SITE INFORMATION AND CORRESPONDENCE_1993-1996

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• Wendy L. Cohen -3- 1 December 1993 Aquifer testing in Zone C also should be conducted to determine if there is hydraulic connection between Zones B and C. 8. Page 18 of the work plan states that because no VOCs are now detected in Zone C, further characterization is not justified at this time. Comment: As stated in Item 2, LVMD 2 and 6 have shown contamination in the past. Both wells (now abandoned) were screened in Zone C which is the largest producer of water and is the aquifer of most concern. The extent of contamination, ground water flow direction and gradient in this zone, and hydraulic connection of this zone with Zone B need to be identified. The work plan must specify the activities to achieve these objectives. 9. Page 18 of the work plan states that a downgradient Zone C well will be needed to further verify the absence of VOCs because of the current downgradient use of Zone C wells, e.g., Well No. 11. Comment: See Item 4. This statement, albeit accurate, is inconsistent with previous statements which said that there is no contamination in Zone C. The recognition of the need to monitor Zone C upgradient of Well 11 presupposes there is contamination in this zone. 10. Page 18 of the work plan states that pilot testing will be needed to evaluate the remedial option for the site. Comment: An evaluation of remedial alternatives should first be performed prior to pilot testing of the remedial option. This will eliminate consideration of remedial alternatives which from the outset are not viable. 11. Page 22 of the work plan states that two of the soil borings with the highest OVA readings, which are anticipated to be SB-55 and SB-60, will be converted to vapor extraction wells for VES pilot testing. Comment: OVA readings are appropriate as a screening tool, but not as a basis for selection of vapor extraction wells. Soil gas and soil sample results will provide the best data to select soil vapor extraction well locations. The soil gas survey conducted in August 1989 identified areas where PCE vapors in the soil gas were significant, i.e., 100 µg/I or greater. These areas were along the sewer line south of Village Cleaners, near the southern end of the Benjamin Holt Drive sewer line crossing, along the sewer line serving the former Norge Cleaning Village parallel to and south of Benjamin Holt Drive, and near MW 4. However, the work plan does not propose additional investigation and extraction wells in the Village Cleaner plume. The 1989 soil gas survey report stated that it was not clear whether the source of the PCE vapor was the sewer, contaminated soil, or contaminated ground water. The uncertainty in the PCE vapor source provides justification for more investigation in the identified source areas. Regardless of the source, the contaminated soil is a threat to water quality and must be remediated.