SITE INFORMATION AND CORRESPONDENCE FILE 1

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4491 Durham Ferry Road Page 3 The summary of shallow groundwater contamination failed to include the results of the grab groundwater samples which were collected from hydropunches, HP1 - HP6 drilled on October 20, 1993. The report estimated that the radius of the groundwater plume was 50 feet. It is difficult to conceptualize this estimate when the radius of the soil vadose zone contamination plume was estimated at 70 feet. The groundwater contamination plume is at least as large as the soil contamination plume. Feasibility Study A series of feasibility tests were conducted between December 19 and December 21 , 1995 to evaluate groundwater extraction, soil vapor extraction and air sparging remedial alternatives. Contaminated groundwater water was produced by the pumping of RW1 which reportedly was stored on site in a 21,000 gallon tank pending removal by a licensed hauler. Please submit documentation for the disposal of this water. A l"groundwater sample was collected on December 20, 1995 from RW1 following the completion of the test and reported on Table 2. Unfortunately, there also was an terror in the reporting of these results on Table 2 that requires revision and re- submittal. The concentration of toluene that was detected was 2.3 ppb rather than 2 ppb. The text of the report indicated that Figure 10 illustrated the water table elevation at the end of the groundwater extraction test when in fact Figure 10 described the pre- and post-sparge test results of dissolved oxygen. The report included the conclusion that it would only be possible to achieve a 35 foot soil vapor extraction radius of influence in RW1 by concurrent groundwater extraction to lower the water table. The report also stated that the radius of influence for VW2 and VW3, without groundwater extraction, was 20 and 17 feet respectively. Radius of influence data was not collected for VW1 which had vacuum versus flowrate characteristics more similar to RW1 than VW2 and VW3. Groundwater extraction may improve the radius of influence that may be acheived; however, the added costs may not justify its application over additional soil vapor extraction wells. Air sparge well, SP2 was reportedly used for air sparge testing. Air pressures of up to 15 psi were used and stabilization achieved at 7 psi with a 13 cfm flow rate, followed by a further reduction to 3 psi with a 10 cfm flow rate, in attempts to capture sparge vapors using VW3 which is approximately 45 feet away. The results were reportedly depicted on Figure 11 when actually it is Figure 10. PHS/EHD questions the results since the concentrations of dissolved oxygen observed in SP2 showed little influence by sparging. The largest change in dissolved oxygen concentrations were actually observed in SW 1 .