2011-03-17_REVISION - C1981008 (2)

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It is important to understand what is truly different from the pre-mine condition to the spoil condition. In the pre-mine condition, very good quality water from precipitation infiltrates through the soil and through the more permeable strata and picks up dissolved solids. The water quality becomes poor (over 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 northeastern end of the Phase 3 reclaimed area spoil may only take 80 days in the spoil to pass through the area. Water passing through the same area in pre-mine conditions would take over 550 days. In general the comparison of water quality has shown an overall improvement in the reclaimed areas versus the natural overburden. The primary impact of the reclamation on water quality has been a minor improvement on ground water quality. D) Impact of spoil water quality on surface water quality. Spoil Water Quality The chemistry of the water interacting with the spoil is described in the previous section. In order to determine the impact of the spoil water quality on the surface water, it is first necessary to predict the expected quality of the spoil leachate for the New Horizon #2 mine. The principal impact from a quality perspective is that irrigation water will seep rapidly through the spoil, increase in TDS and then discharge through a spoil spring at the lower part of the mine area. Water quality analysis of ground water from GW-N40 has shown that the spoil water quality is approximately the same, if not better as the ground water present in the overburden. Impacts To Receiving Waters The downstream receiving water for the Phase 3 release areas is Calamity Draw. No spoil water springs have developed during the 10 years since these areas were backfilled. Therefore, water quality has been analyzed using the well GW-N40 since it is immediately downstream from the release areas. See Map R-2 The primary concern for water quality is the previously mentioned possibility of pyrite oxidation leading to an increase in the acidity of the ground water. This is partially mitigated by the presence of calcite in the spoil backfill, raising the pH of the ground water and increasing the amount of pyrite that can oxidize before the ground water becomes to acidic. Comparison of the pH values from GW-N36 and GW-N40 shows that the ground water has SL-12 CURRENT 11MAR11.wpd 44