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L `"s' `r 1.0 INTRODUCTION This Work Plan has been prepared 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 proposed scope of work includes environmental site investigation tasks, as reviewed with Mr. Michael Infurna, Senior R.E.H.S. of the San Joaquin County Public Health Services Environmental Health Division (PHS/EHD). 1.1 Site and Subsurface 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 and filled using a remote fill to the west of the UST (Figure 2). The site is flat and at an elevation of approximately 15 feet above mean sea level. During a 46- previous subsurface investigation, a Kleinfelder, Inc. (Kleinfelder) geologist logged the soil as interbedded sand, silty sand and silt to a maximum drilling depth of 25.5 feet below ground surface (bgs). This soil stratigraphy is characteristic of delta channel and flood plain depositional environments. Kleinfelder did not encounter free groundwater at their maximum drilling depth of 25.5 feet bgs. As evidenced in wells from nearby sites, first groundwater at the subject site is likely present at approximately 40 feet bgs. 1.2 Previous Work On November 6, 1992, Kleinfelder completed five soil borings including one angle boring to assess subsurface soil conditions in the vicinity of the UST. Soil samples from one of the soil borings (B-5), located beneath the southwest corner of the UST, were found to be 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. In 1996, Fisch Environmental Construction Services of Lodi, California removed the UST. During the removal of the UST system, a soil sample (P-1), collected at a depth of 1.5 to 2.0 feet bgs from the vicinity of the remote fill, contained 1,100 ppm of TPH-as-diesel. 2 r v