SITE INFORMATION AND CORRESPONDENCE FILE 1

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Page 2 4491 Durham FerryRoad "f Table 2 that summarized the groundwater results contained errors which require correction and submittal of a revision. The groundwater samplefrom of 1200 collected on October 19, 1995 actually had detectable ct ppb methyl tertiary butyl .ether (MTBE) and 3,400 pp benzene. Table 2 indicated that on January 5, 1996 the domestic well was sampled. The field notes indicated that the recovery well, RW1 , was gauged but not sampled. k There was no description of how the sample from the domestic well was collected. if it was sampled it was referenced on the chain of custody as WW1 . Also, the chain of custody indicated that no preservative was used in the VOA's used for sample collection. Since chemical preservatives were not used, analysis should have been completed within 7 days, yet according to the laboratory report, analysis occurred on January 18 and 19, 1996; therefore, acceptable holding times were exceeded. This also should have been referenced on the table summarizing the groundwater results. Generally, laboratory cover letters include a summary of the quality control issues, however, the cover letter for the January 5, 1996 sample analysis report was not included. ✓ The report indicated that the soil drill cuttings and auger rinseate were stored on site pending removal and disposal by a licensed waste-hauler. Please submit the documentation for the disposal of these wastes. The report stated that samples were collected using disposable bailers, yet the field notes from both the October 1995 and the January 1996 sampling events indicated that dedicated equipment was used for sampling. Please clarify the methodology that was used. The summary of contamination in the vadose zone failed to include the results of the soil borings drilled and sampled on,December 14, 1987 prior to the tank removals, the soil samples collected on- February 28, 1989 at the time of the tank removals, and the soil samples collected on August 28, 1991 during the installation of MW2 and MW3. The full extent of the vertical extent of the soil contamination has never been assessed. Therefore, it is likely that the extent of soil. contamination was underestimated because the vadose zone estimate used 7 feet for vertical thickness instead of 10 feet which is the difference between 7 and 17 feet and the adsorbed extent of soil contamination was not estimated. _ The report described the vadose zone mass using the calculation to estimate the volume for a cylinder with a radius of 70 feet and 700 ppm maximum TPH-gas. The report estimated a volume of 107,757 cubic feet and a mass of 5,050 lbs of hydrocarbons. Actually the area of the plume is oval shaped with dimensions of 70 feet by 105 feet and a depth of 10 feet; therefore, the volume would be more accurately estimated at 73,500 cubic feet using the equation for a rectangle rather than a spherical cylinder. Since the maximum concentration of TPH-gasoline that was evidenced is 28,000 ppm, at the time of tank removal, the mass of ° hydrocarbons would be estimated at 137,200 lbs rather than 5,050 lbs.