of Land Use and Planning. 2025. CEQA: Transportation Impacts (SB 743). https://lci.ca.gov/ceqa/sb-743/ (accessed October 29, 2025).

U.S. Environmental Protection Agency. 2023. Nonattainment Areas for Criteria Pollutants. https://www.epa.gov/green-book (accessed October 24, 2025).

APPENDIX A
Diamond Bar Objective Design Standards for
Multifamily and Mixed-Use Development

REMOVED (SEE EXHIBIT TO DRAFT ORDINANCE FOR ODS)

APPENDIX B
Mitigation Monitoring and Reporting Program

Mitigation Monitoring & Reporting Program
for the
CITY OF DIAMOND BAR GENERAL PLAN 2040 AND CLIMATE
ACTION PLAN 2040 ENVIRONMENTAL IMPACT REPORT
SCH No. 2018051066
City of Diamond Bar
November 2019

Mitigation Monitoring and Reporting Program for the City of Diamond Bar General Plan 2040 and Climate Action Plan 2040
2 This page intentionally left blank.

Mitigation Monitoring and Reporting Program for the City of Diamond Bar General Plan 2040 and Climate Action Plan 2040
1 1 Purpose
State of California Public Resources Code Section 21081.6(a)(1) requires a lead or responsible agency that approves or carries out a project where an Environmental Impact Report (EIR) has identified significant environmental effects to adopt a reporting or monitoring program for the changes made to the project or conditions of project approval, adopted in order to mitigate or avoid significant effects on the environment. The City of Diamond Bar (the "City") is the lead agency for the EIR prepared for the City of Diamond Bar General Plan 2040 and Climate Action Plan 2040 (SCH No. 2018051066 Project and therefore is responsible for the adoption and implementation of the required mitigation monitoring and reporting program.

An EIR has been prepared for the Proposed Project that addresses potential environmental impacts and, where appropriate, recommends measures to mitigate these impacts.

The Mitigation Monitoring and Reporting Program (MMRP) has been prepared in conformance with Public Resources Code Section 21081.6(a)(1). It is the intent of this program to:

1. Verify satisfaction of the required mitigation measures of the EIR;

2. Provide a methodology to document implementation of the required mitigation;

3. Provide a record of the monitoring program;

4. Identify monitoring responsibility;

5. Establish administrative procedures for the clearance of mitigation measures;

6. Establish the frequency and duration of monitoring; and

7. Utilize existing review processes wherever feasible.

The MMRP describes the procedures that will be used to implement the mitigation measures adopted in connection with the approval of the Proposed Project and the methods of monitoring such actions. A monitoring program is necessary only for impacts which would be significant if not mitigated.

If, during the course of project implementation, any of the mitigation measures identified cannot be successfully implemented, the City shall immediately inform any affected responsible agencies.

The City, in conjunction with any affected responsible agencies, will then determine if modification to the project is required, and/or whether alternative mitigation is appropriate.

The following consists of a monitoring program table noting the responsible entity for mitigation monitoring, the timing, and a list of all project-related mitigation measures.

Mitigation Monitoring and Reporting Program for the City of Diamond Bar General Plan 2040 and Climate Action Plan 2040
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Mitigation Monitoring and Reporting Program for the City of Diamond Bar General Plan 2040 and Climate Action Plan 2040 3 2 Mitigation Monitoring and Reporting Plan
Impact Mitigation Measure Method of Verification Timing of Verification
Responsibility for
Verification
Verification Complete
Date Initial
Air Quality
Construction associated
with implementation of
the Proposed Project
would create new
sources of VOC and
NOx emissions that
exceeds SCAQMD
project-level thresholds
and contribute to the
nonattainment
designation of the South
Coast Air Basin for O3.

MM-AQ-1 Construction Features.

Future development projects
implemented under the General Plan
will be required to demonstrate
consistency with SCAQMD
construction emission thresholds.

Where emissions from individual
projects exceed SCAQMD thresholds,
the following measures shall be
incorporated as necessary to minimize
impacts. These measures do not exclude
the use of other, equally effective
mitigation measures.
• Require all off-road diesel equipment
greater than 50 horsepower (hp)
used for this Project to meet current
USEPA standards, which are
currently Tier 4 final off-road
emission standards or equivalent.

Such equipment shall be outfitted
with Best Available Control
Technology (BACT) devices
including a California Air Resources
Include in project
conditions of
approval.

Prior to
issuance of
construction
permit.

City of
Diamond Bar
Community
Development
Department

Mitigation Monitoring and Reporting Program for the City of Diamond Bar General Plan 2040 and Climate Action Plan 2040 4 Impact Mitigation Measure Method of Verification Timing of Verification
Responsibility for
Verification
Verification Complete
Date Initial
Board certified Level 3 Diesel
Particulate Filter (DPF) or equivalent.

This DPF will reduce diesel
particulate matter and NOX
emissions during construction
activities.
• Require a minimum of 50 percent of
construction debris be diverted for
recycling.
• Require building materials to contain
a minimum 10 percent recycled
content.
• Require materials such as paints,
primers, sealants, coatings, and glues
to have a low volatile organic
compound concentration compared
to conventional products. If low
VOC materials are not available,
architectural coating phasing should
be extended sufficiently to reduce
the daily emissions of VOCs.

Operational sources
under the Proposed
Project would generate
emissions of VOC, NOx,
CO, PM10, and PM2.5 that
exceeds SCAQMD
project-level thresholds
and contribute to the
nonattainment
designation of the SCAB
for O3, PM2.5, and PM10.

MM-AQ-2: Future development.

Under the Proposed Project, future
development would be required to
demonstrate consistency with
projects where operational emissions
exceed regulatory thresholds the
following measures may be used to
reduce impacts. Note the following
measures are not all inclusive and
developers have the option to add or
substitute measures that are equally or
Include in project
conditions of
approval.

Prior to
discretionary
project
approval.

Construction
contractor;
City of
Diamond Bar
Community
Development
Department

Mitigation Monitoring and Reporting Program for the City of Diamond Bar General Plan 2040 and Climate Action Plan 2040 5 Impact Mitigation Measure Method of Verification Timing of Verification
Responsibility for
Verification
Verification Complete
Date Initial
more appropriate for the scope of their
project.
• Develop a project specific TDM
program for residents and/or
employees that provides
opportunities for carpool/vanpools.
• Provide onsite solar/renewable
energy in excess of regulatory
requirements.
• Require that owners/tenants of nonresidential or multi-family residential developments use architectural
coatings that are 10 grams per liter
or less when repainting/repairing
properties.
• Require dripless irrigation and
irrigation sensor units that prevent
watering during rain storms.
• Ensure all parking areas are wired
capability of future EV charging and
include EV charging stations that
exceed regulatory requirements.

Biological Resources
Construction associated
with implementation of
the Proposed Project
could have an adverse
effect on special-status
plant species.

MM-BIO-1A Preconstruction
Surveys for Special-Status Plants:

To mitigate impacts on special status
plant species, the applicant shall
implement the following measures:
• Prior to initiating disturbance
activities, clearance surveys for
special-status plant species shall be
performed by a qualified biologist(s)
Submittal of
preconstruction
surveys.

Prior to
issuance of
construction
permit.

Construction
contractor;
City of
Diamond Bar
Community
Development
Department

Mitigation Monitoring and Reporting Program for the City of Diamond Bar General Plan 2040 and Climate Action Plan 2040 6 Impact Mitigation Measure Method of Verification Timing of Verification
Responsibility for
Verification
Verification Complete
Date Initial
within the boundaries of the future
project disturbances. If any specialstatus plants are found on the Planning Area, a qualified biologist(s)
with a CDFG Scientific Collection
Permit shall prepare a plan to
relocate these species to suitable
habitats within surrounding public
open space areas that would remain
undisturbed. For those species that
cannot be physically transplanted, the
biologist(s) shall collect seeds from
the plants. (Note: Lilies generally can
be transplanted in bulb-form.)
• To the extent feasible the
preconstruction surveys shall be
completed when species are in
bloom, typically between May and
June and reference populations
checked. Two species, the white
rabbit-tobacco and San Bernardino
aster, are perennial herbs that grow
up to three feet in height and can be
identified by their dried stalks and
leaves following their blooming
period.

Construction associated
with implementation of
the Proposed Project
could have an adverse
effect on special-status
plant species.

MM-BIO-1B Special-Status Plant
Planting Plan: Prior to any ground
disturbance for projects that have the
potential to cause direct or indirect
impacts on special-status plants, the
project applicants shall prepare a Special
Status Plant Planting Plan for the species
Submittal of Special
Status Plant Planting
Plan and appropriate
documentation.

Prior to start
of ground
disturbance
activities.

Construction
contractor;
City of
Diamond Bar
Community
Development
Department

Mitigation Monitoring and Reporting Program for the City of Diamond Bar General Plan 2040 and Climate Action Plan 2040 7 Impact Mitigation Measure Method of Verification Timing of Verification
Responsibility for
Verification
Verification Complete
Date Initial
to be transplanted. At a minimum, the
plan shall include a description of the
existing conditions of the project and
receiver site(s), transplanting and/or
seed collection/off-site seeding or
installation methods, an adaptive twoyear monitoring program, any other necessary monitoring procedures, plant
spacing, and maintenance requirements.

In the event that the City of Diamond
Bar determines that agreed success
criteria are not met, additional
remediation may be required beyond
the two-year maintenance/monitoring
period to ensure mitigation
requirements are met. The City shall
also require proof that the plan
preparer consulted with US Fish and
Wildlife Service and California
Department of Fish and Wildlife
personnel or appropriate herbarium
botanists in order to maximize
transplanting success. (Note:

Appropriate botanists include those at
CDFW in Ontario, the Rancho Santa
Ana Botanical Gardens in Claremont,
UC Riverside, or Cal Poly Pomona.)
Construction associated
with implementation of
the Proposed Project
could have an adverse
effect on special-status
plant species.

MM-BIO-1C Listed Endangered
and Threatened Plants: In addition
to MM BIO-1A and -1B, the City shall
require the project applicant to provide
proof of the US Fish and Wildlife
Service and California Department of
Fish and Wildlife permitting the take of
Submittal of USFWS
and CDFW permits
and documentation.

Prior to
issuance of
construction
permit.

Construction
contractor;
City of
Diamond Bar
Community
Development
Department

Mitigation Monitoring and Reporting Program for the City of Diamond Bar General Plan 2040 and Climate Action Plan 2040 8 Impact Mitigation Measure Method of Verification Timing of Verification
Responsibility for
Verification
Verification Complete
Date Initial
listed endangered and threatened plants.

The FESA does not address listed plants
on private property. However, if a
federal action is required for a project
(funding, Clean Water Act compliance,
etc.), a permit from the USFWS and
CDFW to take a listed species is
required.

Implementation of the
Proposed Project could
result in indirect impacts
on special-status plant
species, sensitive natural
communities, preserved
open space, and wildlife
corridors.

MM-BIO-1D Environmental
Awareness Program: In order to
reduce indirect impacts on special-status
plants, sensitive natural communities,
preserved open space and wildlife
corridors, the City shall implement the
following measures:
• The City shall implement an
Environmental Awareness Program
on its web site intended to increase
awareness to developers, residents
and city workers of the sensitive
plants, wildlife and associated
habitats that occur in the preserved
open space areas. The intention of
the program shall be to inform
developers, city workers, and
residents and encourage active
conservation efforts to help
conserve the habitats in the
preserved open space. The program
shall address impacts associated with
the introduction of invasive plant
species as a result of new
development. At a minimum, the
Implementation of
Environmental
Awareness Program.

Ongoing. City of
Diamond Bar
Community
Development
Department

Mitigation Monitoring and Reporting Program for the City of Diamond Bar General Plan 2040 and Climate Action Plan 2040 9 Impact Mitigation Measure Method of Verification Timing of Verification
Responsibility for
Verification
Verification Complete
Date Initial
Environmental Awareness Program
shall include the following
components:
o Informational kiosks shall be
added or modified at
entrance points to hiking
and equestrian trails to
inform city workers,
residents and trail users on
the sensitive flora and fauna
that rely on the habitats
found within the preserved
open space. The intent of
these kiosks is to bring
awareness to the sensitive
plants, wildlife and
associated habitats which
occur in the area.
o The City shall provide
future project applicants a
brochure which includes a
list of sensitive plant and
tree species to avoid
impacting as well as
suggested plant palettes to
be used in residential
landscaping near natural
areas to prevent the
introduction of invasive
plant species to the
surrounding natural
communities.

Mitigation Monitoring and Reporting Program for the City of Diamond Bar General Plan 2040 and Climate Action Plan 2040 10 Impact Mitigation Measure Method of Verification Timing of Verification
Responsibility for
Verification
Verification Complete
Date Initial
Construction associated
with implementation of
the Proposed Project
could have an adverse
effect on special-status
animal species.

MM-BIO-1E Preconstruction
Surveys for Special-Status Wildlife:

Within one (1) week prior to initiating
disturbance activities, clearance surveys
for special-status animal species shall be
performed by a qualified biologist(s)
within the boundaries of the future
project disturbances. If any specialstatus animals are found on the site, a qualified biologist(s) flag the area for
avoidance and discuss possible seasonal
avoidance measures with the developer.

If avoidance is not feasible, the Project
Biologist, with a CDFG Scientific
Collection Permit shall relocate these
species to suitable habitats within
surrounding open space areas that
would remain undisturbed, unless the
biologist determines that such
relocation cannot reasonably be
accomplished at which point CDFG will
be consulted regarding whether
relocation efforts should be terminated.

Relocation methods (e.g., trap and
release) and receiver sites shall be
verified and approved by the CDFG
prior to relocating any animals.

Submittal of
preconstruction
surveys.

Prior to
issuance of
construction
permit.

Construction
contractor;
City of
Diamond Bar
Community
Development
Department
Implementation of the
Proposed Project could
cause direct or indirect
impacts on suitable
habitat for federally or
MM-BIO-IF Listed Endangered
or Threatened Wildlife: Prior to
approval of individual projects that have
the potential to cause direct or indirect
impacts on suitable habitat for federally
or state listed endangered or
Submittal of findings
and documentation.

Prior to
discretionary
project
approval.

City of
Diamond Bar
Community
Development
Department

Mitigation Monitoring and Reporting Program for the City of Diamond Bar General Plan 2040 and Climate Action Plan 2040 11 Impact Mitigation Measure Method of Verification Timing of Verification
Responsibility for
Verification
Verification Complete
Date Initial
state listed endangered
or threatened species.
threatened species, the City shall
require a habitat evaluation to be
completed by a qualified biologist well
versed in the requirements of the
associated species to be completed. If
no suitable habitat for listed species is
identified within 300 feet of
construction or maintenance activities,
no further measures would be required
in association with the project. If
suitable habitat for the species is
identified within 300 feet of such
activities, prior to construction, the City
shall require that a survey be completed
by a qualified biologist for the species in
accordance with protocols established
by the US Fish and Wildlife Service.

Table 3.3-5 provides a listing of
endangered and threatened species by
habitat type and potential for
occurrence.

In the event a state or federal listed
species is determined to occupy the
proposed Planning Area or its
immediate surroundings, the CDFW
and/or USFWS shall be consulted, as
required by CESA and/or FESA. In
order to address and acknowledge the
potential for listed species to occur
within the Planning Area or be impacted
by future development projects, this
assessment acknowledges future actions
by state and federal resource agencies in

Mitigation Monitoring and Reporting Program for the City of Diamond Bar General Plan 2040 and Climate Action Plan 2040 12 Impact Mitigation Measure Method of Verification Timing of Verification
Responsibility for
Verification
Verification Complete
Date Initial
addition to the analyses necessary and
required under CEQA. Compensation
is likely to include one or more of the
following on- or off-site measures:
dedication/preservation of suitable
habitat for the species; habitat
enhancement/creation; and provisions
for long-term habitat management.

Clearing and grading
activities associated with
implementation of the
Proposed Project could
disturb nesting bird
habitats.

MM-BIO-1G Nesting Bird
Surveys: All vegetation clearing for
construction and fuel modification shall
occur outside of the breeding bird
season, if feasible, to ensure that no
active nests would be disturbed unless
clearing and/or grading activities cannot
be avoided during that time period.

If clearing and/or grading activities
cannot be avoided during the breeding
season, all suitable habitats shall be
thoroughly surveyed for the presence of
nesting birds by a qualified biologist
prior to removal. Suitable nesting
habitat on the Planning Area includes
grassland, scrub, chaparral, and
woodland communities. If any active
nests are detected, the area shall be
flagged, along with a 300-foot buffer for
song birds and a 500-foot buffer for
raptorial birds (or as otherwise
appropriate buffer as determined by the
surveying biologist), and shall be avoided
until the nesting cycle is complete or it
Submittal of findings
and documentation.

Prior to start
of clearing
and/or
grading
activities.

City of
Diamond Bar
Community
Development
Department

Mitigation Monitoring and Reporting Program for the City of Diamond Bar General Plan 2040 and Climate Action Plan 2040 13 Impact Mitigation Measure Method of Verification Timing of Verification
Responsibility for
Verification
Verification Complete
Date Initial
is determined by the surveying biologist
that the nest is no longer active.

Implementation of the
Proposed Project could
disturb active golden
eagle nests.

MM-BIO-1H Protection of Eagle
Nests: No development or project
activities shall be permitted within onehalf mile of a determined active golden eagle nest unless the planned activities
are sited in such a way that the activity
has minimal potential to cause
abandonment of the nesting site, as
determined by a qualified biologist. In
addition, the eagle nest (if active) shall
be monitored by a biologist who is
highly familiar with the signs of eagle
distress during the project development
activities. The monitoring shall continue
until the monitoring biologist is
confident the nest will not be disturbed.

The monitoring biologist shall have the
authority to stop project activities as
needed.
(Note: Generally, information regarding
the location of raptorial bird nests is
kept highly confidential. As such it is
recommended that representatives of
CDFW, USFWS and/or the Chino Hills
State Park be notified of any proposed
projects in the SOI or Tres Hermanos
portions of the Planning Area. In
consultation with agency
representatives, it can be determined if
the project is within one-half mile of the
Submittal of findings
and documentation.

Ongoing. City of
Diamond Bar
Community
Development
Department

Mitigation Monitoring and Reporting Program for the City of Diamond Bar General Plan 2040 and Climate Action Plan 2040 14 Impact Mitigation Measure Method of Verification Timing of Verification
Responsibility for
Verification
Verification Complete
Date Initial
eagle nest without the location being
specifically identified.)
Construction associated
with implementation of
the Proposed Project
could disturb bat
roosting habitat.

MM-BIO-1I Use of Buffers Near
Active Bat Roosts: During the
November 1 to March 31 hibernation
season, construction activities shall not
be conducted within 100 feet of
woodland habitat that provides suitable
bat roosting habitat. Bat presence is
difficult to detect using emergence
surveys during this period due to
decreased flight and foraging behavior. If
a qualified biologist who is highly familiar
with bat biology determines that
woodland areas do not provide suitable
hibernating conditions for bats and they
are unlikely to be present in the area,
work may commence as planned.

Submittal of findings
and documentation.

During the
November 1
through
March 31
hibernation
season and
shortly
thereafter.

Construction
contractor;
City of
Diamond Bar
Community
Development
Department
Construction associated
with implementation of
the Proposed Project
could disrupt bat
roosting habitat.

MM BIO-1J Bat Maternity
Roosting Season: Night-time evening
emergence surveys and/or internal
searches within large tree cavities shall
be conducted by a qualified biologist
who is highly familiar with bat biology
during the maternity season (April 1 to
August 31) to determine
presence/absence of bat maternity
roosts near wooded project boundaries.

All active roosts identified during
surveys shall be protected by a buffer to
be determined by a qualified bat
biologist. The buffer will be determined
by the type of bat observed,
Submittal of findings
and documentation.

During the
April 1
through
August 31
maternity
season.

Surveys valid
30 days from
survey date.

Construction
contractor;
City of
Diamond Bar
Community
Development
Department

Mitigation Monitoring and Reporting Program for the City of Diamond Bar General Plan 2040 and Climate Action Plan 2040 15 Impact Mitigation Measure Method of Verification Timing of Verification
Responsibility for
Verification
Verification Complete
Date Initial
topography, slope, aspect, surrounding
vegetation, sensitivity of roost, type of
potential disturbance, etc. Each
exclusion zone would remain in place
until the end of the maternity roosting
season. If no active roosts are identified,
then work may commence as planned.

Survey results are valid for 30 days from
the survey date. Should work
commence later than 30 days from the
survey date, surveys should be repeated.

Construction associated
with implementation of
the Proposed Project
could disrupt bat
roosting habitat.

MM BIO-1K Bat Roost
Replacement: All special-status bat
roosts that are destroyed by the project
must be documented and shall be
replaced at a 1:1 ratio on- or off-site
with a roost suitable for the displaced
species (e.g., bat houses for colonial
roosters). The design of such
replacement habitat shall be coordinated
with CDFG. The new roost shall be in
place prior to the time that the bats are
expected to use the roost as
determined by a qualified biologist who
is highly familiar with bat biology, and
shall be monitored periodically for five
(5) years to ensure proper roosting
habitat characteristics (e.g., suitable
temperature and no leaks). The roost
shall be modified as necessary to
provide a suitable roosting environment
for the target bat species.

Submittal of
documentation.

Prior to the
time the bats
are expected
to use the
roost as
determined
by a qualified
biologist.

Monitoring
shall occur
periodically
over 5 years
thereafter.

Construction
contractor;
City of
Diamond Bar
Community
Development
Department

Mitigation Monitoring and Reporting Program for the City of Diamond Bar General Plan 2040 and Climate Action Plan 2040 16 Impact Mitigation Measure Method of Verification Timing of Verification
Responsibility for
Verification
Verification Complete
Date Initial
Implementation of the
Proposed Project could
result in adverse impacts
to sensitive shrubland
and scrub natural
communities.

MM BIO-2 Sensitive Natural
Communities: To mitigate impacts on
sensitive shrubland and scrub natural
communities, project applicants shall
implement the following mitigation
measures prior to any ground
disturbance:
• If avoidance cannot be reasonably
accomplished, impacts on any
shrubland, scrub or woodland
alliance indicated as sensitive in Table

3.3-2 shall be mitigated through onor off‐site restoration/enhancement.

For off-site
restoration/enhancement, the
applicant shall acquire mitigation land
of similar habitat at a ratio of at least
1:1. On-site
restoration/enhancement shall also
be completed at a ratio of at least
1:1.
• For projects that have the potential
to result in direct or indirect impacts
on sensitive natural communities, a
habitat restoration plan shall be
prepared prior to any ground
disturbance. The Plan shall include
adaptive management practices as
specified by the Department of the
Interior to achieve the specified ratio
for restoration/enhancement. At a
minimum, the Plan shall include a
description of the existing conditions
Submittal of
documentation.

Prior to start
of ground
disturbance.

Construction
contractor;
City of
Diamond Bar
Community
Development
Department

Mitigation Monitoring and Reporting Program for the City of Diamond Bar General Plan 2040 and Climate Action Plan 2040 17 Impact Mitigation Measure Method of Verification Timing of Verification
Responsibility for
Verification
Verification Complete
Date Initial
of the receiver site(s), goals and
timeline, installation methods,
monitoring procedures, plant
spacing, adaptive management
strategies, and maintenance
requirements to ensure the sensitive
communities referred to above reestablished successfully at the ratios set forth above.

Implementation of the
Proposed Project could
result in adverse impacts
on jurisdictional waters.

MM BIO-3 Jurisdictional
Waters: To mitigate for impacts on
jurisdictional waters, the applicant shall
implement the following measures in
consultation with the regulating agencies
(USACE, CDFW, and RWQCB, where
applicable) over the course of the
project:
• The applicant shall provide on- and
off-site replacement and/or
restoration/enhancement of USACE,
RWQCB and CDFG jurisdictional
waters and wetlands at a ratio no
less than 1.5:1 and/or include the
purchase of mitigation credits at an
agency‐approved off‐site mitigation
bank.
• If replacement and/or
restoration/enhancement would
occur, a restoration plan shall be
prepared that describes the location
of restoration and provides for
replanting and monitoring for a
Submittal of
documentation.

Ongoing. Construction
contractor;
City of
Diamond Bar
Community
Development
Department

Mitigation Monitoring and Reporting Program for the City of Diamond Bar General Plan 2040 and Climate Action Plan 2040 18 Impact Mitigation Measure Method of Verification Timing of Verification
Responsibility for
Verification
Verification Complete
Date Initial
three-year period following
construction.

Implementation of the
Proposed Project could
result in a loss of oak
woodland.

MM-BIO-4 Oak Woodlands: In
the event a future project would result
in the loss of an oak woodland, the
project shall be subject to the mitigation
requirements set forth in the Los
Angeles County Oak Woodland
Conservation Management Plan Guide.

If a future project cannot be redesigned
to avoid impacts on oak woodland, then
one of the following measures shall be
implemented:
• Acquire oak woodland habitat that is
comparable to the habitat that was
impacted at a ratio of 1:1.
• Restore degraded oak woodlands
o Off-site restoration should
be prioritized over on-site
restoration and where
feasible, should be located
nearby the impacted
property, preferably within
the same watershed or subdrainage as deemed
appropriate by a qualified
biologist, or within the same
planning area as the
impacted property. Off-site
restoration may include any
of the following: acquiring
off-site fee title for oak
woodland habitat;
Submittal of final
report.

Ongoing.

Mitigation
areas shall be
placed in a
conservation
easement
within 6
months of a
completion.

Project
mitigation
shall be
monitored
and reported
on over a 7-
year period.

Construction
contractor;
City of
Diamond Bar
Community
Development
Department

Mitigation Monitoring and Reporting Program for the City of Diamond Bar General Plan 2040 and Climate Action Plan 2040 19 Impact Mitigation Measure Method of Verification Timing of Verification
Responsibility for
Verification
Verification Complete
Date Initial
replacement planting;
and/or restoring moderately
or severely degraded oak
woodlands (more
specifically, removing
exotics and restoring
appropriate native plant
diversity).
o On-site restoration of a
ratio of at least 1:1 should
be utilized when
circumstances at the site
allow for long-term
sustainability of the
replacement plantings, the
potential to expand/connect
to adjacent oak woodlands,
and/or the improvement of
degraded oak woodlands. If
possible, on-site restoration
areas should be located
adjacent to preserved
natural space. The project
applicant shall
replace/restore lost canopy
area. More specifically, the
project applicant shall
provide mitigation trees of
the same Oak species. All
replacement trees should be
planted on native
undisturbed soil and should
be the same species of oak
(Quercus sp.) as the

Mitigation Monitoring and Reporting Program for the City of Diamond Bar General Plan 2040 and Climate Action Plan 2040 20 Impact Mitigation Measure Method of Verification Timing of Verification
Responsibility for
Verification
Verification Complete
Date Initial
removed tree with
appropriate associated
native vegetation in the
understory. The location of
the replacement tree should
be in the vicinity of other
oak trees of the same
species. If replacement trees
cannot be planted on native
undisturbed soil or are not
in the vicinity of the same
species of oak (Quercus sp.)
as the removed tree, the
city may require
implementation of additional
measures as listed in MMBIO-4 to ensure that trees
thrive.

Mitigation areas or land should be at a
minimum of two (2) to one (1) canopy
cover area for the amount removed.

This is the expected canopy extent of
mature trees. All mitigation areas or
land should be placed in a conservation
easement within six months of a
easement is not possible, the land shall
be protected in perpetuity by other
means deemed acceptable by the City.

Mitigation land may be designated public
open space by the City if deemed
appropriate per the description of Open
Space found in Chapter 2: Land Use of
the proposed General Plan.

Mitigation Monitoring and Reporting Program for the City of Diamond Bar General Plan 2040 and Climate Action Plan 2040 21 Impact Mitigation Measure Method of Verification Timing of Verification
Responsibility for
Verification
Verification Complete
Date Initial
Project mitigation shall be monitored
and reported on over a seven-year
period and shall incorporate an iterative
process of annual monitoring and
evaluation of progress and allow for
adjustments to the program, as
necessary, to achieve desired outcomes
and meet success criteria. Annual
reports discussing the implementation,
monitoring, and management of the
mitigation project shall be submitted to
the City and should contain the
following components: description of
the project impact and mitigation site;
specific objectives/success criteria,
evaluated based on approved survival
rates and percent cover of planted
native species; control of invasive plant
and animal species within the mitigation
site; monitoring and maintenance
activities conducted since the previous
report; and any contingency measures
implemented since the previous report.

Success criteria should be based on a
reference site supporting the desired
oak species and understory that the
mitigation site is designed to achieve.

Once the mitigation project has been
completed, the applicant shall submit a
final report to the City. The report shall
discuss the implementation, monitoring
and management of the mitigation

Mitigation Monitoring and Reporting Program for the City of Diamond Bar General Plan 2040 and Climate Action Plan 2040 22 Impact Mitigation Measure Method of Verification Timing of Verification
Responsibility for
Verification
Verification Complete
Date Initial
project over the seven-year period, and
indicates whether the mitigation project
has, in part, or in whole, been successful
based on established success criteria.

The project shall be extended if success
criteria have not been met at the end of
the seven-year period to the satisfaction
of the City.

Implementation of the
Proposed Project could
result in a loss of oak
woodland.

MM-BIO-5 Walnut Woodlands:

In the event a future project would
result in the loss of a walnut woodland,
then one of the following measures shall
be implemented:
• Acquire walnut woodland habitat
that is comparable to the habitat that
was impacted at a ratio of 1:1.
• Restore degraded walnut woodlands
o Off-site restoration should
be prioritized over on-site
restoration and where
feasible, should be located
nearby the impacted
property, preferably within
the same watershed or subdrainage as deemed
appropriate by a qualified
biologist, or within the same
planning area as the
impacted property. Off-site
restoration may include any
of the following: acquiring
off-site fee title for walnut
woodland habitat;
Submittal of final
report.

Ongoing.

Mitigation
areas shall be
placed in a
conservation
easement
within 6
months of a
completion.

Project
mitigation
shall be
monitored
and reported
on over a 7-
year period.

Construction
contractor;
City of
Diamond Bar
Community
Development
Department

Mitigation Monitoring and Reporting Program for the City of Diamond Bar General Plan 2040 and Climate Action Plan 2040 23 Impact Mitigation Measure Method of Verification Timing of Verification
Responsibility for
Verification
Verification Complete
Date Initial
replacement planting;
and/or restoring moderately
or severely degraded walnut
woodlands (more
specifically, removing
exotics and restoring
appropriate native plant
diversity).
o On-site restoration of a
ratio of at least 1:1 should
be utilized when
circumstances at the site
allow for long-term
sustainability of the
replacement plantings, the
potential to expand/connect
to adjacent walnut
woodlands, and/or the
improvement of degraded
walnut woodlands. If
possible, on-site restoration
areas should be located
adjacent to preserved
natural space. The project
applicant shall
replace/restore lost canopy
area. More specifically, the
project applicant shall
provide mitigation trees of
the same species comprising
the walnut woodland,
including the constituent or
co-dominant oak species.

All replacement trees

Mitigation Monitoring and Reporting Program for the City of Diamond Bar General Plan 2040 and Climate Action Plan 2040 24 Impact Mitigation Measure Method of Verification Timing of Verification
Responsibility for
Verification
Verification Complete
Date Initial
should be planted on native
undisturbed soil and should
be the same species of
walnut (Juglans sp.) and oak
(Quercus sp.) as the
removed tree with
appropriate associated
native vegetation in the
understory. The location of
the replacement tree should
be in the vicinity of other
trees of the same species. If
replacement trees cannot
be planted on native
undisturbed soil or are not
in the vicinity of the same
species as the removed
tree, the city may require
implementation of additional
measures as listed in MMBIO-5 to ensure that trees
thrive.

Mitigation areas or land should be at a
minimum of two (2) to one (1) canopy
cover area for the amount removed.

This is the expected canopy extent of
mature trees. All mitigation areas or
land should be placed in a conservation
easement within six months of a
easement is not possible, the land shall
be protected in perpetuity by other
means deemed acceptable by the City.

Mitigation land may be designated public

Mitigation Monitoring and Reporting Program for the City of Diamond Bar General Plan 2040 and Climate Action Plan 2040 25 Impact Mitigation Measure Method of Verification Timing of Verification
Responsibility for
Verification
Verification Complete
Date Initial
open space by the City if deemed
appropriate per the description of Open
Space found in Chapter 2: Land Use of
the proposed General Plan.

Project mitigation shall be monitored
and reported on over a seven-year
period and shall incorporate an iterative
process of annual monitoring and
evaluation of progress and allow for
adjustments to the program, as
necessary, to achieve desired outcomes
and meet success criteria. Annual
reports discussing the implementation,
monitoring, and management of the
mitigation project shall be submitted to
the City and should contain the
following components: description of
the project impact and mitigation site;
specific objectives/success criteria,
evaluated based on approved survival
rates and percent cover of planted
native species; control of invasive plant
and animal species within the mitigation
site; monitoring and maintenance
activities conducted since the previous
report; and any contingency measures
implemented since the previous report.

Success criteria should be based on a
reference site supporting the desired
walnut woodland species and
understory that the mitigation site is
designed to achieve.

Mitigation Monitoring and Reporting Program for the City of Diamond Bar General Plan 2040 and Climate Action Plan 2040 26 Impact Mitigation Measure Method of Verification Timing of Verification
Responsibility for
Verification
Verification Complete
Date Initial
Once the mitigation project has been
completed, the applicant shall submit a
final report to the City. The report shall
discuss the implementation, monitoring
and management of the mitigation
project over the seven-year period, and
indicates whether the mitigation project
has, in part, or in whole, been successful
based on established success criteria.

The project shall be extended if success
criteria have not been met at the end of
the seven-year period to the satisfaction
of the City.

Implementation of the
Proposed Project could
diminish the integrity of
the Tonner Canyon
movement corridor.

MM-BIO-6 Wildlife Movement
Corridor: In order to ensure the
existing integrity of the Tonner Canyon
movement corridor, the following land
use design criteria shall be adhered to
when reviewing future projects:

Corridor Features
• The corridor should be as wide as
possible. The corridor width may
vary with habitat type or target
species, but a rule of thumb is about
a minimum of 1,000 feet wide (but
larger if possible).
• Maintain as much natural open space
as possible next to any culverts and
road undercrossings to encourage
the use of these by wildlife.

Include in project
conditions of
approval.

Prior to
discretionary
project
approval.

Construction
contractor;
City of
Diamond Bar
Community
Development
Department

Mitigation Monitoring and Reporting Program for the City of Diamond Bar General Plan 2040 and Climate Action Plan 2040 27 Impact Mitigation Measure Method of Verification Timing of Verification
Responsibility for
Verification
Verification Complete
Date Initial
• Maximize land uses adjacent to the
corridor that reduce human impacts
on the corridor.
• Avoid development or other impacts
to project into the corridor to form
impediments to movement and
increase harmful edge effects.
• If development is to be permitted
next to the corridor, put
conservation easements on adjacent
lots to prohibit structures nearest
the corridor.
• Develop strict maximum brightness
restrictions for development
adjacent to the corridor to prevent
light trespass into the corridor.

Lights must be directed downward
and inward toward the development.

Culvert Design
• Bridged undercrossings are
preferable.
• If a bridge is not possible, use a 12-
foot by 12-foot box culvert or bigger
for larger animals.
• Install a small, one-foot diameter
tube parallel to the large box culvert
for small animals. The upstream end
of the small tube should be a few
inches higher than the bottom of the
upstream end of the box culvert, so
that it will stay dry and free of
debris.

Mitigation Monitoring and Reporting Program for the City of Diamond Bar General Plan 2040 and Climate Action Plan 2040 28 Impact Mitigation Measure Method of Verification Timing of Verification
Responsibility for
Verification
Verification Complete
Date Initial
• The culvert bottoms should be as
close as possible to any canyon
bottom and not be perched up a fill
slope.
• Use natural substrate on the bottom
of the culvert, such as dirt with
pebbles.
• On roads above the undercrossings
and culverts, install speed bumps and
wildlife crossing signs to slow the
cars, and avoid street lighting to
facilitate use of the crossing.
• Plant and maintain vegetative cover
(shrubs and low cover) near the
entrance-exits of the culverts,
without visually or physically blocking
the entries.
• Install appropriate fencing (at least
six feet in height) to funnel animals
towards the undercrossings and
culverts.

Vegetation Restoration
• Require maintenance or restoration
of native vegetation, and long-term
management.
• Develop an adequate endowment
program for restoration and
management of the corridor.
• Plant native trees, shrubs, and other
plants to provide food and cover, as
well as nesting opportunities for
birds.

Mitigation Monitoring and Reporting Program for the City of Diamond Bar General Plan 2040 and Climate Action Plan 2040 29 Impact Mitigation Measure Method of Verification Timing of Verification
Responsibility for
Verification
Verification Complete
Date Initial
Management and Enforcement
• If housing is to be permitted adjacent
to the corridor, require the
homeowners associations or each
homeowner to maintain -- on their
own property -- a mowed, 30-foot
to 60-foot buffer along a flat or
slightly sloped grade between the
native vegetation in the corridor and
each adjacent lot, for fire abatement.
• Avoid fencing in the corridor that
would bottleneck the corridor.
• Unleashed domestic pets should not
be allowed in the corridor.
• Educate each landowner adjacent to
the corridor about the regulations
(lighting, mowing the buffer, no
trespass, do not place pet food
outside, etc.) and develop a pamphlet
and convene a community meeting.

In appropriate locations, install
educational signs about the corridor
and the species that could potentially
use the corridor.

Cultural, Historic, and Tribal Cultural Resources
Implementation of the
Proposed Project could
cause adverse impacts
on historical resources.

MM-CULT-1 Prior to development
of any project on a parcel containing at
least one structure more than 45 years
old and until such time a Citywide
historic resource survey is completed,
the project proponent shall retain a
qualified architectural historian, defined
Submittal of findings
and documentation.

Prior to
discretionary
project
approval.

Construction
contractor;
City of
Diamond Bar
Community
Development
Department

Mitigation Monitoring and Reporting Program for the City of Diamond Bar General Plan 2040 and Climate Action Plan 2040 30 Impact Mitigation Measure Method of Verification Timing of Verification
Responsibility for
Verification
Verification Complete
Date Initial
as meeting the Secretary of the
Standards for architectural history, to
conduct a preliminary assessment. If the
property appears to be potentially
eligible for a local, state and/or federal
listing, a full historic resources
assessment shall be required. A full
historic resources assessment shall
include: a records search at the South
Central Coastal Information Center; a
review of pertinent archives, databases,
and sources; a pedestrian field survey;
recordation of all identified historic
resources on California Department of
Parks and Recreation 523 forms; and
preparation of a technical report
documenting the methods and results of
the assessment. All identified historic
resources will be assessed for the
tential to result in direct
and/or indirect effects on those
resources and any historic resource that
may be affected shall be evaluated for its
potential significance under national and
approval of project plans and publication
of subsequent CEQA documents. The
qualified architectural historian shall
provide recommendations regarding
additional work, treatment, or
mitigation for affected historical
resources to be implemented prior to
their demolition or alteration. Impacts

Mitigation Monitoring and Reporting Program for the City of Diamond Bar General Plan 2040 and Climate Action Plan 2040 31 Impact Mitigation Measure Method of Verification Timing of Verification
Responsibility for
Verification
Verification Complete
Date Initial
on historical resources shall be analyzed
using CEQA thresholds to determine if
a project would result in a substantial
adverse change in the significance of a
historical resource. If a potentially
significant impact would occur, the City
shall require appropriate mitigation to
lessen the impact to the degree feasible.

This mitigation measure shall not apply
to minor projects that would otherwise
qualify for an exemption under CEQA,
such as, but not limited to, room
additions, reroofs, and the removal of
minor accessory structures and
landscaping projects.

Implementation of the
Proposed Project could
cause adverse impacts
on archaeological
resources.

MM-CULT-2 Prior to development
of a project that involves ground
disturbance, the project proponent shall
retain a qualified archaeologist, defined
as meeting the Secretary of the
nal Qualification
Standards for archaeology, to conduct
an archaeological resources assessment
including: a records search at the South
Central Coastal Information Center; a
Sacred Lands File search at the Native
American Heritage Commission; a
pedestrian field survey; recordation of
all identified archaeological resources on
California Department of Parks and
Recreation 523 forms; an assessment of
sensitivity and the potential to
encounter subsurface archaeological
Submittal of
archaeological
resources
assessment.

Prior to
discretionary
project
approval.

Construction
contractor;
City of
Diamond Bar
Community
Development
Department

Mitigation Monitoring and Reporting Program for the City of Diamond Bar General Plan 2040 and Climate Action Plan 2040 32 Impact Mitigation Measure Method of Verification Timing of Verification
Responsibility for
Verification
Verification Complete
Date Initial
resources and human remains;
subsurface investigation to define the
horizontal and vertical extents of any
identified archaeological resources; and
preparation of a technical report
documenting the methods and results of
the study. All identified archaeological
resources shall be assessed for the
and/or indirect effects on those
resources and any archaeological
resource that cannot be avoided shall be
evaluated for its potential significance
roject
plans and publication of subsequent
CEQA documents. The qualified
archaeologist shall provide
recommendations regarding protection
of avoided resources and/or
recommendations for additional work,
treatment, or mitigation of significant
resources that will be affected by the
project. This mitigation measure shall
not apply to minor projects that would
otherwise qualify for an exemption
under CEQA, such as, but not limited
to, the construction of a single-family
residences, excavations for swimming
pools, and landscaping projects.

Geology, Soils, and Seismicity
Implementation of the
Proposed Project could
cause adverse impacts
MM-GEO-1 Prior to development
of projects that involve ground
disturbance or excavations in
Submittal of
technical report.

Prior to
discretionary
Construction
contractor;
City of

Mitigation Monitoring and Reporting Program for the City of Diamond Bar General Plan 2040 and Climate Action Plan 2040 33 Impact Mitigation Measure Method of Verification Timing of Verification
Responsibility for
Verification
Verification Complete
Date Initial
on paleontological
resources.
undisturbed native soils, the project
proponent shall retain a paleontologist
meeting the Society of Vertebrate
professional paleontologist (SVP, 2010)
to conduct an paleontological resources
assessment including: a site-specific
database search at the Natural History
Museum of Los Angeles County and/or
other appropriate facilities (such as the
University of California Museum of
Paleontology); geologic map and
scientific literature review; a pedestrian
field survey, where deemed appropriate
by the qualified professional
paleontologist; assessment of the
and paleontological monitoring
requirements (locations, depths,
duration, timing); and preparation of a
technical report that documents the
methods and results of the study. The
report shall be prepared prior to the
project plans and publication of
subsequent CEQA documents.
project
approval.

Diamond Bar
Community
Development
Department
Implementation of the
Proposed Project could
cause adverse impacts
on paleontological
resources.

MM-GEO-2 The City shall require
paleontological resources monitoring
for any project that has a high potential
for encountering subsurface
paleontological resources. The location,
depths, duration, and timing of
monitoring shall be determined by the
qualified professional paleontologist
Submittal of findings
and documentation,
followed by
monitoring report.

Prior to
discretionary
project
approval.

Monitoring
report shall
Construction
contractor;
City of
Diamond Bar
Community
Development
Department

Mitigation Monitoring and Reporting Program for the City of Diamond Bar General Plan 2040 and Climate Action Plan 2040 34 Impact Mitigation Measure Method of Verification Timing of Verification
Responsibility for
Verification
Verification Complete
Date Initial
based on the sensitivity assessment in
the study required as part of MM-GEO1. Prior to the start of ground disturbance, the project proponent shall
retain a qualified monitor meeting the
standards for paleontological resource
monitors (SVP, 2010), and who shall
work under the direct supervision of
the qualified professional paleontologist.

In the event that paleontological
resources are unearthed during grounddisturbing activities, the monitor shall be empowered to halt or redirect grounddisturbing activities away from the vicinity of the discovery until the
qualified professional paleontologist has
determined its significance and provided
recommendations for preservation in
place or recovery of the resource. The
monitor shall keep daily logs detailing
the types of activities and soils
observed, and any discoveries. After
cessation of ground disturbance, the
qualified professional paleontologist shall
prepare a report that details the results
of monitoring.
be prepared
after
cessation of
ground
disturbance.

PLANNING COMMISSION
RESOLUTION NO. 2026-03

A RESOLUTION OF THE PLANNING COMMISSION OF THE CITY OF DIAMOND BAR

RECOMMENDING TO THE CITY COUNCIL APPROVAL OF PROPOSED AMENDMENTS TO TITLE 22 OF THE DIAMOND BAR MUNICIPAL CODE ("DEVELOPMENT CODE"), ADDING CHAPTER22.19 TO ESTABLISH MULTIFAMILY AND MIXED-USE RESIDENTIAL OBJECTIVE DESIGN STANDARDS ("ODS") IN ACCORDANCE WITH STATE HOUSING MANDATES - PLANNING CASE NO. PL2024-51.

A. RECITALS

1. Title 22 (Development Code) of the Diamond Bar City Code (DBCC) establishes allowable uses of property and related development standards within all zoning districts in the City;

2. Several provisions of State law, including, but not limited to, Senate Bill 35 and Senate Bill 330, established mandates for cities and counties to streamline the review process for multifamily housing, including mixed-use residential developments and require local agencies are required to limit their review of qualifying housing projects to objective standards;

3. Implementation of Program H-8 of Diamond Bar's certified 6th Cycle (2021-2029) Housing Element commits the City to update the Development Code to include objective standards as part of its broader obligation to minimize constraints on housing supply and affordability;

4. The City desires to establish ODS applicable to multifamily housing and mixed-use residential development projects in the City in order to implement the Housing Element and to appropriately regulate development in a manner consistent with State law and which facilitates a fair and efficient review process that results in high quality development and buildings that are appropriate for their context and environment;

5. This Project has been reviewed for compliance with the California Environmental Quality Act (CEQA). Pursuant to CEQA Guidelines Section 15164, the City has prepared Addendum No. 2 to the General Plan EIR (No. SCH 2018051066), which demonstrates that adoption of the ODS would not result in new or substantially more severe impacts beyond those that were evaluated in the EIR for the City General Plan 2040; therefore, no subsequent environmental document is required ;

6. Pursuant to Government Code Sections 65090, a notice of at least 1/8 page display was published in the San Gabriel Valley Tribune newspaper on February 4, 2026, and a copy of the public notice was posted at the City's designated community posting sites;

7. On February 24, 2026, the Planning Commission held a duly noticed public hearing regarding the proposed Development Code Amendment reflected in the draft ordinance attached hereto as Exhibit "A" and incorporated by reference into this Resolution, and duly considered all public testimony, evidence, and staff analysis; and

8. All legal prerequisites to the adoption of this Resolution have occurred.

B. RESOLUTION
NOW, THEREFORE, it is found, determined and resolved by the Planning Commission of the City of Diamond Bar as follows:

1. This Planning Commission hereby specifically finds that all of the facts set forth in the Recitals, Part A, of this Resolution are true and correct.

2. Based on the findings and conclusions set forth above, the Planning Commission hereby recommends that the City Council approve Development Code Amendment No. PL2024-51 by adopting amendments to Title 22 of the Diamond Bar Municipal Code described in the draft ordinance attached hereto as Exhibit "A" and incorporated herein by reference.

The Planning Commission Secretary shall:
(a) Certify to the adoption of this Resolution; and
(b) Forthwith transmit a certified copy of this Resolution to the City Council of the City of Diamond Bar.

APPROVED AND ADOPTED THIS 24TH DAY OF FEBRUARY, 2026, BY THE PLANNING COMMISSION OF THE CITY OF DIAMOND BAR.

I, Greg Gubman, Planning Commission Secretary, do hereby certify that the foregoing Resolution was duly introduced, passed, and adopted, at a regular meeting of the Planning Commission held on the 24th day of February, 2026, by the following vote:

AYES:4
NOES:0
Commissioners: Mao, Mehta, Torres, V/C Worthington
Commissioners: None
ABSENT:1 Commissioners: Rawlings
ABSTAIN:0 Commissioners: None
ATTEST: ~ _ --G-re_g_G_u_b_m....,~-- . ___. e~cr-e~ta--ry---=------

MINUTES OF THE CITY OF DIAMOND BAR

REGULAR MEETING OF THE PLANNING COMMISSION
February 24, 2026

1. CALL TO ORDER:

VC/Worthington called the meeting to order at 6:30 p.m. in the Windmill Community Room, 21810 Copley Drive, Diamond Bar, CA 91765.

PLEDGE OF ALLEGIANCE: Torres
ROLL CALL: Mehta, Torres, Mao, V/C Worthington
ABSENT: Rawlings
STAFF PRESENT: Greg Gubman, Community Development Director, Grace Lee, Planning Manager, Mayuko Nakajima, Senior
Planner, Neal Payton, Consultant, Arlene Laviera,
Administrative Coordinator; Dan Cruz, Assistant City
Attorney.

2. PUBLIC COMMENTS: None.

3. CONSENT CALENDAR:

3.1 MINUTES OF THE PLANNING COMMISSION REGULAR MEETING – February 10, 2026.

3.2 2025 GENERAL PLAN STATUS REPORT
Mao moved, and Torres seconded to approve consent calendar, items 3.1 and 3.2.

Motion carried 4-0-0-1 by the following Roll Call vote:

AYES: 4 COMMISSIONERS: Torres, Mao, Mehta, A/C Worthington NOES: 0 COMMISSIONERS: None
ABSTAIN: 0 COMMISSIONERS: None
ABSENT: 1 COMMISSIONERS: Rawlings

4. OLD BUSINESS:

5. NEW BUSINESS:

6. PUBLIC HEARING:

6.1 Development Code Amendment No. PL2024-51 (Objective Design Standards):

Environmental Assessment:

February 24, 2026 PAGE 2 PLANNING COMMISSION
On December 17, 2019, the Diamond Bar City Council certified Final EIR (No. SCH 2018051066) for the Diamond Bar 2040 General Plan and Climate Action Plan. In 2022, the City adopted the 2021-2029 Housing Element Update and concurrently amended the General Plan 2040 Land Use and Economic Development Element. The potential impacts of the 2021-2029 Housing Element Update and concurrent Land Use and Economic Development Element amendment were determined to be within the scope of the Certified EIR. The City concluded that neither a subsequent nor a supplemental EIR was required. Accordingly, the City adopted Addendum No. 1 to the Certified EIR on August 11, 2022.

The draft ODS anticipates residential and mixed-use development consistent with the assumptions in the 2040 General Plan and analyzed in the General Plan EIR. CEQA Guidelines Section 15164(a) states: “The lead agency or responsible agency shall prepare an addendum to a previously certified EIR if some changes or additions are necessary but none of the conditions described in Section 15162 calling for preparation of a subsequent EIR have occurred.” Pursuant to CEQA Guidelines Section 15164, the City has prepared Addendum No. 2 to the General Plan EIR (Attachment 2), which demonstrates that adoption of the ODS would not result in a new significant impact or a substantial increase in the severity of previously identified significant impacts analyzed in the Certified EIR for the City General Plan 2040. In addition, the information throughout the addendum affirms that there is no new information of substantial importance that was previously unknown and is now available. Therefore, a subsequent EIR would not be required pursuant to Section 15162 of the State CEQA Guidelines. The City has thus determined an addendum to the previously Certified EIR to be the appropriate environmental compliance document for the proposed project.

Recommended Action:

Adopt the attached resolution recommending the City Council approve Development Code Amendment No. PL2024-51, amending Title 22 of the Diamond Bar City Code (DBCC), adding Chapter 22.19 to establish multifamily and mixed-use residential ODS.

S/P Mayuko Nakajima presented the staff report.

Neal Payton, Torti Gallas + Partners consultant, provided an overview of the objective design standards.

VC/Worthington opened the public hearing.

Seeing no comments, closed the public hearing.

Torres moved, Mehta seconded to adopt Resolution Nos. 2026-03 recommending the City Council approve Development Code Amendment No. PL2024-51, amending Title 22 of the Diamond Bar City Code (DBCC), adding Chapter 22.19 to establish multifamily and mixedPage 617 of 618 February 24, 2026 PAGE 3 PLANNING COMMISSION
use residential ODS. Motion carried 4-0-0-1 by the following Roll Call vote:

AYES: 4 COMMISSIONERS:Mao, Mehta, Torres, VC/Worthington NOES: 0 COMMISSIONERS:None
ABSTAIN: 0 COMMISSIONERS:None
ABSENT: 1 COMMISSIONERS:Rawlings

7. PLANNING COMMISSION COMMENTS/INFORMATION ITEMS:

8. STAFF COMMENTS/INFORMATIONAL ITEMS:

CDD/Gubman confirmed the next scheduled Planning Commission on March 10, 2026 is cancelled.

9. SCHEDULE OF FUTURE EVENTS:

As noted in the agenda.

10. ADJOURNMENT: With no further business before the Planning Commission, VC/Worthington adjourned the Regular Planning Commission meeting at 6:52 p.m.

The foregoing minutes are hereby approved this 24th day of February, 2026.

Attest:

Respectfully Submitted,
_______________________________________
Greg Gubman, Community Development Director

____________________________
Brian Worthington, Vice Chairperson