2011-08-01_REVISION - M1978210 (15)

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to a 10 psi confining pressure in a triaxial permeameter and using the constant rate of flow method (flow pump), with a minimum gradient of 10, to determine permeability. The tap water at the Advanced Terra Testing laboratory was used as the permeant. 4.4 Backfill Mix Results The permeability of the MDA and MDB were being determined and were not available at the time this report was issued on July 22, 2011. The test results will be issued in the revision of this report. Under field conditions and with the addition of 0.5% dry bentonite, the backfill mixtures are expected to meet the requirements specified in Section 5.6. Laboratory test results are provided in Table IV. The backfill mixes were also designed for grain -size compatibility. A filter criteria approach was used to evaluate the potential for piping of the backfill mix into the sand and gravel formation. This design process resulted in the graded backfill specification presented in section 5.6. We have determined that if the backfill is proportioned as discussed below it should meet the graded backfill requirement. We have determined that to yield a minimum of 30% fines in the backfill mix, 27,000 cy (at windrow density) of import clay borrow is required. This is in addition to the estimated 5,000 cy of west -side overburden. The clay borrow should have a minimum of 60% fines and a minimum PI of 10. The On property borrow site appears to meetsthese requirements. Import requirements were calculated on a dry unit weight basis in order to yield the required 30% fines. When considered on a dry unit weight basis, MDB is approximately 57% sand and 43% import. However, on a volume basis, approximately half of the trench volume will consist of import with the remainder consisting of the on -site materials. These ratios are summarized below along with the ratios for MDA To yield 0.5% dry-added bentonite, 850,000 lb of dry powdered bentonite is required. This amount does not include the bentonite needed to make slurry. The distribution rate for the mix design components has been determined for various reaches of the alignment as shown on Table VI. G:\PROJECTS \111025 Geisert Gravel Pit Slurry Wall\O \OI \Geisert Slurry Wall Design Report.doc 7 Percentage of Mix Design Components Mix Design A Mix Design B Dry Unit Weight Basis Volume Basis Dry Unit Weight Basis Volume Basis Sand 51 45 57 52 Import Clay 28 31 43 48 West -Side overburden 21 24 -- -- Dry Addition Bentonite 0.5 -- 0.5 -- • to a 10 psi confining pressure in a triaxial permeameter and using the constant rate of flow method (flow pump), with a minimum gradient of 10, to determine permeability. The tap water at the Advanced Terra Testing laboratory was used as the permeant. 4.4 Backfill Mix Results The permeability of the MDA and MDB were being determined and were not available at the time this report was issued on July 22, 2011. The test results will be issued in the revision of this report. Under field conditions and with the addition of 0.5% dry bentonite, the backfill mixtures are expected to meet the requirements specified in Section 5.6. Laboratory test results are provided in Table IV. The backfill mixes were also designed for grain -size compatibility. A filter criteria approach was used to evaluate the potential for piping of the backfill mix into the sand and gravel formation. This design process resulted in the graded backfill specification presented in section 5.6. We have determined that if the backfill is proportioned as discussed below it should meet the graded backfill requirement. We have determined that to yield a minimum of 30% fines in the backfill mix, 27,000 cy (at windrow density) of import clay borrow is required. This is in addition to the estimated 5,000 cy of west -side overburden. The clay borrow should have a minimum of 60% fines and a minimum PI of 10. The On property borrow site appears to meetsthese requirements. Import requirements were calculated on a dry unit weight basis in order to yield the required 30% fines. When considered on a dry unit weight basis, MDB is approximately 57% sand and 43% import. However, on a volume basis, approximately half of the trench volume will consist of import with the remainder consisting of the on -site materials. These ratios are summarized below along with the ratios for MDA To yield 0.5% dry-added bentonite, 850,000 lb of dry powdered bentonite is required. This amount does not include the bentonite needed to make slurry. The distribution rate for the mix design components has been determined for various reaches of the alignment as shown on Table VI. G:\PROJECTS \111025 Geisert Gravel Pit Slurry Wall\O \OI \Geisert Slurry Wall Design Report.doc 7