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7h3adwveII&MIO <br /> ' The proposed excavation depth should remove the majority of the identified saturated and <br /> vadose zone soil contamination, and enable removal of a significant amount of contaminated <br /> groundwater Residual soil impacts previously identified deeper than 22 feet bgs should be <br /> addressed by backfilling with ORC The proposed excavation area is underlain by <br /> approximately 4-feet of sand to silt fill, followed by a silt layer down to approximately 19 to <br /> 21 feet bgs The silt is underlain by saturated sand Boring 16B-7b was advanced to 18 5 feet <br /> ibgs, did not penetrate the sand layer, and no groundwater entered the hole after allowing it to <br /> stabilize over night The proposed excavation is designed to reach the sand layer and enable <br /> removal of groundwater and free product that may be present in the sand below the silt layer <br /> Excavation below 22 feet bgs will not be attempted because recent sampling has not encountered <br /> ' soil contamination below this depth, ORC backfill can address residual groundwater <br /> contamination, and because the shored excavation will be engineered for a set depth <br /> 62 Excavation Volumes <br /> The proposed excavation will generate approximately 684 cubic yards or 1,100 tons of soil It is <br /> ' estimated that 2 to 5 excavation volumes of water (one volume is 28' x 30'x 4') will be removed <br /> after soil excavation, or approximately 1.2,000 to 30,000 gallons of water The soil will <br /> DtJ'P, 1,,q-\ <br /> stockpiled and characterized for offsite disposal Clean, shallow oil may be re-used on site <br /> Clean import material will be used as backfill While backfilling procedures will be determined <br /> by the project geotechnical engineer, we anticipate that the bottom 4 to 5-feet of excavation will <br /> be backfilled with pea gravel backfill and ORC compound <br /> 7.0 REMEDIATION SCHEDULE <br /> ' We can begin the excavation xcavatian as soon as this workplan is approved by the SJCEHD The <br /> ' excavation would take approximately one week to shore and another 3-4 days to excavate The <br /> excavation will likely remain open 3 to 7 days to complete the de-watering, which may include <br /> setting up a skimming pump if free product is present Backfilling, recompaction and shoring <br /> removal will take an additional 4 to 7 days <br /> ' 10 <br /> 25971014 DGD 7 April 2004 <br />