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UST Closure Report
<br /> Sharpe Defense Distribution Region West
<br /> Lathrop,California Page 22
<br /> On March 4, a two-foot thick lift of 3/4 inch aggregate base, Class 2, material was placed and
<br /> spread on the drain rock on the bottom of the excavation with a Volvo L120C front-end loader
<br /> with at 4-in-1 bucket. The drain rock was separated from the aggregate base fill by overlapping
<br /> layers of 10 mil-thick plastic sheeting. The aggregate base material was obtained from Teichert
<br /> & Son, transported to the site by Ayala Trucking on December 30 and 31, 1998, and placed in a
<br /> stockpile of about 260 cy just northwest of the excavation. A compaction-moisture density
<br /> determination by Kleinfelder, Inc. on a sample of the material collected on February 26, 1999,
<br /> indicated it had a water content of 5.1%, and that the maximum dry density of 140.2 lb/cu ft
<br /> would be obtained at the optimum water content of 5.7%. The aggregate base fill was compacted
<br /> with a Bomag 13W 213PDB-2 compactor with a vibratory, 84 inch-wide, single `sheep's foot'
<br /> roller. The depth below final surface grade of the top of this lift of aggregate base was 85 inches.
<br /> On March 5, Kleinfelder, Inc. conducted sand cone compaction tests (ASTM D 1556 test
<br /> method) of the first lift of aggregate base fill in two widely separated places. The tests indicated
<br /> that the degree of compaction was 96.7% and 100.7% (see Table below). The required minimum
<br /> degree of compaction below depths of 60 inches below grade is 90%, and above 60 inches, 93%
<br /> (Page 4, Section 02210, Earthwork, Specification#9928).
<br /> On February 26, 1999, CAL INC was notified by Mr. Doug Betz, USACE, that the native
<br /> materials that had been removed from the excavation and stockpiled (stockpile SP-D) could be
<br /> returned to the excavation as backfill. The returned material did not include the MTBE-
<br /> qP fill delineated by the base environmental department around soil sample SPD-6.
<br /> That material was separated from the main stockpile and formed into a new stockpile, SPD-6.
<br /> Tests on two soil samples collected and analyzed by Kleinfelder, Inc. indicated that the moisture
<br /> content of the excavated native soil in stockpile SPD had a water content of about 14% on
<br /> February 28, 1999 (see Compaction-Moisture Density Determination sheets, Appendix 9). Tests
<br /> by Kleinfelder, Inc. on these same samples indicated that the maximum dry density of the
<br /> samples (124.6 and 127.2 lb/cu ft, respectively) is obtained at a moisture content of 8.6%,
<br /> average. Thus, the soil in stockpile SPD had a moisture content about 5.4% above that at
<br /> maximum dry density. Mr. John Clarkson, a field technician with Kleinfelder, Inc., that
<br /> conducted the field compaction tests during backfilling, indicated to CAL INC that, in practice,
<br /> the maximum compaction level could be obtained if the moisture content of the material is about
<br /> 3% greater than the optimum, that is, about 11.6%. In order to reduce the water content of the
<br /> stockpiled soil by about 2.5%, CAL INC aerated the soil on March 3 and 4. Aeration was
<br /> accomplished by spreading the stockpile out in a 6 inch or less, thick layer with a Caterpillar
<br /> D5M XL bulldozer. The soil was then formed into a series of windrows, allowed to dry for a
<br /> half an hour, then reformed into a new series of windrows. The process was repeated for a total
<br /> of 10 hours. Kleinfelder, Inc. found that the moisture content of a sample collected from the
<br /> aerated soil was about 12.5%, or only 1% over that at which maximum field compaction could be
<br /> obtained.
<br /> ® On March 5, after completing compaction tests, the native soil fill that was excavated from the
<br /> UST excavation and stockpiled in stockpile SPD was returned to the excavation as backfill in
<br /> two lifts (not including the soil in stockpile SPD-6). The soil was loaded from stockpile SPD
<br /> with the Volvo front-end loader onto two end-dump trucks operated by G.C.U. Trucking Inc. of
<br /> N:\PROJECTS\3546\Reports\3546 UST Closure Report Draft.doc March 24,1999
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