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FIRST QUARTER, 1999 t <br /> GROUNDWATER MONITORING REPORT <br /> USA STATION#110 - STOCKTON <br /> MARCH, 1999 <br /> 2.2 Monitoring Well Purging - <br /> The monitoring 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 <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 w2hidi `nn a-tnsodium phosphate solution and rifsed-in potable water, pnor to <br /> each usage During the groundwater purging operations, physical parameters such as Ph, <br /> temperature and conductivity were monitored and recorded on field data sheets, which ae <br /> included in Appendix A Purging was discontinued when the physical parameters appeared to <br /> stabilize in the purged groundwater ' <br /> 2.3 Groundwater Sampling <br /> Pnor 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 /> appiopnate 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, time, identifying <br /> well number, then stored in a cooler at V 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, BTEX and MTBE using EPA Methods 8015M <br /> and 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 /> 3.0 SUMMARY AND CONCLUSIONS r <br /> The following sections discuss findings from the groundwater gauging and sampling activities <br /> conducted on January 21, 1999 _ - —— - <br /> 3.1 Groundwater Flow and Gradient <br /> Groundwater data collected at the site indicates that depths to groundwater ranged from 57 73 to <br /> 58 76-feet below ground surface (bgs) The groundwater elevations ranged from 32 79 to 33 15- <br /> feet below mean sea level <br /> 4 <br /> 2 <br />