2011-08-18_HYDROLOGY - M1977306

• Permit No: M1977306
• IBM Index Class Name: HYDROLOGY
• Doc Date: 8/18/2011
• Doc Name: Colorado Discharge Permit System
• From: Water Quality Control Division
• To: Cotter Corporation
• Email Name: GRM
• Media Type: D
• Archive: No

COLORADO DEPARTMENT OF PUBLIC HEALTH AND ENVIRONMENT, Water Quality Control Division
Rationale — Page 10, Permit No. C00036251
To conduct a quantitative RP analysis, a minimum of 10 effluent data points from the previous 5
years, should be used. The equations set out in the guidance for normal and lognormal
distribution, where applicable, are used to calculate the maximum estimated pollutant
concentration (MEPC). For data sets with non - detect values, and where at least 30% of the data
set was greater than the detection level, MDLWIN software is used consistent with Division
guidance to generate the mean and standard deviation, which are then used to establish the
multipliers used to calculate the MEPC. If the MDLWIN program cannot be used the Division's
guidance prescribes the use of best professional judgment.
For some parameters, recent effluent data or an appropriate number of data points may not be
available, or collected data may be in the wrong form (dissolved vs. total) and therefore may not
be available for use in conducting a RP analysis. Thus, consistent with Division procedures,
monitoring will be required to collect samples to support a RP analysis and subsequent decisions
for a numeric limit. A compliance schedule may be added to the permit for the request of a RP
analysis once the appropriate data have been collected.
For other parameters, effluent data may be available to conduct a quantitative analysis, and
therefore a RP analysis will be conducted to determine if there is RP for the effluent discharge to
cause or contribute to exceedances of ambient water quality standards. The guidance specifies
that if the MEPC exceeds the maximum allowable pollutant concentration (MAPC), limits must
be established and where the MEPC is greater than half the MAPC (but less than the MAPC),
monitoring must be established. Tables VI -2A and VI -2B contains the calculated MEPC
compared to the corresponding MAPC, and the results of the reasonable potential evaluation, for
those parameters that met the data requirements for Outfall OO1A and 002A, respectively. The
RP determination is discussed for each parameter in the text below.
Table VI -2A — Reasonable Potential Analysis for Outfall 001A
Zn, TR (µg/1)
Radium 226 +228 (pCi /1)
MEPC
26
30 -Day Average
WQBEL
(MAPC)
2000
4.2 s 5
Reasonable
Potential
No (Qual)
Yes (Qual)
7 -Day Ave or Daily Max
MEPC
26
6.5
Table VI -2B — Reasonable Potential Analysis for Outfall 002A
WQBEL
(MAPC)
Reasonable
Potential
NA
Parameter
Zn, TR (pg/
Radium 226 +228 (pCi /1)
MEPC
30 -Day Average
WQBEL
(MAPC)
Reasonable
Potential
0.018 2000
NA 5
No
0.018
Yes (Quaff) 26
7 -Day Ave or Daily Max
MEPC
WQBEL
(MAPC)
Reasonable
Potential
NA NA
NA ; NA
3. Pollutants Limited by Water Quality Standards
— This parameter is limited by the water quality standards of 6.5 -9.0 s.u., as this range is
more stringent than the range specified under the Regulations for Effluent Limitations and the
federal ELGs. This limitation is the same as that contained in the previous permit . and is imposed
effective immediately, for Outfalls OO1A, OO1B, 002A, 002B and 002C.