Massive Superfund Site Risk Assessment Focuses Remediation

The Hanford Site in Washington State is a 530-square-mile military reservation where six nuclear reactors produced weapons-grade plutonium from the 1940s to the 1970s. In order to clean up this Superfund site, stakeholders needed to understand the potential human health and environmental risks posed by residual contamination in the Columbia River. To figure this out, Woodard & Curran conducted extensive ecological and human health risk assessments for a 96 mile stretch of the Columbia River.

Building the database

The first step in conducting the risk assessments was to organize the existing information and plan and implement additional river sampling. Woodard & Curran built a database to house all the information—a total of more than a million individual records. Sampling included analysis for radionuclides, metals, organic compounds, PCBs, and other contaminants in soil, sediment, surface water, pore water and fish tissue.

Assessing Background Conditions within the River

There are varied natural and anthropogenic sources of chemical and radiological constituents to the Columbia River upstream of the Hanford Site. Woodard & Curran conducted a comprehensive statistical evaluation of upstream and Site river data to identify whether a constituent was “Site-related” (assumed attributable to Hanford) or “reference-related” (assumed attributable to upstream sources). Categorizing constituents was important in determining the cumulative health risks related to the Site versus non-Site sources. This information was later used in the separate remedial investigation and feasibility study that identified remedial objectives and alternatives.

Ecological assessment defines further investigation

Woodard & Curran conducted a modified Screening Level Ecological Risk Assessment (SLERA) to evaluate potential effects on aquatic and terrestrial plants, invertebrates, and animals. The results of the SLERA identified specific constituents and areas for further investigation under existing site programs. 

Human health risk assessment finds main pathway of concern

The human health risk assessment included an evaluation of potential human exposures through direct contact with river surface water, sediment and soil, and ingestion of finfish, as related to recreational use of the river for swimming, boating, and sport fishing. We also evaluated exposures associated with tribal subsistence fishing. The main conclusions of the risk assessment were that nearly all of the cumulative non-cancer hazards and cancer risks for all receptors were attributed to ingestion of PCBs and pesticides in fish tissue, and that, through PCB congener analysis and comparison to background data, these ‘risk drivers’ were most likely unrelated to the Hanford Site. 

As part of the project, Woodard & Curran routinely engaged in public meetings and workshops with state and federal regulators, as well as Native American tribes and other stakeholders to present information and hear stakeholder concerns. We worked hard to make the complex and varied information presented in the risk assessment reports transparent and easy to understand by a variety of audiences. At least one stakeholder noted that the reports were the most readable such reports he had ever seen.

Details

Confidential Client
Benton County, WA

Team

Senior Technical Manager
Corrective Action
Business Unit Leader
TREC, a Woodard & Curran company
Share