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THIRD QUARTER,1998 GROUNDWATER MONITORING REPORT USA STATION 965-LODI AUGUST,1998 To reduce the potential for cross-contamination between wells, all purging and sampling equipment was washed in a trisodium.phosphate solution and rinsed in potable water prior-to each use. Groundwater purged from the wells was placed into Department of Transportation (DOT) approved 55-gallon drums and stored on-site prior to disposal by USA. During the groundwater purging operations, physical parameters such as pH, temperature and conductivity were monitored and recorded on field data sheets. Groundwater purging was discontinued when the physical parameters indicated above stabilized in the purged groundwater. 4.3 Groundwater Sampling Prior to sampling, the wells were allowed to recharge to a minimum of 80 percent of their initial static water levels. Groundwater samples were then collected from each well using a new disposable bailer. The samples were placed into the appropriate laboratory prepared containers, using proper sample handling and chain-of-custody (COC) protocol established under applicable _ SW-846 procedures issued by the USEPA. The samples were labeled with the date, time, identifying well number, stored in a cooler at 4° Centigrade or less, and transported to a state certified laboratory under completed COC documentation. 4.4 Groundwater Analyses . Groundwater samples were analyzed for TPH G, BTEX and MTBE using EPA Methods 8015 Modified and 8020, respectively. The analyses were conducted by Sierra Laboratories, Inc. (Sierra), a California State certified laboratory in accordance with state guidelines and EPA protocol. 3 5.0 SUMMARY AND CONCLUSIONS The following sections discuss findings from the groundwater gauging and sampling activities conducted on July 29, 1998. 5.1 Groundwater Flow and Gradient Groundwater data collected at the site on July 29, 1998 indicate that the depths to groundwater ranged from 3 9.10 to 41.26-feet bgs. The groundwater elevations ranged from 2.11 to 3.38'-feet ~' below MSL. Groundwater elevations have decreased since the second quarter monitoring event. The direction of groundwater flow has been calculated to be to the south southeast with an average-hydraulic gradient of approximately 0.003-feetlfeet across-the site. Historic field data suggests that the groundwater generally flows southerly, with minor fluctuations to the east and/or west, as shown on Figures 4 and 5. 4