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2 9 2 Extraction and Injection Wells The extraction wells tem recovers water from multiple j system p depths Although a number of wells only extract from shallow (above a depth of approximately 325 feet) or deep (deeper than approximately 325 feet) parts of the plume, some wells (E-2-1, 2-2 and E-3-1, 3-2) are paired, one "shallow" and one "deep,"while other wells (E-6, 9, 13, 14, and 15) are screened across multiple depths, both shallow and deep Extraction wells near the leading edge of the plume are typically shallow and wells drilled into the bedrock block are typically classified as deep Wells in the middle of the plume are either paired or screened both shallow and deep Each well is equipped with a submersible pump driven by a variable speed motor controllable from the plant Injection wells are located just downgradient of the leading edge of the plume All extraction wells are constructed of stainless steel continuous-slot screens and steel casing and the well heads are finished with a pitless adapter Injection wells are believed to be constructed in a manner similar to extraction wells, although they have long screens extending up into the vadose zone Injected water is gravity-fed to the injection wells and is conveyed to below the top of the water column in the injection well by a drop pipe 2 9 3 Treatment System Ground water is pumped from the extraction wells directly into a 50,000 gallon surge tank The water levels in the surge tank are interlocked with the well pumps and the transfer pumps If the water level in the tank rises to the high level sensor, the valve in the water line from the wells to the surge tank closes The resulting pressure buildup causes the well pumps to shut off If the water in the surge tank falls to the low level sensor, the transfer pumps stop pumping water to the air stripper During normal operation, water is pumped from the surge tank by two 4,000 gpm centrifugal pumps (with a third pump on standby), to the top of the two air strippers The water line from the pumps to the air strippers is instrumented for measuring the flow rate SEND is also metered into the waterline to sequester any calcium carbonate that may precipitate from the water At the tap of the two air strippers, water is distnbuted uniformly over the 3 5 inch Lanpac plastic packing The depth of the packing is 29 feet The water from the bottom of the air strippers flows by gravity through piping to the injection wells Two 25,000-CFM blowers, with a third blower on standby, provide air to the air strippers The VOCs stripped from the water are emitted from the top of the air strippers directly to the atmosphere without treatment 3 System Objectives, Performance and Closure Criteria 3 1 Current System Objectives and Closure Criteria The current goal of the treatment system is to both contain and remediate the ground water to maximum contaminant levels (MCLS) The current contract for operations requires TCE to be reduced to less than 1 ppb in treated water, however the action level for TCE in the IWL Post Closure Permit is 5 ppb Two wells have been designated as compliance wells, A-7A and B-56 are shallow and deep (bedrock) wells, respectively, immediately down gradient of the IWL The permit will allow the remedial action to be terminated if the concentrations of the CDCs in these compliance wells are reduced to below the action levels There are no potential users of ground warer immediately downgradiem of Liic pluiiie Tlie UILMiate future receptor of the contaminated water is a very large nearby lake The current contract for operations calls for the plant to continuously(24 hours per day, seven days a week) treat water from all designated active extraction wells at least 95% of the time 06/07/99 Page 4 of 14