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3. OBJECTIVES AND RATIONALE The objectives of this data gaps investigation are to: • Evaluate the CSM; • Define the vertical and lateral extent of sulfolane between the Site and the water supply wells; • Define the geologic layering to the top of the Corcoran Clay; and • Collect data to evaluate remedial alternatives to protect the LWD water supply wells. The rationale for each of the proposed boring locations presented in Figure 2 is as follows: • Location 1 —Define the vertical and lateral extent of sulfolane and confirm the geologic layering to the top of the Corcoran Clay between the PSW and LWD-10. Install a sentinel groundwater monitoring well. • Location 2—Define the vertical distribution of sulfolane and confirm the geologic layering to the top of the Corcoran Clay near the PSW. Collect data needed to evaluate potential remediation alternatives near the PSW including in-situ treatment and groundwater extraction. • Location 3 —Define the vertical distribution of sulfolane and confirm the geologic layering to the top of the Corcoran Clay near the BSW. Collect data needed to evaluate potential remediation alternatives near the BSW including in-situ treatment and groundwater extraction. • Location 4—Define the vertical and lateral extent of sulfolane and confirm the geologic layering to the top of the Corcoran Clay along the currently estimated groundwater flow path from the sulfolane source area to LWD-10. • Location 5 —Define the vertical and lateral extent of sulfolane and confirm the geologic layering to the top of the Corcoran Clay along the currently estimated groundwater flow path from BSW to LWD-10. • Location 6—Define the vertical and lateral extent of sulfolane and confirm the geologic layering to the top of the Corcoran Clay along the currently estimated groundwater flow path from BSW to LWD-10. • Location 7—Install a new monitoring well if sulfolane is detected at higher concentrations at Locations 2 or 4 at depths that are not monitored by the existing PW-34 monitoring wells. • Location 8—Install a new monitoring well if sulfolane is detected at higher concentrations at Locations 3, 5, or 6 at depths that are not monitored by the existing PW- 25 monitoring wells. A monitoring well may be installed in each of the borings based on the stratigraphy and grab- groundwater sulfolane results. A monitoring will be installed if sulfolane is detected at a location Site Characterization Work Plan 4 June 22,2018