SITE INFORMATION AND CORRESPONDENCE_1987-1992

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Antonia K. J. Vorster 7 December 18, 1989 6) It appears that the LVMD wells may be conduits for the contamination of the deeper aquifer by the contaminated shallow zone. It must be determined if these wells are the principle, or a contributory, cause of the contamination within the deeper zone. It is suggested that these wells be televised to determine if there are any obvious signs of casing damage and infiltration of shallow zone water into the casing. Another possibility is to inject a tracer into the shallow ground water adjacent to a production well , and to pump the production well and monitor the extracted water for that tracer. A third approach may be to design a well cluster network in the vicinity of the LVMD production wells, that will provide adequate resolution of the PCE concentrations so as to identify the source of the contamination in the deep aquifer. If the contamination of the deep zone is wholly from cross-contamination associated with the LVMD wells, then the distribution of the PCE in the deep zone should be in the downgradient direction from essentially a point source. However, if the contamination of this deep aquifer is due to the downward migration of contaminants from the upper zone through intervening substrata, then the contamination, within the deep aquifer, will be more areally extensive. If the LVMD wells are determined to be responsible for all or part of the contamination of the deep aquifer, remedial actions to eliminate this contaminant pathway must be undertaken as soon as possible. These remedial actions may include the sealing-off of the shallow zone or the abandonment of the LVMD wells per state and local requirements. Other possibilities are the rehabilitation of the contaminated zones, and/or wellhead treatment. 7) The consultant should consider conducting a aquifer pump test to determine aquifer parameters and interrelationships. The proposal for such a test should be made after this second phase of the investigation when the lithology of the site and the extent of the contamination, both vertically and areally, is better defined. However•, if one or more of the production wells are pumped, during the Phase II investigation, water levels within nearby monitoring wells should be measured during the pumping of the production well (s) . 8) The sewer line extending offsite, across Gettysburg Place, has not been eliminated as a potential continuing source of offsite contamination. The soil gas survey indicates that the soil adjacent to the sewer line, in the vicinity of monitoring well #4, has significant levels of PCE (soil gas point #31 = 140 µg/1 ) . Therefore, an assessment of PCE contamination within the residential properties west of the site will be necessary.