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:0: URS Greiner Woodward Clyde Ms: Carol Oz,R.E.H.S. Page 4 LOP/Site Mitigation Unit San Joaquin County—Public Health Services Environmental Health Division March 13, 2000 The project-specific standard purging volume prior.to.sampling will be three well casing volumes of groundwater, although an exception to this standard will be required to allow sampling at low-yield wells if applicable. Low yield welis'will be purged dry and-allowed to recover to 80 percent of its original total volume of water prior to sampling. Purging will be performed by using dedicated,single-use,high density polyethylene bailers. As each well is .purged, temperature,.pH, specific conductivity, turbidity, and dissolve oxygen will be monitored periodically to verify the groundwater entering the-well is indicative of aquifer conditions. When the water volume in each well has recovered to at leasi 80 percent of the pre-purge volume,a water sample will be collected from the well. Each sample will be 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 will be carefully transferred to precleaned,laboratory-provided sample containers. Once collected,the sample bottles will be labeled with the time and date of collection,project and sample identification codes,the sampler's initials, the type of analysis to be performed, and the preservative used, if any. The samples will be then sealed-in plastic bags and stored in an:ice-filled chest.at approximately 40C until delivery to the laboratory. Each groundwater sample will be delivered to the laboratory within the appropriate holding.times and will be accompanied by the COC documents. The groundwater samples will be 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. i To reduce the potential for cross-containination,the groundwater level indicator will be 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 will be stored'in labeled 55-gallon steel drums pending disposal. Purge water will be disposed of following the completion of each round of quarterly sampling. Report Preparation Following the receipt of the analytical results,a draft report will be prepared'summarizing the results of the most recent sampling event. Included in'the report will be a summary of the soil sampling results and well construction specifications,tabulated analytical soil and groundwater data; a groundwater gradient figure, a figure showing monitoring well.locations, and the laboratory,analytical report. l 1:1142 l 4102_TracyMorkplan.doc j