Planning Commission Agenda Packet 102225 (1)

August 7, 2025 Page 5 BKF ENGINEERS project would need to be primarily residential and have a minimum gross density of 40 dwelling units per acre. For a 15 acre site, this would require at least 600 dwelling units; the project is currently projected to have a maximum of 1,300 dwelling units, which would meet this requirement. The project would need to be considered a preserved housing project with deed restriction running at least 55 years, at rent/mortgage rates (including utilities) no greater than 30 percent of the area median household income (AMI) limits adjusted for household size. Additionally, the project would need to demonstrate the technical or economic infeasibility of treating the stormwater with on-site, off-site, or regional LID treatment measures, including demonstrating technical constraints that preclude the use of any onsite landscaped areas for LID treatment. If the project meets these requirements, it would be eligible for LID treatment reduction credits based on the percentage of dwelling units that are in each Area Median Household Income (AMI) category. If all units are free to tenants and do not charge any rent / mortgage, up to 100% of the stormwater may be treated with non-LID treatment methods. Refer to Appendix E for the Special Projects Worksheet used within Alameda County to determine the LID treatment reduction credits a project may qualify for. If the project does not meet the criteria for LID treatment reduction or treatment with a proprietary stormwater media filter is not preferred, the project will need to install LID treatment such as bioretention areas. Assuming the 14.9 acre site is 85% impervious, the estimated required treatment facility area for the project is approximately 22,000 square feet (0.5 acres). 12. Hydromodification Management Changes in the timing and runoff from a site, known as hydromodification, can damage or erode natural creeks and channels. Since 2007, Hydromodification Management (HM) techniques have been required in the Bay Area in areas susceptible to hydromodification. The project site is located in an area susceptible to hydromodification, based on the susceptibility map included in Appendix F. Projects in this area are required to comply with HM requirements if they create and/or replace one acre of more of impervious surface and increase impervious surface over pre-project conditions. In order to comply with HM requirements, the project would need to implement flow duration stormwater control measures (such as large detention systems) to ensure that post-project stormwater discharge rates and durations match pre-project discharge rates and durations. Analysis using the Bay Area Hydrology Model would also be required. Since the existing site discharges stormwater to two different storm drain systems and multiple outfalls to Hewlett Canal, the analysis would need to show that discharge rates and durations are not increased at any of the existing outfall locations. This may require separate flow duration stormwater control measures for each outfall. Since the existing project site is mostly impervious, we recommend that the project seek to decrease the total impervious area on the site, so that the project will not be subject to HM requirements. Decreasing the impervious area can be achieved by providing landscaped areas, bioretention areas, and / or green roofs. If needed, the project may also implement pervious pavement to further decrease the impervious area of the site. DRA F T