HYDRO20461

• Permit No: C1980001
• IBM Index Class Name: Hydrology
• Doc Name: COLOR DISCHARGE PERMIT SYSTEM CDPS RATIONALE AMENDEMENT 1
• Permit Index Doc Type: NPDES
• Media Type: D
• Archive: No

COLORADO DEPARTMENT OF PUBLlC HEALTH AND ENVIRONMENT, Water Quality Control Division
Amendment No. 1 -Rationale. Page 3, Permit No. CO-0032638
2. Calculation o(Water Ouafity-Based E(lluent Limitations: Amass balance equation was used to determine the effluent
concentrations that would not violate the allowable in-srrearn concentrations defined by the water quality standards
(except in the case of pH, where the limits are set directly Jrom stream standards or effluent regulations without
using a mass balance approach). The mass balance equation follows.
MtQt- MrQr
M1 =
Qr
Where:
Q, =Upstream low flows from Pan I/I.B.2
Qr =Average daily effluent Jlow (maximum reported Jlow)
Q, =Combined downstream Jlow (Q, + Q~
Mr =Upstream background pollutant concentration from II/.B.l (Zero)
Mr =Unknown; Mazimurn allowable effluent pollutant concentration calculated using moss balance equation
Mr =Maximum downstream allowable pollutant concentration (stream standard)
The permittee has conducted extensive research and evaluation of stream flow and effluent Jlow patterns and
submitted data showing that a ratio of stream Jlow to combined discharge Jlow for outfalls 002, 003, 004 and 006 is
10:1 or greater. This ratio was used in calculating water quality based effluent limitations jar existing outjall 004
and new outfall 007. Using this ratio satisfies permittee concerns and eliminates the need to determine specific
stream low flows and effluent maximum flows. Regardless of the actual flows, as long as the ratio is not less than
10:1 at any time, the resulting effluent limitations will be protective of the receiving water quality classifications and
standards. This amendment looks at potential limitations for the same pollutants as were looked at in the origins[
renewal permit rationale (see Table V-3) and will specify which pollutants shall be limited. The permittee shall
establish and maintain a stream gaging station in Trout Creek as close as practical upstream of the point of
confluence between Koll Ditch b3 and Trout Creek. The permit as amended will include the requirement jot the
permittee to measure upstream flow at this station and report the results, as well as the ratio between the upstream
flow and the effluent. This will ersable the Division ro verify that this ratio is not exceeded. As stated previously, if
no discharge occurs from both outfalls 004 and 007, the permirtee will not be required to monitor stream Jlow.
Because of the nwthenwtical relationship between Jlow, pollutant concentration and pollutant mass, concentration
limitations calculated using this method implicitly limit insrream pollutant mass to the maximum allowable level.
Thus, only concentration limitations need to be specified in the permit. Mass limitations are not required. A
summary of the mass ba[arsce calculations are shown and discussed in V.A.3.
3. Discussion of Effuent Limitations
a) Regulations (or Effluent Limitations: The Regulations Jor Effluent Limitations (10.1.0), apply to the conventional
pollutants. For this facility, the limitations for Oil and Grease are based on this regulation.
b) Applicable Federal Effuent Guidelines and Standards: The federal guidelines which apply to this type ojjaciliry
are found under 40 CFR 434, titled EfRuenr Guidelines For Coal Mining Facilities. The limitations which apply
are shown in the following table.
Table V-2 -- Federal Standards
Parameter 30 Day Avg Concentration Daily Mos. Concentration
pH, s. u. (minimum -maximum) ---6.0 - 9.0---
Total Suspended Solids, mg/P• 35 70
Total /ton, mg/f • 3.5 7.0
Settleable Solids, mP/P" N/A 0.5
• mess parameters subjerr ro Burden of Proof Rrquiremenu, srr nrxr srrtion.