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water in the pit exceeds the elevation of the piezometric surface in the <br /> adjacent overburden aquifer, ground water flows into the highwall providing <br />' recharge to the overburden aquifer. Ground water flows to the north under the <br /> gradient of the piezometric surface as shown in Map 9, Foidel Creek Mine <br />' Baseline Hydrology. <br />Strip mining operations at the Energy No. 1 Mine ceased in 1980. During <br />the mining operations, ground water inflow from the overburden in the highwall <br />' was minimal. Since that time, infiltration of water from rainfall and snowmelt <br />into the reclaimed spoils has caused leaching of the spoil materials, and this <br />leach ate has accumulated in the final pit at the bottom of the dipslope. The <br />' chemistry of the leach ate water, as well as the water level and chemistry of <br />ground water in the overburden aquifer, have been monitored on a monthly basis <br />' from 1979 to the present. <br />' Monitoring records are listed in Table 54, Energy Mine No. 1 Pit Water <br /> Quality. Thi s data is graphically represented in Figure 16, Leachate <br />' Concentration, Energy Mine No. 1. As shown, actual concentra tions of TDS <br /> fluctuate, due to seasonal variations in snowmelt and precipitation. Average <br />' yearly concentrations of leach ate are shown below: <br /> ENERGY MINE N0. 1 PIT <br /> <br /> Year # Samples Min. TDS Max. TDS Ave. TDS <br />t 1979 21 2080 3850 2948.1 <br /> 1980 37 700 3320 2626.8 <br />' 1981 22 456 2920 2608.5 <br /> 1982 17 324 3320 2863.1 <br />' 1983 24 520 4400 2757.9 <br />' Leachate Testing <br />In 1979, a study of leaching potential of overburden at the Energy No. 1 <br />Mine was conducted. Column leach tests were devised to simulate the dissolution <br />' of solvable minerals in the mine spoils over time. Concentration of TDS was <br />' 3 <br />1 <br />