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r <br /> Former Beacon Station No 419 February 17, 1999 <br /> rStockton, California Additional Subsurface Investigation <br /> from the top of the filter sand at approximately 63 feet bsg to approximately 44 feet bsg and <br /> allowed to hydrate <br /> A 2-inch ID soil vapor extraction well (VW-1) was installed with 10 feet of schedule 40 <br /> PVC well screen with 0 020-inch factory-machined slots (34 to 44 feet bsg) Blank 2-inch <br /> PVC well casing was installed from the top of the screened interval at approximately 34 feet <br /> bsg to the surface The annular space opposite the well screen was backfilled with #3 <br /> Monterey sand to approximately one foot above the screened interval Bentonite pellets <br /> were placed from the top of the filter sand at approximately 33 feet bsg to approximately 25 <br /> feet bsg and hydrated with fresh water <br /> A second 2-inch ID soil vapor extraction well (VW-2) was installed with 10 feet of schedule <br /> I 40 PVC well screen with 0 020-inch factory-machined slots (15 to 25 feet bsg) Blank 2- <br /> inch PVC well casing was installed from the top of the screened interval at approximately 15 <br /> feet bsg to the surface The annular space opposite the well screen was backfilled with #3 <br /> Monterey sand to approximately one foot above the screened interval A two-foot thick seal <br />' of bentonite was then placed above the filter sand (12 to 14 feet bsg) and hydrated with <br /> approximately five gallons of fresh water To complete the annular seal, a mixture of neat <br /> cement and bentonite grout was placed from the bentonite seal to the surface The top of the <br /> well casings were secured with locking watertight expansion caps and a watertight steel <br />' traffic box set slightly above surface grade The construction details are shown on the <br /> corresponding boring log in Appendix C <br /> Well Development and Sampling <br />' On September 30, 1998, Horizon personnel were onsite to perform well development and <br /> groundwater sampling of groundwater monitoring wells MW-7 through MW-10 and air <br />' sparge well AS-1 On December 11, 1998, Horizon personnel returned to the site and <br />' developed and sampled replacement well MW-10 The wells were developed, purged, and <br /> sampled as described in Horizon's Field Methods and Procedures in Appendix B Depth to <br /> groundwater levels were taken before and after development and purging, and were recorded <br />' 1419-12 rpt 7 HORIZON ENVIRONMENTAL INC <br />