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Environmental Checklist For CEQA Compliance Mitigation Measures WQ-1 During final design of the proposed project, the applicant will incorporate and adhere to all structural and nonstructural treatment and control BMPs identified to control water quality and waste water runoff identified in the Water Quality Management Plan (Appendix D) (MDS Consulting 2007). B. No Impact. The proposed project site is currently developed and is not considered a source for groundwater recharge. The proposed project would decrease the pervious area on site from 40% to 20%. Therefore, less than significant impacts would occur. C. Less Than Significant Impact. The existing site is generally impermeable to stormwater due to the impermeable surfaces on site. Currently, stormwater runoff, as sheet flows, is conveyed southerly to MacArthur Boulevard and then easterly to a 10-foot by 14-foot trapezoidal section of the earthen Greenville-Banning Channel (OCFCD Facility Number D03) (MDS Consulting 2007:7). It is finally discharged into Reach 1 of the Santa Ana River near the river mouth at the Pacific Ocean (MDS Consulting 2007: 7). Site drainage after development would be altered. stormwater runoff would be conveyed as sheet flows northerly to Alton Avenue. However, the City has determined and approved that discharge of the proposed project's stormwater into the existing 72-inch storm drain in Alton Avenue is acceptable (MDS Consulting 2007; Chin pers. comm.). The City determined that the change in drainage would be acceptable and can be easily accommodated by the 72-inch storm drain located in Alton Avenue. The stormwater would be treated prior to discharge to the Alton Avenue storm drain through incorporation of onsite BMPs. Additionally, no streams or rivers pass through the proposed project site. Less-than-significant impacts would occur. D. Less Than Significant Impact. The proposed project would not increase flooding potential or result in any substantial change in the drainage patterns on or adjacent to the project site. Because of the urban character of the area and the use of the project site as a warehouse, substantial amounts of stormwater are not readily absorbed into the soil. The proposed project would alter the existing drainage pattern of the project site; however, the City has determined the 72-inch storm drain located in Alton Avenue can accommodate the runoff generated by the project and has approved the discharge of runoff into the Alton Avenue storm drain (MDS Consulting 2007; Chin pers. comm.). Therefore, storm runoff generated by the proposed project would be conveyed as sheet flow to the project's proposed area drains and catch basins (MDS Consulting 2007). It would then be conveyed north to the Alton Avenue storm drain, and then west to the Greenville-Banning Channel (MDS Consulting 2007). The channel would convey it to the Pacific Ocean as in existing conditions. A less- than-significant impact would occur (MDS Consulting 2007). The 72-inch storm drain in Alton Avenue has the capacity to accept the storm runoff from the site. Additionally, the stormwater would meet water quality standards through the incorporation of onsite BMPs prior to discharge to the Alton Avenue storm drain. E. Less Than Significant Impact. The project site is located within the 100-year floodplain associated with the Prado Dam inundation zone (City of Santa Ana 1998: A-41). Prado Dam is a flood control and water conservation project constructed and operated by the U.S. Army Corps of Engineers, Los Angeles District. The Los Angeles District has begun construction to increase the capacity of the reservoir behind Prado Dam. Modifications to the dam are divided into three phases: Alton Court August 2007 Initial Study/Mitigated Negative Declaration 3-28 J&S 00635.07 75A-94