Code of Colorado Regulations
1000 - Department of Public Health and Environment
1002 - Water Quality Control Commission (1002 Series)
5 CCR 1002-73 - REGULATION NO. 73 - CHATFIELD RESERVOIR CONTROL REGULATION
Section 5 CCR 1002-73.15 - STATEMENT OF BASIS, SPECIFIC STATUTORY AUTHORITY AND PURPOSE (1999 REVISIONS)
Current through Register Vol. 47, No. 17, September 10, 2024
Sections 25 8 202 and 25 8 205, C.R.S., provide the specific statutory authority for adoption of the revisions to this regulation. The Commission also adopted, in compliance with Section 24 4-103(4), C.R.S., the following statement of basis and purpose.
BASIS AND PURPOSE
The 1999 Revisions to the Chatfield Reservoir Control Regulation ("Control Regulation") address two major substantive issues:
(1) phosphorus allocations, and
(2) land application discharges.
The revisions pertaining to phosphorus allocations have two primary purposes. First, the revisions clarify and slightly modify the total maximum phosphorus allocation for the Chatfield Reservoir ("Reservoir") and describe in greater detail how the allocations were calculated and distributed. Second, the allocation revisions amend and expand mechanisms for point source dischargers in the Chatfield Watershed to obtain additional phosphorus wasteload allocations.
The revisions concerning land application were adopted for two reasons. First, the modifications introduce a land application return factor into the formulas used to calculate phosphorus wasteloads for land application discharges. This change coordinates aspects of the state augmentation plan process (as decreed in Water Court and administered by the State Engineer) with Control Regulation requirements. Second, the land application revisions clarify and define certain monitoring and reporting requirements for land application dischargers.
Finally, in addition to the phosphorus allocation and land application modifications, this action also implements minor, miscellaneous changes.
Total Phosphorus Allocation
The 1993 revisions to the Control Regulation established a total aggregate phosphorus allocation - or Total Maximum Annual Load ("TMAL") - for loadings to the Reservoir of 59,000 pounds per year at a flow of 261,000 acre-feet per year. The 1999 revisions do not modify the overall TMAL of 59,000 pounds per year, but rather, provide additional explanation for the basis and distribution of the loading.
Explanation of TMAL
The revisions clarify that the TMAL for the Reservoir is based upon the formula of TMAL [59,000 pounds per year] = Chatfield Watershed (Reservoir base load [13,400 pounds per year] + background [20,312 pounds per year] + wasteload allocation [7,358 pounds per year]) + Upper South Platte River Watershed (Reservoir base load [6,000 pounds per year] + background [11,842 pounds per year]+ Summit County Wasteload allocation [88 pounds per year]) + Margin of Safety. The formula takes into consideration that the Chatfield Reservoir receives phosphorus loadings from both the Chatfield Watershed, which is subject to the restrictions in the Control Regulation, and the Upper South Platte River Watershed, which is currently uncontrolled and outside the scope of the Control Regulation. The Chatfield Watershed, which is depicted in Figure 1, is defined as:
Components of TMAL
The revisions provide an expanded explanation and definition of the various components of the TMAL. Previously, the Control Regulation simply provided that point sources of phosphorus to the Reservoir (wasteload allocation) were limited to 7,358 pounds per year, and nonpoint and background sources (load allocation) were limited to 51,642 pounds per year. The 1999 revisions clarify that the TMAL is comprised of loadings from both the Chatfield Watershed (41,070 pounds per year) and the Upper South Platte River Watershed (17,930 pounds per year), and the revisions explain in greater detail the distribution of the loadings within the two watersheds. The loading allocation of 41,070 pounds per year for the Chatfield Watershed is comprised of: 13,400 pounds per year for "Reservoir base load," 20,312 pounds per year for "background," and 7,358 pounds per year for point source wasteload allocations. The 17,930 pounds per year allocation for the Upper South Platte River Watershed consists of: 6,000 pounds per year for Reservoir base load, 11,842 pounds per year for background, and 88 pounds of wasteload allocation to Summit County. For both watersheds, "Reservoir base load" represents the average measured total phosphorus load reaching the Reservoir. For these revisions, the Reservoir base-load was determined using five years of data, 1993-1997. See DRCOG, Chatfield Historical Report, 1997.
Total "background" for the TMAL, 32,154 pounds per year (Chatfield and Upper South Platte River Watersheds combined), was calculated by subtracting total Reservoir base load (19,400 pounds per year) and total wasteload allocations (7,446 pounds per year) from the TMAL (59,000 pounds per year). See Section 73.2 for definition of background. Background, which also has been sub-divided by watershed, is a significant buffer between total measured loadings (Reservoir base-load + wasteload allocations) and the total allowable loading (TMAL) for the Reservoir.
Implicit Margins of Safety in the TMAL
The revisions identify the implicit margins of safety in the TMAL. Although these margins of safety have been incorporated since the TMAL of 59,000 pounds per year was established in 1993 and have not changed, the Water Quality Control Division ("Division") requested further explanation of the margins of safety. The implicit margins of safety were derived from conservative assumptions used in the Reservoir loading model.
The first margin of safety relates to conservative flow assumptions. The annual flow of 261,000 acre-feet/year used to calculate the TMAL figure was established by evaluating a cumulative distribution of flows from six years of data (1985 through 1990) to predict the probability of given annual flows. A conservative assumption of a one in ten year flow, or Q10, was applied to derive an annual flow of 261,000 acre-feet for the TMAL. The Q10 flow of 261,000 acre-feet/year was utilized to develop the TMAL. Q10 is protective, because there is a 90% probability that the Q10 flows and loads under the TMAL will not be exceeded each year. See Woodward-Clyde Consultants, Nonpoint Source Management Plan for the Chatfield Reservoir, Colorado (Sept. 1992) ("Woodward-Clyde Chatfield Report, 1992"). In response to Thornton's concerns that the TMAL model only relied upon 5 years of data, the Authority has confirmed the validity of the Q10 by recalculating the Q10 using 14 years of available data (1985 through 1998), rather than six. The Q10 recalculated with the larger data set was approximately 255,000 acre-feet, within 3% of the original Q10 estimate. Further, monitoring conducted in the Chatfield Watershed also confirms that this implicit margin of safety exists. Data collected since 1986 substantiate that the TMAL's margin of safety has generally ranged between 15,000 and 25,000 pounds per year. See Denver Regional Council of Governments, 1997 Chatfield Watershed Authority Annual Report (May 1998).
The second implicit margin of safety is a 13% upward bias for total loading to the Reservoir. See Woodward-Clyde Chatfield Report, 1992. The model, therefore, slightly overestimates the amount of phosphorus that will reach the Reservoir each year, a conservative and protective assumption.
The third implicit margin of safety concerns phosphorus concentrations in the Reservoir. See Woodward-Clyde Chatfield Report, 1992; and DRCOG, Chatfield Watershed and Reservoir 1986 - 1995 Historical Data Analysis and Monitoring Program Review (July 1997) ("DRCOG, Chatfield Historical Report, 1997"). Due to the conservative assumptions in the model, phosphorus concentrations in the Reservoir could be 32% greater (than the 27 mg/l standard in the Control Regulation) and would still attain the chlorophyll a goal of 17 mg/l. Thus, the model provides a 32% margin of safety for phosphorus concentrations in the lake.
Upper South Platte Allocations
The 1999 revisions clarify that the loading components from the Upper South Platte River Watershed (Reservoir base load, background and wasteload allocation) incorporate all point and nonpoint sources upstream of Strontia Springs Reservoir outfall, including 88 pounds per year of total phosphorus from wastewater that originates in Summit County and is discharged into the Roberts Tunnel. See Footnote 2 (Section 73.3). Sources from the South Platte River upgradient of Strontia Springs Reservoir outfall have been identified as either Reservoir base-load sources or background, but the revised Control Regulation does not sub allocate these South Platte loadings, because loadings from the Upper South Platte River Watershed, including point sources, are not subject to the controls of this regulation. A separate watershed association has been formed for the Upper South Platte River Watershed, and this association should establish, as necessary, allocations for the point and nonpoint sources in the Upper South Platte River Watershed, in order to assure that Reservoir base-load and background limits are achieved in the South Platte above the Strontia Springs Reservoir outfall. (Current monitoring indicates that these upper South Platte base load and background levels are being met at the Strontia Springs Reservoir monitoring station.)
The TMAL revisions modify one point source wasteload allocation. The total point source wasteload allocation for the Chatfield Watershed remains at 7,358 pounds per year, but the 88 pounds per year that were previously allocated to Summit County point sources have been placed in a "reserve/emergency pool" for future allocations. All sources upstream of Strontia Springs Reservoir outfall, including point sources from Summit County, have now been incorporated into the TMAL as Reservoir base load, background and wasteload allocation from the "Upper South Platte River Watershed." (Point sources upgradient of Strontia Springs Reservoir outfall, except Summit County, do not have specific allocations, and such analysis and allocations were beyond the scope of this study.) The remaining wasteload allocations in the Control Regulation have not been modified.
Mechanisms for Point Sources
In addition to modifying and explaining the TMAL, the 1999 revisions address four mechanisms for point sources in the Chatfield Watershed to obtain additional phosphorus wasteload allocations. These mechanisms are:
The existing Control Regulation already provides for nonpoint source to point source trades and alternative treatment arrangements for phosphorus concentration reductions. The revisions clarify and modify these two existing mechanisms and also introduce two new mechanisms, point source transfers and reserve/emergency pool allocations.
For the two existing mechanisms, nonpoint to point source trades and alternative treatment arrangements, the revisions authorize the Chatfield Watershed Authority ("Authority") to approve such trades and arrangements. This change was made to simplify and expedite the process for point sources to obtain additional allocations. Also, the Authority, as the entity with primary responsibility for water quality in the Chatfield Watershed, is well qualified to make informed and timely decisions on applications for wasteload allocations. All Authority approvals of trade credits and alternative arrangements, however, remain subject to review and confirmation by the Division. A modification allows trade ratios for nonpoint-point source trades that are less than 2:1, on a site-specific basis, if such lower ratio is substantiated by greater nonpoint source phosphorus removals. The Authority must develop detailed trading guidelines which will set forth, inter alia, the specific criteria and standards for establishing trade ratios less than 2:1, before trades with ratios less than 2:1 will be approved.
The revisions also introduce two new mechanisms for point source allocations: point source transfers and reserve/emergency pool allocations. In point source transfers, one point source discharger may agree to transfer all or part of its phosphorus wasteload allocation to another point source discharger. In reserve/emergency pool allocations, point source dischargers in the Chatfield Watershed may apply to the Authority for phosphorus wasteload allocation pounds from the reserve/emergency pool. Currently, the reserve/emergency pool for future allocations contains 88 pounds per year. As with nonpoint to point source trades and alternative arrangements, the Authority may approve point source transfers and emergency/reserve pool allocations, subject to review and confirmation by the Division.
Finally, the 1999 revisions explicitly provide that the Authority may utilize any of the four mechanisms for additional phosphorus wasteload allocations - nonpoint to point source trades; alternative treatment arrangements for concentration reductions; point source transfers; or reserve/emergency pool allocations - to approve allocations for new point source dischargers not listed at Section 73.3(2)(b).
Return Flow Factors
The revisions modify the formula for determining phosphorus loads from land application dischargers by incorporating a "land application return factor" into the equations at Section 73.4 used to determine monthly phosphorous loads for land treatment and land disposal dischargers. The land application return factor represents the estimated percent of water discharged by a wastewater treatment plant utilizing land application that reaches the streams, tributaries, or alluvium in the Watershed system subject to the Control Regulation. Return flows can vary considerably depending on site location and geology.
The revised Control Regulation establishes two simple formulas for determining the specific land application return factor for each land application site:
The augmentation plan return flow percents are premised on the scientific and legal findings of the Office of the State Engineer, Division of Water Resources ("State Engineer") and Water Court. The return flow percent in an augmentation plan is a scientifically-based figure that will have been previously scrutinized by the State Engineer and judicially decreed in Water Court pursuant to 37-90-137(9)(c)(I), C.R.S. In this administrative and judicial process, moreover, the State Engineer and Water Court already will have considered the unique conditions at the site, including: the location of the site in the Watershed, site geology and hydrology, and the distance from the land application site to streams, tributaries and alluvium. The most common method determining return flow percents for augmentation plans is the Glover technique, which calculates return flow volumes and models the time required for return flows to accrue in a river system. The State Engineer relies on the Glover technique, and other accepted methods and models such as Modflow, to calculate return flow percents for specific areas. Computations are based upon site-specific information for the study area, including physiography, geology, groundwater hydrology, groundwater flux assessments, drainage, and hydrology. The Water Court also has endorsed these methods as appropriate techniques for quantifying return flow factors for the State of Colorado. Because this particular formula utilizes information from decreed augmentation plans, the formula is, as a practical matter, limited to those dischargers at sites covered by augmentation plans that include return flow percentages. This is a reasonable approach, because the information considered and approved in the augmentation plan process establishes a sound, scientific basis for land application return factors. Discharges without augmentation decrees with return flow percentages, or discharges who opt not to use this method, will apply a land application return factor based on the lysimeters and area ratio of their sites.
Consistent with the addition of a land application return factor, the revisions also specify an alternative formula at 73.4, in addition to the existing formula (as amended to include a return flow factor), for determining phosphorus loads from land treatment discharges. The new equation calculates the monthly phosphorus load for a discharger as the sum of the individually-calculated monthly loads from each land treatment site. The new formula accounts for potential return flow variability, because it applies return factors separately for each land treatment site, whereas the existing formula applies one return factor to all of a facility's discharges. Therefore, if a single discharger land applies to multiple areas with different land application return factors, the new formula reflects these differences, proportionally, in the total load.
Phosphorus Concentration
The revised Control Regulation allows land treatment dischargers to sample for phosphorus concentration either (1) at the land application site below the surface and above the seasonal high groundwater level, or (2) in their systems prior to land treatment. The revisions also confirm that concentrations for land disposal discharges must be measured prior to land application.
The former version of the Control Regulation did not specify where land treatment discharges must sample phosphorus concentration, but implied that phosphorus concentrations should be measured in lysimeters. The revisions clarify these requirements and authorize land treatment dischargers to either reflect nutrient uptake by soils and vegetation when measuring phosphorus or comply with phosphorus limitations before land application. If a discharger chooses to measure phosphorus below the surface, the facility may use lysimeters, piezometers, or any other appropriate measurement devices.
Exemption
The revised Control Regulation provides that the Division may determine that a land application discharger has no phosphorus discharge, or a reduced phosphorus discharge, if the discharger demonstrates that it land applies at agronomic rates and that it has installed, or will install, soil moisture probes or other systems to assure treatment at agronomic rates. Agronomic rates, which vary by vegetative species, measure the rate at which plants consume constituents in the soil, like nutrients. Information on agronomic rates for particular species is primarily available from governmental or educational institutions such as Colorado State University. In addition, for such dischargers treating at agronomic rates, the Division may grant a partial exemption from monthly volume or phosphorus monitoring requirements. These provisions are intended to address a common scenario in which a land application discharger treats at very efficient rates and, thus, rarely measures any reportable discharge or phosphorus. The no discharge determination and the exemption allow dischargers that can demonstrate treatment at agronomic rates to avoid burdensome monitoring and reporting requirements.
Site Approvals
The revisions provide that the Division shall use the return flow percent specified in an augmentation plan to calculate phosphorus discharge loads for the site application of a land application discharger, if:
The 1999 revisions specifically enumerate Douglas and Jefferson counties as the two counties subject to the requirements in Sections 73.5 and 73.6 for monitoring, annual reporting, and nonpoint source controls. The revisions also clarify that the requirements of Sections 73.5 and 73.6 may be implemented by water quality entities as separate management agencies or jointly as a watershed association. Finally, the revisions provide that the Water Quality Control Commission may adjust TMAL allocations, modify water quality monitoring requirements or specify nonpoint source management measures, if the nonpoint point source management programs mandated in Section 3.6 are not implemented.
Based on issues raised by some of the parties to the rulemaking hearing, the Commission recommended that, for the next triennial review, the Authority and the Upper South Platte Watershed Protection Association, in consultation with the Division, monitor and validate the modeling assumptions and partitioning of load allocations for each watershed proposed in the amended regulation.
Section 73.2 - Definitions
Definitions for the following terms were added to Section 73.2: "Background," "Land application return factor," "Margin of safety," "Reserve/Emergency Pool," "Reservoir base-load," "TMAL," and "Upper South Platte River Watershed." Figure also has been updated, and Figure 2, which depicts the Upper South Platte River Watershed, has been added. The term "Chatfield Sub watershed" has been changed to "Chatfield Watershed" to more properly describe the nature of the watershed area subject to the Control Regulation, and the definition has been modified to clarify that the Chatfield Watershed includes all portions of Plum Creek, and its tributaries, as well as the South Platte River downgradient of the Strontia Springs Reservoir outfall. The term "Chatfield Basin Authority" has been amended to "Chatfield Watershed Authority" to reflect the Authority's name change. Lastly, the definition of "Nonpoint Source" has been modified to state that nonpoint source means any activity or facility other than a point source in the Chatfield Watershed with a wasteload allocation specified at Section 73.3 (2)(b).
Section 73.3 - Total Maximum Annual Load Allocation
The titles of Sections 73.3 and 73.3(1) have been revised to more properly refer to the total phosphorus allocation for the Chatfield Watershed as a "Total Maximum Annual Load" rather than a "Wasteload Allocation."
Section 73.3 sets forth, in detail, the Total Maximum Annual Load ("TMAL") for the Chatfield Reservoir. The TMAL is defined as: TMAL = Chatfield Watershed (Reservoir base load + background + wasteload allocation) + Upper South Platte River Watershed (Reservoir base load + background + Summit County wasteload allocation) + Margin of Safety. The margin of safety is an implicit component of the TMAL based upon conservative modeling assumptions. The allocation for the Chatfield Watershed consists of Reservoir base load, background, and a wasteload allocation for point sources, and the allocation for the Upper South Platte River Watershed is comprised of Reservoir base load, background, and Summit County wasteload allocation. The Upper South Platte River Watershed allocation also incorporates all point and nonpoint sources upstream of the Strontia Springs Reservoir outfall, including 88 pounds per year of total phosphorus from point source wastewater originating in Summit County and discharged into the Roberts Tunnel. The "Reservoir base load" for both watersheds represents the average measured total phosphorus load reaching the Reservoir. A table has been added to Section 73.3 to enumerate the different components of the TMAL. Both Reservoir base load and background are comprised of loadings from both the Chatfield Watershed and the Upper South Platte River Watershed.
The 88 pounds per year of total phosphorus allocated to the reserve/emergency pool in the 1999 revisions was previously allocated to Summit County in the prior version of the Control Regulation. The former allocation was premised on a written agreement between Summit County and the Denver Water Department that allowed for the direct discharge of tertiary treated wastewater effluent into the Robert's Tunnel, which discharges into the North Fork of the Upper South Platte River near Grant. A DRCOG Technical Memorandum dated November, 1986, which was included as part of the Chatfield Basin Master Plan, quantified the 88 pounds per year from Summit County.
It is still anticipated that treated effluent in Summit County could be discharged into the Robert's Tunnel in the future. Because the transport of phosphorus from the Upper South Platte River to the Reservoir is not well understood, it is reasonable for Summit County's allocation to remain with the allocation for the Upper South Platte River Watershed.
Section 73.3 , which lists specific phosphorus wasteload allocations by individual point source, has been amended to reflect that 88 pounds per year have been placed in a "Reserve/Emergency Pool" for future phosphorus allocations.
Section 73.3 , which explained the 88 pounds per year allocation to Summit County, has been deleted, and thus 73.3(2)(d) now becomes 73.3(2)(c). And, sequentially, Section 73.3 now becomes 73.3(2)(d), and 73.3(2)(f) now becomes 73.3(2)(e).
Sections 73.3 (formerly 73.3.(2)(e)), regarding allocations of phosphorus trade credits, and Section 73.3 (formerly Section 73.3), regarding alternative treatment arrangements for phosphorus concentration reductions, have been amended to allow the Authority to approve trade credit awards and alternative treatment arrangements. All Authority approvals of trade credit allocations and alternative treatment arrangements remain subject to review and confirmation by the Division.
New Section 73.3 provides that the Authority may approve phosphorus allocation transfers from one point source to another point source. Both dischargers must jointly apply to the Authority for the transfer with a written agreement that specifies modifications in wastewater flows and treatment performance. The Authority may approve point source to point source transfers, subject to review and confirmation by the Division.
New Section 73.3 authorizes the Authority to award allocations from the reserve/emergency pool to point source wastewater dischargers in the Chatfield Watershed. Dischargers desiring allocations must apply to the Authority and specify the number of pounds desired, and the Authority may approve such allocations, subject to review and confirmation by the Division. Reserve/emergency pool allocations will be applied to the discharger's wasteload allocation and incorporated as amendments to the allocations in Section 73.3 at the next triennial review of the Control Regulation.
New Section 73.3 provides that the Authority may approve phosphorus wasteload allocation pounds for new point source dischargers in the Chatfield Watershed. Phosphorus wasteload allocation pounds for such new dischargers may be derived from:
Section 73.4 - Determination of Wasteload
Section 73.4 , which previously did not contain a heading, was renamed "Direct Discharge," and the provisions in 73.4(1) pertaining to land disposal were moved to Section 73.4(2).
Section 73.4 was renamed "Land Application" and was reorganized into four subsections, (a) - (d). Section 73.4 , "Land Treatment," and section 73.4 , "Land Disposal," modify the equations for calculating phosphorus loads from land treatment and land disposal discharges, respectively, by adding a land application return factor to the formulas. Also, section 73.4 includes an additional, alternative formula for determining phosphorus loads from land treatment discharges. In the new formula, monthly loads are calculated by adding the individual monthly loads from each land application site rather than in the aggregate. Sections 73.4 and 73.4 also were amended to clarify requirements for measuring phosphorus concentration. Section 73.4 provides that land treatment dischargers may monitor for phosphorus either at the land application site below the surface or in their systems prior to land application. Section 73.4 confirms that land disposal dischargers must measure phosphorus before land application.
Section 73.4 , "Exemption," was added to provide that the Division may determine that a land application discharger has zero phosphorus discharge, or a reduced phosphorus discharge, if the discharger demonstrates that it land applies at agronomic rates and that it has installed, or will install, systems to assure land application at agronomic rates. Section 73.4 also authorizes the Division to partially exempt such dischargers from volume or phosphorus monitoring requirements.
Section 73.4 , "Site Approval," was added to provide that the Division shall use the return flow in an augmentation plan to calculate phosphorus loads for a land application discharger's site application, if:
Section 73.5 - Monitoring and Annual Report, and Section 73.6 - Nonpoint Source Controls
In Section 73.5 and Section 73.6 , the term "counties" has been replaced by "Douglas County, Jefferson County" to clarify that these two counties are responsible for the monitoring, annual reporting, and nonpoint source control requirements under the Control Regulation. Section 73.5 and 73.6 also have been modified to specify that the requirements for monitoring, annual reporting, and nonpoint source controls may be implemented by individual entities as separate management agencies or jointly as a watershed association. Section 73.6 has been revised to clarify that the limitation for total nonpoint sources to the Chatfield Watershed is 33,712 pounds per year (Reservoir base-load + background), and that stormwater and nonpoint management controls in the Chatfield Watershed must be implemented to assure that this limit is not exceeded.
Section 73.6 has been modified to provide that if nonpoint source control programs are not implemented, the Commission may adjust phosphorus allocations under the TMAL, amend water quality monitoring requirements, or specify a nonpoint source management program in the Chatfield Watershed.
Section 73.6 has been amended to clarify that monitoring of best management practices ("BMPs") in the Chatfield Watershed shall be conducted by one or more of the following entities: the Authority, other agencies, owners of BMPs, or dischargers.
PARTIES TO THE RULEMAKING HEARING
