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4 <br /> SECOND QUARTER,2002 <br /> I . GROUNDWATER MONITORING REPORT <br /> USA STATION#110,STOCKTON <br /> JUNE 2002 <br /> 2.2 Monitoring Well Purging <br /> The monitoring wells were purged using a 2-mch 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 <br /> To reduce the potential for cross contamination between the wells, all purging and sampling <br /> equipment was washed in a trisodium phosphate solution and rinsed in potable water,prior 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 are <br /> included in Appendix A Groundwater purging was discontinued when the physical parameters <br /> 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%of their initial static <br /> water levels Groundwater samples were collected from MW-1P through MW-6P,MW-1 and <br /> MW-2 using new disposable bailers The samples were placed into the appropriate laboratory <br /> prepared containers,using proper sample handling and chain-of-custody(COC)protocol issued <br /> by the USEPA The samples were labeled with the date,time and identifying well number,then <br /> ° ed to a California State certified <br /> stored m a cooler at 4 Centigrade or less, and transport <br /> laboratory under completed COC documentation <br /> I � <br /> 2.4 Groundwater Analyses <br /> Groundwater samples were analyzed for TPH G,BTEX, 1,2-DCA, and the oxygenated fuel <br /> additives MTBE,DIPE,TAME,ETBE, and TBA using EPA Methods 8015K 8020 and 8260B, <br /> respectively The analyses were conducted by Sierra Analytical(Sierra), a California State <br /> certified laboratory, in accordance with state guidelines and EPA protocol. <br /> 3.0 SUMMARY AND CONCLUSIONS <br /> The following sections discuss fundings from the groundwater gauging and sampling activities <br /> conducted on April 12,2002 <br /> 2 <br />