5 Colo. Code Regs. § 1002-41.30
The provisions of C.R.S. sections 25-8-202; 25-8-203; 25-8-204; 25-8-402, provide the specific statutory authority for adoption of this regulation. The Commission also adopted, in compliance with section 24-4-103(4) the following statement of basis and purpose.
BASIS AND PURPOSE
In this rulemaking the commission considered revisions to criteria and revisions to division point of compliance provisions. The commission adopted changes as detailed below.
The commission adopted revised and new organic chemical standards in section 41.5 . In an effort to keep groundwater and surface water organic chemical standards consistent, the changes to section 41.5 were also adopted for the statewide surface water organic chemical standards in Regulation No. 31 (Basic Standards and Methodologies for Surface Water).
In adopting these new and revised organic chemical standards, the commission continued to rely on its past policy decisions and precedence documented in Commission Policy 96-2, along with best science practices set forth in the CWA § 304(a) criteria development method. As per Departmental policy, the commission has relied on the United States Environmental Protection Agency's (EPA) Integrated Risk Information System (IRIS) as its first tier source of toxicological data. Review of the IRIS data that had been updated since the last revisions to 41.5(C)(3) indicated adoption of standards for four new chemicals (hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), CAS 121-82-4; 1,2,3-trimethylbenzene, CAS 526-73-8; 1,2,4-trimethylbenzene, CAS 95-63-6; and 1,3,5-trimethylbenzene, CAS 108-67-8) were necessary. Additionally, the water quality standards for benzo(a)pyrene (BaP), CAS 50-32-8 and related chemicals [benzo(a)anthracene, CAS 56-55-3; benzo(b)fluoranthene, CAS 205-99-2; benzo(k)fluoranthene, CAS 207-08-9; chrysene, CAS 218-01-9; dibenzo(a,h)anthracene, CAS 53-70-3; and indeno(1,2,3-cd)pyrene, CAS 193-39-5], needed to be revised. Water quality standards for RDX and the three trimethylbenzenes use updated exposure factors of a mean adult (21 years and older) body weight of 80 kilograms and a drinking water ingestion rate of 2.4 liters per day. Use of these updated exposure factors relies on more recent exposure data than those used to derive the exposure factors in the commission Policy 96-2. Policy 96-2 is a retrospective policy and will be updated accordingly to reflect the updated exposure factors at the time of the next review. Though, this will create misalignment with the exposure factors used previously to derive existing organic chemical standards in Regulation No. 41, the division will work towards bringing previous standards up-to-date as well, as resources to do so become available. Additional details regarding aspects of these standards revisions are provided below.
RDX is characterized in IRIS with the cancer descriptor "Suggestive evidence of carcinogenic potential" per EPA 2005 guidelines. This designation is comparable to the cancer group designation of "C - Possible human carcinogen" from the 1986 EPA guidelines. Per Policy 96-2: "for Group C compounds that have both carcinogenic (cancer slope) and toxic (reference dose) data the Commission decided, in accordance with their past practice, to base the standards for these compounds on the reference dose approach, but to adjust the resulting standard with an uncertainty factor of 10 to account for any unknown carcinogenic effects." However, this approach is not aligned with best science practices set forth in the CWA § 304(a) criteria development method for these types of chemicals, under which both cancer-based and non-cancer-based water quality standards would be calculated and the lower of the two standards selected for use protection. Therefore, the commission adopted the proposed calculation of the RDX Water Supply standard, which uses the lower, cancer-based water quality standard of 0.42 µg/L, based on the IRIS cancer slope factor of 0.008 per mg/kg-day. This approach follows the more protective, 304(a)-compliant approach of selecting the lower of the two calculated standards (cancer-based or non-cancer-based). Derivation of previous standards for "Group C carcinogens" has not been consistent; therefore, the division will, ongoing, follow the practices set forth in the CWA § 304(a) criteria development method for these types of chemicals. The division will also work towards bringing previous standards up-to-date, as resources to do so become available.
The commission also adopted a new footnote "3b" to Table A in Regulation No. 41 to reflect the updated approach used for RDX.
The Water Supply standard uses most of the default exposure assumptions from Policy 96-2, along with updated exposure factors of a mean adult (21 years and older) body weight of 80 kilograms and a drinking water ingestion rate of 2.4 liters per day, as discussed above.
The commission adopted new Water Supply standards for 1,2,3-trimethylbenzene, CAS 526-73-8; 1,2,4-trimethylbenzene, CAS 95-63-6; and 1,3,5-trimethylbenzene, CAS 108-67-8, calculated using the non-cancer equations and most of the default exposure assumptions from Policy 96-2 in combination with the RfD of 0.01 mg/kg-day from IRIS. The Water Supply standards use updated exposure factors of a mean adult (21 years and older) body weight of 80 kilograms and a drinking water ingestion rate of 2.4 liters per day, as discussed above. The calculations resulted in Water Supply standards of 67 µg/L.
The commission adopted a revised Water Supply standard for BaP based on updates to the EPA IRIS assessment. In addition to providing an updated cancer slope factor, the IRIS assessment identified BaP as a mutagen. Therefore, the standards adopted by the commission were calculated using age-dependent factors, following EPA 2005 guidance on risk assessment for mutagenic compounds and Minnesota's Human Health-based Water Quality Standards Technical Support Document, in combination with the default Incremental Lifetime Cancer Risk of 1E-06 from Policy 96-2, and the oral cancer slope factor of 1 per mg/kg-day from IRIS. Age-bracketed upper 90th percentile, per capita, combined direct and indirect, water ingestion rates for community water sources from Table 3-13 of the 2019 revision to the Exposure Factors Handbook were used to derive the Water Supply standards.
Previously, water quality standards of several related polycyclic aromatic hydrocarbons (PAHs) [benzo(a)anthracene, benzo(b)fluoranthene, benzo(k)fluoranthene, chrysene, dibenzo(a,h)anthracene, and indeno(1,2,3-cd)pyrene] were set equal to those for BaP; therefore, the Water Supply standard for these PAHs was also revised. Table 1 summarizes the revised standards for BaP and the other, related PAHs adopted by the commission. The commission adopted revised standards for these PAHs calculated by applying the estimated order of potential potency (EOPP) factor, for each chemical relative to BaP, presented in EPA's 1993 Provisional Guidance for Quantitative Risk Assessment of Polycyclic Aromatic Hydrocarbons. In this approach, the potencies of other PAHs relative to benzo(a) pyrene are determined. These EOPP factors were applied using the revised cancer slope factor for BaP from IRIS and using age-dependent factors appropriate for use with mutagenic chemicals. Treatment of the related PAHs as mutagens, based on that determination for BaP, is consistent with the approach described in EPA's 1993 guidance. Footnote 8 was added to indicate that BaP and related PAH standards were calculated as mutagens. In 2010, EPA provided a draft of updated guidance, which applied new relative potency factors (RPFs). However, since the guidance was never finalized, the new RPFs are typically used in EPA risk assessment framework, and are thus not used for the derivation of the revised water quality standards.
Table 1. Summary of standards proposed for BaP and the other, related PAHs | ||
Parameter | CAS No. | Water Supply Standard (µg/L) |
benzo(a)anthracene | 56-55-3 | 0.16 |
benzo(a)pyrene | 50-32-8 | 0.016 |
benzo(b)fluoranthene | 205-99-2 | 0.16 |
benzo(k)fluoranthene | 207-08-9 | 1.6 |
chrysene | 218-01-9 | 16 |
dibenzo(a,h)anthracene | 53-70-3 | 0.016 |
indeno(1,2,3-cd)pyrene | 193-39-5 | 0.16 |
Previous to revision, the Water Supply standard for BaP adopted by the commission was a hybrid standard that ranged from the concentration protective of human-health to the drinking water maximum contaminant level (MCL). The hybrid standard approach was adopted in the 2004 rulemaking in response to ongoing debate dating back to 1989 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 groundwater 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 groundwater as a resource. In response, the commission adopted a hybrid standard approach that provided much of the benefits advocated for each of the above options. This hybrid approach had the intention to allow for existing contamination to be addressed at levels that are deemed acceptable according to the Safe Drinking Water Act, but allowed for the protection of groundwater as a resource by implementing a more protective human-health health based standard for future contamination.
There are more appropriate alternative regulatory pathways, such as variances, through which dischargers can seek regulatory relief. Furthermore, recent litigation in Idaho has resulted from attempts to adopt water quality standards that are not fully protective of the beneficial uses. In May 2016, EPA entered into a consent decree with Northwest Environmental Advocates to reconsider EPA's 2010 approval of Idaho's human health criteria for arsenic, which were based on the MCL in drinking water. In September 2016, EPA disapproved Idaho's MCL-based criteria, citing that the criteria "are not protective of Idaho's designated uses, including primary and secondary contact recreation and domestic water supply". EPA also noted that there are significant differences between the allowable factors for developing MCLs and water quality criteria to protect designated uses under CWA section 303(c). EPA points out that MCLs are in some cases based on feasibility considerations, including the availability of technology to achieve the regulatory level and the cost of such treatment. In other cases, MCLs are based on concentrations that can be measured reliably rather than concentrations expected to be protective of human health. In contrast, water quality standards must be based on a sound scientific rationale and protect the designated use, rather than being based on available treatment technology, costs, or other feasibility considerations. In addition, water quality standards regulations at 40 CFR 131.11(a)(1) are explicit that states must adopt water quality criteria that protect designated uses.
For BaP, the Colorado Hazardous Materials and Waste Management Division (at the time of rulemaking) uses the risk-based water quality standard to derive the groundwater protection level for BaP. Furthermore, the MCL for BaP is 0.2 µg/L; the incremental lifetime cancer risk factor resulting from this concentration would be 1.21x10-5, which is more than an order of magnitude greater than the risk factor that has been considered to be the appropriate level risk by the commission in past determinations (1x10-6). Therefore, the commission adopted a risk-based Water Supply standard for BaP of 0.016 µg/L that is protective of human-health.
The commission adopted changes to the existing language in Regulation 41.6(D), which provides specific direction to the division when it determines points of compliance for groundwater permits. The commission revised the language to clarify that Regulation 41.6(D) applies to points of compliance in both Regulation No. 42 specified areas and unclassified areas governed by the interim narrative standard, consistent with the existing direction in Regulation 41.6(A) that Regulation 41.6(D) should apply to all activities regulated by the division.
The commission also removed the previous distinction in Regulation 41.6(D) between points of compliance for "new" and "existing" activities. Instead, the commission adopted one set of criteria for the division to use going forward in its adoption of points of compliance for all activities. These criteria are intended to allow for consideration and balance of a number of important factors, including but not limited to the use of land treatment technologies and/or groundwater dilution to achieve compliance with applicable standards, while ensuring that domestic water supplies and other uses are afforded the highest degree of protection that is technologically and economically feasible.
There are several standards for inorganic parameters in Tables 1, 2 and 3 of Regulation No. 41 that are currently expressed using the dissolved fraction. The division originally proposed to change the fraction for the majority of these parameters from the dissolved fraction to the total recoverable fraction (TREC). The division proposed these changes to accurately reflect the fraction of each inorganic parameter upon which the standards were developed to protect Water Supply or Agriculture uses, and also to better align with the use of the TREC fraction expression for these parameters in Regulation No. 31. The division also proposed to include a modified footnote "d" to Tables 1, 2, and 3 at 41.8, stipulating that the dissolved fraction for these parameters could still be considered for regulatory implementation purposes, as appropriate.
The division retracted these proposals based on concerns related to potential differences between measured concentrations of inorganics on a TREC or dissolved basis, especially in monitoring wells, possible misalignment with historically collected data and resulting impacts to ongoing monitoring programs, and a lack of information about the practicality, cost, or other impacts of evaluating the difference between dissolved and TREC concentrations for a particular parameter, at a particular site.
Existing Footnote "d" to Tables 1, 2, and 3 in Regulation No. 41 states that, while the standards are measured in dissolved concentrations, the TREC concentration may be considered on a case-by-case basis. The commission added the phrase "for the protection of groundwater uses" to the existing Footnote d to clarify that any case-by-case determinations requiring measurement of samples as the TREC concentration (as opposed to dissolved) are intended to serve the regulation's stated purpose, that is, to protect existing and potential beneficial uses of groundwater. The commission does not intend for this clarifying language to result in changes to the scope of implementation of the footnote, but rather to clarify the underlying use protection purpose when the division and implementing agencies make such case-by-case determinations going forward.
For example, the TREC fraction should be considered as an alternative to the dissolved fraction at sites where hydrogeological conditions exist such that the dissolved fraction does not accurately represent groundwater quality within the aquifer and the source of groundwater pollution is hydraulically connected to (and has the potential to impact) domestic/agricultural wells or areas where potential future domestic/agricultural wells could be established. Furthermore, measurement of the TREC fraction is more appropriate than the dissolved fraction when assessing risks from direct exposures to potentially contaminated groundwater (e.g., when assessing any potential adverse effects from ingestion of groundwater from a private drinking well).
At this time, the commission did not receive any information that would suggest that the use of the dissolved fraction of inorganics, as currently stipulated in Regulation No. 41 Tables 1-3, presents a widespread risk to groundwater uses. Additionally, use of the TREC fraction on a case-by-case basis, as stipulated in footnote "d" to Regulation No. 41 Tables 1-3, if appropriately implemented, should provide adequate protection to groundwater uses where consideration of only the dissolved fraction would not. Dissolved concentration remains the default method of measurement.
The commission adopted a change from "ground water" to "groundwater" throughout the regulation. 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.
The commission added clarification to a number of items and corrected minor typographical errors:
* Alignment of footnote assignments for the following organic chemical standards between Regulation Nos. 31 and 41: biphenyl; carbofuran; 1,2 dibromo-3-chloropropane (DBCP); dibromoethane 1,2; dichloromethane (methylene chloride); dioxane 1,4; hexachloroethane; tetrachloroethane 1,1,2,2; tetrachloroethylene (PCE); and trihalomethanes
* Corrected the spelling of chlorpyrifos
* Corrected the spelling of trichloroacetic acid
* Corrected the spelling of chloronaphthalene
* Changed the order of appearance for a number of organic chemicals in Table A, to better align with Regulation No. 31 and display the correct alphabetical order: dichlorobenzidine, endosulfan sulfate, nitrosodiphenylamine N, and trichloroacetic acid
* Superscripted footnotes in Tables 2 and 3
* Added a synonym reference for chlorodibromomethane and dibromochloromethane to better align in Regulations 31 and 41.
5 CCR 1002-41.30