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. MTBE These low concentrations indicate that vertical migration of petroleum hydrocarbons has been minimal Well MW-13 was drilled in the southeast corner of the site Just outside of the former UST complex Soil samples collected from this boring at 10 fbg contained ND levels of TPPH, 0 029 ppm benzene, and 1 7 ppm MTBE Soil samples collected from MW-13 at 30, 50, 55, 60, 70, and 80 tbg did not contain detectable concentrations of TPPH, BTEX, and MTBE These findings indicate that any vertical migration of contaminants that may have occurred in the source area has not spread laterally DISTRIBUTION OF PETROLEUM HYDROCARBONS IN GROUND WATER Shallow Monitoring Wells The highest level of petroleum hydrocarbons at this site have been detected in Well MW-5, RW-lA and MW-8 Wells MW-5 and RW-1A are located in or near the source area, in the southeastern corner of the site Well MW-8 is located in the southwestern corner of the site The extent of petroleum hydrocarbons in ground water appears to be primarily confined to the vicinity of the former UST complex and the southwestern corner of the site The newly installed wells to the south and southwest of the site (MW-9, MW-10, and MW-11) do not contain detectable levels of petroleum hydrocarbons or MTBE indicating that the lateral extent of contaminants in ground water is delineated to the south and southwest of the site Well MW-3 located off-site near the southeastern corner of the site has been ND for TPPH and MTBE since installation The highest level of benzene detected in this well has been 1 2 ppb This well delineates the lateral extent of contaminants in ground water southeast of the site Well MW-4 has contained maximum TPPH concentrations of 280 ppb and has not contained detectable levels of benzene Maximum MTBE concentrations of 5,100 ppb have been detected in this well, although recent data shows a decrease in concentrations down to the 500 to 600 ppb range Well MW-6 was installed northeast of MW-4 in response to the MTBE detected in MW-4 This well has not contained detectable levels of TPPH or benzene, and has contained MTBE at concentrations ranging from 7 5 to 79 ppb Well MW-2, located in the northwestern portion of the site, has contained TPPH and benzene concentrations as high as 9,000 ppb and 1,100 ppb, respectively and has shown a steady decrease in concentrations Well MW-7, located northwest of MW-2, has been ND for TPPH since it was installed in January 1997 With the exception of the December 1997 sampling event it has not 240-0783 17