REV02192

• Permit No: C1981022
• IBM Index Class Name: Revision
• Doc Date: 7/1/1999
• Doc Name: UPDATE PHC TR 34 SANBORN CREEK MINE PN C-81-022 OXBOW MINING INC
• From: DMG
• To: OXBOW MINING INC
• Type & Sequence: TR34
• Media Type: D
• Archive: No

(2) A submittal to the Division of any required written approval from the Colorado
Department of Public Health and the Environment (CDPHE) for this discharge
rate. The currently approved Colorado Water Quality Control Division NPDES
permit states that the average flow at outfall Olt (the mine water discharge
point) can not exceed 0.278 million gallons per day (193 gallons per minute)
while the maximum daily flow at that point can not exceed 0.38 million gallons
per day (264 gallons per minute).
(3) An update of the PHC [hat provides mass balance analyses [hat predict [he effect
of the mine water dischazge on the water quality in the North Fork of the
Gunnison River. The mass balance analyses should be performed using the
geochemical data from the most recent water quality analysis of the mine water
and should be run for those chemical constituents whose concentrations are
close to the compliance limits for receiving stream standazds. The Division
suggests that Total Dissolved Solids (TDS), chloride and iron be included in this
list. The Division also suggests that the analyses should use the lowest daily
minimum flow of the North Fork of the Gunnison River for each month that the
discharge will continue;
(4) If the mass balance analyses mentioned above demonstrate that the water
quality in the North Fork of the Gunnison River is approaching compliance
limits for material damage or CDPHE receiving stream standards, the Division
may require that the permit application be updated with the list of current
surface and ground water users within one half mile of the permit area. The
Division may require that the surface and ground water uses closest to the point
of dischazge of mine water be monitored for field pazameters. This hydrologic
monitoring would include representation of baseline conditions as well as for
the period during which the 2,000 gpm mine water discharge rate is being used;
(5) If the above mentioned analyses show that the water quality in the North Fork of
the Gunnison River will exceed compliance limits due to the mine water
discharge rate of 2,000 gpm, the Division will request that OMI lower the rate
of mine water discharge until the compliance limits aze met. The lower rate of
mine water discharge possibly would vary depending on the monthly variations
in the flow in the North Fork of the Gunnison River and would be based on
calculations submitted to the Division by OMI.
(6) During the period when the mine water dischazge rate is at 2,000 gpm, the
Division believes that a monthly full suite analysis and a weekly field analysis
should be performed on the mine water at the NPDES outfall;
B. If OMI intends to discharge mine water at the original maximum discharge rate of
425 gpm discussed in the PHC, then the Division would like OMI to submit to the
Division the following information: