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1 Ge010gecal7'eckauslac Page 2 ' Groundwater Monitoring Report Project No 770 2 July 7,2005 numerous agricultural, commercial and residential wells near the MarcyP arcel and the influences from these wells are the probable cause for the groundwater direction fluctuations ' In our March 3, 2005 work plan and subsequent addenda GTI has proposed conducting additional site investigation using Cone Penetrometer Testing (CPT) technology The San 1 Joaquin County Environmental Health Department (SJC/EHD) has approved the work plan and the data will used to update the site conceptual model (SCM) ' 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 February 25, 2005, the water table well groundwater elevation averaged -40 22 feet mean sea level (MSL) For the June 13, 2005, monitoring event the water table well groundwater elevation averaged —39 81 feet MSL A net increase of 0 41 feet was recorded between the February 2005 and June 2005 sounding events Groundwater gradient calculations indicate that the flow in the water table wells was S62°E with a slope of 0 008 ft/ft on June 13, 2005 while the deeper aquifer gradient was N89°E with a slope of 0 001 ft/ft Groundwater elevation and gradient data are summarized in Tables 1 and 2, Appendix A ' The water table and sleep well gradient directions are shown in Figures 2 and 3, respectively, for the June 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 ' fourteen 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 ' Vertical Groundwater Gradients Under vertical groundwater flow conditions, the water level in a monitoring well is a function of the length of the well screen and its depth or vertical position in the aquifer As with horizontal flow conditions, the diameter of the well or piezometer is immaterial The following procedure is used to calculate vertical groundwater gradient