Code of Colorado Regulations
1000 - Department of Public Health and Environment
1002 - Water Quality Control Commission (1002 Series)
5 CCR 1002-42 - REGULATION NO. 42 - SITE-SPECIFIC WATER QUALITY CLASSIFICATIONS AND STANDARDS FOR GROUND WATER
Section 5 CCR 1002-42.38 - STATEMENT OF BASIS, SPECIFIC STATUTORY AUTHORITY AND PURPOSE: APRIL 13, 2020 RULEMAKING; FINAL ACTION MAY 11, 2020; EFFECTIVE DATE JUNE 30, 2020

A. Background

The commission applied the classification of limited use and quality to the groundwater contained within oil and gas bearing formations of Colorado in which injection wells have been established under Colorado Oil and Gas Conservation Commission's (COGCC) Drilling, Development, Production and Abandonment rules 324(B). It should be noted that groundwater in formations above those identified in the specified areas are not designated, and therefore have the interim narrative standard applied to them. The approach the commission has taken is to buffer the well locations by a mile. The commission did this in order to add a margin of protection around the maximum permitted area of these injection wells of 1/2 of a mile. Each of these new areas have specific strata that these designations apply to and are generally well below any depths used for the production of drinking water. The strata that were used in the specified areas were extracted from the COGCC well database. Each strata named in the specified area has at least one well permitted for it as identified by COGCC. The latitude and longitude of each well was used to define the centroid on multiple smaller polygons. The latitude and longitude used for the well represents the positions COGCC provides for the bottom of the borehole. Because Specified Areas 55-61 cover multiple counties, the commission used this approach instead of large polygons in order to minimize the area located in specified areas with limited standards. By placing the latitude and longitude into the description of the specified area, the regulation will be easier to update as new injection wells come online in the appropriate specified area. The vast majority of this produced water is placed back into the formations from which it comes by injection into wells.

Hydrogeologic information including produced water quality, depths of these formations, and COGCC data indicate that the groundwater in these formation is of limited use and quality. Regulation 41.4(B)(5)(a) states that when the groundwater within the area has TDS equal to or greater than 10,000 mg/L TDS or (b) when the groundwater has been exempted under Rule 324(B) of COGCC, that shall be classified as "Limited Use and Quality". All of the injection wells within Specified Areas 55-61 meet the criteria of 41.4(B)(5)(b). The commission, therefore, concluded that the application of the "Limited Use and Quality" classification to the groundwater within these specified areas is appropriate. This classification and the application of site-specific standards for organic chemicals ensures consistency between implementation of Underground Injection Control (UIC) Program requirements and commission standards and classification.

B. Site-Specific Classification and Standards Setting

Site-specific classification of groundwater begins with the identification of the use of the water. The groundwater in these oil and gas basins is co-produced with oil and gas and is considered a waste. It is not currently used nor can it be reasonably expected to be used in the future for domestic or agricultural purposes. It is not in communication with any surface water bodies within the specified area so that water quality standards of any classified surface water bodies are not affected by this groundwater.

COGCC permits injection wells under one of two frameworks which are guided by total dissolved solids (TDS) concentrations. COGCC Rule 324(B) governs wells that are completed in formations that have TDS concentrations between 3,000 mg/L and 10,000 mg/L. These wells go through an aquifer exemption process which involves consultation between the division and COGCC in order to approve these wells. The other framework is for wells that have a TDS concentration greater than 10,000 mg/L. These wells are approved under the EPA UIC rules delegated to COGCC and do not require consultation with the division (40 CFR § 144.16 and COGCC Rule 325). Groundwater that has TDS greater than 10,000 mg/L and does not supply a public water system falls outside of the EPA definition of Underground Source of Drinking Water (USDW)(40 CFR § 144.3).

Consistent with the classification, the groundwater quality standards in Tables 1 through 4 of the Basic Standards for Groundwater, Regulation No. 41 and the statewide standards for certain specified organic chemicals associated with oil and gas production activities will not apply within the specified area. However, to provide some protection of the potential future use of water resources in the specified area, the commission's action provides that the statewide standard for radionuclides, as well as the statewide organic chemical standards, other than those for benzene, toluene, ethylbenzene, xylenes, and benzo(a) pyrene, will continue to apply to this groundwater.

EPA provided a comment that the bottom of the bore hole would provide more accurate information for directionally drilled wells than the surface location. Therefore, the commission adopted the division's revised proposal that utilized the location of the bottom of the borehole for directional wells as the locational information for specified areas as appropriate.

C. Change of Ground Water to Groundwater

The commission adopted a change from "ground water" to "groundwater". This change is consistent with common technical usage and usage in the Water Quality Control Act. This change is part of a broad initiative to change the spelling program-wide, and to increase consistency.