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. A S S O C I A T E S I N C
<br /> 4, MW-5, and MW-6 The three new wells were developed and sampled along with the original monitoring wells
<br /> MW-1, MW-2, and MW-3 Analytical results of groundwater samples collected from the six monitoring wells
<br /> Indicated the presence of elevated concentrations of petroleum hydrocarbons in the vicinity of MW-3 and MW-6,
<br /> in the northeastern comer of the site
<br /> In November 1998, ATC conducted a subsurface site investigation to evaluate the vertical and horizontal
<br /> extent of hydrocarbon impacted soil ATC supervised the installation of three soil borings SBI, SB2, and
<br /> SB3 from approximately 30 to 50 feet bgs Analytical results of soil samples indicated the vertical extent
<br /> of soil contamination had been defined, but the horizontal extent of impacted soil was not fully identified in,
<br /> the northeastern corner of the site Site activities are summarized in ATC's Summary Report ofAdditaonal
<br /> Subsurface Investigation, dated January 27, 1999
<br /> SAMPLING ACTIVITIES
<br /> On July 10, 2003, ATC personnel collected groundwater samples from momtoring wells MW-1 through
<br /> MW-6 The locations of the monitoring wells are shown on Figure 2 Prior to collection of groundwater
<br /> samples, the depth to water, pH, electrical conductivity, and temperature were measured in the monitoring
<br /> wells and recorded A minimum of three well casing volumes was purged from each well prior to
<br /> sampling The wells were allowed to recover and samples were collected from each well using dedicated
<br /> disposable bailers Purged well water was contained on site in DOT approved 55 gallon drums and labeled
<br /> • for disposal pending receipt of lab results
<br /> The groundwater samples collected from each well were submitted to Argon Laboratories, a state-certified
<br /> laboratory (ELAP cert no 2359) located in Ceres, California, for analyses Laboratory analyses consisted
<br /> of total petroleum hydrocarbons quantified as gasoline (TPHg) utilizing EPA Method 8015B, benzene,
<br /> toluene, ethylbenzene, total xylenes (BTEX) utilizing EPA Method 8021B, and methyl tertiary butyl ether
<br /> (MTBE) utilizing EPA Method 8260B Groundwater well purge and sample logs are contained in
<br /> Attachment 1
<br /> ANALYTICAL RESULTS
<br /> The samples collected from wells MW-1, MW-4, MW-5, and MW-6 contained no detectable
<br /> concentrations of TPHg, BTEX, or MTBE TPHg, toluene, ethylbenzene, and total xylenes were detected
<br /> in the groundwater sample collected from MW-2 at concentrations of 5,700, 12, 49, and 60 micrograms
<br /> per liter (µ/L), respectively TPHg, benzene, toluene, and ethyl benzene were detected in the groundwater
<br /> sample collected from MW-3 at concentrations of 520 µIL, 1 5 µ/L, 0 6 µ/L, and 1 0 µ/L, respectively A
<br /> summary of current and historical laboratory analytical results is presented in Table 1 Hydrographs of
<br /> groundwater elevations and analytical data are contained in Attachment 2 Laboratory data sheets and
<br /> cham-of-custody documentation are contained in Attachment 3
<br /> GROUNDWATER FLOW DIRECTION
<br /> Groundwater level measurements were collected from MWA through MW-6 on July 10, 2003
<br /> Groundwater levels ranged from 26 49 to 27 36 feet below the tops of the well casings, representing an
<br /> • average decrease in the water table elevation of approximately 0 26 feet since April 2003 The water level
<br /> data were used to develop the groundwater elevation contour map (Figure 3) Assuming that horizontal
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