Dames & Moore, 1999 - USDA Forest Service

tunnel which starts at the ventilator portal extends approximately 13,200 feet to the southeast; the tunnel
does not daylight and, based on a review of both underground mine and topographic maps, there is at least
800 feet of bedrock cover for the entire length of the tunnel. Figure 4.1-12 only displays the portion of the
1500-level tunnel which was noted on the maps to contain mineable concentrations of the economic metals.
The ore was removed by a process described as a "modified form of sublevel stoping" (McWilliams, 1958).
The ore body was drilled from the tunnels, or drifts, installed parallel to the ore body. A series of ore chutes
were constructed in the rock to connect the ore body with the primary tunnels below the chutes. The rock
was then blasted and the broken rock removed utilizing ore cars which transported the ore to the mill
through the 1500-level main tunnel. The openings developed in the ore rock are known as stopes. The
width of the stopes was limited to the width of the ore body, which was approximately 80 feet. The height
of the stopes varied throughout the mine. As the mining proceeded, the stopes were enlarged as much as
practicably possible in order to take advantage of the fall to break the rock after it had been blasted.
Referring to Figure 4.2-14, which is oriented parallel to the ore body, the largest of the stopes are located
above the 1500-level, and is noted to be approximately 600 feet in height.
Figure 4.1-5c also shows that the different levels of the mine above the 1500-level were connected by a
series of inclines, two shafts, and air passage ways. As the mining proceeded below the 1500-level, the ore
had to be removed utilizing one of two shafts. Sumps were installed in each of the shafts to pump water
during operation. The pumps ,are noted in mine specifications to be 600 gallons per minute capacity
(McWilliams, 19'58); no records of actual pumping rates were discovered. An interview with a mining
I
engineer who was en~ployed at the mine for the entire period of operation, indicated that the majority of the
mine water originated from diffuse sources above the 1500-level. The water from above the 1500-level was
intercepted, when possible, to the drainage trench in the floor of the 1500-level tunnel (personal
communication with John Blye, 1997).
The mining extended below the 1500-level to the 2500-level, which is approximately 800 feet below the
floor of the Railroad Creek valley at the Site. Referring to Figures 4.1-13 and 4.2-14, the northernmost of
the mine workings is the 2,325 level which is noted to terminate slightly north of the 1500-level ventilator
portal. Approximately two-thirds of the stopes below the 1500-level were backfilled with slurried tailings
materials by constructing concrete bulkheads.after sealing the fractures and joints in the .rock with
pumping in the slurry behind the walls, and decanting the water after the slurry was placed (McWilliams,
1958).
The initial scope of the RI included sampling and analysis of the water within the mine. The proposed
sampling program assumed that the one of the two portals at the 1500 level were open and safe for human
access. However, it was discovered during the RI that both of the 1500-level portals were collapsed, and
four of the remaining six mine portals above the 1500 level were also collapsed. A review of the mine
workings and mine maps by both a mining engineer and a mining subcontractor to Dames & Moore
indicated that the mine was not safe for entry without first making repairs to and reopening the 1500-level
portal (personal communications with James Knowlson, JSK & Assoc., 1997, and Okie Ross, Atlas Fausett
Contracting, 1997). However, it appears that the mine maps and mine portal drainage chemistry provide
adequate data for RI characterization (refer to Section 6.5.1 for additional discussion of the underground
mine and portal drainage chemistry).
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17693-005-0 19Uuly 19.1999;4:5 1 PM:DRAFT FINAL RI REPORT