2010-10-01_REVISION - C1981008 (11)

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precipitation and from the irrigation ditches infiltrates through the soil and through the more permeable strata and picks up dissolved solids. The water quality becomes poor (approx. 3000 ppm TDS), but this process takes a very long time since the water moves very slowly through the tight strata with low hydraulic permeabilitites, which are in the range of 3.5 to 5.5 ft/day. In the case of the spoil, the hydraulic permeability is increased to 40 ft/day and much more irrigation water is recharged rapidly through the permeable, broken spoil material. This good quality water picks up dissolved solids as in the case of the overburden, it simply does it much more rapidly. Water infiltrating into the spoil at the upper end of the New Horizon #1 spoil may only spend 15-45 days in the spoil before the water is discharged at the spring. Yet, during this short time, it has managed to become approximately the same quality as the overburden water. The average TDS of the irrigation ditch water is nnly 104 to 2R4 intnm, Diu-, to the increased porosity and higher level of oxygen in the rapidly infiltrating precipitation water and irrigation water, the pyrite breaks down at a faster rate but is buffered by the calcite, as described above. Therefore, the overall impacts to water quality are the following: A) In the pre-mine condition, a large portion of the irrigation water runs off the surface and picks up some TDS in the fields and is gathered in return ditches. In the post-mine condition, a large portion of the irrigation water will infiltrate and recharge the spoil due to the increase in porosity. The TDS of the spoil water at the New Horizon #1 Mine will increase approximately 6% compared to that of the overburden water immediately after re-establishment of irrigation. This is approximately 3300 ppm of TDS. Since the flowpath through the New Horizon #2 spoil is greater than the New Horizon #1 spoil, the expected increase in TDS for this water is 10% over background TDS in the overburden water. This is approximately 3425 ppm of TDS. A potential maximum is 4000 ppm TDS. Water movement through the spoil will also be considerably faster than the movement in the overburden. B) Spoil springs will be present at both reclaimed mine areas which discharge the majority of the spoil water to the surface. This is an impact since no spoil springs existed in the pre-mine condition. C) Once the pyrite and easily dissolved salts are washed out of the spoil, the water in both spoil springs will gradually get lower in TDS until sometime many years from now, the spoil spring water quality will get better than the overburden quality. At a time much more distant in the future and much more difficult to calculate, the spoil water will approach the irrigation water quality. Time periods for this to occur are given later in this section. As can be seen from the table, the TDS of the NPDES 001 discharge at the New Horizon #1 Mine fluctuates inversely in response to flows during irrigation season. The overburden wells and Spoil Spring #1 fluctuate to a lesser extent. The 38