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"Otogtcal rahAics Inc Page 2 Groundwater Monitormg Report Project No 723 2 January 19,2004 ' monitoring report for the Shell site that indicates that a gasoline release has occurred from the facility at some point in time It is possible that a co-mingled plume exists beneath the ' site GTI recommends that interim remediation be considered before this plume migrates any ' further and the cost for cleanup continues to increase GTI's September 8, 2003 "Feasibility Study Work Plan - Dual Phase Soil Vapor and Groundwater Extraction Pilot Test" was approved by SJC PHS/EHD in their November 15, 2003 letter We are currently soliciting contractor bids in accordance with USTCFP requirements for the work ' 1.0 GROUNDWATER MONITORING ' 1.1 Hydrogeology of Site A site-specific groundwater gradient and bearing were calculated from computer-generated ' contours The groundwater was flowing N71°E at a gradient of 0 0061 ft/ft The average elevation of groundwater at the site was 27 08 feet below mean sea level This represents a decrease of 0 45 feet since the September 2003 monitoring event and a cumulative decrease of 4 35 feet since March 2003 Figure 2 is a groundwater gradient map for the November 26, 2003, event. Figure 3, Groundwater Gradient Rose Diagram, includes historical groundwater directions and gradients Table 1 in Appendix A contains the groundwater elevations and gradients for the site ' 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 A vertical gradient was calculated for well pair MW-3/MW-201 These wells are located approximately 5 feet apart The following procedure is used to calculate vertical groundwater gradient ❑ Determine vertical distance between the two measuring devices by the distance from the ' mid-point between the top and bottom seal of the deep well (MW-201) and the mid- point between the groundwater elevation and the bottom seal in the shallow well (MW- 3) ❑ Measure the head in both wells used in the calculations ❑ If the lateral distance between the well pair is greater than a few feet, then calculations must be made to correct the down-gradient piezometric head to account for the sloping