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• <br />-5- <br />are shown. This method is inappropriate for closed conduit designs. The <br />applicant should use a closed conduit hydraulics to design the culverts (see <br />nomograph attached). Several of the culverts have no design information given. <br />Dorchester Coal Company must present designs for all of the culverts to satisfy <br />4.03.1(4)(e) and 4.03.2(4)(e). <br />6. Ditch Designs: The parameters needed to determine the peak flow using the <br />SCS method referenced in the permit application are not given in the application. <br />Dorchester Coal Company must: <br />A. Submit copies of the calculations used to estimate peak flows for each <br />of the ditches including: <br />i. contributing areas, <br />ii. curve numbers, and <br />iii. surface slope. <br />B. Provide a map which delineates the watershed areas contributing to the <br />upslope diversions (perimeter ditches). <br />7. Ditch designs for the western portion of the perimeter diversion and collection <br />system are not given in the recent application. The applicant must present <br />design dimensions for the entire perimeter/diversion ditch system. Design <br />dimensions for the section of the permimeter diversion labeled D to E are incomplete. <br />The applicant must submit the top width dimension in order to completely define <br />the geometry of the channel. <br />8. Actual ditch velocities in the diversion/collection system are very high <br />and erosive. The applicant claims these channels are not erodible and conver- <br />sations with personnel who have inspected the site confirm this. However, <br />areas of erodible soils are crossed in some parts of the system especially near <br />the sediment ponds. Protection measures taken at these sites must be detailed <br />in order to estimate their effectiveness in controlling erosion. <br />9. The applicant must provide a detailed drawing of Pond No. 1 as no drawing <br />of this structure is provided. <br />10. The drawing supplied by the applicant of Pond No. 2, does not provide <br />sufficient dimensional information to determine the elevation difference be- <br />tween the dam crest and the crest of the spillway. This information is necessary <br />to determine if the passage of the 25-year event allows the required 1' of free- <br />board. Please: <br />A. Provide drawings of both sediment ponds with sufficient dimensional <br />detail to determine the elevation difference between the dam crest and <br />that of the spillway crest. <br />B. Estimate the head necessary to generate the design flow and insure that <br />the 1' of freeboard required (4.05.6(S)(d)) will be allowed. <br />11. The applicant has not indicated the calculation of the minimum sediment <br />storage volume or provisions for periodic sediment removal as required by <br />4.05.6(3)(b). Please provide this information. Also, please indicate whether <br />inflow from the mine workings will be pumped into the pond if encountered. <br />The capacity of the pond must allow for this. <br />