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Site No: 17 792 4. Supplemental Site Assessment Work EMCON measured PID headspace readings beneath each gasoline dispenser on July 11, 1994. Volatile organic vapors were detected under five of the six dispensers. The PID readings ranged from 1.1 ppm at the southernmost of the northern pump islands to 28.3 ppm at the northernmost of the southern pump islands. On November 9 and 10, 1994, EMCON conducted supplemental assessment activities at the site. Four exploratory soil borings (THP-1 through THP-4) were advanced using CPT drilling methods. The location of the four soil borings is shown in Figure A-1. The borings were advanced to depths of approximately 26 to 36 feet bgs. Soil types logged during drilling included silty clay, sandy clay, and sand to the total depths explored. Groundwater was not encountered in borings THP-1 and THP-2. No product odor was noted on the drilling logs (labeled HP-1 through HP-4; Attachment D). PID readings were obtained every 5 feet, if possible. The highest PID reading was 4.6 ppm at 25 feet bgs in boring THP-4. Two soil samples were collected and submitted for laboratory analysis from each boring for BTEX, TPH-G, TPH-D, and TPH-O. The deepest sample from each boring was also analyzed for a-IVOCs (EPA Method 8010). bone of the constituents analysed for was detected in the soil samples (Table A-1). A groundwater sample was collected from borings THP-3 and THP-4 by using HydroPunch'f equipment. They were submitted for laboratory analysis of the same list of parameters as the soil samples. THP-0 (2,200 ppb) and toluene (0.7 ppb) were detected in the groundwater sample collected from HydroPunch boring THP-3 (Table A-1). TPH-O (1,400 ppb) and 1,2-DCA (4.2 ppb) were detected in the groundwater sample collected from HydroPunch boring THP-4. A copy of the laboratory report is included in Attachment D. 5. Baseline Summary A review of the most recent relevant data available in existing files, observations made during site visits, and data collected during the environmental investigation performed in accordance with the BP/Tosco purchase agreement have determined the presence of hazardous substance contamination in the soil and groundwater at this site. Such review has further determined evidence of contamination and sources of contamination which could result in the presence of hazardous substance contamination not yet detected. B/TOS/RPT/11192R".d07-94/LAM/Ib:5 Rev.0, 12127!94 0952-090.03 6