Red Rock Road Probabilistic Risk Assessment

Red Rock Road, located near Sutherlin, Oregon, is a 17-mile long former railroad bed composed of mine tailings containing arsenic. Much of the road is overgrown and located in rural areas, while some portions are located closer to homes or recreational areas. A simple deterministic risk assessment found that arsenic in Red Rock Road soil may pose unacceptable risks to hypothetical residents.

SLR’s risk assessment team developed a model to create probabilistic distribution of risks from soil ingestion and dust inhalation for several residential exposure scenarios. The model evaluated uncertainty and variability associated with exposure assumptions, allowing the team to perform a quantitative analysis of model sensitivity to each exposure assumption distribution.

SLR presented a workshop for all risk assessors and interested parties at Oregon Department of Environmental Quality (ODEQ) to educate regulators on probabilistic methods and model functions. This project represents the first approval of a probabilistic risk assessment by a regulatory agency for a cleanup site in Oregon.