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FIRST QUARTER,. Q TER,2400 GROUNDWATER MONITORING REPORT USA STATION#110-STOCKTON MAY,2000 2.2 Monitoring Well Purging The monitoring wells were purged using a 2-inch diameter, submersible Rediflo groundwater pump or disposable bailer, until a minimum of three egwvalent 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 1 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 Prior to sampling, the wells were allowed to recharge to a minimum 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, tune, identifying well number, then stored in a cooler at 4° Centigrade or less, and transported to a Caliform State certified laboratory under completed COC documentation 1 2.4 Groundwater Analysis ' Groundwater samples were analyzed for TPH G, BTEX and MTBE using EPA Methods 8015M and 8020, respectively The groundwater sample with the highest concentration of MTBE was analyzed for all oxygenates using EPA Method 8260B. The analysis were conducted by Siena Laboratories (Sierra) 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 January 13, 2000 3.1 Groundwater Flow and Gradient Groundwater data collected at the site on January 13, 2000 indicates that depths to groundwater . ranged from 56 55 to 57 71-feet below ground surface (bgs) for the first quarter gauging event ' The groundwater elevations ranged from 30 94 to 32 14-feet below mean sea level 2