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Tony Adkins Page 2 <br />April 9, 2001 <br />the spoil mass. As explained in paragraph c, below, the source of the dilution is most likely <br />freshwater seeping into the spoil from the Mid-Lower West Return Ditch. <br />b) There currently are insufficient monitoring data to confidently predict the long-term water <br />quality of Spoil Spring #1. To remove the dilutional effect caused by varying discharge rates, <br />concentrations for each uniform discharge rate would have to be graphed separately. Attached <br />Figure 2 shows that if there is any trend evident in sulfate concentrations at Spoil Spring #I, it <br />may be an increasing trend. The Division believes, however, the data set is too small for <br />confidently predicting the long-term water quality. <br />c) Irrigation water seeping into the spoil in the New Horizon #2 PR-OS expansion area will <br />travel 4000 feet farther through spoil than the water in the spoil at New Horizon #l mine. <br />Much of the water in the spoil at New Horizon #I probably comes from irrigation water seeping <br />from the Mid-Lower West Retum ditch (see attached Figures 3 and 4). This water travels about <br />400 ft. through spoil before discharging at Spoil Spring #l. In contrast, at New Horizon #2, <br />irrigation water from the West Lateral ditch will travel at least 4000 ft. through spoil before <br />discharging at the predicted spoil spring. The Division believes this much longer flow path will <br />allow the water to become saturated with sulfate (via pyrite oxidation), and will result in sulfate <br />concentrations of at least 2250 mg/I as observed at Spoil Spring #I in the years prior to dilution <br />from ditch water (see attached Figure 5). <br />Please either explain why the Division's foregoing observations are invalid, or resubmit a response to the <br />Division's original comment 7 that projects: <br />1) The source of high TDS in discharges from the predicted spoil spring (for example, oxidation of <br />pyritic sulfur in the spoil); <br />2) The expected exhaustion time of the source [Table 18 of Williams and Clark's (1994) study may <br />be used as a model, possibly utilizing New Horizon's overburden pyritic sulfur content reported <br />in the permit in Vol. A, Appendix 6-4]; and <br />3) The maximum TDS concentration of the predicted spoil spring for the following two scenarios: <br />with irrigation water seeping into the spoil, and without irrigation water seeping into the spoil. <br />The Division can provide further guidance on items 2 and 3 <br />Comment 8. Page 2.04.7-47. No further response is needed now, but this page may need to be revised <br />after the Division reviews your next response to Comment 7. <br />Comment 10. Page 2.04.7-22. No further response is needed now, but this page may need to be revised <br />after the Division reviews your next response to Comment 7. <br />Comment 11. Page 2.04.7-9, second paragraph last sentence. Please revise this sentence to reflect that <br />infiltrating precipitation comprises a significant percentage (one-third) of infiltration. (Your response 3i <br />estimates one-third.) <br />The Division has the following additional new comments regarding the update of the PHC. (Comment <br />numbering is a continuation of the numbering sequence of previous comments.) <br />15 - 27. (These comments are shown in call-out boxes on the attached scanned pages from New <br />Horizon's permit.) <br />