5 Colo. Code Regs. § 1002-38.57
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
Some renumbering and/or creation of new segments was made in the basin due to information which showed that:
Upper So. Platte segment 6 was split into segments 6a, 6b and 6c to reflect the difference in water quality standards and land use, namely segment 6a is the portion above the Chatfield Reservoir, segment 6b is the reservoir, and segment 6c is the portion below the reservoir.
Upper So. Platte segment 16 was divided into 16a, 16b and 16c to reflect the difference between Sand Creek and the other tributaries, and to recognize the uses of Aurora Reservoir. The mainstem of Sand Creek became segment 16a; Aurora Reservoir became 16 b, and the all remaining tributary portion became 16c.
Clear Creek segment 13 was divided into two segments to address differences in water quality and uses. Segment 13a is the mainstem and tributaries above Black Hawk's water supply; 13b is the mainstem and tributaries below Black Hawk's water supply to the confluence with Clear Creek.
Clear Creek segment 14 was split into segments 14a and 14b to reflect differences in access for recreational use. The dividing point is the Denver Water conduit #16 crossing, approximately .5 miles above Youngfield Street, with 14b, the lower segment having a recreation 1a classification.
Clear Creek segment 16 was split into segments 16a and 16b to reflect actual water supply uses. Lean Gulch and its tributaries above the outlet of Maple Grove Reservoir will be segment 16a.
Clear Creek segment 17 was divided into two segments to recognize the difference in uses of Arvada reservoir. Arvada Reservoir is now segment 17a, with the remaining tributaries to Ralston Creek as segment 17b.
Clear Creek segment 18b was reconfigured to reflect actual water supply uses. Kelly Lake and Van Bibber Creek above the Kelly Lake diversion were moved to Clear Creek segment 18a.
St. Vrain Creek segment 4 was divided into two segments to address the water quality in James Creek which has been affected by historical mining. Segment 4a is now Lefthand Creek and tributaries except for James Creek, and Segment 4b is James Creek and its tributaries.
Big Thompson segment 4 was split into segment 4a, 4b and 4c to reflect differences in uses and water quality characteristics. The dividing point between 4a and 4b is the Greeley-Loveland Canal diversion. Segment 4a, above the diversion will have water supply and aquatic life cold 2 uses. The dividing point between segments 4b and 4c is County Road 11H, above the Loveland wastewater treatment plant.
Cache la Poudre segments 1 and 2 were combined into a new segment 1. This combines those waters within the Rawah, Neota, Comanche Peak and Cache la Poudre Wilderness Areas with those in the Rocky Mountain National Park into 1 segment.
Cache la Poudre segments 3 and 4 were combined into segment 2. This combines the mainstem, and waters tributary to the Upper Cache la Poudre (and not in segment 1) into 1 segment. Segments 3 and 4 were deleted.
Middle South Platte segment 3 was split into segment 3 and segment 5 to reflect differences in recreational uses. Segment 3 remains the "all tributaries" segment; segment 5 will be Lone Tree, Crow, and Boxelder Creeks.
Lower So. Platte segment 2 This "all tributaries" segment was split into portions that have perennial flow and support diverse aquatic communities and those that do not. Segment 2b is the portion on the north side of the river with aquatic communities and segment 2a is the portion without. Vancil Reservoir was moved to segment 5.
Republican River segment 6 was reconfigured to reflect aquatic life uses. Chief Creek was moved to segment 3 which has an aquatic life cold 1 classification.
In March 1993, the Commission amended the Basic Standards and Methodologies for Surface Water, Regulation #31 (5 CCR 1002-31) to include wetlands in the stream classification and standards system for the State. Due to that action, it became necessary to revise the segment description for all segments of the "all tributary" type to clarify that wetlands are also part of the tributary system for a given mainstem segment. All tributary wetlands now clearly carry the same classifications and standards as the stream to which they are tributary as provided for in 31.13(1)(e)(iv).
The aquatic life manganese criterion was initially changed in the 1997 revisions to the Basic Standards (5 CCR 1002-31) from a single chronic dissolved criterion to acute and chronic hardness-based equations. The equations were further modified in the 2000 revisions to the Basic Standards. The new manganese acute and chronic equations were added as table value standards in 38.6(3). As a result of the adoption of these new TVS, all segments classified for aquatic life use that had a chronic total recoverable manganese standard of 1,000 ug/l had the 1,000 standard stricken and replaced with Mn (ac/ch)=TVS.
The regulation in 38.6 (3) listed the table value standards for selenium as Acute=135 ug/L and Chronic=17 ug/L. This was updated to reflect the existing acute and chronic criteria for selenium listed in the Basic Standards as Acute= 18.4 ug/L and Chronic= 4.6 ug/L which was adopted in 2000 by the Commission. This change means that all segments with standards for selenium given as TVS now have these lower acute and chronic standards. Because of this change, on all segments classified for a water supply use, the chronic total recoverable selenium of 10 ug/L was stricken and replaced with Se (ac/ch)=TVS.
Several segments or waterbodies were designated outstanding waters (OW) due to their meeting certain criteria pursuant to section 31.8 . Other segments that already had the OW designation but whose classifications and/or standards were inconsistent with the those prescribed by the Commission for OW waters in other basins in Colorado were corrected. These changes are discussed below for each segment.
Upper So. Platte segment 1b
Bear Creek segment 7
Clear Creek segment 19
Boulder Creek segment 1
St. Vrain segment 1
Big Thompson segment 1
Cache La Poudre segment 1 (newly configured)
Laramie River segment 1
There were several segments which had temporary modifications that were reviewed, and decisions were made as to delete them or to extend them, either as is or with modification of the numeric limits.
Upper So. Platte segment 2b, Mainstem of Mosquito Creek from the confluence with South Mosquito Creek to its confluence with the Middle Fork of the South Platte River: This segment had a temporary modification for zinc. The TMDL for iron, lead, manganese, cadmium and zinc in the Mosquito Creek areas was submitted to EPA in June 2000. The Commission determined, after review of the information presented at the hearing, that the temporary modification should be revised to reflect data collected from the segment in the past few years. It was determined that an expiration date of 6/30/04 would provide sufficient time for the Division, the Division and Minerals and Geology, and the stakeholders to determine the appropriate steps to address the issue.
Upper So. Platte segment 2c, South Mosquito Creek from the source to the confluence with Mosquito Creek: This segment had temporary modifications for cadmium, iron, zinc and manganese. Water quality in segment 2c is highly affected by the discharge of water from two tunnels, and waters in segment 2c flow into segment 2b, discussed above. The temporary modifications were revised to reflect current information and extended to 6/30/04.
Upper So Platte segment 15 Mainstem of South Platte River from the Burlington Ditch Diversion in Denver to a point immediately below the confluence with Big Dry Creek: Temporary modifications for fecal coliform and E. coli at existing quality, for chronic selenium of 5.2 ug/L and acute selenium of 18.4 ug/L were adopted for this segment that will expire 6/30/04.
Upper So Platte segment 16a Mainstem of Sand Creek from the source to the confluence with the South Platte River: Temporary modifications for chronic selenium of 12 ug/L with no acute selenium standard were adopted for this segment that will expire 6/30/04.
Clear Creek segment 14, Mainstem of Clear Creek from the Farmers Highline Canal diversion in Golden Colorado to Youngfield Street in Wheatridge, Colorado: This segment had temporary modifications for cadmium and manganese. The temporary modifications were reviewed and deleted to reflect data collected recently from the segment.
Big Dry Creek segment 5, Mainstems of North and South Walnut Creek including all tributaries, lakes and reservoirs, from their sources to the outlets of ponds A-4 and B-5, on Walnut Creek, and Ponds C-2 on Woman Creek. All three ponds are located on Rocky Flats property: This segment had temporary modifications for americium and plutonium set to expire 6/30/01 and nitrate and nitrite set to expire 12/31/09. The Commission decided to delete the americium and plutonium temporary modifications. The original reason for adopting those modifications was to expedite 401 certification of the NPDES permit. Since DOE has chosen not to reconfigure the outfall and that proposed reconfiguration formed part of the basis for the americium and plutonium temporary modifications, these modifications are no longer needed on that basis. In regards to the nitrate and nitrite temporary modifications, the Commission decided to keep the expiration date.
Big Dry Creek segment 4a: Mainstem and all tributaries to Woman and Walnut Creeks from sources to Standley Lake and Great Western Reservoir except for specific listings in Segments 4b and 5. This segment had temporary modifications for nitrate and nitrite set to expire 12/31/09. The Commission decided to keep the expiration date.
Big Dry Creek segment 4b, North and South Walnut Creek and Walnut Creek, from the outlet of ponds a-4 and b-5 to Indiana Street This segment had temporary modifications for nitrate and nitrite set to expire 12/31/09. The Commission decided to keep the expiration date.
Big Thompson segment 4c, Mainstem of the Big Thompson from County Road 11 to I-25: A temporary modification for fecal coliform of 2000 and E coli of 181 was adopted for this segment that will expire 6/30/2004.
Big Thompson segment 5, Mainstem of the Big Thompson River from I-25 to the confluence with the South Platte River: Temporary modifications for chronic selenium of 8 ug/L, and fecal coliform of 2000 /100 ml were adopted for this segment that will expire 6/30/2004.
Big Thompson segment 9, Mainstem of the Little Thompson River from the Culver Ditch diversion to the confluence with the Big Thompson River: A temporary modification for chronic selenium of 12 ug/L was adopted for this segment that will expire 6/30/2004.
Clear Creek segment 13b, Mainstem of North Clear Creek including all tributaries, lakes reservoirs, and wetlands from a point just below the City of Black Hawk's water supply intakes to the confluence with Clear Creek: Temporary modifications were adopted for chronic cadmium (6.9 ug/L), copper (45 ug/L), total recoverable iron (17,292 ug/L), manganese (4,570 ug/L) and zinc (1750 ug/L) which will expire 6/30/2004.
The biological standards were updated to include the dual standards for E. coli and fecal coliform, which were adopted by the Commission in the 2000 revisions to the Basic Standards. As stated in the statement of basis for the Basic Standards revisions, the Commission intends that dischargers will have the option of either parameter being used in establishing effluent limitations in discharge permits. In making section 303(d) listing decisions, in the event of a conflict between fecal coliform and E coli data, the E. coli data will govern. The Commission believes that these provisions will help ease the transition from fecal coliform to E. coli standards.
In a continuation of the Commission's efforts to comply with the requirements contained in the federal Clean Water Act that all waters of the nation should be suitable for recreation in and on the water (known as the "swimmable" goal), the Commission reviewed all Recreation Class 2 segments. In Colorado, the "swimmable" goal translates into Recreation Class 1a, with the 200/100 ml fecal coliform and 126/100 ml E. Coli standards, and Class 1b with the 325/100 ml fecal coliform and 205/100 ml E. coli standards. Class 1a indicates waters where primary contact uses have been documented or are presumed to be present. Class 1b indicates waters where a reasonable level of inquiry has not documented any class 1 uses, but no use attainability analysis has been performed demonstrating that a recreation class 2 classification is appropriate. To maintain the existing Recreation Class 2 with the 2000/100 ml standard on a segment, it must be shown that there is minimal chance that a Recreation Class 1 activity could exist (e.g. ephemeral or small streams that have insufficient depth to support any type of Recreation Class 1 use or very restricted access).
The classifications for segments previously classified Recreation Class 1 were changed in this hearing to Class 1a, to reflect the revisions to the Basic Standards. This does not represent a substantive change in the status for these segments. A recreation 1a classification of a segment is not intended to imply that primary contact recreation would be allowed by the owner or operator of any water body in the segment. A recreation 1a classification is intended to only affect the segment's use classification and water quality standards, and does not imply public or recreational access to waters with restricted access within the segment.
Based on the information received in the record that showed Recreation Class 1a uses are in place in at least a portion of the segment, the Commission changed the following formerly Class 2 segments to Class 1a with a 200/100 ml fecal coliform and 126/100 ml E. coli standard:
Upper South Platte segments: 1a, 14
Saint Vrain segments: 6
Middle South Platte segments: 1, 3
Big Thompson segments: 4a(from 5/1 - 10/15), 4b(from 5/1 - 10/15). 4c(from 5/1 - 10/15), 6, and 14
Cache La Poudre segments: 11, 12, 13a
The following segments were classified Recreation Class 1a based on the policy reflected in the Basic Standards and Methodologies for Surface Water without a factual determination that there are existing Class 1 uses on these segments. These include segments for which the Division's Exhibit 2 for this hearing states that there are "documented or potential" uses, without other evidence of existing Class 1 uses being present in the record.
Upper So. Platte segments: 1b, 4, 5a, 5b, 5c, 7, 9, 10a, 10b, 11a, 15, 16a, 16b, 16c, 17a
Cherry Creek segments: 1, 3, and 4
Bear Creek segments: 1a, 1b, 2, 3, 4a, 5, 7
Clear Creek segments: 1, 5, 8, 12, 13a, 13b, 14b, 15, 16a, 17b
Big Dry Creek segment: 4a
Boulder Creek segments: 1, 3, 5, 6, 7a, 7b, 8, 10, 11
Saint Vrain segments: 1, 2, 3, and 5
Middle So. Platte segment 4
Big Thompson segments: 9, 10
Cache La Poudre segments: 7, 8, 10, 15, and 16
Lower So. Platte segments: 1, 2b
Republican segments: 1, 3, 4, and 5
For the segments listed immediately above, the last paragraph of section 31.6 will apply to future changes to the recreation classification where a proper showing is made through a use attainability analysis that a recreation Class 2 classification is appropriate, without application of the other downgrading criteria in this section. Moreover, the Commission is relying in part on testimony from EPA that completion of a use attainability analysis showing that a lower recreation classification is appropriate satisfies applicable downgrading criteria. Based on these factors, the Commission intends that in a future rulemaking hearing the test for adopting a recreation Class 2 classification would be the same as if it had been considered in this hearing.
Based on evidence in the record that a reasonable level of inquiry has failed to identify any existing class 1 recreation uses, the Commission changed the following segment to Class 1b with a 325/100 ml fecal coliform and 205/100 ml E. coli standard:
Big Thompson segment 5(from 5/1 - 10/15)
The following segments retained their Recreation Class 2 classification with 2,000/100mL fecal coliform and 630/100 ml E. coli standard because use attainability analyses demonstrate that a Recreation Class 1a or 1b use is unattainable.
Clear Creek segments: 7, 14a, 16b, 17a, 18a, and 18b
Big Dry Creek segments: 1, 3, 4b, 5, 6
Big Thompson segments: 4a, 4b, 4c, 5 (10/16 - 4/30)
Cache La Poudre segment 13b
Lower So. Platte segment 2a
Republican segments: 6, 7
The classification for Clear Creek segment 14a is based on the fact that access to this portion of the stream is restricted, since it is located principally on Coors Brewery property, is fenced and patrolled. The classifications for Clear Creek segments 16b, 18a, and 18b and Big Dry Creek segments 1 and 6 are based on the fact that these are narrow, shallow streams and that no evidence was presented that any portion of the streams are conducive to full body immersion. In addition, for Big Dry Creek segment 1, there was evidence that canoeing has occurred only on a supervised basis for a limited stretch, and the decision also considers the steepness of the stream banks, thick riparian vegetation that limits access, the fact that the bike path is set back from the stream in many areas and that the lower portion of the stream runs through a primarily agricultural area. Also, for Big Dry Creek segment 6 there was evidence that this is an ephemeral stream and that Fortune Reservoir will not be releasing water to this stream. For Clear Creek segment 17a, Arvada Reservoir, the basis for the Class 2 conclusion is that the reservoir is fenced, posted as no swimming, and patrolled, with only boating
The Commission reviewed information regarding Aquatic Life Class 2 segments where the full set of inorganic aquatic life protection standards have not been applied. Generally, these are dry segments with only rudimentary aquatic life. The Commission's policy has been that rather than adopt the full set of inorganic standards for these segments, standards for dissolved oxygen, pH and fecal coliform provide sufficient protection. The segments which were reviewed in this hearing and for which sufficient evidence was received for them to retain their present classifications and standards are:
Lower So. Platte segment 2a
Clear Creek segment 8
Boulder Creek segment 4c (numerics are for water supply)
Republican segments 6, 7
Segments where investigation showed that fish populations were present were upgraded with the addition of the full suite of inorganic standards. These segments are:
Upper So. Platte segments 11a, 16a, 16b, and 16c
Cherry Creek segment 4
Clear Creek segments 16, 18b
Big Dry Creek segment 1
Boulder Creek segments 8, 11
Saint Vrain segment 6
Middle So. Platte segment 3
Big Thompson segments 6, 10
Cache La Poudre segments 8, 13
Lower So. Platte segment 2b
There are several segments in the South Platte Basin that contain ambient standards. Ambient standards are adopted where natural or irreversible man-induced conditions result in water quality levels higher than table value standards. EPA had requested that the Commission review 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 Division reviewed the reason for the ambient standards and provided testimony that justified ambient standards being retained without adjustment on the following segments:
Upper So. Platte segments 2b, 2c, 5a, 14, and 15
Clear Creek segment 11 (Cu, Mn, Zn only)
Clear Creek segments 2,13b, 14
Big Dry Creek segments 2, 3, 4a, 4b, 5, 6
The Division reviewed the information about ambient water quality levels and provided testimony that justified the ambient standards on Upper So. Platte segment 6c, Mn(ch) = 90 ug/l (dis).
The ambient standard for gross beta on the Woman Creek portion of Big Dry Creek segment 4a was corrected. It had originally been proposed and adopted as 8, not the value of 5 as shown in the table.
Ambient standards were removed from the following segments due to new data and/or changes to the basic standards which indicated ambient standards were no longer appropriate:
Clear Creek segment 3a, changed to Pb(ac/ch) = TVS
Clear Creek segment 11, changed to Cd(ac/ch) = TVS
Middle So. Platte segment 1, changed to Fe(ch) = 1000(trec)
Lower So. Platte segment 1, changed to Fe(ch) = 1000(trec)
Big Thompson segment 9, changed to Fe(ch) = 1000(trec)
The organic standards were updated to include changes which were adopted by the Commission in the 2000 revisions to the Basic Standards (see 31.11 in Regulation No. 31). "Water + Fish" organic standards 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. The "Fish Ingestion" organic standards are 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. Existing site-specific applications of additional organics (as noted in the Qualifier column of Table 38.6) were modified to conform to this change.
Information was reviewed regarding Aquatic Life Class 2 segments that have fish that are presently being taken for human consumption or have fisheries that would indicate the potential for human consumption. That information showed that additional segments had the potential for consumption of fish. These waterbodies, which include the urban and rural lakes where fishing routinely occurs, were designated to receive the full protection of numeric Fish Ingestion organic standards:
Upper South Platte segment 16c
Middle South Platte segments 1 and 3
Big Thompson segments 4 and 6
Cache La Poudre segments 11 and 12
The waterbodies which also have water supply classifications and therefore need water + fish organics are:
Clear Creek segments 17a, 17b
Cache la Poudre segment 8
Water bodies that had existing "additional organics" were examined to determine which needed water + fish organics and which needed fish ingestion organics. The following segments changed to water + fish organics:
Bear Creek segments 1b, 4a, 4b, 4c and 5
Big Thompson segment 3
Cache la Poudre segments 7, 10
The following segment changed from additional organics to fish ingestion organics:
Middle So. Platte segment 4
These segments had the Water Supply classification added to them. The associated water supply standards will now apply to segments:
Clear Creek segments 2, 13a and 16a
Cache La Poudre segment 8
Big Thompson 4a
Water supply standards were modified to conform to the changes made by the Commission in the 2000 revisions to the Basic Standards (see Regulation No. 31 at 31.11(6)). The Commission modified the water supply standards for iron, manganese, and sulfate that are based on secondary drinking water standards (based on esthetics as opposed to human-health risks). The numeric values in the tables were changed to Fe(ch) = WS(dis), Mn(ch) = WS(dis), and SO4 = WS. These abbreviations mean that for all surface waters with an actual water supply is, the less restrictive of the following two options shall apply as numerical standards, as discussed in the Basic Standards and Methodologies 31.11(6): either (i) existing quality as of January 1, 2000; or (ii) iron = 300 ug/L (dissolved); Manganese = 50 ug/L (dissolved); Sulfate = 250 mg/l (dissolved). 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 determined as the result of a site-specific rulemaking hearing that such standards are appropriate.
Upper So Platte segment 5c: The upper pH limit was corrected and changed from 8.5 to 9.0.
Upper So Platte segment 14: The seasonal class 1 recreational designation was changed to a year round class 1a.
Upper So. Platte segment 15: As a result of this hearing, the Commission has decided to revise the pH standard for a two mile reach of Segment 15 of the So Plate River (Segment 15) to expand the permissible pH range of this reach to a range of 6.0 to 9.0. The Metro District submitted evidence that its effluent periodically can be depressed below a pH of 6.5 through natural biological treatment processes; however, its effluent does not go below a pH of 6.0. The Metro District would not consistently be able to meet a pH permit limit set at the current pH stream standard of 6.5.
In making its decision to change the pH standard, the most important question for the Commission was the protection of aquatic life in Segment 15. The Metro Waste Water Reclamation District submitted good scientific evidence that the fish and biota in Segment 15 would be protected at the pH level of 6.0. The District also showed that the River pH naturally rebounds even when the Metro District's pH level is below 6.5. The Commission also considered evidence showing that a number of other states have pH range standard of 6.0 to 9.0. Finally, the Metro District also submitted information showing that adding chemicals to its effluent to raise pH or changing facilities and operations to raise pH would be an unnecessary and unreasonable expenditure of public funds.
Upper So. Platte segment 17c, Bowmar Lake. The site-specific aluminum standard was changed from Al(ch) = 200, to Al(ch) = TVS. The dissolved oxygen criterion was corrected and changed from 6.0 to 5.0 mg/l. This reflects the water quality for an Aquatic Life Warm 1 fishery.
Big Thompson segment 13. This segment lacked Aquatic Life, Recreation, and Agriculture Classifications. Aquatic Life Warm 2, Recreation 1, and Agriculture Classifications with their associated standards were added to this segment.
Cache la Poudre segment 13b. A site-specific ammonia standard of 0.1 mg/L was set for this segment.
Boulder Creek segment 11. Water supply classification was added.
Lower So. Platte segment 3. The dissolved oxygen standard was corrected and changed from 6.0 to 5.0. This reflects the water quality standards for warm water fisheries.
The Farmers Reservoir and Irrigation Company (FRICO) proposed the adoption of total phosphorus and total nitrogen standards and more restrictive fecal coliform standards for Upper South Platte River segments 14 and 15 and for Middle South Platte River segments 1, 3 and 4. Based upon the evidence submitted in this rulemaking, the Commission has decided not to adopt the standards proposed by FRICO.
With respect to the proposed fecal coliform standards, the available evidence does not support a determination that the risks posed by agricultural worker contact with irrigation water or by consumption of raw edible crops is greater than the risk posed by primary contact recreation uses. The Commission is adopting recreation class 1a standards for each of these five segments as a result of this hearing. Therefore, no need has been demonstrated at this time for the adoption of more restrictive fecal coliform standards to protect the designated uses of these segments.
FRICO proposed the adoption of nitrogen and phosphorus standards to address the eutrophic conditions in Barr Lake and Milton Lake. Although the evidence does indicate concerns regarding the existing water quality in both of these reservoirs, the Commission does not believe that an adequate technical basis has been provided at this time for the specific numerical nutrient standards proposed. The Commission does believe that there is a need for an effort to address the issue of South Platte plains reservoir eutrophication, and that consideration should be given to a possible Clean Lakes Study as one alternative to advance the understanding of these systems.
Finally, the Commission does not believe that the evidence submitted supports the contention by FRICO that the proposed 2.0 mg/l total nitrogen standard is necessary to protect sensitive crops irrigated by water from the segments in question.
The City of Thornton (Thornton) advanced two alternative proposals in this hearing. Alternative 1 proposed that numerical standards be added to Upper South Platte River segments 6 and 14 for giardia lamblia, nitrate, total organic carbon (TOC) and phosphorus. In its prehearing statement, Thornton withdrew its nitrate proposal. Alternative 2 proposed the adoption of a narrative standard providing that the water quality in these segments "be improved and maintained to remove present impairments to water supply uses and to allow water supply uses applying the standards of 5 CCR 31.13 at all times." The proposed standard also provided that: "Implementation of the narrative standard will be by agreement of the stakeholders on required numeric water quality standards and the means to achieve those standards." Based upon the evidence submitted in this rulemaking, the Commission has decided not to adopt either Thornton proposal.
With respect to alternative 1, the evidence submitted does not support the proposed giardia lamblia standard as an appropriate pathogen indicator or as a direct measurement of human health risk. The evidence does not distinguish giardia levels or risk at these locations as compared to other waters in the state, and does not demonstrate that the proposed standard is needed to protect the water supply use for these segments. With respect to TOC, the evidence does not support a conclusion that the gross measure of TOC is an appropriate or effective measurement to address potential human health concerns regarding specific organic compounds such as disinfection by-products. Finally, although phosphorus levels may have an impact on the trophic condition of the terminal storage reservoirs that are filled by water from the segments in question, the Commission does not believe that an adequate technical basis has been provided at this time for the specific numerical standards proposed.
The Commission has decided not to adopt alternative 2 because it believes that more analysis is needed before reaching conclusions regarding the adequacy of the existing water quality in these segments for water supply use and potential implementation mechanisms to assure that adequate quality is maintained. The Commission believes that the issue of adequate water quality for effluent-dominated water supply segments warrants further consideration. The Commission urges the interested parties to work together on resolving this issue, with leadership from the Division.
PARTIES TO THE RULEMAKING HEARING
5 CCR 1002-38.57