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CLEARWATER Ertvirartmrn ra! �.rr+ccs 3.0 WORKPLAN FOR CONFIRMATION SOIL BORINGS 3 1 Proposed Scope of Work The purpose of the proposed work is to demonstrate that the SVE /AS system operation and remo,�al of 7,377 lbs of gasoline from the subsurface resulted in a significant reduction in gasoline contarrunants in soil beneath the site To accomplish this goal, four soil borings will be dnlled in the area of the former UST system and in areas of previously known vadose zone/capillary fringe contamination (Figure 5) Soil samples collected from zones of previously known contamination will be retained for laboratory analysis Analytical results for these samples will be compared to those collected during UST removal and initial site investigation phase to determine efficacy of clean-up All work will be conducted in accordance with the LUFT Field Manual. the Tri-Regional Board Staff Recommendations, and Article I 1 Corrective fiction Regulations of Chapter 16 Under Storage Tanks Regulations Specific project tasks are summarized below 3 2 Field Methods Prior to drilling, Clearwater will prepare site specific Health and Safety Plan for drilling activities Prior to conducting and drilling, the site will be marked by Underground Service Alert (USA) to identify utilities leading to the site Appropriate drilling permits will be obtained from the SICPHS/EHD prior to drilling All fieldwork will be conducted in accordance with Clearwaters Field Protocols (attached) The bonngs will be advanced in locations where contamination was previously observed or documented in order to compare pre- and post-remediation contaminant levels Confirmation borings CB-I and CB-2 will be drilled in the locations of the former south UST and the former dispenser island, respectively (Figure 5) Due to access constraints (low overhead), a boring cannot be drilled exactly in the location the second forrner UST Howe-,er. boring C13-2 is located with several feet from the side of the former north UST, and therefore will suffice for reassessment of that area TPHg levels were reported to have been greater than 10,000 mg/kg in soil samples collected from the base of the excavations during UST removal at a depth of 10 feet bgs Additionally,previous assessment data from 1IW-2, RW-I and VW-3 indicated that TPHg concentrations at a depth of approximately 15 feet bgs ranged between 450 and 700 mg/kg (Figure 6) The remaining two confirmation borings,CB-3 and CB-4,will be located near VW--I and MW-1,respectively Although no soil sample data exist for this area,drilling observations/OVM readings and the previous presence of SPH in the area of MW-1 suggest that TPHg concentrations were elevated at depths between 10 and 15 feet bgs, the histoncal range for groundwater fluctuation For the sake of comparison,it is assumed that pre-remediation TPHg concentrations in this area were also likely between 450 to 700 mg/kg(Figure 6) A direct push drill ng will be used to advance the confirmation bonngs Drilling will be performed by a C-57 licensed driller under the supervision of a Clearwater geologist It is assumed that the four boring will be drilled to a maximum depth of 15 feet bgs During drilling,soil samples will be collected at five-foot intervals Soil types will be documented, as well as depth to groundwater, if encountered Soil samples will be collected in accordance with local regulatory D-107 4Q99 GW&WP Confirmation Borings 4 November 15 1999