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KLEINFELDER 1 EXECUTIVE SUMMARY Kleinfelder conducted a soil assessment at the Canlis Building at 24 S. Hunter Street in Stockton, California to assess the potential presence of petroleum hydrocarbons in the vicinity of an underground fuel storage tank. A 20,000-gallon diesel tank, which is no longer used and — is presently empty, is located at the site. The tank is located within 5 feet of the building and the S. Hunter Street sidewalk and roadway. Due to the tank's size and proximity to the street and building, San Joaquin County General Services intends to abandon the tank in place. Prior to approving an in-place tank closure, the San Joaquin County Public Health Services, Environmental Health Division (SJCEHD) requested that the San Joaquin County Purchasing Division assess the soil beneath the tank for the presence of petroleum hydrocarbons. San Joaquin County General Services retained Kleinfelder to conduct the soil assessment. After SJCEHD comments and revisions to the assessment work plan, Kleinfelder proceeded accordingly. _ Five soil borings were advanced in the vicinity of the tank. One soil boring was drilled at a 45 degree angle to obtain a soil sample from beneath the tank bottom. The remaining four soil borings were drilled vertically around the tank. Soil samples were screened in the field with an organic vapor detector. There were no readings in the first five borings; however, organic vapor readings were observed in three of the samples from boring B-5. Nine soil samples were submitted for chemical analysis. Petroleum hydrocarbons were not _ detected in the first four borings (B-1 through B-4). Total petroleum hydrocarbons (TPH) as gasoline (97 and 35 mg/kg) and TPH as diesel (740 and 690 mg/kg) were detected in the two samples collected from boring B-5 at approximate depths of 20.5 and 25.5 feet, respectively. Petroleum hydrocarbons have impacted the soil near the southwest corner of the tank. The source of the petroleum hydrocarbons has not been confirmed; however, operation of the diesel tank appears to be the source. The TPH concentrations decreased slightly with depth, but the lateral and vertical extent of petroleum hydrocarbon migration near the southwest corner of the tank has not been assessed. FR8-92-211 Page 1 of 8 24-220191-A00 Copyright 1992 Kleinfelder, Inc.