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<br />I~ <br />LI <br />Where multiple existing drainages are present, then multiple branching drains <br />will be required. The size of the drains can vary. Drain sizes are specified by CDMG <br />regulations for fills which classify as Valley Fills. As discussed in the previous section <br />PROPOSED DISPOSAL AREAS, two of the fills (Fills 4 and 8) classify as Valley Fills. <br />Specifications for Valley Fill drains are shown on Fig. 6. The regulations require a <br />minimum height and width, resulting in a minimum drain area. For fills which do not <br />classify as Valley Fills, smaller drain systems are considered feasible Drain <br />recommendations are summarized on Fig. 6. <br />We evaluated the flow capacity of several drain sizes and expected infiltration of <br />• - <br />water into the spoil. A study of infiltration into spoil fills (Reference 4) indicates about <br />3.5 inches of infiltration per year. The surface area of Phase I is about 200 acres. <br />Assuming the water exits equally out the six drains over a 3 month period results in an <br />estimated flow of about 40 gallons per minute for each drain. <br />The estimated capacity of various sized drains was estimated using Leps (1973) <br />method as outlined in CTL/Thompson, Reference 4. The capacity at a 1 percent slope <br />for various drain sizes is shown on Table C below. <br />TABLE C <br />UNDERDRAIN FLOW CAPACITY <br />(Estimated for 1 % Slope) <br />Size Capacity (gpm) "Factor of Safety" <br />3' x 6' 250 6 <br />6' x 72' 1000 25 <br />8' x 16' 3500 90 <br />12' x 22' <br />(Minimum for Valley Fill) 7200 180 <br />• LORENCITO COAL COMPANY, LLC <br />LORENCITO SURFACE MINE -PHASE I <br />CTLR 3Z, 671 <br />15 <br />