SITE INFORMATION AND CORRESPONDENCE

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JAMES GIOTTONINI PAGE 2 The analytical results from soil samples from the piping and dispenser area showed significant contamination. The full extent of this contamination source is not known. Those areas not completely defined with physical data may be inferred for now, however a conservative inference must be made. The radius of influence for the remedial system should encompass the entire area of known and suspected impact. Groundwater Characterization The estimate of impacted groundwater presented in the report appears to be justified with the physical data collected from the site. The outer lying wells, with the exception of monitoring well MW#5, show contamination intermittently. The groundwater contaminant plume extends from the area of the former tank pit out to these wells, and possibly somewhat beyond. Therefore, this groundwater plume area must be included in the proposed remediation area and this may be accomplished with additional vapor extraction wells in these areas. Sail Va or Extraction The lack of pictorial presentation of the soil lithology, the contaminant distribution and the vapor well schematics in areas of known and suspected impact makes an evaluation of the effectiveness of the proposed system difficult. it is evident, however, that with the existing wells and the estimated radius of influence shown in the report, the entire suspected soil plume will not be affected, particularly to the north of soil boring SB#15 and to the south of former tank#2. it is also apparent that additional soil vapor extraction wells must be installed at the site to encompass the entire identified plume, including the groundwater plume. In addition, passive air inlet wells designed to reduce the degree of stagnation zones in between vapor wells should be considered in the final remedial plan (existing and future vapor extraction wells can be plumbed for this, using valves to control inlet or outlet of air flow). Groundwater Extraction PHSIEHD does not have the results from the October 1992 pump test. The discussion presented in the FRP mentions that the production well exhibited negligible non-linear head losses, suggesting a high efficiency and proper design. This does indeed suggest a high efficiency of groundwater removal over the length of the screen portion of the well. However, this also suggests that negligible drawdown of the watertable will be evidenced, indicating that the lowering of the watertable will be difficult. In addition, the efficiency of groundwater removal may not be indicative of the efficiency of hydrocarbon removal. In fact, extensive published data on groundwater extraction show this treatment alternative to be a costly and an extremely inefficient remedial alternative for groundwater. Typically, these systems remove a great volume of water but only a small and insignificant mass of hydrocarbons. With the initiation of the vapor extraction system and the prompt addition of several vapor extraction wells in the areas of groundwater contamination, the need for hydraulic containment at this site may not be warranted at this time. Based only on the discussion in the FRP, it is uncertain whether groundwater containment would even be achievable at this site. Results from other vapor extraction systems within this county show this alternative to have a beneficial effect on groundwater plumes as well as soil plumes. The effectiveness, however, is dependant on the efficiency of the system design.