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S l� • Introduction and Background Underground storage tanks were removed from the Mr Ed's site in the past Previous investigators have installed three groundwater monitoring wells and initiated a quarterly groundwater monitoring program Contaminants had moved along the capillary fringe and dissolved in groundwater to the north An investigation and Problem Assessment Report were prepared by Wright Environmental Services, Inc (Wright) in July, I996 The results of the July, 1996 capillary fringe sampling study showed that a plume of degraded petroleum hydrocarbon fuel contaminants were present on the east side of the Mr Ed's site and had migrated about 300 feet north and Just slightly onto Tracy High School property Since groundwater contamination was present, additional subsurface investigation was required by the County of San Joaquin County Public Health Services Environmental Health Division(PHS-EDH), which is presented in this report Field Activities and Methods Exploratory Borings Six exploratory borings were drilled at the locations shown on Figure 1 Drilling and well installation permits were secured from PHS-EHD prior to doing the field work (Permit No SR#013081) All boreholes were converted to groundwater monitoring wells The boreholes were drilled with truck mounted hollowstern auger drilling equipment All drilling equipment and sampling tools were cleaned prior to amvmg, and before leaving the site The augers were advanced to the desired sampling depth interval, and a drive split spoon sampler was driven ahead of the drill bit The sampler was then retrieved and dissembled, and the soil filled brass liner was sealed with Teflon paper and plastic endcaps, labeled, logged onto cham-of-custody forms and place in a chilled ice chest . The borehoics were logged using the Unified Soil Classification System under the supervision of a registered geologist Additional lithologic information was collected to describe the subsurface geology The samples were collected at five-foot intervals, at intervals of obvious contamination and at stratigraphic features of interest Upon completion of the borehole drilling and collection of information, the boreholes were converted to monitoring wells Monitoring Well Installation Six monitoring wells were installed, five on-site and one off-site on Tracy High School property (see Figure 1) The wells were cased with Sch 40 PVC casing, threaded together, glues were not used The slotted interval was a 0 020 inch slot and the annular space around the slots were backfilled with a 2112 size sand Previous experience has shown this to be a reliable well design in fine grained and stratified depositional environments Final well design was modified to the site specific lithologic and groundwater conditions encountered in the borehole during drilling Once the aquifer strata was defined, the casing was lowered to the bottom of the borehole, leaving a portion of slotted interval and sand pack above the occurrence of groundwater to observe for floating product The sand pack was placed to a point about one to two feet above the slots A bentonite seal was placed atop the sand pack, and a cement grout seal placed atop the bentonite using a tremie line, filling from the bottom to top of the annular space A traffic rated well head access box and security device completed each well Well Head Survey All wells were surveyed to mean sea level and tied into the existing array using a known datum This will allow accurate measurements and groundwater gradient to be calculated Monitoring Well Sampling and Develo meet All monitoring wells were developed to remove the drilling muck, grade the sand pack and provide a more complete hydraulic connection to the aquifer The well volume was calculated and a number of those volumes were removed until the water became clear and the amount of sand pumped is minimal The well was allowed to recover prior to sampling and a log of the development was kept for each well Page 3