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Mitigation Monitoring and Reporting Program B. Infraztrucmre Systems: Drainage <br />Page 9 <br />INFRASTRUCTURE SYSTEMS: DRAINAGE <br />Mitigation Measure: Bla. Provide for onaite detention/retention of storm waters to offset <br />the efI'eMS of the increase in runoff to the Arroyo resulfing from !, <br />site development, and prepare a maintenance plan for deters- 'I <br />tiodretentim facilities. '~ <br />Impact to be Mitigated: Runoff from the site under the 100-year flood may contribute [o cumula- <br /> tive downstream flooding and channel erosion if onsi[e facilities are <br /> improperly sized or managed. <br />AgencyQndividual <br />Responsible for (1, 2) Site developer <br />Implementation: (3, 4) City of Pleasanton <br />Implementation Timing: (1) Prior to and during site preparation (e.g., grading) on any parcel <br /> (2) Upon completion of grading of the site <br /> (3) Prior to final inspection for [he firs[ building on [he site <br /> (4) .Ongoing over the life of the project <br />Mitigation Specifications: Requirement: <br />The DEIR states that, with development consistent with the proposed <br />project, runoff from the site would increase by approximately 82 cubic <br />Fee[ per second (cfs), and that this amount of runoff could be accommo- <br />dated by a detention basin with capacity of 24 acre-feet. <br />Authority: <br />The August, 2000 Specific Plan includes two policies and two guidelines <br />that provide the authority for implementation of this mitigation measure: <br />Storm Drainage Policy 2: Flood Control. Minimize the effects of <br />downstream flooding az a result of increased impervious surface due <br />to Plan Area development, and protect the Planning Area from <br />flooding. <br />Guideline 2.1: hr developing the Phase I public <br />improvements, incorporate stone water detention basins into the <br />Phase II portion of [he project which are capable of remining the <br />increase in post-development peak mnoff from the site resulting <br />from a 100-year storm event. <br />