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1 <br /> FOURTH QUARTER, 1998 ' <br /> GROUNDWATER MONITORING REPORT <br /> USA STATION#110-STOCKTON <br /> JANUARY, 1999 <br /> 2.2 Monitoring Well Purging <br /> The morutoring wells were purged using a 2-inch diameter, submersible Rediflo groundwater <br /> pump or disposable bailer, until a minimum of three equivalent well volumes of water were <br /> removed from each well Groundwater purged from the wells was placed into Department of 1 <br /> Transportation approved 55-gallon drums and stored on-site prior to disposal by USA To <br /> reduce the potential for cross contamination between the wells, all purging and sampling <br /> equipment were washed in a trisodium phosphate solution and rinsed in potable water, prior to <br /> each-usage=During the groundwater plu ging operatians,—physical parameters such as pH and <br /> conductivity were monitored and recorded on field data sheets, which are included in Appendix <br /> A Temperature was not measured this quarter due to equipment malfunction Groundwater , <br /> purging was discontinued when the physical parameters appeared to stabilize in the purged <br /> groundwater <br /> 2.3 Groundwater Sampling <br /> 1 <br /> Prior to sampling, the wells were allowed to recharge to a minimum of 80 percent of their initial ' <br /> static water levels Groundwater samples were collected from MW-1, MW-2, MW-1-P through <br /> MW-4-P, and MW-6-P using new disposable bailers The samples were placed into the <br /> appropriate laboratory prepared containers, using proper sample handling and chain-of-custody <br /> (COC) protocol issued by the USEPA The samples were labeled with the date, tune, identifying <br /> well number, then stored in a cooler at 4° Centigrade or less, and transported to a state certified ' <br /> laboratory under completed COC documentation <br /> 2.4 Groundwater Analyses ' <br /> Groundwater samples were analyzed for TPH G and BTEX using EPA Methods 8015M and <br /> 8020, respectively The analyses were conducted by Sierra Laboratories (Sierra), a California r <br /> State certified laboratory, in accordance with state guidelines and EPA protocol <br /> 3.0 SUMMARY AND CONCLUSIONS <br /> The following sections discuss findings from the groundwater gauging and sampling activities <br /> ` conducted on October 20, 1998 <br /> 31 Groundwater Flow and Gradient <br /> Groundwater data collected at the site indicates that depths to groundwater ranged from 59 39 to <br /> 60 57-feet below ground surface (bgs) The groundwater elevations ranged from 34 50 to 34 96- <br /> feet below mean sea level <br /> 2 <br />