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1 <br /> FIRST QUARTER,1998 <br /> GROUNDWATER MONITORING REPORT <br /> USA STATION#110-STOCKTON <br /> MARCH,1998 ' <br /> 2.2 Monitoring Well Purging <br /> The monitoring wells were purged using a 2-inch diameter, submersible Rednflo 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 Prior to <br /> each usage, all purging and sampling equipment was washed in a tnsodium phosphate solution <br /> and rinsed in potable water to reduce the potential for cross contamination between wells During <br /> the groundwater purging operations, physical parameters such as pH,temperature and <br /> conductivity were monitored and recorded on field data sheets, which are included in Appendix <br /> A Groundwater purging was discontinued when the physical parameters appeared to stabilize in ' <br /> the purged groundwater <br /> 2.3 Groundwater Sampling ' <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 /> MW4-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, time, 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 8915M 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 /> 3.0 SUMMARY AND CONCLUSIONS ' <br /> The following sections discuss findings from the groundwater gauging and sampling activities <br /> conducted on January 22, 1998 ' <br /> 3.1 Groundwater Flow and Gradient <br /> Groundwater data collected at the site indicates that depths to groundwater ranged from 64 60 to <br /> 65 78-feet below ground surface (bgs) The groundwater elevations ranged from 39 64 to ' <br /> 40 05-feet below mean sea level <br /> 2 ' <br />