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adjacent New Horizon Mine. The USGS study methodology was used as a basis to predict the <br />time frames of slightly elevated TDS in the spoil water at the New Horizon Mine, (see New <br />Horizon #2 Area permit Section 2.05.6(3)). The sulfur content in the overburden at NHN is <br />similar to that at the New Horizon Mine (see Table 2.04.6-2, Section 2.04.6 of this application). <br />The result of that prediction indicated that about 800 years would be required to oxidize the <br />sulfur in the overburden at the New Horizon Mine and therefore about 800 years to oxidize the <br />sulfur at NHN Mine. As the oxidation of the pyrite is the main source of increased TDS in <br />backfill water quality, elevated TDS from spoil water springs could remain for several centuries. <br />The N14N Mine will have two significant differences to the results observed at Seneca Il. First, <br />the calcite present in the spoil at NHN permit area seems to react with acid produced by the <br />oxidation of pyrite and take a substantial amount of sulfate from solution directly into solid <br />calcium sulfate. This keeps the dissolved solids content somewhat constant no matter how high <br />or low the inflow water quality is with regard to TDS. Second, the Seneca II site is a dry -land <br />reclaimed area where the only recharge into the spoil is a minor amount from precipitation and <br />seepage from the underburden aquifers. Total measured discharge from the spoil was only 3" per <br />year. The NHN Mine will be partially irrigated with water of better quality over a large portion <br />(45%) of the year. As described earlier, this results in a total movement through the spoil of <br />approximately 13" per year (81 ac -ft). Since the amount of water moving through the NHN <br />backfill is greater, it should oxidize the pyrite more rapidly and also flush other salts which are <br />contributing to the increase in TDS at a higher rate. For this reason, a ratio of the discharge at <br />both sites could be used to predict the time frame of slightly elevated spoil water quality. This <br />ratio - 3"/13", as applied to 1500 years results in a time frame of 346 years until all the pyrite is <br />oxidized. When considering all the variables involved, this means that it could dissipate within a <br />range of 200 to 500 years. The TDS should begin to drop before this time. Once the pyrite is <br />fully oxidized and other salts are flushed out, the backfill water quality should approach the <br />existing stream water quality, possibly dropping to 800 to 1200 mg/1 TDS. It is not likely that the <br />backfill water will ever reach the low TDS of the ditch- run water as seepage from the <br />overburden zones into the backfill will continue as long as the 2nd Park irrigation continues. <br />Impacts To Receiving Waters — Tuttle Draw As described earlier, drainage through the NHN <br />backfill material will move to the south following the path of least resistance along the pit floor <br />and issue at the general location of Spoil Spring # 1, (see Map 2.04.7-1). Spoil Spring #1, is the <br />spoil water discharge from the old Peabody Nucla Mine (New Horizon #1 Area permit) and has <br />been monitored since 1987. Spoil Spring #1 water mixes with irrigation runoff and return water <br />from Nygren Draw and then discharges into Tuttle Draw located about 1600 ft. downstream <br />from the spoil spring. Tuttle Draw enters the San Miguel River approximately 2 miles to the <br />southwest. <br />Section 2.05.6(3) Page 27 Sept. 2015 (TR -11) <br />