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X 5r In July 1994, a RESNA field geologist observed the drilling of four additional groundwater monitoring wells (MW4, MW5, MW6, and MW7) at the site to further characterize subsurface conditions Groundwater samples collected from these additional wells contained no detectable petroleum hydrocarbons A detailed discussion of the Phase II Subsurface Investigation can be found in RESNA's "Summary Report, July 1994 Investigation, "dated August 26, 1994 In PHS/EHD correspondence dated March 1995, regulatory approval was given to sample wells MW3 and MW5 and wells MW4, MW6 and MW7 on an alternating semi-annual basis MW 1 and MW2 were to be sampled every quarter, conditions permitting To further evaluate the extent of residual soil contamination in the vicinity of the former underground fuel storage tank (UST), Smith Technology supervised the advancement of four soil borings (SB-1, SB-2, SB-3, and SB-4) on February 29, 1996 to depths of approximately 16 to 26 feet bgs Total petroleum hydrocarbons as gasoline (TPHg), benzene, toluene, ethylbenzene, and xylenes (BTEX) were detected above method detection limits at low to moderate concentrations in samples collected at depths between 10 and 15 feet bgs in borings SBA, SB-2, and SB-3 A detailed discussion of this subsurface investigation can be found in Smith Technology's "Subsurface Investigation Report, " dated April 30, 1996 •� GROUNDWATER MONITORING AND SAMPLING ATC personnel performed groundwater monitoring and sampling on December 29, 1999 Field work consisted of measuring the depth-to-water in wells MW1 through MW7, using an electronic water/product interface probe to determine if free product was present, purging and sampling wells MW1, MW3 and MW5, and servicing the passive skimmer placed in well MW2 Static groundwater elevations were measured in each monitoring well on December 29, 1999 Groundwater was measured at an average of approximately 12 39 feet bgs A groundwater gradient map was created with the December 29, 1999 data using a computer kriging progiam The gradient map, presented as Figure 2, depicts a southerly groundwater gradient averaging 0 003 ft/ft or approximately 16 feet/mile The water table elevation has increased an average of 0 32 feet since the previous measurements were collected in September 1999 Groundwater monitoring data are summarized in Table 1 On December 29, 1999, groundwater samples were collected by ATC from monitoring wells MW1, MW3, and MW5 Groundwater samples were collected from the monitoring wells after stabilization of pH, electrical conductivity (EC), and temperature All wells monitored were purged and sampled according to Smith Technology's Quality Assurance/Quality Control Plan on file with the PHS/EHD A minimum of approximately eight casing volumes of water was removed from each sampled well A dedicated disposable bailer was used to collect each water sample Field parameters and purged volumes are shown on well purge logs included in Attachment I 625811QUARTLYI4QR-1999 DOC 2