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Page 2 Mike Savage December 19, 1980 the use of 0.90 to 1.00 for areas mined and regraded. Your alternative is to assume worst case conditions using a C factor in the range quoted above, or submit a mining sequence table which incorporates and averages C valves over a one year period of mining. The latter procedure is outlined in "Hydrology and Sedimentology of Surface Mined Lands" by Barfield and Naan. In response to your request of a one year sediment storage volume approval, I have discussed the issue with Carol Pahlke and Jerry Zimpfer of our staff. We will allow approval of a 1 year storage only if TBM can demonstrate that a 20 year 24 hour storm will result in a sediment volume that is less than 50% of your design sediment storage volume. You would have to submit calculations of sediment yield from a 10 year 24 hour storm. Your alternative to this would be to design all ponds with a 2 year sediment storage volume. q9. TBM must indicate that topsoil will be stripped from all areas to be disturbed during pond construction including areas under and adjacent to the embankment as well as the area under the 100 sediment storage of the pond. ~t10. Carol Pahlke has indicated to me that a collection ditch is located along the county road below the coal stockpile area. If this ditch is used to collect water from a portion of the disturbed area into pond 15-PI then the designs and location on a map must be submitted. N12. Culvert C4 is under a haul road and must comply with Section 715.17(1) (2)(iii). It makes no difference who installed the culvert. Also culvert C-6 is vital to your sediment control system. If this culvert is not designed to handle a 10 year event, then water will back up and flow into your collection ditch to pond 25-P1. The culvert design must be submitted to check capacity or we will require Pond 15-P1 to be designed to handle runoff from undisturbed areas. I have some additional comments that pertain to sediment control structures and culverts that have at present not been addressed. Culvert Designs A complete review of culverts throughout the mine area is not possible until additional information is submitted. Information for all culverts must include: a. whether the pipe is helical, annular, no corrugations, etc.; b. the type of pipe used (i.e. CMP, concrete, structural plate, etc.); c. whether the culverts are projecting, mitered, inlet controlled or outlet control; d. the design headwater; e. whether rock, cement, or metal headwalls will be used; f. the length of the culvert and the tailwater depth if the culvert is outlet controlled;