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ti.. 1.0 INTRODUCTION This site investigation was completed at the request of Mr. Craig Ogata, Director of Facilities Management, for the County of San Joaquin under Purchase Order No. 148-440580-1. The scope of work was approved and supervised by Mr. Michael Infurna, Senior R.E.H.S. of the San Joaquin County Public Health Services Environmental Health Division (PHSIEHD). r Lr 1.1 Site Description �. The Canlis Building site is located at 24 South Hunter Street in the city of Stockton (San Joaquin County), California (Figure 1). The property is an active county government administration building. One, 10,000-gallon capacity, underground diesel fuel storage tank (UST) existed in the northwest section of the site (Figure 2). The former UST was located in a landscaped area an filled using a remote fill to the west of the UST (Figure 2). The site is flat and at an elevation of 4. approximately 15 feet above mean sea level. 1.2 Previous Work On November 6, 1992, Kleinfelder completed five soil borings including one angle boring to *AM assess subsurface soil conditions in the vicinity of the UST. Soil samples from one of the soil borings (13-5), located beneath the southwest corner of the UST, were Impacted by petroleum hydrocarbons. The soil sampled at the bottom depth (25.5 feet bgs)from soil boring (B-5) �. contained 690 parts per million (ppm) of Total Petroleum Hydrocarbons (TPH)-as-diesel, 35 ppm of TPH-as-gasoline and 0.008 ppm of benzene. The sample collected at 20 feet bgs from B-5 contained 740 ppm of TPH-as-diesel and 97 ppm of TPH-as-gasoline. Petroleum hydrocarbons were not detected in any of the soil samples collected from the four other borings. Results of the soil sample analyses are summarized in Table 1. Kleinfelder logged the soil as interbedded sand, silty sand and silt to a maximum drilling depth of .L . 25.5 feet below ground surface (bgs). This soil stratigraphy is characteristic of delta channel and flood plain depositional environments. Kleinfelder did not encounter groundwater at their maximum drilling depth of 25.5 feet bgs. In 1996, Fisch Environmental Construction Services of Lodi, Califomia removed the UST. During the removal of the UST system, a soil sample (P-1), collected ata depth of 1.5 to 2.0 feet bgs from the vicinity of the remote fill, contained 1,100 ppm of TPH-as-diesel. 4