Established in 1998, the Anaconda Regional Water, Waste & Soils (ARWWS) Operable Unit (OU) is the largest and most diverse Operable Unit in the Anaconda Smelter NPL site. As a result, the OU was separated into fifteen Remedial Design Units (RDUs) and two Expansion Areas based upon factors such as location, source and type of contamination, and remedial needs. Click here for more information about the ARWWS OU.
Dutchman Creek Expansion Area was added to the Anaconda Regional Waters, Wastes & Soils (ARWWS) Operable Unit (OU) following sampling and investigation activities that identified smelter-related impacts. This area was formerly included in RDU 7 – North Opportunity, but was later removed in 2005 as the design requirements of each area differed to a greater extent than originally believed.
East of Anaconda and Galen Road, the Dutchman Creek Expansion Area is a wetland environment. In addition to numerous smaller creeks and springs, the area encompasses portions of the Warm Springs Creek, Dutchman Creek, and Lost Creek floodplains. As a wetland environment, various species of wildlife have been observed frequenting the area including moose, deer, and coyote. Elevated concentrations of arsenic were identified in over 3,000 acres of surface soils, as well as arsenic concentrations in the ground water that exceed drinking water standards. This ground water directly discharges into surface water in the area, causing surface water arsenic concentrations that also exceed current standards. Contamination is a direct result of aerial emissions from the Washoe, Lower and Upper Works Smelters, as well as from natural transportation (dust and surface waters). Despite the presence of high arsenic levels, the Dutchman Creek Expansion Area generally well-vegetated due to sub-irrigation from the shallow ground water table.
After being designated as an individual expansion area, Atlantic Richfield took steps in 2005 to limit grazing (agricultural and wildlife) in the area due to high arsenic levels. Pre-design and design investigations began in 1998, while the Dutchman Creek Expansion Area was still a part of RDU 7 – North Opportunity. This information, in coordination with additional investigations in 2009 and 2011, was used after to develop remedial designs specifically for the Dutchman Creek Expansion Area.
These investigations indicated levels of arsenic in surface soils as well as ground and surface waters that were technically impracticable to remediate to current standards. As a result, the Dutchman Creek Expansion Area was designated as a High Arsenic Area, which allows for higher arsenic concentrations in surface soils as well as ground and surface waters. Restrictions for land use and development were established to minimize human exposure to contaminants. Institutional controls, including a Ground Water Management Plan and Surface Water Management Plan, were also implemented in the Dutchman Creek Expansion Area to minimize human exposure to arsenic and prevent unacceptable releases of contaminants to the environment.
Visit the Superfund Library, located on the Arrowhead Foundation’s website, to review documents and research regarding the Anaconda Smelter NPL site. Additional information can also be found on the EPA’s website.