5 Colo. Code Regs. § 1002-38.88
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
Pursuant to the requirements in the Basic Standards (at 31.7(3)), the Commission reviewed the status of Temporary Modifications scheduled to expire before December 31, 2015, to determine whether the Temporary Modification should be modified, eliminated or extended. Temporary Modifications standards on twenty-six segments were reviewed.
Allow to expire, delete: The Commission took no action on the Temporary Modification of the selenium standard on Upper South Platte segment 14. This Temporary Modification was deleted from the table because it expires 12/31/2013.
No action, will be reviewed again: The Commission took no action on the temporary modifications on the following segments. These temporary modifications will be reviewed again at the annual temporary modification hearing in December 2014.
* Site-specific compliance with ammonia criteria: Temporary Modifications of the ammonia standards for Upper South Platte segment 15 and Middle South Platte segment 1a were granted to allow time for compliance with revised ammonia standards. Metro Wastewater Reclamation District presented evidence that they are on schedule to make water quality improvements and that the Temporary Modification will no longer be needed after December 2014.
* Biotic ligand model-based copper Temporary Modifications: Individual SP CURE members and other interested regulated entities presented evidence that progress is being made to develop a biotic ligand model-based site specific standards. They are on schedule to make water quality standards proposals for consideration by the Commission in the basin-wide hearing in June 2015.
Upper South Platte segments 14, 15, 16g and 16i
Clear Creek segments 14a, 14b and 15
Boulder Creek segment 9
* Other Temporary Modifications: The following Temporary Modifications were reviewed and the Commission took no action. They will be reviewed again at the annual temporary modification hearing in December 2014, and again at the the basin-wide hearing in June 2015.
Upper South Platte segment 14 temperature
Upper South Platte segment 15 temperature
Upper South Platte segment 16g temperature
Bear Creek segment 1c chlorophyll a and phosphorus
Clear Creek segment 2a cadmium and zinc
Clear Creek segment 2c copper
Clear Creek segment 9a copper
Clear Creek segment 11 cadmium
Clear Creek segment 13b cadmium and temperature
Clear Creek segment 14a temperature
Clear Creek segment 14b temperature
Clear Creek segment 15 temperature
Boulder Creek segment 8 selenium
St Vrain Creek segment 2b copper
St Vrain Creek segment 6 selenium
Middle South Platte segment 1a selenium
Middle South Platte segment 4 pH
Big Thompson River segment 2 (Wapiti Meadows) DO, E coli, ammonia, nitrate boron,
cadmium, copper, lead, mercury, nickel, selenium, silver and zinc
Big Thompson River segment 4b selenium
Big Thompson River segment 5 selenium
Big Thompson River segment 9 selenium
Cache La Poudre River segment 11 selenium
Cache La Poudre River segment 13b selenium
Lower South Platte segment 1 selenium
Site Specific Selenium Standards: The Commission considered site-specific ambient-based selenium standards for Upper South Platte Segment 16g (Marcy Gulch) and similar nearby tributaries to South Platte River Segment 14. Evidence submitted by Centennial Water & Sanitation District showed that selenium loading to Segment 16g results from natural sources and is not exacerbated by point source discharges or reversible anthropogenic factors. Marcy Gulch and nearby tributaries cross areas of selenium-bearing shale and groundwater that comes into contact with the shale increases in selenium concentration, which in turn contributes selenium when the groundwater enters the streams.
* Marcy Gulch (segment 16g): Although the Centennial sewer system does not have a large amount of inflow and infiltration, some groundwater with high selenium concentrations enters the system from residential areas within the Marcy Gulch drainage. This inflow increases the Centennial WWTP effluent selenium concentration at times to concentrations that exceed the table value standards. Centennial was not able to identify any industrial sources of selenium. Treatment at the Centennial WWTP results in incidental removal of selenium, and therefore further reductions in inflow and infiltration to control effluent selenium concentration would result in a loss of incidental treatment and a net increase in selenium loading to Marcy Gulch and the South Platte River. The Commission concluded that the contribution of selenium from groundwater to Marcy Gulch and to the Centennial WWTP is a natural or irreversible human-induced condition. Therefore, for Segment 16g, the Commission adopted site-specific ambient-based chronic and acute dissolved selenium standards. The chronic (13 µg/L) and acute (21 µg/L) standards are based on the 85th and 95th percentiles, respectively, of samples taken the same day from sites located upstream and downstream of the Centennial WWTP. In order to preserve the wide spatial and temporal variability of selenium concentrations in the segment and to protect against deterioration, the Commission defined assessment methods at Reg. 38.6(4)(g) in order to ensure that future assessment is consistent with the methods used to derive the standards. The Commission removed the temporary modification for selenium of "current conditions" that had previously been in place for Segment 16g
* Nearby tributaries Lee Gulch, Little's Creek Big Dry Creek and Little Dry Creek, (segment 16j): The Commission also re-segmented Upper South Platte Segment 16c (All tributaries to the South Platte River from Chatfield Reservoir to Big Dry Creek), to facilitate the adoption of site-specific ambient-based selenium standards for several tributaries to the South Platte River near Marcy Gulch. The evidence submitted by Centennial, the City of Littleton and the City of Englewood demonstrated that each of the tributaries have natural or irreversible human-induced elevated selenium concentrations, that result from regional geology similar to that found in Marcy Gulch and in the Toll Gate Creek drainages. None of the tributaries have point source discharges contributing to selenium concentrations. Urbanization of the area is an irreversible condition that could contribute to an increase in groundwater coming into contact with selenium-bearing shale. The Commission created new Upper South Platte Segment 16j with site-specific ambient-based selenium standards as follows: Lee Gulch Se(ac/ch)=(TVS/10), Little's Creek, Se(ac/ch)= (TVS/6), Big Dry Creek Se(ac/ch)=(26/23), and Little Dry Creek Se(ac/ch)=(TVS/11). The selenium standards for Segment 16j were calculated using data from locations near the confluence of each tributary with the South Platte River. The Commission specified assessment locations at Reg. 38.6(4)(h) in order to ensure that future assessment is consistent with the methods used to derive the standards. Other than the selenium standards, Segment 16j inherits the use classifications, antidegradation designation, and water quality standards from Segment 16c because the evidence was limited to selenium standards.
Clear Creek segment 13b (North Fork of Clear Creek): The Commission considered the temporary modification for Clear Creek segment 13b. Black Hawk/Central City Sanitation District and the City of Black Hawk ("BH/CCSD") proposed extending the temporary modification for cadmium in Clear Creek Segment 13b. Evidence submitted by BH/CC shows that the metals concentrations in Clear Creek are the result of a combination of natural and human-induced conditions which are currently the focus of Superfund cleanup work. Additional cleanup is planned as part of OU4, including the construction of a new mine wastewater treatment plant to treat discharges from the National Tunnel, Gregory Gulch and Gregory Incline. Additional cleanup is also planned for the Quartz Hill mine tailings pile, including re-grading and capping. These efforts are not expected to be completed until 2015 at the earliest, and are expected to result in significant water quality improvements within Clear Creek, segment 13b. The degree of improvement is still uncertain and will not be known until after the treatment measures are implemented and the improvements are quantified.
The BH/CCSD has a predicted water quality-based effluent limit compliance problem for cadmium, however they do not have a predicted compliance problem for the other metals. Therefore, the Commission deleted the temporary modifications for manganese, zinc and iron. In addition, the
Commission extended the expiration date of the temporary modification for dissolved cadmium on Clear Creek Segment 13b to December 31, 2018, to allow time for the treatment measures to be implemented and the improvements to be quantified. The temporary modifications will be reviewed in the 2016 and 2017 annual temporary modification review hearing. A 2018 expiration date will allow for a 2016 review of the status of the temporary modification prior to the BH/CCSD permit renewal in 2017, and may lead to an extension of the temporary modification if that is determined appropriate based on information available at the 2016 review.
PARTIES TO THE RULEMAKING HEARING
5 CCR 1002-38.88