The Alder Mill site was an ore concentrating mill for gold and copper. The site is situated on a 75 acre plot located in Okanogan County approximately 0.4 mile from the Town of Twisp, Washington and is in close proximity to the Methow River. The Alder Gold and Copper Company, owned by Mr. Eugene Feltz of Portland Oregon, is responsible for the site. The mill was operated from 1949 to 1952. Historically, two unlined and undiked ponds (upper and lower) were used to store wastewater and silt (tailings) from the mill’s operation. The tailings ponds occupy approximately 10 acres of the site. The upper pond is situated in the bed of an unnamed intermittent stream, and is approximately 650 feet long, 150 feet wide, and an average of 12 feet deep. The upper pond is partially vegetated. A perennial standing water pond fed by springs is located at the upstream end of the tailings impoundment. The lower, smaller pond is located approximately 400 feet from an irrigation ditch and is completely unvegetated. Mill tailings were disposed of into the ponds between 1949 and 1952. Runoff events caused by heavy rainfall have sporadically resulted in the release of contaminants of concern off the site. A 1952 failure of the upper pond resulted in the transportation of tailings approximately 2,200 feet downstream to a nearby residence. Contaminated water infiltrated down the sides of the well casing, rendering the water unfit to drink.
EPA is overseeing a removal action being performed by the PRP under an Agreed Order on Consent. Activities to date include review of PRP documents, site visits to oversee pre-removal site preparation activities, and completion of an XRF field screening characterization of pre-removal concentrations along access roads. Documents reviewed include a workplan for decontamination of the mill structures and excavation and off-site disposal of the tailings in the lower tailings pond. Other documents reviewed include plans for pre-decontamination site preparation activities.
a) Mill Buildings
The mill buildings will be demolished after materials have been removed. Soils surrounding the mill buildings will be removed or removed and capped (such that positive drainage is maintained) to meet MTCA method A levels, as deemed practical. Soils from the building may be placed in an on-site repository, or taken to an acceptable off-site landfill, as deemed appropriate. Materials from the building may be recycled, if materials such as wood or steel can be decontaminated through cleaning and/or planing. Intermediate process materials and concentrates will be sent to smelters if materials are recoverable. If not, these materials will be disposed of appropriately in an offsite landfill. The foundation of buildings will be evaluated to determine if they may be adequate caps to prevent migration of any contaminants that may be located below it. If it is deemed adequate, it will be left in place after decontamination to meet MTCA method A levels, as deemed practical. If foundations are inadequate to serve as caps or are nonexistent, underlying soil will be removed as above. Disturbed areas will be seeded with native grasses.
b) Mill Pond (also known as the lower tailings pond)
The mill pond located immediately adjacent to the mill buildings will permanently fenced to preclude access or be removed to an onsite or offsite repository to meet MTCA method A levels, as deemed practical. If removed, the site will be graded to maintain positive drainage and seeded with native grasses.
c) Tailings Pond (also known as the upper tailings pond)
The tailings pond encompasses approximately 10 acres of the site. The evaluation of whether this area poses a threat to area groundwater is ongoing. If action is warranted, this will be addressed in an Amendment to this Action Memorandum.
d) Other Activities
The site including the mill buildings, mill pond, and upper tailings pile, will be fenced to preclude access. This will prevent unauthorized access while the mill buildings are still standing and prevent direct contact hazards with the ponds for trespassers and some terrestrial wildlife. This will also control access during construction activities.
Following completion of structure decontamination and removal of tailings from the lower tailings pond, confirmation samplings will be performed in accordance with a QAPP/SAP currently being prepared by the START. Upon satisfactory completion of decontamination and tailings/soil removal efforts, the mill structures will be demolished, and disturbed areas will be graded and seeded with native vegetation.
Progress of planned removal activities has been somewhat hindered by late and incomplete submissions by the PRP.
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