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~' MEMORANDUM TO MIKE~AGE....Con tinued • Page 2 <br />., ~ <br />3) Culverts in Mann Draw <br />The application states that two 60" circular culverts will be used to pass <br />the 10-year 24-hour peak flow. This is not the case in the field. There <br />are five pipe-arch culverts presently in place at the crossing. WCC must <br />provide the dimensions and slope of the culverts to verify the adequacy of <br />the installation. WCC should be aware that culverts with an end area <br />greater than 35 ft.2 must be capable of passing the 20-year 24-hour storm <br />peak flow (4.03.1 (4) (e) (i)). WCC needs only supply the above requested <br />information and adequacy will be determined by this office. <br />4) Structural Strenth of Culverts <br />This Division is required to determine the ability of the installed culverts <br />"to sustain the vertical soil pressure, the passive resistance of the founda- <br />tion, and the weight of vehicles to be used." WCC must submit the following <br />information: cover depth, gross vehicle weight of coal haul trucks, thickness <br />of the culvert pipe, size and type of corregations and the size of pipe <br />used for each culvert installation. <br />S) Culvert Designs <br />There are four other culvert installations on the haul road. No design <br />information was provided in the application for any culvert installations <br />other than the Mann Draw installation. WCC must provide the following in- <br />formation for each culvert installation: <br />(1) 20-year 24-hour storm peak flow and, <br />a) methodology and assumptions used in the determination; <br />b) drainage basin area, slope, land use condition and soil type. <br />(2) Diameter and slope of installed culverts. <br />6) Pond Dewa ter <br />The pond dewatering system shown in the application is substantially different <br />than that which is in place at the site. The ponds at the site have gated <br />outlets. These outlet works appear to be within the sediment storage volume. <br />WCC should state what the purpose of these gates is. <br />The only item which I feel must be addressed prior to issuance of a permit <br />is item 6. Keep me informed of alI future submittals by WCC. <br />RD:ms <br />