Reso 2004-069 - Laserfiche WebLink

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PO f E\TIA1.Ll~ POTS\TIALLY SIG\FIG~~~1~ LESSTIIAX ISSUES SIGSIFIGIAT L,ALFSS SIGAIH'ICAAT ~~~ SOCRCES ISSCES b1rIIG4'r10A 1A'IPACT 1~7PACf I~CORPORAI~t~D EXPLANATIOIV~: a-k) The DMMS represents a modif red hydrologic condition. Dredging, with disposal of dredged sediments into the DMMS, occurs approximately every four to five years. The site would continue to be operated in accordance with the DMMS Management Plan. The site would be seasonally flooded by retaining rainwater and by bringing tidal water to the site from the adjacent Shoreline Marshlands enhancement area. Drainage patterns will remain unchanged. Absorption rates could change when the DMMS is flooded, but the amount and rate of runoff from Uie site would not change because all water will be contained on site. All flow from the site is strictly controlled with the four weirs on the northern le~~ee. All rainfall, including that generated during a 100-year storm event could be stored on site. No other off-site water flows onto the site. Cun-ently, the DMMS seasonally ponds captured rainwater and also contains a weir designed to allow periodic tidal flooding. The. proposed project would enhance this tidal flooding through an existing inundation weir by lowering DMMS ground elevations, enabling seasonal water coverage of at ]east 50 percent of the total DMMS under optimal conditions. This inundation would cake place during the winter months and when the site is not receiving or drying dredged material. Inundation of the site in this manner would enhance its value for shorebirds during the winter and spring season. Recent and past analyses of the sediments «•ithin the DMMS indicate that all constituent concentrations are below that considered acceptable by the Regional Water Quality Control Board using the most stringent criteria applied to sediment placement projects such as this (see Table 4-]). In particular, recent analysis of the sediments in the San Leandro Marina Entrance Channel prior to the maintenance dredging affirmed that the quality of these sediments is similar to that of sediments previously present in the DMMS. Consequently, the beneficial reuse of the dredged sediments would not result in any significant water quality impacts. San Leandro Dredged Material Management Site 6 March / 2004 Sediment Remo~~al Project