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UST Closure Report Sharpe Defense Distribution Region West Lathrop,California Page 21 40 March 1999 (ECI has a backlog of tanks requiring cleaning). A copy of the Certificates of Disposal will be forwarded to the USAGE as soon as CAL INC receives them from ECI. The piping from product and vapor return lines was loaded into a 20 cubic yard-capacity roll-off bin (No. 256N) supplied by Ecological Control Industries on February 2 and 4, 1999. ECI transported the piping (estimated at 1,000 lineal feet and 4,000 lbs) to their treatment and disposal facility at 255 Parr Blvd., Richmond, CA on February 9, 1999, under State Manifest Document No. 98459482 (Appendix 5) 6.4 Contaminated Soil As of the date of this report the two stockpiles of excavated material with MTBE contamination remained at a site 400 feet southeast of the UST excavation (see Figure 7). Stockpile SPD-6 contains 19 cy of native, silty sand removed from the UST excavation. Sample SPD-6 contained 210 µg/kg MTBE and 200 mg/kg lead. Stockpile SPC-new is just 10 feet south of stockpile SPD-6 and comprises about 60 cy of native silty sand excavated from the piping trenches. A composite of two soil samples from the stockpile SPC-4+SPC-2) contained 28 mg/kg TPH-diesel and 55 µg/kg MTBE. The stockpiles are placed on, and covered by, plastic sheets. 6.5 Concrete Wastes The concrete from the demolished dispenser islands and drive pads were loaded into ten, 10 cubic yard-capacity bins on January 12, 13 and 26, 1999. The bins with concrete were transported by Delta Container Corporation of 1145 West Charter Way, Stockton, CA 95206 (telephone (209)466-5192) to their facility for recycling. 7.0 SITE RESTORATION The sites of the UST excavation and piping trenches were restored to the original grade by backfilling with imported aggregate base fill and the native fill removed from the excavation. All backfill materials were compacted in lifts. The degree of compaction of each lift was tested by the sand cone method. The results of the tests are summarized in a table at the end of Section 7.1. 7.1 Backfilling UST and Piping Excavations A total of 116 tons of 1 % inch drain rock (about 90 cy assuming 1.3 tons/cy) were deposited on top of the concrete hold-down slabs in the base of the UST excavation on December 31, 1998 and January 4, 1999. The drain rock was obtained from the Tracy plant of Teichert & Son, Inc. The purpose of the drain rock was to provide a firm base that spans the water table. The depth of the excavation prior to placing the drain rock was about 12 to 13 feet. The excavation was about 9 feet below surface grade in the deepest part of the excavation after placing it. N:\PROJECTS\3546\Reports\3546 UST Closure Report Draft.doc March 24,1999