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ou ri • Report on Backfilling Excavation and Sod Treatment Cell Construction September 14, 1993 Manna Pro, 4004 South EI Dorado, Stockton, CA 2 detectable concentrations of BTEX, TPH-G, or TPH-D The laboratory reports and chain-of-custody record are presented in Attachment 2 Before backfilling, the rainwater was pumped from the excavation into an on-site drainage ditch on March 31, 1993, with the approval of SJCPHS Backfilling the Excavation According to the amended work plan, the bottom of the excavation was filled with approximately 2 feet of pea gravel and covered with geotextde fabric on March 31, 1993 On April 1, 2, and 5, 1993, the excavation was backfilled and compacted with 1400t-thick lifts using the fill material generated during the installation of new sewer transmission lines On April 5, 1993, that portion of the stockpiled soil on the western edge of the site with nondetectable concentrations of TPH or BTEX (stockpile samples SP1-1, SP1-2, SP1-3, SP2-1, SP2-2, SP4-2, SP4-3, and SP5-1) was used to complete the backfilling from approximately 5 feet below grade to surface grade A summary of the soil sample analytical results from the stockpiled sods is presented in Attachment 3, Table 1 The full results of the December 1992 sod sampling were reported in the December 15, 1992 and February 1, 1993 letters from Groundwater Technology to the SJCPHS Attachment 4 presents photographs taken during backfilling activities (Photographs 1 through 6) During backfilling, a Meld representative from Bay Area Geotechnical Group measured the percent compaction by testing the density of the backfilled material From approximately 4 to 10 feet below grade the backfill material was compacted to at least 90 percent From 4 feet to surface grade, the backfill material was compacted to at least 95 percent A copy of the field soil density report Is presented in Attachment 5 Soil Treatment Cell Construction The remaining stockpiled sod was moved to the north end of the site (Figure 2) into a 140-foot-by- 160-foot (outside diameter) sod treatment cell The treatment cell berm was constructed using stockpiled soil containing no greater than 21 parts per million (ppm) TPH-D (Sod piles SP3-1, SP4-1, and SP1-4) A 6-inch-thick layer of clean sand was spread over the surface of the treatment cell to protect the 20-millimeter polyethylene liner, which was installed on April 7, 1993 by McCoy Supply Co The remaining stockpiled sod (approximately 2,600 cubic yards) was moved into the treatment cell on April 8 and 9, 1993 The soil was placed in the cell from west to east, beginning with sod containing the lowest TPH-D concentrations and ending with soil containing the highest concentrations Attachment 4 presents photographs taken during treatment cell construction (Photographs 7 through 18) 281OR013 GROUNDWATER TECHNOLOGY, INC