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4\ G 1 • Introduction and Background Underground storage tanks were removed from the site in the past Wright Environmental Services, Inc (Wright) has installed three groundwater monitoring wells and initiated a quarterly groundwater monitoring program in 1994 A Problem Assessment Report was prepared by Wright in May, 1996 The results of the May, 1996 study showed that a plume of highly degraded petroleum hydrocarbon fuel contaminants were present on the north side of the M and M site and had migrated about 50 feet under 10th Street Since groundwater contamination was present in monitoring well MW-1, 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 Two 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 Nos SR#013175 and 013728) One borehole was converted to a groundwater monitoring well The boreholes were drilled with truck mounted hollowstem auger drilling equipment All drilling equipment and sampling tools were cleaned prior to arriving, 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 or aluminum foil and plastic endcaps, labeled, logged onto chain-of-custody forms and placed in a chilled ice chest The boreholes 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 borehole on the north side of the street was converted to a monitoring well Monitoring Well Installation One monitoring well was installed (see Figure 1) The well was 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 2/12 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 conditions lithologic and groundwater conditions encountered in the borehole during drilling and by direction of the PHS-EHD representative in the field Once the aquifer strata was defined, the casing was lowered to the bottom of the borehole,