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31 January 1997 <br /> AGE-NC Project No 95-0125 <br /> Page 2 of 7 <br /> Soil removed during the USTs excavation was subsequently backfilled in the tank excavation Clean <br /> backfill material was then used to cover the impacted soil Based upon the shallow depth to ground <br /> water at the site, the PHS-EHD required a subsurface investigation of the former UST areas <br /> 23 MONITORING WELL INSTALLATION AND SAMPLING <br /> Between 1987 and 1992, a total of ten ground water monitoring wells were installed at the site by <br /> Groundwater Technology, Inc (GTI) Petroleum hydrocarbons were detected in one soil samples <br /> analyzed during installation of the wells, Sample MW-6A This sample was collected from below <br /> the level of the water table and was saturated with the ground water from the site The results of the <br /> investigation were detailed in the GTI Problem Assessment Report, dated 16 July 1990 <br /> Ground water sampling events were conducted irregularly between 1987 and 1995 Field observation <br /> of selected monitoring wells were performed on an infrequent basis between 1993 and 1994 by <br /> representatives of LSD Historical ground water depth at the site has varied between 5 and 10 feet <br /> below surface grade (bsg) The prevailing ground water flow direction has been to the northwest <br /> • Petroleum hydrocarbons have been detected in ground water only in the vicinity of the former <br /> dispensers Previous sampling events have established an ellipse-shaped ground water plume, <br /> extending from MW-2 at the south to near MW-5 at the north The center of the plume has <br /> apparently remained near MW-6 (GTI Quarterly Report, dated 3 March 1992) <br /> 24 LIMITED SUBSURFACE INVESTIGATION <br /> On 26 June 1995, five soil probe borings were advanced at the site to a depth of ten feet bsg <br /> Discrete soil samples were collected at depths of five, seven and ten feet bsg In addition to soil <br /> samples, a grab ground water sample was obtained from one probe boring Petroleum hydrocarbons <br /> were detected in soil samples collected during the investigation Results of the investigation were <br /> detailed in AGE Quarterly Report, dated 25 September 1995 <br /> 25 EXCAVATION OF HYDROCARBON-IMPACTED SOIL <br /> Based on the soil samples collected from the installation of the monitoring wells and soil borings, <br /> a limited quantity of hydrocarbon-impacted soil remained in the area of the former USTs In order <br /> to reduce the mass of the residual impacted soil, an interim corrective action was initiated at the site <br /> • On 20 and 21 December 1995, approximately 285 cubic yards of soil suspected to be impacted with <br />