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Waste Disposal Area Topsoil Stock~e Sediment Pond- The proposed pond at the coal <br />processing waste pile topsoil stockpile is designed [o hold a volume of runoff and <br />sediment of 0.31 acre-feet. This capacity allows for the storage of runoff from one and <br />one-half 10-year events (0.18 acre-feet) as well as storage of~2.1 years' volume of <br />sediment accumulation (0.18 acre-feet). The Division requires that a sediment clean-out <br />marker be installed to indicate the level at which sufficient storage remains for both <br />runoff and sediment generated by the 10-year, 24-hour storm event. <br />The collector ditch into the pond will be stable under the flow from the 10-yeaz, 24-hour <br />storm event. The emergency spillway is designed to convey flow from the 25-year, <br />24-hour event without eroding. Due to the small size and incised nature of the pond, <br />dewatering will be accomplished through the use of a pump once the water quality meets <br />or exceeds effluent standazds. <br />D. Surface and Ground Water Monitoring <br />Surface Water <br />The information dealing with surface water quality and quantity were reviewed by the <br />Division. This information can be found in Section 4.5 of Volume I and Section 4.3 of <br />Volume VI of the application. <br />Grand Valley Coal Company has supplied data indicating characteristics ofwater <br />quantity and quality for East Salt Creek in the vicinity of Munger Canyon and for the <br />drainage in Munger Canyon. Total dissolved solids in East Salt Creek have been noted <br />over a range of 600 mg/1 to 10,000 mg/l. Water is typically a sodium sulfate type. <br />In Munger Creek, like most semi-arid ephemeral drainages, dissolved constituents in <br />surface water ofren reach high levels during storm runoff. Dissolved solids measured in <br />Munger Canyon ranged from 92 mg/1 in December to 956 mg/1 in April. <br />Subsequent to issuance of the initial permanent regulatory program permit, Grand Valley <br />Coal Company implemented a plan for the collection, recording and reporting of surface <br />water quality and quantity data. The program consists of surface water monitoring above <br />and below the disturbance in the Munger Canyon tributary, along Munger Canyon before <br />the confluence with East Salt Creek and along East Salt Creek upstream and downstream <br />of the confluence with Munger Canyon. This monitoring plan will be sufficient to <br />identify any effects of the operation on the surface water hydrology. <br />Grand Valley Coal Company has committed to the following surface water monitoring <br />program: <br />30 <br />