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Report of Investigation <br /> Former Underground Storage Tanks <br /> 3105 South El Dorado Street Stockton,Califorrua <br /> Sierra-Pacific Project No 96-620 01 <br /> ispaces in the filter pack A 2-foot thick bentorute plug,constructed of bentonite chips,hydrated in place, <br /> was set above this filter material to prevent cement grout from entering the filter pack A neat cement- <br /> grout mixture was placed into the annular space from the top of the bentonite plug to within two feet of <br /> the surface A traffic-rated flush-mount well vault was installed around the wellhead,which was set with <br /> iPortland cement concrete <br /> After construction, the well was thoroughly developed by surging and purging to remove residual <br /> drilling material (grout cement) and native silt and clay from the filter pack Approximately 3 boring <br /> ivolumes (20 well volumes) of ground water were removed during the well development process The <br /> well was then allowed to settle and equilibrate for at least 72 hours, prior to further purging and <br /> sampling All purged water was contained in DOT-approved 55-gallon drums, was properly labeled, <br /> and was temporarily stored onsite, pending laboratory analyses <br /> M <br /> i 3 4 Well Purging and Ground Water Sampling <br /> The water level in the monitoring well was measured prior to purging and sample collection on January <br /> i9, 1997, using an electronic water level indicator (see Appendix C) At least three wetted-well volumes <br /> of water were removed from the well with a PVC bailer Before sampling the well, Sierra-Pacific <br /> imonitored three parameters (pH, conductivity, and temperature) of the purged water until these <br /> parameters had stabilized, such that consecutive readings vary less than 10 percent from previous <br />' readings (Appendix B) A grab sample was also obtained from soil borings B-3 and B-4 during drilling, <br /> using a pre-cleaned disposable Teflon' bailer <br /> i <br /> 3.5 Laboratory Analyses <br /> iAs described below, soil and ground-water samples collected were submitted to Sierra-Pacific's <br /> subcontracted laboratory, ExeIchem Environmental Labs in Roseville, California, for analysis <br /> Sierra-Pacific Groundwater Consultants, Inc 7 <br />