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Table 17.7. Total phosphorus load (lbs/yr) entering and exiting several of the major <br />proposed detention basins and infiltration basins. <br />BMP and Sub - <br />watershed (see <br />Figure 12.1) <br />lbs TP/yr <br />With central corridor <br />facilities only <br />With additional on -site storage <br />Detention basin in In <br />sub -watershed 7 <br />Out <br />Infiltration basin in In <br />sub -watershed 8 <br />Out <br />Detention basin in In <br />sub -watershed 18 <br />Out <br />Infiltration basin in In <br />sub -watershed 19 <br />Out <br />27.3 15.6 <br />10.2 <br />31.5 <br />0 <br />35.2 <br />9.5 <br />32.1 <br />0 <br />4.3 <br />16.0 <br />0 <br />20.4 <br />3.7 <br />16.9 <br />0 <br />Detention basin in <br />sub -watershed 25 <br />Detention basin in <br />sub -watershed 26 <br />(south of TH10) <br />In <br />Out <br />64.6 <br />38.4 <br />In 38.4 <br />Out 24.0 <br />24.0 <br />Infiltration basin in <br />sub -watershed 26 <br />(south of TH10) <br />In <br />Out <br />34.6 <br />20.2 <br />20.2 <br />12.6 <br />12.6 <br />18.9 9.5 <br />Summary of tpvironmental Impact. The incorporation of a stormwater management <br />system into the RTC site as it develops raises the need for proper collection, routing and <br />storage of runoff. The standard routing of the 100-year frequency event without <br />consideration of any infiltration, in accordance with LRRWMO regulations, yields a <br />volume of 113 ac-ft that must be accounted for in on -site or near -site storage. When <br />infiltration is considered, the volume can be reduced to 105 ac-ft. For events with a <br />return frequency less than 100-years, infiltration can be designed to reduce volume <br />substantially and provide continued recharge to a certain degree. <br />Miti g ttion element. The conversion of agricultural land to urban land ultimately <br />increases s the amount and rate of runoff leaving the land. Minimizing the impact of that <br />increased runoff is the objective of this mitigation plan. <br />17-13 <br />