COLORADO DEPARTMENT OF PUBLIC HEALTH AND ENVIRONMENT 
WATER QUALITY CONTROL COMMISSION 
5 CCR 1002-37
REGULATION NO. 37
CLASSIFICATIONS AND NUMERIC STANDARDS
FOR
LOWER COLORADO RIVER BASIN
. . . .
37.6 	TABLES
. . . .
(2)	Abbreviations:
. . . .
(d)	Temporary Modification for Water + Fish Chronic Arsenic Standard
(i)	The temporary modification for chronic arsenic standards applied to segments with an arsenic standard of 0.02 mg/l that has been set to protect the Water+Fish qualifier is listed in the temporary modification and qualifiers column as As(ch)=hybrid.
(ii)	For discharges existing on or before 6/1/2013, the temporary modification is:  As(ch)=current condition, expiring on 12/31/2021.
(iii)	For new or increased discharges commencing on or after 6/1/2013, the temporary modification is:  As(ch)=0.02-3.0 mg/l (Trec), expiring on 12/31/2021.
(a)	The first number in the range is the health-based water quality standard previously adopted by the Commission for the segment.
(b)	The second number in the range is a technology based value established by the Commission for the purpose of this temporary modification.
(c)	Control requirements, such as discharge permit effluent limitations, shall be established using the first number in the range as the ambient water quality target, provided that no effluent limitation shall require an “end-of-pipe” discharge level more restrictive than the second number in the range.
(3)	Table Value Standards
. . . .

REGION:11

BASIN:  Lower Yampa River/Green River	

Desig	

Classifications	
NUMERIC STANDARDS	
TEMPORARY
MODIFICATIONS
AND
QUALIFIERS	

Stream Segment Description			PHYSICAL
and
BIOLOGICAL
	
INORGANIC
mg/l	
METALS
ug/l		
2.	Mainstem of the Yampa River from a point immediately below the confluence with Elkhead Creek to the confluence with the Green River.		Aq Life Warm 1
Recreation E
Water Supply
Agriculture	T=TVS(WS-II) oC
D.O. = 5.0 mg/l
pH = 6.5-9.0
E. Coli=126/100ml	NH3(ac/ch)=TVS
Cl2(ac)=0.019
Cl2(ch)=0.011
CN=0.005	S=0.002
B=0.75
NO2=0.05
NO3=10
Cl=250
SO4=WS	As(ac)=340
As(ch)=0.02(Trec)
Cd(ac/ch)=TVS
CrIII(ac)=50(Trec)
CrVI(ac/ch)=TVS
Cu(ac/ch)=TVS	Fe(ch)=WS(dis)
Fe(ch)=1000(Trec)
Pb(ac/ch)=TVS
Mn(ac/ch)=TVS
Mn(ch)=WS(dis)
Hg(ch)=0.01(tot)
	Ni(ac/ch)=TVS
Se(ac/ch)=TVS
Ag(ac/ch)=TVS
Zn(ac)=TVS
Zn(ch)=TVS(sc)	

Temporary modification:
As(ch)=hybrid
Expiration date of 12/31/21.	
3c.	Mainstem of Milk Creek, including all tributaries and wetlands, from Thornburgh (County Rd 15) to the confluence with the Yampa River except for the specific listings in Segment 3b and 3e.		Aq Life Warm 1
Recreation P
Water Supply
Agriculture	T=TVS(WS-II) oC
D.O. = 5.0 mg/l
pH = 6.5-9.0
E. Coli=205/100ml	NH3(ac/ch)=TVS
Cl2(ac)=0.019
Cl2(ch)=0.011
CN=0.005	S=0.002
B=0.75
NO2=0.05
NO3=10
Cl=250
SO4=WS	As(ac)=340
As(ch)=0.02(Trec)
Cd(ac/ch)=TVS
CrIII(ac)=50(Trec)
CrVI(ac/ch)=TVS
Cu(ac/ch)=TVS	Fe(ch)=WS(dis)
Fe(ch)=1000(Trec)
Pb(ac/ch)=TVS
Mn(ac/ch)=TVS
Mn(ch)=WS(dis)
Hg(ch)=0.01(tot)	Ni(ac/ch)=TVS
Se(ac/ch)=TVS
Ag(ac/ch)=TVS
Zn(ac/ch)=TVS	

Temporary modification:
As(ch)=hybrid
Expiration date of 12/31/21.	
4.	North and South Fork of Fortification Creek, including all wetlands and tributaries, from their sources to their confluence.  Little Cottonwood Creek, including all  tributaries and wetlands from the source to the confluence with Fortification Creek.		Aq Life Cold 1
Recreation P
Water Supply
Agriculture	T=TVS(CS-I) oC
D.O. = 6.0 mg/l
D.O. (sp)=7.0 mg/l
pH = 6.5-9.0
E. Coli=205/100ml	NH3(ac/ch)=TVS
Cl2(ac)=0.019
Cl2(ch)=0.011
CN=0.005	S=0.002
B=0.75
NO2=0.05
NO3=10
Cl=250
SO4=WS	As(ac)=340
As(ch)=0.02(Trec)
Cd(ac)=TVS(tr)
Cd(ch)=TVS
CrIII(ac)=50(Trec)
CrIII(ch)=TVS
CrVI(ac/ch)=TVS
Cu(ac/ch)=TVS	Fe(ch)=WS(dis)
Fe(ch)=1000(Trec)
Pb(ac/ch)=TVS
Mn(ac/ch)=TVS
Mn(ch)=WS(dis)
Hg(ch)=.01(Trec)	Ni(ac/ch)=TVS
Se(ac/ch)=TVS
Ag(ac)=TVS
Ag(ch)=TVS(tr)
Zn(ac)=TVS
Zn(ch)=TVS(sc)	

Temporary modification:
As(ch)=hybrid
Expiration date of 12/31/21.	
10.	Mainstem of the East Fork of Williams Fork River including all tributaries and wetlands, from the boundary of Routt National Forest to the confluence with the South Fork of the Williams Fork River.		Aq Life Cold 1
Recreation E
Water Supply
Agriculture	T=TVS(CS-I) oC
D.O. = 6.0 mg/l
D.O. (sp)=7.0 mg/l
pH = 6.5-9.0
E.Coli=126/100ml	NH3(ac/ch)=TVS
Cl2(ac)=0.019
Cl2(ch)=0.011
CN=0.005	S=0.002
B=0.75
NO2=0.05
NO3=10
Cl=250
SO4=WS	As(ac)=340
As(ch)=0.02(Trec)
Cd(ac)=TVS(tr)
Cd(ch)=TVS
CrIII(ac)=50(Trec)
CrVI(ac/ch)=TVS
Cu(ac/ch)=TVS	Fe(ch)=WS(dis)
Fe(ch)=1000(Trec)
Pb(ac/ch)=TVS
Mn(ch)=WS(dis)
Mn(ac/ch)=TVS
Hg(ch)=0.01(tot) 	Ni(ac/ch)=TVS
Se(ac/ch)=TVS
Ag(ac)=TVS
Ag(ch)=TVS(tr)
Zn(ac)=TVS
Zn(ch)=TVS(sc)	

Temporary modification:
As(ch)=hybrid
Expiration date of 12/31/21.	
18.	Mainstem of Slater Creek, including all tributaries and wetlands, from the source to a point just below the confluence with Second Creek.  The mainstems of Fourmile and Willow Creeks, including all tributaries and wetlands, from their sources to the boundary of the Routt National Forest.		Aq Life Cold 1
Recreation P
Water Supply
Agriculture	T=TVS(CS-I) oC
D.O. = 6.0 mg/l
D.O.(sp)=7.0 mg/l
pH = 6.5-9.0
E.Coli=205/100ml	NH3(ac/ch)=TVS
Cl2(ac)=0.019
Cl2(ch)=0.011
CN=0.005	S=0.002
B=0.75
NO2=0.05
NO3=10
Cl=250
SO4=WS	As(ac)=340
As(ch)=0.02(Trec)
Cd(ac)=TVS(tr)
Cd(ch)=TVS
CrIII(ac)=50(Trec)
CrIII(ch)=TVS
CrVI(ac/ch)=TVS
Cu(ac/ch)=TVS	Fe(ch)=WS(dis)
Fe(ch)=1000(Trec)
Pb(ac/ch)=TVS
Mn(ch)=WS(dis)
Mn(ac/ch)=TVS
Hg(ch)=0.01(tot)	Ni(ac/ch)=TVS
Se(ac/ch)=TVS
Ag(ac)=TVS
Ag(ch)=TVS(tr)
Zn(ac)=TVS
Zn(ch)=TVS(sc)	

Temporary modification:
As(ch)=hybrid
Expiration date of 12/31/21.	

REGION:11

BASIN:  White River	

Desig	

Classifications	
NUMERIC STANDARDS	
TEMPORARY
MODIFICATIONS
AND
QUALIFIERS	

Stream Segment Description			PHYSICAL
and
BIOLOGICAL
	
INORGANIC
mg/l	
METALS
ug/l		
4.	All tributaries to the North Fork of the White River, including all wetlands, from the Flat Tops Wilderness Area boundary to the confluence with the South Fork of the White River except for the specific listings in Segment 1.		Aq Life Cold 1
Recreation E
Water Supply
Agriculture	T=TVS(CS-I) oC
D.O. = 6.0 mg/l
D.O. (sp)=7.0 mg/l
pH = 6.5-9.0
E.Coli=126/100ml	NH3(ac/ch)=TVS
Cl2(ac)=0.019
Cl2(ch)=0.011
CN=0.005	S=0.002
B=0.75
NO2=0.05
NO3=10
Cl=250
SO4=WS	As(ac)=340
As(ch)=0.02(Trec)
Cd(ac)=TVS(tr)
Cd(ch)=TVS
CrIII(ac)=50(Trec)
CrVI(ac/ch)=TVS
Cu(ac/ch)=TVS	Fe(ch)=WS(dis)
Fe(ch)=1000(Trec)
Pb(ac/ch)=TVS
Mn(ch)=WS(dis)
Mn(ac/ch)=TVS
Hg(ch)=0.01(tot)	Ni(ac/ch)=TVS
Se(ac/ch)=TVS
Ag(ac)=TVS
Ag(ch)=TVS(tr)
Zn(ac/ch)=TVS	

Temporary modification:
As(ch)=hybrid
Expiration date of 12/31/21.	
7.	Mainstem of the White River from a point immediately above the confluence with Miller Creek to a point immediately above the confluence with Piceance Creek.		Aq Life Cold 1
Dec 1 to March 1
Recreation P
March 2 to Nov. 30
Recreation E
Water Supply
Agriculture
	T=TVS(CS-II) oC
D.O.= 6.0 mg/l
D.O.(sp)=7.0 mg/l
pH = 6.5-9.0
Dec. 1 to March 1
E.Coli=205/100ml
March 2 to Nov. 30
E.Coli=126/100ml	NH3(ac/ch)=TVS
Cl2(ac)=0.019
Cl2(ch)=0.011
CN=0.005	S=0.002
B=0.75
NO2=0.05
NO3=10
Cl=250
SO4=WS	As(ac)=340
As(ch)=0.02(Trec)
Cd(ac)=TVS(tr)
Cd(ch)=TVS
CrIII(ac)=50(Trec)
CrVI(ac/ch)=TVS
Cu(ac/ch)=TVS	Fe(ch)=WS(dis)
Fe(ch)=1000(Trec)
Pb(ac/ch)=TVS
Mn(ch)=WS(dis)
Mn(ac/ch)=TVS
Hg(ch)=0.01(tot)	Ni(ac/ch)=TVS
Se(ac/ch)=TVS
Ag(ac)=TVS
Ag(ch)=TVS(tr)
Zn(ac/ch)=TVS	

Temporary modification:
As(ch)=hybrid
Expiration date of 12/31/21.	
10b.	Mainstem of Big Beaver Creek, Miller Creek, and North Elk Creek, including their tributaries and wetlands, from their boundary with national forest lands to their confluences with the White River.  Mainstem of Coal Creek, including all tributaries and wetlands, from the source to the confluence with the White River.		Aq Life Cold 1
Recreation P
Water Supply
Agriculture	T=TVS(CS-I) oC
D.O. = 6.0 mg/l
D.O.(sp)=7.0 mg/l
pH=6.5-9.0
E.Coli=205/100ml	NH3(ac/ch)=TVS
Cl2(ac)=0.019
Cl2(ch)=0.011
CN=0.005	S=0.002
B=0.75
NO2=0.05
NO3=10
Cl=250
SO4=WS	As(ac)=340
As(ch)=0.02(Trec)
Cd(ac)=TVS(tr)
Cd(ch)=TVS
CrIII(ac)=50(Trec)
CrVI(ac/ch)=TVS
Cu(ac/ch)=TVS	Fe(ch)=WS(dis)
Fe(ch)=1000(Trec)
Pb(ac/ch)=TVS
Mn(ch)=WS(dis)
Mn(ac/ch)=TVS
Hg(ch)=0.01(tot)	Ni(ac/ch)=TVS
Se(ac/ch)=TVS
Ag(ac)=TVS
Ag(ch)=TVS(tr)
Zn(ac/ch)=TVS	

Temporary modification:
As(ch)=hybrid
Expiration date of 12/31/21.	
12.	Mainstem of the White River from a point immediately above the confluence with Piceance Creek to a point immediately above the confluence with Douglas Creek.		Aq Life Warm 1
Recreation E
Water Supply
Agriculture	T=TVS(WS-II) oC
D.O. = 5.0 mg/l
pH = 6.5-9.0
E.Coli=126/100ml	NH3(ac/ch)=TVS
Cl2(ac)=0.019
Cl2(ch)=0.011
CN=0.005	S=0.002
B=0.75
NO2=0.05
NO3=10
Cl=250
SO4=WS	As(ac)=340
As(ch)=0.02(Trec)
Cd(ac/ch)=TVS
CrIII(ac)=50(Trec)
CrVI(ac/ch)=TVS
Cu(ac/ch)=TVS
	Fe(ch)=WS(dis)
Fe(ch)=1000(Trec)
Pb(ac/ch)=TVS
Mn(ch)=WS(dis)
Mn(ac/ch)=TVS
Hg(ch)=0.01(tot)	Ni(ac/ch)=TVS
Se(ac/ch)=TVS
Ag(ac/ch)=TVS
Zn(ac/ch)=TVS	

Temporary modification:
As(ch)=hybrid
Expiration date of 12/31/21.	
21.	Mainstem of the White River from a point immediately above the confluence with Douglas Creek to the Colorado/Utah border.		Aq Life Warm 1
Recreation E
Water Supply
Agriculture	T=TVS(WS-II) oC
D.O. = 5.0 mg/l
pH = 6.5-9.0
E.Coli=126/100ml
	NH3(ac/ch)=TVS
Cl2(ac)=0.019
Cl2(ch)=0.011
CN=0.005	S=0.002
B=0.75
NO2=0.05
NO3=10
Cl=250
SO4=WS	As(ac)=340
As(ch)=0.02(Trec)
Cd(ac/ch)=TVS
CrIII(ac)=50(Trec)
CrIII(ch)=TVS
CrVI(ac/ch)=TVS
Cu(ac/ch)=TVS  	Fe(ch)=WS(dis)
Fe(ch)=1000(Trec)
Pb(ac/ch)=TVS
Mn(ch)=WS(dis)
Mn(ac/ch)=TVS
Hg(ch)=0.01(tot)
	Ni(ac/ch)=TVS Se(ac/ch)=TVS
Ag(ac/ch)=TVS
Zn(ac/ch)=TVS	

Temporary modification:
As(ch)=hybrid
Expiration date of 12/31/21.	
23.	Mainstems of East Douglas Creek and West Douglas Creek, including all tributaries and wetlands, from their sources to their confluence.		Aq Life Cold 1
Recreation E
Water Supply
Agriculture
	T=TVS(CS-I) oC
D.O.= 6.0 mg/l
D.O.(sp)=7.0 mg/l
pH = 6.5-9.0
E.Coli=126/100ml	NH3(ac/ch)=TVS
Cl2(ac)=0.019
Cl2(ch)=0.011
CN=0.005	S=0.002
B=0.75
NO2=0.05
NO3=10
Cl=250
SO4=WS	As(ac)=340
As(ch)=0.02(Trec)
Cd(ac)=TVS(tr)
Cd(ch)=TVS
CrIII(ac)=50(Trec)
CrVI(ac/ch)=TVS
Cu(ac/ch)=TVS	Fe(ch)=WS(dis)
Fe(ch)=1000(Trec)
Pb(ac/ch)=TVS
Mn(ch)=WS(dis)
Mn(ac/ch)=TVS
Hg(ch)=0.01(tot)	Ni(ac/ch)=TVS
Se(ac/ch)=TVS
Ag(ac)=TVS
Ag(ch)=TVS(tr)
Zn(ac/ch)=TVS	

Temporary modification:
As(ch)=hybrid
Expiration date of 12/31/21.	

REGION:11

BASIN:  Lower Colorado River	

Desig	

Classifications	
NUMERIC STANDARDS	
TEMPORARY
MODIFICATIONS
AND
QUALIFIERS	

Stream Segment Description			PHYSICAL
and
BIOLOGICAL
	
INORGANIC
mg/l	
METALS
ug/l		
1.	Mainstem of the Colorado River from the confluence with the Roaring Fork River to immediately below the confluence with Rifle Creek.		Aq Life Cold 1
Recreation E
Water Supply
Agriculture	T=TVS(CS-II) oC
D.O. = 6.0 mg/l
D.O.(sp)=7.0 mg/l
pH=6.5-9.0
E.Coli=126/100ml	NH3(ac/ch)=TVS
Cl2(ac)=0.019
Cl2(ch)=0.011
CN=0.005	S=0.002
B=0.75
NO2=0.05
NO3=10
Cl=250
SO4=WS	As(ac)=340
As(ch)=0.02(Trec)
Cd(ac)=TVS(tr)
Cd(ch)=TVS
CrIII(ac)=50(Trec)
CrVI(ac/ch)=TVS
Cu(ac/ch)=TVS	Fe(ch)=WS(dis)
Fe(ch)=1000(Trec)
Pb(ac/ch)=TVS
Mn(ch)=WS(dis)
Mn(ac/ch)=TVS
Hg(ch)=0.01(tot)	Ni(ac/ch)=TVS
Se(ac/ch)=TVS
Ag(ac)=TVS
Ag(ch)=TVS(tr)
Zn(ac/ch)=TVS	

Temporary modification:
As(ch)=hybrid
Expiration date of 12/31/21.	
2a.	Mainstem of the Colorado River from immediately below the confluence with Rifle Creek to immediately above the confluence of Rapid Creek.		Aq Life Warm 1
Recreation E
Water Supply
Agriculture	T=TVS(WS-II) oC
D.O. = 5.0 mg/l
pH = 6.5-9.0
E.Coli=126/100ml	NH3(ac/ch)=TVS
Cl2(ac)=0.019
Cl2(ch)=0.011
CN=0.005	S=0.002
B=0.75
NO2=0.05
NO3=10
Cl=250
SO4=WS	As(ac)=340
As(ch)=0.02(Trec)
Cd(ac/ch)=TVS
CrIII(ac)=50(Trec)
CrVI(ac/ch)=TVS
Cu(ac/ch)=TVS	Fe(ch)=WS(dis)
Fe(ch)=1000(Trec)
Pb(ac/ch)=TVS
Mn(ch)=WS(dis)
Mn(ac/ch)=TVS
Hg(ch)=0.01(tot)
	Ni(ac/ch)=TVS
Se(ac/ch)=TVS
Ag(ac/ch)=TVS
Zn(ac/ch)=TVS	

Temporary modification:
As(ch)=hybrid
Expiration date of 12/31/21.	
2b.	Mainstem of the Colorado River from a point immediately above the confluence with Rapid Creek to immediately above the confluence of the Gunnison River.		Aq Life Warm 1
Recreation E
Water Supply
Agriculture	T=TVS(WS-II) oC
D.O. = 5.0 mg/l
pH = 6.5-9.0
E.Coli=126/100ml	NH3(ac/ch)=TVS
Cl2(ac)=0.019
Cl2(ch)=0.011
CN=0.005	S=0.002
B=0.75
NO2=0.05
NO3=10
Cl=250
SO4=WS	As(ac)=340
As(ch)=0.02(Trec)
Cd(ac/ch)=TVS
CrIII(ac)=50(Trec)
CrVI(ac/ch)=TVS
Cu(ac/ch)=TVS	Fe(ch)=WS(dis)
Fe(ch)=1000(Trec)
Pb(ac/ch)=TVS
Mn(ch)=WS(dis)
Mn(ac/ch)=TVS
Hg(ch)=0.01(tot)	Ni(ac/ch)=TVS
Se(ac/ch)=TVS
Ag(ac/ch)=TVS
Zn(ac/ch)=TVS	

Temporary modification:
As(ch)=hybrid
Expiration date of 12/31/21.	
5.	All tributaries to the Colorado River, including wetlands, which are within the boundaries of White River National Forest, except for the specific listing in Segments 9a and 9c.		Aq Life Cold 1
Recreation P
Water Supply
Agriculture	T=TVS(CS-I) oC
D.O.=6.0 mg/l
D.O.(sp)=7.0 mg/l
pH=6.5-9.0
E.Coli=205/100ml	NH3(ac/ch)=TVS
Cl2(ac)=0.019
Cl2(ch)=0.011
CN=0.005	S=0.002
B=0.75
NO2=0.05
NO3=10
Cl=250
SO4=WS	As(ac)=340
As(ch)=0.02(Trec)
Cd(ac)=TVS(tr)
Cd(ch)=TVS
CrIII(ac)=50(Trec)
CrVI(ac/ch)=TVS
Cu(ac/ch)=TVS	Fe(ch)=WS(dis)
Fe(ch)=1000(Trec)
Pb(ac/ch)=TVS
Mn(ch)=WS(dis)
Mn(ac/ch)=TVS
Hg(ch)=0.01(tot)	Ni(ac/ch)=TVS
Se(ac/ch)=TVS
Ag(ac)=TVS
Ag(ch)=TVS(tr)
Zn(ac/ch)=TVS	

Temporary modification:
As(ch)=hybrid
Expiration date of 12/31/21.	
7a.	Mainstem of Mitchell, Canyon, Elk, Garfield, Beaver, and Cache Creeks, including all tributaries and wetlands, from the boundary of the White River National Forest to their confluences with the Colorado River.  Battlement Creek from the most downstream boundary of BLM lands to the confluence with the Colorado River.		Aq Life Cold 1
Recreation E
Water Supply
Agriculture	T=TVS(CS-I) oC
D.O.=6.0 mg/l
D.O.(sp)=7.0 mg/l
pH=6.5-9.0
E.Coli=126/100ml	NH3(ac/ch)=TVS
Cl2(ac)=0.019
Cl2(ch)=0.011
CN=0.005	S=0.002
B=0.75
NO2=0.05
NO3=10
Cl=250
SO4=WS	As(ac)=340
As(ch)=0.02(Trec)
Cd(ac)=TVS(tr)
Cd(ch)=TVS
CrIII(ac)=50(Trec)
CrVI(ac/ch)=TVS
Cu(ac/ch)=TVS	Fe(ch)=WS(dis)
Fe(ch)=1000(Trec)
Pb(ac/ch)=TVS
Mn(ch)=WS(dis)
Mn(ac/ch)=TVS
Hg(ch)=0.01(tot)	Ni(ac/ch)=TVS
Se(ac/ch)=TVS
Ag(ac)=TVS
Ag(ch)=TVS(tr)
Zn(ac)=TVS
Zn(ch)=TVS(sc)	

Temporary modification:
As(ch)=hybrid
Expiration date of 12/31/21.	
7b.	Mainstem of Divide Creek, including all tributaries and wetlands, from the boundary of the White River National Forest to the confluence with the Colorado River.		Aq Life Cold 1
Recreation E
Water Supply
Agriculture	T=TVS(CS-II) oC
D.O.= 6.0 mg/l
D.O.(sp)=7.0 mg/
pH=6.5‑9.0
E.Coli=126/100ml	NH3(ac/ch)=TVS
Cl2 (ac)=0.019
Cl2 (ch)=0.011
CN=0.005	S=0.002
B=0.75
NO2=0.05
NO3=10
Cl=250
SO4=WS	As(ac)=340
As(ch)=0.02(Trec)
Cd(ac)=TVS(tr) 
Cd(ch)=TVS 
CrIII(ac)=50(Trec)
CrVI(ac/ch)=TVS
Cu(ac/ch)=TVS	Fe(ch)=WS(dis)
Fe(ch)=1000(Trec)
Pb(ac/ch)=TVS
Mn(ch)=WS(dis)
Mn(ac/ch)=TVS
Hg(ch)=0.01(tot)	Ni(ac/ch)=TVS
Se(ac/ch)=TVS
Ag(ac)=TVS
Ag(ch)=TVS(tr)
Zn(ac/ch)=TVS	

Temporary modification:
As(ch)=hybrid
Expiration date of 12/31/21.

	
10.	West Rifle Creek, including all tributaries and wetlands, from the source to Rifle Gap Reservoir.  East Rifle Creek, including all tributaries and wetlands, from the White River National Forest boundary to Rifle Gap Reservoir.  Rifle Creek, including all tributaries and wetlands, from Rifle Gap Reservoir to the confluence with the Colorado River.		Aq Life Cold 1
Recreation E
Water Supply
Agriculture	T=TVS(CS-II) oC
D.O.=6.0 mg/l
D.O.(sp)=7.0 mg/l
pH=6.5-9.0
E.Coli=126/100ml	NH3(ac/ch)=TVS
Cl2(ac)=0.019
Cl2(ch)=0.011
CN=0.005	S=0.002
B=0.75
NO2=0.05
NO3=10
Cl=250
SO4=WS	As(ac)=340
As(ch)=0.02(Trec)
Cd(ac)=TVS(tr)
Cd(ch)=TVS
CrIII(ac)=50(Trec)
CrVI(ac/ch)=TVS
Cu(ac/ch)=TVS	Fe(ch)=WS(dis)
Fe(ch)=1000(Trec)
Pb(ac/ch)=TVS
Mn(ch)=WS(dis)
Mn(ac/ch)=TVS
Hg(ch)=0.01(tot)	Ni(ac/ch)=TVS
Se(ac/ch)=TVS
Ag(ac)=TVS
Ag(ch)=TVS(tr)
Zn(ac/ch)=TVS	

Temporary modification:
As(ch)=hybrid
Expiration date of 12/31/21.

REGION:11

BASIN:  Lower Colorado River	

Desig	

Classifications	
NUMERIC STANDARDS	
TEMPORARY
MODIFICATIONS
AND
QUALIFIERS	

Stream Segment Description			PHYSICAL
and
BIOLOGICAL
	
INORGANIC
mg/l	
METALS
ug/l		
14b.	Clear Creek, including all tributaries and wetlands, from a point immediately below the confluence with Tom Creek to the confluence with Roan Creek.  Roan Creek, including all tributaries and wetlands, from a point immediately above the confluence with Clear Creek to a point immediately below the confluence with Kimball Creek.		Aq Life Cold 1
Recreation P
Water Supply
Agriculture	T=TVS(CS-II) oC
D.O.=6.0 mg/l
D.O.(sp)= 7.0 mg/l
pH=6.5‑9.0
E.Coli=205/100ml	NH3(ac/ch)=TVS
Cl2(ac)=0.019
Cl2 (ch)=0.011
CN=0.005	S=0.002
B=0.75
NO2=0.05
NO3=10
Cl=250
SO4=WS	As(ac)=340
As(ch)=0.02(Trec)
Cd(ac)=TVS(tr)
Cd(ch)=TVS
CrIII(ac)=50(Trec)
CrVI(ac/ch)=TVS
Cu(ac/ch)=TVS	Fe(ch)=WS(dis)
Fe(ch)=1000(Trec)
Pb(ac/ch)=TVS
Mn(ch)=WS(dis)
Mn(ac/ch)=TVS
Hg(ch)=0.01(tot)	Ni(ac/ch)=TVS
Se(ac/ch)=TVS
Ag(ac)=TVS
Ag(ch)=TVS(tr)
Zn(ac/ch)=TVS	

Temporary modification:
As(ch)=hybrid
Expiration date of 12/31/21.	
14c.	Mainstem of Roan Creek including all tributaries and wetlands, from a point immediately below the confluence with Kimball Creek to the confluence with the Colorado River.		Aq Life Warm 1
Recreation P
Water Supply
Agriculture	T=TVS(WS-II) oC
D.O.=5.0 mg/l
pH=6.5-9.0
E.Coli=205/100ml	NH3(ac/ch)=TVS
Cl2(ac)=0.019
Cl2(ch)=0.011
CN=0.005	S=0.002
B=0.75
NO2=0.05
NO3=10
Cl=250
SO4=WS	As(ac)=340
As(ch)=0.02(Trec)
Cd(ac/ch)=TVS
CrIII(ac)=50(Trec)
CrVI(ac/ch)=TVS
Cu(ac/ch)=TVS	Fe(ch)=WS(dis)
Fe(ch)=1000(Trec)
Pb(ac/ch)=TVS
Mn(ch)=WS(dis)
Mn(ac/ch)=TVS
Hg(ch)=0.01(tot)
	Ni(ac/ch)=TVS
Se(ac/ch)=TVS
Ag(ac/ch)=TVS
Zn(ac/ch)=TVS

Temporary modification:
As(ch)=hybrid
Expiration date of 12/31/21.	
15.	Mainstem of Plateau Creek including all tributaries and wetlands, from its source to the HWY 330 bridge in Collbran. Kimball Creek, Grove Creek, Big Creek, Cottonwood Creek, Bull Creek, Spring Creek, Coon Creek, and Mesa Creek, including all wetlands and tributaries, from their sources to their confluences with Plateau Creek.		Aq Life Cold 1
Recreation E
Water Supply
Agriculture	T=TVS(CS-I) oC
D.O.=6.0 mg/l
D.O.(sp)= 7.0 mg/l
pH=6.5-9.0
E.Coli=126/100ml	NH3(ac/ch)=TVS
Cl2(ac)=0.019
Cl2(ch)=0.011
CN=0.005	S=0.002
B=0.75
NO2=0.05
NO3=10
Cl=250
SO4=WS	As(ac)=340
As(ch)=0.02(Trec)
Cd(ac)=TVS(tr)
Cd(ch)=TVS
CrIII(ac)=50(Trec)
CrVI(ac/ch)=TVS
Cu(ac/ch)=TVS	Fe(ch)=WS(dis)
Fe(ch)=1000(Trec)
Pb(ac/ch)=TVS
Mn(ch)=WS(dis)
Mn(ac/ch)=TVS
Hg(ch)=0.01(tot)	Ni(ac/ch)=TVS
Se(ac/ch)=TVS
Ag(ac)=TVS
Ag(ch)=TVS(tr)
Zn(ac)=TVS
Zn(ch)=TVS(sc)	

Temporary modification:
As(ch)=hybrid
Expiration date of 12/31/21.	
16.	Plateau Creek including all tributaries and wetlands, from the HWY 330 bridge in Collbran, to the confluence with the Colorado River, excluding specific listings in segment 15.		Aq Life Cold 1
Recreation E
Water Supply
Agriculture	T=TVS(CS-II) oC
D.O.=6.0 mg/l
D.O.(sp)= 7.0 mg/l
pH=6.5‑9.0
E.Coli=126/100ml	NH3(ac/ch)=TVS
Cl2(ac)=0.019
Cl2 (ch)=0.011
CN=0.005	S=0.002
B=0.75
NO2=0.05
NO3=10
Cl=250
SO4=WS	As(ac)=340
As(ch)=0.02(Trec)
Cd(ac/ch)=TVS
CrIII(ac)=50(Trec)
CrVI(ac/ch)=TVS
Cu(ac/ch)=TVS	Fe(ch)=WS(dis)
Fe(ch)=1000(Trec)
Pb(ac/ch)=TVS
Mn(ch)=WS(dis)
Mn(ac/ch)=TVS
Hg(ch)=0.01(tot)	Ni(ac/ch)=TVS
Se(ac/ch)=TVS
Ag(ac/ch)=TVS
Zn(ac/ch)=TVS	

Temporary modification:
As(ch)=hybrid
Expiration date of 12/31/21.	
17a.	Mainstem of Rapid Creek, including all tributaries and wetlands, from its source to a point immediately below the confluence with Cottonwood Creek including Kruzen Springs.	
OW	Aq Life Cold 1
Recreation P
Water Supply
Agriculture	T=TVS(CS-II) oC
D.O. = 6.0 mg/l
D.O.(sp)=7.0 mg/l
pH = 6.5-9.0
E.Coli=205/100ml	NH3(ac/ch)=TVS
Cl2(ac)=0.019
Cl2(ch)=0.011
CN=0.005	S=0.002
B=0.75
NO2=0.05
NO3=10
Cl=250
SO4=WS	As(ac)=340
As(ch)=0.02(Trec)
Cd(ac)=TVS(tr)
Cd(ch)=TVS
CrIII(ac)=50(Trec)
CrVI(ac/ch)=TVS
Cu(ac/ch)=TVS	Fe(ch)=WS(dis)
Fe(ch)=1000(Trec)
Pb(ac/ch)=TVS
Mn(ch)=WS(dis)
Mn(ac/ch)=TVS
Hg(ch)=0.01(tot)
	Ni(ac/ch)=TVS Se(ac/ch)=TVS
Ag(ac)=TVS
Ag(ch)=TVS(tr)
Zn(ac/ch)=TVS	

Temporary modification:
As(ch)=hybrid
Expiration date of 12/31/21.	
18.	Mainstem of Little Dolores River, including all tributaries and wetlands, from its source to immediately below the confluence with Hay Press Creek.		Aq Life Cold 1
Recreation P
Water Supply
Agriculture	May-Sept
T(DM)=24.4 oC
T(MWAT)=TVS(CS-I) oC
Oct-Apr
T(DM)=13.9 oC
T(MWAT)=TVS(CS-I) oC
D.O. = 6.0 mg/l
D.O.(sp)=7.0 mg/l
pH = 6.5-9.0
E.Coli=205/100ml	NH3(ac/ch)=TVS
Cl2(ac)=0.019
Cl2(ch)=0.011
CN=0.005	S=0.002
B=0.75
NO2=0.05
NO3=10
Cl=250
SO4=WS	As(ac)=340
As(ch)=0.02(Trec)
Cd(ac)=TVS(tr)
Cd(ch)=TVS
CrIII(ac)=50(Trec)
CrVI(ac/ch)=TVS
Cu(ac/ch)=TVS	Fe(ch)=WS(dis)
Fe(ch)=1000(Trec)
Pb(ac/ch)=TVS
Mn(ch)=WS(dis)
Mn(ac/ch)=TVS
Hg(ch)=0.01(tot)	Ni(ac/ch)=TVS
Se(ac/ch)=TVS
Ag(ac)=TVS
Ag(ch)=TVS(tr)
Zn(ac/ch)=TVS	

Temporary modification:
As(ch)=hybrid
Expiration date of 12/31/21.	

. . . .
37.31	STATEMENT OF BASIS SPECIFIC STATUTORY AUTHORITY AND PURPOSE APRIL 8, 2013 RULEMAKING; FINAL ACTION MAY 13, 2013 EFFECTIVE DATE SEPTEMBER 30, 2013
The provisions of C.R S. 25-8-202(1)(a), (b) and (2); 25-8-203; 25-8-204; and 25-8-402; provide the specific statutory authority for adoption of these regulatory amendments.  The Commission also adopted in compliance with 24-4-103(4) C.R.S. the following statement of basis and purpose.
BASIS AND PURPOSE
In August of 2005, the Commission adopted revisions to the Basic Standards and Methodologies for Surface Waters (Regulation #31) to add a Water + Fish (W+F) table value standard for chronic arsenic of 0.02 micrograms per liter (μg/L). W+F standards are numeric human health-based water quality standards that are calculated protective values that take into account the combined exposure from the pollutant in drinking water and the pollutant accumulated in fish flesh. This criterion automatically went into effect for Aquatic Life Class 1 waters which also have a Domestic Water Supply use, when the changes to the Basic Standards became effective.  It was also adopted on a segment by segment basis for Aquatic Life class 2 waters with Domestic Water Supply where the Commission determined there are fish of a catchable size of species that are normally consumed.  Because of the complicated nature of the arsenic standards, specific values were added to the basin tables in the basin hearings between 2006 and 2009.
In this hearing, the Commission adopted temporary modifications for W+F chronic arsenic where a permitted discharger with a water quality–based effluent limit compliance problem exists. The adopted temporary modification is listed in the regulation tables as “As(ch)=hybrid”. An explanation of the temporary modification and its expected implementation into control requirements, such as Colorado Discharge Permit System (CDPS) effluent limitations, is described in 37.6(2)(d). The temporary modification was established by the Commission to allow for a temporarily less stringent application of the chronic arsenic standard in control requirements for both existing discharges and new or increased discharges. 
For discharges existing on or before 6/1/2013, the temporary modification adopted for W+F chronic arsenic is “current condition”, expiring on 12/31/2021. The Commission intends that, when implementing the temporary modification of “current condition” in a CDPS permit, the Division will assess the current effluent quality, recognizing that it changes over time due to variability in treatment facility removal efficiency and influent loading from natural or anthropogenic sources, and due to changes in the influent flow and concentration over time. Maintaining the current condition will include maintaining permitted total arsenic loading to a treatment facility from arsenic contributors at the levels existing on the effective date of the temporary modification, while expressly allowing for variability in such loading due to changes in effluent quality as described above and due to changes in the influent flow and concentration over time within the permitted design flow of that facility. The Commission understands that the Division's past practice implementing this requirement in permits has been through reporting regarding the arsenic loading to the facility, and not through numeric effluent limitations. The Commission intends that the Division will continue this practice. For facilities that lack enough representative data to quantify arsenic loading, the permittee may satisfy reporting requirements through narrative descriptions of potential sources of arsenic. No permit action shall be approved that allows an increase in permitted total arsenic loading to a treatment facility. The expiration date of the temporary modification was set at 12/31/21 to allow for CDPS permits that are issued prior to the effective date of anticipated changes to the chronic arsenic standard in the 2016 Basic Standards Rulemaking to not have the temporary modification expire within the term of a permit. The Commission adopted this temporary modification to allow time for the Division, dischargers and stakeholders to continue a workgroup process to resolve the uncertainty regarding the appropriateness of the W+F chronic arsenic standard of 0.02 μg/L with respect to a technologically feasible level of treatment. 
For new or increased discharges that commence on or after 6/1/2013, the temporary modification adopted is As(ch) = 0.02–3.0 μg/L (Trec), expiring on 12/31/2021. The Commission decided that since the technologically achievable arsenic level is less stringent than the calculated W+F criterion, the temporary modification for new or increased discharges will be a range of 0.02-3.0 μg/L. The first number in the range is the health-based value, based on the Commission’s established methodology for human health-based standards that protect against the combined exposure of drinking water and eating fish. The second number in the range is the Commission’s initial determination of a technologically achievable value for arsenic, set at 3.0 μg/L. Control requirements, such as discharge permits effluent limitations, shall be established using the first number in the range as the ambient water quality target, provided that no effluent limitation shall require an “end of pipe” discharge level more restrictive than the second number in the range during the effective period for this temporary modification. The expiration date of the temporary modification was set at 12/31/21 to allow for CDPS permits that are issued prior to the effective date of anticipated changes to the chronic arsenic standard in the 2016 Basic Standards Rulemaking to not have the temporary modification expire within the term of a permit. The Commission adopted this temporary modification to allow time for the Division, dischargers and stakeholders to continue a workgroup process to resolve the uncertainty regarding the appropriateness of the W+F chronic arsenic standard of 0.02 μg/L with respect to a technologically feasible level of treatment. 
The technologically feasible level of 3.0 μg/L for arsenic is based upon testimony heard by the Commission at the December 13, 2011 Emergency Revisions to Regulation #38. At the December 13, 2011 hearing, the Commission determined, as a practical manner, that 3.0 μg/L is the lowest level that is technologically achievable for common types of water treatment facilities. At the April 8, 2013 Rulemaking, the Commission heard testimony that concurred with the finding from December 13, 2011 that an initial reasonable  lower limit of treatment technology for arsenic is 3.0 μg/L, pending further investigation by the Division, dischargers and stakeholders. The Division intends to address the uncertainty of the W+F chronic arsenic standard with respect to a technologically feasible level of treatment through a continued workgroup process, and propose a revised W+F chronic arsenic standards as part of the 2016 Basic Standards Rulemaking Hearing
Temporary modifications were adopted on the following segments. The segments identified have the previously adopted W+F chronic arsenic standard of 0.02 μg/L and an identified CDPS permit or permits that discharge immediately to or directly above the identified segment. 
Lower Yampa River, Green River 2
Lower Yampa River, Green River 3c
Lower Yampa River, Green River 4
Lower Yampa River, Green River 10
Lower Yampa River, Green River 18
White River 4
White River 7
White River 10b
White River 12
White River 21
White River 23
Lower Colorado River 1
Lower Colorado River 2a
Lower Colorado River 2b
Lower Colorado River 5
Lower Colorado River 7a
Lower Colorado River 7b
Lower Colorado River 10
Lower Colorado River 14b
Lower Colorado River 14c
Lower Colorado River 15
Lower Colorado River 16
Lower Colorado River 17a
Lower Colorado River 18
PARTIES TO THE RULEMAKING HEARING
1.	Colorado Mining Association
2.	Union Gold, Inc.
3.	Colorado Department of Transportation
4.	City of Colorado Springs and Colorado Springs Utilities
5.	Town of Crested Butte
6.	Mountain Coal Company
7.	Centennial Water and Sanitation District
8.	MillerCoors, LLC
9.	Plum Creek Wastewater Authority
10.	Tri-State Generation & Transmission Association
11.	Climax Molybdenum Company
12.	Littleton/Englewood Wastewater Treatment Plant
13.	Eagle River Water and Sanitation District
14.	City of Boulder
15.	City and County of Denver
16.	Parker Water and Sanitation District
17.	U.S. Energy Corp.
18.	U.S. Environmental Protection Agency
19.	City of Greeley