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Work Plan For Additional Groundwater Assessment 3 Ranch Market.23569 South Santa Fe Road,Riverbank,California May 10 2001 In July 2000, SECOR oversaw the drilling of four GeoprobeTM 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, MWA 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 (SVE/AS) 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 SVE/AS feasibility test was 102 pound and 1.9 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 setting 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. Domestic Wells Four domestic water supply wells are located within 340 feet of the former tank pit (Figure 2). Well# Location from Tank Pit Comments DW-1 90 feet west of tank pit Onsite well DW-2 120 feet south of tank pit Down gradient of tank pit (Well destroyed January 11, 2001) DW-3 245 feet south of tank pit Down gradient of tank pit DW-4 340 feet south of tank pit Down gradient of tank pit DW-21Z 200 feet south of tank pit Down gradient of tank pit (Well installed December 21, 2000, through January 8, 2001) File:Ranch MarkeAWorkPlan\Rb-CPT Workplan.doc