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I 2 .3 Previous Work ' On January 4 , 1988 , a 550-gallon underground storage tank was removed from the site by RAMCON, Inc. of West Sacramento. The tank stored gasoline and was used to fuel vehicles for the former tenants, a plumbing company and a sheet metal company. ' After the tank was removed, RAMCON collected soil samples from a depth of approximately 17 feet. Total petroleum hydrocarbons (TPH ' as gasoline) and volatile aromatics (BTE&X) were detected in soil samples. Investigation of the contamination associated with the UST was then ' continued with the drilling of two soil borings (B-1 and B-2) on July 7 , 1988 . The soil borings were installed by Applied GeoSystems of Sacramento. B-1 was advanced to a depth of 30 feet, and B-2 was ' advanced to a depth of 80 feet. Contamination was detected, and B-2 was completed as monitoring well MW-1 . Benzene and TPH as gasoline were detected in a water sample from this well. However, during the ' following two years, MW-1 , with a total depth of approximately 80 feet, went dry and could no longer be sampled. GeoAudit was subsequently retained by Marlowe Properties to install a replacement well for MW-1 . After consultation with Ms. Mary Meays of EHD regarding the optimal location, MW-2 was installed on December 21, 1992 southwest of the former tank excavation, ' approximately 35 feet from MW-1 (Figure 2) . No soil contamination was detected in this well, but halogenated hydrocarbons and benzene were detected in the water sample from this well in January 1993 . The well was sampled again in April of 1993 and slight increases in contaminant concentrations were reported. Based on these results, further groundwater assessment, in the form of at least two additional monitoring wells, was required by PHS/EHD. 3. 0 PROCEDURES 3 . 1 Drilling and soil Sampling Two additional monitoring wells (MW-3 and MW-4) were installed at the site on September 29 and 30 , 1993 . The locations of MW--3 and MW-4 are illustrated on Figure 2 . MW-3 was drilled to a depth of 100 feet; MW-4 was drilled to a depth of 105 feet. The monitoring wells were drilled using a CME-75 truck-mounted drill rig. The CME- 75 and two man crew were supplied by West HazMat Drilling of Rancho Cordova. Discrete soil samples were collected at five-foot intervals using a 140--1b hammer to advance a split-spoon sampler loaded with three 2-inch by 6-inch brass sleeves. The number of blows required to advance the sampler 18 .inches was recorded on the boring log (see Appendix A) . To avoid cross contamination, the sampling equipment 4