ARCHIVED REPORTS_XR0003866 - Laserfiche WebLink

Home Browse Search

Q010gkofT¢c{uucslxc Page 2 Groundwater Monitonng Report Project No 770 2 November 9, 2005 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 ' 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 Joaquin Count' Environmental Health Department (SJC/EHD) approved the work plan and the data willed to update the site conceptual model (SCM) The work was performed in October — November 2005 and a report will be submitted pending receipt and analysis of laboratory results from soil and groundwater samples 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 for a period 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 August 25, 2005, the water table well groundwater elevation averaged -42 81 feet mean sea level (MSL) This represents a net decrease of 3 feet since the June 2005 sounding events Groundwater gradient calculations indicate that the flow in the water table wells was S 15°E with a slope of 0 003 ft/ft on August 25, 2005 while the deeper aquifer gradient was ' S85°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 August 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 has been consistently to the east 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 an easterly direction 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