GSI performs long-term monitoring and maintenance activities to evaluate the effectiveness of the groundwater and sediment cap remedy for this Superfund site.


The McCormick & Baxter Superfund site, on the shore of the Willamette River in Portland, includes 41 acres of land and 23 acres of sediments beneath the river. McCormick & Baxter Creosoting Company operated between 1944 and 1991, treating wood products with creosote, pentachlorophenol, and inorganic preservative solutions containing metals. The company discharged process wastewaters on site or directly into the river. As a result, significant concentrations of wood-treating chemicals seeped into the soil and groundwater at the site and in river sediments adjacent to the site. The EPA listed the site on the National Priorities List in 1994.

The contingency groundwater remedy was designed and implemented in 2003, consisting of a combination of steel sheet pile and soil bentonite slurry wall surrounding 18 acres of the site to prevent migration of creosote to the river. The sediment remedy, implemented in 2004, primarily consisted of an amended sand cap placed over 23 acres of contaminated sediment.

In 2006, GSI and our teaming partner began managing the technical elements of the project as a subcontractor to the Oregon Department of Environmental Quality (DEQ). Since then, we have implemented several complex research and monitoring projects.

GSI’s work included:

  • Conducting an ebullition study to determine the significance of ebullition as a potential contaminant pathway, the remaining capacity of the organophilic clay used to sorb oils and prevent them from reaching the river, and biodegradation occurring within the sediment cap. The study concluded that the organoclay retains sufficient sorption capacity and permeability, and that ebullition is an insignificant pathway for contamination.
  • Performing a DNAPL Data Gap Investigation that concluded that upland NAPL recovery could be discontinued at the site.
  • Designing and implementing multiple conventional and passive porewater and surface water sampling events to evaluate cap performance. Based upon the results of these events, DEQ and EPA determined that the sediment remedy is protective as well as operational and functional.
  • Assisting DEQ in preparing the third and fourth Five-Year Review reports, which document and evaluate whether the selected remedy is protective of human health and the environment. The most recent review concluded that response actions at the site are in accordance with the remedy selected by EPA, and that the groundwater, soil, and sediment remedy continues to be protective of human health and the environment in the short term.
  • Managing site-wide monitoring data and assisting in preparation of annual reports.

The work on this project was featured as a case study in the EPA’s guidance document: Use of Amendments for In-site Remediation at Superfund Sediment Sites.