Remedial Action Report Construction Phase

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Groundwater quality was compared with the RBCA Tier I RBSLs for the appropriate potential exposure pathway (volatilization of impacted groundwater into outdoor air) to evaluate the potential risk of impacted groundwater. In addition, total petroleum hydrocarbon analyses was used on most groundwater samples as a preliminary screen for polynuclear aromatic hydrocarbons (PAHs) in accordance with OAR 340-122-340(4). 4.1 Work Area Designation Prior to initiating the construction phase of the project, two distinct work areas were designated at the site: Clean Areas and Remediated Areas. Clean Areas were those areas with no confirmed or suspected contamination, including areas of clean backfill placed during the pre-construction remedial actions. Remediated Areas were those areas in which previously discovered contaminated soil was excavated or remained in-place. New areas of soil and/or groundwater contamination discovered during the construction activities were also designated as Remediated Areas. No DEQ- imposed restrictions applied to the workers w-orking within the Clean Areas. In addition, no DEQ use or disposal restrictions applied to soil excavated from Clean Areas or areas where clean backfill did not eYtend beyond previous remedial excavation limits. 4.2 Soil Excavation and End Use As required by the DEQ, a representative of Century West was onsite during all mass excavation activities to characterize potentially contaminated soil and groundwater prior to determining if excavations were to proceed as Clean or Remediated Areas. As illustrated in the remedial excavation strategy flow chart, Century West used a photoionization detector (PID) to screen soil excavated from Clean and Remediated Areas. Based on the results from the field screening, soil sampling and, if necessary, remediation were completed in accordance with the excavation strategy. Contaminated soil excavated from these areas was either stockpiled onsite for later transport and disposal, or directly loaded onto trucks for immediate transport and disposal. Contaminated soil temporarily stockpiled onsite was covered with plastic sheeting to prevent contact with surface water and leaching of the contamination. All contaminated soil transported off-site was disposed of at the USA Waste - Riverbend landfill facility in McMinnville, Oregon. Copies of the petroleum contaminated soil disposal receipts are provided in Appendix A. Following mass excavation, lo~~~ volume excavations were performed for approximately one month to accommodate structures such as footings. In a letter to the DEQ dated July 9, 1999, Century West proposed limited excavation oversight following mass excavation. On July 16, 1999, the DEQ approved the proposal in a telephone message to Century West. Construction Phase - Remedial Actions - 6- 4080600127 Courthouse Square November 9, 1999