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Crealogkal uchda I/M Page 2 Groundwater Momtonng Report Project No 770 2 November 8,2004 ' A site conceptual model (SCM) report dated August 23, 2004 was submitted to San Joaquin County Public Health Services/Environmental Health Divisions (SJC PHS/EHD) for approval Additional recommendations regarding the site will be forthcoming from GTI pending comments from the SJC PHS/EHD on the site conceptual model ' 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 8 V 1113®'0V On June 7, 2004, the water table well groundwater elevation averaged -40 P4 feet mean sea level (MSL) For the August 19, 2004, event the water table well groundwater elevation averaged —43 09 feet MSL A net decrease of 2 25 feet MSL was recorded between the June and August 2004 sounding events Groundwater gradient calculations indicate that the flow M in the water table wells was S38°E with a slope of 0 002 ft/ft on August 19, 2004 while the deeper aquifer gradient was S54°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 Figure 2 and Figure 3, respectively, for the August 2004 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 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