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6 SEDIMENT POND NO. 003 <br />The design and storage capacity and detention time of Sediment Pond No. <br />003 was evaluated to answer the concerns of the Divsion in their review <br />of the Seneca II Permit Renewal. The existing spillway will be modified <br />to meet the requirements for sedimentation ponds (4.05.6). <br />The total drainage area of Pond 003 is 30.14 acres, see Exhibit "7 -7 ", <br />Surface Hydrology Map, Drainage Area III. For design purposes, 16.67 <br />acres is considered to be undisturbed ground and 13.47 acres is <br />considered disturbed bare ground. The weighted curve number was <br />calculated to be 73 and the weighted "k" factor was determined to be <br />0.26 (see Table 1 and 2). The curve number and "k" factors for the <br />individual soil types were taken from Tables 7 -6 -1 and 7 -6 -2, <br />respectively. <br />The unit hydrograph type that was selected,to be used in the SEDIMOT II <br />olavkl <br />16) computer model was for a disturbed drainage condition since about half <br />of the drainage area was disturbed ground. <br />The time of concentration was calculated using the following formula <br />(Barfield et al, 1981). <br />tc = L 0.8 (S + 1 )0.7 <br />1140 Y0.5 <br />where L = hydraulic length of watershed = 3400 ft. <br />Y = average watershed slope = 11.0% <br />S = maximum retention <br />s = 1000 - 10 = 1000 - 10 = 3.70 <br />M_ <br />then tc = (3400) 0.8 (3.70 + 1) = 0.522 hrs. <br />1140 (11.0) ' <br />Next, a particle size - percent finer distribution of the soil type in the <br />Pond 003 watershed was determined from a soil sample taken from the <br />reclaimed area in April of 1986. This sample was used because it <br />closely represents the watershed soils. The input particle distribution <br />is as follows: <br />7 -6b -2 Revised 8/27/86 <br />