Section 307.6 - Toxic Materials(a) Application. The toxic criteria set forth in this section apply to surface water in the state and specifically apply to substances attributed to waste discharges or human activity. With the exception of numeric human health criteria, toxic criteria do not apply to those instances where surface water, solely as a result of natural phenomena, exhibit characteristics beyond the limits established by this section. Standards and procedures set forth in this section are applied in accordance with § 307.8 of this title (relating to Application of Standards) and § 307.9 of this title (relating to Determination of Standards Attainment).(b) General provisions. (1) Water in the state must not be acutely toxic to aquatic life in accordance with § 307.8 of this title.(2) Water in the state with designated or existing aquatic life uses of limited or greater must not be chronically toxic to aquatic life, in accordance with § 307.8 of this title.(3) Water in the state must be maintained to preclude adverse toxic effects on human health resulting from contact recreation, consumption of aquatic organisms, consumption of drinking water or any combination of the three. Water in the state with sustainable fisheries or public drinking water supply uses must not exceed applicable human health toxic criteria, in accordance with subsection (d) of this section and § 307.8 of this title.(4) Water in the state must be maintained to preclude adverse toxic effects on aquatic life, terrestrial life, livestock, or domestic animals, resulting from contact, consumption of aquatic organisms, consumption of water, or any combination of the three.(c) Specific numerical aquatic life criteria.(1) Numerical criteria are established in Table 1 of this paragraph for those specific toxic substances where adequate toxicity information is available and that have the potential for exerting adverse impacts on water in the state. Attached Graphic
(2) Numerical criteria are based on ambient water quality criteria documents published by the EPA. EPA guidance criteria have been appropriately recalculated to eliminate the effects of toxicity data for aquatic organisms that are not native to Texas, in accordance with procedures in the EPA guidance documents entitled Guidelines for Deriving Numerical Site-specific Water Quality Criteria (EPA 600/3-84-099) and Revised Deletion Process for the Site-Specific Recalculation Procedure for Aquatic Life Criteria (EPA-823-R-13-001). Additional EPA guidelines that may be used to establish aquatic life criteria are detailed in the guidance documents.(3) Specific numerical acute aquatic life criteria are applied as 24-hour averages, and specific numerical chronic aquatic life criteria are applied as seven-day averages.(4) Ammonia and chlorine toxicity are addressed by total toxicity (biomonitoring) requirements in subsection (e) of this section.(5) Specific numerical aquatic life criteria for metals and metalloids in Table 1 of paragraph (1) of this subsection apply to dissolved concentrations where noted. Dissolved concentrations can be estimated by filtration of samples prior to analysis, or by converting from total recoverable measurements in accordance with procedures approved by the commission in the standards implementation procedures (RG-194) as amended. Specific numerical aquatic life criteria for non-metallic substances in Table 1 of paragraph (1) of this subsection apply to total recoverable concentrations unless otherwise noted.(6) Specific numerical acute criteria for toxic substances are applicable to all water in the state except for small zones of initial dilution (ZIDs) at discharge points. Acute criteria may be exceeded within a ZID and below extremely low streamflow conditions (one-fourth of critical low-flow conditions) in accordance with § 307.8 of this title. There must be no lethality to aquatic organisms that move through a ZID, and the sizes of ZIDs are limited in accordance with § 307.8 of this title. Specific numerical chronic criteria are applicable to all water in the state with designated or existing aquatic life uses of limited or greater, except inside mixing zones and below critical low-flow conditions, in accordance with § 307.8 of this title.(7) For toxic materials where specific numerical criteria are not listed in Table 1 of paragraph (1) of this subsection, the appropriate criteria for aquatic life protection may be derived in accordance with current EPA guidelines for deriving site-specific water quality criteria. When insufficient data are available to use EPA guidelines, the following provisions are applied in accordance with this section and § 307.8 of this title. The LC50 data used in the subsequent calculations are typically obtained from traditional laboratory studies; however, if LC50 data are unavailable or incomplete, other methodologies (such as quantitative structure-activity relationships) may be used: (A) acute criteria are calculated as 0.3 of the LC50 of the most sensitive aquatic species; LC50 × (0.3) = acute criteria;(B) concentrations of nonpersistent toxic materials must not exceed concentrations that are chronically toxic as determined from appropriate chronic toxicity data obtained in accordance with procedures in the EPA guidance document entitled Guidelines for Deriving Numerical National Water Quality Criteria for the Protection of Aquatic Life and Their Uses (EPA 822-R-85-100) or calculated as 0.1 of acute LC50 values to the most sensitive aquatic species; LC50 × (0.1) = chronic criteria;(C) concentrations of persistent toxic materials that do not bioaccumulate shall not exceed concentrations that are chronically toxic as determined from appropriate chronic toxicity data obtained in accordance with procedures in the EPA guidance document entitled Guidelines for Deriving Numerical National Water Quality Criteria for the Protection of Aquatic Life and Their Uses (EPA 822-R-85-100) or calculated as 0.05 of LC50 values to the most sensitive aquatic species; LC50 × (0.05) = chronic criteria; and(D) concentrations of toxic materials that bioaccumulate must not exceed concentrations that are chronically toxic as determined from appropriate chronic toxicity data obtained in accordance with procedures in the EPA guidance document entitled Guidelines for Deriving Numerical National Water Quality Criteria for the Protection of Aquatic Life and Their Uses (EPA 822-R-85-100) or calculated as 0.01 of LC50 values to the most sensitive aquatic species; LC50 × (0.01) = chronic criteria.(8) For toxic substances where the relationship of toxicity is defined as a function of pH or hardness, numerical criteria are presented as an equation based on this relationship. Site-specific values for each segment are given in the standards implementation procedures (RG-194) as amended.(9) Criteria for most metals are multiplied by a water-effect ratio (WER) in order to incorporate the effects of local water chemistry on toxicity. The WER is assumed to be equal to one except where sufficient site-specific data are available to determine the WER for a particular water body or portion of a water body. A WER is only applicable to those portions of a water body that are adequately addressed by site-specific data. WERs that have been determined for particular water bodies are listed in Appendix E of § 307.10 of this title (relating to Appendices A - G) when standards are revised. A site-specific WER that affects an effluent limitation in a wastewater discharge permit, and that has not been incorporated into Appendix E of § 307.10 of this title, must be noted in a public notice during the permit application process. An opportunity for public comment must be provided, and the WER may be considered in any public hearing on the permit application.(10) Freshwater copper aquatic-life criteria include a multiplier (m) to incorporate effects of local water chemistry on toxicity. Site-specific criteria may be based on either a WER or a biotic ligand model. The WER multiplier is assumed to be equal to one except where sufficient site-specific data are available to determine the multiplier for a particular water body or portion of a water body. The WER multiplier or biotic ligand model result is only applicable to those portions of a water body that are adequately addressed by site-specific data. The biotic ligand model is based on the dissolved portion of copper, and the freshwater equation is not used in this case. As WER multipliers and criteria based on biotic ligand models are determined for particular water bodies, they are listed in Appendix E of § 307.10 of this title when standards are revised. A site-specific WER multiplier or biotic ligand model result that affects an effluent limitation in a wastewater discharge permit, and that has not been incorporated into Appendix E of § 307.10 of this title, is noted in a public notice during the permit application process. An opportunity for public comment must be provided, and the WER multiplier or biotic ligand model result may be considered in any public hearing on the permit application.(11) Additional site-specific factors may indicate that the numerical criteria listed in Table 1 of paragraph (1) of this subsection are inappropriate for a particular water body. These factors are applied as a site-specific standards modification in accordance with § 307.2(d) of this title (relating to Description of Standards). The application of a site-specific standard must not impair an existing, attainable, or designated use. Factors that may justify a temporary variance or site-specific standards amendment include the following: (A) background concentrations of specific toxics of concern in receiving waters, sediment, or indigenous biota;(B) persistence and degradation rate of specific toxic materials;(C) synergistic, additive, or antagonistic interactions of toxic substances with other toxic or nontoxic materials;(D) measurements of total effluent toxicity;(E) indigenous aquatic organisms, which may have different responses to particular toxic materials;(F) technological or economic limits of treatability for specific toxic materials;(G) bioavailability of specific toxic substances of concern, as determined by WER tests or other analyses approved by the commission; and(H) new information concerning the toxicity of a particular substance.(d) Specific numerical human health criteria.(1) Numerical human health criteria are established in Table 2 of this paragraph. Attached Graphic
(2) Categories of human health criteria.(A) Concentration criteria to prevent contamination of drinking water, fish, and other aquatic life to ensure that they are safe for human consumption. These criteria apply to surface waters that are designated or used for public drinking water supplies, including all water bodies identified as having a public drinking water supply use in Appendix A of § 307.10 of this title or as a sole-source surface drinking water supply in Appendix B of § 307.10 of this title. (Column A in Table 2 of paragraph (1) of this subsection.)(B) Concentration criteria to prevent contamination of fish and other aquatic life to ensure that they are safe for human consumption. These criteria apply to surface waters that have sustainable fisheries and that are not designated or used for public water supply or as a sole-source surface drinking water supply. (Column B in Table 2 of paragraph (1) of this subsection.)(3) Specific assumptions and procedures (except where noted in Table 2 of paragraph (1) of this subsection). (A) Sources for the toxicity factors to calculate criteria were derived from EPA's IRIS database; EPA's National Recommended Water Quality Criteria: 2002, Human Health Criteria Calculation Matrix (EPA-822-R-02-012); EPA inputs for calculating the 2015 updated national recommended human health criteria; EPA Health Effects Assessment Summary Tables (HEAST); Assessment Tools for the Evaluation of Risk (ASTER); EPA's QSAR Toxicity Estimation Software Tool, version 4.1; and the computer program, CLOGP3.(B) For known or suspected carcinogens (as identified in EPA's IRIS database), an incremental cancer risk level of 10-5 (1 in 100,000) was used to derive criteria. An RfD (reference dose) was determined for carcinogens and noncarcinogens where the EPA has not derived cancer slope factors.(C) Consumption rates of fish and shellfish were estimated as 17.5 grams per person per day, unless otherwise specified in Table 2 of paragraph (1) of this subsection.(D) Drinking water consumption rates were estimated as 2.0 liters per person per day.(E) For carcinogens, a body-weight scaling factor of 3/4 power was used to convert data on laboratory test animals to human scale. Reported weights of laboratory test animals are used, and an average weight of 70 kilograms is assumed for humans.(F) Childhood exposure was considered for all noncarcinogens. Consumption rates for fish and shellfish were estimated as 5.6 grams per child per day and drinking water consumption rates were estimated as 0.64 liters per child per day. A child body weight was estimated at 15 kilograms. Both the water consumption rate and body weight are age-adjusted for a six-year-old child. The consumption rate for fish and shellfish for children is from Table 10-61 of EPA's 1997 Exposure Factors Handbook (EPA/600/P-95/002Fa-c).(G) Numerical human health criteria were derived in accordance with the general procedures and calculations in the EPA guidance documents entitled Technical Support Document for Water Quality-based Toxics Control (EPA/505/2-90-001); Guidance Manual for Assessing Human Health Risks from Chemically Contaminated Fish and Shellfish (EPA/503/8-89-002); and Methodology for Deriving Ambient Water Quality Criteria for the Protection of Human Health (2000) (EPA-822-B-00-004).(H) If a calculated criterion to prevent contamination of drinking water and fish to ensure they are safe for human consumption (Column A in Table 2 of paragraph (1) of this subsection) was greater than the applicable maximum contaminant level (MCL) in Chapter 290 of this title (relating to Public Drinking Water), then the MCL was used as the criterion.(I) If the concentration of a substance in fish tissue used for these calculations was greater than the applicable United States Food and Drug Administration Action Level for edible fish and shellfish tissue, then the acceptable concentration in fish tissue was lowered to the Action Level for calculation of criteria.(4) Human health criteria for additional toxic materials are adopted by the commission as appropriate.(5) Specific human health concentration criteria for water are applicable to water in the state that has sustainable fisheries or designation or use as a public drinking water supply or as a sole-source drinking water supply except within mixing zones and below stream flow conditions as specified in § 307.8 of this title. The following waters are considered to have sustainable fisheries: (A) all designated segments listed in Appendix A of § 307.10 of this title, unless specifically exempted;(B) perennial streams and rivers with a stream order of three or greater, as defined in § 307.3 of this title (relating to Definitions and Abbreviations);(C) lakes and reservoirs greater than or equal to 150 acre-feet or 50 surface acres;(D) all bays, estuaries, and tidal rivers; and(E) any other waters that potentially have sufficient fish production or fishing activity to create significant long-term human consumption of fish.(6) Waters that are not considered to have a sustainable fishery, but that have an aquatic life use of limited or greater, are considered to have an incidental fishery. Consumption rates assumed for incidental fishery waters are 1.75 grams per person per day. Therefore, numerical criteria applicable to incidental fishery waters are ten times the criteria listed in Column B in Table 2 of paragraph (1) of this subsection.(7) Specific human health criteria are applied as long term average exposure criteria designed to protect populations over a life time. Attainment measures for human health are addressed in § 307.9 of this title.(8) For toxic materials of concern where specific human health criteria are not listed in Table 2 of paragraph (1) of this subsection, the following provisions apply: (A) For known or suspected carcinogens (as identified in EPA's IRIS database), a cancer risk of 10-5 (1 in 100,000) is applied to the most recent numerical criteria adopted by the EPA and published in the Federal Register. If an MCL or equivalent agency guideline for protection of drinking water sources is less than the resulting criterion, then the MCL applies to public drinking water supplies in accordance with paragraph (3)(H) of this subsection.(B) For toxic materials not defined as carcinogens, the most recent numerical criteria adopted by the EPA and published in the Federal Register are applicable. If an MCL or equivalent agency guideline for protection of drinking water sources is less than the resulting criterion, then the MCL applies to public drinking water supplies in accordance with paragraph (3)(H) of this subsection.(C) In the absence of available criteria, numerical criteria may be derived from technically valid information and calculated in accordance with the provisions of paragraph (3) of this subsection.(9) Numerical criteria for bioconcentratable pollutants are derived in accordance with the general procedures in the EPA guidance document entitled Assessment and Control of Bioconcentratable Contaminants in Surface Water (March 1991). The commission may develop discharge permit limits in accordance with the provisions of this section.(10) Numerical human health criteria are expressed as total recoverable concentrations for nonmetals and selenium and as dissolved concentrations for other metals and metalloids.(11) Additional site-specific factors may indicate that the numerical human health criteria listed in Table 2 of paragraph (1) of this subsection are inappropriate for a particular water body. These factors are applied as a site-specific standards modification in accordance with § 307.2(d) of this title. The application of site-specific criteria must not impair an existing, attainable, presumed, or designated use or affect human health. Factors that may justify a temporary variance or site-specific standards amendment include the following:(A) background concentrations of specific toxics of concern in receiving waters, sediment, or indigenous biota;(B) persistence and degradation rate of specific toxic materials;(C) synergistic or antagonistic interactions of toxic substances with other toxic or nontoxic materials;(D) technological or economic limits of treatability for specific toxic materials;(E) bioavailability of specific toxic substances of concern;(F) local water chemistry and other site-specific conditions that may alter the bioconcentration, bioaccumulation, or toxicity of specific toxic substances;(G) site-specific differences in the bioaccumulation responses of indigenous, edible aquatic organisms to specific toxic materials;(H) local differences in consumption patterns of fish and shellfish or drinking water, but only if any changes in assumed consumption rates are protective of the local population that frequently consumes fish, shellfish, or drinking water from a particular water body; and(I) new information concerning the toxicity of a particular substance.(e) Total toxicity. (1) Total (whole-effluent) toxicity of permitted discharges, as determined from biomonitoring of effluent samples at appropriate dilutions, must be sufficiently controlled to preclude acute total toxicity in all water in the state with the exception of small ZIDs at discharge points and at extremely low streamflow conditions (one-fourth of critical low-flow conditions) in accordance with § 307.8 of this title. Acute total toxicity levels may be exceeded in a ZID, but there must be no significant lethality to aquatic organisms that move through a ZID, and the sizes of ZIDs are limited in accordance with § 307.8 of this title. Chronic total toxicity, as determined from biomonitoring of effluent samples at appropriate dilutions, must be sufficiently controlled to preclude chronic toxicity in all water in the state with an existing or designated aquatic life use of limited or greater except in mixing zones at discharge points and at flows less than critical low-flows, in accordance with § 307.8 of this title. Chronic toxicity levels may be exceeded in a mixing zone, but there must be no significant sublethal toxicity to aquatic organisms that move through the mixing zone.(2) General provisions for controlling total toxicity. (A) Dischargers whose effluent has a significant potential for exerting toxicity in receiving waters as described in the Procedures to Implement the Texas Surface Water Quality Standards (RG-194) as amended are required to conduct whole effluent toxicity biomonitoring at appropriate dilutions.(B) In addition to the other requirements of this section, the effluent of discharges to water in the state must not be acutely toxic to sensitive species of aquatic life, as demonstrated by effluent toxicity tests. Toxicity testing for this purpose is conducted on samples of 100% effluent, and the criterion for acute toxicity is mortality of 50% or more of the test organisms after 24 hours of exposure. This provision does not apply to mortality that is a result of an excess, deficiency, or imbalance of dissolved inorganic salts (such as sodium, calcium, potassium, chloride, or carbonate) that are in the effluent and are not listed in Table 1 of subsection (c)(1) of this section or that are in source waters.(C) The latest revisions of the following EPA publications provide methods for appropriate biomonitoring procedures: Methods for Measuring the Acute Toxicity of Effluents and Receiving Waters to Freshwater and Marine Organisms, Short-term Methods for Estimating the Chronic Toxicity of Effluents and Receiving Waters to Freshwater Organisms, Short-term Methods for Estimating the Chronic Toxicity of Effluents and Receiving Waters to Marine and Estuarine Organisms, and the Technical Support Document for Water Quality-based Toxics Control. The use of other procedures approved by the agency and the EPA is also acceptable. Toxicity tests must be conducted using representative, sensitive aquatic organisms as approved by the agency, and any such testing must adequately determine if toxicity standards are being attained.(D) If toxicity biomonitoring results indicate that a discharge is not sufficiently controlled to preclude acute or chronic toxicity as described in this subsection, then the permittee will be required to eliminate sources of toxicity and may be required to conduct a toxicity reduction evaluation (TRE) in accordance with the permitting procedures of the commission. In accordance with the standards implementation procedures (RG-194), permits are amended to include appropriate provisions to eliminate toxicity. Such provisions may include total toxicity limits, chemical-specific limits, best management practices, or other actions (such as moving a discharge location) designed to reduce or eliminate toxicity. Where sufficient to attain and maintain applicable numeric and narrative state water quality standards, a chemical-specific limit, best management practices, or other actions designed to reduce or eliminate toxicity rather than a total toxicity limit may be established in the permit. Where conditions may be necessary to prevent or reduce effluent toxicity, permits must include a reasonable schedule for achieving compliance with such additional conditions.(E) Discharge permit limits based on total toxicity may be established in consideration of site-specific factors, but the application of such factors must not result in impairment of an existing, attainable, presumed, or designated use. These factors are applied as a site-specific standards modification in accordance with § 307.2(d) of this title. A demonstration that uses are protected may consist of additional effluent toxicity testing, instream monitoring requirements, or other necessary information as determined by the agency. Factors that may justify a temporary variance or site-specific standards amendment include the following:(i) background toxicity of receiving waters;(ii) persistence and degradation rate of principal toxic materials that are contributing to the total toxicity of the discharge;(iii) site-specific variables that may alter the impact of toxicity in the discharge;(iv) indigenous aquatic organisms that may have different levels of sensitivity than the species used for total toxicity testing; and(v) technological, economic, or legal limits of treatability or control for specific toxic material.30 Tex. Admin. Code § 307.6
The provisions of this §307.6 adopted to be effective July 10, 1991, 16 TexReg 3400; amended to be effective July 13, 1995, 20 TexReg 4701; amended to be effective August 17, 2000, 25 TexReg 7722; amended to be effective July 22, 2010, 35 TexReg 6294; amended to be effective March 6, 2014, 39 TexReg1450; Amended by Texas Register, Volume 43, Number 08, February 23, 2018, TexReg 1102, eff. 3/1/2018; Amended by Texas Register, Volume 47, Number 38, September 23, 2022, TexReg 6216, eff. 9/29/2022; Amended by Texas Register, Volume 47, Number 40, October 7, 2022, TexReg 6590, eff. 9/29/2022