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• system Extremely steep horizontal piezometric gradients are observed in the vicinity of the southern edge of the uplifted bedrock block and another area of steep, though less pronounced, gradients are found on its northern edge The piezometric gradients within the bedrock block are comparable to the gradients in the alluvium Although the permeability of the bedrock material itself is very low, there is strong evidence for extensive fracturing in the bedrock that allows considerable ground-water flow The steep gradients on both sides of the bedrock block may indicate low-permeability material along its margins that inhibits flow into the block Beyond the Installation's northern boundary, a deeper aquifer with distinctly different water quality(higher TDS) has been found 2 7 Ground Water Depths and Flow Direction Depth to ground water within the project area varies from slightly over 100 feet near the northern Installation boundary to as much as approximately 400 feet within the Industrial Complex Ground water is typically found at depths of 150-300 feet within the project area Ground water recharge occurs along the valley margins and flows generally northwestward beneath the Installation toward discharge areas in the central and northern parts of valley Ground water flow in the project area is northwest The ground water within the northeast plume flows to the northeast Piezometric gradients are low in the alluvium and within the bedrock block, from less than 0 001 ft/ft to 0 0025 ft/ft The higher gradients along the edges of the bedrock block may exceed 0 1 ft/ft 2 8 General Hydraulic Properties of the Aquifer In general, the aquifer system beneath the Installation is considered to be very productive Discharges to production wells range over 1,000 gallons per minute (gpm) with specific capacities of greater than 20 gpm/foot Hydraulic conductivities of the bedrock aquifer were determined by various means and found to vary significantly, ranging from 2 gallons per day per square foot (gpd/ft2) in quartzite with clay-filled fractures to 2,000 gpd/ft2 in quartzite with open, interconnected fractures The alluvial aquifer displays a variety of hydraulic conductivities Short- and long-term pumping yielded horizontal hydraulic conductivities ranging from 1 to 5,300 gpd/ft2 and averaging approximated at 1,500 gpd/ft2, while the average vertical hydraulic conductivity was approximately 225 gpd/ft2 2 9 System Description 2 9 1 System Overview The remediation system consists of 16 extraction wells (one of which is not currently operating), 13 injection wells, extraction pumps, extraction and injection water piping, a 50,000 gallon surge "equalization" tank, three large transfer pumps (4,000 gpm capacity each, one is a standby unit), a cnemical feed system for the addition of souiuiiz i,exailietap hosp hate kk3 ), anu two 12-foot diameter, 60-foot tall air strippers operated in parallel The plant is capable of treating 8000 gpm SHMP is added to influent water prior to air stripping to control the formation of inorganic precipitates that caused pipeline and well plugging early in the operation of the plant 06/07/99 Page 3 of 14