colorado department of public health and environment
WATER QUALITY CONTROL COMMISSION
5 CCR 1002-38
regulation no. 38
classifications and numeric standards
for
south platte river basin, laramie river basin
republican river basin, smoky hill river basin
38.1	AUTHORITY
These regulations are promulgated pursuant to section 25-8-101 et seq C.R.S., as amended, and in particular, 25-8-203 and 25-8-204.
38.2	PURPOSE
These regulations establish classification and numeric standards for the South Platte River, the Laramie River, the Republican River and the Smoky Hill River, including all tributaries and standing bodies of water as indicated in section 38.6.  The classifications identify the actual beneficial uses of the water.  The numeric standards are assigned to determine the allowable concentrations of various parameters. Discharge permits will be issued by the Water Quality Control Division to comply with basic, narrative, and numeric standards and control regulations so that all discharges to waters of the state protect the classified uses.  (See section 31.14).  It is intended that these and all other stream classifications and numeric standards be used in conjunction with and be an integral part of Regulation 31.0 - BASIC STANDARDS AND METHODOLOGIES FOR SURFACE WATER.
38.3	INTRODUCTION
These regulations and Tables present the classifications and numeric standards assigned to stream segments listed in the attached Tables (See section 38.6).  As additional stream segments are classified and numeric standards for this drainage system, they will be added to or replace the numeric standards in the Tables in section 38.6).  Any additions or revisions of classifications or numeric standards can be accomplished only after public hearing by the Commission and proper consideration of evidence and testimony as specified by the statute and the “basic regulations”.
38.4	DEFINITIONS
See the Colorado Water Quality Control Act and the codified water quality regulations for definitions.
38.5	BASIC STANDARDS
(1)	TEMPERATURE
All waters of the South Platte, Laramie, Republican and Smoky Hill River Basins are subject to the following standard for temperature.  (Discharges regulated by permits, which are within the permit limitations, shall not be subject to enforcement proceedings under this standard).  Temperature shall maintain a normal pattern of diurnal and seasonal fluctuations with no abrupt changes and shall have no increase in temperature of a magnitude, rate, and duration deemed deleterious to the resident aquatic life.  This standard shall not be interpreted or applied in a manner inconsistent with section 25-8-104, C.R.S.  
(2)	QUALIFIERS
See Basic Standards and Methodologies for Surface Water for a listing of organic standards at 31.11 and metal standards found at 31.16 Table III.  The column in the tables headed “Water Fish” are presumptively applied to all aquatic life class 1 streams which also have a water supply classification, and are applied to aquatic life class 2 streams which also have a water supply classification, on a case-by-case basis as shown in the Tables 38.6.  The column in the tables at 31.11 headed “Fish Ingestion” is presumptively applied to all aquatic life class 1 streams which do not have a water supply classification, and are applied to aquatic life class 2 streams which do not have a water supply classification, on a case-by-case basis as shown in the Tables in Tables 38.6.
(3)	URANIUM
(a)	All waters of the South Platte River Basin are subject to the following basic standard for uranium, unless otherwise specified by a water quality standard applicable to a particular segment.  However, discharges of uranium regulated by permits which are within these permit limitations shall not be a basis for enforcement proceedings under this basic standard.
(b)	Uranium level in surface waters shall be maintained at the lowest practicable level.
(c)	In no case shall uranium levels in waters assigned a water supply classification be increased by any cause attributable to municipal, industrial, or agricultural discharges so as to exceed 30 µg/l or naturally-occurring concentrations (as determined by the State of Colorado), whichever is greater.
(d)	In no case shall uranium levels in waters assigned a water supply classification be increased by a cause attributable to municipal, industrial, or agricultural discharges so as to exceed 30 µg/l where naturally-occurring concentration are less than 30 µg/l.
38.6	TABLES
(1)	Introduction
The numeric standards for various parameters in the attached tables were assigned by the Commission after a careful analysis of the data presented on actual stream conditions and on actual and potential water uses.
Numeric standards are not assigned for all parameters listed in the Tables attached to 31.0.  If additional numeric standards are found to be needed during future periodic reviews, they can be assigned by following the proper hearing procedures.
(2)	Abbreviations:
(a)	The following abbreviations are used in the attached tables:
ac	=	acute (1-day)
Ag	=	Silver
Al	=	Aluminum
As	=	Arsenic
B	=	Boron
Ba	=	Barium
Be	=	Beryllium
oC	=	degrees celsius
Cd	=	Cadmium
ch	=	chronic (30-day)
CL	=	cold lake temperature tier
Cl	=	Chloride
CLL	=	cold large lake temperature tier
Cl2	=	residual chlorine
CN	=	free cyanide
CrIII	=	trivalent chromium
CrVI	=	hexavalent chromium
CS-I	=	cold stream temperature tier one
CS-II	=	cold stream temperature tier two
Cu	=	Copper
dis	=	Dissolved
D.O.	=	Dissolved oxygen
DM	=	daily maximum
E. coli	=	Eschericia coli
F	=	Fluoride
Fe	=	Iron
Hg	=	Mercury
mg/l	=	milligrams per liter
ml	=	Milliliters
Mn	=	Manganese
MWAT	=	maximum weekly average temperature
NH3	=	ammonia as N(nitrogen)
Ni	=	Nickel
NO2	=	nitrite as N (nitrogen)
NO3	=	nitrate as N (nitrogen)
OW	=	outstanding waters
P	=	Phosphorus
Pb	=	Lead
S	=	sulfide as undissociated H2S (hydrogen sulfide)
Sb	=	Antimony
Se	=	Selenium
SO4	=	Sulfate
sp	=	Spawning
T	=	temperature
Tl	=	Thallium
Tr	=	Trout
Trec	=	total recoverable
TVS	=	table value standard
U	=	Uranium
µg/l	=	micrograms per liter
UP	=	use-protected
WAT	=	weekly average temperature
WL	=	warm lake temperature tier
WS-I	=	warm stream temperature tier one
WS-II	=	warm stream temperature tier two
WS-III	=	warm stream temperature tier three
WS-IV	=	warm stream temperature tier four
Zn	=	Zinc
(b)	In addition, the following abbreviations are used:
Fe(ch)	=	WS(dis)
Mn(ch)	=	WS(dis)
SO4	=	WS
These abbreviations mean:  For all surface waters with an actual water supply use, the less restrictive of the following two options shall apply as numerical standards, as specified in the Basic Standards and Methodologies at 31.11(6);
(i)	existing quality as of January 1, 2000; or
(ii)	Iron		=	300 µg/l (dissolved)
Manganese	=	50 µg/l (dissolved)
SO4		=	250 mg/l
For all surface waters with a “water supply” classification that are not in actual use as a water supply, no water supply standards are applied for iron, manganese or sulfate, unless the Commission determines as the result of a site-specific rulemaking hearing that such standards are appropriate.
(c)	As used in the “Temporary Modifications and Qualifiers” column of the tables, the term “type i” refers to a temporary modification adopted pursuant to subsection 31.7(3)(a)(i) of the Basic Standards and Methodologies for Surface Water (i.e., “where the standard is not being met because of human-induced conditions deemed correctable within a twenty (20) year period”).  The term “type iii” refers to a temporary modification adopted pursuant to subsection 31.7(3)(a)(iii) of the Basic Standards and Methodologies for Surface Water (i.e., “where there is significant uncertainty regarding the appropriate long-term underlying standard”).
(3)	Table Value Standards
In certain instances in the attached tables, the designation “TVS” is used to indicate that for a particular parameter a “table value standard” has been adopted.  This designation refers to numerical criteria set forth in the Basic Standards and Methodologies for Surface Water.  The criteria for which the TVS are applicable are on the following table.
TABLE VALUE STANDARDS
(Concentrations in µg/l unless noted)
PARAMETER(1)	TABLE VALUE STANDARDS (2)(3)	
Ammonia (4)	Cold Water = (mg/l as N)Total

	Warm Water = (mg/l as N)Total

	
NH3 = old TVS 	Cold Water Acute = 0.43/FT/FPH/2(4 old) in mg/l (N)	
	Warm Water Acute = 0.62/FT/FPH/2(4 old) in mg/l (N)	
Cadmium	Acute = (1.136672-[ln(hardness) x (0.041838)])*e(0.9151[ln(hardness)]-3.1485)
Acute(Trout) = (1.136672-[ln(hardness) x (0.041838)])*e(0.9151[ln(hardness)]-3.6236)
Chronic = (1.101672-[ln(hardness) x (0.041838)])*e(0.7998[ln(hardness)]-4.4451)	
Chromium III(5)	Acute = e(0.819[ln(hardness)]+2.5736)
Chronic = e(0.819[ln(hardness)]+0.5340)	
Chromium VI(5)	Acute = 16
Chronic = 11	
Copper	Acute = e(0.9422[ln(hardness)]-1.7408)
Chronic = e(0.8545[ln(hardness)]-1.7428)	
Lead	Acute = (1.46203-[ln(hardness)*(0.145712)])*e(1.273[ln(hardness)]-1.46)
Chronic = (1.46203-[(ln hardness)* (0.145712)])*e(1.273[ln(hardness)]-4.705)	
Manganese	Acute= e(0.3331[ln(hardness)]+6.4676)
Chronic= e(0.3331[ln(hardness)]+5.8743)	
Nickel	Acute = e(0.846[ln(hardness)]+2.253)
Chronic = e(0.846[ln(hardness)]+0.0554)	
Selenium(6)	Acute = 18.4
Chronic = 4.6	
Silver	Acute = ½ e(1.72[ln(hardness)]-6.52)
Chronic = e(1.72[ln(hardness)]-9.06)
Chronic(Trout) = e(1.72[ln(hardness)]-10.51)	
Temperature
	TEMPERATURE TIER	TIER
CODE	SPECIES EXPECTED TO BE PRESENT	APPLICABLE MONTHS	TEMPERATURE
STANDARD (OC)	
					(MWAT)	(DM)	
	Cold Stream
Tier I	CS-I	Brook trout, cutthroat trout	June – Sept.	17.0	21.2	
				Oct. - May	9.0	13.0	

Temperature
	Cold Stream
Tier II	CS-II	Brown trout, rainbow trout, mottled sculpin, mountain whitefish, longnose sucker, Arctic grayling	April – Oct.	18.2	23.8	
				Nov. - March	9.0	13.0	
	Cold Lake	CL	Brook trout, brown trout, cutthroat trout, lake trout, rainbow trout, Arctic grayling, sockeye salmon	April – Dec.	17.0	21.2	
				Jan. - March	9.0	13.0	
	Cold Large
Lake (>100 acres surface area)	CLL	Rainbow trout	April – Dec.	18.2	23.8	
				Jan. - March	9.0	13.0	
	Warm Stream Tier I	WS-I	Common shiner, Johnny darter, orangethroat darter	March – Nov.	24.2	29.0	
				Dec. – Feb.	12.1	14.5	
	Warm Stream Tier II	WS-II	Brook stickleback, central stoneroller, creek chub, longnose dace, Northern redbelly dace, finescale dace, white sucker	March – Nov.	27.5	28.6	
				Dec. – Feb.	13.7	14.3	
	Warm Stream Tier III	WS-III	Razorback sucker	March – Nov.	27.7	31.3	
				Dec. – Feb.	13.9	15.2	
	Warm Stream Tier IV	WS-IV	Other Warmwater Species	March – Nov.	28.7	31.3	
				Dec. – Feb.	14.3	15.2	
	Warm Lakes	WL	Yellow perch, walleye, pumpkinseed, smallmouth bass, striped bass, white bass, largemouth bass, bluegill, spottail shiner, Northern pike, tiger muskellunge, black crappie, common carp, gizzard shad, sauger, white crappie, wiper	April – Dec.	26.5	29.3	
				
Jan. - March	
13.3	
14.6	
Uranium	Acute = e(1.1021[ln(hardness)]+2.7088)
Chronic = e(1.1021[ln(hardness)]+2.2382)	
Zinc	Acute = 0.978 e(0.8525[ln(hardness)]+1.0617)
Chronic = 0.986 e(0.8525[ln(hardness)]+0.9109)	
TABLE VALUE STANDARDS - FOOTNOTES
(1)	Metals are stated as dissolved unless otherwise specified.
(2)	Hardness values to be used in equations are in mg/l as calcium carbonate and shall be no greater than 400 mg/L.  The hardness values used in calculating the appropriate metal standard should be based on the lower 95 per cent confidence limit of the mean hardness value at the periodic low flow criteria as determined from a regression analysis of site-specific data.  Where insufficient site-specific data exists to define the mean hardness value at the periodic low flow criteria, representative regional data shall be used to perform the regression analysis.  Where a regression analysis is not appropriate, a site-specific method should be used. In calculating a hardness value, regression analyses should not be extrapolated past the point that data exist.
(3)	Both acute and chronic numbers adopted as stream standards are levels not to be exceeded more than once every three years on the average.
(4)	FT = 100.03(20-TCAP);
Where TCAP is ≤ T ≤ 30
FT = 100.03(20-T);
Where 0 is ≤ T ≤ TCAP
TCAP = 20o C cold water aquatic life species present
TCAP = 25o C cold water aquatic life species absent
FPH = 1; Where 8 < pH ≤ 9
FPH = 1 + 10(7.4-pH);
              1.25		Where 6.5 ≤ pH ≤ 8
FPH means the acute pH adjustment factor, defined by the above formulas.
FT Means the acute temperature adjustment factor, defined by the above formulas.
T means temperature measured in degrees celsius.
TCAP means temperature CAP; the maximum temperature which affects the toxicity of ammonia to salmonid and non-salmonid fish groups.
NOTE:  If the calculated acute value is less than the calculated chronic value, then the calculated chronic value shall be used as the acute standard.
(5)	Unless the stability of the chromium valence state in receiving waters can be clearly demonstrated, the standard for chromium should be in terms of chromium VI.  In no case can the sum of the instream levels of Hexavalent and Trivalent Chromium exceed the water supply standard of 50 µg/l total chromium in those waters classified for domestic water use.
(6)	Selenium is a bioaccumulative metal and subject to a range of toxicity values depending upon numerous site-specific variables.

(4)	Assessment Criteria
The following criteria shall be used when assessing whether a specified waterbody is in attainment of the specified standard.
(a)	Upper South Platte Segment 6b, Chatfield Reservoir: Assessment Thresholds
chlorophyll = 11.2 µg/l, summer average, 1 in 5 year allowable exceedance frequency
phosphorus(Tot) = 0.035 mg/l, summer average, 1 in 5 year allowable exceedance frequency.
(b)	Upper South Platte Segment 16h: Selenium Assessment Locations
●	Toll Gate Creek (TG6): Downstream of the confluence of East and West Toll Gate Creeks, at 6th Avenue near the gage station.
●	East Toll Gate Creek (ET1): Upstream of the confluence with West Toll Gate Creek, at Chambers Road and 1st Avenue.
●	West Toll Gate Creek (WT1): Upstream of the confluence with East Toll Gate Creek, at 2nd Avenue.
(c)	Upper South Platte Segment 15 and Middle South Platte Segment 1a:  Dissolved Oxygen Assessment Locations
For the purpose of determining attainment of the standard, dissolved oxygen measurements shall only be taken in the flowing portion of the stream and at mid depth, and at least six inches above the bottom of the channel.  Dissolved oxygen measurements in man-made pools are not to be used for determination of attainment of the standards.
(d)	Big Dry Creek Segment 1:  Selenium Assessment Locations
●	bdc 1.5:  upstream of Broomfield Wastewater Treatment Plant
●	bcd 2.0:  upstream of Westminster Big Dry Creek Wastewater Treatment Facility
●	bcd 4.0: upstream of Northglenn Wastewater Treatment Plant
(e)	Big Dry Creek Segment 2 (Standley Lake): Assessment Thresholds
Chlorophyll  = 4.4 ug/L, Mar-Nov average, 1 in 5 yr allowable exceedance frequency
. . . . 
38.72	STATEMENT OF BASIS, SPECIFIC STATUTORY AUTHORITY AND PURPOSE:  MARCH 10, 2009 RULEMAKING REGARDING CHERRY CREEK RESERVOIR; FINAL ACTION AUGUST 10, 2009; EFFECTIVE DATE JANUARY 1, 2010 
The provisions of C.R S. 25-8-202(1) (b), (c) and (2); 25-8-204; 25-8-205 and 25-8-402; C.R.S. 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.
At the same time that these changes were adopted in Regulation #38, the Commission adopted consistent changes in Regulation #72, Cherry Creek Reservoir Control Regulation (5 CCR 1002-72).  
BASIS AND PURPOSE
The classified uses for the Cherry Creek Reservoir (Reservoir) include warm water aquatic life class 1, recreation class E (formerly 1a), water supply, and agriculture.  The Reservoir is mildly eutrophic and has limited releases given the primary role of Cherry Creek Dam as a flood control structure.  As a result of the data and analyses brought forward as part of the March 2009 Rulemaking Hearing, the Commission adopted revisions to the water quality standard for chlorophyll a in the Reservoir.  Specifically, the Commission has changed the seasonal chlorophyll a standard from15 µg/l to18 µg/l to be attained four out of five years. The Commission also adopted the “class E” recreation classification to replace the previous “class 1a” label, and replaced the fecal coliform numeric standard with an E. coli numeric standard of 126/100ml to be consistent with Regulation #31 (5 CCR 1007-31).  In conjunction with the adoption of a revised chlorophyll a standard, the Commission also adopted a number of changes to Regulation #72 (5 CCR 1002-72).
Background and Overview
During the September 2000 Rulemaking Hearing, the Commission repealed the prior total phosphorus water quality standards for the Reservoir and adopted a chlorophyll a standard of 15 µg/l (previously a “goal”), to be measured in the upper three meters of the water column during July through September. At that time, the Commission recognized that further data was needed to establish a scientifically appropriate chlorophyll a standard.  To this end, the Commission directed the Cherry Creek Basin Water Quality Authority (Authority), with oversight by the Water Quality Control Division (Division), to conduct a number of special studies.
In 2000, the Commission also retained a Total Maximum Annual Load (TMAL) of 14,270 pounds of total phosphorus to the Reservoir provided in Regulation #72, with a consideration that this be a “phased TMAL” while the Authority completed the requested studies.  An in-lake phosphorus goal, which was a July through September seasonal average, was set at 40 µg/l based on the Division’s 90% confidence level that this goal would result in the attainment of the chlorophyll a standard.  
The Commission further recognized in the 2000 Rulemaking Hearing the uncertain relationship between chlorophyll a and total phosphorus, such that the correlation resulting from that Rulemaking Hearing could change based on the analysis of the additional data obtained by the identified studies.  The Commission’s recognition of that uncertainty and the data modeling information obtained since that time provide the basis for adjusting the chlorophyll a standard in this rulemaking.
Chlorophyll a Standard
Between 1999 and 2008, the Authority gathered data to expand the data set used by the Commission to reach its decisions in the September 2000 Rulemaking.  The Authority used this data and previously collected data in its modeling efforts to evaluate whether a chlorophyll a standard of15 µg/l could feasibly be attained nine out of ten years.  The Authority concluded that such a standard could not be attained and set forth to identify a feasibility-based chlorophyll a standard.  
	The Current Standard is not Attainable.  Based on the evidence presented in the prehearing filings and at the March 2009 rulemaking hearing, the Commission agrees that a chlorophyll a standard of15 µg/l cannot be feasibly attained nine out of ten years.  
The Commission reaches this conclusion, based on the evidence presented throughout this process, for three reasons.  First, the current chlorophyll a standard was an admitted compromise between parties with competing interests, where scarce Reservoir data existed to support the parties’ respective positions.  Second, to achieve a chlorophyll a standard of15 µg/l, the Reservoir’s long-term seasonal (July to September) mean chlorophyll a concentration would need to be less than10 µg/l, a value not observed within the Reservoir since 1991.  The only way to achieve a long-term average summer chlorophyll a concentration at that level would be to require the reduction of flow-weighted total phosphorus concentrations into the Reservoir by more than 30 percent beyond the lowest value observed entering the Reservoir.  Finally, even the background concentrations are substantially above the concentration needed to achieve a chlorophyll a concentration of15 µg/l. 
	Current Water Quality Protection Efforts.  The evidence indicates that although the Cherry Creek Basin has experienced unprecedented growth during the past 20 years, the Authority and its partners have succeeded in implementing nutrient controls to help maintain the Reservoir’s water quality.  The Commission acknowledges that the Authority, its member agencies, and partners have improved wastewater treatment and have installed best available technology, installed nonpoint source controls, and utilized its land use agency responsibilities to control phosphorus in the watershed and inflow to the Reservoir.  
The evidence also indicates that the Authority considered additional watershed management practices that it could implement in the future.  By reviewing the outcome of the Authority’s analyses presented during this rulemaking process, the Commission concludes that the additional practices identified to date are not feasible at this time.  Some practices would be exorbitantly expensive, and it is unclear when and to what extent additional nutrient reductions might be realized within the Reservoir.  Nutrient reductions depend in part on future development and current economic conditions create uncertainty regarding the pace and scope of future development. In addition, access and liability-based legal issues may preclude the Authority from implementing certain future practices.  
The Commission also acknowledges that the Authority and its member agencies are committed to continuing watershed improvements, understanding that the watershed conditions are expected to improve with time and effort. While the Commission acknowledges that the additional future watershed management practices considered by the Authority are infeasible at this time, the Commission expects current water quality management strategies to continue and, as necessary, become more aggressive over time to attain water quality objectives and protect the uses of the Reservoir.
	 Science and Policy Support the Commission’s Adoption of a 18 µg/l Chlorophyll a Standard.  Based on the evidence advanced by the parties to this rulemaking, the Commission concludes that the appropriate assessment period by which to measure attainment with the standard should be five years, with attainment expected in four out of five years.  The Commission understands that an assessment period of five years will allow the Division and the Authority to respond more promptly to attainment issues, such that water quality can be managed more effectively.  Moreover, the Commission acknowledges that this adjusted assessment period would also preclude longer periods of time during which the standard could be exceeded, which could have a greater adverse impact on the Reservoir’s water quality. 
	Recognizing that the 15 µg/l standard is not attainable, the Commission has chosen to set a standard that provides protection of reservoir uses to the maximum degree practical, recognizing present uncertainty as to the specific chlorophyll a level that will prove to be attainable over time.  The Commission has determined as a matter of policy that it would be premature to set a chlorophyll a standard based solely on the assumption that no additional improvement is feasible.  The Commission believes that it is important to retain the goal of full protection of the Reservoir’s uses.
The adopted standard (18 µg/L) was developed from a prediction of the “most likely” chlorophyll a concentration and a measured variability component.  Prediction of the most likely chlorophyll a concentration (16.2 µg/L) was based on an equation, created through the reservoir modeling effort, relating chlorophyll to input, flow-weighted phosphorus concentration (0.177 mg/L).  The most likely chlorophyll concentration represents a long-term mean, which is not the appropriate value for a standard to be attained 80% of the time (in four of five years).  The 80th percentile value is calculated from the long-term mean and a measured variability component (standard deviation of 2.3 µg/L).  The standard deviation used in this calculation is smaller than the one proposed by the CCBWQA, which had argued that it should be based on an 8-year record of “existing conditions.”  However, the Commission chose to base the standard on the most recent five years of data as a matter of policy, to better reflect optimism about what can be achieved for this reservoir.  Because chlorophyll concentrations have been less variable over the last five years than over the last eight years, a smaller standard deviation is employed in development of the appropriate standard.  
Future Watershed Practices
Given the Authority’s duty to continue its water quality control management strategies, the Commission’s adoption of a 18 µg/l chlorophyll a standard will not result in a reduction or change in the Authority’s commitment to controlling chlorophyll a in the Reservoir.  The Commission’s adoption of revisions to Regulation #72 (5 CCR 1002-72) reflect the Authority’s commitment to maintain current water quality management strategies and, as necessary, become more aggressive over time to attain water quality objectives and protect the uses of the Reservoir.  
In accordance with statutory requirements, both the control regulation and the underlying standards will be revisited as efforts are implemented over time, such that more information is developed regarding influences on, and the attainability of, identified levels of Reservoir water quality.
PARTIES TO THE RULEMAKING
1.	Cherry Creek Basin Water Quality Authority
2.	Parker Water and Sanitation District
3.	Colorado Division of Wildlife
4.	Arapahoe County Water and Wastewater Authority
5.	Meridian Metropolitan District
6.	City of Greenwood Village
7.	U. S. Environmental Protection Agency (EPA), Region 8
8.	City of Aurora Water Department
9.	Denver Water
38.73	STATEMENT OF BASIS, SPECIFIC STATUTORY AUTHORITY AND PURPOSE:  MAY 11, 2009 RULEMAKING; FINAL ACTION AUGUST 10, 2009; EFFECTIVE JANUARY 1, 2010
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
The Commission revised the site-specific narrative nutrient criteria to include numeric standards for chlorophyll and total phosphorus for Bear Creek Reservoir (Bear Creek segment 1c).
Current Review: The Commission directed the Division to undertake a technical review of the scientific basis for the Bear Creek Reservoir narrative nutrient standard and Control Regulation (Regulation #74) for the following reasons: 
A.	There are no numeric goals for assessing water quality conditions related to excessive algal growth.
B.	There is no firm basis for determining what level of nutrient control is consistent with the water quality goals. 
C.	The allowable load is not specified in the Control Regulation, making it impossible to determine the appropriateness of allocations.
D.	There is an implied acceptance of aeration as a permanent basis for treating the symptoms of algal productivity that is higher than the target specified in the narrative standard.
The technical review showed: 
A.	Current Condition:  Water quality has been monitored in Bear Creek Reservoir since 1987.  The reservoir is more productive than allowed by the existing narrative standard, which specifies a target trophic condition between mesotrophic and eutrophic.  A more productive condition has been sustained despite significant reductions in external phosphorus load.  The present level of productivity would cause depletion of hypolimnetic oxygen (also contrary to the narrative standard) if aerators were not operated to destratify the reservoir.
B.	Characterizing Chlorophyll:  Chlorophyll concentrations declined after phosphorus loads were reduced.  Since 1995, typical summer average chlorophyll is about 24 µg/L, but there are large differences among years.  The differences appear to be associated with hydraulic residence time such that the highest average chlorophyll concentrations tend to be the years of longest residence time (lowest inflow).
C.	Role of Internal Phosphorus Load:  External phosphorus loads were reduced significantly in the early 1990s largely through efforts made by domestic dischargers to control effluent phosphorus concentrations.  As a result, phosphorus concentrations at the beginning of summer are relatively low.  However, through the process of internal release, phosphorus concentrations increase steadily through the summer months.  The net effect of internal release is more conspicuous in low-flow years, because high inflows provide more dilution.  Over the long term, internal release should diminish because the external load has been reduced, but it could take 10-15 years until internal release becomes negligible.
D.	Characterizing Phosphorus: Phosphorus concentrations declined sharply after controls were imposed in the early 1990s.  Since 1995, typical summertime concentrations of phosphorus have been about 44 µg/L, but there are large differences among years.  Differences are associated with hydraulic residence time as mentioned previously for chlorophyll.  It is appropriate to set a numeric standard for phosphorus because of its importance in characterizing trophic condition, and because it is the direct link to the control regulation.
E.	Defining a Chlorophyll-Phosphorus Linkage:  The simple ratio of chlorophyll to phosphorus defines the site-specific, net responsiveness of the resident algal community to the availability of phosphorus.  It is a “net” value because it reflects the balance of growth (nutrients, light, temperature) and loss (grazing, washout, settling) processes. For the purpose of linking chlorophyll and phosphorus standards, which are summer average concentrations, the response ratio also must be a seasonal value derived from Bear Creek Reservoir.
F.	Allowable Frequency of Exceedance:  There is no general precedent for setting an allowable frequency of exceedance for nutrient criteria, which are assessed once a year on the basis of a seasonal average, but the Division believes that one exceedance in five years is an appropriate frequency for allowable exceedances.
Revised Water Quality Standards for Bear Creek Reservoir: With the benefit of the lengthy historical record now available, the Commission believes it is appropriate to set numeric chlorophyll and phosphorus standards.  Both standards are considered attainable when the internal release of phosphorus becomes negligible, which is expected to occur in less than 20 years.  Each standard has an allowable exceedance frequency of once in five years.
A.	Chlorophyll Standard: The Commission adopted a chlorophyll standard of 10 µg/L.  The existing narrative was translated to a numeric value by defining the chlorophyll concentration at the mesotrophic-eutrophic boundary.  A concentration of 8 µg/L, which represents the boundary according to the OECD trophic classification scheme, was accepted as the typical condition expected for Bear Creek Reservoir.  The typical value was translated to an 80th percentile (once-in-five year exceedance threshold) using a very strong statistical relationship developed from a set of Colorado lakes.  The 80th percentile value, which is 10 µg/L, is the chlorophyll standard.
B.	Phosphorus Standard:  The Commission adopted a phosphorus standard of 32 µg/L.  The standard is calculated by use of a response ratio that relates the observed summer average chlorophyll concentration to the observed summer average phosphorus concentration.  The median of historical distribution of response ratios (0.318) was used on the assumption that all historical values are equally likely to represent future conditions.  The Commission heard testimony that a larger ratio (and thus a smaller phosphorus standard) might be preferred, but was not persuaded that a statistical argument or a mechanistic explanation would support that position.
C.	Assessment:  Because the phosphorus and chlorophyll standards are defined as seasonal averages, some additional guidance is required concerning timing and location of samples to be used in calculating the average. Samples are to be collected at a site in deep water near the dam and should be representative of conditions in the mixed layer. Past monitoring has resulted in 5 or 6 samples during the summer months (July, August, and September); it is anticipated that the same level of effort will be applied in the future. For assessment, the average (arithmetic mean) is calculated for the summer samples in each year.
At the same time that this change was adopted in Regulation #38, the Commission considered changes in the Control Regulation for Bear Creek Reservoir (Regulation #74) that would be consistent with the revised standard.  The Commission decided to make no changes to Regulation #74 at this time, preferring instead to wait for TMDL development to establish new phosphorus allocations that can be implemented in the Control Regulation.
Adoption of a Temporary Modification for Chlorophyll and Phosphorus Standards in Bear Creek Reservoir:  The underlying standards are not being attained in most years due to the seasonal augmentation of phosphorus concentrations from internal sources.  It is uncertain how long internal release will persist, although it is expected that it will disappear within 20 years.  In addition, the existing TMDL with wasteload allocations is now canceled by the new standard, and there is uncertainty about how the new standards might be translated into point source permit limits.  A type iii temporary modification set at “existing conditions” to expire 12/31/2014, is adopted in order to recognize the uncertainty regarding how soon the internal load will be reduced.  It will also provide certainty regarding effluent limits over the short term while a TMDL is completed which will include new wasteload allocations.  During the interim, sediment monitoring will be initiated to track internal phosphorus levels over time.  Progress on resolving uncertainty will be reviewed in the annual temporary modification hearings in December 2012 and 2013.
PARTIES TO THE RULEMAKING
1.	Colorado Division of Wildlife
2.	Bear Creek Watershed Association
3.	U. S. Environmental Protection Agency (EPA), Region 8
4.	Denver Water
38.74	STATEMENT OF BASIS, SPECIFIC STATUTORY AUTHORITY AND PURPOSE; JUNE 8, 2009 RULEMAKING, FINAL ACTION AUGUST 10, 2009, EFFECTIVE JANUARY 1, 2010
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:
A.	Waterbody Segmentation
The Commission decided to split lakes and reservoirs from segments that contained both streams and lakes and reservoirs so that new temperature standards could be adopted.  The water supply use was presumptively applied to these segments in the absence of information indicating that the water supply use is neither existing nor potentially existing.  Lakes and reservoirs were deleted from the following segments that previously encompassed both streams and lakes and reservoirs:
Upper South Platte River Segments 1a, 1b, 2a, 3, 4, 5b, 7, 8, 9, 11a, 11b, 16c, and 16g
Cherry Creek Segment 4
Bear Creek Segments 1a, 3, 4a, 5, and 7
Clear Creek Segments 1, 2, 3a, 6, 9a, 9b, 10, 12, 13a, 13b, 16a, 17b, 18a, and 19
Big Dry Creek Segment 1
Boulder Creek Segments 1, 2, 3, 4a, 4b, 6, 8, and 11
St. Vrain Creek Segments 1, 2, 4a, 4b, 5, and 6
Middle South Platte River Segment 3a
Big Thompson River Segments 1, 2, 6, 8, and 10
Cache La Poudre River Segments 1, 2, 6, 8, and 13a
Laramie River Segments 1 and 2
Lower South Platte River Segments 2a and 2b
Republican River Segments 6 and 7
The following lakes and reservoirs segments were created:
Upper South Platte River Segments 18, 19, 20, 21, 22, and 23
Cherry Creek Segments 5 and 6
Bear Creek Segments 1d, 8, 9, 10, 11, and 12
Clear Creek Segments 20, 21, 22, 23, 24, and 25
Big Dry Creek Segment 7
Boulder Creek Segments 13, 14, 15, 16, and 17
St. Vrain Creek Segments 8, 9, 10, 11, 12, and 13
Middle South Platte River Segment 7
Big Thompson River Segments 15, 16, 17, 18, and 19
Cache La Poudre River Segments 17, 18, 19, 20, 21 and 22
Laramie River Segments 3 and 4
Lower South Platte River Segments 4 and 5
Republican River Segment 8
The following segments were deleted when the constituent waterbodies were merged with other segments:
Upper South Platte River Segments 6c and 10b
Bear Creek Segments 4b and 4c
Some renumbering and/or creation of new segments was made due to information which showed that:  a) the original reasons for segmentation no longer applied; b) new water quality data showed that streams should be resegmented based on changes in their water quality; and/or c) certain segments could be grouped together in one segment because they had similar quality and uses.  In particular, segmentation was changed to facilitate adoption of the new temperature standards into individual segments.  The following changes were made:
Upper South Platte River 1a:  The segment description was amended to exclude lakes and reservoirs, and the segment now ends at the inlet of Cheesman Reservoir.  Lakes and reservoirs formerly included in this segment are now part of Segment 19.  The portion of the segment from Cheesman Reservoir to a point immediately above the confluence with the North Fork of the South Platte River is now part of Segment 6a.  The alteration of the segment boundary, the amendment of the description, and the resultant creation of Segment 19 were necessary to facilitate the adoption of appropriate temperature standards.
Upper South Platte River 1b:  The segment description was amended to exclude lakes and reservoirs.  Lakes and reservoirs formerly included in this segment are now part of Segment 18.  The amendment of the description and the resultant creation of Segment 18 were necessary to facilitate the adoption of appropriate temperature standards.
Upper South Platte River 2a:  The segment description was amended to exclude lakes and reservoirs.  Lakes and reservoirs formerly included in this segment are now part of Segment 19.  The amendment of the description and the resultant creation of Segment 19 were necessary to facilitate the adoption of appropriate temperature standards.
Upper South Platte River 3:  The segment description was amended to exclude lakes and reservoirs.  Lakes and reservoirs formerly included in this segment are now part of Segment 19.  The amendment of the description and the resultant creation of Segment 19 were necessary to facilitate the adoption of appropriate temperature standards.
Upper South Platte River 4:  The segment description was amended to exclude lakes and reservoirs.  Lakes and reservoirs formerly included in this segment are now part of Segment 19.  The amendment of the description and the resultant creation of Segment 19 were necessary to facilitate the adoption of appropriate temperature standards.
Upper South Platte River 5b:  The segment description was amended to exclude lakes and reservoirs.  Lakes and reservoirs formerly included in this segment are now part of Segment 19.  The amendment of the description and the resultant creation of Segment 19 were necessary to facilitate the adoption of appropriate temperature standards.
Upper South Platte River 5d:  This segment was created to encompass the portion of Gooseberry Gulch and its tributaries downstream of Sunset Trail in order to retain trout-specific standards for acute cadmium and chronic silver that are being deleted from Segment 5c.  This segment was formerly a portion of Segment 5c.  
Upper South Platte River 6a:  The segment description now begins at the outlet of Cheesman Reservoir.  The added portion of the segment, which extends from the Cheesman outlet to a point immediately above the confluence with the North Fork of the South Platte River, was formerly in Segment 1a.  The alteration of the segment boundary was necessary to facilitate the adoption of appropriate temperature standards.
Upper South Platte River 6c:  The Commission deleted segment 6c and revised the description for Segment 14, incorporating the section of the mainstem South Platte River currently in segment 6c into Segment 14.  This change was necessary for the purpose of setting appropriate temperature standards.  This change was based on use-attainability analyses provided by Centennial Water and Sanitation District and the Division, which indicated this portion of the South Platte River has temperature and fish communities more appropriately classified as warm water aquatic life with warm stream tier II as the appropriate temperature standard.  This finding is based on fish community sampling conducted over a 20-yr period and temperature data collected for nearly 9 years.  The retention of water in Chatfield Reservoir sufficiently warms the water in the South Platte River so that a cold water biological community cannot be fully supported, nor can a cold water temperature standard be attained.  Most of the aquatic community consists of warm water species.
Although the Commission has determined that the aquatic community and ambient temperatures are not consistent with a cold water aquatic life classification for the stretch of the river below Chatfield Reservoir, the Commission recognizes the continued presence of trout in this stream reach.  The Commission also recognizes that the upper reaches of the South Platte below Chatfield Reservoir provide an important urban fishery resource, including a trout fishery supported by Colorado Division of Wildlife stocking.  Therefore, the Commission strongly supports the ongoing efforts of stakeholder groups to improve the fishery habitat below Chatfield.  Maintaining and improving this fishery that provides nearby fishing access for those in the Denver metropolitan area is an important and worthwhile goal.
Upper South Platte River 7:  The segment description was amended to exclude lakes and reservoirs.  Lakes and reservoirs formerly included in this segment are now part of Segment 19.  The amendment of the description and the resultant creation of Segment 19 were necessary to facilitate the adoption of appropriate temperature standards.
Upper South Platte River 8:  The segment description was amended to exclude lakes and reservoirs.  Lakes and reservoirs formerly included in this segment are now part of Segment 20.  The amendment of the description and the resultant creation of Segment 20 were necessary to facilitate the adoption of appropriate temperature standards.
Upper South Platte River 9:  The segment description was amended to exclude lakes and reservoirs.  Lakes and reservoirs formerly included in this segment are now part of Segment 20.  The amendment of the description and the resultant creation of Segment 20 were necessary to facilitate the adoption of appropriate temperature standards.
Upper South Platte River 10a: The segment description was amended to incorporate a remnant of Segment 10b (described below). Lakes and reservoirs which would have been included in this segment are now part of Segment 20. The amendment of the description and the resultant creation of Segment 20 were necessary to facilitate the adoption of appropriate temperature standards.
Upper South Platte River 10b: The segment has been deleted to address a long-standing lack of clarity about the disposition of West Plum Creek and its tributaries.  The small portion of West Plum Creek above Perry Park pond, as well as Stark Creek and Gove Creek below the National Forest boundary, that were formerly in this segment are now part of Segment 10a.  Lakes and reservoirs which would have been included in this segment are now part of Segment 20. The amendment of the description and the resultant creation of Segment 20 were necessary to facilitate the adoption of appropriate temperature standards.
Upper South Platte River 11a:  The segment description was amended to exclude lakes and reservoirs.  Lakes and reservoirs formerly included in this segment are now part of Segment 21.  The amendment of the description and the resultant creation of Segment 21 were necessary to facilitate the adoption of appropriate temperature standards.
Upper South Platte River 11b:  The segment description was amended to exclude lakes and reservoirs.  Lakes and reservoirs formerly included in this segment are now part of Segment 21.  The amendment of the description and the resultant creation of Segment 21 were necessary to facilitate the adoption of appropriate temperature standards.
Upper South Platte River 14:  The segment description now begins at the outlet from Chatfield Reservoir.  The portion of the segment from the Chatfield outlet to Bowles Avenue was formerly in Segment 6c.  The alteration of the segment boundary was necessary to facilitate the adoption of appropriate temperature standards.
Upper South Platte River 16c: The segment description was amended to exclude lakes and reservoirs. Lakes and reservoirs formerly included in this segment are now part of Segment 22 or 23. The amendment of the description and the resultant creation of Segments 22 and 23 were necessary to facilitate the adoption of appropriate temperature standards.
Upper South Platte River 16g: The segment description was amended to exclude lakes and reservoirs. Lakes and reservoirs formerly included in this segment are now part of Segment 22 or 23. The amendment of the description and the resultant creation of Segments 22 and 23 were necessary to facilitate the adoption of appropriate temperature standards.
Upper South Platte River 18:  The segment description was created to encompass lakes and reservoirs within the boundaries of the Lost Creek and Mt. Evans Wilderness areas.  This segment includes lakes and reservoirs formerly within Upper South Platte River Segment 1b.
Upper South Platte River 19:  The segment description was created to encompass lakes and reservoirs in the South Platte River system from headwaters to Chatfield Reservoir, except for specific listings in Segment 18.  It includes Antero, Spinney Mountain, Elevenmile, Cheesman, and Strontia Springs.  This segment includes lakes and reservoirs formerly within Upper South Platte River Segments 1a, 2a, 3, 4, 5b, and 7.
Upper South Platte River 20: The segment description was created to encompass lakes and reservoirs in the Plum Creek system within National Forest boundaries, and lakes and reservoirs in the Bear Creek drainage (part of the Plum Creek system) between the National Forest boundary and to the inlet of Perry Park Reservoir (Douglas County). This segment includes lakes and reservoirs formerly within Upper South Platte River Segments 8, 9, and 10b.
Upper South Platte River 21:  The segment description was created to encompass lakes and reservoirs in the Plum Creek system except for specific listings in Segment 20.  This segment includes lakes and reservoirs formerly within Upper South Platte River Segments 11a and 11b.
Upper South Platte River 22: The segment description was created to encompass lakes and reservoirs in watersheds tributary to the South Platte River from the outlet of Chatfield Reservoir to a point immediately below the confluence with Big Dry Creek, except for specific listings in the subbasins of the South Platte River, and in Segments 16b, 17a, 17b, 17c, and 23. This segment includes lakes and reservoirs formerly within Upper South Platte River Segments 16c and 16g.
Upper South Platte River 23: The segment description was created to encompass lakes and reservoirs in watersheds tributary to the South Platte River within City and County of Denver, except for specific listings in the subbasins of the South Platte River, and in Segments 16b, 17a, 17b, and 17c.  This segment includes lakes and reservoirs formerly within Upper South Platte River Segments 16c and 16g.
Cherry Creek 4:  The segment description was amended to exclude lakes and reservoirs. Lakes and reservoirs formerly included in this segment are now part of Segment 5 or 6.  The amendment of the description and the resultant creation of Segments 5 and 6 were necessary to facilitate the adoption of appropriate temperature standards.
Cherry Creek 5:  The segment description was created to encompass lakes and reservoirs in the Cherry Creek system from the source of East and West Cherry Creeks to the confluence with the South Platte River, except for specific listings in Segments 2 and 6.  This segment includes lakes and reservoirs formerly within Cherry Creek Segment 4.
Cherry Creek 6:  The segment description was created to encompass lakes and reservoirs in the Cherry Creek system that are within the boundaries of the City and County of Denver.  This segment includes lakes and reservoirs formerly within Cherry Creek Segment 4.
Bear Creek 1a: The segment description was amended to exclude lakes and reservoirs, and the segment now ends at the inlet of Evergreen Lake.  Lakes and reservoirs formerly included in this segment are now part of Segment 1d (Evergreen Lake) or 9.  The portion of the segment from Evergreen Lake to the Harriman Ditch is now new Segment 1e. The alteration of the segment boundary, the amendment of the description, and the resultant creation of Segments 1e and 9 were necessary to facilitate the adoption of appropriate temperature standards.  The description also was amended to exclude the mainstem of Bear Creek from the source to the boundary of the Mt. Evans Wilderness Area; that portion of the mainstem was moved to Segment 7, which includes all tributaries within the Wilderness Area.
Bear Creek 1c: The segment description now contains only Bear Creek Reservoir. Soda Lakes were moved to the new Segment 11, which is a warm water aquatic life segment.  The fish species present in Soda Lakes are more representative of a warm water lake.
Bear Creek 1d: The segment description was created for Evergreen Lake, which was formerly within Segment 1a.  Creation of Segment 1d was necessary to facilitate the adoption of appropriate temperature standards.
Bear Creek 1e: The segment description was created for the portion of the Bear Creek mainstem between the outlet of Evergreen Lake and the Harriman Ditch, which was formerly part of Segment 1a.  Creation of Segment 1e was necessary to facilitate the adoption of appropriate temperature standards.
Bear Creek 3:  The segment description was amended to exclude lakes and reservoirs.  Lakes and reservoirs formerly included in this segment are now part of Segment 9.  The amendment of the description and the resultant creation of Segment 9 were necessary to facilitate the adoption of appropriate temperature standards.
Bear Creek 4a: The segment description was amended to exclude lakes and reservoirs and to adjust the downstream boundary consistent with a change to Segment 1a.  Lakes and reservoirs formerly included in this segment are now part of Segment 11. The amendment of the description and the resultant creation of Segment 11 were necessary to facilitate the adoption of appropriate temperature standards.  The boundary change necessitates moving Cub Creek to Segment 5.
Bear Creek 4b: The segment has been deleted.  Swede Gulch and associated wetlands formerly in this segment were incorporated into Segment 5.  Lakes and reservoirs formerly included in this segment are now part of Segment 10. The amendment of the description and the resultant creation of Segment 10 were necessary to facilitate the adoption of appropriate temperature standards.
Bear Creek 4c: The segment has been deleted.  Swede Gulch and associated wetlands formerly in this segment were incorporated into Segment 5.  Lakes and reservoirs formerly included in this segment are now part of Segment 10.  The amendment of the description and the resultant creation of Segment 10 were necessary to facilitate the adoption of appropriate temperature standards.
Bear Creek 5:  The segment description was amended to exclude lakes and reservoirs, and to remove streams in the Turkey Creek system.  Lakes and reservoirs formerly included in this segment are now part of Segment 10 or 12. Streams in the Turkey Creek system are now part of Segment 6a.  The description also has been amended to incorporate Swede and Kerr Gulches formerly included in Segments 4b and 4c, and Cub Creek, which was formerly part of Segment 4a.  The amendments of the description and the resultant creation of Segments 6a, 10, and 12 were necessary to facilitate the adoption of appropriate temperature standards.
Bear Creek 6a:  The segment description was created for the portion of the Turkey Creek system that was formerly part of Segment 5.  Creation of Segment 6a was necessary to facilitate the adoption of appropriate temperature standards.  The decision to create Segment 6a and companion Segment 6b, rather than assign a higher (unused) number, was influenced by a desire to keep the elements of Turkey Creek in close proximity in the tables.
Bear Creek 6b:  The segment description matches that of former Segment 6.
Bear Creek 7:  The segment description was amended to exclude lakes and reservoirs.  Lakes and reservoirs formerly included in this segment are now part of Segment 8.  The amendment of the description and the resultant creation of Segment 8 were necessary to facilitate the adoption of appropriate temperature standards.  In addition, the description was amended to incorporate the mainstem of Bear Creek within the Wilderness Area, which formerly was part of Segment 1a.
Bear Creek 8:  The segment description was created to encompass lakes and reservoirs in the Bear Creek system from the sources to the boundary of the Mt. Evans Wilderness area.  This segment includes lakes and reservoirs formerly within Bear Creek Segment 7.
Bear Creek 9:  The segment description was created to encompass lakes and reservoirs in the Bear Creek system from the boundary of the Mt. Evans Wilderness area to the outlet of Evergreen Lake.  This segment includes lakes and reservoirs formerly within Bear Creek Segments 1a and 3, except for Evergreen Lake.
Bear Creek 10:  The segment description was created to encompass lakes and reservoirs in drainages of Swede Gulch, Sawmill Gulch, Troublesome Gulch, and Cold Springs Gulch from source to confluence with Bear Creek. This segment includes lakes and reservoirs formerly within Bear Creek Segments 4b, 4c, and 5.
Bear Creek 11:  The segment description was created to encompass lakes and reservoirs from the outlet of Evergreen Lake to the confluence with the South Platte River, except as specified in Segments 1c, 10, and 12; it includes Soda Lakes. This segment includes lakes and reservoirs formerly within Bear Creek Segments 1c and 4a.
Bear Creek 12:  The segment description was created to encompass lakes and reservoirs in the Turkey Creek system from the source to the inlet of Bear Creek Reservoir.
Clear Creek 2a:  This segment was created to encompass the mainstem of Clear Creek, including all tributaries and wetlands, from the I-70 bridge above Silver Plume to a point just above the confluence with West Fork Clear Creek, except for specific listings in Segments, 3a and 3b.  The resegmentation of Segment 2 was necessary in order to better represent differences in water quality between this segment and Segments 2b and 2c.
Clear Creek 2b:  This segment was created to encompass the mainstem of Clear Creek, including all tributaries and wetlands, from the confluence with West Fork Clear Creek to a point just below the confluence with Mill Creek, except for specific listings in Segments 4 through 8.   The resegmentation of Segment 2 was necessary in order to better represent differences in water quality between this segment and Segments 2a and 2c.
Clear Creek 2c:  This segment was created to encompass the mainstem of Clear Creek, including all tributaries and wetlands, from a point just below the confluence with Mill Creek to a point a point just above the Argo Tunnel discharge, except for specific listings in Segments 9a, 9b, and 10.  The resegmentation was necessary in order to better represent differences in water quality between this segment and Segments 2a and 2b. 
Clear Creek Segment 20:  This segment was created to encompass lakes and reservoirs within the boundary of the Mt. Evan Wilderness Area.  This segment includes lakes and reservoirs formerly within Segment 19.
Clear Creek Segment 21:  This segment was created to encompass lakes and reservoirs within the Clear Creek system from its source to the Farmer’s Highline Canal diversion in Golden, Colorado, except for those in Segments 20, 22, and 25; and Upper Long Lake.  This segment includes lakes and reservoirs formerly within Segments 1, 2, 3a, 6, 9a, 9b, and 10.
Clear Creek Segment 22:  This segment was created to encompass lakes and reservoirs within the North Clear Creek drainage from a point just below the confluence with Chase Gulch to its confluence with Clear Creek.  This segment includes lakes and reservoirs formerly within Segment 13b.
Clear Creek Segment 23:  This segment was created for Ralston Reservoir.  This segment includes a lakes/reservoir formerly within Segment 17b.
Clear Creek Segment 24:  This segment was created to encompass lakes and reservoirs in the Clear Creek system from the Farmers Highline Canal diversion in Golden, Colorado to the confluence with the South Platte River, except for specific listings in Segments 17a, 21, and 23.
Clear Creek Segment 25:  This segment was created for Guanella Reservoir.  Guanella Reservoir was formerly within either Segment 2 or 5.  It is not clear to which segment it belonged.
Big Dry Creek Segment 7:  This segment was created to encompass lakes and reservoirs in the Big Dry Creek system from the source to the confluence with the South Platte River, except for specific listings in Segments 2, 3, and 5.  This segment includes lakes and reservoirs formerly within Segment 1.
Boulder Creek Segment 2a:  This segment description was amended to remove the portion of the Boulder Creek system from a point immediately below the confluence with North Boulder Creek to a point immediately above the confluence with South Boulder Creek.  The Commission moved that portion of the Boulder Creek system to a newly created Segment 2b, to facilitate the adoption of appropriate temperature standards.
Boulder Creek Segment 2b:  This segment was created to encompass the Boulder Creek system from a point immediately below the confluence with North Boulder Creek to a point immediately above the confluence with South Boulder Creek.  The Commission created this segment from portions of the Boulder Creek system split from Segment 2a to facilitate the adoption of appropriate temperature standards.
Boulder Creek Segment 13:  This segment was created to encompass lakes and reservoirs tributary to Boulder Creek that are within the boundary of the Indian Peaks Wilderness Area.  This segment includes lakes and reservoirs formerly in Segment 1.
Boulder Creek Segment 14:  This segment was created to encompass lakes and reservoirs tributary to Boulder Creek from the source to a point immediately above the South Boulder Creek confluence.  This segment includes lakes and reservoirs formerly in Segments 2 and 3.
Boulder Creek Segment 15:  This segment was created to encompass lakes and reservoirs tributary to South Boulder Creek from the source to Highway 93 and all lakes and reservoirs tributary to Coal Creek from the source to Highway 93.  This segment includes lakes and reservoirs formerly in Segments 4a, 4b and 6.
Boulder Creek Segment 16:  This segment was created to encompass lakes and reservoirs tributary to South Boulder Creek from Highway 93 to the confluence with Boulder Creek and all lakes and reservoirs tributary to Coal Creek from Highway 93 to the confluence with Boulder Creek.  This segment includes lakes and reservoirs formerly in Segments 4b and 8.
Boulder Creek Segment 17:  This segment was created to encompass lakes and reservoirs tributary to Boulder Creek from a point immediately below the South Boulder Creek confluence to the confluence with St. Vrain Creek.  This segment includes lakes and reservoirs formerly in Segment 11.
St. Vrain Creek Segment 2a:  The segment description was amended to remove the portion of the St. Vrain Creek system from the eastern boundary of the Roosevelt National Forest to Hygiene Road.  The Commission moved that portion of the St. Vrain Creek system to a newly created Segment 2b, to facilitate the adoption of appropriate temperature standards.
St. Vrain Creek Segment 2b:  This segment was created to encompass the St. Vrain Creek system from the eastern boundary of the Roosevelt National Forest to Hygiene Road.  The Commission created this segment from portions of the St. Vrain Creek system split from Segment 2a to facilitate the adoption of appropriate temperature standards.	
St. Vrain Creek Segment 4a:  This segment description was amended to remove the portion of the Left Hand Creek system from a point immediately below the confluence with James Creek to Highway 36.  The Commission moved that portion of the Left Hand Creek system to a newly created Segment 4c, to facilitate the adoption of appropriate temperature standards.
St. Vrain Creek Segment 4c:  This segment was created to encompass the Left Hand Creek system from a point immediately below the confluence with James Creek to Highway 36.  The Commission created this segment from portions of the Left Hand Creek system split from Segment 4a to facilitate the adoption of appropriate temperature standards.
St. Vrain Creek Segment 8:  This segment was created to encompass lakes and reservoirs tributary to St. Vrain Creek that are within the boundary of the Indian Peaks Wilderness Area and Rocky Mountain National Park.  This segment includes lakes and reservoirs formerly in Segment 1.
St. Vrain Creek Segment 9:  This segment was created to encompass lakes and reservoirs tributary to St. Vrain Creek from sources to Hygiene Road.  This segment includes lakes and reservoirs formerly in Segment 2.
St. Vrain Creek Segment 10:  This segment was created to encompass lakes and reservoirs tributary to Left Hand Creek from sources to Highway 36.  This segment includes lakes and reservoirs formerly in Segments 4a and 4b.
St. Vrain Creek Segment 11:  This segment was created to encompass Barbour Ponds.  This segment includes lakes and reservoirs formerly in Segment 3.
St. Vrain Creek Segment 12:  This segment was created to encompass lakes and reservoirs tributary to Left Hand Creek from Highway 36 to the confluence with St. Vrain Creek.  This segment includes lakes and reservoirs formerly in Segment 5.
St. Vrain Creek Segment 13:  This segment was created to encompass lakes and reservoirs tributary to St. Vrain Creek from Hygiene Road to the confluence with the South Platte River.  This segment includes lakes and reservoirs formerly in Segment 6.
Middle South Platte River Segment 5a: This segment description was amended to remove Crow Creek and Box Elder Creek from their sources to their confluences with the South Platte River.  The Commission moved those portions of Crow Creek and Box Elder Creek to a newly created Segment 5c, to facilitate the adoption of appropriate temperature standards.
Middle South Platte River Segment 5c: This segment was created to encompass Crow Creek and Box Elder Creek from their sources to their confluences with the South Platte River.  The Commission created this segment by splitting Crow Creek and Box Elder Creek from Segment 5a to facilitate the adoption of appropriate temperature standards. 
Middle South Platte River Segment 7:  This segment was created to encompass lakes and reservoirs tributary to the South Platte River from a point immediately below the confluence with Big Dry Creek to the Weld/Morgan County line.  This segment includes lakes and reservoirs formerly in Segment 3a.
Big Thompson River Segment 15:  This segment was created to encompass lakes and reservoirs tributary to the Big Thompson River within Rocky Mountain National Park.  This segment includes lakes and reservoirs formerly in Segment 1.
Big Thompson River Segment 16:  This segment was created to encompass lakes and reservoirs tributary to the Big Thompson River from the boundary of Rocky Mountain National Park to the Home Supply Canal diversion.  This segment includes lakes and reservoirs formerly in Segment 2.
Big Thompson River Segment 17:  This segment was created to encompass lakes and reservoirs tributary to the Big Thompson River from the Home Supply Canal diversion to the confluence with the South Platte River.  This segment includes lakes and reservoirs formerly in Segment 6.
Big Thompson River Segment 18:  This segment was created to encompass lakes and reservoirs tributary to the Little Thompson River from the source to the Culver Ditch diversion.  This segment includes lakes and reservoirs formerly in Segment 8.
Big Thompson River Segment 19:  This segment was created to encompass lakes and reservoirs tributary to the Little Thompson River from the Culver Ditch diversion to the confluence with the Big Thompson River.  This segment includes lakes and reservoirs formerly in Segment 10.
Cache La Poudre River Segment 2a: This segment description was amended to remove the portion of the Cache La Poudre River system from a point immediately below the confluence with the South Fork Cache La Poudre River to the Monroe Gravity Canal/North Poudre Supply canal diversion.  The Commission moved that portion of the Cache La Poudre system to a newly created Segment 2b, to facilitate the adoption of appropriate temperature standards.
Cache La Poudre River Segment 2b: This segment was created to encompass the Cache La Poudre system from a point immediately below the confluence with the South Fork Cache La Poudre River to the Monroe Gravity Canal/North Poudre Supply canal diversion.  The Commission created this segment from portions of the Cache La Poudre system split from Segment 2a to facilitate the adoption of appropriate temperature standards.
Cache La Poudre River Segment 13a: This segment description was amended to remove North Branch Boxelder Creek, South Branch Boxelder Creek and Sand Creek from their sources to their confluences with the mainstem of Boxelder Creek.  The Commission moved that portion of the Cache La Poudre system to a newly created Segment 13c, to facilitate the adoption of appropriate temperature standards.  
Cache La Poudre River Segment 13c:  This segment was created to encompass North Branch Boxelder Creek, South Branch Boxelder Creek and Sand Creek from their sources to their confluences with the mainstem of Boxelder Creek.  The Commission created this segment from portions of the Cache La Poudre system split from Segment 13a to facilitate the adoption of appropriate temperature standards.
Cache La Poudre River Segment 17:  This segment was created to encompass lakes and reservoirs tributary to the Cache La Poudre River from within Rocky Mountain National Park and the Rawah, Neota, Comanche, and Cache La Poudre Wilderness Area.  This Segment includes lakes and reservoirs formerly in segment 1.
Cache La Poudre River Segment 18:  This segment was created to encompass lakes and reservoirs tributary to the Cache La Poudre River from the boundaries of Rocky Mountain National Park and the Rawah, Neota, Comanche, and Cache La Poudre Wilderness Area to the Monroe Gravity Canal/North Poudre Supply Canal diversion.  This Segment includes lakes and reservoirs formerly in segment 2.
Cache La Poudre River Segment 19:  This segment was created to encompass lakes and reservoirs tributary to the North Fork of the Cache La Poudre River from the source to the inlet of Halligan Reservoir.  This segment includes lakes and reservoirs formerly in Segment 6.
Cache La Poudre River Segment 20:  This segment was created to encompass lakes and reservoirs tributary to the North Fork of the Cache La Poudre River from the inlet of Halligan Reservoir to the confluence with the Cache La Poudre River.  This segment includes lakes and reservoirs formerly in Segment 8.
Cache La Poudre River Segment 21:  This segment was created to encompass lakes and reservoirs tributary to the Cache La Poudre River from the Monroe Gravity Canal/North Poudre Supply Canal diversion to the confluence with the South Platte River.  This segment includes lakes and reservoirs formerly in Segment 13a, with the exception of Fossil Creek Reservoir.
Cache La Poudre River Segment 22:  This segment was created to encompass Fossil Creek Reservoir, which was formerly in Segment 13a.
Laramie River Segment 2a: This segment description was amended to remove the portion of the Laramie River mainstem from the National Forest boundary to the Colorado/Wyoming border.  The Commission moved that portion of the Laramie River mainstem to a newly created Segment 2b, to facilitate the adoption of appropriate temperature standards.
Laramie River Segment 2b: This segment was created to encompass the Laramie River mainstem from the National Forest boundary to the Colorado/Wyoming border.  The Commission created this segment from portions of the Laramie River system split from Segment 2a to facilitate the adoption of appropriate temperature standards.
Laramie River Segment 3: This segment was created to encompass lakes and reservoirs tributary to the Laramie River from within the Rawah Wilderness Area.  This segment includes lakes and reservoirs formerly in Segment 1.
Laramie River Segment 4: This segment was created to encompass lakes and reservoirs tributary to the Laramie River from the Rawah Wilderness Area to the Colorado/Wyoming border.  This segment includes lakes and reservoirs formerly in Segment 2.
Lower South Platte River Segment 2b:  This segment description was amended to remove a portion of Beaver Creek from its source to the Fort Morgan Canal.  This upper portion of Beaver Creek is now in Segment 2a.
Lower South Platte River Segment 4: This segment was created to encompass lakes and reservoirs tributary to the South Platte River from the Weld/Morgan County line to the Colorado/Nebraska border.  This segment includes lakes and reservoirs formerly in Segment 2a.
Lower South Platte River Segment 5: This segment was created to encompass lakes and reservoirs tributary to the South Platte River north of the South Platte River and below 4,500 feet in elevation in Morgan County, north of the South Platte River in Washington County, north of the South Platte River and below 4,200 feet in elevation in Logan County, north of the South Platte River and below 3,700 feet in elevation in Sedgwick County, and the mainstems of Beaver Creek, Bijou Creek and Kiowa Creek from their sources to the confluence with the South Platte River.  This segment includes lakes and reservoirs formerly in Segment 2b.
Republican River Segment 8: This segment was created to encompass lakes and reservoirs tributary to the Republican and Smoky Hill Rivers in Colorado.  This segment includes lakes and reservoirs formerly in Segments 6 and 7.
B.	Revised Aquatic-Life Use Classifications 
The Commission reviewed information regarding existing aquatic communities.  The following changes to the aquatic-life use classification were made based on review of the fish communities:
Upper South Platte River Segment 10b: Cold 1 to Warm 1 (now part of Segments 8 and 10a)
Upper South Platte River Segment 12: Cold 1 to Warm 1
Upper South Platte River Segment 6c: Cold 1 to Warm 1 (now part of Segment 14)
Bear Creek Segment 1c (Soda Lakes only): Cold 1 to Warm 2 (now part of Segment 11)
C.	Recreation Classifications and Standards
As part of the Basic Standards hearing of 2005, recreation classifications were revised into four new classifications.  The Commission reviewed the previous segment classifications (1a, 1b and 2) and determined the appropriate new classification based on classification criteria presented as part of the Basic Standards Hearing, use attainability analyses or other basis.  In addition, during the 2005 Basic Standards Hearing, the transition from the use of the fecal coliform standard to E. coli standard was completed.  Fecal coliform criteria were deleted from the numeric standards. 
Based on information that showed existing primary contact recreation use is in place in at least a portion of the segment, the Commission converted the following segments from Recreation Class 1a to Recreation Class E with a 126/100 ml E. coli standard:
Upper South Platte River Segments 1a, 1b, 2a, 2b, 2c, 3, 4, 5a, 5b, 6a, 6b, 7, 8, 9, 10a, 11a, 11b, 12, 13, 14, 15, 16a, 16b, 16c, 16d, 16e, 16f, 16g, 16h, 17a, 17b, and 17c
Cherry Creek Segments 1, 2, 3, and 4
Bear Creek Segments 1a, 1b, 1c, 2, 3, 4a, 5, 6b, and 7
Clear Creek Segments 1, 2a, 3a, 3b, 4, 5, 6, 8, 9a, 9b, 10, 11, 12, 13a, 13b 14b, 15, 16a, 18a, and 19
Big Dry Creek Segments 2 and 4a
Boulder Creek Segments 1, 2a, 3, 4a, 4b, 4c, 4d, 5, 6, 7a, 7b, 8, 9, 10, and 11
St. Vrain Creek Segments 1, 2a, 3, 4a, 4b, 5, 6, and 7
Middle South Platte River Segments 1a, 1b, 3a, 3b, and 4
Big Thompson River Segments 1, 2, 3, 4a, 4b, 4c, 6, 7, 8, 9, 10, 11, 12, 13, and 14
Cache La Poudre River Segments 1, 2a, 6, 7, 8, 9, 10, 11, 12, 13a, 14, 15, and 16
Laramie River Segments 1 and 2a
Lower South Platte River Segments 1, 2b, and 3
Republican River Segments 1, 2, 3, 4, and 5
The following segments were converted from Recreation Class 1b to Recreation Class P with a 205/100 ml E. coli standard:
Big Dry Creek Segment 1
Big Thompson River Segment 5
Cache La Poudre River Segment 13b
Based on a review of existing Use Attainability Analyses showing that primary contact recreation does not occur or is not attainable, the following segments were converted to Recreation Class N classification with a 630/100 ml E. coli standard:
Clear Creek Segments 7, 14a, 16b, and 18b
Big Dry Creek Segments 3, 5, and 6 
Middle South Platte River Segments 5a, 5b, and 6
Big Thompson River Segments 4a, 4b, 4c, and 5
Cache La Poudre River Segment 13b
Lower South Platte River Segment 2a
Republican River Segments 6 and 7
The following segment was converted from Recreation Class 2 to Recreation Class N classification, with a 126/100 ml E. coli standard in conformance with Commission decisions in 2004.
Clear Creek Segment 17a
The Department of Energy (DOE) provided information supporting the appropriateness of retaining the recreation N use classification for the portion of Big Dry Creek Segment 5 located within the Central Operable Unit (COU) in its responsive pre-hearing statement.  The Hazardous Materials and Waste Management Division confirmed this information to be accurate.  Recreational activities are currently prohibited within the COU and are expected to continue to be prohibited for the next 20 years. The final record of decision for the Rocky Flats Site, the Rocky Flats Legacy Management Agreement (RFLMA), and the environmental covenants currently prohibit recreational uses for the COU.  Fences, “no trespassing” signs, and operational controls currently prevent public access to the COU.  A portion of Big Dry Creek Segment 5, North Walnut Creek from its source to the western edge of the COU, lies outside of the COU.  DOE proposed and the Commission agreed to move this portion of North Walnut Creek from Segment 5 to Segment 4b.  Additionally, DOE proposed and the Commission agreed to move a portion of Big Dry Creek Segment 4b, which lies inside the COU, to Segment 5.
Based on conditions that have changed from those originally limiting the recreational use in an existing Use Attainability Analysis, the following segment was converted to from Recreation Class 2 to Recreation Class P with a 205/100 ml E. coli standard:
Big Dry Creek Segment 4b
Because there has not been a reasonable level of inquiry about existing recreational uses and no recreational use attainability analysis has been completed, the following segment was converted from Recreation 1a to Recreation Class U with a 126/100 ml E.coli standard:
Upper South Platte Segment 5c
The following segment was converted from a Recreation Class 1a to Recreation Class U (with the same numeric criterion) since there is no public access allowed at Ralston Reservoir and there is no information that primary contact is an existing use.
Clear Creek Segment 17b
Newly created segments had the same Recreation use classification as the segment they were split from, unless there was insufficient evidence to support keeping that classification or evidence to show that the use classification was inappropriate.  The newly created segments for which the Recreation use classification was changed are now classified Recreation Class U with a 126/100 ml E. coli standard:
Upper South Platte Segment 5d
Clear Creek Segments 23 and 24
Lower South Platte Segment 4
Republican River Segment 8
D.	Addition of Water Supply Use Classification and Standards
Based on review of information regarding the location of public water supplies, Water Supply use classifications and standards were added to the following segment:
Cache La Poudre Segment 13a
The Water Supply use classification and standards were added presumptively to the following new lake segments:
Upper South Platte Segments 19 (only those lakes incorporated from Segment 7), 21, and 22
Cherry Creek Segment 5
Boulder Creek Segment 16
St Vrain Segments 11 and 13
Middle South Platte Segment 7
Big Thompson Segments 17 and 19
Lower South Platte Segments 4 and 5
Republican Segment 8
E.	Agriculture Standards
A review of the standards associated with the Agriculture use classification showed that many segments were missing a nitrate standard protective of the use.  A nitrate standard, NO3=100, was added to the following segments classified for Agriculture use:
Upper South Platte River Segments 5a, 7, 11a, 11b, 16a, 16c, 16d, 16e, 16f, 16g, 16h, 17a, 17b, and 17c
Cherry Creek Segment 4
Boulder Creek Segments 7a and 7b
St. Vrain Creek Segments 3 and 6
Middle South Platte River Segments 3a, 3b, and 5a
Big Thompson River Segments 4b, 4c, 5, 6, 9, and 10
Cache La Poudre River Segments 11, 12, 13b, and 16
Lower South Platte River Segments 2b and 3
Republican River Segment 4
F.	Changes to Antidegradation Designation
As part of the 2005 Basic Standards hearing, the Commission revised the criteria for antidegradation designations.
Maintaining UP Protection:  The twelve-parameter test was applied where possible to determine if use-protection remains warranted for segments classified for warm-water aquatic life class 2; however, that showing can be overcome if there is adequate data showing that the water is effluent-dominated.  The Commission maintained the Use Protected designation for the following segments based on a showing that the segments are effluent dominated:
Upper South Platte River Segment 15 
Middle South Platte River Segment 1a
Decoupling Aquatic Life Cold 2 and UP:  The Commission eliminated the direct linkage between cold-water aquatic life class 2 and the use-protected designation and in the absence of data showing that the water quality is not high quality, the cold 2 segments revert to reviewable.  All cold-water aquatic life class 2 segments that are use-protected were reviewed to determine if that designation is still warranted.  The following segments are now reviewable:
Upper South Platte River Segments 5c and 7
Bear Creek Segments 1b and 5
Clear Creek Segments 12, and 17b
Boulder Creek Segment 6
Big Thompson River Segments 3 and 4a
Cache La Poudre River Segments 7, 8 and 10
Decoupling Aquatic Life Warm 2 and UP   The Commission decided that the presence of a warm-water aquatic life class 2 would still be a presumptive basis for applying a use-protected designation; however, that presumption can be overcome if there is data showing that the water is of high quality.  All warm water aquatic life class 2 segments were reviewed to determine if the use protected designation is still warranted.  The following segment(s) are now reviewable:
Upper South Platte River Segments 16a and 16h
Cherry Creek Segments 1 and 3
Bear Creek Segment 4a
Boulder Creek Segment 7b
St. Vrain Creek Segment 5
Middle South Platte River Segments 1b, and 5a
Big Thompson River Segments 4b, 4c, 5, and 9
Cache La Poudre River Segments 11, 12, and 13b
Lower South Platte River Segment 1
Republican River Segment 5
Removing UP from Aquatic Life Warm 1:  The twelve-parameter test was applied where possible to determine if use-protection remains warranted for segments classified for warm-water aquatic life class 1.  The following segments are now reviewable:
Upper South Platte River Segments 10a and 17a
Bear Creek Segment 2
Clear Creek Segment 15
Boulder Creek Segments 5 and 10
St. Vrain Creek Segment 3
Republican River Segment 1
Removing UP from Aquatic Life Cold 1:  The twelve-parameter test was applied where possible to determine if use-protection remains warranted for segments classified for cold-water aquatic life class 1.  The following segment is now reviewable:
Clear Creek Segment 5
G.	Ambient Quality-Based Standards
There are 18 segments in the Basin that have ambient standards.  Ambient standards are adopted where natural or irreversible man-induced conditions result in exceedances of table value standards.  The Commission reviewed the information that is the basis for these standards as well as any new information that would indicate whether they are still appropriate, need to be modified, or should be dropped.  The Commission did not adopt any changes to the following ambient quality-based standards. 
Upper South Platte River Segment 2b: Zn(ch) = 220 µg/L
Upper South Platte River Segment 2c: Zn(ch) = 280 µg/L
Upper South Platte River Segment 5a (all metals Trec unless otherwise noted): Cd(ch)=2 µg/L,
     CrVI(ch)=25 µg/L, Cu(ch)=18 µg/L (dis), Fe(ch) = 1200 µg/L, Pb(ch)=4, Mn(ch)=530 µg/L(dis),
     Hg(ch)=0.05 µg/L, Ni(ch)=50 µg/L, Ag(ch)=1 µg/L
Upper South Platte River Segment 14: Mn(ch) = 190 µg/L (dis)
Upper South Platte River Segment 15: Mn(ch) = 400 µg/L (dis)
Clear Creek Segment 7:  all metals 
Clear Creek Segment 9b:  Zn(ch) = 200 µg/L
Clear Creek Segment 11:  Cu(ch) = 17 µg/L
Clear Creek Segment 13b:  Fe(ch) = 5400 µg/L (Trec), Cu(ch) = 64 µg/L
Big Dry Creek Segment 1:  Se(ch) = 7.4 µg/L (April 1 to October 31); Se(ch) = 15 µg/L 
     and Se(ac) = 19.1 µg/L (November 1 to March 31)
Big Dry Creek Segments 2, 3, 4a, 4b, and 5:  Plutonium, Americium, Tritium, and 
     Uranium (see Table 2 of Regulation 38 for individual numbers), Be(ch) = 4 µg/L
Middle South Platte River Segment 5b:  D.O.(ch) = 4.7 mg/l (qualifier) 
The Commission did adopt changes to the following ambient quality based standards:
Clear Creek Segment 14a:  Mn(ch) = 500 µg/L, modified to 244 µg/L
Clear Creek Segment 14b:  Mn(ch) = 500 µg/L, modified to 244 µg/L
H.	Water Effects Ratios (WERs)
The Commission reviewed the basis for pre-existing WER-based site-specific copper and zinc standards.  
Copper:  Current information indicates that the WER may not be the most appropriate method to use to set site-specific standards for copper.  However, EPA’s guidance for implementing the Biotic Ligand Model to set site-specific copper standards is not yet fully developed.  The Commission replaced the standards based upon WERs with temporary modifications (set at the WER values) for the following segments.  These type iii temporary modifications will expire 12/31/2014.
Upper South Platte River Segments 10a, 14, 15, 16a, 16g
Clear Creek Segments 14a, 14b, and 15
Zinc:  The zinc WER was adopted in 1994.  The Commission reviewed the summary report from the 1994 study.  Although much has changed in the watershed, the Commission concludes that the zinc WER is still protective of the use for the following segments: 
Clear Creek Segments 14a, 14b, and 15
I.	Aquatic Life Metals Standards
New Table Value Standards:  As part of the Basic Standards hearing of 2005, new zinc and cadmium table values were adopted.  The acute and chronic zinc and cadmium equations in 38.6(3) were modified to conform to Regulation No. 31. 
Chromium III Standards:  A review of chromium III standards showed that the standard associated with the Water Supply use classification was not protective of aquatic life where the average hardness was less than 61 mg/l.  A chromium standard, CrIII(ch)=TVS was added to following segments with an Aquatic Life use classification and average hardness values less than 61 mg/l.
Upper South Platte River Segments 2a, 3, 4, 5b, and 9
Bear Creek Segments 1a, 1b, 3, and 7
Clear Creek Segments 1, 3a, 3b, 6, 9a, 10, and 17b
Boulder Creek Segments 1, 2, and 3
St. Vrain Creek Segments 1 and 2
Big Thompson River Segments 1 and 2
Cache La Poudre River Segments 1, 2, and 6
J.	Arsenic Standards
For arsenic, each use (except recreation) has a different arsenic (“As”) value, including Fish Ingestion (FI) and Water Plus Fish (W+F).  In different combinations of uses, different values become the most limiting.  In order to eliminate the confusion, the Commission added the operative value to the individual segments.  The following matrix displays the most limiting arsenic criteria.  

Most Limiting Arsenic Criteria Depending on the Possible Combinations of Uses and Qualifiers	
If the Use Classifications were: 	These Arsenic Standards were Applied
(dissolved unless otherwise noted)	
Class 1 aquatic life, water supply	As(ac) = 340, As(ch) = 0.02(Trec)	
Class 2 aquatic life (water + fish standards), water supply	As(ac) = 340, As(ch) = 0.02(Trec)	
Class 2 aquatic life (no fish ingestion standards), water supply 	As(ac) = 340, As(ch) = 0.02 - 10(Trec)	
Class 1 aquatic life	As(ac) = 340, As(ch) = 7.6(Trec)	
Class 2 aquatic life (fish ingestion standards)	As(ac) = 340, As(ch) = 7.6(Trec)	
Class 2 aquatic life (no fish ingestion standards), agriculture	As(ac) = 340, As(ch) = 100(Trec)	
Agriculture only	As(ch) = 100(Trec)	
Water supply only	As(ch) = 0.02 - 10(Trec)	
K.	Uranium Standards
At the 2005 Basic Standards rulemaking hearing, the Commission changed the drinking water supply table value for uranium from 40 pCi/L to 30 µg/L. 
L.	Water +Fish and Fish Ingestion Standards
The reference to “Water+Fish Organics” was corrected to “Water+Fish Standards” and the reference to “Fish Ingestion Organics” was corrected to “Fish Ingestion Standards” to incorporate the appropriate standards from both the organics table and the metal parameter table in Regulation #31.
For the following segments, the Fish Ingestion Standards were removed
Upper South Platte Segment 16c:  Fish Ingestions standards were applied to this segment in 2000, based on evidence that fishing was occurring in urban and rural lakes and ponds (see 38.57.J).  In this hearing the lakes and reservoirs were moved to Segment 22 and accordingly, the Fish Ingestions standards were removed from Segment 16c and placed on Segment 22.
Middle South Platte Segment 1a:  Fish Ingestions standards were applied to this waterbody before it was divided into 1a and 1b at the confluence with St. Vrain Creek, based on evidence that fish were being taken or had the potential to be taken for human consumption and that fishing takes place on a recurring basis.  It was later divided, recognizing the substantial flow is contributed by St. Vrain Creek.  Aquatic life sampling data for the upper portion (Segment 1a) presented by the Metro District provided evidence that the fish assemblage in Segment 1a is dominated by small, native minnow species that do not reach a catchable size.  In addition, the Metro Districts’ routine biweekly sampling has not found evidence that fishing occurs on a recurring basis in Segment 1a.   Accordingly, the Commission removed the Fish Ingestion qualifier from Segment 1a.  The Commission made no change to the Fish Ingestion standards on Segment 1b. 
M.	Temporary Modifications
All temporary modifications were re-examined to determine whether to delete or extend them, either as existing or with modifications of the numeric standards.  Because of the June 2005 changes to Regulation #31, temporary modifications were not automatically extended if non-attainment persisted.  
Ammonia:  The following segments have type i temporary modifications for chronic ammonia that were amended to clarify the chronic standard’s value as either 0.06 or 0.10 mg/l, rather than just “TVS old.”  As specified in 61.8(2)(c)(iii) (the Permit Rules, Regulation #61), where a temporary modification has been adopted, limits in permits are to be set based on the temporary modification and the provision strictly limiting the loading from the facility does not apply.  These temporary modifications will be subject to review and rulemaking for the two years before their scheduled expiration in order to track progress towards the full attainment of water body standards and uses.
Segments amended to read NH3(ch)=0.06 mg/L:
Upper South Platte River Segments 10a, 11b, 14, 16c, and 16g
Clear Creek Segment 15
Boulder Creek Segments 7b, 9, and 10
St. Vrain Creek Segment 3
Cache La Poudre River Segments 13a and 22
Lower South Platte River Segment 2b
Segments amended to read NH3(ch)=0.10 mg/L:
Upper South Platte River Segments 15 and 16a
Cherry Creek Segments 3 and 4
Bear Creek Segment 4a
Big Dry Creek Segments 1 and 3 
St. Vrain Creek Segment 6
Middle South Platte River Segments 1a and 3a
Big Thompson River Segments 5, 6, 9, and 10
Cache La Poudre River Segments 11, 12, and 13b
Lower South Platte River Segment 1
Other Ammonia temporary modifications:  Upper South Platte Segment 5c has a type iii temporary modification for ammonia.  The expiration date has been extended from 12/31/2010 to 12/31/2011.  Mountain Water and Sanitation District (MWSD) has been making progress toward resolving uncertainty regarding the appropriate underlying standard.  During the course of the extended temporary modification, MWSD will investigate what ammonia standards are feasible based upon economic considerations and EPA may release an updated ammonia guidance containing new information pertinent to the determination of an appropriate underlying standard.
“Current Condition”:  The Commission adopted temporary modification for the following segments and pollutants with the notation of “current condition” rather than a numeric value.  The Commission’s intent of using this notation is to preserve the status quo during the term of the temporary modification.  Discharges to those segments shall continue to be authorized to discharge the subject pollutant at their current permitted concentration and flow levels.  Although the permitted levels authorize the discharges to increase pollutant loading over past levels, the Commission expects that actual discharge levels will be variable and that existing water quality may be marginally changed, since discharge flow levels may increase and concentration levels will likely continue similar to actual levels to date in order for the discharger to assure that the effluent limitations continue to be met.  The Commission does not intend that temporary modifications set at "current condition" apply to new or expanded facilities.  With respect to existing facilities, the Commission intends that for facilities discharging into segments having a temporary modification, implementation of the underlying standard into permits is to take place as soon as feasible after the standard becomes effective in accordance with established requirements of the Basic Standards and Methodologies for Surface Water.  The progress on resolving the uncertainty will be reviewed in the annual Temporary Modification hearing in December of the two years preceding the expiration.
Upper South Platte Segment 14, selenium:  Public Service Company of Colorado proposed a type iii temporary modification for selenium on Upper South Platte Segment 14.  There is significant uncertainty concerning the long-term underlying selenium standard.   Time is needed to (1) determine the source of the upstream selenium, which exceeds the underlying selenium standard of 4.6 µg/L; (2) wait for EPA’s new selenium criteria and implementation guidance;  (3) determine a standard that will protect the aquatic life use in Segment 14; and (4) evaluate selenium treatment options.  The temporary modification will expire on December 31, 2013.  
Upper South Platte Segments 14, 15 and 16g, temperature:  The Commission adopted type iii temporary modifications of the temperature standard for these segments.  The temporary modifications will expire on 12/31/2014.  During the term of the temporary modification, the Commission expects that the domestic wastewater facilities will, in cooperation with other dischargers and the Division, explore options for developing new underlying site-specific temperature standards including refined numeric site-specific standards, ambient–based site-specific standard and narrative site-specific standards although permit implementation strategies are not yet fully developed for all of these. In addition, although not currently available, a facility–specific variance approach may be permissible by the end of the temporary modification period. This option, the framework of which still needs to be developed, may be an appropriate solution for the following facilities and other discharges to address temperature-related issues within their respective segments:
Upper So Platte Segment 14: Littleton/Englewood Wastewater Treatment Facility
Upper So Platte Segment 15:  Metro Wastewater Reclamation District
Upper So Platte Segment 16g:  Centennial Water and Sanitation District 
Clear Creek Segment 13b, temperature:  The Commission adopted a type iii temporary modification of the temperature standard for Segment 13b.  The temporary modification will expire on 12/31/2014.  During the term of the temporary modification CERCLA and Black Hawk / Central City Sanitation District will characterize the fish species that are expected to be present and will gather data to more accurately characterize the temperature of the discharge and the temperature of Clear Creek. 
Clear Creek Segments 14a, 14b, and 15, temperature:  The Commission adopted a type iii temporary modification of the temperature standard for Segments 14a, 14b and 15.  The temporary modification will expire on 12/31/2014.  During the term of the temporary modification and as part of the study dealing with the appropriate Aquatic Life classification, MillerCoors will perform additional fish sampling, flow, and temperature analysis with the objective of resolving the uncertainty associated with the appropriate use classification and temperature standards.  MillerCoors will also further address issues associated with attainability of the temperature standards.  
Boulder Creek Segment 9, copper:   The Commission extended the type iii temporary modification of the copper standard for Boulder Creek Segment 9.  The City of Boulder is still in the process of evaluating the Biotic Ligand Model (BLM) for possible development of a site-specific copper standard and also evaluating a copper translator to apply to the current wastewater treatment facility copper effluent limit.  Additional time is needed to conduct further sampling and to wait for EPA’s guidance on use of the BLM to develop site-specific criteria.  
Middle South Platte Segment 4, pH :  The Division proposed a type iii temporary modification of the pH standard for Barr Lake and Milton Reservoir (Middle South Platte Segment 4) because investigations suggest that the standards may not be attainable through achievable controls of nutrient inputs.  However, the Commission has not determined at this time that the underlying standards are not attainable and reserves this determination until future hearings.  Water quality investigations conducted as part of the TMDL development work indicate non-attainment of the pH standard.  Regardless, the TMDL will be written to the underlying pH standard.  The opportunity to consider a temporary modification in this hearing arose before the TMDL modeling has been completed, and the feasibility of controls have been fully assessed.  The Commission finds that there is enough uncertainty regarding the standard to warrant a type iii temporary modification in addition to evidence that point source dischargers would likely have compliance problems with probable effluent limits.  This temporary modification will assure that individual wasteload allocations in the TMDL will not be implemented before the uncertainty regarding the underlying standard is resolved (see 31.14(15)(b)(i)).  The temporary modification is set at expire on 12/31/2014.  During the term of the temporary modification, the TMDL will be completed and focus will then shift to assessing the feasibility of necessary nutrient controls.
Big Thompson Segment 2, Wapiti Meadows D.O., E. coli, NH3, NO3, B, Cd, Cu, Pb, Hg, Ni, Se, Ag, Zn:  The Commission extended the temporary modification for these constituents until 12/31/2014.  During the interim, Upper Thompson Sanitation District, in consultation with the Division, EPA and CDOW, will prepare a Plan of Action to continue sampling of water into and out of the Wapiti Meadows, characterize the functions of the wetland, explore regulatory and treatment alternatives, and develop a proposal for the appropriate classification and standards for the wetland. 
Other Temporary Modifications, numeric
Temporary modifications (type iii) for selenium and copper were adopted where there were both exceedances of the current standard and dischargers on the segment.  The temporary modifications will expire on 12/31/2014 which should cover the time it takes for EPA to promulgate new criteria (for selenium) and finish implementation guidance (for selenium and copper).  These temporary modifications will be reviewed in 2012 and 2013.
Boulder Creek Segment 8: Se(ch) = 12.2 µg/l (dis)
St. Vrain Segment 2b: Cu(ch) = 6.0 µg/l (dis)
Middle South Platte Segment 1a: Se(ch) = 6.9 µg/l (dis)
Big Thompson Segment 2: Cu(ch) = 2.5 µg/l (dis)
Big Thompson Segment 5: Se(ch) = 5.7 µg/l (dis)
Big Thompson Segment 9: Se(ch) = 13.1 µg/l (dis)
Cache La Poudre Segment 11: Se(ch) = 5.4 µg/l (dis)
Cache La Poudre Segment 12: Se (ch) = 7.1 µg/l (dis)
Cache La Poudre Segment 13b: Se(ch) = 13.0 µg/l (dis)
Lower South Platte Segment 1: Se(ch) = 12.3 µg/l (dis)
Copper WERs:  The Commission replaced the standards based upon Copper WERs with temporary modifications (set at the WER values) for the following segments.  These type iii temporary modifications will expire 12/31/2014. (See section H, above)
Upper South Platte River Segments 10a, 14, 15, 16a, 16g
Clear Creek Segment 14a, 14b, and 15
The following temporary modifications (expire 12/31/2014) were revised based upon resegmentation:
Clear Creek Segment 2a:  Zn(ch) = 353 µg/l (dis) (type i)
Clear Creek Segment 2c:  Cu(ch) = 11.4 µg/l (dis) (type iii)
The new temporary modifications (expire 12/31/2014) were set to ambient quality-based numeric values for the following segments:
Clear Creek Segment 2a:  Zn(ac) = 586 µg/l (dis)(type i) , Cd(ch) = 1.54 µg/l (dis)(type iii)
Clear Creek Segment 11:  Cd(ch) = 1.42 µg/l (dis) (type iii)
The following temporary modifications were deleted:
Clear Creek Segment 2a (formerly part of 2):  Cu(ch) = 7.4 µg/l (dis)
Clear Creek Segment 11:  Zn(ch) = 325 µg/l (dis)
The following segments had temporary modifications that were deleted from the tables since, as part of the Commission action in December 2008, they were to be allowed to expire: 
Cache la Poudre River Segments 11, 12:  copper
N.	Temperature
As part of the Basic Standards hearing of 2007, new table values were adopted for temperature.  Temperature standards were applied to individual segments based upon the distribution of fish species, as provided by the CDOW, temperature data, and other available evidence. 
The following segments are cold stream tier one (CS-I):
Upper South Platte River Segments 1a, (summer season adjusted to April – Oct)
Upper South Platte River Segments 1b, 2a, 2b, 2c, 3, 4, 5a, 5b, 8, and 9 
Bear Creek Segments 1a, 3, 6b, and 7
Clear Creek Segments 1, 2a, 2b, 2c, 3a, 3b, 4, 5, 6, 7(also CL), 8, 9a, 9b, 10, 11, 13a, 13b, and 19
Boulder Creek Segments 1, 2a, 3, and 4a
St. Vrain Creek Segments 1, 2a, 4a, and 4b
Big Thompson River Segment 1
Cache La Poudre River Segments 1, 2a, 6, and 13c
Laramie River Segments 1 and 2a
The following segments are cold stream tier two (CS-II):
Upper South Platte River Segments 5c, 5d, 6a, 7, and 13 
Bear Creek Segments 1b, 1e, 5, and 6a
Clear Creek Segments 12 and 17b 
Boulder Creek Segments 2b, 4b, and 6
St. Vrain Creek Segments 2b and 4c
Big Thompson River Segments 2, 3, 4a, 7, and 8
Cache La Poudre River Segments 2b, 7, 8, 9, and 10
Laramie River Segment 2b
Republican River Segment 3
The following segments are warm stream tier one (WS-I):
Upper South Platte River Segments 10a, 11b, 12, and 15
Upper South Platte River Segments 14 (summer season adjusted to Feb 14-Nov)
Bear Creek Segment 4a
Big Dry Creek Segments 1, 4a, and 6
St. Vrain Creek Segments 3 and 5
Middle South Platte River Segments 3a and 5a
Big Thompson River Segments 4b, 4c, 5 and 6
Cache La Poudre River Segments 11, 12, and 13a
Republican River Segments 1, 4, 5, and 6
The following segments are warm stream tier two (WS-II):
Upper South Platte River Segments 11a, 16a, 16c, 16g, and 16h
Cherry Creek Segments 1, 3, and 4
Bear Creek Segment 2
Clear Creek Segments 14a, 14b, 15, 16a, 16b, 18a, and 18b
Big Dry Creek Segments 4b and 5 (also WL)
Boulder Creek Segments 4c, 4d, 5, 7a, 7b, 8, 9, 10, and 11
St. Vrain Creek Segment 6
Middle South Platte River Segments 1a, 1b, and 5c
Big Thompson River Segments 9 and 10
Cache La Poudre River Segment 13b
Lower South Platte River Segments 1, 2a, and 2b
The following segments are warm stream tier four (WS-IV):
Upper South Platte River Segments 16d, 16e, and 16f
Middle South Platte River Segments 3b, 5b, and 6
Republican River Segment 7
The following segments are cold lakes (CL):
Upper South Platte River Segments 18, 19 (also CLL), and 20
Bear Creek Segments 8, 9, 10, and 12
Clear Creek Segments 7 (also CS-I), 20, 21, 22, and 25
Boulder Creek Segments 13, 14 (also CLL), and 15 (also CLL)
St. Vrain Creek Segments 8, 9 (also CLL), and 10
Big Thompson River Segments 15, 16 (also CLL), and 18
Cache La Poudre River Segments 15, 17, 18 (also CLL), 19, and 20 (also CLL)
Laramie River Segments 3 and 4
The following segments are cold lakes larger than 100 acres surface area (CLL):
Upper South Platte River Segments 6b and 19 (also CL)
Bear Creek Segments 1c and 1d
Clear Creek Segments 17a and 23
Boulder Creek Segments 14 (also CL) and 15 (also CL)
St. Vrain Creek Segment 9 (also CL)
Big Thompson River Segments 11 and 16 (also CL)
Cache La Poudre River Segments 14, 18 (also CL), and 20 (also CL)
The following segments are warm lakes (WL):
Upper South Platte River Segments 16b, 17a, 17b, 17c, 21, 22,and 23
Cherry Creek Segments 2, 5, and 6
Bear Creek Segment 11
Clear Creek Segment 24
Big Dry Creek Segments 2, 3, 5 (also WS-II) and 7
Boulder Creek Segments 16 and 17
St. Vrain Creek Segments 7, 11, 12, and 13
Middle South Platte River Segments 4 and 7
Big Thompson River Segments 12, 13, 14, 17, and 19
Cache La Poudre River Segments 16, 21, and 22
Lower South Platte River Segments 3, 4, and 5
Republican River Segments 2 and 8
Ambient-based summer temperature standards were adopted for several large lakes and reservoirs (collectively referred to as lakes).  The table value WAT standard is not attainable in many large lakes (>100 acres in surface area) including many lakes with apparently healthy fish populations.  Summertime temperature for large lakes and reservoirs (collectively referred to as lakes) is very well correlated to the lake's elevation.  Since the thermal properties are natural or man-induced irreversible (in the case of reservoirs) the Commission adopted ambient temperature standards for large lakes wherever data were available to characterize a WAT.  For lakes, the WAT is assumed to be equivalent to the average temperature of the mixed layer.
Upper So. Platte Segment 6b	Chatfield Res.		April-December T(WAT)= 23.5ºC
Upper So. Platte Segment 19	Antero Res		April-December T(WAT)= 19.6ºC
				Spinney Mt. Res.	April-December T(WAT)= 20.2ºC
				Eleven Mile Res.	April-December T(WAT)= 19.8ºC
				Cheesman Res.		April-December T(WAT)= 21.9ºC
				Strontia Spr. Res.	April-December T(WAT)= 22.6ºC
				Platte Canyon Res.	March-Dec	T(WAT)= 25.0ºC
Bear Creek Segment 1c 	Bear Cr Res.		April-December T(WAT)= 23.3ºC
Boulder Creek Segment 15	Gross Res.		April-December T(WAT)= 19.4ºC
Big Thompson Segment 11 	Carter Lake		April-December T(WAT)= 22.7ºC
Cache La Poudre Segment 14	Horsetooth Res.	April-December T(WAT)= 22.8ºC
Cache La Poudre Segment 20	Seaman Res.		April-December T(WAT)= 22.5ºC
Lower So. Platte Segment 3 	Jackson Res.		April-December T(WAT)= 28.1ºC
				No. Sterling Res.	April-December T(WAT)= 26.1ºC
				Jumbo Res.		April-December T(WAT)= 27.0ºC
O.	Big Dry Creek Segment 2, Standley Lake, Numeric Nutrient Criteria:  
The Commission adopted a new numeric standard for chlorophyll for Standley Lake and modified the existing narrative trophic status standard by removing a sentence about implementation.
Background:  In 1988, the Commission began consideration of nutrient standards for Standley Lake when the Cities of Westminster and Thornton proposed numeric standards.  The Commission did not adopt the criteria and asked the stakeholders to work together to gather data upon which to base permanent water quality standards to protect Standley Lake as a water supply.  In 1993, the parties returned to the Commission with proposals for narrative standards and a control regulation for point and nonpoint sources of nutrient in the Standley Lake Drainage.  At the conclusion of the February 1994 hearing, the Commission adopted an alternative to the original proposal that states: “The trophic status of Standley Lake shall be maintained as mesotrophic as measured by a combination of common indicator parameters such as total phosphorus, chlorophyll a, secchi depth, and dissolved oxygen. Implementation of this narrative standard shall only be by Best Management Practices and controls implemented on a voluntary basis.” (Reg. 38) 
Over the 16 years since adoption, federal and State drinking water regulations have become more stringent.  Of particular concern to the Public Water Systems that rely on Standley Lake is compliance with regulations for potentially carcinogenic disinfection byproducts.  Higher concentrations of algae can lead to higher levels of disinfection byproduct precursors as well as trigger taste and odor compounds that are not readily treated or controlled with conventional water treatment.  Despite evolution in the nature of concerns, there has been no advancement in finding agreement on a quantitative definition of “mesotrophic” (although there is general agreement that the lake has been mesotrophic during this time period).  These concerns led the Cities of Westminster, Northglenn, and Thornton, (the “Standley Lake Cities”), to request adoption of a site specific numeric standard for chlorophyll a for Standley Lake set at a level to characterize the status quo, or current condition.  
Revised Water Quality Standards for Standley Lake:  The Cities have monitored water quality in Standley Lake for many years.  The last 14 years of chlorophyll data and seven years of total phosphorus data have been placed in the record.  Those years represent periods suitable for defining current condition.
With the benefit of the lengthy historical record now available, the Commission believes it is appropriate to set a chlorophyll standard consistent with the conditions that have been maintained.  The Commission adopted a chlorophyll standard of 4 µg/L to preserve the current conditions and protect uses.  This standard is to be attained in four of five years.  
The chlorophyll standard is defined as a 9-month average (the average of the nine monthly averages of samples taken from March through November); winter samples are excluded because they cannot be collected safely in all years.  Samples are to be collected in a manner consistent with the historical record (photic zone at site 10). It is anticipated that the level of sampling effort applied in the future will be the same as that applied in the past (i.e., at least one sample in each of the nine months). For assessment, the average (arithmetic mean) is calculated each year.
The Water Quality Control Division proposed that a numeric phosphorus standard also be adopted for Standley Lake, but the Commission has declined to adopt such a standard at this time.  The chlorophyll standard is adopted principally to address the public health concern raised by the Standley Lake Cities.  A chlorophyll standard based on current conditions is intended to control the contribution of algae to the formation of disinfection byproduct precursors.  This chlorophyll standard is not intended as a substitute for the current narrative standard regarding the overall trophic status of the reservoir, and therefore the Commission has decided as a matter of policy to retain the narrative standard at this time, with a slight modification.  The Commission deleted the sentence regarding implementation of the narrative standard as unnecessary.  The Commission encourages the Standley Lake Cities to work with the Division and other interested parties to explore the development of numeric nutrient standards for Standley Lake in the future.
Development of Assessment Thresholds:  Consistent with methodology developed for Chatfield Reservoir, a distinction is made between the standard and an assessment threshold.  The assessment threshold is designed to address the concern about the risk of incorrectly counting an exceedance when a high summer value is the result of natural variability, but does not indicate a substantive change in current conditions.  The approach is justified by the special nature of the parameter (chlorophyll is not toxic) and the site-specific nature of the concern about false exceedances.  Another reason for establishing an assessment threshold that is different than the standard is that the site-specific standard is derived from historical data, which creates the expectation that a number of exceedances will occur.  Natural variability, especially for chlorophyll, is sufficient to produce much more uncertainty in the assessed value than in the standard, which was derived from the set of all 9-month averages.  An assessment threshold was developed by calculating the standard error of each 9-month average from which the 90th percentile value of the average was determined.  A regression of the 90th percentile value (upper confidence limit) on the average provides an equation that can be used to specify the upper confidence limit (90%) for any particular concentration (e.g., the standard).  Using a standard of 4.0 µg/L, the assessment threshold was determined to be 4.4 µg/L.  This value was added in section 38.6(4) with a reference in the standards table “qualifier” column.”  
P.	Other Site-Specific Revisions:
Upper South Platte River Segment 5c:  The trout-specific standards for chronic silver and acute cadmium were deleted.
Upper South Platte River Segment 15, Mercury:  Existing site-specific standards for mercury are removed in absence of recent data to support maintaining them.  Standard is changed to Hg(ch)=0.01(Tot).
Upper South Platte River Segment 15 and Middle South Platte Segment 1a,  Dissolved Oxygen Assessment Criteria:  The Commission added assessment criteria to clarify the assessment of dissolved oxygen standards for these segments.  In 1996, the Commission adopted Statement of Basis and Purpose language indicating that for the purpose of determining the attainment of the site-specific dissolved oxygen standards for these segments, dissolved oxygen measurements in man-made pools are not to be used.  This provision was added to section 38.6(4)(c).
Clear Creek Segments 2a, 2c, 3a, 3b, and 11:  Site-specific recalculated acute and chronic zinc standards were adopted for these segments.  The recalculated equations were developed to be protective of the community which is expected to occur in the riverine portions of the Upper Clear Creek Watershed.
Colorado Trout Unlimited proposed that segment 2a be further divided into two segments, with the boundary at Georgetown Reservoir, with ambient quality-based standards that are sometimes more restrictive than the recalculation-based standards adopted for the new lower segment.  The Commission declines to adopt this proposal.  As noted above, the recalculation-based standards adopted for this segment are appropriate to protect the aquatic life use.  The Commission acknowledges that the water quality improves in the lower portion of Segment 2a (the mainstem from Georgetown to the West Fork).  The Commission supports efforts to maintain and improve the water quality in this portion of the stream but does not believe that the adoption of standards based on ambient quality that is better than that determined necessary to protect the aquatic life use is the appropriate means to do so.  This segment is reviewable and antidegradation provisions will apply to any future proposals for a new or increased discharge of pollutants to this segment. Improvements to existing quality will be dependent principally on the extent of future CERCLA clean-ups in this basin.
Big Dry Creek Segment 1:  The Commission added assessment locations to section 38.6(4) to record the assessment strategy for the seasonal ambient quality based site-specific standards for selenium applicable to Big Dry Creek Segment 1 that were adopted in December 2007 and recorded in the Statement of Basis at that time.  Attainment of the standard is to be assessed with data based on three specific instream monitoring locations (bdc1.5, bdc2.0 and bdc4.0) upstream of the three municipal wastewater treatment plant discharges.
Boulder Creek Segment 8: To reflect the Agriculture use classification and absence of a Water Supply use classification, NO3=10 was changed to NO3=100.
Cache La Poudre Segment 13a:  To reflect the addition of the Water Supply use classification, CrIII(ac/ch)=TVS was changed to CrIII(ch)=TVS and NO3=10, Cl=250, SO4=WS, CrIII(ac)=50(Trec), Fe(ch)=WS(dis), and Mn(ch)=WS(dis) were added.
Lower South Platte Segment 2b,  Resegmentation of Beaver Creek:  Based on the results of a Use Attainability Analysis prepared by the Metro Wastewater Reclamation District, the Commission determined that it is appropriate to move the portion of Beaver Creek beginning at its source to the Fort Morgan Canal from Lower South Platte segment 2b to Lower South Platte Segment 2a.  Segment 2a has standards necessary to protect the following uses:  Aquatic Life Warm 2 (with numeric standards only to protect rudimentary aquatic life), Recreation N (Not primary contact recreation), and Agriculture.  Evidence presented showed that this is a naturally ephemeral reach of Beaver Creek, consistent with the other tributaries included in Lower South Platte Segment 2a.
Q.	Other changes
The Commission corrected several typographical and spelling errors, and clarified segment descriptions.  The abbreviation for chlorine was changed from Cl2 to Cl2, and the (ac) and (ch) designations were removed from the inorganic standards where that designation was not appropriately applied.
The Commission made the following segment-specific typographical corrections:
Upper South Platte Segment 5a:  added B=0.75, which is present for all other comparable segments.
Upper South Platte Segment 7:  added CrIII(ch)=TVS to complete the standard for aquatic life.
Upper South Platte Segment 16b:  changed the following standards, which were inconsistent with the aquatic life classification of this segment: changed standards for D.O.=5.0 mg/L and NO2=0.5; added Cd(ac)=TVS and Ag(ch)=TVS to replace existing salmonid equation; removed D.O.(sp)=7.0 mg/L.
Clear Creek Segment 7:  The segment description was modified to specify the inclusion of Lower Urad Reservoir.
Clear Creek Segment 9a:  replaced “to” with “of” in the segment description.  Added “20” to expiration date of “2014.”  
Clear Creek Segment 13b:  replaced “(trec)” with “(ch)” in temporary modification for iron and added “(Trec)” at the end for consistent nomenclature.
Clear Creek Basin footnotes:  deleted “* REFER TO STATEMENT OF BASIS AND PURPOSE” because it did not appear to have a reference.
Big Dry Segments 4a and 4b:  changed Hg(ac)=0.01(Tot) to Hg(ch) = 0.01(Tot).
Middle South Platte Segment 1b:  deleted the temporary modification for ammonia in order to reflect changes that were made as a part of the December 10, 2007 temporary modifications Rulemaking Hearing.
The Commission clarified segment descriptions through the following changes:
Upper South Platte Segment 17a: change “City Park Lake” to “City Park Lakes” because it should encompass all lakes in the park.
Clear Creek Segment 3a:  Added “Segments” to the description preceding 3b and 19 for clarification.
Clear Creek Segment 11:  Added “a point just above” to clarify the segment description.
Clear Creek Segment 13a:  Revised description to include North Clear Creek from its source to Chase Gulch, all of Four Mile Gulch, Chase Gulch itself, and Eureka Gulch.  The terminal points on this new segment approximately coincide with the lowest actual and potential water supply intakes located on each of these streams.
Clear Creek Segment 13b:  Added “a point just below the confluence with Chase Gulch” to clarify the origin of the segment in relation to Segment 13a.
Clear Creek Segment 14b: Added “a point just below” to the segment description in order to clarify that the segment originates at a point just below Youngfield Street.
Clear Creek Segment 16a:  replaced “outlet” with “inlet” for clarity because Maple Grove Reservoir is no longer part of the segment.
Boulder Creek Segment 6: Revised “highway” to read “Highway”. 
Boulder Creek Segment 7a: Revised “highway” to read “Highway”.
St. Vrain Creek Segment 5:  Revised “highway” to read “Highway”.
St. Vrain Creek Segment 6:  Added Segment “4c” to clarify the segment exceptions.
Middle South Platte River Segment 3a: Deleted Segment “4” from the list of exceptions because lakes and reservoirs were removed from this segment.
Big Thompson River Segment 1: This segment description was clarified to include the mainstem of Big Thompson River from its source to the boundary of Rocky Mountain National Park.  The Commission clarified this description because the previous description excluded the mainstem of the Big Thompson River while including only streams and wetlands tributary to the Big Thompson River within the boundaries of Rocky Mountain National Park.
Big Thompson River Segment 10:  Added “confluence with the” to clarify the segment description.
Cache La Poudre River Segment 13a: Deleted Segments “14”, “15” and “16” and added Segments “6”, “7”, “8” and “13c” to clarify the segment exceptions.  Modified the segment description to include tributaries and wetlands to the Cache La Poudre from the Monroe Gravity Canal/North Poudre Supply canal diversion to a point immediately above the confluence with the North Fork of the Cache La Poudre River. 
Cache La Poudre River Segment 13b:  Revised “la” to read “La”.
Lower South Platte River Segment 2a: Deleted Segment “3” from the list of exceptions because lakes and reservoirs were removed from this segment.
R.	Other Revisions Considered
Several site-specific revisions proposed by parties to the hearing were considered by the Commission and not adopted, including those summarized below:
Upper South Platte Segment 6a
The Chatfield Watershed Authority proposed that this segment should be divided into two segments, split at the point of the Roxborough Water and Sanitation District/Dominion Metropolitan District wastewater discharge.  A temporary modification for temperature would have been applied to the lower segment.  The Commission declined to adopt the requested resegmentation or temporary modification.  The Commission believes that the potential impact described by the Authority is speculative at this time.  The design capacity of the currently permitted wastewater discharge is small enough that dilution precludes the need for a temperature effluent limitation, and the Roxborough facility has connected its effluent to the Littleton/Englewood facility so that it no longer discharges at this point, The timing and volume of a future Dominion discharge at this location is currently speculative.
Upper South Platte Segment 10a
Plum Creek Wastewater Authority proposed that a separate segment be created for West Plum Creek.  The Commission determined that the evidence does not support different temperature standards for West Plum Creek, based on expected aquatic life species.  Because the two segments would have the same standards, there is no reason to resegment the existing segment 10a into two segments.
Upper South Platte Segment 15
The Metro Wastewater Reclamation District originally proposed that a temporary modification for mercury be adopted for this segment.  After discussions with the Division, Metro withdrew its request.  However, Public Service Company of Colorado continued to support the proposal.  The Commission declines to adopt the requested temporary modification.  The Commission determined that this proposed temporary modification is not necessary, since the evidence submitted does not demonstrate that Metro will have a compliance problem in meeting an effluent limitation based on the mercury standard and that a compliance problem for Xcel has not been demonstrated at this time.
Cherry Creek Segment 5
Reuter-Hess Reservoir, which is currently under construction, is located within the new Cherry Creek segment 5 created by this rulemaking.  Parker Water and Sanitation District proposed that no water quality classifications or standards be adopted at this time for Reuter-Hess Reservoir.  The Commission rejects this proposal, which means that the classifications and standards adopted for Cherry Creek segment 5 will apply to Reuter-Hess.  The water quality classifications and table value standards adopted for segment 5 are appropriate for the protection of water quality in lakes and reservoirs in the absence of information indicating that other classifications or standards are appropriate.  The Commission notes that because Reuter-Hess Reservoir is not yet filled there is currently no site-specific water quality data for the reservoir.  Revisions to the adopted classifications and standards can be considered in future triennial reviews if warranted based on data.
Cache la Poudre Segment 10
The Northern Colorado Water Conservancy District proposed that site-specific, ambient quality-based temperature standards be adopted for Cache la Poudre segment 10.  The Commission has determined that adoption of site-specific standards for this segment is not appropriate at this time, since there has not yet been an adequate study to determine whether such standards are appropriate, and whether any site-specific standards would warrant resegmentation.  The Commission encourages Northern Water to work with the Division and other interested parties to further examine the appropriate temperature standards for these waters prior to the next triennial review.
PARTIES TO THE RULEMAKING
1.	Parker Water and Sanitation District
2.	Mountain Water and Sanitation District
3.	Plum Creek Wastewater Authority
4.	Chatfield Watershed Authority
5.	Centennial Water and Sanitation District
6.	Littleton/Englewood Wastewater Treatment Plant
7.	Bear Creek Watershed Association
8.	Metro Wastewater Reclamation District
9.	Public Service Company of Colorado
10	Upper Clear Creek Watershed Association
11.	Standley Lake Cities (Cities of Westminster, Northglenn, and Thornton)
12.	City of Boulder
13.	Upper Thompson Sanitation District/Bureau of Reclamation
14.	Colorado Division of Wildlife
15.	Colorado Trout Unlimited
16.	Farmers Reservoir and Irrigation Company
17.	Clear Creek Watershed Foundation
18.	City of Arvada
19.	City and County of Denver
20.	Denver Water
21.	City of Black Hawk and the Black Hawk / Central City Sanitation District
22.	Department of Energy, Office of Legacy Management
23.	City of Golden
24.	East Cherry Creek Valley Water and Sanitation District
25.	Barr Lake and Milton Reservoir Watershed Association
26.	Northern Colorado Water Conservancy District
27.	Hazardous Materials and Waste Management Division / U.S. EPA Superfund Remediation Programs
28.	City and County of Broomfield
29.	City of Fort Collins
30.	MillerCoors, LLC
31.	Climax Molybdenum Company
32.	Waste Management of Colorado, Inc.
33.	South Platte Coalition for Urban River Evaluation (SP CURE)
34.	U. S. Environmental Protection Agency (EPA), Region 8
35.	City of Greeley
36.	City of Aurora
37.	North Front Range Water Quality Planning Association
38.	Clear Creek County
39.	Suncor Energy (U.S.A.), Inc.
40.	City of Littleton
41.	Town of Empire
42.	Town of Silver Plume