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~- <br />• i <br />' - from SB-2 could enter into the gravel processing operations. <br />Because of this situation, it has been decided to construct an <br />' _ interceptor ditch along the south side of SB-2 to collect the <br />drainage flows and route them into the existing pond. This is <br />shown in the grading and drainage plans that have been prepared for <br />' the Phase I portion of the work. <br />' - IV. PEAK DISCHARGES <br />Presented in Table I is a summary of the 100 year discharge values <br />' - for both the on-site and off-site basins. The discharge values are <br />based upon the SCS soil groupings and metho- dology presented in <br />_ the SCS Technical Release 55 (TR-55, June 1986). Copies of the <br />' calculations are presented in the Appendix of this report. <br />Examination of the SCS soil maps show that the project site <br />' (including off-site basins) consists of soil groupings B 6 C. The <br />soils include sedillo, pescar, and sycle. The soils that are in <br />the soil grouping of "B" were the ones that were affected by the <br />storm flows. Based upon these soil groups, type of vegetation <br />cover and proposed development, weighted curve numbers and <br />corresponding discharges were determined. <br />V. RETENTION REQUIREMENTS <br />As shown in Table I, developed discharges were determined for the <br />' on-site basins, SB-4, and SB-5. From the changes in discharge <br />amounts for the basins, retention requirements were determined <br />' _ based upon the "Modified Rational Method" and are included in the <br />Appendix. <br />' For SB-4, it is planned to route the storm flows into an intercep- <br />tor ditch and into a small small oil/grease seperation pond. From <br />1 this pond, the flows could enter the secondary settling pond. From <br />_ the settling pond, the storm flows will enter the larger pond by <br />' infiltration. Hased upon the piping outlet configuration, the <br />smaller flows (5, 10 year storm events) would leave the oil/grease <br />' pond and enter the existing channel that flows towards the Los <br />Pinos River. It is intended that the oil/grease pond would act as <br />a stormwater detention pond for smaller storm events and would <br />' allow larger storm waters to the routed to the larger settling pond <br />as necessary. <br />-2- <br />