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spoil condition. In the pre-mine condition, very good quality water from precipitation <br />and from the irrigation ditches infiltrates through the soil and through the more <br />permeable strata and picks up dissolved solids. The water quality becomes poor <br />(approx. 3000 ppm TDS), but this process takes a very long time since the water <br />moves very slowly through the tight strata with low hydraulic permeability values that <br />range from 3.5 to 5.5 ft/day. <br />In the case of the spoil, the hydraulic permeability is increased to 40 ft/day and more <br />irrigation water is rechazged rapidly through the permeable, broken spoil material. <br />This good quality water picks up dissolved solids as in the case of the overburden, but <br />does so much more rapidly. Water infiltrating into the spoil at the upper end of the <br />New Horizon #1 spoil may only spend 15-45 days in the spoil before the water is <br />discharged at the spring. Yet, during this short time, it is approximately the same <br />quality as the overburden water. The average TDS of the irrigation ditch water is only <br />100 to 280 ppm. Due to the increased porosity and higher level of oxygen in the <br />rapidly infiltrating precipitation water and irrigation water, the pyrite breaks down at a <br />faster rate but is buffered by the calcite, as described above. Therefore, the overall <br />impacts to water quality are as follows: <br />A) In the pre-mine condition, a lazge portion of the imgation water runs off the <br />surface and picks up some TDS in the fields and is gathered in return ditches. In the <br />post-mine condition, a lazge portion of the irrigation water will infiltrate and recharge <br />the spoil due to the increase in porosity. The TDS of the spoil water at the New <br />Horizon #1 Mine will increase approximately 6% compazed to that of the overburden <br />water immediately after reestablishment of irrigation. This is approximately 3300 ppm <br />of TDS. <br />B) Spoil springs will be present at both reclaimed mine azeas which dischazge the <br />majority of the spoil water to the surface. This is an impact since no spoil springs <br />existed in the premine condition. <br />C) Once the pyrite and easily dissolved salts aze washed out of the spoil, TDS in both <br />spoil springs will gradually get lower until some time many yeazs from now. <br />Eventually, the spoil spring water quality will get better than the overburden quality. <br />At a time much more distant in the future and much more difficult to calculate, the <br />spoil water will approach irrigation water quality. Time periods for this to occur aze <br />given later in this section. <br />The TDS of the NPDES 001 dischazge at the New Horizon #1 Mine fluctuates <br />inversely in response to flows during irrigation season. The overburden wells and <br />Spoil Spring #1 fluctuate to a lesser extent. <br />Spoil Water Inftltration into Low-wall <br />Water infiltration will build up in the spoil downgradient and begin to seep into the <br />26 <br />