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(V:ATc &A, A S S O C I A T E S I N C �I `- Summary Report of Additional Subsurface Investigation Former Continental Grain Facility 1805 Harbor Street Stockton, California �•• ATC Project No. 54.62500.0001 V 1.0 INTRODUCTION ATC Associates Inc. has prepared this letter report, on behalf of Conti Group to summarize findings of the additional subsurface investigation performed at the above referenced site (Figure 1). The purpose of the subsurface investigation was to attempt to determine the lateral and �" vertical extent of impacted groundwater at the site. This work was done at the request of San . Joaquin County Public Health Services Environmental Health Division (PHS/EHD) in correspondence dated April 23, 1999. The findings of the subsurface investigative study are summarized in the following paragraphs. 1.1 Site Location The site is located on the north side of Harbor Street and south of the Deep Water Channel in �. Stockton, California, as shown on Figure 1. The location is an industrial and residential area and the site is currently occupied by Penny-Newman Grain Company. +• 1_2 Background ' In January 1988, two 12,000-gallon diesel underground storage tanks (USTs), one 10,000-gallon I` gasoline UST, one 750-gallon UST, and all associated piping were removed from the site. The location of the 10,000-gallon UST is shown on Figure 2. One soil sample was collected from beneath the 750-gallon UST and one soil sample was collected from each end of the 12,000- gallon and the 10,000-gallon USTs. Analytical testing indicated the samples collected from beneath the 10,000-gallon and 750-gallon gasoline USTs contained detectable concentrations of .L. petroleum hydrocarbon constituents. The excavations were subsequently backfilled. e In October 1997, an ATC geologist supervised the advancement of one soil boring to 31 feet L„ below ground surface (bgs), one soil boring to 26 feet bgs, and five soil borings to 20 feet bgs. Soil borings SB 1 through S136 were placed in the vicinity of the former 10,000-gallon UST and soil boring S137 was placed in the vicinity of the former 750-gallon UST. A site plan with soil F LM boring locations SB I through SB6 is shown on Figure 2. The borings were advanced using a t truck mounted Geoprobe® narrow diameter rig employing direct push technology. Soil and grab w:154.625001reportslsumiR.doc 1 a..