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Christy Woodward <br />July 31, 2008 <br />Page 10 <br />may be mobilized from mine rock at problematic concentrations under near-neutral pH <br />conditions include selenium, arsenic, and molybdenum. <br />The MWMP is used to evaluate the potential for constituents to be mobilized from mine rock <br />by meteoric water. The procedure consists of a single-pass column leach over a 24-hour <br />period using a mine rock sample to extraction fluid (effluent) ratio of 1:1. The extraction fluid <br />is Type II reagent grade water (e.g. distilled or deionized water). <br />The results of the MWMP are reported as concentrations of the constituents in the column test <br />extract solution (e.g. milligrams per liter). These data can be interpreted in several ways. If <br />leachate concentrations are very low, the data can be compared to relevant surface water or <br />groundwater standards such as those contained in CDPHE Regulations 31 and 41, <br />respectively. Constituent concentrations in the test leachate that do not exceed either surface <br />or groundwater standards are not considered problematic. Constituent concentrations in the <br />test leachate that do exceed surface or groundwater standards may be problematic depending <br />on site-specific conditions. In this case, it is necessary to evaluate the fate and transport of the <br />constituents prior to determining whether mine rock has the potential to cause adverse effects <br />to surface water or groundwater quality. <br />• <br />The Sunday and Van 4 mines are located in an and environment where potential evaporation • <br />greatly exceeds precipitation. Seepage from the development rock areas is not commonly <br />observed at the site. It's necessary to understand the volume of seepage that occurs at the <br />development rock areas to evaluate the potential for the development rock to affect the <br />environment. This will be evaluated based on unsaturated flow modeling, because time is not <br />available to measure the leachate volume using lysimeters or other empirical methods. The <br />modeling approach considers precipitation, evapotranspiration, and the site specific <br />hydrologic characteristics of the development rock; and estimates the volume of leachate that <br />occurs from the development rock areas. <br />Potential for Development Rock Leaching to Surface Waiter or Groundwater <br />Although constituents may be mobilized from development rock at concentrations that <br />exceed surface or groundwater standards, it is important to consider the pathway of potential <br />leachate formed by development rock piles. In the case of the Sunday Group mines, the <br />development rock piles are miles away from the nearest perennial surface water body <br />(Delores River) and the piles are underlain by several hundred feet of low permeability shale <br />(Brushy Basin Member of the Morrison Formation). This shale unit reduces the potential for <br />the development rock piles to affect groundwater. <br />Natural attenuation processes include adsorption, dilution, advection, dispersion, and other <br />processes. These processes are important to consider in the evaluation of the potential for <br />constituents within development rock leachate to migrate through soil or shale underlying or <br />adjacent to the piles and into underlying groundwater. <br />1. <br />0:164986 - Denison\Task Order 3 - DMO Sampling and Analysis Plan%Task 3.1 - Soil Ore Rock Data Colledion Plan% inal Denison Sunday Mines Group Soil Ore Rode Data <br />Collection Work Ran.doc