HYDRO23049

• Permit No: C1981023
• IBM Index Class Name: Hydrology
• Doc Date: 5/23/2000
• Doc Name: REVISED PROBABLE HYDROLOGIC CONSEQUENCES CHIMNEY ROCK MINE
• Media Type: D
• Archive: No

Probable Hydrologic Contrpuencet - Chimnry Rack Mine
The saturation index (SI) is used to determine if a mineral will dissolve into or precipitate from
solution. A negative SI indicates that the water is undersaturated with respect to the mineral and,
if present, the mineral should dissolve. If the SI is positive, the water is supersaturated with
respect to the mineral, and the mineral should precipitate from solution. An SI near zero indicates
a condition neaz equilibrium (Williams and Clark, 1994).
Table 1
Saturation Indices
Chimney Rock Mine
Mineral Phase
Well Name Carbonate Minerals Sulfate Minerals
Calcite Dolomite Gypsum Epsomite
W6 -0.13 -0.95 -2.00 -4.93
W16 0.49 0.96 -1.47 -3.76
The SIs as presented in this table are very similar to those determined in Williams and Clark
study. Examining the SIs from the well W 16, the calcite and dolomite materials have positive
saturations indices; therefore, the water is saturated with respect to these minerals and increases
in TDS due to these minerals are not anticipated. Sulfate minerals (gypsum and epsomite) have
negative 5is; therefore, the water is not saturated with respect to these minerals and increases in
TDS would occur if sulfate minerals are present in the spoil. Oxidation of pyrite in the spoil could
produce sulfate at Chimney Rock.
The duration of the elevated TDS can be predicted based upon the oxidation of pyrite in the
reclaimed spoils pit aquifer. Based upon these analyses performed by Williams and Clark
regarding the Seneca II Mine the dominant anion would most likely be sulfate and that the
oxidation of the pyrite would be the main source of TDS in the spoil pit water. The average
pyritic sulfur concentration in the spoils is 0.36% by weight (six samples, Table 4, section 2.04.6
of the Chimney Rock permit application). Since pyrite is 53 % sulfur by weight, then the pyrite
roughly comprises 0.53 %p of the spoil. Based upon the exhaustion time for 0.20%p pyrite of 300
years (Williams and Clark, 1994), then the time of the elevated TDS discharge would be over 600
years. The 600 year duration would be reduced indirect proportion to the amount of "piping" that
occurs as a result of channelization within the spoils. This type of flow has been documented at
other mines, and results in not all the pyrite in the spoil being oxidized. Prediction of the amount
of piping that will occur is not possible, but assuming that 25% of the water could pipe through
the spoils pile, then the duration of elevated TDS concentrations could be reduced by 25 %p to 450
years.
Renscd hydrologic-05;~p5-23-0(g'OOAM) 11