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(YVATC � ASSOCIATES i NC and results were presented in ATC's report titled Summary Report of Subsurface Investigation, dated February 2002 In September and October 2002, cone penetration testing (CPT) borings CPT1 and CPT2, Geoprobe (direct push) bonngs CPTIa and CPT2a, and groundwater monitoring wells MW-4 through MW-8 were installed at the site CPTI and CPT2 borings were advanced to 120 and 139 feet bgs, respectively, to provide continuous stratigraphic definition in the borings Grab groundwater samples were collected from CPTl a and CPT2a at depths of 109 and 114 feet bgs, respectively Monitoring wells MW-4 through MW-8 were completed to a total depth of 65 feet bgs CrV1 was not detected in soil samples collected from the boreholes of MW-4 through MW-8 CrV1 was detected in groundwater samples collected from wells MW-2 through MW-7 in September 2002, with the highest concentration detected at 4 0 mg/l in the groundwater sample collected from well MW-3 CrV1 was detected at concentrations of 0 170 and 0 012 mg/l ui grab groundwater samples collected from borings CPT1 a and CPT2a, respectively These grab samples were collected from the deeper water-bearing zone Total chronuum was detected in the water samples collected from all the wells, including the facility well, with the highest concentration detected at 6 2 mg/l in the groundwater sample collected from MW-3 The grab groundwater samples collected from CPTla and CPT2a were not analyzed for total chromium These findings and results were presented in ATC's report titled Summary Report of Additional Subsurface Investigation, dated November 1, 2002 On April 29 and 30, 2003, ATC supervised the installation of monitoring well MW-9 MW-9 was installed in the northern portion of the site to a depth of 113 feet bgs to correspond with the deeper water-bearing zone encountered in boring CPT1 Laboratory analytical results of a groundwater sample collected from MW-9 on May 5, 2003, indicated that CrV1 and total chromium were detected at concentrations of 0 0049 and 0 0081 mg/l, respectively Refer to ATC's report Summary Report of Additional Subsurface Investigation Deep Well Investigation, dated May 8, 2003 for additional information SOII.AND GROUNDWATER SAMPLE COLLECTION Soil and groundwater samples will be collected at the site and submitted to PRIMA Environmental in Roseville, Cahforiva to be utilized in the bench scale treatability study Historical information indicates the soil sample collected by WA from below Vault 8 at a depth of 14 8 feet bgs contained the highest concentration of CrVI (75 milligrams per kilogram [mg/kg]) Groundwater samples collected from MW-3 have historically contained the highest concentrations of CrV1 with respect to the other moritorung wells Baseline Analyses and Characterization Soil and groundwater samples will be collected and analyzed for specific constituents to provide for baseline characterization, in addition to bench scale testing, to evaluate the potential of ferrous iron solution and calcium polysulfide to reduce and stabilize CrV1 via injection into the subsurface A soil sample will be collected from the area of highest documented CrV1 concentrations (beneath Vault 8) by advancing an angle boring with a hollow stem auger drilling rig Soil samples will be collected from approximately 15 to 17 feet below Vault 8 with a California modified split spoon sampler Soil samples will also be collected in a sinular manner from beneath Vault 8 at depths of approximately 25 to 27 feet and 35 to s lenvironments11625831repmu\RevisedWKP-Bench test.doc 3