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"6014"'T"hma!nc Page 2 Groundwater Monitormg Report Project No 770 2 November 19,2003 Geological Technics Inc has submitted a work plan to San Joaquin CountyEHD to perform a soil vapor extraction pilot test This pilot test will utilize higher vacuum pressures than ' used with standard SVE (up to 26 inch Hg vacuum) This work will start pending approval from San Joaquin County EHD and the USTCFP 1.0 GROUNDWATER MONITORING 1.1 Hydrogeology of Site ' The site exhibits a primarily silty/clayey geology with minor sand layers/lenses, pebbles, black organics and iron staining occasionally present The groundwater monitoring schedule was modified to include monthly depth to groundwater measurements in 2002 This was necessary to better define the gradients that have varied greatly in the past The water table well groundwater elevation on July 22, 2003 averaged —40 60 feet mean sea ' level (MSL) or —64 feet below grade surface (bgs) For the August 20 event, the water table well groundwater elevation decreased to an average of—40 97 feet MSL or —64 5 feet bgs On September 18, 2003 the average depth to groundwater in the water table wells was again approximately 65 5 feet legs and elevation averaged —41 84 feet MSL The third quarter 2003 experienced three consecutive monthly declines in groundwater elevation A net ' decrease of 3 69 feet in groundwater elevation was recorded between the April and September 2003 sounding events ' Groundwater gradient calculations indicate that on July 22, 2003 the water table well gradient was S33°E with a slope of 0 002 ft/ft On August 20, 2003 the water table well gradient was S36°E with a slope of 0 002 ft/ft, and on September 18, 2003 it was S36°E with ' a slope of 0 002 ft/ft The data are very consistent for this quarter The groundwater gradient in the deeper aquifer monitored by wells MW-104, 105 & 106 ' was calculated for two of the three sounding events in the third quarter 2003 On July 22, 2003 the deeper aquifer gradient was N78°E with a slope of 0 0011 ft/ft On August 20, 2003 a gradient was not calculated because a vehicle was parked over well MW-105 and it ' was inaccessible On September 18 the deeper aquifer gradient was S86°E with a slope of 0 0014 ft/ft ' Groundwater elevation and gradient data are summarized in Tables 1 and 2, Appendix A Water table well gradient directions are shown on Figure 2A, 3A & 4A for the July, August and September 2003 events, respectively Wells MW-4 and MW-5 are excluded from the contouring due to anomalous values that contort the contours in the central portion of the site The deep well gradient directions for the same events are illustrated in Figures 213, 3B and 4B, respectively