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Fortner Beacon Station No 419 February 17, .P1)9 Stockton,California Additional Subsurface Investigation grouted from the total depth up to approximately 65 feet bsg, a three-foot thick bentonite seal was placed from 62 feet to 65 feet bsg, and a 2-inch ID groundwater monitoring well (MW-10) was installed in the boring Well MW-10 was completed with 20 feet of schedule ' 40 PVC well screen with 0 020-inch factory-machined slots The bottom of the screened interval was approximately 62 feet bsg Blank 2-inch PVC well casing was installed from the top of the screened interval at approximately 42 feet bsg to the surface The annular space opposite the well screen was backfilled with #3 Monterey sand to approximately three ' feet above the screened interval After placing the filter sand, the driller surged the well with a surge block to settle the filter sand and placed additional filter sand, as needed A two-foot ' thick seal of bentonite was then placed above the filter sand and hydrated with approximately five gallons of fresh water To complete the annular seal on the well, a mixture of neat cement and bentonite grout was placed with a tremae pipe from the bentonite seal to the surface The top of the well casing was secured with a locking watertight ' expansion cap and a watertight steel traffic box set slightly above surface grade Well MW-10 failed and was destroyed by overdrilling to 62 feet bsg with 10-inch diameter augers and 2-inch ID well casing was re-installed on December 2, 1998 The replacement well MW-10 was constructed similar to the previous well MW-10 The construction details are shown on the corresponding boring logs in Appendix C ' Air Sparge and Vapor Extraction Well Installations Soil boring SB-6 was completed with three 2-inch ID wells one air sparge well (AS-1) and ' two soil vapor extraction wells (VW-1 and VW-2) The boring was backfilled through the augers with weighted bentonite pellets from the total depth of approximately 91'/2 feet bsg to ' 69 feet bsg The boring was then reamed with 10-inch diameter augers to approximately 69 feet bsg and a 2-inch ID air sparge well (AS-1) was installed with 5 feet of schedule 40 PVC twell screen with 0 010-inch factory-machined slots (64 to 69 feet bsg) Blank 2-inch PVC well casing was installed from the top of the screened interval at approximately 64 feet bsg to the surface The annular space opposite the well screen was backfilled with #3 Monterey sand to approximately one foot above the screened interval Bentonite pellets were placed ' 1419.12 rpt 6 HORIZON ENVIRONMENTAL INC.