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Ms. Christine Johnston Mountain Coal Company Page 23 April 14, 1997 94. The culvert performance curves of the March 7, 1997 Sedcad submittal shows zeroes for most of the dischazges. Please explain. Also, most of the culvert designs use a maximum headwater of 5.5 feet. Is there that much headwater in the field for each of these culverts? 95. Referring to Drawing E611304A, it appears that the pond SG-1 embankment is very close to, or within, the drainage azea of Sylvester Gulch. Please demonstrate that, during a 100 year-24 hour precipitation event, no Sylvester Gulch drainage flow will flow onto the pond embankment and compromise the embankment stability. 96. Please provide certifications for the E611xxx series of drawings. 97. Please recheck the cross-sectional area for culvert CSLY-4. Chart 42 of the March 7, 1997 Sedcad design for that culvert used across-sectional area of 88 square feet. My calculations show that the cross-sectional azea would be around 70 square feet. Please revise the culvert sizing diagram, and any other references to this culvert's size, if this is correct. Also, Chart 42 shows a discharge of about 620 cfs. The March 7, 1997 Sedcad submittal shows a discharge of 651.17 cfs. Please modify Chart 42 if you agree. If the above modifications need to be made, the possibility exists that there will be a headwater/diameter ratio greater than one for culvert CSLY-4. In other wards, during the peak flow fora 100 year-24 hour event, water would back up behind the culvert CSLY-4 inlet. If this is possible, please demonstrate that water would not flow onto the pond SG-1 embankment, and compromise the stability of that embankment. 98. Is culvert CSLY-7 positioned correctly to allow all runoff to pass under the road leading to the electric borehole? [t appears that the road can get washed out by drainage from sub- basin 43B. 99. In Table 43E of the March 7, 1997 submittal, the values of runoff and discharge are reversed, for pond SG-I. Please provide a revised Table 43E. 100. In Attachment 43E-1, Watershed Runoff Summary, under the headings of 10-year discharge and 10-year runoff, most of the values aze for the 25-yeaz event yeaz, while only a few are for the l0-yeaz event. Please clarify. 101. In Attachment 43E-1, Watershed Runoff Summary, under the heading of 100-year discharge, please change the value for sub-basin 45A from 3 cfs to 21.69 cfs, if you agree. 102. In the March 7, ] 997 Sedcad run for ditch DCW-6C, the discharge value used is 6.00 cfs. However, the 100-yeaz discharge is 19.52 cfs, as shown in Table 44E. If you agree, please revise the ditch design and any reference to that ditch size.