5 Colo. Code Regs. § 1002-41.24
The provisions of sections 25-8-202; 25-8-204; 25-8-402, C.R.S., provide the specific statutory authority for adoption. 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:
This hearing was held to consider changes recommended in an Informational Hearing for Regulation 41, The Basic Standards for Ground Water. The majority of the changes involved modifications to the organic chemical standards in Table A, as well as the addition of new standards for twenty-one carcinogenic organic chemicals. During this hearing the Commission also considered the organic chemical standards contained in Regulation 31, The Basic Standards and Methodologies for Surface Water. Other changes, for Regulation 41, included renaming Tables 1 and 2 to parallel the nomenclature used in Policy 96-2, the Commission's policy on human-health based water quality criteria. Additionally, several footnotes for Tables 1 and 2 were updated to clarify and identify the source of the associated numeric standards. References to Practical Quantitation Limits (PQL) were modified to reflect the Commission's decision to remove the determination of appropriate PQLs from the Rulemaking process. The Commission understands that the Water Quality Control Division is developing a PQL guidance document, which will contain those PQLs deemed acceptable to the Division. In addition, the Water Quality Control Division, or applicable implementing agency, may establish site-specific or discharge-specific PQLs. Finally, additional clarification was added to the table of Radioactive Standards to reflect the Commission's decision to allow discretion in considering appropriate sampling techniques in implementing these standards.
In November 2000, EPA disapproved surface water standards for several Group C organic chemicals because the proposed standards were not based on carcinogenic risk. Group C carcinogens are typically classified, based on limited evidence, as possible human carcinogens. Historically, due to the lack of substantive carcinogenic evidence, the Commission has not established carcinogenic-based standards for Group C chemicals, but rather adopted standards based on toxicity.
Based on published human-health risk data there are three classes of Group C compounds, which include:
Those compounds with published toxicity (RfD) values, Those compounds with published cancer slope factors (q1*), and Those compounds with published RfD and q1* values.
Previously, the Commission has promulgated standards for the Group C compounds in the first and third class based on toxicity and for the second class based on carcinogenicity. However, this treatment of the class 3 Group C compounds resulted in EPA disapproving the standards.
In order to resolve this issue with EPA, during this hearing, the Commission adopted a standard for these Group C compounds based on toxicity, but with an additional margin of safety to account for any unknown carcinogenic effects. Using this method the standards for Group C compounds, with both RfD and q1* values, are based on toxicological data, and then adjusted downward using an uncertainty factor of 10. The Commission believes that this methodology is consistent with SDWA practices and will be protective of human health.
The Commission also decided to add numeric standards for twenty-one additional organic chemicals that are classified as either Group A, known human carcinogens, or Group B, probable human carcinogens.
One of the new standards that was the subject of extensive written and oral testimony in this hearing is a standard for 1,4-dioxane. Based upon the current status of the scientific evidence as disclosed at the hearing, with specific reference to the number for 1,4-dioxane found in EPA's IRIS database, the Commission adopted a standard of 6.1 ug/l to apply for a period of five years, with a standard of 3.2 µg/l becoming effective at the end of the five-year period. The Commission is aware of the fact that EPA is re-examining its criteria for 1,4-dioxane. However, that effort likely will take a number of years and the result is uncertain, and there is a current need to address this chemical in the water quality standards context. Because 6.1 ug/l is the value typically used to date for 1,4-dioxane remedial activities in Colorado, the adoption of this value as a water quality standard will provide a basic level of protection of human health while essentially preserving the status quo regarding clean-up requirements for the next five years. This standard provides protection within the same order of magnitude as the 3.2 ug/l standard that results from application of the Commission's generally accepted methodology for establishing health-based standards. The Commission sees no reason in this matter to deviate from its policy regarding the order of magnitude of risk used for the protection of human health.
If no further action is taken by the Commission, the 3.2 ug/l standard will go into effect after five years. If EPA's pending review of 1,4-dioxane results in a revision of the current IRIS value, the Commission can consider a corresponding revision of its water quality standards at that time.
The Commission notes that the adopted standards are consistent with the Department of Public Health and Environment's policy on the use of IRIS in setting standards. The Commission understands that remediation action levels applied by implementing agencies at currently contaminated sites may be set at a different, higher number based on a site-specific risk analysis as referenced in the CDPHE policy. The Commission also notes that it may adopt site-specific standards for 1,4-dioxane if warranted by a site-specific risk assessment. The Commission has adopted numerous site-specific standards for other chemicals where it was determined that such standards appropriately account for site-specific circumstances.
Further, to clarify the use of this standard in a regulatory context, the Commission requests that the Division promptly develop a practical quantitation limit (PQL) for 1,4-dioxane. Consistent with other provisions of this regulation, the PQL will be used as the compliance threshold for implementation of these standards. The Commission notes that it may be appropriate to establish a site-specific PQL for individual discharges, if warranted by the unique characteristics of a particular discharge.
In adopting standards for 1,4-dioxane, the Commission has considered the factors listed in section 25-8-204, C.R.S., as follows:
1,4-dioxane is a Group B2, probable human carcinogen and has been found as a ground water contaminant in the State of Colorado. In addition, following treatment ground water contaminated with 1,4-dioxane is discharged to Colorado surface waters.
1,4-dioxane is most commonly treated with a combination of advanced oxidation processes (AOP) in combination with ultraviolet light (UV). This remediation technology, though relatively new, is rapidly becoming a more common technique. The AOP/UV treatment techniques will have minimal impact on water quantity. Evidence was submitted indicating that 1,4-dioxane treatment costs could be substantial in some circumstances, although there was conflicting evidence regarding treatment costs. Because the standard that will be in effect for the next five years is set at the level already most commonly used as a 1,4-dioxane remediation goal, the adopted standard will not have a major impact on treatment costs during this period. The Commission intends that discharge permits issued while the 6.1 ug/l standard is in effect will include effluent limits based on that standard until the expiration of the existing permit. Renewal permits will be subject to the standard in effect at the time of renewal. Moreover, to the extent that the adopted standards do result in increased treatment costs, the Commission believes that such costs must be weighed against the benefits of the protection of public health, including the preventative benefits of reducing the likelihood of future exposure to 1,4-dioxane.
As to the extent to which this pollutant is significant, since 1, 4-dioxane is primarily used as a solvent stabilizer, it will most likely be found in areas with known chlorinate solvent contamination. Chlorinated solvents have been in use since the 1960s, with more widespread use occurring in the late 1970s and early 1980s due to the increasing production of electronic circuits.
1,4-dioxane is characterized by a high solubility (infinitely soluble/miscible), moderate vapor pressure, and low Henry's Law Constant, all of which indicate that this chemical will be persistent within the aquatic environment. Additionally, the available data indicate that 1,4-dioxane will not readily degrade in the environment.
The Hazardous Materials and Waste Management Division reports that 1,4-dioxane has been found at 9 sites and is suspected at 19 others. The standards adopted by the Commission establish the maximum extent of 1,4-dioxane to be tolerated as a human health goal, for the reasons set forth in this Statement of Basis and Purpose.
The 1,4-dioxane standards are adopted to protect domestic water supply uses.
1,4-dioxane is a highly persistent contaminant. Very little degradation is observed in the ambient environment. The standards are being adopted to protect human health, so humans are the affected "organisms". 1,4-Dioxane is classified by EPA as a probable human carcinogen (Group B2). Conflicting evidence was submitted regarding the level at which 1,4-dioxane poses a human health risk. Some parties argued that a different toxicity model than that used to develop the current IRIS value for 1,4-dioxane should be used to characterize its toxicity. Some parties also argued that a 1,4-dioxane standard should be established based on a PQL for this chemical, but the Commission believes that the standard should be health-based. The Commission acknowledges that there are conflicting scientific interpretations of the available information and that further review and analysis of the toxicity of 1,4-dioxane is warranted. However, the outcome of that further review is uncertain and the Commission does not believe that there is sufficient evidence to invalidate the current EPA IRIS value at this time. The Commission believes that the record supports the scientific and technical validity of the standards that it is adopting. Moreover, in the face of conflicting scientific information, as a matter of policy the Commission has decided to err in the direction of protection of public health in approving the 6.1 ug/l and 3.2 ug/l standards for 1,4-dioxane.
Since the 1989 hearing, there has been debate about whether standards for parameters with MCLs should be based on the MCLs or purely health-based numbers. The arguments for MCLs focused on whether it is reasonable to require ground water remediation to a level below that required for drinking water. The arguments for health-based standards focused on maximizing human-health protection, putting the clean-up burden on pollution sources, and protection of ground water as a resource.
In this hearing, the Commission adopted a hybrid MCLG/MCL proposal that provides much of the benefits advocated for each of the above options. This hybrid approach allows for existing ground water contamination to be addressed at levels that are deemed safe for drinking water sources, but allow for the protection of ground water as a resource by implementing a more protective human-health health based standard for future contamination. The Commission decided that implementation of this range of standards should be based on the date of the discharge that subsequently caused contamination of the ground water. In some cases, especially where the ground water contamination may not be discovered immediately, the contamination will have subsequently migrated. In these instances, it is the Commission's intent that the original date of the release that caused the contamination, not the date of the identification or subsequent extent of any migration of that contamination, shall be used to determine the appropriate standard for the resulting contaminant plume.
Additionally, the hybrid MCLG/MCL proposal was concurrently considered for Regulation 31, The Basic Standards and Methodologies for Surface Water, and the adoption of this rule for ground water provides a consistent approach to addressing water quality for all waters of the State.
For existing aquifer storage and recovery facilities an issue, which was presented to the Commission regarding the MCLG/MCL proposal, was the potential impact this rule could have on existing aquifer storage and recovery, or artificial recharge projects. Cognizant of both the drought and the corresponding potential future implementation of the various forms of anthropogenic recharge, the Commission decided adopt a total trihalomethanes (TTHM) standard. In order to assure that the ground water quality standards do not limit continued aquifer storage and recovery at these facilities using potable finished water, the Commission adopted a standard for TTHM. However, the Commission also elected to leave the existing standards for bromodichloromethane, bromoform, chloroform and dibromochloromethane in place in order to address ground water contamination due to other possible sources of these chemicals (e.g. from spills or industrial activity).
The applicability of Footnote 7 (allowing compliance with TTHMs rather than the separate standards for bromodichloromethane, bromoform, chloroform, and dibromochloromethane) to other sources of water and aquifers requires further evaluation. The Commission requests that the Division coordinate with stakeholders using and developing aquifer storage and recovery projects regarding these organic standards and their statewide applicability and provide a status report regarding whether modifications to the statewide organic standards for aquifer storage projects will likely be proposed.
The Commission is not aware of other instances where the ground water quality standards are likely to limit the ability to undertake such ground water recharge projects. If such circumstances should arise in the future the Commission can revisit other aspects of this regulation at that time. Alternatively, proponents of such projects could request site-specific ground water quality classifications and standards.
Tables 1 and 2 were renamed and revised to be more consistent with the description of the various standards in both Regulation 31 and Policy 96-2. Several footnotes were added or modified to further clarify the existing numeric standards.
A footnote was added to the radioactive standards table to reflect the Commission's decision in 1996 (41.20) to allow the Division latitude in requiring total or dissolved samples. In the 1996 hearing the Commission decided to allow the Division discretion to consider appropriate sampling techniques in implementing the radionuclide standards. Since that time there has been considerable interest in additional clarification of the implementation of these standards, and therefore the Commission elected to adopt additional footnotes clarifying the radioactive standards.
PARTIES TO THE RULEMAKING HEARING
5 CCR 1002-41.24