Remedial Action Report Construction Phase

Home Browse Search

and groundwater quality in accessible portions of the property prior to demolition and construction. Analytical results from the investigation were used to assist in planning remedial actions. Soil and groundwater samples were collected from nineteen investigative borings completed during the subsurface investigation. Pre-Construction Investigation and Remedial Actions From October 16, 1997 through January 2, 1998, Century West conducted pre-construction investigation and remedial actions at the Courthouse Square block (Century West 1997c, 1997d, 1998a, 1998b). The objectives were to further characterize environmental conditions and complete remedial actions at 17 areas with known or suspected subsurface contamination. Figure 3 shows the location of each of the 17 areas. During pre-construction, nine USTs were discovered and decommissioned. Approximately 7,300 tons of petroleum-impacted soil was excavated from the site and transported to the USA Waste - Riverbend landfill facility in McMinnville, Oregon for disposal. Approximately 367,700 gallons of petroleum-impacted groundwater were pumped from excavations, treated on-site using sparge tanks and carbon filtration, and discharged under a National Pollutant Discharge Elimination System (NPDES) 1500A permit. 3.3 Corrective Action Plan Based on the concentrations and extent of soil contamination left in place at the former Chevron property, Century West prepared a Corrective Action Plan for this property (Century West 1998b). The Corrective Action Plan included a Risk Based Corrective Action (RBCA) Tier I evaluation of the contaminated soil and groundwater using the DEQ's Interim Guidance on Incorporating Risk Based Corrective Action_for Petroleirm Releases (DEQ 1996). The exposure pathway assessment identified three potential exposure pathways for the forrner Chevron property: 1) volatilization of impacted soil into outdoor air; 2) direct ingestion of, inhalation of, or contact with impacted soil; and 3) volatilization of impacted groundwater into outdoor air. Based on a comparison between the soil and groundwater analytical results for the Chevron property and the appropriate Risk Based Screening Levels (RBSLs), the impacted soil left in place on this properiy does not pose a threat to human health or the environment. 3.4 Area 8 Investigation In response to the DEQ letter dated August 11, 1998, Century West conducted additional investigation at Area 8 located in the northwest portion of the Courthouse Square block (Figure 3). The objectives of the additional investigation included: 1) delineating the extent of petroleum hydrocarbon contamination left in-place in the area north of Area 8, and 2) determining if the petroleum hydrocarbon contaminated soil left in-place contains constituents of petroleum at concentrations which exceed the DEQ's RBCA Tier I RBSLs. The findings from the Area Construction Phase - Remedial Actions - 4- 4080600127 Courthouse Square November 9, 1999