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April 20, 1987 <br /> AGS Job 8691-6 <br /> Page 2 <br /> Data obtained by WEGE are summarized in Table 1. All vapor <br /> samples collected from depths less than 30 feet showed low levels <br /> of hydrocarbons, which would probably represent concentrations <br /> not detectable with standard EPA-approved analytical methods for <br /> soil samples. The drilling method used reached refusal due to <br /> hard subsurface material in most of the holes. For this reason, <br /> only holes 1 and 6 reached depths corresponding to the ground <br /> water surface. Vapor samples taken near the ground water surface <br /> in these holes showed 1, 344 to 4,748 parts per million total <br /> volatile hydrocarbons. These values are vapor concentrations, <br /> and are significantly higher than actual levels of soil <br /> contamination. However, vapor analyses in hole 1 show an <br /> increase of hydrocarbons with depth, suggesting that ground water <br /> has been impacted. Water samples could not be collected from <br /> these holes. Samples collected at 25 feet and 32 . 5 feet in hole <br /> 5 showed only low levels of hydrocarbons. <br /> A water sample collected from the borehole of MW-5 was analyzed <br /> by WEGE on March 18. This sample showed low levels of <br /> hydrocarbons ( 0 . 3 parts per million) in a head space analysis by <br /> WEGE. This result is generally in accordance with a water sample <br /> collected from the well after development and purging operations, <br /> which showed 0. 0488 parts per million total volatile hydrocarbons <br /> when analyzed by EPA method 602 . <br /> These data, in combination with information collected during tank <br /> removal and testing operations, indicate that contamination is <br /> concentrated in the area of the tank cavity. There is no <br /> evidence of leakage associated with the product lines or <br /> dispensers. It is not possible at the present time to exclude <br /> the possibility that the soil vapor contamination detected in <br /> samples from holes 1 and 6 is related to leakage from product <br /> tanks off-site to the north. The data may also be consistent <br /> with lateral migration from the tank cavity on site. <br /> WEGE interpeted a northward migration direction on the basis of <br /> their data. This conclusion is based on a very limited number of <br /> data points, and is probably erroneous. Northward migration is <br /> inconsistent with other data, including water level elevation and <br /> gradient calculations. <br /> .4,o o/ieof GeoSystems <br />