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G-2.2.3 Lower Aquifer The Lower Aquifer is contained within the fractured oil shale and marlstones of the Parachute Creek Member of the Green River Formation. The Lower Aquifer extends from the middle of the Mahogany Zone to the top of the Saline Zone (Daub et. al., 1985). The leached zone (Figure G-2) extends from the middle of the R-8 Zone down to the base of the lower aquifer which is also known as the Dissolution Surface (Daub et. al., 1985). Percolating groundwater has removed the saline minerals that once existed across this interval. In the past the area across the Lower Aquifer contained an abundance of saline minerals, but now has enhanced porosity and permeability due to the removal of these minerals. The boundary between the Leached Zone and the underlying Saline Zone, below which minerals have not been dissolved, is called the Dissolution Surface. Near the Lease area, the depth to the top of the Lower Aquifer is approximately 1,250 to 1,300 feet below surface, and its thickness is approximately 400 feet (Welder and Saulnier, 1978 and Hardy and Goodrich, July, 1996). In this location, ground water flow in the Lower Aquifer is northeastward (BLM, 1985). Ground water in the Lower Aquifer is generally classified as a sodium-bicarbonate-chloride type with TDS concentrations ranging from approximately 600 mg/1 along the Basin margins to greater than 70,000 mg/1 in the northern and north-central part of the Basin . Water quality analyses for the Lower Aquifer from one well near the Lease area are presented in Table G-3. Water in the Lower Aquifer near the Lease area is of poorer quality than water in the Upper Aquifer, but it is acceptable for agriculture use. As the Dissolution Surface is approached, water quality in the Lower Aquifer degrades with a significant corresponding increase in total dissolved solids (TDS). No perched aquifers have been identified on the Rock School Lease. G:tt.MM78545.00NteelamatioMRadamexh.DOC G-9