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' BENDER READY -MIX CONCRETE MANUFACTURING PROJECT Initial Study /Mitigated Negative Declaration C) Substantially alter the existing drainage pattern of the site or area, including through the alteration of the course of stream or river, in a manner which would result in substantial erosion ' or siltation on- or off -site? Less Than Significant Impact With Mitigation Incorporated. The proposed project site is generally ' flat and has been disturbed by existing development. As stated in Responses 4.6(b) and 4.9(a), construction- related erosion and siltation impacts would be less than significant upon implementation of Mitigation Measure GEO-2. ' As stated above, the proposed project area is fully developed and industrialized. The site lacks permanent on -site stormwater conveyance facilities, and drainage currently either sheet flows towards South Santa Fe Street, ponds on -site, or is recycled along with wash water utilize during operations. ' Drainage that sheet flows off -site is conveyed by an existing gutter along South Santa Fe Street to an existing concrete drainage channel located approximately 500 feet southeast of the project site .4 ' None of the improvements associated with the project would substantially alter drainage patterns at the site. The proposed project would implement three segments of 24 -inch bottomless trench that would drain into landscaped areas or the proposed detention /desilting basin. These water quality ' improvements would result in a beneficial impact in relation to erosion and siltation on- and off -site. Thus, long -term operational impacts would be less than significant. ' Mitigation Measures: Refer to Mitigation Measure GEO -2. No additional mitigation is required. d) Substantially alter the existing drainage pattem of the site or area, including through the ' alteration of the course of a stream or river, or substantially increase the rate or amount of surface runoff in a manner which would result in flooding on- or off -site? No Impact The proposed project site has been historically developed with industrial uses and has not ' been subject to substantial flooding due to the alteration of drainage patterns in the site vicinity. Aesthetic, drainage, water quality, and .safety improvements associated with the project would not substantially alter the existing drainage pattern of the site. Rather, beneficial impacts would occur since the amount of pervious area would be increased due to proposed landscaping and water quality features on -site. No impacts would occur in this regard. ' Mitigation Measures: No mitigation is required. e) 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? Less Than Significant Imnact With Mitigation Incorporated. Refer to Responses 4.6(b) and 4.9(a), 4.9(c), and 4.9(d). Construction - related erosion and siltation impacts would be less than significant ' upon implementation of Mitigation Measure GEO -2. The project would result in beneficial impacts related to long -term operations since drainage /water quality features would be implemented on -site, and the amount of pervious area would be increased. Thus, impacts would be less than significant ' upon implementation of the recommended mitigation measure. Mitigation Measures: Refer to Mitigation Measure GEO -2. No additional mitigation is required. 4 CalCoast Engineering & Design Group, Hydrology Study, Bender Ready Mix, May 30, 2011. JULY 2011 4.9 -3 HYDROLOGY AND WATER QUALITY 31A-67