5 Colo. Code Regs. § 1002-32.71
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 reviewed the basis, available information, and progress toward achieving the alternative effluent limits (AELs) and implementing Pollutant Minimization Programs (PMPs) for the three discharger-specific variances (DSVs) in Regulation No. 32.
The commission adopted non-substantive revisions to the format of these DSVs in Section 32.6(6) and the Appendix 32-1 tables to provide clarity and consistency. In addition, the acronym "AEL" was defined at 32.6(2)(a).
Lower Arkansas River Segment 1a (COARLA01a): The commission reviewed the DSV for acute and chronic selenium, and chronic sulfate, adopted in the June 2018 Arkansas Basin Hearing for the City of Pueblo's James R. DiIorio Water Reclamation Facility (expires 12/31/2028). See Section 32.6(6)(a) and 32.61(J). The commission reviewed Pueblo's progress toward achieving the narrative alternate limits (AELs) for selenium and sulfate, Pueblo's updated economic feasibility analysis, and updated alternatives analysis. The commission determined that the narrative AELs continue to represent the highest attainable water quality that is feasible for Pueblo to achieve. Therefore, the commission determined that the selenium and sulfate DSV is still appropriate and does not require revision at this time.
Pueblo will continue to implement its DSV and pollutant minimization program at 32.6(6)(c) and complete the associated interim milestones and activities adopted by the commission (2018 Reg. No. 32 RMH, Pueblo Exhibits 5 and 24). The commission will next review and reevaluate the DSV in 2028 prior to its expiration on December 31, 2028. The commission expects that Pueblo will submit annual reports to the division describing the progress made on DSV implementation until the end of the DSV and engage with the division and interested stakeholders in the two years leading up to the review in 2028 regarding whether compliance with WQBELs (calculated from the underlying standards) are feasible for the city, or if the city plans to propose a subsequent DSV.
Lower Arkansas River Segment 1b (COARLA01b): There is currently a DSV for acute and chronic selenium, which applies to the City of La Junta (expires 12/31/2026). See Section 32.6(6)(b)(i), 32.57(B), and 32.61(J). The plan for the City of La Junta was included in the division's Exhibit Y in the October 2016 Regulation No. 32 DSV rulemaking hearing. The commission reviewed the City of La Junta's progress toward achieving the AELs for selenium and determined that the AELs adopted in 2016 continue to represent the highest attainable water quality that is feasible for the facility to achieve. However, the commission adopted a PMP that includes improved selenium data collection, completion of analysis for previously completed projects (e.g., rerouting RO concentrate, removal of raw water blend from wastewater treatment stream), sampling and analysis of wells to minimize selenium in raw water, continuation of the city's water conservation plan, progress reporting on PMP activities, and a full alternative analysis to continue to improve water quality in the receiving segment. The PMP is included in the City of La Junta's Prehearing Statement (Exhibit B).
As part of its DSV requirements, the City of La Junta was required to implement a plan that included water conservation, increasing efficiency in the water treatment plant, and piloting treatment of the reverse osmosis concentrate utilizing the new wastewater treatment plant (WWTP). The City has continued its water conservation efforts, including residential, municipal, commercial, and industrial water restrictions; however, usage reductions have not been significant to date, and the City plans to propose new conservation and water restriction policies in 2023. The City completed construction of a new WWTP in 2019; the plant was designed for, and is successfully treating, biological oxygen demand (BOD), suspended solids, ammonia, total inorganic nitrogen, and current phosphorous limits. During construction of the WWTP, the City modified the design to include an inlet for the reverse osmosis (RO) concentrate to be introduced into the treatment process. Attempts at treating the RO concentrate at the WWTP have been unsuccessful so far, due to plant capacity issues (the permitted RO concentrate is 2.5 times the hydraulic capacity of the WWTP) and impacts to the treatment system. At this time, treating the RO concentrate at the WWTF is not feasible for the City due to cost. The City is currently prioritizing maintenance of its aged collection system to be proactive against increasing infiltration and inflow (I&I) issues.
Due to staffing changes at the City, as well as COVID-19 pandemic-related travel, illness, and supply chain problems, the City's progress on exploration of alternative treatment processes has been delayed. However, the City has made progress in its investigations. For example, the City is considering participating in the Arkansas Valley Conduit projects as a means of reducing its selenium discharge; however, costs related to this project may be infeasible for the City. The City is also exploring electrolysis as another alternative and is awaiting results of preliminary analyses. The economic feasibility of costs related to the startup, operation, and maintenance of any treatment processes remains a concern for the City.
After considering all of the information presented, the commission determined that this DSV is still appropriate with the revisions to the PMP. The commission expects that the City of La Junta will submit annual reports to the division describing the progress made on PMP implementation until the end of the DSV.
Lower Arkansas River Segment 1b (COARLA01b): There is currently a DSV for chronic selenium, which applies to the City of Las Animas (expires 12/31/2025). See Section 32.6(6)(b)(ii) and 32.61(J)). The PMP for the City of Las Animas was included in Las Animas' Rebuttal Exhibit 2 in the June 2018 Regulation No. 32 rulemaking hearing. The commission reviewed the City of Las Animas' progress on the plans set forth in its PMP and determined that the narrative AEL for selenium adopted in 2018 continues to generally represent the highest attainable water quality that is feasible for the facility to achieve under existing conditions. The commission deleted one element of the narrative AEL and existing PMP to allow the City to direct its limited resources to its efforts to obtain new source water via the Arkansas Valley Conduit (AVC). The commission also revised the PMP to include additional milestones including efforts related to the AVC and a revised timeline to continue to improve water quality in the receiving segment. The revised PMP is included in the City of Las Animas' Prehearing Statement (Exhibit B).
As part of its DSV requirements, the City of Las Animas was required to work on source well optimization, conservation of potable water, reducing losses from the water distribution system, and reducing groundwater infiltration to the collection system. The City has completed and continues to implement a well source optimization plan to maximize use of wells with lower selenium concentrations, a water conservation plan was developed and supported starting in September 2021, and water main and service line replacements have been accomplished to reduce losses in the distribution system. In addition, several thousand feet of wastewater collection system pipelines have been either rehabilitated or replaced to minimize infiltration. Smoke testing of the collection system was accomplished to identify locations of inflow to the system and guide improvements to eliminate that source of extraneous flow to the collection system.
In developing the existing DSV adopted by the commission in 2018, it was concluded that the source of selenium was the source water in the City's water supply. The monitoring and analysis work of the City since that time has continued to verify that is the only significant source of selenium in the discharges from the City's system to segment 1b. The analysis in the development of the DSV adopted in 2018 also addressed the potential for a new source water from the AVC as a means to significantly decrease the selenium discharged to the Arkansas River. At that time there was little certainty as to the start of construction and the time at which a new source water could be delivered to the City. Since that time, there has been much progress with design, construction phase procurements and mobilization for construction of the AVC.
The City of Las Animas has found that implementation of a new source water supply is the most cost effective and beneficial means to control selenium discharges. The new source water has its own benefits to the City from a potable water supply standpoint, will significantly decrease the discharge of selenium from treatment of local source water with reverse osmosis processes and is a more sustainable means of selenium control than added end of pipe treatment processes and systems. In addition to reducing the discharge of selenium, the new source water will permit control of other constituents presently discharged and subject to compliance schedules for attainment including manganese, uranium and sulfate. The City has made financial commitments to the AVC project through a participation agreement with the Southeastern Colorado Water Conservancy District and has funded its share of the design for the water transmission facilities between the AVC and the City's distribution system. The City is an active participant in the on-going planning and implementation of the AVC project which is presently planned to reach the eastern terminus of the AVC at Lamar in 2033, or before.
The commission determined that this DSV is still appropriate with the revisions to the narrative AEL and PMP; however, adoption of another DSV for selenium may not be necessary if participation in the AVC project makes compliance with current WQBELs feasible for the city. The narrative AEL and PMP were revised to redirect the City's efforts from the wetlands pilot project to its work related to the AVC. The commission determined that supporting the delivery of supplemental source water has greater benefit to the City than using those limited financial resources to construct a pilot or demonstration system, which may not benefit the reduction of selenium discharges to the Arkansas River. The commission expects that the facility will submit annual reports to the division describing the progress made on PMP implementation until the end of the DSV.
In April 2013 (32.51) and subsequent rulemaking hearings (32.58, 32.61, 32.65), the commission has adopted and extended temporary modifications for arsenic of "As(ch)=hybrid" (expiration date of 12/31/24) on many segments with the 0.02 µg/L Water + Fish numeric arsenic standard. The arsenic temporary modification recognizes existing and predicted compliance issues, instream nonattainment, and the uncertainty regarding the water quality standard necessary to protect current and/or future uses and the extent to which ambient concentrations of arsenic are natural or irreversible (31.7(3)). The division submitted a plan to resolve uncertainty in the 2019 Temporary Modifications rulemaking (32.63(B)).
The division plans to propose revised standards for arsenic as soon as possible following updated toxicological information from EPA's Integrated Risk Information System (IRIS) and completion of ongoing studies to better understand arsenic conditions in Colorado. Furthermore, per the conditions of the revised and extended temporary modification at 32.6(2)(c) (effective 6/30/2020 and expires 12/31/2024), and based on the widespread need to make progress to understand sources of arsenic and set forth processes for lowering arsenic in discharges, additional permit Terms and Conditions (T&Cs) are being implemented for facilities benefitting from the "current condition" temporary modification. These T&Cs may include requirements for additional monitoring, source identification, and characterization of source control and treatment options for reducing arsenic concentrations in effluent. The commission recognizes the need to resolve the uncertainty in the arsenic standards and ensure that human health is adequately protected.
The commission identified segments where an arsenic temporary modification had previously been inadvertently omitted. The commission adopted arsenic temporary modifications on the following segments:
Upper Arkansas River: 14c (COARUA14c), 29 (COARUA29), 31 (COARUA31), 35 (COARUA35), and 38 (COARUA38)
Middle Arkansas River: 4c (COARMA04c), 14 (COARMA14), and 21 (COARMA21)
Fountain Creek: 7a (COARFO07a)
Lower Arkansas River: 4a (COARLA04a), 7 (COARLA07), and 10 (COARLA10)
To remain consistent with the commission's decisions regarding arsenic in section 32.51, all existing temporary modifications for arsenic of "As(ch)=hybrid" (expiration date of 12/31/24), with the exception of those listed below, were retained.
Where evidence indicated the requirements to qualify for a temporary modification were not met, temporary modifications were deleted. The commission deleted chronic arsenic temporary modifications (expiring 12/31/2024) on several segments due to a lack of evidence of a demonstrated or predicted water quality-based effluent limit compliance problem for these segments. These segments have all been designated as Outstanding Waters, have no CDPS permitted dischargers with WQBELs for arsenic, and are without dischargers on upstream segments who may receive WQBELs based on protection of downstream uses. Temporary modifications for arsenic were deleted from the following segments:
Fountain Creek: 1b (COARFO01b) and 3b (COARFO03b)
5 CCR 1002-32.71