5 Colo. Code Regs. § 1002-93.19

Current through Register Vol. 47, No. 11, June 10, 2024

Section 5 CCR 1002-93.19 - STATEMENT OF BASIS, SPECIFIC STATUTORY AUTHORITY AND PURPOSE; MAY 2021 RULEMAKING; FINAL ACTION JUNE 15, 2021; EFFECTIVE DATE OF AUGUST 14, 2021

The provisions of C.R.S. 25-8-202(1)(a), (b) and (i), (2) and (6); 25-8-203; 25-8-204; and 25-8-401; 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.Revisions to 303(d) List

1. List Development

a. Listing Methodology

The "Section 303(d) Listing Methodology - 2022 Listing Cycle" contains a description of the listing process and the criteria for listing. This Listing Methodology sets forth the criteria that generally were used to make decisions regarding which waters to include on the 2022 Section 303(d) List and the 2022 Monitoring & Evaluation List (M&E list). This document was adopted in May of 2020 with limited changes from the previous Section 303(d) Listing Methodology. Changes included modifying the Regulation #93 rulemaking hearing from occurring in December of odd numbered years to May of odd numbered years.

This methodology was not adopted by the commission as a rule. The commission, therefore, has the flexibility to take into account other appropriate factors in making site-specific listing decisions.

b. Information Considered

The commission has considered all existing and readily available information in developing the 2022 Section 303(d) List. In determining whether data and information are existing and readily available, it has taken into account such data and information as the division has utilized in the preparation of those identification processes, calculations and models referenced in 40 CFR § 130.7(b)(5)(i), (ii) and (iv) and that credible data and information presented in a readily usable format and submitted in reports provided to the division as referenced in 40 CFR § 130.7(ab)(5)(iii). In addition, the commission accepted credible data and information that was submitted in accordance with the listing process schedule, whether submitted by EPA or any other interested party. The division also continues to independently collect and analyze new data on a rotating basin basis as part of its triennial review efforts and will utilize such data and information in making future listing determinations. Existing data which were not brought forward through one of the above mechanisms or otherwise presented to the commission in accordance with the schedule were not treated as "readily available" for purposes of making the 2022 listing decisions. Such information will be considered in the next listing cycle.

This Regulation #93 rulemaking hearing cycle focused on the San Juan and Dolores River Basins (Regulation #34) and the Gunnison, Lower Dolores River Basins (Regulation #35), and where there were outstanding issues statewide. This approach follows the rotating basin structure described in the 2022 303(d) Listing Methodology.

2. Incorporation of TMDLs into Table 93.3 of Regulation #93

The commission incorporated category 4 waterbodies (impaired but where a TMDL is not needed) into the main table within Regulation #93, instead of in a separate table at the end of the regulation as they have been in previous versions of this regulation. This organizes all impaired waterbodies and waterbodies under investigation of being impaired into one table. Table 93.3 now includes the following category 4 listings:

1. Category 4a - Impaired waterbodies with a completed TMDL

2. Category 4b - Impaired waterbodies where other pollution control requirements are reasonably expected to result in the attainment of the water quality standard in the near future.

3. Category 4c - Impaired waterbodies where the impairment is not caused by a pollutant.

Combining these tables eliminates the need for section 93.4 (Impaired Water Bodies Not Requiring TMDLs), and therefore, this section was deleted from the regulation. Additionally, combining these tables required a title change to table 93.3. The commission changed the title from "Water Bodies Requiring TMDLs or Identified for Monitoring and Evaluation" to "Waterbodies That Are Impaired or Identified for Monitoring and Evaluation."

3. New Sub Categories 1a (Attaining) and 1b (Attaining with TMDL)

Two new reporting subcategories were created for classifying the attainment status of waterbody segments in order to distinguish between waterbodies in attainment of water quality standards (category 1a) and waterbodies in attainment of water quality standards with approved TMDLs (category 1b). This distinction is important because even after a waterbody is reclassified for a given analyte from 4a (TMDL completed) to 1 (attaining), the TMDL remains in effect. The TMDL remains in place so that the practices that were implemented to improve water quality maintain the restored level of water quality. As more waterbodies with TMDLs are no longer impaired, it is helpful to have a subcategory to quickly locate attaining waterbodies with TMDLs. This will help:

* Potential and existing dischargers understand the locations where waste load allocations may exist.

* Division permit writers find TMDLs on waterbodies in attainment.

* Watershed groups dedicate resources to support continued pollution reduction efforts.

During the Regulation #93 rulemaking hearing, subcategories 1a (attaining) and 1b (attaining with TMDL) are visible within the division's proposal to indicate the proposed action to be taken by the commission to change the attainment status of a waterbody. However, because Regulation #93 reports on waterbodies that are impaired or identified for the M&E List, attaining waterbodies (i.e., subcategories 1a, and 1b) are removed from the final Regulation #93 document. These subcategories will be presented in Colorado's Integrated Water Quality Monitoring and Assessment Report (IR), which is approved by the commission every even numbered year, in an administrative action hearing.

While subcategories 1a and 1b are useful to the state of Colorado as described above, the EPA recognizes them both as category 1. This is similar to other instances in which Colorado developed subcategories such as 3a (no water quality data has been collected), and 3b (waterbody placed on M&E List). In these cases, the EPA recognizes each as simply category 3, insufficient data to determine whether or not the classified uses are being attained.

4. Removal of Adequate Refuge Clause from Regulation #31

In 2016, the commission removed footnote 5(c)(iii) from Regulation #31 which allowed lake and reservoir surface water temperatures to exceed the applicable temperature standards if adequate refuge existed in deeper layers of the water column. Adequate refuge was defined as concurrent attainment of the temperature and dissolved oxygen standard below the surface of the lake or reservoir in deeper layers. The footnote was proposed for removal by the division because an elevation based temperature standard was being considered for adoption by the commission. Although the commission did not adopt the elevation based standard, the footnote allowing for adequate refuge as a part of the lake temperature standard was deleted in error.

Due to the removal of this footnote, data assessed for the 2020 and 2022 Regulation #93 listing cycles were compared to the lakes and reservoir temperature standards without consideration for adequate refuge. This resulted in numerous lakes and reservoirs with exceedances of the temperature standard in the surface layer more than once in 3 years. These lakes and reservoirs would have otherwise been considered attaining temperature standards if the refuge footnote was still in place. For the 2020 303(d) List, the following 7 lakes and reservoirs were added to the 303(d) List as impaired for temperature because adequate refuge was not considered: Lake Avery (COLCWH25_A), Big Creek Reservoir (COUCNP09_B), North Delaney Lake (COUCNP09_C), Lake John (COUCNP09_D), South Delaney Lake (COUCNP09_E), Pearl Lake (COUCYA22_D) and Steamboat Lake (COUCYA22_E). For the 2022 303(d) List, the following 7 new lakes and reservoirs were added to the 303(d) List as impaired for temperature because adequate refuge was not considered: Blue Mesa Reservoir (COGUUG38_C), Grand Lake (COUCUC12_E), McPhee Reservoir (COSJDO04b_B), Lake Nighthorse (COSJAF22_A), Ridgway Reservoir (COGUUN19_A), Vallecito Reservoir (COSJPN03_A) and Willow Creek Reservoir (COUCUC12_D).

For the June 2021 Regulation #31 rulemaking hearing, the commission is considering a proposal by the division to reinstate language that would allow for adequate refuge when assessing temperature for lakes and reservoirs. Reinstatement of the adequate refuge provision is expected to result in attainment of the temperature standards for all of the lakes and reservoirs listed above. In light of this proposed change, the division proposed that the lakes and reservoirs above be included on the 303(d) List with low priority for TMDL development. If the adequate refuge provision is added to the lake temperature standard in June of 2021, the division will prioritize the assessment of the lakes and reservoirs listed above for the 2024 303(d) List, regardless of the division's basin of focus.

5. For the secondary water supply standards of dissolved iron, dissolved manganese and sulfate, the less restrictive of the following two options apply as the numeric standard: existing quality as of January 1, 2000, or the table value criteria in Regulation #31, Tables II and III. For dissolved iron, the table value standard (TVS) is 300 ug/l. For dissolved manganese, the TVS is 50 ug/l. For sulfate, the TVS is 250 mg/l.

The 303(d) Listing Methodology, includes language regarding the determination of existing quality from the year 2000 (EQ 2000). This includes a minimum data requirement and the ability to use data collected after the year 2000 when characterizing existing quality from 2000. The utilization of data collected past the year 2000 is contingent upon there being no new or increased sources of these parameters in the segment being assessed since 2000.

Table 1. summarizes the secondary water supply assessment values used for dissolved iron, manganese, and sulfate for 303(d) or M&E listing actions:

Table 1. Values Used for the Assessment of Dissolved Iron, Dissolved Manganese, and Sulfate Water Supply Standards.
Portion ID	Analyte	Category / List	Listing Action	TVS or 20001	POR for 2000 Dataset	Sample Size of 2000 Dataset	Value	Units
COGULD03a_B	SO4	ME	Delist	2000	1995-2019	10	891.5	mg/l
COGULG02 A	Mn-D	303d	Delist	TVS	N/A	N/A	50	ug/l
COGULG02_A	SO4	303d	Retain	2000	1995-1999	92	297	mg/l
COGULG02 B	Mn-D	303d	Retain	TVS	N/A	N/A	50	ug/l
COGULG02_B	SO4	303d	Delist	2000	1995-1999	92	297	mg/l
COGULG04a_D	Mn-D	303d	Retain	2000	1995-1999	13	84.4	ug/l
COGULG04a_D	SO4	303d	Retain	2000	1995-1999	59	4160	mg/l
COGULG04a_E	Mn-D	ME	Retain	2000	1995-1999	13	84.4	ug/l
COGULG07b_C	SO4	303d	Delist	2000	1995-2009	24	617.25	mg/l
COGULG12_B	Mn-D	303d	Retain	2000	1995-2004	18	94.35	ug/l
COGULG12_B	SO4	ME	Retain	2000	1995-2004	18	962.5	mg/l
COGUNF03_B	Mn-D	303d	Retain	2000	1995-1999	57	72	ug/l
COGUNF03_C	Mn-D	303d	Retain	2000	1995-1999	57	72	ug/l
COGUNF04b E	Mn-D	ME	List	TVS	N/A	N/A	50	ug/l
COGUNF06b_B	SO4	303d	Retain	2000	1995-2009	48	1585.5	mg/l
COGUNF06b_B	Mn-D	303d	Delist	2000	1995-2009	20	783	ug/l
COGUNF06b_C	SO4	303d	Retain	2000	1995-2009	48	1585.5	mg/l
COGUNF06b C	Fe-D	303d	Retain	TVS	N/A	N/A	300	mg/l
COGUNF06b_C	Mn-D	303d	Retain	2000	1995-2009	20	783	ug/l
COGUSM02 D	Mn-D	ME	List	TVS	N/A	N/A	50	ug/l
COGUSM02 F	SO4	ME	List	TVS	N/A	N/A	250	mg/l
COGUSM02 F	Mn-D	303d	List	TVS	N/A	N/A	50	ug/l
COGUSM02 F	Fe-D	303d	List	TVS	N/A	N/A	300	ug/l
COGUSM04a B	Mn-D	ME	List	TVS	N/A	N/A	50	ug/l
COGUSM07_B	SO4	ME	List	2000	1995-2009	32	377.5	mg/l
COGUSM07_C	SO4	ME	List	2000	1995-2009	32	377.5	mg/l
COGUSM07 C	Fe-D	303d	List	TVS	N/A	N/A	300	ug/l
COGUSM07 C	Mn-D	303d	List	TVS	N/A	N/A	50	ug/l
COGUSM08 A	Mn-D	ME	List	TVS	N/A	N/A	50	ug/l
COGUUG01_B	Fe-D	ME	Delist	2000	1995-2014	15	456	ug/l
COGUUG01_C	Fe-D	ME	Retain	2000	1995-2014	15	456	ug/l
COGUUG02 D	Mn-D	303d	Delist	TVS	N/A	N/A	50	ug/l
COGUUG09 G	Mn-D	303d	List	TVS	N/A	N/A	50	ug/l
COGUUG09 G	Fe-D	303d	List	TVS	N/A	N/A	300	ug/l
COGUUG12_C	Mn-D	303d	Delist	Site-Specific2	N/A	N/A	191	ug/l
COGUUG15a_B	Fe-D	303d	Retain	2000	1995-2004	16	745	ug/l
COGUUG15a_B	Mn-D	303d	Retain	2000	1995-2004	25	66.4	ug/l
COGUUG17b_A	Mn-D	ME	Retain	2000	1995-2004	13	162	ug/l
COGUUG19 B	Mn-D	303d	Retain	TVS	N/A	N/A	50	ug/l
COGUUG19 B	Fe-D	ME	List	TVS	N/A	N/A	300	ug/l
COGUUG24 B	Fe-D	ME	List	TVS	N/A	N/A	300	ug/l
COGUUG29a_B	Fe-D	303d	Retain	2000	1995-2004	52	2181.1	ug/l
COGUUG29a C	Mn-D	303d	Retain	TVS	N/A	N/A	50	ug/l
COGUUG29a D	Mn-D	ME	Retain	TVS	N/A	N/A	50	ug/l
COGUUG29a I	Mn-D	ME	Retain	TVS	N/A	N/A	50	ug/l
COGUUG30 B	Mn-D	ME	List	TVS	N/A	N/A	50	ug/l
COGUUG32_A	Mn-D	303d	Retain	2000	1995-2009	13	170.6	ug/l
COGUUN02_B	Mn-D	303d	Retain	2000	1995-2004	27	119.89	ug/l
COGUUN02_C	Mn-D	303d	Delist	2000	1995-2004	27	119.89	ug/l
COGUUN03a_A	Mn-D	303d	Retain	2000	1995-1999	39	588.7	ug/l
COGUUN03b_A	Mn-D	303d	Retain	2000	1995-1999	44	413.6	ug/l
COGUUN03c_A	Mn-D	303d	Delist	2000	1995-1999	85	180	ug/l
COGUUN04a_B	SO4	ME	Retain	2000	1995-2004	13	266	ug/l
COGUUN04a_C	SO4	ME	List	2000	1995-2004	13	266	ug/l
COGUUN04b A	Mn-D	303d	Retain	TVS	N/A	N/A	50	ug/l
COGUUN05 C	Mn-D	303d	Retain	TVS	N/A	N/A	50	ug/l
COGUUN05 E	Mn-D	303d	Retain	TVS	N/A	N/A	50	ug/l
COGUUN05 G	Mn-D	ME	List	TVS	N/A	N/A	50	ug/l
COGUUN08 A	Mn-D	ME	List	TVS	N/A	N/A	50	ug/l
COSJAF04b_A	Mn-D	ME	Delist	2000	1995-1999	24	635.45	ug/l
COSJAF05a_B	Mn-D	303d	Retain	2000	1995-1999	360	177.75	ug/l
COSJAF05a_C	Mn-D	303d	Retain	2000	1995-1999	360	177.75	ug/l
COSJAF09_A	Fe-D	303d	List	2000	1995-1999	276	2902	ug/l
COSJAF09_A	Mn-D	303d	List	2000	1995-1999	285	479.4	ug/l
COSJDO04b A	Fe-D	ME	Retain	TVS	N/A	N/A	300	ug/l
COSJDO04b A	Mn-D	ME	Retain	TVS	N/A	N/A	50	ug/l
COSJLP04a_E	Mn-D	TMDL	Retain	2000	1995-2009	12	582	ug/l
COSJLP04a E	S04	303d	List	TVS	N/A	N/A	250	ug/l
COSJLP04a E	Fe-D	303d	List	TVS	N/A	N/A	300	ug/l
COSJLP04a_F	Mn-D	TMDL	Correction	2000	1995-2009	12	582	ug/l
COSJLP04c_D	Mn-D	TMDL	Delist	2000	1995-1999	16	78	ug/l
COSJLP04c_G	Mn-D	303d	List	2000	1995-1999	16	78	ug/l
COSJLP05 B	Fe-D	ME	Delist	TVS	N/A	N/A	300	ug/l
COSJLP05 B	Mn-D	303d	List	TVS	N/A	N/A	50	ug/l
COSJLP05_B	S04	ME	Retain	2000	1995-1999	146	966.18	mg/l
COSJLP08_A	S04	303d	Retain	2000	1995-1999	64	3000	mg/l
COSJLP08_B	S04	303d	Retain	2000	1995-1999	64	3000	mg/l
COSJLP08_C	S04	303d	Retain	2000	1995-1999	64	3000	mg/l
COSJLP08_E	S04	303d	Retain	2000	1995-1999	64	3000	mg/l
COSJSJ06b_B	Mn-D	ME	Retain	TVS	N/A	N/A	50	ug/l

Table 1. Footnotes:

1) Where this column indicates that the appropriate standard is the existing quality as of the year 2000 (as indicated with '2000' in this column), information for the subsequent columns is only reported where 10 or more samples are available.

2) The appropriate assessment value for dissolved manganese in COGUUG12_C is a site-specific standard established in the 2012 rulemaking hearing for Regulation #35. See 5 CCR § 1002-35.34(L).

6. Parties to the rulemaking hearing:

5 CCR 1002-93.19

39 CR 03, February 10, 2016, effective 3/1/2016

39 CR 21, November 10, 2016, effective 11/30/2016

41 CR 03, February 10, 2018, effective 3/2/2018

43 CR 03, February 10, 2020, effective 3/1/2020

43 CR 10, May 25, 2020, effective 6/14/2020

44 CR 14, July 25, 2021, effective 8/14/2021