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Quarterly Monrtonng and Sampling Report(Q4 2001) 2 Ranch Market,23569 Santa Fe Road Riverbank,California January 3 2002 . decline in total petroleum hydrocarbon as gasoline (TPHg) concentrations from 4,140 milligrams per kilograms (mg/kg) at 20 feet bgs to 6 mg/kg at 30 feet bgs (Table 1) A grab water sample was also collected from boring B-1 that contained elevated concentrations of benzene, toluene, ethylbenzene, xylenes (BTEX), and TPHg (Table 2) In November 1998, Arrowhead Consultants oversaw the installation of four groundwater monitoring wells at the site MW-1 in the former tank pit and MW-2, MW-3, and MW-4 centered around the former tank pit (Figure 2 and Table 2) Soil samples collected during monitoring well installation contained reportable concentrations of BTEX and TPHg (Table 1) The first monitoring and sampling event conducted in December 1998 revealed all four wells contained reportable concentrations of dissolved BTEX, TPHg, and methyl-tert-butyl ether (MtBE) (Table 3) No reportable concentrations of tertiary butanol (TBA), MtBE, dilsopropyl ether (DIPE), ethyl-tert-butyl ether (EtBE), and tert-amyl-methyl ether(TAME) were detected in the water samples collected in December 1998 In July 2000, SECOR oversaw the drilling of four GeoprobeTT' soil borings (GP-1 through GP-4) and two continuous core borings (SB-1 and SB-2, Table 2) Soil samples collected from GP-2, SB-1, and SB-2 contained reportable concentrations of BTEX, MtBE, and TPHg (Table 1) In August 2000, SECOR oversaw the installation of five groundwater monitoring wells at the site MW-5, MW-6, MW-7, MW-8, and MW-9 (Table 2) Soil samples collected during . monitoring well installation did not contain reportable concentrations of BTEX, TPHg, or MtBE (Table 1) Soil samples were not collected from MW-5 or MW-7 In September 2000, SECOR oversaw the installation of six soil vapor extraction (SVE) and 1 air sparge (AS) well on or adjacent to the former tank pit at the site (Figure 3, Table 2) Soil samples collected from V-1, V-2, V-3, and AS-1 contained elevated concentrations of BTEX, TPHg, and MtBE (Table 1) Soil Vapor Extraction & Air Sparge Feasibility Testing In October 2000, SECOR conducted a two-day soil vapor extraction and air sparge (SVEIAS) feasibility test using six SVE wells and one AS well Based on the test results, the total mass of TPHg and benzene removed during the S VEIAS feasibility test was 102 pounds and 19 pounds, respectively Based on the induced vacuum response (0 2 inches of water at 40 feet) and the slight rise in groundwater levels in off see g monitoring wells, the SVE radius of influence was estimated to be 40 feet Although the air sparging did not result in an immediate increase in TPHg vapor concentrations, the increase in dissolved oxygen concentration and slight rise in the water table in offsetting wells indicates a radius of influence of approximately 30 feet Details related to the feasibility test are presented in SECOR's Problem Assessment Report, dated November 8, 2000 File Ranch Market\Report\Rrverbank-01-4Q