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S [E cC0 R 7-Eleven Store #32262 Work Plan for Additional Site Assessment and Interim Remediation March 19, 2004 Page 4 Grant Line Food and Gas Site, the groundwater flow direction at the site has been to the north- northwest for ten of twelve monitoring events Distribution of Dissolved MtBE Dissolved MtBE concentrations in the former Grant Line Food and Gas, Shell, and 7-Eleven site wells were plotted to show the extent of dissolved MtBE at the three sites The 5 ug/L MtBE isoconcentration contour presented on Figure 5 extends from the source area across Grant Line Road to the north northeast Based on the presence of low to moderate concentrations of MtBE in MW-6(V) and MW-4(S), the downgradient extent of the dissolved MtBE plume has not been defined SCOPE OF WORK Additional Assessment In order to further define the lateral limits of dissolved MtBE, SECOR recommends installation of three shallow groundwater monitoring wells • MW-7 to define the western edge of the plume, • MW-8 to define the down gradient extent of the plume, and • MW-9 to define the eastern edge of the plume on the north side of Grant Line Road In addition, one onsite cone penetrometer test (CPT) boring (CPT-1), and one offsite CPT boring (CPT-2) will be advanced to define any high permeability sand beds and to allow collection of grab groundwate"amples to further define the vertical extent of the dissolved hydrocarbon plume The locations of the proposed wells and CPT borings are shown on Figure 5 Proposed depths and construction details are provided in Table 3 Feasibility Testing and Interim Remediation As part of the proposed interim remediation plan, SECOR proposes installing one groundwater extraction well (EX-1) and one oxygen injection well (S-1) that will be used to conduct a groundwater extraction pump test and an oxygen infection feasibility test If the groundwater extraction results are favorable, Interim remediation via extraction of groundwater from well EX-1 may be started The following scope of work is proposed HEALTH AND SAFETY SECOR will modify our existing site-specific Health and Safety Plan for the proposed scope of work as required by the Occupational Health and Safety Administration (OSHA) Standard "Hazardous y Waste Operations and Emergency Response" guidelines (29 CFR 1910 120) The document will be reviewed and signed by all SECOR personnel and subcontractors prior to performing work at the site PERMITTING AND UTILITY CLEARANCE SECOR will obtain soil boring and well installation permits from the SJCEHD Access agreements will be obtained from the property owner of the vacant parcel northwest of the site for the installation • of MW-8 and advancement of GPT-2 An encroachment permit will be obtained from the City of Tracy Department of Development and Engineering Services for the installation of MW-9 Prior to 32262 Offsite well install and interim remediation workplan doc SECOR International Incorporated 4