The EPA Region 9 Removal Program continues to assist the Remedial Program by conducting a second intermin removal action at the Iron King Mine-Humboldt Smelter NPL site in Dewey-Humboldt, Arizona. Site features include the Iron King Mine and vicinity, the Humboldt Smelter, impacted surface waterways and residential properties. This Action will address threats to human health and the environment from soils with elevated levels of arsenic and lead on residential properties.
Previous removal actions took place at the Site in 2006 and again in 2011, each focusing predominantly on residential properties. In 2006 ERS conducted sampling at 17 residential properties in the vicinity of the Chaparral Gulch and directed excavation of contaminated soils from 4 of these properties under an enforcement agreement with the Ironite Products Company. In 2011, ERS conducted removal actions at 11 additional residential properties in the vicinity of Sweet Pea Lane. These properties were located downgradient of the smelter and ore cart conveyance rail tracks. Also in 2011, one distinct tailings pile, located on the Iron King Mine property but adjacent to one residential property, was removed. Excavated soils from each of these actions were disposed at the Iron King Mine.
At the time of the 2011 Action Memo, EPA had assessed approximately 190 residential yards. Further Remedial Investigation activities at the Site took place in multiple phases between 2012 and 2016. In 2016, EPA completed the Remedial Investigation at the Site, after sampling an additional 190 residential and commercial properties, bringing the total to approximately 380. Most of the additional 190 properties were residential. During this time, EPA also completed a full Site-specific risk assessment including a Site-specific bioavailability determination in order to refine removal action Site cleanup goals.
Among the additional 190 residential properties sampled, approximately 35 additional residential yards were identified with contamination that posed an unacceptable threat to human health for residents living at those properties, especially children. Lead at concentrations up to 20,500 mg/kg and arsenic at levels up to 1,630 mg/kg are present at some of these properties. These additional properties had not yet been sampled at the time of the previous Action Memorandum. These 35 residential yards represent the basis for the continuation of the response.
