07/25/2007 Env Bd Packet - Laserfiche WebLink

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• • the 2.8 -inch infiltration /retention standard, existing surface would be subject only to an 0.8 -inch standard (Paragraph 3(b)(ii)(c). Finally, the rule specifically would exempt pure mill and overlay work on roads or other linear projects from the permit requirement (Paragraph 2(g)). C. Volume Control and Water Quality A prominent focus of this rule revision is to promote on -site stormwater management for purposes of water quality and local water resource and habitat protection. In addition, on -site management can be more cost - effective and require less maintenance than downgradient "end of pipe" controls. The present rules require construction of detention basins for stormwater management (Paragraph 3(f)) and state a preference for a regional approach to management (Section 1). The proposed rules, instead, state a policy to "[m]aximize infiltration on individual sites through Better Site Design practices and advanced stormwater management to control runoff volume increases" (Section 1). The rules, however, do recognize that for certain site conditions, it will be infeasible to fully infiltrate on site and that water quality and peak flow management will require use of a National Urban Runoff Program (NURP) pond (designed to hold the 2.5 -inch storm event) or other basin. In this case, absent local groundwater concerns the District retains its preference for regional basins as they are more efficient from a land use perspective and more reliably maintained (Paragraph 3(b)(i)(a)). Further, the District recognizes that some existing basins were designed, built and funded to provide for regional treatment under certain build -out assumptions. While this does not make development within the contributing area immune from the evolution of stormwater management standards, the District intends to take these circumstances into account (Paragraph 3(b)(i)(a)). The present rule requires the use of Best Management Practices to meet the criterion of infiltrating the median (0.34 -inch) storm within 72 hours (Paragraph 3(k)). A separate provision (Paragraph 3(f)) requires treatment to the National Urban Runoff Program (NURP) standard of 50 percent phosphorus removal through stormwater detention. • Under the proposed rule, these criteria would be combined into a single standard requiring infiltration, or where not feasible detention, of the two -year (2.8 -inch) storm 7