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-4- <br />2. Designation of Drainage Areas <br />Several of the drainage area designations shown on the Hydrology <br />Map (sheet 2 of 4) of the adequacy response are somewhat different than <br />one would expect considering the existing topography. One example is <br />the tributary area for Pond 4. Unless a diversion exists, the applicant <br />must expand the tributary area and show the pond to be capable of <br />meeting all requirements of (4.05.6). (See the Diversion section for <br />a further discussion.) <br />3. Small Area Exemptions <br />During the period when the interim permit regulations were in effect, <br />several small area exemptions for sediment control wez•e requested and <br />granted as follows: <br />Area Approval Date <br />Truck Scale 1•farch 25, 1981 <br />Road 5 Topsoil Stockpile April 14, 1981 <br />Substation k'2 and Powerline September 22, 1981 <br />The small area exemptions must be shown on the Hydrology hfap. Since <br />some drainages will be modified under the new plan, justification for <br />the necessity of each small area exemption must be readdressed. <br />4. Sediment and Water Storage Volumes <br />As was shown in Section 2.05.6(3) of the adequacy response, sediment <br />pond kl is used in the coal preparation plant water system as well as <br />fot a sediment pond. The engineeriny designs must take into account <br />this dual function. The items to be considered are: <br />a. the anpunt of sediment being generated by the plant and by <br />the surrounding areas, <br />b, maintenance scheduling, and <br />c. sediment pond storage volumes must be in addition to the maximum <br />storage volumes for the use as a plant water pond. Note: the <br />application must state the maximum total sediment storage volumes <br />and the maximum level of water retention with a storm event. <br />5. Pond Spillway Designs <br />The method shown for spillway design in Volume 2-A (2.05.3(4)) is <br />incomplete and inaccurate. The method employs (3ernoulli's equatibn and <br />~` head-loss coefficients to determine the required head under design flow <br />conditions. The method used was referenced from the "Handbook of Steel <br />Drainage and Highway Construction Products". The procedure described in <br />that handbook was followed, with the following exceptions: <br />