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

Table A -5b
Low Flows for the Dolores River at the JD -7 And JD -9 Mines' WWTF
Low Flow
(cfs)
Annual
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
1E3
Acute
1.60
21.00
22.00
25.00
19.00
3.30
1.80
1.70
1.60
2.20
7.50
15.00
18.00
7E3
Chronic
1.90
21.00
21.00
25.00
24.00
7.30
2.00
1.90
1.90
2.30
8.50
15.00
19.00
30E3
Chronic
3.30
21.00
23.00
30.00
19.00
3.30
3.30
3.30
3.30
3.30
9.00
15.00
20.00
Cotter Corporation Water Quality Assessment C00036251
Stream Segment COGULD02 - Mainstem of the Dolores River
To determine the low flows of the Dolores River upstream of East Paradox Creek, data from USGS gage
station 09169500 (Dolores River at Bedrock, CO) were used. This flow gage is located less than three
miles upstream of the confluence of East Paradox Creek with the Dolores River and provides a
representative measurement of the upstream flow because there are no diversions or confluence of
significance between the flow gage and the confluence of East Paradox Creek with the Dolores River.
To determine the low flows of the Dolores River upstream of Bull Canyon, the same flow data above
were used. Although the USGS gage station 09169500 is located approximately 30 miles downstream of
the confluence of Bull Canyon with the Dolores River, the local Water Commissioner indicated that the
Dolores River would not gain flow of any significance between the two locations. The local Water
Commissioner confirmed that flow data from USGS gage station 09169500 would be representative of
flow at the confluence of Bull Canyon with the Dolores River.
The annual 1 E3, 7E3 and 30E3 low flows were calculated using U.S. Environmental Protection Agency
(EPA) DFLOW software. The output from DFLOW provides calculated acute and chronic low flows for
each month.
Flow data from January 01, 1999 through December 30, 2009 were available from the gage station. The
gage station and time frames were deemed the most accurate and representative of current flows and
were therefore used in this analysis.
Based on the low flow analysis described previously, the low flows available to the JD -7 and JD -9
Mines' WWTF were calculated and are presented in Table A -5b.
During the months of April, May, and November the acute low flow (1E3) calculated by DFLOW
exceeded the chronic low flow. The chronic 7E3 low flow exceeded the chronic DFLOW during the
month of November. In accordance with Division standard procedures, the acute low flow (and 7E3 low
flow) was thus set equal to the chronic low flow for these months.
JD -7 Mine - Outfall 001
The ratio of the low flow of the Dolores River to the JD -7 Mine's WWTF design flow is 11:1.
Appendix A (WQA V 7.0)
Page 13 of 23 Last Revised 06/10/10 /AO