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taken into account for piping through the spoil (assumed to be 25%) and lower annual <br />precipitation (12 inches at New Horizon versus 17 inches at Seneca). The calculated <br />800-yeaz duration is not meant to be a precise prediction of the duration of elevated <br />dissolved solids, but indicates the elevated solids can be expected to last, possibly, <br />several centuries. <br />The New Horizon Mine has two significant differences to the results observed at <br />Seneca II. First, the calcite present in the spoil at New Horizon seems to react with <br />acid produced by the oxidation of pyrite and take a substantial amount of sulfate from <br />solution into solid calcium sulfate. This keeps the dissolved solids content somewhat <br />constant no matter how high or low the the inflow water quality is with regazd to TDS. <br />Second, the Seneca II site is a dryland reclaimed area where the only rechazge into the <br />spoil is a minor amount from precipitation and seepage from the underburden <br />aquifers. Total measured dischazge from the spoil was only 3" per year. The New <br />Horizon Mine is principally irrigated with water of very good quality over a large <br />portion of the yeaz. As described eazlier, this results in a total movement through the <br />spoil of approximately 16" per year. Since the amount of water moving through the <br />New Horizon spoil is so much greater, it should oxidize the pyrite much more rapidly <br />and also flush other salts which are contributing to the increase in TDS at a much <br />higher rate. For this reason, a ratio of the discharge at both sites could be used to <br />predict the time frame of slightly elevated spoil water quality. This ratio, 3/16", as <br />applied to 1500 yeazs, results in a time frame of 280 yeazs until all the pyrite is <br />oxidized. When considering all the variables involved, this means that it could <br />dissipate within a range of 100 to 500 yeazs. The TDS should begin to drop before this <br />time. Once the pyrite is fully oxidized and other salts aze flushed out, the spoil water <br />quality should approach the irrigation water quality, possibly dropping to 300 ppm <br />TDS. <br />Impacts To Receiving Waters <br />Since these spoil springs were never present in the pre-mine landscape, their impact to <br />the quality of the receiving waters must be addressed. The sample point Spoil Spring 1 <br />represents the spoil water dischazge from the New Horizon #1 Mine and has been <br />monitored since 1987. Spoil Spring I dischazges into Tuttle Draw a short distance <br />downstream. Tuttle Draw enters the San Miguel River approximately 2 miles to the <br />southwest. <br />Sample site SW-N1 is located in Tuttle Draw immediately upstream of any influence <br />from the mine. Sample data over the past 12 yeazs from sites SW-N1 and Spoil Spring <br />1 have shown that the TDS of the waters drops significantly when irrigation is active <br />in the azea. Therefore, the impacts to the receiving waters will be studied for both <br />cases, with and without irrigation. The irrigation case corresponds to the <br />September/October time period when flows are fairly low in the San Miguel River. <br />The non-irrigation period corresponds to Mazch/April when flows in the San Miguel <br />aze usually at peak. <br />29 <br />