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7.B. - Page 86 2 Environmental Analysis <br /> c)Substantially alter the existing drainage pattern of the site or area, including through the <br /> alteration of the course of a stream or river,in a manner which would result in substantial <br /> erosion or siltation on- or off-site? <br /> The stormwater collected at the replacement pump station and wet well would discharge through an <br /> existing 24-inch line. The new pump station would have a wet-well structure capable of collecting up <br /> to 2,900 cubic feet of stormwater. The new pump station would be capable of discharging up to <br /> 32.40 cfs, the predicted flow from the 100-year storm,which would decrease the potential for <br /> flooding in the area. <br /> The discharge rate from the pump station would increase from 13.37 cfs to 32.40 cfs. The new <br /> station would interconnect to the existing 24-inch pipeline to the creek. During peak storms,the <br /> flow through the existing pipeline would increase from approximately 4.3 fps to 10.3 fps. The <br /> increase in discharge into the creek would occur during storm events when runoff was greater than <br /> the discharge from the current pump station. During these events, the water level in the creek would <br /> be higher than normal. The increased flow of 10.3 fps would slightly exceed the 10.0 fps design <br /> criteria for the existing 24-inch pipe, but would not result in substantial erosion or siltation of the <br /> creek bed. (Less than Significant Impact) <br /> d)Substantially alter the existing drainage pattern of the site or area, including through the <br /> alteration of the course of a stream or river, or substantially increase the rate or amount of <br /> surface runoff in a manner which would result in flooding on- or off-site? <br /> See the discussion in item c above concerning the proposed changes to the existing drainage pattern <br /> in the site area. The upgraded pump station would reduce the potential for flooding in the Bair <br /> Island drainage area,and the increased discharge to Redwood Creek during peak storm events would <br /> be an insignificant increase in channeled downstream flows to the Bay. (Less than Significant <br /> Impact) <br /> e) Create or contribute runoff water which would exceed the capacity of existing or planned <br /> stormwater drainage systems or provide substantial additional sources of polluted runoff? <br /> The proposed joint-use path and sidewalks would add approximately 9,000 square feet (0.20 acres) of <br /> new impervious surfaces to the existing area. Stormwater along the joint-use path would be collected <br /> and discharge through a new 24-inch pipe. The new impervious surfaces would not substantially <br /> alter the existing drainage patterns of the project area given the small footprint and relatively flat <br /> nature of the project. The new pump station and wet well would be underground, and the emergency <br /> generator housing would be smaller than the existing pump station. The additional impervious <br /> surface represents 0.004 percent of the existing total watershed area of Redwood Creek <br /> The pump station replacement project would not alter surface drainage patterns in the 22.28-acre <br /> collection area along Bair Island Road,which includes 4.94 acres of Peninsula Park development that <br /> drain into the station. Under the proposed project, the City would install approximately 35 linear feet <br /> 2-46 US 101 Pedestrian Undercrossing and Bair <br /> Island Road Storm Drain Pump Station Project <br />