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February 15, 1983 Project 116-1.4 - 3 - The bottom of the trench was fitted with a compacted clay liner with a thickness of 3' beneath the floor drains and sump and 2' beneath the remainder of the trench. The trench floor -was graded to drain at a slope of 1/2q to the north. This resulted in a depth below original grade of approximately 21' in the south end and 25' in the north. Surplus soil removed from the trench was placed adjacent to the north, east and south walls of the trench to result in a final maximum depth of t 401. Additional surplus soil was placed as a 2' cap over Group 1 Trenches #1, #2 and #3. This top cover was to be graded to promote uniform drainage of surface runoff to a master drain ditch south and east of the Group 1 trenches. Prior to completion of Trench #4, we were informed by representatives of you Toxic Waste Unit that Group 1 Trenches would henceforth require side-wall liners consisting of compacted clay. These side-wall liners were subsequently placed on the east, north and south trench walls. Clay soil used in the liners was excavated from the west trench wall. All side-wall liners were approximately 12' wide following placement and they were sub- sequently trimmed to a final thickness of approximately 51.. Final trench walls have slope angles of approximately 3/4:1 (horizontal: vertical). Future Group 1 Trenches will be excavated by advancing the unlined trench wall to the west. Heavy rain which occurred during late October, early November, 1982 prevented completion of final dress-grading and drain trench excavation in Trench #4. Final compaction and dress-grading of the additional clay cap over Trenches i.. #1, #2 and #3 was also incomplete. (See previous discussion) Samples of fine-grained soil used in all trench liners was tested in the laboratories of J. H. Kleinfelder and Associates, Stockton, California. A member of Kleinfelder's staff was present during the placement and compac- tion of all trench liners. Copies of their initial laboratory tests and records of all field density testing are attached as Appendix A. Trench design details are shown on Plate 1. Interim Disposal of,FMC Waste Based upon your letter dated 28, December, 1982, we are no longer,. accepting- shipments of FMC•:waste. In an effort to resume acceptance of the ,FMC waste, we are suggesting implementation of one of the following interim -design alternatives: v1 Alternative #1 - Place a compacted earth berm across the floor of the trench as shown on Plate 2. } J Beta Associates - a