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Permit Revision No. 7 -Responses March 7, ]997 Page 7 38. The SEDCAD run has been revised accordingly in regazds to the elevations ofthe weep holes on the pond discharge structure. 39. Elevations of all relevant points have been added to the plan and cross-section views of the SG-1 embankment as shown on drawing number E611304A. 40. The type of decant system proposed for SG-1 is relatively common for applications where suspended solids, rather than chemical contaminants, are the primary parameter of concern. Golder Associates has designed similar decant systems for sediment ponds at other sites in the U. S. and has had no problems with their performance. The decant system has been conservatively sized to convey the peak flow necessary for proper operation of the sediment pond. Routine maintenance of the decant system will insure that the decant system does not become clogged. The decant system has also been designed for easy clean out and sand placement should the system become clogged. MCC is comfortable that the decant system will work as designed and plugging of the drain will not be an issue. The pond itself has been oversized to include additional storage volume, so it is highly unlikely that the pond would overtop should the decant system become plugged. In addition, the pond will be located in an area that will be visited by mine personnel at least once a day, but probably more, and the water level of the pond will be observed. As with the other sediment ponds on site, sampling will be performed to ensure that eflluent sediment concentration requirements are met before discharge. The 180 degree bend has been eliminated from the design of the decant system. 41. Best Management Practices (BMPs) such as silt fences and straw bales will be utilized for primary sediment control for Small Area Exemptions. MCC's experience has shown that these control practices are effective. SEDCAD soflwaze does not have the capability to accurately model these controls. SAE demonstrations modeled with SEDCAD show that if the primary control practices fail, it will not be likely that sediment will reach the natural channel as it will be filtered through existing vegetation and vegetative debris. This demonstration is similar to other SAE demonstrations that have been performed at West Elk and other mine sites and approved by the Division. If there is concentrated flow off the site, sampling will be performed to verify that ellluent standards are being met. The November 12, 1996 letter from Golder Associates has been revised. 42. Clear-water upland diversion ditches have been included in the SEDCAD designs for the SAES. These ditches for the topsoil piles are shown on construction drawing E611305A and the ditch for the substation is shown on construction drawing Etil l lOSA. All the channels will be grass lined and one foot deep (see channel type A on construction drawing E611307A). 43. The SEDCAD runs have been revised accordingly.