TECHNICAL MEMORANDUM
To: Sean Singletary (City of Culver City)
From: Katie Harrel, PE, ENV SP, QSD
Brianna Martilla
Date: July 8, 2025
Subject: Addendum to the Project Description in the Mitigated Negative Declaration for the Washington Boulevard Stormwater and Urban Runoff Diversion Project
1. Introduction
The City of Culver City (City) is implementing the Washington Boulevard Stormwater and Urban Runoff Diversion Project (Project) to capture and treat stormwater and urban runoff associated with dry- and wet-weather to assist the City in achieving the goals set forth in the approved Enhanced Watershed Management Program (EWMP) Plan for the Marina del Rey (MdR) Watershed.
An Initial Study and Mitigated Negative Declaration (IS/MND) was prepared and released for public review in June 2020. A Notice of Determination (NOD) was filed in August 2020. It was determined that the Project will not have a significant effect on the environment. The Project was advertised for construction bids in June 2023. However, the bids received exceeded the available budget. Therefore, alternative designs were explored to reduce the construction cost. This Technical Memorandum (TM) was prepared to summarize the updated project description, identify IS/MND sections that may have different impacts based on the updated project description, and assess the overall environmental impact of the proposed design modifications.
2. Updated Project Description
The original Project design involves diverting stormwater into subsurface storage systems before discharging to the sanitary sewer, where it would then be treated at Hyperion Water Treatment Plant, which is illustrated in Figure 2-1. Construction bids received in June 2023 exceeded the budget for the original design approach hence the construction contract was not awarded and the City sought alternative designs to reduce the construction costs while maintaining water quality benefits. The proposed modification is to install a smaller subsurface storage system beneath the sidewalk on Glencoe Avenue along with subsurface vaults where runoff will be filtered and treated by an Ultra-Violet (UV) Technical Memorandum
Addendum to the Project Description in the Mitigated Negative Declaration for the Washington Boulevard Stormwater and Urban Runoff Diversion Project
July 8, 2025
system. The treated stormwater and dry-weather runoff will be routed back to the storm drain via gravity flow. A small portion of flows will be retained in the subsurface storage system, which will be used to offset adjacent median irrigation. The improvements are illustrated in Figure 2-2.
The original Project was sized to capture the runoff volume from approximately 40 acres of areas within the City, whereas the modified Project will capture runoff from a larger drainage area of approximately 56 acres (including the Cities of Culver City and Los Angeles), improving benefits such as runoff volume and captured pollutants.
The Project aligns with the goals of the EWMP, as it improves water quality; captured runoff will be treated and discharged to the stormwater system to reduce the quantity of pollutants reaching the MdR Harbor.
Figure 2-1 Original Design Approach: Diversion to Sanitary Sewer
Technical Memorandum
Addendum to the Project Description in the Mitigated Negative Declaration for the Washington Boulevard Stormwater and Urban Runoff Diversion Project
July 8, 2025
Figure 2-2 Proposed Design Approach: Treat and Release
3. IS/MND Impact Assessment
The 2020 IS/MND was reviewed in comparison with the updated project design to identify differences in environmental impacts. Changes to specific Environmental Checklist sections are discussed and summarized in Table 3-1. The table only includes sections that have differences in environmental impacts or additional discussion of the impacts.
Technical Memorandum
Addendum to the Project Description in the Mitigated Negative Declaration for the Washington Boulevard Stormwater and Urban Runoff Diversion Project
July 8, 2025
Table 3-1 IS/MND Environmental Checklist Section Assessments Section Original Description Updated Description
3.9 Hydrology and
Water Quality
(Discussion)
The Project will reduce off-site
stormwater runoff by capturing that
runoff and eventually pumping it into
the sanitary sewer system.
Stormwater runoff will be treated with
a pretreatment and UV treatment
system before being directed back to
the storm drain via gravity flow. A
small portion of flows will be retained
in the subsurface storage system,
which will be used to offset onsite
irrigation. This modification does not
change the level of significance noted
in the IS/MND.
3.16 Transportation and
Traffic
(Environmental
Issue f)
Impacts are less than significant with
mitigation incorporated. Mitigation
Measure TRAF-1, the City shall
prepare a construction Traffic
Management Plan (TMP), will be
incorporated. A SYNCHRO model will
also be developed for modeling and
optimizing traffic signals timings.
Impacts are less than significant with
mitigation incorporated. Mitigation
Measure TRAF-1 will be implemented.
Traffic Control Plans have been
developed and indicate contractor
responsibilities and requirements. The
construction work area footprint is
smaller than the original design (no
subsurface storage on Washington
Boulevard). This modification does not
change the level of significance noted
in the IS/MND.
4. Conclusion
Section 15162 of the CEQA Guidelines requires a Subsequent CEQA document (Environmental Impact Report [EIR] or Mitigated/Negative Declaration) when the associated CEQA document has already been adopted or certified and one or more of the following circumstances exist:
1. Substantial changes are proposed in the project which will require major revisions of the previous CEQA document due to the involvement of new significant environmental effects or a substantial increase in the severity of previously identified significant effects;
2. Substantial changes occur with respect to the circumstances under which the project is undertaken, which will require major revisions of the previous CEQA document due to the involvement of new significant environmental effects or a substantial increase in the severity of previously identified significant effects; or
3. New information of substantial importance, which was not known and could not have been known with the exercise of reasonable diligence at the time the previous CEQA document was certified as complete/adopted, shows any of the following:
a. The project will have one or more significant effects not discussed in the previous CEQA document;
Technical Memorandum
Addendum to the Project Description in the Mitigated Negative Declaration for the Washington Boulevard Stormwater and Urban Runoff Diversion Project
July 8, 2025
b. Significant effects previously examined will be substantially more severe than shown in the CEQA document;
c. Mitigation measures or alternatives previously found not to be feasible would in fact be feasible, and would substantially reduce one or more significant effects of the project, but the project proponents decline to adopt the mitigation measure or alternative; or d. Mitigation measures or alternatives which are considerably different from those analyzed in the previous CEQA document would substantially reduce one or more significant effects on the environment, but the project proponents decline to adopt the mitigation measure or alternative.
As demonstrated by the analysis herein, the Project modifications would not result in new additional significant impacts, nor would it substantially increase the severity of previously anticipated significant impacts. Rather, the impacts associated with the Project modifications fall within the envelope of impacts addressed in the MND and do not constitute a new or substantially increased significant impact. Based on this determination, the Project modifications do not meet the requirements for preparation of a Subsequent or Supplemental CEQA document pursuant to Section 15162 of the CEQA Guidelines.