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' SECOND QUARTER,2001 GROUNDWATER MONI'T'ORING REPORT USA STATION#110, STOCKTON ' JUNE 2001 To reduce the potential for cross contamination between the wells, all purging and sampling equipment was washed in a trisodium phosphate solution and rinsed in potable water,prior to ' each usage. During the groundwater purging operations, physical parameters such as pH, temperature and conductivity were monitored and recorded on field data sheets, which are included in Appendix A. Groundwater purging was discontinued when the physical parameters ' appeared to stabilize in the purged groundwater. ' The groundwater sample from monitoring well MW-5P was collected following purging 39- gallons from the well. This well has gravel in it from its construction. All efforts to remove the sediment have failed. During this gauging event the total depth of the well was 77-feet below ' ground surface (bgs). This well was completed to 88-feet bgs. However, since construction in January of 1998 this well has contained pea gravel to 60-feet bgs. ' 2.3 Groundwater Sampling Prior to sampling, the wells were allowed to recharge to a minimum of 80% of their initial static ' water levels. Groundwater samples were collected from MW-1P through MW-6P, MW-1 and MW-2 using new disposable bailers. The samples were placed into the appropriate laboratory prepared containers, using proper sample handling and chain-of-custody(COC) protocol issued ' by the USEPA. The samples were labeled with the date, time, identifying well number, then stored in a cooler at 4' Centigrade or less, and transported to a California State certified laboratory under completed COC documentation. 2.4 Groundwater Analyses ' Groundwater samples were analyzed for TPH G, BTEX, 1,2-DCA, and the oxygenated fuel additives MTBE, DIPE, TAME, ETBE, and TBA using EPA Methods 8015M, 8020 and 826013, ' respectively. The analyses were conducted by Sierra Laboratories (Sierra), a California State certified laboratory, in accordance with state guidelines and EPA protocol. 3.0 SUMMARY AND CONCLUSIONS The following sections discuss findings from the groundwater gauging and sampling activities conducted on April 30, 2001. 31 Groundwater Flow and Gradient ' Groundwater data collected at the site indicates that depths to groundwater ranged from 50.92- feet below ground surface (bgs) in MW-5P to 56.42-feet bgs in MW-6P. The groundwater ' elevations ranged from-29.79-feet below mean sea level(MSL)in MW-1 to -30.73-feet MSL in MW-1P. Groundwater elevation measurements indicate groundwater was flowing to the east at a hydraulic gradient of approximately 0.001-feet/feet. ' 2