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FOURTH QUARTER, 1997 <br /> GROUNDWATER MONITORING REPORT • <br /> USA STATION#110- STOCKTON <br /> DECEMBER, 1997 ' <br /> 2.2 Monitoring Well Purging <br /> The monitoring wells were purged using a 2-inch diameter, submersible Rediflo groundwater ' <br /> pump, until a minimum of three equivalent well volumes of water were removed from each well <br /> Groundwater purged from the wells was placed into Department of Transportation approved 55- <br /> gallon drums and stored on-site prior to disposal by USA. All purging and sampling equipment <br /> was washed in a tnsodium phosphate solution and rinsed in potable water prior to each usage to <br /> reduce the potential for cross contamination between wells During the groundwater purging ' <br /> operations, physical parameters such as pH and conductivity were monitored and recorded on <br /> field data sheets, which are included in Appendix A Groundwater purging was discontinued <br /> when the physical parameters appeared to stabilize in the purged groundwater ' <br /> 2.3 Groundwater Sampling <br /> Prior to sampling, the wells were allowed to recharge to a minimum of 80 percent ' <br /> g p cent of their initial <br /> static water levels Groundwater samples were collected from MWA, and MWA-P through <br /> MW-6-P using new disposable bailers Samples were placed into the appropriate laboratory <br /> prepared containers, using proper sample handling and chain-of-custody (COC) protocol <br /> established under applicable SW-846 procedures issued by the USEPA_ The samples were • <br /> labeled with the date, time, identifying well number, then stored in a cooler at 4° Centigrade or ' <br /> less, and transported to a state certified 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 <br /> State certified laboratory, in accordance with state guidelines and EPA protocol <br /> 1 <br /> 3.0 SUMMARY AND CONCLUSIONS <br /> The following sections discuss findings from the groundwater gauging and sampling activities ' <br /> conducted on October 31, 1997 p g <br /> 3.1 Groundwater Flow and Gradient <br /> Groundwater data collected at the site indicates that depths to groundwater ranged from 66 29 to <br /> 67 52-feet below ground surface (bgs) The groundwater elevations ranged from 41 62 to <br /> 4191-feet below mean sea level <br /> • <br /> 2 <br />