Dames & Moore, 1999 - USDA Forest Service

native soil is of higher permeability than the tailings materials, the water is relatively confined, creating a
hydrostatic head pressure in the groundwater beneath a portion of the tailings piles. The pressure likely
forces some of the groundwater upward into the tailings materials during the spring months.
However, as the snowmelt diminishes and groundwater flow decreases, the hydrostatic head decreases and
eventually diminishes. By September, and for the remainder of the fall and winter months. the groundwater
is assumed to generally flow from the tailings materials into the groundwater beneath the piles. Data
loggers installed in seven of the groundwater monitoring wells in May-June 1997 will allow further
confirmation of this phenomenon during the winter months.
8.2.5 Other Physical Site Features
8.2.5.1 Mine and Honeymoon Heights
The underground mine features were evaluated by reviewing maps completed during and after the mining
was conducted. The mine was not entered as part of the RI due to safety considerations. The review of the
mine maps indicated the presence of over 56 miles of underground workings. The majority of underground
workings below the 1500-level main portal were backfilled with tailings during the operation of the mine.
The workings above the main portal level are reported to be open and were not backfilled.
The mine includes 16 primary levels and approximately the same number of secondary levels which are
connected by two shafts and a series of inclines. The lowest level in the mine, the 2500 'level, is
approximately 800 feet below the Railroad Creek valley floor at the Site. The uppermost level of the mine,
the 300 level, is approximately 1,400 feet above the valley floor.
The majority of the mine workings were completed in the area generally beneath the 1100- to 300-level
portals; the horizontal distance of the majority of the mine workings is approximately 3,000 feet. The north
westernmost extent of the underground mine workings is on the 2325-level that was terminated beneath the
1500-level ventilator portal, and is approximately 800 feet below the valley floor. The south easternmost
extent of the mine is on the 1500-level that was terminated approximately 13,600 feet from the 1500-level
ventilator portal, and is approximately 700 to 800 feet below Copper Creek Basin. No near-surface stopes
are noted to exist on the mine and geologic maps below the 1000-level portal. The transverse faults which
intersect both of the 1500-level tunnels are noted to be covered with glacial till below the 1100-level mine
portal.
8.2.5.2 Mill, Mine Support Area, and Waste Rock Piles
The interior of the mill facility was not evaluated in depth due to safety considerations and because the
USGS had completed an assessment earlier. A sample of wall insulation was collected during the RI to
assess the presence or absence of asbestos-containing inaterials (ACMs); no ACMs were found. Some
unprocessed ore-(less than approximately 20 cub'ic yards), as well as limited quantities of concentrate, are
located in the remains of the mill building.
The maintenance building is located northwest of the mill building. The initial building was constructed by
Howe Sound Company and was utilized to maintain vehicles. The building was lost to a fire but was
replaced in the 1970s by Holden Village for maintenance of the transport vehicles and other equipment.
Petroleum hydrocarbons in the form of fuel products and lubricants are utilized in the operations. A newer
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17693-005-019Uuly 28. 1999;10:24 AM;DRAFTFINAL RI REPORT