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Colowyo, C1981 -019, PR3 adequacy No. 3 16 July 22, 2011 <br />mining, and possible migration of coal spoil Ieachate from pit backtill into downdip bedrock <br />units after mining is completed (pitwall seepage). Dewatering and leaclmte migration are <br />affects on ground water systems on or oft the permit area; therefore, bedrock ground water <br />monitoring is required under Rule 4.05.13(1)(c). Please propose a bedrock monitoring well <br />that is property located for detecting changes in ground water quantity and quality caused by <br />the dewatering and Ieachate migration. <br />For the reasons stated in our letter of July 22, 2011, please propose a bedrock monitoring well <br />location. Although hydrologic material damage to bedrock units may be predicted to have a <br />low probability of occurrence, there is enough error inherent in predicting such impacts to <br />warrant verification by monitoring. <br />6. Colowyo has created a new water monitoring plan for Collard, independent of the existing <br />monitoring plan. However, in the past, the plan for a new area (South Taylor) was included in <br />the original monitoring plan. Left unchanged, the Colowyo permit will have two separate <br />water monitoring plans for the three distinct areas. Please include Collom water monitoring in <br />a single water monitoring plan for the entire permit area. <br />DRNIS will complete its review of the proposed hydrologic monitoring plan after iecen ine the <br />requested change to ground watcnnoninaing and calculations of pmvall sccpagc, spoil <br />sat Ural ion, and spoil spring discharges. <br />DRMS will complete its review of the proposed hydrologic monitoring plan after receiving the <br />requested changes to ground water monitoring and the evaluation of spoil spring impacts. <br />Rule 4.09 Disposal of Excess Spoil <br />A large (250,000,000 cy) temporary ( -20 -year) excess spoil pile is proposed. A Geotechnical Study <br />for the Collom Temporary Spoil Fill, conducted by Shannon & Wilson (S &W), is provided in Exhibit <br />23, Item 1. The fill qualifies as a "Valley Fill ". Map 29C shows plan and cross - sectional views of the <br />proposed pile. General information regarding the pile is provided in Rule 2, pp. 98 -99; Rule 4, pp. 22- <br />23 describes the proposed construction and inspection plans. <br />?. Exhibit 7 Item 26, Fig. 2 illustrates a proposed °Collom Sump ". It appears that this sump pond <br />may be located new the toe of the proposed excess spoil pile. Please ensure that S &W are <br />informed of the presence of the sump, and its position in the mining sequence, so that any <br />potential effects it may have on the pile itself or the foundation materials may be considered in <br />the stability evaluation. <br />Cohm-No states in the %-larch response letter that it will obtain confirmation from S &W, or, it <br />necessary, re -run the stability analyses. Please provide the Division with correspondence &oat <br />S &Ni addressing any ettw:ts the Sump may or nuy not havo on the tentporarc czccea spoil pile. <br />This item has been resolved with the August 9, 2011 submittal. <br />