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1. Runoff Curve Number (CN) <br /> Cover description CN Soil Group Area(Acre) <br /> porous gravel 86 C 0.050 <br /> CN (weighted) : 86.0 <br /> Total Area: 0.050 Acre <br /> 2. Runoff <br /> Return Period: 100-Year <br /> Rainfall, P: 3.00 in <br /> Runoff, Q: 1.6625 in <br /> Runoff Volume: 0.0069 Acre-Ft <br /> This area of.0069 acre feet is 11.1 cubic yards Therefore, the 3 sided swale must be able to <br /> hold this volume to prevent a discharge. The swale and road will be created to contain this <br /> volume. It should be kept in mind that all mine road runoff has never been subject to <br /> discharge permits at coal mines <br /> Since the new access road on the north side of the River is longer due to its milder grade, the <br /> road will be graded at approximately 2% to the outside (west side) where a ditch of 8 inches <br /> depth will be constructed. Four small sumps of 12 cubic yards each will be installed at equal <br /> distances starting from the bottom of the road to the road crossing. At each sump, a small <br /> swale of approximately]foot height in the road will direct road runoff to the sump. By <br /> having four such sumps, no large amount of water can accumulate in the ditch, and no water <br /> can leave the site. The attached sketch titled North Access Road Hydrology Detail shows how <br /> this sediment control design will be installed A full comprehensive Stormwater Management <br /> Plan will be developed for the site and will be submitted to the Division once it is finalized. <br />