HYDRO24575

• Permit No: C1981019
• IBM Index Class Name: Hydrology
• Doc Date: 2/4/1999
• Doc Name: RATIONALE FOR PUBLIC NOTICE
• Permit Index Doc Type: NPDES
• Media Type: D
• Archive: No

COLORAL>0 DEPARTiNEM OF PUBLIC HEALTH AND ENVIRONMEM, Y4ater Q~aliry Control Division
Rationale Page 12. Permit No. CO-0045!61
For rainfall. to waive TSS and total iron limitations, it is necessary to cemonstrate that discharge occurred
within 48 hours after measurable precipitation has stopped. To waive :'ettleable solids limitations, it is
necessary to prove that discharge occurred within 48 hours after precipitation greater than the 10-year,
24-hour event has stopped.
For snowmelt, to waive TSS and total iron limitations, it is necessary to demonstrate that discharge
occurred within 48 hours after pond inflow has Stopped. To waive settleable solids limitations, it is
necessary to prove that discharge occurred within 48 hours after pond inflow volume greater than the
10-year, 24-hour event has stopped.
c) Antidea,~radation: Since the receiving waters are designated as Use P,~otected, an antidegradation review is
not required for these discharges pursuant to section 31.8(2) (b) of ~Ite Basic Standards and Methodologies
fgr Surface Water.
d) . alinity Regulations: In compliance with section 61.8 (2) (1) of the Colorado Discharge Permit Svstem
Regulations. the permittee shall monitor for total dissolved solids on a quarterly basis. Samples shall be
taken at the effluent discharge points. Salinity requirements are included in Part I.B.2. of the permit.
e) Whole F~Iuent Toxicity (WEB Testing: No discharges from this facility are subject to WEI'testing
requirements at this time.
Surface runoff outfalls (OOla, 002a, 003a, 004a, OOSa, 006x, 007a, 008x, 009a, OIOa) are exempted
because:
i) Iron is the primary constituent with the potential for toxicity in thtr facility surface runoff discharges.
Iron is much less toxic than other metals -the toxicity fevel far aquatic life is much higher for iron;
ii) Contact time is short, little time is available for oxidation to significantly increase the concentration of
iron in a discharge;
iii) Surface runoff discharges are expected to occur when stream flows are high and instream quality is
deteriorated by non-point source pollution and other sources. Temperatures of surface runoff (especially
snowmelt) are expected to be typically lower than the temperature of mine drainage and pit water. This
would slow oxidation.
If specific information is received in the furore that indicates the discharge has reasonable potential to cause
toxidry to aquatic life, the Division can reopen the permit as necessary to add WET requirements.
the permittee has agreed to meet a limitation of 1.0 mg/Pfar total recoverable iron for pit ptunpage water
(outfalls 004b, 007b, 0086, 0096, OIOb) and vehicle wash water (outfall 002b) in lieu of performing WET
testing on this water. They have stated that they will not pump this water to a pond unless laboratory
analysis shows that TSS and total recoverable iron limitations will not be exceeded.
Reference literature is incomplete and not consistent regarding the concentration where iron becomes toxic.
However, 1.0 mg/P is commonly accepted as a level where toxicity is rot found in alkaline water such as
that in Colorado. Additionally, this value is the total recoverable iron standard for segmeru I, which
includes the Yampa River below confluence with the immediate receiving waters. Discharges meeting this
limitation will protect the uses in the Yampa River.
3. Storritwater Evaluation: Starmwater from active and inactive coal mining sites that has been contaminated by
contact with overburden, raw material, intermediate products, byproducts, finished products or waste products
located at the site is required to be covered by a Colorado Discharge Permit System (CDPS) permit in order to
be discharged to waters of the state. Ibis coverage may be obtained under either a CDPS Industrial
Wastewater Discharge Permit or a CDPS Stormwater Discharge Permit.