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the Nucla Mine are low to very low. The overburden and underburden aquifers have the <br />highest values and the coal aquifer has the lowest transmissive properties. Tables 7-5 <br />and 7-6, which summarize the aquifer characteristics show that there is an approximately <br />one order of magnitude range in the transmissi vity and hydraulic conductivity values for <br />the overburden, coal and underburden aquifers. This suggests that there is a high degree <br />of spatial variability within the aquifers. Storage coefficient for the various aquifers <br />vary by four orders of magnitude. The alluvial aquifer has the largest storage <br />-2 -5 <br />coefficient (10 ) and the coal and underburden aquifers average about 10 The spoils <br />monitoring well (GW-N27) was completed in the fall of 1987. A short term specific <br />capacity and transmissivity test was conducted at the time of water quality sampling at <br />Well CW-N27. A K value of 40 ft/day was determined from the following computation: <br />T = 264 x 3.1 gpm = 1,949 gpd/f t; 261 ft2/day = 40 ft/day <br />.42 ft 6.44 sat. interval <br />This highest specific capacity and hydraulic conductivity values for any of the aquifers <br /> was measured in the spoils aquifer. <br />• <br /> In summary, aquifer yields at the Nucla Mine are very low. The better aquifers, in terms <br /> of transmissi vities and hydraulic contluctivi ties, are the overburden and the underburden. <br /> Yields were so low that constant discharge tests were only attempted on one alluvia), one <br /> overburden and one underburden well. The aquifer characteristics show spatial variability <br /> suggesting anisotropic properties within the medi um and probable boundary effects. <br />Ground Water Quality. The following section discusses the regional geochemical reactions <br />that affect ground water chemistry and details site specific ground water quality. <br />The general geochemical processes that affect the ground water quality in the Nucla area <br />are as follows. Water containing carbon dioxide percolates below ground surface, <br />dissolves carbonate minerals and possibly gypsum, and exchanges calcium and magnesium ions <br />for sodium ions. The following reactions illustrate these processes more specifically. <br />In a near-surface environment, carbon dioxide gas (C02) from the atmosphere and from <br />organic decay reacts with water (HZ ): <br />• C02 + H2O ~= H2C03 (1) <br />7-28 Revised 04/11/88 <br />