SECTION 350.74. Development of Risk-Based Exposure Limits

(a) General requirement. The person shall use the criteria provided in subsections (b) - (j) of this section and the risk-based exposure limit (RBEL) equations provided in the following figures, as applicable, to establish RBELs appropriate for the type of chemical of concern (COC), the complete and reasonably anticipated to be completed exposure pathways, receptors, and land uses. The person shall establish RBELs for carcinogenic COCs and noncarcinogenic COCs using the default exposure factors provided in the following figure for residents and commercial/industrial workers, unless the executive director approves the use of alternate exposure factors in accordance with subsection (j) of this section.

Attached Graphic

(b) Air inhalation RBEL. The air inhalation RBEL (^Air RBEL_Inh ) is the protective concentration of a COC in air at the point of exposure (POE) for human inhalation.

(1) Under Tiers 2 and 3 as described in §350.75 of this title (relating to Tiered Human Health Protective Concentration Level Evaluation), the person may use the lower of available eight-hour time-weighted average occupational inhalation criteria (i.e., Occupational Safety and Health Administration Permissible Exposure Limits, or American Conference of Governmental Industrial Hygienists Threshold Limit Values), as ^Air RBEL_Inh for inhalation pathways for commercial/industrial workers within the limits of affected commercial/industrial properties which have a health and safety plan in place. The health and safety plan shall be designed to ensure compliance with the applicable occupational inhalation criteria and require the monitoring of COC levels in the working air environment, and specify actions that will be taken in the event of exceedance of the occupational inhalation criteria. When occupational inhalation criteria are used, the person shall provide documentation of the health and safety plan, certify that the plan is followed, and demonstrate that the off-site receptors are protected as required by §350.71(h) of this title (relating to General Requirements). The use of occupational inhalation criteria as RBELs shall require the person to comply with the institutional control requirements in §350.111(b) and (b)(14) of this title (relating to Use of Institutional Controls).

(2) The air RBELs may not exceed any other applicable federal or state air quality standards.

(c) Soil dermal contact RBEL. The soil dermal contact RBEL (^Soil RBEL_Derm ) is the protective concentration of a COC at the POE in soil based upon direct dermal contact to soil by humans. The soil dermal contact RBEL shall also be based on COC-specific values for dermal absorption fraction (ABS.d) and gastrointestinal absorption fraction (ABS_GI ) provided in the following figure, unless the executive director approves the use of alternate ABS.d and ABS_GI values in accordance with subsection (j)(1)(A) and (B) of this section. It is not necessary to calculate a soil dermal contact RBEL for COCs with vapor pressure in mm of Hg greater than or equal to 1.

Attached Graphic

(d) Soil ingestion RBEL. The soil ingestion RBEL (^Soil RBEL_Ing ) is protective concentration of a COC at the POE in soil based upon human ingestion.

(e) Vegetable ingestion RBELs. The vegetable RBELs (^AbgVeg RBEL_Ing and ^BgVeg RBEL_Ing ) are the protective concentration of a COC in aboveground vegetables and below-ground vegetables, respectively, for ingestion by residents. The person shall establish RBELs for ingestion of aboveground vegetables for all carcinogenic and noncarcinogenic COCs which are metals. In addition, the person shall establish RBELs for ingestion of below-ground vegetables for all carcinogenic and noncarcinogenic COCs with a dimensionless Henry's Law Constant less than 0.03, as shown in the figure in §350.73(f) of this title (relating to Determination and Use of Human Toxicity Factors and Chemical Properties), when either of the following criteria are met:

(1) the COC is a metal; or

(2) the COC has a logarithmic octanol-water partition coefficient (Log K_ow ) greater than four as shown in the figure in §350.73(f) of this title ; or

(f) Groundwater ingestion RBEL.

(1) The groundwater ingestion RBEL ( ^GW RBEL_Ing ) is the protective concentration of a COC at the POE in groundwater based upon human ingestion of groundwater. However, if available, the person shall use the lower of the two values established under paragraphs (2) and (3) of this subsection instead.

(2) The person shall use the primary maximum contaminant level (MCL) as provided in 40 Code of Federal Regulations (CFR) Part 141, as amended, or the most currently available federal action level for drinking water (e.g., lead and copper) as the RBEL when available for the COC.

(3) The person shall use the secondary MCLs established for individual COCs as provided in 40 CFR Part 143, as amended, as RBELs, or other scientifically valid published criteria in cases where COCs are present at concentrations which present objectionable characteristics such as taste or odor (e.g., methyl tertiary butyl ether) under the following circumstances:

(A) when the COCs are present in class 1 groundwater;

(B) when the COCs are present in class 2 groundwater that is within 1/2 mile of a well used to supply drinking water and is also within or is likely to migrate, based upon the chemical properties of the COCs and the hydrogeology, to the groundwater production zone of such drinking water supply well; or

(C) when the COCs are present in class 2 groundwater and there are no alternative water supplies available.

(g) Class 3 groundwater RBEL. The class 3 groundwater RBEL (^GW RBEL_{Class 3} ) is the acceptable concentration of a COC at the POE in class 3 groundwater.

(h) Surface water RBEL. The surface water RBEL (^SW RBEL) is the protective concentration of a COC at the POE in surface water. To establish ^SW RBEL for a COC, the person shall determine the lowest value from paragraphs (1) - (5) of this subsection for each COC, unless the person has sufficient surface water quality information specific to the particular surface water body to support an adjustment to the RBEL in accordance with paragraph (6) of this subsection. The ^SW RBEL value determined pursuant to paragraphs (1) - (6) of this subsection may require modification in response to the requirements of paragraphs (7) and (8) of this subsection. The^SW RBEL value for a given COC shall be protective of relevant downgradient water bodies in consideration of the water body use (e.g., designated drinking water supply or sustainable fishery), the water body type (e.g., estuary or perennial freshwater stream), the standards applicable to the type of water body/use, and the fate and transport characteristics of the COC in question at the particular affected property.

(1) The person shall apply the lower of the acute or chronic criteria for fresh or marine waters as applicable, based on the classification of the surface water, to protect aquatic life as provided in §307.6, Table 1 of this title (relating to Toxic Materials), as amended. The person shall determine the applicability of aquatic life criteria related to the water body aquatic life use and flow conditions in accordance with the procedures contained in §§307.3, 307.4, and 307.6 of this title (relating to Definitions and Abbreviations; General Criteria; and Toxic Materials, respectively), and the agency's Implementation Procedures, as amended, as defined in §350.4 of this title (relating to Definitions and Acronyms), as amended. For fresh waters, the person shall calculate aquatic life criteria for metals with hardness-dependent criteria using the hardness value for the nearest downstream classified segment, as listed in the agency's Implementation Procedures, as amended. Where no value is provided in the Implementation Procedures, a hardness value of 50 mg/l CaCO₃ shall be used. When applicable, the person shall convert total metal concentrations in surface water or groundwater to dissolved concentrations as described in the agency's Implementation Procedures, as amended. The person may use the basin-specific pH values provided in §307.6, Table 2 of this title, as amended, relevant to the particular affected property for purposes of determining the appropriate values for the pH dependent criteria. The person shall use the total suspended solids concentration for the nearest classified segment, as listed in the agency's Implementation Procedures, as amended.

(2) The person shall apply the human health criteria to protect drinking water and fisheries as provided in Table 3 of §307.6 of this title, as amended. When applicable, the person shall convert total metal concentrations in surface water or groundwater to dissolved concentrations as described in the agency's Implementation Procedures, as amended. The person shall determine the applicability of human health criteria according to the water body uses (e.g., public water supply, sustainable fishery, incidental fishery, and contact recreation) in accordance with the procedures contained in §307.3 and §307.6 of this title, as amended, and the Implementation Procedures, as amended. When a water body is not being evaluated as a drinking water source, the person must determine the necessity to evaluate exposure pathways associated with contact recreation such as incidental ingestion of surface water and dermal contact with surface water. The person shall use the total suspended solids concentration for the nearest classified segment, as listed in the agency's Implementation Procedures, as amended.

(3) The person shall apply the effluent limitations specified in Texas Pollutant Discharge Elimination System (TPDES) General Permit Number TXG830000, as amended, for any release of groundwater or storm water that has been impacted by petroleum fuel (as defined in the general permit).

(4) The person shall apply United States Environmental Protection Agency guidelines or alternate provisions in accordance with §307.6(c)(7) of this title, as amended, when criteria for aquatic life protection are not provided for a COC in §307.6 of this title, Table 1, as amended. In addition, the person shall apply federal guidance criteria (i.e., lower of a federal numerical criterion, MCL, or equivalent state drinking water guideline) or alternate provisions in accordance with §307.6(d)(8) of this title, as amended, when human health criteria for a COC are not provided in Table 3 of §307.6 of this title, as amended.

(5) The person shall apply the numerical criteria, as appropriate, for chlorides, sulfates, total dissolved solids, and pH for classified segments as specified in §307.10(1) of this title (relating to Appendices A - G ), as amended.

(6) The person may apply additional provisions where data on surface water quality for a specific surface water body at the affected property is available or can be reasonably obtained.

(A) The person may determine property-specific hardness, based on sampling data, for calculating metals criteria in accordance with the procedures contained in the agency's Implementation Procedures, as amended.

(B) The person may determine property-specific total suspended solids, based on sampling data, for estimating ''dissolved'' metals in accordance with the Implementation Procedures, as amended.

(C) The person may determine the actual pH of the particular surface water body at the affected property.

(7) The additional numeric and narrative criteria listed in subparagraphs (A) and (B) of this paragraph may require development of a surface water RBEL (e.g., where a nutrient is a COC) or modification to the surface water RBEL (e.g., lower a RBEL value to minimize foaming on the water's surface) determined pursuant to paragraphs (1) - (5) of this subsection.

(A) General criteria related to aesthetic parameters, nutrient parameters, and salinity in accordance with §307.4(b), (e), and (g) of this title , as amended.

(B) General provisions related to the preclusion of adverse toxic effects on aquatic and terrestrial life, livestock, or domestic animals in accordance with §307.6(b) of this title, as amended.

(8) If the executive director determines that the release has the potential to lower the surface water dissolved oxygen, then the executive director may require the person to apply the dissolved oxygen criteria for classified segments specified in §307.10(1) of this title, as amended, or the dissolved oxygen criteria for unclassified waters specified in §307.10(4) of this title, as amended, §307.4(h) of this title, as amended, and §307.7(b)(3)(A) of this title (relating to Site Specific Uses and Criteria), as amended.

(i) Aesthetics. For COCs for which a RBEL cannot be calculated by the procedures of this section, or the RBEL concentration for the COC otherwise adversely impacts environmental quality or public welfare and safety, presents objectionable characteristics (e.g., taste, odor), or makes a natural resource unfit for use, the person shall comply with paragraphs (1) - (3) of this subsection as appropriate. For response actions which are triggered for an area solely for purposes of this subsection (i.e., there is no other human health or ecological hazard remaining), the executive director will evaluate the seriousness, probable longevity of the matter, and suitability of the proposed remedy with the landowner in order to site-specifically determine whether or not institutional controls and financial assurance are warranted. The person shall provide all information reasonably necessary to support such a determination to the executive director. The default presumption is that financial assurance and institutional controls are required for exposure prevention remedies. If the executive director determines that institutional controls and financial assurance are not warranted, then persons shall not be required to comply with the provisions of §§350.31(g), 350.33(e)(2)(C) and 350.111(b)(3) or (6) of this title (relating to General Requirements for Remedy Standards; Remedy Standard B; and Use of Institutional Controls), specifically relating to the physical control matters for the portion of affected property with the aesthetics issue.

(1) In accordance with §101.4 of this title (relating to Nuisance), as amended, the person may be required by the executive director to address COCs which present objectionable odors.

(2) The maximum total soil concentration of COCs which are liquid at standard temperature and pressure shall not exceed 10,000 mg/kg within the soil interval of 0 - 10 feet, unless it can be demonstrated that:

(A) no free liquids (e.g., no mobile NAPL) or sludges exist; or

(B) higher concentrations do not adversely impair surface use of the affected property.

(3) Other scientifically valid published criteria such as, but not limited to, non-COC specific secondary MCLs for water may be required by the executive director to be used as the RBEL.

(j) Requirements for variance to default RBEL exposure factors.

(1) Under Tiers 2 or 3 as provided in §350.75 of this title (relating to Tiered Human Health Protective Concentration Level Evaluation) and with prior executive director approval, the person may vary the following default exposure factors shown in the figures in subsections (a) and (c) of this section based on conditions or exposure levels at a particular affected property and in accordance with the conditions specified. A person shall provide the supporting documentation to justify the use of such alternative factors to the executive director.

(A) Gastrointestinal absorption fraction (ABS_GI ). A person or the executive director may use an alternative scientifically justifiable gastrointestinal absorption fraction value. Only in cases where the gastrointestinal absorption fraction is less than 50% shall the oral slope factor and oral reference dose be adjusted using equation RBEL-2 as shown in the figure in subsection (a) of this section, as applicable, to calculate the corresponding dermal slope factor and dermal reference dose. The person shall not use the gastrointestinal absorption fraction to modify the oral slope factor or oral reference dose for any exposure pathway other than the dermal exposure pathway. In the event the executive director determines a more scientifically valid gastrointestinal absorption fraction, that fraction shall be presumed to be the appropriate fraction and the person shall use that fraction unless a person rebuts that value with a scientifically valid study or by other credible published authority.

(B) Dermal absorption fraction (ABS.d). A person or the executive director may conduct a scientifically valid study using property-specific soils or may use alternative scientifically justifiable dermal absorption values. In the event the executive director determines a more scientifically valid dermal absorption fraction, that fraction shall be presumed to be the appropriate fraction and the person shall use that fraction unless a person rebuts that fraction with a scientifically valid study using property-specific soils or by other credible published authority.

(C) Relative bioavailability factor (RBAF). A person or the executive director may conduct a scientifically valid bioavailability study using property-specific soils or may conduct mineralogical evaluations of the chemical form of a COC present in soils at the affected property. In the event the executive director determines a more scientifically valid relative bioavailability factor, that factor shall be presumed to be the appropriate relative bioavailability factor and the person shall use that factor unless a person rebuts that factor with a scientifically valid bioavailability study using property-specific soils, mineralogical evaluation of the chemical form of a chemical of concern present in soils at the affected property, or by other credible published authority.

(2) Under Tiers 2 or 3 as provided in §350.75 of this title , a person may request that the executive director allow a variance to the following default commercial/industrial exposure factors for the affected property as shown in the figure in subsection (a) of this section: averaging time for noncarcinogens (AT.w), exposure duration (ED.w), and exposure frequency (EF.w). This shall only be allowed for facilities that have or will have, as a condition of the approval of this variance, restricted property access. The executive director shall not delegate this decision to agency staff.

(A) The person shall submit information to the executive director which demonstrates that variance from the default exposure factors is supported by property-specific information; historical, current, and probable future land use; redevelopment potential; and compatibility with surrounding land use. The person shall also provide written concurrence from the landowner for the placement of the institutional control in the county deed records, as required in subparagraph (L) of this paragraph, unless the property is subject to zoning or governmental ordinance which is equivalent to the deed notice, Voluntary Cleanup Program certificate of completion or restrictive covenant that otherwise would have been required.

(B) The person requesting such variance shall provide public notification as described in subparagraphs (D) and (E) of this paragraph for any request to vary the default exposure factors at the same time that variance-based protective concentration levels (PCLs) are submitted to the executive director for approval. If the natural physical condition of the on-site commercial/industrial area for which the variance is sought essentially prohibits full commercial/industrial use (e.g., marshes and cliffs), and the variance would not necessitate a lesser commercial/industrial use of that area, then the executive director will determine the need for public notice on a site-specific basis for the prohibited use area. The person may request the executive director or his staff to review the variance-based PCLs or the variance request for completeness (e.g., administratively complete, mathematical accuracy, compliance with other PCL development procedures) in advance of initiating the public notification process. The required public notice shall be completed prior to consideration of the variance request for approval by the executive director. The public notice provisions may be performed in conjunction with or as part of another public participation/notification process required for permitting or other applicable state or federal statute or regulation provided the requirements of subparagraph (E) of this paragraph are also met. Additionally, an alternative mechanism that may exist under the other public participation/notification process which effectively provides broad public notice of the variance request, such as notification to an existing citizens' advisory board for the affected property/facility, may substitute for the requirements of subparagraph (D) of this paragraph, provided the completion of the notification is sufficiently documented.

(C) The notice shall contain, at a minimum, the following information:

(i) the name, address and telephone number of the person requesting the variance;

(ii) the address and the physical description for the location of the property and the agency case designation number;

(iii) the modified value(s) the person seeks to use and the associated default exposure factor(s) as shown in the figure in subsection (a) of this section without any statements or other indications that such variance has been approved or otherwise considered favorably by the executive director or the executive director's staff other than that it has been reviewed for completeness;

(iv) a clear and concise explanation as to the effect the variance will have on the future use of the subject property and on surrounding properties;

(v) a statement that more detailed information regarding the variance request is available for review at the agency's central office in Austin, Texas, 8:00 am - 5:00 pm Monday thru Friday; and

(vi) a notice to the public of the opportunity to submit written information, within 30 calendar days after the date of the initial published notice (publish the actual date), to the executive director which demonstrates that the proposal for variance from the default exposure factors would be compatible or incompatible with existing neighboring land uses and preservation of the active and productive land use of the subject property.

(D) The notice shall be published in a newspaper distributed daily, if available, and generally circulated in the county or area where the property is located. The notice shall be published once a week for three weeks, with at least one of the notices appearing in a Sunday edition, if available.

(E) The notice shall be sent to the following persons in clauses (i) - (viii) of this subparagraph by certified mail, return receipt requested:

(i) all adjacent landowners;

(ii) the local municipality planning board or similar governmental unit, if applicable;

(iii) local taxing authorities;

(iv) the mayor and health authorities of the city in which the property is located, if applicable;

(v) the county judge and county health authority of the county in which the property is located;

(vi) the agency's Public Interest Counsel;

(vii) all persons or organizations who have requested the notice or expressed interest; and

(viii) other persons or organizations specified by the executive director.

(F) The person shall provide copies of each notice sent by mail, copies of the published notice, and copies of the signed publisher's affidavit for the initial notice to the agency's Austin office and to the appropriate agency region office within 10 calendar days after the initial publication and mailing. Copies of the signed publisher's affidavits for the subsequent notices shall be provided to the agency's Austin office and to the appropriate agency region office within 10 days of both subsequent notices.

(G) At the executive director's request, and at the expense of the person, the person shall schedule and hold a public meeting at a time and place which are convenient for persons identified in subparagraph (E) of this paragraph. The forum chosen for the meeting shall comply with the Americans with Disabilities Act. Prior to scheduling the public meeting, the person shall coordinate the scheduling of the public meeting with the executive director's office to ensure the availability of agency personnel for the meeting. The person shall confirm with the executive director's office the date, time, and location of the meeting not less than 15 days prior to the meeting. The meeting shall be open to the public to provide information on the request to vary the default exposure factors and to allow for comments by the public. The person shall again confirm with the executive director's office on the time and place of the meeting at least 72 hours prior to the meeting.

(H) In order to inform persons of the public meeting, the person shall, at least 30 calendar days prior to the public meeting, follow the notification process required in subparagraphs (C) - (F) of this paragraph with the following exceptions:

(i) the notice shall be supplemented to include the date, time, and location of the public meeting and to indicate that the meeting is open to the public for the purposes of providing information on the request to vary default exposure factors and to provide the public the opportunity to provide comments on the request;

(ii) the notice shall indicate that the public shall have 15 calendar days after the date of the public meeting to submit written information to the executive director which demonstrates that the proposal for variance from the default exposure factors would be compatible or incompatible with existing neighboring land uses and preservation of the active and productive land use of the subject property; and

(iii) the notice by publication of the public meeting shall only be published once and shall be placed in a Sunday edition, if available.

(I) The executive director's decision on the request for a variance from the default exposure factors shall occur at least 15 calendar days after any public meeting or if no public meeting is held, at least 45 days after the date of the initial published notice. The executive director's decision shall be based upon property-specific data; historical, current, and probable future land use; redevelopment potential; and compatibility with surrounding land use. The executive director shall not consider the costs incurred for any actions taken by the person in anticipation that the variance would be approved by the executive director.

(J) At the same time that the executive director's decision is mailed to the person requesting the variance, a copy of this decision shall also be mailed to all persons identified in subparagraph (E) of this paragraph. The notice of the executive director's decision shall explain the method for submitting a motion for reconsideration of the executive director's decision by the commission.

(K) The person requesting the variance and persons identified in subparagraph (E) of this paragraph may file with the chief clerk a motion to overturn related to the request for variance, in accordance with §50.139 of this title (relating to Motion to Overturn Executive Director's Decision).

(L) A person who receives a variance from the default exposure factors shall comply with the institutional control requirements in §350.111(b), (b)(12), or (13) of this title (relating to Use of Institutional Controls), as applicable, and provide proof of compliance with the institutional control requirements within 90 days of the approval by the executive director of the response action completion report.

(3) The person shall not vary the following exposure factors shown in the figure in subsection (a) of this section.

(A) averaging time for residents for noncarcinogens (AT.A.res and AT.C.res) or carcinogens (ATc);

(B) body weight for adults and children (BW.A, BW.C, BW_(0<6) , BW_(6<18) , and BW_(18<30) );

(C) exposure duration for residents (ED.A.res, ED.C.res, ED_(0<6) , ED_(6<18) , and ED_(18<30) );

(D) exposure frequency for residents (EF.res);

(E) ingestion rate for soil, water, or vegetables (IRsoil.AgeAdj.res, IRsoil.C.res, IRsoil.w, IRw.AgeAdj.res, IRw.C.res, IRw.w, IRabg.AgeAdj.res, IRbg.AgeAdj.res, IRabg.C.res, IRbg.C.res);

(F) toxicity modifying factor (MF);

(G) skin surface area (SA.C.res, SA_(0<6) , SA_(6<18) , SA _(18<30) , SA.w);

(H) soil-to-skin adherence factors (AF.C.res, AF _(0<6) , AF_(6<18) , AF _(18<30) , and AF.w).

Source Note: The provisions of this §350.74 adopted to be effective September 23, 1999, 24 TexReg 7436; amended to be effective March 19, 2007, 32 TexReg 1526; amended to be effective May 14, 2020, 45 TexReg 3130