Homestake-King Mill: Contaminated Site Mitigation
The NPS is investigating and cleaning up Homestake-King Mill Site pursuant to CERCLA and the NCP. Congress enacted CERCLA, also known as Superfund, in 1980 to address releases and threatened releases of hazardous substances into the environment.
CERCLA gives the President broad powers to respond to hazardous substance releases and threatened releases as the President deems necessary to protect the public health or welfare or the environment, including enforcement authority with respect to parties responsible for the releases. The President has delegated this authority to a number of federal departments and agencies, including the Department of the Interior. The NPS, an agency within the Department of the Interior, is the CERCLA lead agency for the Site.
The NPS has determined that that a non-time-critical removal action (NTCRA) is appropriate for the Site.
The Site is located in the Bullfrog Hills, Nye County, Nevada in an area of Death Valley National Park known as the "Nevada Triangle." (Latitude: 36.9395° North, Longitude: -116.8886° West). The Site covers approximately 5 acres and consists of the remains of the Homestake-King Mill building and mill tailings. The Site contains a series of five, reinforced-concrete foundations that are between 66 and 100 feet long, 3 feet thick at the base, and up to 16 feet high. The structures are located on a steep slope. As of 2014, floors of the mill rooms, machinery, vat foundations, and building debris remained on site. The mill tailings are visible near the mill and several locations downslope from the mill. Stormwater runoff from the site travels south and east into an unpopulated area in Amargosa Valley. The tailings have eroded into an ephemeral stream that flows from the base of the mill downslope. A gravel access road to the site crosses the stream and is currently blocking the tailings from migrating further downstream.
The mill operated only from 1908-1909 and treated gold ore by plate amalgamation and cyanide. At the time, Homestake-King Mill was described as a "well-equipped" with up to 30 stamps. The Homestake-King Mine was the largest-producing Bullfrog Mining District producer that is now in the park.
A Preliminary Assessment (PA) was conducted in 2014, which described the historical uses of the Site, current state of the Site, and approximated by visual means only the extent of various waste rock and mill tailings at the Site.
As a follow-up to PA, a Site Inspection (SI) was conducted at the Site in 2016. Because soils are the primary media of concern at the Site, soil samples were collected from five areas referred to as decision units (DUs) at the Site. Those areas included mill foundations (DU-1), mill tailings (DU_2), mine waste stockpile (DU-3), downgradient mill tailings (DU-4), and background native soils for comparison (DU-5). Eroded mill tailings in DU-4 extend approximately 3,900 feet downgradient of the Site. The samples were analyzed for metals, cyanide, and pH. Also, select samples were analyzed for their acid-generating ability (ABA).
The soil samples from DU-1 through DU-4 showed elevated levels of antimony, arsenic, beryllium, cadmium, copper, lead, mercury, selenium, silver, thallium, vanadium, and zinc compared to their respective background concentrations in DU-5. Results of ABA testing indicated no net potential for acid generation.
The results of the SI sampling indicated that the Site contains several metals above USEPA regional screening level (RSL) for residential soil and the NPS ecological screening values (ESVs). Cyanide was also detected in samples exceeding RSL and ESV.
Current and Future Site Activities
The NPS is conducting an engineering evaluation and cost analysis as part of a non-time-critical removal action to gather additional information to fully characterize the nature and extent of Site contamination. The EE/CA process will include additional site sampling to further understand the impacts of the previous mining and milling activities at the Site. Risk assessments will be conducted to evaluate human health and ecological concerns, and cleanup goals will be established. If cleanup is required, the EE/CA will also develop, present, and evaluate cleanup alternatives. As part of the alternatives development and evaluation process, NPS will consider the requirements of Section 106 of the National Historic Preservation Act, among other relevant requirements.
The final draft EE/CA Report prepared during this process will be made available for public review and comment during a 30-day period. Following the review and comment period, the EE/CA Report will be revised as necessary and issued in final form. NPS will draft a responsiveness summary that summarizes and responds to significant public comments which will be issued along with the Final EE/CA Report. Following the release of those documents, NPS will issue an Action Memorandum formally selecting the response action alternative for the Site. Once those steps have been taken, NPS will seek funding to implement the selected response action for the Site. Once funding is secured, Site cleanup can proceed.
Public Information Officer
Death Valley National Park