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• will not cause erosion of the coarse-grained material that comprises the lower <br /> yard area. <br /> The maximum slope of the ditch banks is 2h:1v for areas where the ditch must <br /> be constructed in areas of high topographic relief. For other areas, a bank slope <br /> of 5h:1v will be constructed to facilitate easy maintenance with rubber-tired <br /> loaders. <br /> 2.3.1.3 Storm Water Capture and Treatment (BMPs) <br /> In 1994, Henderson constructed a sediment trap north of Pond 1.2. This trap <br /> was designed to remove sediment from storm water prior to discharge. Wheeler <br /> revisited the design of this trap and compared its design with criteria used by the <br /> Urban Drainage and Flood Control District to determine its continued suitability. <br /> 2.3.2 Results of Evaluation — Snowmelt and Runoff <br /> • <br /> 2.3.2.1 Sub-Basin Designation <br /> As per Figure 4, three sub-basins were designated for analysis. <br /> • Basin Al — Al includes the upper yard area around No. 3 Shaft and the <br /> Plant Services building. This basin is bounded on the south by the paved <br /> road through the No. 1 Shaft yard. Drainage south of this boundary flows to <br /> the ditch behind No. 1 Shaft. The east and west boundaries were chosen <br /> based on whether runoff would drain onto the Pond 1.2 area, towards No. 1 <br /> Pond, or onto the lower yard in the vicinity of the sewage treatment plant. <br /> The area of this sub-basin is 2.14 acres. <br /> • Basin A2 — A2 is the sludge impoundment area in Pond 1.2. Al will be <br /> separated from A2 by construction of an interceptor ditch along the toe of the <br /> slope below No. 1 Shaft. The area of A2 is 2.63 acres. <br /> AM <br /> 8 <br /> June]9.1999 <br /> TR . <br />