2018-03-01_HYDROLOGY - C1981010 ‎(2)‎

• Permit No: C1981010
• IBM Index Class Name: Hydrology
• Doc Date: 3/1/2018
• Doc Name: CDPS/NPDES Permit
• From: Department of Public Health & Environment
• To: DRMS
• Permit Index Doc Type: NPDES
• Email Name: RAR
• Media Type: D
• Archive: No

COLORADO
1 Department of Public
A�6 l Health b Environment
Determination of the Antidegradation Based Average Concentrations
Water Quality Assessment
Antidegradation based average concentrations (ADBACs) are determined for all parameters except ammonia,
by using the mass -balance equation, and substituting the SCT in place of the water quality standard, as shown
in the following equation:
Where,
ADBAC = SCT X Q3- MI x QI
Q2
Qi = Upstream low flow (1 E3 or 30E3 based on either the chronic or acute standard). For
aquatic life parameters, this is zero
02 = Current design capacity of the facility
03 = Downstream flow (Q, + 02)
M1 = Current ambient water quality concentration (From Section III)
SCT= Significant concentration threshold
The ADBACs were calculated using the SCTs, and are set forth in Table A -16a.
Concentration Significance Tests
The concentration significance determination test considers the cumulative impact of the discharges over
the baseline condition. In order to be insignificant, the new or increased discharge may not increase the
actual instream concentration by more than 15% of the available increment over the baseline condition. The
Pae 36 of 40 . .
4300 Cherry Creek Drive S., Denver, CO 80246-1530 303-692-2000 www.colorado.gov/cdphe/wqcd I
Table A-16
SCTs and ADBACs Outfall 025
Pollutant
Ql(cfs)
Q2 (cfs)
I Q3 (cfs)
I M1
SCT
ADBAC
Aquatic Life Parameters
As, Dis (pg/1)
0
3.3 3.3 0.38
51
51
Cd, Dis (pg/l)
0
3.3 3.3 0
0.075
0.075
Cr+3, Dis (pg/l)
0
3.3 3.3 0
13
13
Cu, Dis (pg/l)
0
3.3 3.3 0.89
6.8
6.8
Fe, TR (pg/1)
0
3.3 3.3 600
150
150
Pb, Dis (pg/l)
0
3.3 3.3 0.0083
0.56
0.56
Mn, Dis (pg/l)
0
3.3 3.3 1772
285
285
Hg, Tot (pg/1)
0
3.3 3.3 0
0.0015
0.0015
Ni, Dis (pg/1)
0
3.3 3.3 2.4
10
10
Se, Dis (pg/1)
0
3.3 3.3 0.77
1.3
1.3
Ag, Dis (pg/1)
0
3.3 3.3 0
0.069
0.069
Zn, Dis (pg/l)
0
3.3 3.3 2.1
25
25
Human Health Parameters
As, TR (pg/1)
113
3.3 116.3 0
0.02
0.7
Cr+3, TR (pg/l)
113
3.3 116.3 0
15
529
Hg, Tot (pg/1)
113
3.3 116.3 0
0.0015
0.053
Concentration Significance Tests
The concentration significance determination test considers the cumulative impact of the discharges over
the baseline condition. In order to be insignificant, the new or increased discharge may not increase the
actual instream concentration by more than 15% of the available increment over the baseline condition. The
Pae 36 of 40 . .
4300 Cherry Creek Drive S., Denver, CO 80246-1530 303-692-2000 www.colorado.gov/cdphe/wqcd I