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Report of Secondary Investigation 1 Pre red for Barbara Drake 26485 Thornton Rd Thornton CA May 4 1995 10 INTRODUCTION This report is submitted by Groundwater Technology, Inc to summarize the methods and results of additional environmental assessment work conducted on February 16, 1995 at the former Drake property located at 26485 Thornton Road in Thornton, California (Figure 1) All work was conducted in accordance with Groundwater Technology's Work Plan for Soil Excavation/Additional Assessment, dated October 6, 1994, and the addendum to the Work Plan dated January 27, 1995 The Work Plan and addendum were approved by San Joaquin County Department of Public Health Services- Environmental Health Dmsion (SJCPHS-EHD) pnor to inflating work at the site Excavation of hydrocarbon-impacted soil was postponed at the site pending the results of the additional assessment Assessment work completed at the site included the following tasks ■ background review to determine areas of concern on site ■ a wellhead survey to determine groundwater flow direction for more beneficial placement of soiltwater sampling locations ■ preparation of a site specific Health and Safety Plan ■ procurement of access agreements with current property owner ■ permitting of soil/groundwater sampling locations with SJCPHS-EHD and County Public Works ■ soil/groundwater sampling at ten sampling locations (B1-810) ■ laboratory analysis of soil/groundwater samples for petroleum hydrocarbons ■ preparation of this report 20 SITE HISTORY The site is located on the corner of North Thornton and Walnut Grove Roads in Thornton, California (Figures 1 and 2) The site is a grass covered lot, encompassing approximately two acres with several concrete pads on the surface where former buildings were located The site was used as a small filling station and a restaurant from 1947 through 1956 Dunng this penod gasoline was distributed by two pumps located south of the concrete slab The pumps were supplied by two 1,000-gallon steel underground storage tanks(USTs) installed in 1947 located in the southern UST pit shown on Figure 2 Remodeling of the service station occurred in 1956 and included the addition of four new gas pumps, relocation of the pumps to the eastern pump island location, installation of two additional 1,000-gallon USTs in the northern UST pd location (Figure 1) and removal of the former dispensers The new dispensers were supplied by all four USTs The service station ceased operation in 1975, at which time the dispensers were removed and the USTs were emptied The USTs located in the northern UST pit 0053EAR RPT ❑❑.1 GROUNDWATER ❑❑❑ TECHNOLOGY