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' Ms. Linda Turkatte Project OF90-002.03 January 27, 1993 Page 2 Also, in September 1987, wells MW-4 and MW-5 were installed to assess impact to groundwater, if any, resulting from the release. ' Removal of Tank C-12 Tank C-12, a 10,000-gallon-capacity regular gasoline storage tank, was removed ' in August 1988 (see Drawing 1). Two soil samples were collected from the tank excavation for chemical analysis. One of the samples contained detectable concentrations of benzene,toluene, ethylbenzene,and xylenes(BTEX). BTEX was ' not detected in the other sample, and total petroleum hydrocarbons as gasoline (TPHG) was not detected in either sample. In September 1988, the area was overexcavated. Confirmation soil samples were collected from the bottom of the ' excavation. Petroleum hydrocarbons were not detected in any of the confirmation soil samples collected during this overexcavation activity. ' Groundwater Characterization Groundwater sampling and analysis has been conducted at the site since January ' 1987. Following confirmation of groundwater impact,overexcavation activities were performed in September 1987 (as discussed in preceding sections of this document) to remove a potential source of additional groundwater impact. Wells MW-1, MW-2, and MW-3 were installed in January 1987; however, well MW-1 was damaged and well MW-2 was removed in September 1987 during the ' overexcavation of the impacted soil near the former tank complex. Wells RAW-4 and MW-5 were installed in September 9987. Since that time, the groundwater elevation has dropped, and these wells, as well as well MW-3, are now dry. To ' continue with groundwater monitoring, deeper wells (MW-9, MW-10, and MW-11) were installed in March 1990. ' Concentrations of petroleum hydrocarbons in wells MW-9, MW-10, and MW-11 have historically been relatively low or nondetectable. Since March 1990, 14 samples have been collected from wells MW-9, MW-10, and MW-11. Nine of ' the samples did not contain detectable concentrations of petroleum hydrocarbons. Toluene was not detected in any of the other five samples; xylenes were detected in one of the samples; benzene was detected in two samples; and total petroleum ' hydrocarbons were detected in three samples. Based on groundwater flow directions and gradients reported by Elder Engineering, ' Inc., the predominant flow direction of first-encountered groundwater was to the northwest with a gradient of 0.0075 foot per foot. This information is for the time period from March 29, 1990, to June 10, 1991. ' During the third quarter of 1992, EMCON Associates conducted additional site characterization activities, including drilling three exploratory soil borings (B92-1 , MW-12, and MW-13) and converting two of the borings to groundwater monitoring pjOV9010900020.3az