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Arsenic Trioxide Site

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Site Description

The Arsenic Trioxide site covers about 568 square miles in southeastern North Dakota. Elevated levels of arsenic in groundwater are attributed to the use of arsenic-laced baits that were used from the 1890s to 1940s to combat grasshopper infestations. A Remedial Investigation (RI) conducted in 1985 identified several groundwater wells that exceeded the Safe Drinking Water Act Maximum Contaminant Level (MCL) for arsenic, which, at the time, was 50 micrograms per liter (ug/L). The groundwater is used as a source of drinking water for both public water systems and private wells.

Current Site Status and Cleanup Actions to Date

  • The Site was listed in September 1983 as the State's "silver bullet" NPL pick.
  • Construction of the remedy, a water treatment/distribution system meeting the Safe Drinking Water Act MCL of 50 ug/L of arsenic was completed in June 1993. The original remedy included constructing or expanding over 300 miles of water distribution lines and three water treatment plants.
  • The Site was deleted from the NPL in July 1996.
  • A Five Year Review conducted in 2004 found the remedy will no longer be protective when the new arsenic MCL of 10 ug/L goes into effect in January 2006.
  • The proposed plan to upgrade the existing three water treatment plants and their distribution systems to municipal and rural households is in the design phase. The upgrades are designed to meet the new 2006 arsenic MCL.
  • The options were outlined for the public in an alternatives analysis study that will be used to obtain public comment.
  • The vast majority of the residents within the Superfund site boundary would be connected to water from water treatment plants.
  • Approximately 600 residences could be either connected to the water treatment plants by expanding the distribution lines or provided point of use filtration systems.

Current Funding Status

  • In 2006, EPA is providing $600,000 to fund several common elements to the upgrading of the water treatment plants.
  • EPA is gathering information that will be used to make the final remedy decision on how best to provide safe drinking water to the residents living within the impacted areas of this site.

For more information on the projects at this site, please read the Arsenic Trioxide Fact Sheet on the Region 8 Superfund Web site.

Key Accomplishments

  • In 2006, EPA is providing $600,000 to fund several common elements for upgrading the water treatment plants.
  • The Site was deleted from the NPL in July 1996.
  • Construction of the original remedy, a water treatment/ distribution system, was completed in June 1993.


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