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3. Projected characteristics of spoil springs. The Division believes a spoil spring at New Horizon Mine would have the following characteristics, based on the preliminary analysis shown on attached Figure I. a) When discharge will begin - 30 years after the installation of the pipe that the permittee plans to install for carrying West Lateral ditch water. The 30- year period is the assumed end of the useful life of the pipe; b) Discharge volume - 226 gpm: c) Concentration of total dissolved solids (TDS) of discharge- 4,000 mg/I; d) Duration of discharge -More than 1.000 years; e) Increase in TDS concentration of San Miguel River caused by spoil spring - (Division has not yet calculated). Please provide the Division your projection of each characteristic "a" through "f' of any spoil springs that may form at the New Horizon Mine, and please document the analysis on which each projection is based. Once the Division verifies your projection, then the probable hydrologic consequences section of the permit can be updated to reflect the projection. (CDMG's analysis in Figure I assumes flow in [he West Lateral ditch is in an unlined open channel, rather than a pipe. The HDPE pipe described in the PR-OS application is assumed to have an expected life of 30 years if it is protected from ultraviolet light degradation. Replacement of the pipe at the end of its useful life would depend on the economics confronting the ditch owner. The ditch owner has not previously installed a pipe at [he mine location; therefore, it is assumed [he owner would not replace the pipe.) 4. Useful life of HDPE pipeline. What is the expected useful life of the pipeline, as installed, that is planned for catriing the flow of West Lateral ditch water across [he permit area? 5. Impacts on West Lateral irrigation ditch. Prior to mining, seepage from the unlined channel of the ditch has been restricted by the underlying, low-permeability bedrock of the Dakota Sandstone. After mining, this restriction will be removed when highly permeable spoil replaces the bedrock a short distance from the ditch (assuming the proposed pipeline installation is not permanent). If the proposed pipeline is not permanent, then please add to the appropriate pan of your submittal a description of the impacts that you expect mining will have on the ditch. Please include a calculation of pre-mining and projected post-.mining seepage losses from the ditch. 6. Locations of pit effluent discharges to ground water. Please identify the location(s) where pit effluent will discharge into ground water through the unmined lowwall/highwallnnce the backfilled spoil is resaturated. Duration of spoil spring impacts to ground water, Page 2.05.6(3)(b)(v) - 1 of existing perjnit application. The second paragraph on this page says that "....replaced spoil wilt only have a minimal short term impact on ground water quality." Please revise this statement to reflect a longer duration if the projected impact is longer than a few years, as [he Division believes (see following paragraphs). The USGS projected a time period of "hundreds to thousands of years" fur elevated TDS levels in Williams Fork formation spoil aquifer water at the Seneca II Mine in Routt County (Williams and Clark, 1994, "Hydrology and Geochemistry of a Surface Mine in Northwestern Colorado", USGS Water-Resources Investigations Report 92-4187, 1994, page 60). Williams and Clark's projection may be applicable to the New Horizon Mine as explained in the following paragraphs. Williams and Clark suegest on page 56 of their report that oxidation of pyrite in spoil is the primary reaction that produces increased TDS in reclaimed spoil aquifer water. The sulfur released by pyrite oxidation combines with oxygen to form sulfate in the spoil aquifer water, thus increasing the concentration of total dissolved solids. TDS levels remain high until the