SITE INFORMATION AND CORRESPONDENCE

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Mr. Philip Isorena Proposal P93-040.31 July 12, 1993 Page 6 flexibility in determining vertical extent if C-zone impacts are discovered. Stratigraphic data on the extent of D-zone sands from the CPT will permit HydroPunch sampling of D-zone sands as part of the phase II program. Cone penetrometer testing will be conducted at a minimum of eight locations across the site to further define stratigraphy into the top of the D-water-bearing zone (depths of approximately 75 to 100 feet below ground surface). These depths were determined based on soil boring and CPT data from previous environmental assessments conducted at the ARCO terminal. This depth interval will provide stratigraphic data on the base of the B-zone, the thickness of the B/C aquitard, the C-zone, and the upper D-zone. A resistivity cone will be used with the CPT data to evaluate the degree of hydraulic connection between the various water-bearing zones. Figure 1 shows the proposed locations for the CPTs. Decontamination procedures and data gathering methods will be consistent with the procedures used during the interim pollution assessment. A description of the equipment and procedures is included in the IPAR. CPT borings will be grouted to ground surface using either a bentonite cement grout or a bentonite grout tremied from the base of the boring to the ground surface. Task 6. Field Screening Program Groundwater samples will be collected at selected locations to evaluate petroleum hydrocarbon concentrations within the B- and C-zones (and D-zone if required). B-zone samples are proposed for 13 locations, and C-zone samples are proposed for 16 locations (see Figure 1). The sample intervals will be determined following evaluation of existing and new CPT profiles, with sample locations adjacent to CPT locations. The HydroPunch 11 will be driven to the target interval using the CPT rig. The advantage of the HydroPunch II is that a larger sample volume may be collected by lowering a bailer through the center of the CPT rods to the sampling chamber than can be obtained by sampling with the BAT system. The larger sample volumes are required for total petroleum hydrocarbons as diesel (TPHD) analysis. EMCON proposes to collect multiple water samples from the same boring by advancing the sampler to the upper sample interval, collecting the sample, and removing the sampler for decontamination. Following decontamination of the sampler and rods, the sampler will be lowered into the existing boring and advanced to the lower sample interval. SAC/PR"93\P9304031.bc-93 lmc:5