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Ms.Vicki McCartney,SJCEHD August 29,2008 Work Plan for Bench-Scale Test and Injection Well Installation Project No.2046-3250-01 Parkinson's I-5 ARCO Service Station,Stockton,California Page 3 �4y one deep exploratory soil boring (SB-Deep) was advanced ad" nt to well MW-1 to evaluate the ,jAvertical extent of methyl tert-butyl ether(MTBE) in soil and groundwater. r�.►ti In June 2002, IT completed a 5-day dual phase extraction (DPE) feasibility test using well MW-1 During the test, IT estimated that approximately 23 pounds of hydrocarbons,predominately in the vapor phase, were removed from the subsurface via DPE. Results of the DPE test were documented in Shaw's Assessment and Interim Remedial Report, dated November 8, 2002. This report concluded that DPE was a viable remedial alternative for mitigating residual and dissolved phase impact, and controlling migration of hydrocarbons dissolved in groundwater. In September 2003, Shaw oversaw the advancement of four cone penetrometer test (CPT) borings (CPT-1 through CPT-4) and subsequent grab groundwater sampling. The CPT borings were each advanced to a depth of approximately 90 feet bgs. In an adjacent boring, four depth-discrete grab groundwater samples were collected at various depths. Based on the findings of this investigation, Shaw concluded that the majority of the petroleum hydrocarbon and MTBE impact to groundwater was situated in the upper 30 feet of the subsurface. In October 2004, Shaw submitted a Corrective Action Plan, dated October 26, 2004. Although DPE and monitored natural attenuation were both evaluated for cost-effectiveness and implementability, the CAP recommended in-situ groundwater remediation using 03 injection. In a letter dated May 27, 2005, SJCEHD concurred with Shaw's recommendation to install an 03 microsparge system, but caveated their concurrence with the statement that before implementation, the Regional Water Quality Control Board, Central Valley Region (RWQCB-CV) must approve the proposed 03 injection. Also in this letter, SJCEHD requested the installation of one discretely screened deep monitoring well. In July 2006, Stratus installed one off-site deeper groundwater monitoring well (MW-6) screened from approximately 57.5 to 62.5 feet bgs using hollow-stem auger equipment and permanent steel conductor casing. Results of this investigation were documented in Stratus' Well Installation Report, dated September 5, 2006. GEOLOGY AND HYDROGEOLOGY Subsurface conditions beneath the site and site vicinity have been explored by the advancement and sampling of twelve soil borings (GP-1 through GP-5, MW-1 through MW-6, and SB-Deep) and four CPT borings (CPT-1 through CPT-4) to depths of up to 90 feet bgs. Selected intervals of boring SB-Deep (30 to 54 feet bgs)and MW-6 (45 to 64 feet bgs) were also continuously cored and logged. From the ground surface to depths of approximately 5 to 8 feet bgs, predominantly fine-grained soils (CL, CH, and ML) have been encountered. Beneath this uppermost fine-grained horizon, predominately sandy soils (SP, SM, SW, and minor ML) have been encountered to depths of K:\Parkinsons Hammer I-5 Arco\Work Plans\Work Plan for Ozone Bench Scale Test.doc