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' ¢ola ualTeck�treslxc Page 2 G g Groundwater Monitoring Report Project No 770 2 June 15,2004 ' April and May 2003 sounding events and GTI's monitoring efforts confirm that groundwater direction vanes from month to month at the site There are numerous ' agricultural, commercial and residential wells near the Marci parcel and the influences from these wells are the probable cause for the groundwater direction fluctuations Geological Technics Inc submitted our September 17, 2003 "Soil Vapor Extraction Pilot Test" work plan to address the residual soil contamination at the site The San Joaquin County Environmental Health Department has expressed some concerns regarding the proposed test and GTI is preparing a response to their concerns ' 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 vaned greatly in the past On January 22, 2004, the water table well groundwater elevation averaged—40 95 feet mean sea level (MSL) or—65 feet below grade surface (bgs) For the February 26, 2004 event, the water table well groundwater elevation increased to an average of—40 41 feet MSL On March 15, 2004 the average depth to groundwater in the water table wells increased again to approximately 63 feet bgs and elevation averaged —39 45 feet MSL A net increase of 2 61 ' feet in groundwater elevation was recorded between the December 2003 and March 2004 sounding events ' Groundwater gradient calculations indicate that the flow in the water table wells was S54°E with a slope of 0 002 ft/ft on January 22, 2004 On February 26 the water table well ' gradient was S55°E with a slope of 0 002 ft/ft, and on March 15, 2004 it was S37E with a slope of 0 002 ft/ft ' The groundwater gradient in the deeper aquifer monitored by wells MW-104, 105 & 106 was'also calc lated for the three sounding events On January 2004, the geeper aquiferm G� gradient was!9 88°E with a slope of 0 0012 ft/ft, on February 26 it was N86'R with a slope ' of 0 0015 ft/ft, and on March 15, 2004 it was S89°E with a slope of 0 0018 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 January, February and March 2004 events, respectively Wells MW-4 and MW-5 are excluded from the contouring due to anomalous values that contorts the contours in the central portion of 1