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3.46 Retention pond design was based on the capacity to store two 100 year storms to <br /> the pond rim. The pond sideslopes will be 4:1 to comply with County Standards. <br /> Base elevation of the pond will be 5 ft above the highest ground water according <br /> to County Flood control records for 1984-86, which show depth to ground water of <br /> approximately 15 feet (depth is approximately 28 ft..Kleinfilder November. 1992). <br /> Attachment I is retention pond design sizing calculations. <br /> It should be noted that the transfer tunnel and recvcling storage areas are both <br /> below the grade of the proposed retention water surface under er storage of the nvo <br /> 100 vear storms (elev WS =23.9). <br /> The pond will be provided with an 8 foot chain link fence around the perimeter <br /> and an entry gate for maintenance. <br /> 3.48 Inlet Criteria <br /> Type I or 2 inlets will be used for curb and gutter areas (D-13 &14). combination <br /> manhole catch basins (24 inch grate) or Std 18 inch inlets will be used in other <br /> areas (D-15). <br /> .1.51 Alignment of drainage facilities <br /> The alignment of pipelines was based on straight line connection of inlets placed <br /> based upon surface flows. This generally will not result in pipes beneath and <br /> 0 — <br /> aligned along roadways because of the diverse alignment of roads and large paved <br /> areas. Junction catch basins will serve as manholes. <br /> 3.53 Closed conduit design <br /> Storm drain pipes will be reinforced concrete pipe (RCP, Class IV). The <br /> minimum cover over pipes according to calculations is 1.9 feet (Attachment 2). <br /> 3.54 Manholes and junction Boxes <br /> The majority of catch basins were also designed as manholes because of the <br /> changing slopes, directions, and sizes of pipes required. Maximum spacing will be <br /> 500 feet. Manholes will be 48 inch precast with inlet covers. <br /> 3.59 <br /> Pump Stations <br /> Two pumping stations are proposed for the project. One will be located in the <br /> transfer tunnel scale area. This sump pump will lift drainage from the transfer <br /> lane. The second will be located near the retention pond and will lift gravity flows <br /> from the depressed recycling storage area to the retention pond. A backup pump <br /> will be provided in both sumps. Preliminary pump station designs are in <br /> Attachment 3. <br /> 07549001.012-Ap,DE 2 Sepmmber 1-1.1993 <br />