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~. 816.41 to 816.54 - Ground Uater. (vl; pp 779-11 to 779-84, v2, pp 780-144 to 780-201, v3 pp 816-50 to 816-64) A. Description of Ea:is[ing Environment Structure Twenty Mile Par?< in which Eckman Park is located contains an enclosed ground water basin forioed by several synclinal folds. Tlie combination of dipping aquifer strata and a lithologic sequence of permeable layers confined by impermeable layers results in artesian aquifer conditions. Almost all of the wells drilled into confined aquifers in the Twenty Park Basin display artesian water levels, many flow at [he surface. Of the EFC monitoring wells shown on the Twenty Ali le Park Hydrolog}• Map, of total of 15 flow at the surface. Stratigraphy The strata to be disturbed by mining in Eckman Park consist bf the Lw'adge Coal Seam and as much as 120 feet of shale, siltstone, and sandstone overburden. The k'adge Coal is overlain by approximately 73 ft. of siltstone which underlines the Lennox seam. The Lennox Coal is overlain by afine-grained standstone grading upward to a shale at the surface. .The sandstone immediately over the Lennox seam is [he most permeable layer. The (;adge coal also produces water due to secondary permeability. The vertical permeability between the Lennor. and lJadge coals is 0.1 gal/day/ft.2. The horizontal permeability of [he 73 ft. thick permeable zone is '-.9 gpd/ft2 The shales and siltstones [hat confine the I.er.nox coal/sandstone aquifer are relatively impermeable. This low permeability minimizes recharge into the overburden aquifer in the proposed mine plan area. The majority of the recharge originates in the S. E. portion of the mine plan area which will not be disturbed by mining. Flow Ground water flow in the confined aquifer ~in the mine plan area and adjacent areas is generally to the north toward the center of the synclinal basin. Artesian pressures within the confined aquifers in the heart of the Twenty Mile Park ground water basin have been calculated in monitor well b'-35 to exceed 700 pounds per square inch at a depth of 1630 ft. This high pressure causes water to leak upward at the center of the basin and discharge to Fish Creek. Quality Ground water quality in the vicinity of the permit area can be considered poor for domestic use but could be used for livestock and irrigation. Ground water contains relatively high amounts of dissolved salts and calcium carbonate hardness. The base line ground water data shows the water to be of [he sodium bicarbonate type with minor smoun[s of calcium and magnesium cations and sulfate anions. The average baseline concentrations of dissolved salts in the overburden aquifer was found [o be 641 mg/1, mean carbonate hardness of 249.8 mg/1, mean iron 0.15 mg/1 and mean nitrate nitrogen 0.13 mg/1.