Background:
Pipe-coating businesses, operated by Northwest Pipe and Casing and Hall Processing Company (NWPC), operated on the southern part of the 53 acre Site from 1956 to 1985. During pipe-coating operations, contaminants were released at the Site into the soil and groundwater. These contaminants included volatile organic compounds (VOCs), polynuclear aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs).
In 1993, EPA performed a time-critical removal action at the Site to restrict public access, demolish existing buildings, and to dispose of demolition debris both on- and off-Site.
A Remedial Investigation/Feasibility Study (RI/FS) process was initiated in 1996 and was completed in 1999. The FS report was followed by the ROD for the OU1 in 2000, and the ROD for the Groundwater OU (OU2) in 2001. The first phase of the OU1 remedy, which included soil excavation and on-Site thermal treatment followed by off-Site disposal of soil, was initiated in 2001 and completed in the summer of 2002. The second phase of the OU1 remedy, which included placement of a two-foot thick clean soil cap over Parcel B, was initiated in 2003 and completed in September 2004. The selected remedy for OU2 was implemented in 2003, and included source control, treatment of groundwater through in-situ air stripping wells, contaminant attenuation through natural processes, and institutional controls to protect against groundwater use on-Site.
In 2006, EPA conducted the first Five Year Review (FYR) of the Site, and determined that the remedy for OU1 was protective, and that progress to meet the OU2 groundwater remedial goals (RGs) was being made through an operating groundwater treatment system. During the second FYR in 2011, EPA determined that the groundwater circulation wells (GCW) were not functioning as intended and were not effective in removing contaminant mass or hydraulically containing impacted groundwater from monitoring. Eight GCWs were shut down in 2006 and the remaining seven were shut down in 2007.
In 2008, Parametrix implemented a Focused Field Investigation (FFI) to determine why the GACs installed as part of the groundwater OU2 remedy were not functioning as intended. This investigation located three dense non-aqueous phase liquid (DNAPL) bodies presumably composed of coal tars in the subsurface. The EPA Region 10 Remedial Program determined that the three DNAPL bodies must be removed before the groundwater remedy could prove effective. In May 2009, the EPA Region 10 Remedial Program requested assistance from the EPA Region 10 Removal Program in removing the bulk of soil contamination identified during the FFI. In August 2009, EPA performed a second removal action to excavate and dispose of the contaminated source material found in this area.
In January 2014, an investigation was conducted by Ecology and Environment (E&E). Eight (8) boreholes were installed and collection of up to two samples per borehole were shipped off-Site for laboratory analyses of VOCs. The analytical results generally confirmed the known magnitude and extent of subsurface soil contamination near the outside boundary of the former Plant 4 building, with PCE concentrations in soil of up to 280,000 µg/kg.
In November 2014, Parametrix performed a Site-wide groundwater monitoring sampling event (Parametrix 2015). Analytical results showed that the maximum on-Site concentrations of PCE in the shallow WBZ occur in the vicinity of the former Plant 4 building contaminated soil source. PCE and other COCs were also detected in the intermediate and deep WBZs.
EPA returned to the Site in September 2015 to perform a three month non-time-critical removal action to remove the contaminated subsurface soil from the outside boundary of the former Plant 4 building. In addition, additional soil source investigation and a comprehensive sampling of existing groundwater monitoring wells will be performed, and certain groundwater monitoring wells will be closed and a deep aquifer well may be installed.
