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7.4 Stormwater Routing and Retention <br />The retention pond volume was calculated using the Haestad Pond Pack software utilizing SCS <br />methods. DRMS requires complete retention of the 10 -year runoff, with the ability to properly <br />pass the 100 -year flows downstream. Analysis of the proposed retention pond indicates it will <br />exceed this standard by being large enough to collect and completely store onsite runoff from the <br />100 -year event with no discharge downstream. Worksheets and results of the stormwater routing <br />and retention calculations are included in the attachments, but a summary follows: <br />ONSITE BASIN TOP OF POND ELEV 100 - YR WATER SURFACE <br />Basin 30 Top of bank: 6360.00 6357.10 <br />7.5 Recommended Modifications to Existing BMP Structures <br />Given the information provided in this report, analysis has shown that the proposed site BMPs <br />(diversion channels, berms, and retention pond) are properly sized and capable of managing <br />stormwater for the site in compliance with DRMS criteria. <br />8.0 Stormwater Management Plans <br />8.1 Best Management Practices <br />BMPs for the site include the following: <br />• Divert off -site runoff around stockpile areas <br />• Retention of onsite surface runoff <br />• Secondary containment of above ground fuel tank <br />• Proper storage of petroleum products <br />• Good site housekeeping <br />The above ground diesel fuel tank should be locked when personnel are not present at the site. <br />Secondary containment at the site includes a lined retention basin capable of containing at least <br />110 percent of the volume of the tank. Periodic inspections of the containment area are to ensure <br />that precipitation is pumped from the containment area as needed. <br />All small quantities of petroleum products should be stored indoors out of the weather in the <br />maintenance shed. Any spills in the shed should be cleaned immediately and the waste oils <br />properly disposed. <br />Good housekeeping procedures should be implemented at the site at all times. Trash, especially <br />used lubricating and hydraulic oil containers, should be picked up and periodically removed from <br />the site. Oil spills should be cleaned up and the stained soils placed in containers or on plastic <br />sheets and allowed to evaporate. <br />ESWMP -7 <br />