Dawn Mining Company (DMC) was licensed by the federal government to operate the uranium mill located near Ford, Washington, on 820 acres. The millsite is adjacent to the Spokane Indian Reservation; Chamokane Creek defines the northern and western boundary of the millsite and the eastern boundary of the reservation. DMC's Midnite Mine is located on the Spokane Indian Reservation, about 25 miles from the mill, and is under the jurisdiction of the federal government.
Washington State assumed full licensing and regulatory authority from the U.S. Nuclear Regulatory Commission (NRC).
Washington State Department of Health amended DMC's license, authorizing the disposal of uranium mill tailings into Tailings Disposal Area 4 (TDA-4). TDA-4 is a below-grade impoundment, lined with high-density polyethylene (HDPE). TDA-4 was constructed to hold 44 million cubic feet of tailings, but only received 4 million cubic feet before shutdown.
After processing about 58 million cubic feet of ore, uranium milling ceased and the facility was placed in a care and maintenance mode.
DMC submitted a closure and reclamation plan for the millsite to the Department of Health.
After groundwater contamination from below TDAs 1, 2, and 3 was detected in wells and in seeps discharging to Chamokane Creek, the Department of Health issued a groundwater remediation order and established groundwater protection standards.
DMC submitted a revised closure and reclamation plan, which would provide for:
Department of Health issued a Final Environmental Impact Statement (EIS), rejecting DMC's TDA-4 fill proposal of NORM (naturally occurring radioactive material).
DMC resubmitted their closure plan, with an alternate TDA-4 fill proposal for off-site uranium mill tailings.
Department of Health issued a supplement to the Final EIS, which found that DMC's alternative fill proposal was environmentally acceptable and posed no threat to human health and safety.
Department of Health renewed DMC's radioactive materials license to allow them to implement its closure plan. Receipt of out-of-state uranium mill tailings depended on the following license conditions being met:
DMC completed construction of passive evaporation ponds that were designed to accept contaminated groundwater and process solution from TDA-4. The five ponds were built over the unlined tailings disposal areas (TDAs 1, 2, and 3) and are lined with 60-mil HDPE, covering about 110 acres of the site.
The water was removed from TDA-4 and TDA-4 access was stabilized, and work begun to prepare TDA-4 for the receipt of fill material. Pumping of groundwater into the evaporation ponds was resumed.
Department of Health renewed DMC's radioactive materials license which continued to allow DMC to import out of state uranium mill tailings for TDA-4 fill material. An extensive public process preceded license renewal.
|Department of Health amended DMC's radioactive materials license to disallow disposal of off-site uranium mill tailing, to change the reclamation date from 2019 to 2013, to allow the direct disposal of sludge/filtercake from the Midnite Mine water treatment plant into TDA-4, and to require milestones for individual reclamation tasks. The license amendment process included many public meetings. The Department of Health determined that the groundwater pump-back system in the unlined tailings disposal area was no longer effective in reducing contamination and directed DMC to prepare a Corrective Action Assessment with alternatives for remediation. DMC began groundwater testing to assess the effectiveness of creating a bio-remediation barrier to reduce uranium concentrations.
|DMC demolished the mill building and associated facilities, and disposed the debris into TDA-4.
|DMC completed major components of the millsite soil cleanup, including contaminated soils along State Highway 231 and the county entrance road. DMC excavated contaminated soils and disposed them into TDA-4.
|Following Department of Health approval, DMC ceased the bio-remediation corrective action for the tailings disposal area groundwater contamination. The field-scale assessment results showed that bio-remediation did not reduce contaminants to meet site groundwater protection standards. The Department of Health required DMC to continue monitoring groundwater quality and assessing the tailings disposal area contaminant plume.
|DMC discovered groundwater contamination below the ore stockpile area, and initiated characterization studies of the ore stockpile area soil and groundwater.
|DMC completed installation of an HDPE liner over TDA-4 to cover the waste placed to date: tailings, mill debris, contaminated soils, water treatment plant sludge from Midnite Mine.
|DMC constructed a new evaporation pond (EP6) with double-lined leak detection and 120-acre-feet capacity, divided into four 30-acre-feet cells. DMC transferred all remaining process water into EP6 and began installing the final cover over the unlined tailings disposal areas (TDAs 1, 2, and 3).
The Department of Health amended DMC's radioactive materials license to reflect current closure status. This included terminating Midnite Mine water treatment plant sludge disposal, updating environmental monitoring, incorporating a groundwater protection plan to address groundwater corrective actions for the tailings and ore stockpile areas, and completing surface reclamation by the end of 2016. DMC constructed a cover over the stockpile area to minimize infiltration of precipitation, inhibit further migration of uranium into the groundwater, and isolate any uranium that may still be present in soils. DMC continued installing the final cover over the unlined tailings disposal areas (TDAs 1, 2, and 3) and continued with process water evaporation in EP-6.
|The Department of Health approved DMC's groundwater protection plan, in which DMC stated they would apply for alternate concentration limits (ACLs). The company believes that it is not practically achievable to comply with the site groundwater protection standards, required at point of compliance (POC) wells, using technologies DMC identified in past corrective action plans. DMC completed installation of final cover soils over two-thirds of the unlined tailings, and conducted radon flux measurements over the area. DMC demolished most of the remaining structures, septic system, power poles and wiring, and disposed the materials into TDA-4. During soil cleanup activities, DMC discovered soils contaminated with bunker oil on the west side of the demolished mill building, and found soils with elevated thorium levels. DMC continued with process water evaporation in EP-6.
DMC characterized the oil and thorium contamination along the tailings line and implemented cleanup activities. The Department of Health approved implementing their final status survey work plan to guide final soil cleanup. DMC completed demolition of the dry and security buildings. DMC also completed installation of the final cover soils over the unlined tailings disposal areas (TDAs 1, 2, and 3) and continued with process water evaporation in EP-6. Due to a longer than anticipated timeframe to address contaminated soils, DMC plans to close TDA-4 and complete the final radon barrier by the end of 2017.
The Department of Health amended DMC's radioactive materials license to complete the surface reclamation by the end of 2017. DMC demolished the original 1950s-era office (the last remaining millsite structure) and installed the final radon barrier over tailings disposal area 4 (TDA 4). The Department of Health amended DMC's radioactive materials license again at the end of the year to require complete installation of rip-rap erosion protection over the final radon barrier by the end of 2018. DMC continued with soil cleanup activities and with process water evaporation.
|DMC will install rip-rap erosion protection over the final radon barrier embankments and complete radon flux monitoring in 2018. The only structures remaining onsite in 2018 are a portable trailer used as an office and a storage shed located adjacent to EP-6. Department of Health expects DMC to submit their final status survey report in 2018 and will confirm DMC's results based on 70 split soil samples. DMC will continue data collection for their ACL application, which they anticipate submitting to DOH in 2018. Evaporation of process water from EP-6 will be a priority for DMC in 2018.
|DMC submitted their draft completion report for Phase 1 of soil cleanup, covering all areas of the millsite except for Evaporation Pond 6, and submitted initial and revised Alternate Concentration Limit (ACL) applications. ACLs are groundwater protection standards that consider site-specific water use. Our regulations allow licensees to apply for ACLs if the groundwater protection standards listed in our regulations are not practically achievable at compliance wells. DMC's application comes after 30 years of groundwater characterization and assessment of groundwater remedial alternatives and is a significant step towards decommissioning of the uranium millsite. DMC also completed and revegetated the final soil and riprap barriers over the waste disposal areas. The only structures remaining onsite are a portable trailer used as an office and a storage shed located adjacent to Evaporation Pond 6. Evaporation of process water from EP-6 is a priority for DMC in 2018 and 2019.
The Department of Health renewed DMC's radioactive materials license to reflect current closure conditions.This included deletion of license conditions that are no longer relevant to millsite closure, addition of a license condition to allow bench and pilot scale testing of process water, revised operating and reporting requirements for Evaporation Pond 6 (EP-6), and inclusion of a December 31, 2022, milestone for EP-6 decommissioning. Ongoing closure activities are reduction of process water in Evaporation Pond 6, continued soil cleanup and review of DMC's alternate concentration limit (ACL) application.