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1 September 11, 1997 Harding Lawson Associates 38737 002 ' Ms Mary Meays San Joaquin County Public Health Services Environmental Health Division Page 3 Groundwater Gradient and Flow Directions Based on quarterly monitoring data collected from September 1987 to March 1991, groundwater flow directions have varied at the Site from mainly from northwest through south-southwest and once towards the northeast Based on these data the dominant flow directions appear to be southwest through ' northwest Groundwater gradients varied from 0 0023 to 0 018 feet per foot (ft/ft), averaging approximately 0 004 ft/ft. Depth to groundwater beneath the Site during flus period has varied from approximately 7 to 12 feet bgs More recently, water levels about 5 feet bgs have been measured (SECOR, draft) ' Groundwater Analytical Data Analytical data from the six monitoring wells collected from September 1987 through June 1994 are ' compiled in Table 1 These data indicate that only groundwater samples from MW-4 have consistently contained detectable concentrations of total petroleum hydrocarbons as gasoline (TPHg), with concentrations that have ranged from 9 1 milligrams per liter (mg/1) (September 1987) to 0 24 mg/l {June 1993) With one exception, none of the other wells (MW-1, MW-2, MW-3, MW-5, or MW-6) have contained detectable petroleum hydrocarbons in any sample collected during the three years of monitoring after June 1991 The single exception was 0 08 mg/L of TPHg detected in well MW-1 during the September 1993 sampling event (this detection was qualified as a non-gasoline mixture, see laboratory analytical reports, (WaterWork, 1993)) The presence of detectable petroleum hydrocarbons in wells other than MW-4 prior to September 1993 is summarized as follows Monitoring well MW-1 samples have contained detectable TPHg in only 4 of 22 ' sampling events, MW-3 samples have contained detectable TPHg in only 3 sampling events, and samples from wells MW-2, MW-5, and MW-6 have contained detectable TPHg only once Soil Analytical Data ' Based an analytical data from previous investigations, soil with concentrations of TPHg (greater than 100 mg/kg) appears to be located within the saturated zone west of the UST location, and extends at least 20 feet beneath the forklift building ' WORK PERFORMED DURING THIRD QUARTER 1997 All field operations were conducted in accordance with HLA's site specific Site Safety Plan, dated August 6, 1997, and with the procedures and analytical program described in the Recommended Additional Work section of HLA's recent report (August 5, 1997) Well Purging and Quarterly Sampling ' During the third quarter of 1997, the six onsite wells at the TVG facility, MW-1, MW-2, MW-3, MW-4, MW-5, and MW-6 (Plate 3), were purged and sampled on August 7, 1997 Water levels were measured to the nearest 0 01 foot on August 6, 1997, using an electrical water level motor Following the water level measurements, the wells were purged by hand bailing with a clean stainless steel bailer to remove at least five casing volumes of water from each well, 10 casing volumes were purged from well MW-4 During the purging process indicator parameters including pH, temperature, and electrical conductivity were recorded periodically These field data were recorded on standard HLA Groundwater Sampling Forms (Appendix A) Purged water was placed in labeled DOT-approved 55-gallon drums for subsequent disposal 1