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1 In January 1993, Greyhound implemented the Supplemental Site Assessment A total of four soil borings were advanced to characterize the vertical and horizontal extent of soil contamination at the site. Soil borings were advanced to a maximum depth of 46 feet. Samples were field screened every 5 feet using a photoionization detector (PID) and for total petroleum hydrocarbons (TPH) analysis using an ' immunoassay technique. All samples tested in the field were found to have TPH concentrations less than 100 ppm A total of four soil samples were submitted for laboratory analysis. The sample from each borehole with the highest photoionization detector reading in the field was submitted to a California-certified laboratory for analysis of BTEX and TPHD. Toluene was the only BTEX compound detected in the samples Concentrations ranged from 0.7 to 3.4 µg/kg TPHD was not detected in any of the soil samples tested The Supplemental Site Assessment Report was submitted to PHS-EHD during April 1993. ' After meeting with PHS-EHD in June of 1993, Greyhound requested that PHS- EHD consider a semi-annual, rather than monthly, monitoring program. PHS-EHD approved the semi-annual monitoring and groundwater sampling program in a faxed transmission to Engmeermg-Science on July 22, 1993. On January 26, 1994, PHS-EHD provided a letter to Greyhound with comments on the December 1993 semi-annual groundwater monitoring report. In this letter, PHS- ' EHD directed Greyhound to continue semi-annual groundwater monitoring and reporting, and to further investigate the extent of soil contamination beneath the site. A work plan to address PHS-EHD's concern was submitted by Greyhound in May 1994 and approved without revision in June 1994 The field investigation was performed in August 1994 This report details the field activities and analytical results of that investigation. SITE DESCRIPTION Local Description, Surrounding Land Use, and Climate ' The Greyhound Terminal is located at 121 South Center Street in Stockton, San Joaquin County, California, near the corner of Center and Washington Streets (Figure ' 1). Land use surrounding the terminal mixed commercial and residential. The terminal is bordered on the north by Market Street, the south by a Chevron service station and Washington Street, the east by Center Street and the Chevron station, and ' the west by Commerce Street (Figure 2). The surface topography in the area is nearly flat. The climate of this area is characterized by wet, mild winters and long, dry hot summers. Rainfall occurs intermittently, concentrated between September and March. Average annual precipitation in the Stockton area has been approximately 14.1 inches over the past 30 years (NOAA, 1991). Local Geology and Hydrology The facility is located in the San Joaquin Valley portion of the Great Central Valley Geomorphic Province of California. The Stockton area is underlain by non- marine, Pleistocene and Holocene sediments of fluvial and lacustnne origins (Horns PARFSSYROIIVOLI wP1725386 08969125386R02 DOC ' 2