Construction: Pre-Construction Remedial

Home Browse Search

Mr. Bruce Scherzinger August 25, 1997 Page 2 The general pre-construction remedial approach for this site includes excavation and off-site disposal of soil exceeding Leve12 concentrations to the extent practicable. Excavation will extend to a minimum of the construction excavation depth (approximately 12 feet bgs). Excavation of soil contamination exceeding cleanup levels located below 12 feet bgs will generally not proceed beyond three feet below the groundwater table (for a maximum excavation depth of approximately 16 feet bgs). Note that the parking structure slab will cover the entire block at approximately 12 feet bgs, in effect capping the site and eliminating potential exposure to potential remaining contaminants. The lateral extent of remedial excavation will continue until confirmation samples are below DEQ cleanup levels as practicable to support site closure; excavation will not extend beyond the property line into the street. Individual excavations will generally be left open to be incorporated into construction excavation activities to the extent allowed under safety regulations. Contaminated soil will be placed in stockpiles, sampled, and analyzed prior to off-site disposal. If groundwater is encountered while excavating contaminated soil, it will be pumped out into portable storage tanks for characterization and appropriate off-site treatment/disposal. Groundwater recharged into the excavation will be sampled and analyzed per OAR 340-122-340. Confirmation Sampling and Analyses Confirmation soil samples will be collected from each excavation for laboratory analysis. Confirmation soil samples (and groundwater, if applicable) will be collected and analyzed per OAR 340-122. It is anticipated that the closure approach for underground storage tank (UST)- related excavations will utilize the Numeric Soil Cleanup Standards for a Leve12 site. Representative soil samples collected in the vicinity of the former used oil UST on the former Chevron parcel will be additionally analyzed for polychlorinated biphenyls (PCBs), leachable chromium, cadmium, and lead, and volatile organic compounds. Confirmation soil samples in non-UST decommissioning excavations will be collected from the excavation walls at apparent zones of contamination or at the soil/water interface at approximately a 25-foot lateral frequency. Representative soil samples will also be collected from the excavation floor. A Risk-Based Corrective Action (RBCA) approach may be utilized, particularly for the former Chevron parcel. Therefore, constituent analyses, including benzene, toluene, ethylbenzene, and xylenes (BTEX), polynuclear aromatic hydrocarbons (PAHs), ethylene dibromide, ethylene dichoride, lead, and methyl-t-butyl ether, will be conducted in addition to TPH analyses to potentially support a RBCA closure. Constituent analyses will be conducted on select samples with the highest TPH concentrations.