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of Salt Load from Spoil Material Based on Drill Samples. 17 Wadge overburden samples were collected from four <br />holes approximately one mile apart. These holes were drilled into the same overburden strata as that found in the <br />• Foidel Creek Mine Permit Area. <br />Various size fractions were screened from the overburden samples and leached separately. Composite samples <br />were also leach tested. The results of the study indicated that the <O.Smm size fraction represents 90 percent of all <br />spoil fragments and contributes virtually all of the salts. <br />Each of the 17 samples was placed in a sealed leach cylinder 9 cm high and 10.5 cm in diameter. Samples were <br />packed to a bulk density of 1.45 gm/cc. A water source was connected to the top of each cylinder such that a <br />constant head was maintained and the flow regulated to about SOmm per day. The pH of the water was maintained <br />at a constant value of 7.1. When the leachate began to flow from the bottom of each cylinder, the instantaneous <br />electrical conductivity (EC) and the cumulative weight of leachate were measured and recorded on about 20 ml <br />fractions. When the volume of the leachate from the sample exceeded the volume of the sample, the water source <br />was turned off and the measurements stopped. <br />Raw data compiled from the leach study are in the form of spoil and leach solution quantities, EC, and cumulative <br />leachate weight measurements for each incremental stage of the leaching process. Each of the 218 incremental <br />stages was measured for EC correlation of the incremental EC with TDS values of the leachate samples, results in <br />a TDS/EC ratio of 0.73. Using this ratio, multiplication of incremental EC values by 0.73 will give an estimated <br />TDS value. Initial concentrations of leachate are in the order of 4000 mg/I, which is very similar to observed <br />concentrations of actual spoil, discharges at the adjacent Eckman Park Mine. Water chemistry characteristics of <br />leachate and spoil discharge is also very similar. This indicates that the leaching tests yield a reasonably good <br />prediction of initial water quality that might be expected to occur in the caved overburden material after flooding <br />of the mine workings. The approximately 50% higher TDS values observed in some areas of the mine indicate <br />• that the flushing times calculated from these tests may have to be increased by as much as 50%. <br />The primary purpose of the leaching study was to determine the time interval required for the solute concentration <br />of the leachate to return to the baseline level. The leaching study indicated that significant decreases in EC levels <br />occur when the ratio of the volume of leachate to the weight of overburden material is about 0.9 Ukg (Exhibit 38, <br />Figure 3). Using a bulk density of 1.45, this is equivalent to leaching of approximately 0.6 and 1.0 (r) pore <br />volumes of the overburden material. Based upon the results of the leach study, when the volume of water which <br />has percolated through the caved overburden material is equivalent to about 1.5 Ukg of overburden material, the <br />ground water TDS value will be at the baseline level, and no additional salt concentrations will occur above <br />baseline at that point. <br />The leaching ratios to reduce TDS levels to a given value can be converted to time by applying factors far a rate of <br />water movement through the caved overburden and assuming values for the pore volume of the caved areas. This <br />is determined from the equation: <br />t = rV <br />R <br />where: <br />t = time in years to reduce TDS to required level <br />r = water volume/caved material pore volume ratio to reduce <br />TDS to required level (from leach test results) <br />V = Pore Volume of caved material in acre-feet <br />R = Rate of movement of ground water through caved material <br />in acre-feet per year <br />APPROVED FEB o 8 2000 <br />TR 99-32 2.05-144 1 l / 15/99 <br />