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' Beacon Station o No.474 December 23, 1997 rf r-Q.,Investigation Report also the total drilled depth of each boring, was approximately 76 feet below surface grade (bsg). Blank PVC well casing was installed from the top of the screened interval at 56 feet bsg to the surface. The annular space opposite the well screen was backfilled with # 3 ' Monterey sand to approximately one feet above the screened interval. A two-foot seal of bentonite was then placed above the filter sand, hydrated with approximately five gallons of fresh water, and additional fresh water added at the direction of the SJC PHS/EHD inspector. A neat cement/bentonite grout was used to complete the annular seal to the ' surface. The grout was pumped through grout hoses placed in the boring immediately above the bentonite seal and withdrawn with the rising grout level in one continuous operation. The top of the well casing was secured with a locking water-tight expansion cap and a 12- inch diameter steel, water-tight traffic box set slightly above grade with a concrete apron. ' The construction details are shown on the corresponding boring logs in Appendix D. iSoil 7apor Well InstallatiQn The 10-inch diameter soil borings B-5 and B-6 were each drilled and sampled to 66 feet bsg. Each boring was identically completed with three nested soil sing - vapor extraction wells using P 2 ' inch ID schedule 40 PVC well screen with 0.02.0-inch factory-machined slots. Wells VW-1, VW-2 and VW-3 were installed in boring B-5, and wells VW-4, VW-5 and VW-6 were installed in boring B-6. A one-foot seal of bentonite was placed in the bottom of each boring. The screened intervals were: VW-I and VW-4 = 50 to 65 feet bsg, VW-2 and VW-5 ' = 37 to 47 feet bsg, and VW-3 and VW-6 = 23 to 33 feet bsg. Blank PVC well casing was installed from the top of each screened interval to the surface. The annular space opposite ' each well screen was backfilled with # 3 Monterey sand, and a seal of bentonite was placed in the intervals between the top of the filter sand and the bottom of the screened interval of ' the next nested well (from 33 to 37 feet and 47 to 50 feet). The upper bentonite seal was placed from 21 to 23 feet bsg. A neat cement/bentonite grout was used to complete the annular seal from approximately,21 feet bsg to-the surface.- A PVC cap was placed on the top of each well until the wells are plumbed into a soil vapor extraction system. The top of ' each well cluster was sealed with a 12-inch diameter water-tight steel traffic box set slightly g Y 1474-12.rpt 5 HORIZON ENVIRONMENTAL INC.