HYDRO31270

• Permit No: M1980244
• IBM Index Class Name: Hydrology
• Doc Date: 6/3/1994
• Doc Name: RATIONALE FOR PUBLIC NOTICE
• Media Type: D
• Archive: No

t .
COLORADO DEPARTMENT OF HEALT ,Water Quality Cantral Division
Rationale -Page 3, Permit Na. CO-0024562
Hydrogeologic studies have examined the effects that this operation may have upon the quantity and quality
of waterJlowing jrom the Carlton Tunnel. The results ojllu studies indicate that the Jlowrate from the
tunnel may increase very slightly -ors the order 0.] rfs, and that pH and metal concentrations may remain
unaffected. While there is uncertainty associated with the various factors that wen considered in the
analyses that wen performed, it is likely that the monitoring of tiu Carlton Tunnel that is currently required
through the permit will be adequau to detect any sign(ficant changes in flow, pH or metals concentrations
that may be caused by the mining operation. This should apply even to metals that are not currently being
monitored, as the same jacton that would cause an increase in un-monitored metals concentrations would
similarly increase monitored metals concentrations.
With respect to cyanide, no monitoring ojthe Carlton Tunnel is currently required Even though the
Cresson mining project has been developed with the intent to contain all cyanide solutions within the
distribution system or impervious liners, it is possible jar spills or leaks to occur. Also, the project includes
plans for using cyanide contaminated tailings as part of the liner system. In the event of a release of
cyanide contaminated water, it is likely that such waters would Jlow to surface drainages in the vicinity of
the leach pad, and a separate permit is being written in order to address the potential for such discharges
jrom the Cresson operation.
Stilt, due to presence of various tunnels throughout the mining district which have intercepted and drained
groundwater underlying the area !o be mined, it is possible /hat cyanide contaminated Jlowt may travel
underground and reach the CarUan Tunnel. In order to allow such Jlows to be detected, this permit will be
amended to require quarterly cyanide monitoring of the Carhon Tunnel discharge. This will be done
through the amendment of page Ic and 4.
C. Whole E(Jluent Toxicity
The Division has recently developed new polities and permit requirements related to Whole Effluent Toxicity
(WET). The permit will be amended to include the new requirements, which are explained in the following
discussion.
For this facility, chronic WET testing is required. (See Pans I.A. and /.B. of the permit.)
1) Pnroose of WET Testinv: TTu Water Quality Control Division has established the use ojWET testing as
a method for ident(lying and controlling toxic discharges jrom wastewater treatment facilities. WET
resting is being utilized as a means to ensure that there are no discharges of pollutants "in amounts,
concentrations or combinations which are harmful to the beneficial uses or toxic to humans, animals,
plants, or aquatic 1((e" as required by Section 3.1.11 (1) ojthe Basic Standards and Melhodolosries for
Surface Waters.
2) Instream Waste Concentration i/R'Cl: Where monitoring or lirr+itattans jar WET are deemed
appropriate by the Division, chronic instream dilution as represented by the chronic /WC is critical in
determining whether acute or chronic conditions shall apply. For those discharges where the chronic
IWC is greater than (>) 9.196, chronic conditions apply, where the IWC is less than or equal to (5)
9.1 acute conditions apply. The chronic IWC is determined using tiu following equation:
IWC = [Facility Flow (FFj/(Stream Chronic Low Flow (annual) + FF)j X 100%