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Ms.Margaret Lagorio, SJCEHD October 21,2003 Joe's Truck Plaza Project No.2033-15600-01 Work Plan for Additional Site Assessment Page 5 • Evaluate the lateral extent of the base of the hard clay stratum, the lateral extent and thickness of the lower sandy zone, the hydraulic flow regime within the lower sandy zone, and the extent of impact within the lower sandy zone by installing wells DW-1 though DW-7 and boring B-26, • Assess the feasibility of utilizing GWE and DPE to remediate residual and dissolved hydrocarbon mass from the source area (surrounding the northern UST's) by installing and then extracting from well EX-1, and utilizing wells MW-1, MW-2, MW-3, MW-7, MW-8, MW-18, and DW-2 as observation wells during testing, and • Initiate interim remedial activities by installing ozone sparge wells (IW-1 through IW-15), and utilizing wells MW-7 through MW-12 and MW-18 to monitor changes in MTBE concentrations and aquifer chemistry related to ozone sparging. Rationale The lateral extent of the MTBE plume in the upper sandy zone has not been completely characterized to the east and northeast. Concentrations up to 550 gg/L have been reported in well MW-3, up to 40 gg/L in well MWO-2, and up to 6.5 gg/L in well MW-4. Proposed wells MW-14 through MW-17 will be installed to approximately 15 feet bgs (to the base of the upper sandy zone) to provide additional characterization of the dissolved plume to the east and northeast. Dissolved MTBE is reported in well MWO-2, but not in well MWO-1. However, there is approximately 280 feet between these wells. Proposed well MW-13 will further constrain the northern extent of the dissolved plume in the upper sandy zone. Additional characterization of dissolved mass between the subject site and off-site wells MWO-1 through MWO-3 is necessary. Proposed wells MW-9 through MW-12 will provide the monitoring points necessary to further constrain the dissolved MTBE plume, and better estimate the dissolved MTBE mass off-site. Proposed wells MW-7, MW-8, and MW-18 will provide additional monitoring points to further constrain the lateral extent of the dissolved mass beneath the subject site. Proposed wells MW-7 through MW-13 and MW-18 will also be installed to approximately 15 feet bgs (to the base of the upper sandy zone). As discussed in the SCM, the base of the hard clay, and the thickness and lateral extent of the lower sandy zone have not been characterized. Proposed wells DW-1 through DW-7 and proposed boring B-26 will be advanced to approximately 28 feet bgs (the base of the lower sandy zone as logged in boring MWO-1X. 'Lithologic observations from these borings will be used to assess the lateral extent of the base of the hard clay stratum, and the lateral extent and thickness of the lower sandy zone. Wells DW-1 through DW-7 will be screened wholly within the lower sandy zone. Monitoring and sampling data from these deeper-screened wells will make it possible to evaluate if groundwater in the lower PAJoe's Truck Plaza\Work Plans\Joes workplan 102103.doc