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SECOND QUARTER,2000 GROUNDWATER MONITORING REPORT USA STATION#110 -STOCKTON ' JULY,2000 2.2 Monitoring Well Purging rThe monitoring wells were purged using a 2-inch diameter, submersible Rediflo groundwater pump or disposable bailer, until a minimum of three equivalent well volumes of water were removed from each well Groundwater purged from the wells was placed into Department of Transportation approved 55-gallon drums and stored on-site prior to disposal by USA ' To reduce the potential for cross contamination between the wells, all purging and sampling equipment was washed in a trisodium phosphate solution and rinsed in potable water, prior to each usage During the groundwater purging operations,physical parameters such as pH, temperature and conductivity were monitored and recorded on field data sheets, which are included in Appendix A Groundwater purging was discontinued when the physical parameters appeared to stabilize in the purged groundwater 2.3 Groundwater Sampling p g Prior to sampling, the wells were allowed to recharge to a mwnmum of 80% of their initial static water levels Groundwater samples were collected from MW-1-P through MW-6-P, MW-1 and MW-2 using new disposable bailers The samples were placed into the appropriate laboratory prepared containers, using proper sample handling and chain.-of-custody(COC) protocol issued by the USEPA. The samples were labeled with the date, time, identifying well number,then ' stored in a cooler at 4° Centigrade or less, and transported to a California State certified laboratory under completed COC documentation 2.4 Groundwater Analyses Groundwater samples were analyzed for TPH G, BTEX, 1,2-DCA, and oxygenated fuel additives including MTBE,DIPE, TAME, ETBE, TBA, and ethanol using EPA Methods 8015M, 8020 and 8260B, respectively The analyses were conducted by Sierra Laboratories (Sierra), a California State certified laboratory, in accordance with state guidelines and EPA protocol 3.0 SUMMARY AND CONCLUSIONS The following sections discuss findings from the groundwater gauging and sampling activities conducted on April 6, 2000 ' 3.1 Groundwater Flow and Gradient 1 Groundwater data collected at the site indicates that depths to groundwater ranged from 55 15- feet below ground surface (bgs) in MW-1 to 56 23-feet bgs in MW-6P The groundwater elevations ranged from 29 54-feet below mean sea level(MSL) in MW-1 to 30 62-feet MSL in ' MW-6P ' 2