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and quality of any groundwater which may discharge to the surface water system. The following <br />sections characterize groundwater occurrence and conditions as a basis for evaluation of these <br />• potential impacts. <br />Mine Area Hydrogeology, Groundwater Occurrence, and Relationship to Mining Disturbance <br />- The regional groundwater conditions were described in Section 2.04.5. Within the Mine Permit <br />and adjacent areas, groundwater conditions have been studied using data obtained from a series of <br />monitoring wells completed in five water - bearing hydrostratigraphic zones: the underburden <br />beneath the Wadge Coal, the Wadge Coal, the overburden above the Wadge Coal, alluvium along <br />the Little Grassy Creek and Grassy Creek drainages, and mine spoils. The wells were selected after <br />consultation with the CDRMS and further evaluation of existing wells constructed at the Seneca II <br />Mine to monitor groundwater levels and groundwater chemical quality, and for testing to determine <br />the hydraulic properties of the various zones. The locations of the wells are shown on Map 2.04.7 - <br />Ml, Hydrology. A summary of the groundwater monitoring intervals when data was collected and <br />the wells were sampled is presented in Table 2.04.7 -T1, Summary of Groundwater Monitoring. <br />As discussed on a regional basis in Section 2.04.5, groundwater occurrence and movement in the <br />Mine Permit area and adjacent area are generally controlled by the climate, stratigraphy, geologic <br />structure, surface drainage patterns and, to a lesser degree, the area topography and adjacent <br />previous surface coal mining. These conditions are generally illustrated by Figure 2.04.6 -F1 and <br />the geologic cross - sections presented in Exhibit 2.04.6 -E1, Geologic Information — Geologic Cross <br />Sections (confidential). Water well lithologic and completion logs are presented in Exhibit 2.04.7 - <br />E1, Hydrologic Information. <br />• Potentially Affected Groundwater Units and Groundwater Aquifer Characteristics — <br />Groundwater potentially related to the proposed mining activities occurs in the five <br />hydrostratigraphic units within and adjacent to the PSCM permit area. The two shallow aquifers <br />include the mine spoils aquifer at the adjacent Seneca II Mine and the alluvial aquifer along Little <br />Grassy Creek and Grassy Creek. The three bedrock units include the Wadge coal and the <br />underburden and overburden below and above the coal. The bedrock units form part of the basal <br />Williams Fork aquifer described by Robson and Stewart (1990). Those and other authors of <br />previous studies, as well as monitoring at the nearby Twentymile Mine, indicate that the major <br />regional sandstone aquifers ( Twentymile and Trout Creek aquifers) are hydrologically isolated from <br />the units to be disturbed by mining at the PSCM and are unlikely to be affected by the proposed <br />mining. The isolation is created by the very low hydraulic conductivities (0.00081 ft/d horizontal <br />and 0.00044 ft/d vertical [Robson and Stewart, 1990]) of the intervening shale sequences above and <br />below the Wadge coal and its overburden and underburden. Additional details on the stratigraphy <br />and hydrogeologic characteristics are provided in Section 2.04.5. <br />Recharge to the groundwater system occurs primarily as infiltration of precipitation and snowmelt <br />in the up -dip, upland areas near and beyond the boundaries of the Permit Area (Map 2.04.5 -M1, <br />Regional Geology and Hydrology), as described in Section 2.04.5. Robson and Stewart (1990) <br />reported that recharge varies as a function of precipitation, increasing with increasing precipitation, <br />and that the average recharge rate to bedrock aquifers in the area is 0.31 inch per year. Recharge to <br />the potentially affected units occurs where those units are exposed in the southwest and southeast <br />parts of the permit area. The proposed PSCM is down -dip of and adjacent to backfilled spoils from <br />• the Seneca II Mine. The spoils receive approximately three inches per year of recharge from <br />infiltrating precipitation and snowmelt (Williams and Clark, 1994). <br />PSCM Permit App. 2.04 -35 Revision 12/17/09 <br />