HYDRO23023

• Permit No: C1981020
• IBM Index Class Name: Hydrology
• Doc Date: 4/22/1991
• Doc Name: RATIONALE FOR PUBLIC NOTICE
• Permit Index Doc Type: NPDES
• Media Type: D
• Archive: No

COLORADO DEPARTMENT OF HEALTH, Water Quality Control Division
R:stionale - Page 6. Permit No. CO-0040827.
'/I. TERMS AND CONDITIONS OF PERMIT
a) Active Mining: Even though the mine is not presently being
wor e~ermit is written for an active mine. The permit tee
has requested an active mining permit so as to be able to start
mining without waiting for reactivation of the permit.
The only limitations which are applicable for discharge point
002 are indicated in Table VI-2. Because discharge point 002 is
strictly for mine drainage, this discharge is not eligible for
the storm event exemption conditions under active mining
requirements.
The following discussion is applicable for discharge points 001,
003, 004, 005, 007 and 008.
Limitations for pH and oil and grease apply to all discharges,
regardless of precipitation conditions. Additionally, TSS and
total iron samples should always be taken. The permittee may
submit documentation proving that the discharge was
precipitation induced, if it wishes to obtain a waiver of the
total iron and total suspended solids limitations. The proof of
the size of the precipitation event consists of:
(i) rain gauge data or the volume of water contained in the
snow, based upon calculations from actual snow samples;
(ii) the sample results for TSS, iron, pH, settleable solids and
oil and grease; and
(iii) influent/effluent metered flow.
It is only upon acceptance by the Division of said proof that
the settleable solids limitation will apply in place of the TSS
and total iron limitations for precipitation events that are
less than or equal to the 10-year, 24-hour storm event. Failure
to submit the required information will result in the
disallowance of any exemption.
Similarly, for precipitation events greater than Che 10-year,
24-hour event (or equivalent snowmelt volinoe), proof of the size
of the storm will consist, again, of (i)-(iii), above. Upon
acceptance of proof that discharge was caused by precipitation,
compliance with TSS, total iron and settleable solids
limitations will be exempted. This means such a discharge would
be subject to pH and oil and grease limitations only for the
exempted timeframe. The Division allows these exemptions for a
period of up to 48 hours after measurable rainfall has stopped.
For snowmelt, the Division allows these exemptions for a period
up to 48 hours after inflow to the sedimentation pond has
ceased. Again, failure to submit the required information will
result in the disallowance of the exemption.