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Ciealogfcal7eckrcicslnc Page 2 ' Groundwater Monitoring Report Project No 770 2 . Apn125,2005 groundwater direction for the April and May 2003 sounding events and GU's monitoring efforts confirm that groundwater direction varies 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 ' A site conceptual model (SCM) report dated August 23, 2004 was submitted to San Joaquin County Public Health Services/Environmental Health Divisions (SJC PHS/BHD) for approval The SCM included recommendations for performing a Cone Penetrometer Testing (CPT) investigation to address data gaps GTI submitted our March 3, 2005 "Additional Site Characterization Work Plan" to perform the proposed CPT investigation SJC PHS/EHD responded in a March 14, 2005 letter that required additional information A work plan ' (addendum) is being prepared to address the County correspondence in regards to work plan ' 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 On December 09, 2004, the water table well groundwater elevation averaged -42 80 feet mean sea level (MSL) For the February 25, 2005, event the water table well groundwater ' elevation averaged —40 22 feet MSL A net increase of 2 58 feet MSL was recorded between the December 2004 and February 2005 sounding events Groundwater gradient calculations indicate that the flow in the water table wells was S33°E with a slope of 0 006 ft/ft on ' February 25, 2005 while the deeper aquifer gradient was S89'E with a slope of 0 002 ft/ft Groundwater elevation and gradient data are summarized in Tables 1 and 2, Appendix A The water table and deep well gradient directions are shown in Figures 2 and 3, respectively, for the February 2005 event ' The historical water table gradients are illustrated in Figure 4 & 5 Groundwater Gradient Rose Diagrams for Water Table and Deep Wells, respectively The site's shallow aquifer displays highly variable shifts in groundwater direction It is noted that groundwater direction has been predominantly to the southeast since additional wells were installed in May 2002 The deeper aquifer flow had been consistently to the east for the previous seven sounding events But on April 28 and May 23, 2003, the gradient reversed 180° from an easterly direction to a westerly direction The direction reversed again to the east for the remainder of the sounding events