ARCHIVED REPORTS XR0004808 - Laserfiche WebLink

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! TreadvvelOW10 due to the presence of Fremont Street, and because of the proposed excavation depth below the water table The proposed excavation should remove all of the identified vadose zone soil contamination, ' much of the saturated soil contamination, and enable removal of some contaminated groundwater The proposed excavation area is underlain by approximately 7 5 to 10-feet of sand ! fill, followed by a silts and clays down to at least 34 feet bgs Groundwater recharge was slow 1n the borings, and it is expected that groundwater will flow relatively slowly into the excavation Residual soil impacts identified deeper than 23 feet bgs should be addressed by backfilling with ORC Excavation below 23 feet bgs will not be attempted because ORC backfill will address ! residual groundwater contamination, and because the shored excavation will be engineered for a set depth 54 Excavation Volumes The proposed excavation will generate approximately 512 cubic yards or 820 tons of soil It is estimated that 1 to 2 excavation volumes of water (one volume is 14' x 43'x 4') will be removed after soil excavation, or approximately 18,000 to 36,000 gallons of water The soil will be stockpiled and characterized for offsite disposal Clean, shallow soil may be re-used on site Clean import material will be used as backfill as needed While backfilling procedures will be determined by the project geotechnical engineer, we anticipate that the bottom 4 to 5 feet of excavation will be backfilled with pea gravel backfill and ORC compound 60 REMEDIATION SCHEDULE We can begin the excavation as soon as this workplan is approved by the SJCEHD The ! excavation would take approximately one week to shore and another 3 to 4 days to excavate The excavation will likely remain open 3 to 7 days to complete the dewatering Backfilling, recompaction and shoring removal will take an additional 4 to 7 days !R 9 25971013 DGD 12 April 2004