HYDRO20248

• Permit No: M1980244
• IBM Index Class Name: Hydrology
• Doc Date: 10/11/1994
• Doc Name: RATIONALE FOR PUBLIC NOTICE
• Media Type: D
• Archive: No

COLORADO DEPARTMENT OF HEALT7i, Water Quality Control Division
Rationale -Page 2, Permit No. CO-0043648
/n order to detect, assess and control any such unplanned discharges should they occur, this permit it intended
to address all potential point source discharges t f pollutants to surface waters of the State which would either
be entirely composed of process waters, or wou4~ be process waters which have been combined with
stormwater.
Current Division policy defines stormwater as a discharge of precipitation induced runoff which results from a
unique storm event. A stormwater discharge commences soon after the beginning of an event and ceases at the
end of the event or soon thereafter, allowing for interflow and discharge. The ezception to this is detention
ponds designed far the sole purpose of collection and/or treatment of stotmwater. Such ponds may discharge
for a short time, such as 36 or 48 hours after the event ceases.
Division policy also defines process water as those discharges which originate from an area of disturbance
which includes areas where ore rs handled, stockpiled, or processed; waste rock rs stockpiled or disposed;
topsoil is stockpiled; adits; tailings ponds; railing piles; mills and mine pits; and stockpiled spent ores. While
waters on the surface running offsuch areas/piles during a unique storm event may be considered as
stormwarer, waters which percolate through a pile and discharges at the toe over an extended period of time,
or water which flows below the ground surface and later resurfaces, are process water.
Examples of the types of discharges to surface waters that will be controlled through this permit are: seepage
from existing tailings piles, teaks or spills from ryanide solution distribution or storage systems, and
stormwater mixed with seepage from waste rock areas.
Orseharges that. will not be controlled through this permit include [hose which consist only of stormwater, or
those which flow to groundwater and do not resurface. Stormx~ater discharges will be addressed separately
through the CDPS stormwater permitting program, and discharges to groundwater that do not resurface and
which are caused by mining operations such as this one are under the jurisdiction of the State's Division of
Minerals and Geology.
With respect to the development ojdischarge points for this permit, it should be noted that some of the
discharge points defined below incorporate a differentiation between flows that include stormwater and those
that do not include stormwater. This will allow data that is collected during baseflow periods to be evaluated
separately from data collected during runoff periods, which may otherwise complicate the detection and
evaluation of any discharges that may occur.
/t should also 6e noted that some consideration x~as initially given to developing separate discharge points for
each phase of the project, in order to account for the different sources of pollutants that will exist, or the
change in their locution over rime. But, since the changes in water qun[iN that might result from any
discharge from rhesr sources would likely be gradual, without n distinct shift occurring at any clearly
discernable pan[ in time, it was decided that having separate discharge paints far each phtue might be an
unnecessan' complicnrion. Still, in order to assist in the ana/uses of the rlnta that will be submitted to the
Division under the ternu ojthis permit, the perminee will he required m indicate in such submittals when
sign~cnnt changes in pollutant sources occurred.
Also, with respect to the construction phase of the project, due to the potential for mobile or temporary
sources of pollutants, there will be no special "Construction Phase" discharge points. However, the permit
will include Besr Management Practices (BMP'sJ jot preventing the discharge of process water or combined
storm/process water into waters of the State during construction operations.

And, with respect to the reclamation phase of the project, the permit will ecpire aul need to be renewed before
reclmruttion of the mine .rite 6egitu. Therefore, d fferent discharge points or special provisions that may be
applicable to the reclamation phase can be added during the permit renewal process.