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. Chevron U.S .A. <br /> Page 13 <br /> Based on the results of chemical analysis, the <br /> excavation activities were ceased and aeration of soils was <br /> commenced (see Section 5.3) . <br /> 5.2 Backfill and Compaction <br /> Soil removed during the remediation effort was <br /> segregated, based on field screening, into "clean" and <br /> "dirty" stockpiles. The "clean" materials were replaced in <br /> the pit as an engineered fill. <br /> Filling began on February 19, 1990. Due to safety <br /> considerations associated with the excavation sidewalls, the <br /> bottom 15 feet of the excavation was not checked for <br /> compaction. <br /> Fills were placed using a sheepsfoot roller at the end <br /> of the excavator arm. A minimum of seven passes were <br /> observed to be made on each lift. Fill placed above the 15- <br /> feet level was compacted using a vibratory sheepsfoot roller. <br /> Compaction testing of fills above the 15-feet level was <br /> performed by Twining Laboratories of Modesto, California. <br /> Specifications for compaction called for a minimum of 90% <br /> relative compaction based on the ASTM D-1557-78 test method <br /> for moisture content/density relationships. Fills were <br /> tested at a maximum interval of 2 vertical feet <br /> 16000-250-044 <br /> Corrected <br /> D NtOORE <br />