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cv�\V'yI it i i �iI I I I ii . A S S O C 1 A r E S I N C concentrations of petroleum hydrocarbons Field activities and analytical results were detailed in ATC's Summary Report ofAdditional Investigation, dated October 19, 1998 SAMPLING ACTIVITIES On May 21, 1999, groundwater samples were collected by ATC personnel from monitoring wells MW 1 through MW3 The locations of the monitoring wells are shown on Figure 2 Prior to collection of groundwater samples, the depth to water, pH, electrical conductivity, and temperature were measured in the monitoring wells and recorded A minimum of three well casing volumes were purged from each well prior to sampling The wells were allowed to recover and samples were collected from each well using dedicated disposable bailers The groundwater samples collected from each well were submitted to State-certified Sequoia Analytical (FLAP Cert No 1210) for chemical analysis of total petroleum hydrocarbons as gasoline (TPHg)and total petroleum hydrocarbons as diesel (TPHd) utilizing EPA methods 8015 modified, and benzene, toluene, ethylbenzene, and xylenes (BTEX) and methyl tertiary butyl ether (MTBE) utilizing EPA methods 8020 Groundwater well purge and sample logs are contained in Attachment 1 • ANALYTICAL RESULTS TPHd was detected above laboratory detection limits in the samples collected from wells MW2 and MW3 at concentrations of 94,000 parts per billion (ppb) and 770 ppb, respectively The chromatogram patterns indicated that the concentrations of TPHd were weathered or non-diesel mixture TPHg was detected above laboratory detection limits in the samples collected from wells MW2 and MW3 at concentrations of 1,300 ppb and 234 ppb, respectively The chromatogram patterns indicated that the concentrations of TPHg were weathered The sample collected from well MW1 contained no detectable concentrations of TPHg, TPHd, or BTEX None of the samples contained detectable concentrations of MTBE A summary of analytical results is presented in Table 2 Laboratory data sheets and chain-of-custody documentation are contained in Attachment 2 GROUNDWATER FLOW DIRECTION Water level measurements were collected from wells MW1 through MW3 on May 21, 1999 Water levels ranged from 9 35 to 10 77 feet below the tops of the well casing elevations, representing an average decrease in the water table elevation of approximately 136 feet since February 1999 The water level data were used to develop the groundwater elevation contour map (Figure 2) Assuming that horizontal isotropic conditions prevail, groundwater in the uppermost aquifer beneath the site flowed towards the southwest The average hydraulic gradient on May 21, 1999 was calculated to be 0 0006 ft/ft or approximately 3 2 ft/mile A summary of .` groundwater monitoring data is presented in Table 1 w 1625001quartlyUgr-1999 doc 2