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URS Greiner Woodward Clyde Ms. Carol Oz,R.E.H.S. Page LOP/Site Mitigation Unit ` San Joaquin County—Public Health Services Environmental Health Division September 14, 2000 Quarterly Groundwater Monitoring Well Sampling The three newly installed groundwater monitoring wells were sampled on June 28, 2000 to complete the first of two scheduled groundwater monitoring events. The groundwater monitoring activities at the Site were conducted +... as follows. Prior to approaching each well, VOC field measurements were taken from the well head area, inside of the vault. and inside the well casing. These field measurements were used in the evaluation of the proper personnel protection equipment for each well location. Before purging, the depth to groundwater and total depth of each well was measured to an accuracy of 0.01 feet to a known surveyed point at each well location with an electronic water level indicator. These measurements were used to calculate the purging volume for each well and the groundwater gradient and flow direction at the Site. Based on the calculated groundwater elevations,the groundwater gradient at the Site on June 28, 2000 was 0.004 feet per foot in a north-northwesterly direction (see Figure 2 in Attachment 1). The project-specific standard purging volume prior to sampling was three well casing volumes of groundwater. Purging was performed by using dedicated, single-use, high-density polyethylene bailers. As each well was purged,temperature,pH, specific conductivity and turbidity were monitored periodically to verify the groundwater entering the well was indicative of aquifer conditions. When the parameters indicated that the water in each well was representative of the aquifer, a water sample was collected from the well. A copy of the well sampling data sheets is included as Attachment IV. Each sample was collected by lowering a new precleaned, dedicated bailer slowly to the water line and allowing it to fill while causing a minimum of agitation to the water column. Groundwater samples were carefully transferred to precleaned, laboratory-provided sample containers. Once collected, the sample bottles were labeled with the time and date of collection, project and sample identification codes, the samplers initials,the type of analysis to be performed,and the preservative used, if any. The samples were then sealed in plastic bags and stored in an ice-filled chest at approximately 4°C until delivery to the laboratory. Each groundwater sample was delivered to the laboratory within the appropriate holding times and was accompanied by the COC documents. The groundwater samples were submitted to Curtis&Tompkins and analyzed for TPH-G by EPA Method 8015 modified, and BTEX,MTBE,TBA, DIPE,ETB, and TAME by EPA Method 8260. L" To reduce the potential for cross-contamination, the groundwater level indicator was decontaminated between sampling events using a laboratory-grade detergent solution, rinsed twice in tapwater, and a final rinse with deionized water. Groundwater sampling purge water was stored in labeled 55-gallon steel drums pending disposal. w.. �.. IIURS_SAClkWPROCESSU4214162_TRACYITRACY REPORT-2.DOC