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M i 5-S i_ for the analytical results from the excavation and stockpile soil samples are included in Attachment H. W On behalf of Sheldon, BC recommended in a September 24, 1993, letter to the County that the excavation be lined with a low permeability clay and backfilled with the previously excavated soil, and the site be closed. BC recommended that five feet of clean imported material be placed on top of the clay liner and that the previously excavated material be used as backfill material. The County approved the plan for closure, along with the use of the stockpiled material as backfill, on September 28, 1993. The letter to the County and their approval of the recommendations are included in Attachment H. it J.H. Kleinfelder and Associates (Kleinfelder) was contracted by Aprotek for the design and certification of the backfilling of the excavation. Kleinfelder recommended to Aprotek, in ` a letter dated September 21, 1993 (Attachment I), that the excavation be lined with multiple layers 10 millimeter visqueen with proper overlapping and caulked seams,pea gravel be imported and placed in the excavation up to a depth of approximately 25 feet below ground surface, and �. the remainder of the excavation be backfilled with native material. The use of a plastic liner over a clay liner was recommended by Kieinfelder because of safety concerns. The County verbally agreed to the change in the backfilling specifications on October 1, 1993. i_ Aprotek began lining the excavation on September 30, 1993, and began backfilling the excavation with pea gravel on October 4, 1993. Approximately 2,077 tons of pea gravel were Lo placed in the excavation to bring the level of the pea gravel to 25 feet below grade. The pea gravel was compacted to approximately 95-percent compaction using a vibratory compactor. Aprotek began placing the stockpiled material on top of the pea gravel on October 11, 1993. The stockpiled material was layed in 2-foot lifts and compacted to approximately 95-percent compaction (as confumed by Kleinfelder) using a vibratory compactor. All of the material originally excavated from the area was used as fill material. The backfilling was completed w- during the middle of November 1993. The site will be returned to its original paved condition as soon as weather permits. LM it Use or disclosure of data contained on this street is subject to the restriction specified at the beginning of this doctanent. 12R2193\E\76CPMFPORISSKENT-0fL CLO Q.MS-P52200 W