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and more irrigation water is recharged rapidly through the permeable, broken <br />spoil material. This good quality water picks up dissolved solids as in the case <br />of the overburden, but does so much more rapidly. Water infiltrating into the <br />spoil at ;the upper end of the New Horizon #1 spoil may only spend 15-45 <br />days in the spoil before the water is discharged at the spring. Yet, during this <br />short time, it is approximately the same quality as the overburden water. The <br />average TDS of the irrigation ditch water is only 100 to 280 ppm. Due to the <br />increased porosity and higher level of oxygen in the rapidly infiltrating <br />precipitation water and irrigation water, the pyrite breaks down at a faster rate <br />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 large portion of the irrigation water runs off <br />1. ,. ....u«F.... .. Qi 1 .. .. d« .. T C, <br />tl tihl.._ fields .? is 4t...he..1 <br />fe,s lace id.? PICKS er Some 1Do in the and gathered In return <br />ditches. In the post-mine condition, a large portion of the irrigation water <br />will infiltrate and recharge the spoil due to the increase in porosity. The <br />TDS of the spoil water at the New Horizon #1 Mine will increase <br />approximately 6% compared to that of the overburden water immediately <br />after reestablishment of irrigation. This is approximately 3300 ppm of <br />TDS. <br />B) Spoil springs will be present at both reclaimed mine areas which <br />discharge the majority of the spoil water to the surface. This is an impact <br />since no spoil springs existed in the pre-mine condition. <br />C) Once the pyrite and easily dissolved salts are washed out of the spoil, <br />TDS in both spoil springs will gradually get lower until sometime many <br />years from now. Eventually, the spoil spring water quality will get better <br />than the overburden quality. At a time much more distant in the future <br />and much more difficult to calculate, the spoil water will approach <br />irrigation water quality. Time periods for this to occur are given later in <br />this section. <br />The TDS of the NPDES 001 discharge 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 Infiltration into Low-wall <br />Water infiltration will build up in the spoil downgradient and begin to seep into the <br />low-wall. This spoil water may enter one or more of the minor sandstone beds of <br />the overburden (Dakota Sandstone). This annual infiltration is calculated below, <br />assuming a 10' thick somewhat permeable bed in the low-wall strata: <br />Seepage into low-wall for the New Horizon #2 Mine = (10' ft. thick permeable <br />sandstone bed in low wall)(8500' ft. wide seepage area)(0.10 ft. per day seepage <br />32