SECTION 350.76. Approaches for Specific Chemicals of Concern to Determine Human Health Protective Concentration Levels

(a) General.

(1) Due to the unique nature of the toxicity and/or exposure, the person shall use the COC-specific approaches described in this section for the following COCs:

(A) cadmium;

(B) lead;

(C) polychlorinated biphenyls;

(D) polychlorinated dibenzodioxins and dibenzofurans;

(E) polycyclic aromatic hydrocarbons; and

(F) total petroleum hydrocarbons.

(2) Except for the specific provisions contained in this section, the person shall establish RBELs and PCLs in accordance with the standard procedures outlined in the previous sections of this subchapter.

(3) This section addresses only those exposure pathways for which PCL equations are provided in this subchapter. When dealing with other exposure pathways as required in §350.71(c) of this title (relating to General Requirements), the executive director will specify how those pathways should be addressed for these COCs using the best available science.

(4) The person shall use the figures as required in subsections (b) - (g) of this section.

(b) Cadmium.

(1) In calculating residential soil PCLs that are protective for noncarcinogenic effects for all tiers, the person shall incorporate age-adjusted exposure assumptions for the soil ingestion, vegetable ingestion, and dermal soil exposure pathways. Accordingly, 30 years of cadmium exposure shall be partitioned into three specific exposure periods: <1 - 6 years, 6 - 18 years, and 18 - 30 years. Cadmium intake shall be calculated for each of these periods, based on the period-specific exposure assumptions. The soil PCL for cadmium shall be a function of the final integrated intake estimate, which shall be determined by time-weighting intake from each of the three exposure periods. The age-adjusted RBEL equations and default parameters to be used for cadmium are provided in the following figure. The soil PCL for cadmium shall be calculated by combining the pathway-specific PCLs as outlined in §350.75(i)(6) of this title (relating to Tiered Human Health Protective Concentration Level Evaluation).

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(2) In calculating residential and commercial/industrial soil PCLs for all tiers, the person shall use the reference dose values for cadmium in food in evaluating exposures to cadmium through the soil ingestion, vegetable ingestion, and dermal soil exposure pathways.

(c) Lead.

(1) The Tier 1 residential soil PCL ( ^Tot Soil_Comb ) for lead is 500 mg/kg.

(2) Subject to prior approval by the executive director, the person may use property-specific data in conjunction with a lead model approved by the executive director (e.g., EPA Integrated Exposure Uptake Biokinetic model for lead in children (version 1.0 from 2005)) to calculate a Tier 3 residential soil PCL (^Tot Soil _Comb ) for lead. The person shall submit information to the executive director which demonstrates that variance from default model inputs is supported by property-specific information (e.g., data from a scientifically valid bioavailability study using property-specific soils). Property-specific model input values must be approved by the executive director. Consistent with the development of residential RBELs for COCs without chemical-specific approaches in accordance with §350.74 of this title (Development of Risk-Based Exposure Limits), variance from certain model default exposure factors such as soil/dust ingestion rates and exposure frequency to less conservative (i.e., lower) numerical values shall not be allowed.

(3) The commercial/industrial soil PCL ( ^Tot Soil_Comb ) is based only on the soil ingestion pathway (^Soil Soil _Ing ). The person shall use the exposure algorithm and default exposure factors in the following figure for calculating the Tier 1 commercial/industrial ^Soil RBEL_Ing value.

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(4) The person may use a different exposure algorithm as presented in the following figure that considers soil and dust separately for calculating the Tier 2 and 3 commercial/industrial ^Soil RBEL_Ing value in cases where the person has adequate direct measurement data on the concentrations of lead in both soil and dust at the affected property. In addition, in calculating Tier 2 or 3 ^Soil RBEL_Ing values, the person may deviate from the default exposure factors as shown in the figure in paragraph (3) of this subsection and the following figure if property-specific or defensible alternative data (e.g., from open literature or privately funded studies) adequately support such an approach. The specific exposure factors for which the person may use property-specific or scientifically defensible alternative values are the following:

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(A) individual geometric standard deviation (GSD _i );

(B) baseline blood lead (PbBO);

(C) absolute absorption fraction of lead in soil/dust (Afsd);

(D) absolute absorption fraction of lead in soil (AFs); and

(E) absolute absorption fraction of lead in dust (Afd).

(d) Polychlorinated Biphenyls.

(1) In calculating Tier 1 residential and commercial/industrial soil and groundwater PCLs, the person shall use the upper-reference point of the upper-bound slope factors (2 (mg/kg-day)^-1 ) for the soil ingestion, dermal contact with soil, vegetable ingestion, and inhalation (both vapor and particulate phases) exposure pathways.

(2) For Tiers 2 and 3, the person may use alternative slope factors when the following conditions are met:

(A) The person may use the lower reference point of the upper bound slope factors (0.4 (mg/kg-day)^-1 ) to calculate an inhalation unit risk factor when evaluating inhalation exposures to volatilized polychlorinated biphenyls. The person must still use the upper reference point of the upper bound slope factors (2 (mg/kg-day)^-1 ) to evaluate inhalation exposures to particulate phase polychlorinated biphenyls.

(B) The person may conduct congener or isomer analyses. The person may use the lowest reference point of the upper-bound slope factors (0.07 (mg/kg-day)^-1 ) for the soil ingestion, dermal contact with soil, and inhalation exposure pathways if congener or isomer analyses verify that congeners with more than four chlorines comprise less than one-half percent of total polychlorinated biphenyls in a given exposure medium. The upper reference point of the upper-bound slope factors (2 (mg/kg-day)^-1 ) shall be used for all other exposure pathways regardless of the results of the congener- or isomer-specific analyses. If congener or isomer analyses indicate that congeners with more than four chlorines comprise greater than one-half percent of total polychlorinated biphenyls in a given exposure medium, then the person shall use the upper-reference point of the upper-bound slope factors (2 (mg/kg-day)^-1 ) for all pathways for that specific exposure medium. Further, when congener concentrations are available, the contribution of dioxin-like polychlorinated biphenyls to total dioxin equivalents shall be considered. The person shall apply the toxicity equivalency factors specified in the following figure to the measured concentrations for each of the dioxin-like polychlorinated biphenyls. These values shall then be summed to obtain a 2,3,7,8-TCDD toxicity equivalency quotient. Toxicity equivalency quotients for dioxin-like polychlorinated biphenyls shall then be added to those for other dioxin-like compounds as specified in subsection (e) of this section to yield a total toxicity equivalency quotient concentration. This total toxicity equivalency quotients concentration shall then be compared with the critical PCL for TCDD, 2,3,7,8-(dioxin). When addressing dioxin-like polychlorinated biphenyls in this manner, the person shall subtract the concentration of dioxin-like polychlorinated biphenyls from the total polychlorinated biphenyls concentration to avoid overestimating dioxin-like polychlorinated biphenyls by evaluating them twice.

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(3) In evaluating inhalation exposures under Tiers 2 or 3, the person shall convert the appropriate slope factor to an inhalation unit risk factor, based on the following equation: Inhalation Unit Risk Factor (risk per µg/m³ )= oral slope factor x 20 m³ /day divided by 70 kg x 10 ^-3 mg/µg.

(4) In Tiers 2 and 3, and only when applicable for a specific site, the person may set soil PCLs based on the requirements of the Toxic Substances Control Act, 40 Code of Federal Regulations Parts 750 and 761, as amended. Sites must comply fully with all applicable Toxic Substances Control Act, as amended, requirements when establishing the soil PCL for polychlorinated biphenyls in this manner.

(e) Polychlorinated Dibenzo-p-Dioxins and Dibenzofurans.

(1) In demonstrating attainment of the critical PCL for TCDD, 2,3,7,8-(dioxin), the person shall apply the toxicity equivalency factor as shown in the figure in subsection (d)(2)(B) of this section to the measured concentrations in accordance with the following procedures.

(A) When analytical data are only available for total dioxins/furans, the person shall assume that the mixture consists solely of 2,3,7,8-TCDD, and a toxicity equivalency factor value of 1.0 shall be applied to the measured concentration to yield the 2,3,7,8-TCDD toxicity equivalency quotient concentration for the sample.

(B) When homologue-specific analytical data are available (e.g., tetrachlorodibenzodioxins), the person shall assume that each homologue class is comprised solely of 2,3,7,8-substituted congeners, and the toxicity equivalency factor specified for the 2, 3, 7, 8-substituted congeners in the homologue class shall be applied to the measured concentrations for that homologue class. A toxicity equivalency factor value of 0.5 should be used for the pentachlorodibenzofuran homologue class. The toxicity equivalency quotient concentrations for each homologue class shall be summed to obtain a total toxicity equivalency quotient concentration for the sample.

(C) When congener-specific analytical data are available (e.g., 1, 2, 3, 4, 7, 8-hexachlorodibenzofuran), the person shall apply the toxicity equivalency factor for the 2, 3, 7, 8-substituted congeners to the measured concentrations. The toxicity equivalency quotient concentrations for each 2, 3, 7, 8-substituted congener shall then be summed to obtain a total toxicity equivalency quotient concentration for the sample.

(2) The person shall then compare the total toxicity equivalency quotient concentration established in paragraph (1) of this subsection to the critical PCL for TCDD, 2, 3, 7, 8-(dioxins).

(3) The critical soil PCL for residential properties for all three tiers is 1 part per billion (ppb) and for commercial/industrial properties for all three tiers is 5 ppb.

(f) Polycyclic Aromatic Hydrocarbons.

(1) In calculating residential and commercial/industrial PCLs for all tiers, the person shall evaluate the following seven polycyclic aromatic hydrocarbons as carcinogens:

(A) benzo {a} anthracene;

(B) benzo {b} fluoranthene;

(C) benzo {k} fluoranthene;

(D) benzo {a} pyrene (B {a} P);

(E) chrysene;

(F) dibenzo {a, h} anthracene; and

(G) indeno {1, 2, 3-c, d} pyrene.

(2) The person shall use the relative potency factors outlined in the following figure to estimate cancer slope factors and unit risk estimates for each of the polycyclic aromatic hydrocarbons identified in paragraph (1) of this subsection for all exposure pathways (e.g., the soil ingestion, vegetable ingestion, inhalation, dermal contact with soil, and groundwater ingestion (in the absence of a primary MCL) exposure pathways):

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(3) The cancer slope factors and inhalation unit risk factors for the seven carcinogenic polycyclic aromatic hydrocarbons, shall be calculated according to the equations set forth in the following figure:

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(4) The person shall not apply the relative potency factor for any pathways when evaluating noncarcinogenic endpoints.

(5) For class 1 or 2 groundwater, the person shall establish PCLs according to the procedures in subparagraphs (A) and (B) of this paragraph.

(A) In evaluating residential and commercial/industrial exposures to class 1 and 2 groundwater for all tiers, the person shall use the most currently available primary MCL for benzo{a}pyrene as ^GW GW_Ing for benzo{a}pyrene.

(B) In establishing ^GW GW_Ing for class 1 and 2 groundwater for the six remaining carcinogenic polycyclic aromatic hydrocarbons, the person shall use the higher of the calculated ^GW RBEL _Ing or the primary MCL for B{a}P as ^GW GW_Ing for that specific polycyclic aromatic hydrocarbon. In the event that primary MCLs for the other carcinogenic polycyclic aromatic hydrocarbons become available, those MCLs would serve as ^GW GW_Ing for these compounds.

(g) Total Petroleum Hydrocarbons.

(1) The person shall follow the methodology prescribed by this subsection to establish PCLs for total petroleum hydrocarbons, unless the executive director approves the use of an alternate method.

(2) In order to establish PCLs for total petroleum hydrocarbons, the person shall establish PCLs for each of the aliphatic and aromatic hydrocarbon fractions listed in the following figure (e.g., aliphatic >C ₆ -C₈ ) for the mandatory and complete or reasonably anticipated to be completed exposure pathways as required in §350.71(c) of this title (relating to General Requirements):

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(3) The person shall use the specific toxicity factors for the specific surrogates as shown in the figure in paragraph (2) of this subsection for a hydrocarbon fraction. If a reference concentration is not available, then the person shall not be required to comply with §350.73(c) of this title (relating to Determination and Use of Human Toxicity Factors and Chemical Properties). The PCLs established under this subsection shall be based on noncarcinogenic effects.

(4) The person shall ensure that the PCLs established for each hydrocarbon fraction comply with the hazard quotient criteria as set forth in §350.72 of this title (relating to Carcinogenic Risk Levels and Hazard Indices for Human Health Exposure Pathways).

(5) The person shall ensure that the PCLs established for the total petroleum hydrocarbons comply with the hazard index criteria as set forth in §350.72 of this title considering only the hydrocarbon fractions as shown in the figure in paragraph (2) of this subsection. The person shall follow the methodology prescribed in §350.72(d) of this title to adjust the hydrocarbon fraction PCLs to meet the hazard index criteria for the total petroleum hydrocarbons.

(6) The person shall use an analytical method approved by the executive director to determine the concentration of the hydrocarbon fractions at the affected property.

(7) When the bulk total petroleum hydrocarbons composition can be assumed to be relatively consistent based on process knowledge, the person may establish mixture-specific (e.g., gasoline, diesel, transformer mineral oil, or other petroleum product) PCLs based on property-specific mixture compositions or mixture compositions considered to be representative of the mixture. The person shall comply with the other provisions of this subsection in the development of the mixture-specific PCLs, but the person shall be allowed to determine compliance with the mixture-specific total petroleum hydrocarbons PCL with a bulk total petroleum hydrocarbons analytical method acceptable to the executive director in lieu of analysis of the concentration of each hydrocarbon fraction.

(8) The PCLs established for each individual aliphatic and aromatic hydrocarbon fraction used to establish the mixture specific PCLs shall not exceed a hazard quotient of 1 and the mixture-specific PCL shall not exceed a hazard index of 10.

Source Note: The provisions of this §350.76 adopted to be effective September 23, 1999, 24 TexReg 7436; amended to be effective March 19, 2007, 32 TexReg 1526