SECTION 350.75. Tiered Human Health Protective Concentration Level Evaluation

(a) General.

(1) The person shall decide whether to use Tier 1, 2, and/or 3 to determine the PCLs for an affected property, except as provided in paragraph (2) of this subsection and unless required by subsection (b), (c), or (d) of this section.

(2) The executive director may require the person to establish PCLs in accordance with Tier 1, 2, and/or 3 for state-funded response actions at affected properties.

(b) Tier 1 PCLs.

(1) Tier 1 is a risk-based analysis to derive non-site-specific PCLs for complete or reasonably anticipated to be completed exposure pathways. Tier 1 is based on default exposure factors and affected property parameters in the applicable PCL equations provided in the following figure and assumes exposure occurs at, above or below the source area (i.e., no lateral transport).

Attached Graphic

(2) No lateral transport equations may be used for a Tier 1 evaluation other than to ensure that receptors at off-site POEs are protected when on-site commercial/industrial land use is assumed. The person shall assume a 0.5 acre source area for an affected property with a 0.5 acre or less source area and a 30 acre source area for an affected property with a source area in excess of 0.5 acres. The size of the source area in soil and groundwater shall be determined using the soil or groundwater assessment level calculated for a 0.5 acre source area. The executive director may require that the source area include all areas of the affected property which exceed the assessment level and not just contiguous areas when such assumption is appropriate considering the distribution of the COCs.

(3) The person shall establish PCLs using parameters which are specific to the affected property when use of the Tier 1 default affected property parameters would not be protective or when requested by the executive director. The person shall then establish PCLs in accordance with subsections (c) or (d) of this section.

(4) The person shall establish PCLs in accordance with subsections (c) or (d) of this section for any groundwater, soil, surface water, air, or sediment human health exposure pathway which is complete or reasonably anticipated to be completed at an affected property and for which an equation is not referenced in this subsection.

(c) Tier 2 PCLs.

(1) Tier 2 is a risk-based analysis to derive site-specific PCLs for complete or reasonably anticipated to be completed exposure pathways utilizing site-specific exposure factors, as allowable, and/or affected property parameters and Tier 1 equations. Tier 2 PCLs may also include lateral transport considerations.

(2) The person shall use:

(A) the relevant RBELs appropriate for the type of COC, exposure pathway, receptor, and land use provided in §350.74 of this title (relating to Development of Risk-Based Exposure Limits);

(B) PCL equations provided by the executive director in guidance, in addition to the PCL equations as shown in the figure in subsection (b)(1) of this section;

(C) the Tier 1 default affected property parameters or appropriately collected and representative site-specific affected property parameters in the PCL equations, unless an entry of "No" in the column titled "Change To Tier 1 Default Allowed?" in the figure as shown in subsection (b)(1) of this section indicates that a particular Tier 1 affected property parameter value shall not be modified under a Tier 2 evaluation; and

(D) PCLs established in accordance with subsection (d) of this section for any groundwater, soil, surface water, air, or sediment exposure pathway which is complete or reasonably anticipated to be completed at an affected property and for which an equation is not referenced either in this subsection or in subsection (b)(1) of this section.

(d) Tier 3 PCLs.

(1) Tier 3 is a risk-based analysis to derive site-specific PCLs for complete or reasonably anticipated to be completed exposure pathways. Tier 3 PCLs are based on measured natural attenuation factors and/or natural attenuation factor models/equations other than those provided for Tier 1 or 2; and may also include site-specific exposure factors, as allowable, and/or affected property parameters.

(2) The person shall use:

(A) field measured natural attenuation factors and/or appropriate natural attenuation factor equations/models other than the Tier 1 and 2 PCL equations;

(B) appropriate equations/models for any remaining surface water, air, or sediment human exposure pathway which is complete or reasonably anticipated to be completed at an affected property and for which an equation is not referenced in subsection (b) or (c) of this section; and

(C) the Tier 1 default affected property parameters or appropriately collected and representative site-specific affected property parameters in the PCL equations, unless an entry of "No" in the column titled "Change To Tier 1 Default Allowed?" in the figure as shown in subsection (b)(1) of this section indicates that a particular Tier 1 affected property parameter value shall not be modified under a Tier 3 evaluation.

(e) Natural attenuation factor documentation. The person must document the use of all natural attenuation factor equations/models other than the natural attenuation factor equations/models provided in this subchapter or agency guidance, such that the derivation of the model and its site-specific application can be understood, and the results of the model reproduced by the executive director. The executive director may require the person to obtain prior approval for the use of alternative natural attenuation factor equations/models in a Tier 3 evaluation.

(f) Decay factors. When the person uses decay factors in any cross-media or lateral transport natural attenuation factor equation in either Tier 2 or 3, the person shall use sufficient monitoring data (i.e., vapor, soils and groundwater samples for COCs or other degradation indicators) to verify the COC is degrading.

(g) Verification. When natural attenuation factor modeling outputs are inconsistent with monitoring data for environmental media at an affected property, the person and the executive director shall generally place more weight on the monitoring data. The executive director may require the person to provide sufficient monitoring data to verify that PCLs established under any tier are based on an appropriate understanding of conditions at the affected property.

(h) Data adequacy. The person shall collect any additional data necessary to support the development of PCLs under any of the tiers.

(i) Pathway specific PCL Considerations.

(1) PCLs for ingestion of COCs in class 1 or 2 groundwater (^GW GW_Ing ). The person shall establish this PCL using the applicable equation shown in the figure in subsection (b)(1) of this section.

(2) PCLs for COCs in class 3 groundwater ( ^GW GW_{Class 3} ). The person shall establish this PCL using the applicable equation in the figure in subsection (b)(1) of this section.

(3) PCLs for inhalation of volatile emissions in outdoor air from COCs in groundwater-bearing units (^Air GW_Inh-V ). The person shall establish this PCL using the applicable equations as shown in the figure in subsection (b)(1) of this section for Tier 1.

(4) PCLs for COCs in groundwater discharge to surface water (^SW GW). The person shall set ^SW GW equal to ^SW SW divided by the surface water dilution factor. The ^SW SW is the lesser of the ^SW RBEL established in accordance with §350.74(h) of this title and the SW_Eco established in accordance with §350.77 of this title (relating to Ecological Risk Assessment and Development of Ecological Protective Concentration Levels). The surface water dilution factor shall be determined in accordance with subparagraph (A) or (B) of this paragraph. The person shall use the PCL equation as shown in the figure in subsection (b)(1) of this section to establish ^SW GW. In the case that different surface water dilution factors may be applicable to the ^SW RBEL and the SW _Eco , the person shall first divide the ^SW RBEL and the SW_Eco by their respective surface water dilution factors and set ^SW GW equal to the lowest resulting quotient.

(A) The person shall assume a surface water dilution factor of one when the concentration of all COCs in groundwater at the zone of discharge to surface water is less than or equal to the ^SW SW for those COCs at the time the affected property assessment required in §350.51 of this title (relating to Affected Property Assessment) is conducted. The person shall also assume a surface water dilution factor of one for those specific COCs which are listed as impairing the nearest classified segment at or downstream of the affected property. Impaired water bodies are provided in the current Clean Water Act, §303(d) list, as amended.

(B) When the concentration of a COC in groundwater at the zone of discharge to surface water exceeds the ^SW SW for that COC at the time the affected property assessment required in §350.51 of this title is conducted, the person may establish a surface water dilution factor in accordance with subparagraph (C), (D), or (E) of this paragraph.

(C) The person may use a surface water dilution factor of 0.15 for non-flowing surface waters such as lakes, estuaries, tidal rivers; and fresh water streams and rivers (where the groundwater discharge is clearly less than 15% of the 7Q2 stream flow as defined in §307.3(a)(34) of this title (relating to Definitions and Abbreviations)), as amended. The person shall use the 7Q2 flows as listed in §307.10(2) of this title (relating to Appendices A - E), as amended, for groundwater discharges directly to a classified segment as listed in §307.10(3) of this title, as amended. For groundwater discharges which are not directly to a classified segment, site-specific 7Q2 values must be determined for the water body directly receiving the groundwater discharge.

(D) For freshwater streams and rivers where the groundwater discharge is clearly greater than 15% of the 7Q2 flow, the person shall estimate property-specific surface water dilution factors based on 7Q2 flows for chronic aquatic-life criteria, 25% of 7Q2 flows for acute aquatic-life criteria, and harmonic mean flows as defined in §307.3(a)(19) of this title, as amended, for human health criteria in accordance with the procedures contained in the Implementation Procedures, as amended. The person shall divide the ^SW SW by the estimated property-specific dilution factor. The person shall use the 7Q2 flows listed in §307.10(2) of this title, as amended, for groundwater discharges directly to a classified segment as listed in §307.10(3) of this title, as amended. For groundwater discharges which are not directly to a classified segment, site-specific 7Q2 values must be determined for the water body directly receiving the groundwater discharge.

(E) As an alternative to using the dilution factor of 0.15 as specified in subparagraph (C) of this paragraph, the person may measure and/or estimate the groundwater dilution in surface water from appropriate models of groundwater plume dispersion, tracer studies, receiving water and sediment sample analyses, analytical calculations, or other techniques upon the executive director's approval using site-specific base flow conditions for groundwater, 7Q2 conditions for receiving streams, and critical mixing conditions for lakes, estuaries, and tidal streams. The executive director may require a receiving water study to ensure that benthic communities in the sediment are not adversely impacted. In cases where groundwater COCs include bioaccumulative COCs, the executive director may require a receiving water study or empirical analysis to ensure that the release of that particular COC is not causing, or will not result in harmful levels in the tissue of aquatic and terrestrial organisms that feed in the water body.

(F) The person may be required by the executive director to take appropriate action to ensure that discharging groundwater plumes do not result in exceedances of surface water quality standards in significant areas of the potentially affected surface water body.

(5) PCLs for other complete or reasonably anticipated to be completed groundwater exposure pathways. The person shall establish PCLs for exposure pathways other than those listed in paragraphs (1) - (4) of this subsection when, in the executive director's determination, those other exposure pathways are complete or reasonably anticipated to be completed.

(6) PCLs for the combined exposure pathways of inhalation of volatile emissions and particulates from COCs in surface soil, dermal contact with COCs in surface soil, ingestion of COCs in surface soil, and for affected residential properties, ingestion of aboveground and below-ground vegetables grown in surface soil containing COCs (^Tot Soil_comb ). The person shall establish this PCL using the applicable equation as shown in the figure in subsection (b)(1) of this section for Tier 1.

(7) PCLs for groundwater protection from leachate containing COCs from surface and subsurface soil (^GW Soil).

(A) The person shall establish ^GW Soil for each COC present in the surface and subsurface soil such that soil leachate is protective for:

(i) the critical groundwater PCL established in §350.78 of this title (relating to Determination of Critical Protective Concentration Levels) when the use of a plume management zone is not authorized in §350.33(f)(4) of this title (relating to Remedy Standard B);

(ii) the attenuation action level for the nearest monitoring point when the use of a plume management zone is authorized under §350.33(f)(4) of this title; and/or

(iii) the maximum concentration of COCs in the groundwater source area at the time of RAP submittal when a plume management zone is authorized for class 2 groundwater in response to §350.33(f)(4) of this title.

(B) The person shall establish this PCL using the applicable equations as shown in the figure in subsection (b)(1) of this section for Tier 1.

(C) The person may not be required to establish a soil leachate-to-groundwater PCL in accordance with subparagraphs (A) and (B) of this paragraph when a demonstration can be made with appropriate soil and groundwater monitoring data that the soils will attain the soil response objectives for groundwater protection set forth in Subchapter B of this chapter (relating to Remedy Standards). The determination that the soils are adequately protective shall be based on soil sample data, the concentration trends of groundwater monitoring data over time when groundwater is impacted, probable time since release occurred, adequate identification of the soil source areas, appropriate leachate test results, or other hydrogeologic or property-specific information. The executive director may also require that the change in soil concentrations over time be documented to support this evaluation in a property-specific situation. The executive director may require the person to install a sufficient number of groundwater monitoring wells to demonstrate that groundwater is not affected when soil COC concentration data are inadequate to sufficiently substantiate that groundwater is not affected.

(8) PCLs for inhalation of volatile emissions in outdoor air from COCs in subsurface soils (^Air Soil _Inh-V ). The person shall establish this PCL using the applicable equations as shown in the figure in subsection (b)(1) of this section for Tier 1.

(9) Theoretical soil saturation limit (C _sat ). The person may establish a property-specific theoretical soil saturation limit for the volatilization exposure pathways required in paragraphs (6) and (8) of this subsection under Tiers 2 or 3. The C _sat shall be based on the same property-specific parameters as those used to calculate ^Air Soil _Inh-V . If the property-specific ^Air Soil_Inh-VP or ^Air Soil_Inh-V is greater than the property-specific C_sat , then that exposure pathway shall not be considered a relevant exposure pathway for that COC.

(10) Residual soil saturation limit (Soil _Res ). The person shall establish the residual saturation level for each organic COC present in surface and subsurface soils which is a liquid at standard temperature and pressure using the applicable equation as shown in the figure in subsection (b)(1) of this section to estimate the mobile NAPL concentration and to determine if NAPL may be present.

(11) PCLs for other complete or reasonably anticipated to be completed surface and subsurface soil exposure pathways. The person shall establish PCLs for surface and subsurface soil exposure pathways other than those listed in paragraphs (6) - (8) of this subsection when, in the executive director's determination, those other exposure pathways are complete or reasonably anticipated to be completed.

(12) Air inhalation exposure pathways ( ^Air Air_Inh ). For air inhalation exposure pathways, the person may be required by the executive director to establish ^Air Air_Inh solely for the purposes of determining the protective concentration that must be met in air at the POE. The person shall use the applicable equation as shown in the figure in subsection (b)(1) of this section to establish ^Air Air_Inh .

(13) Surface water exposure pathways ( ^SW SW). The person may be required by the executive director to establish ^SW SW when COCs are present in surface water or when COCs will enter into surface water due to a release, and a surface water response action is necessary to protect human or ecological receptors. The person shall use the applicable equation as shown in the figure in subsection (b)(1) of this section to establish ^SW SW.

(14) Other air and surface water exposure pathways. The person shall establish PCLs for air and surface water exposure pathways other than those listed in paragraphs (12) and (13) of this subsection when, in the executive director's determination, those other exposure pathways are complete or reasonably anticipated to be completed.

(15) The person shall establish PCLs for complete or reasonably anticipated to be completed sediment exposure pathways when, in the executive director's determination, those exposure pathways are complete or reasonably anticipated to be completed.

(j) The person is not required to combine exposure pathways for a single environmental medium when determining PCLs with the exception of the combined exposure pathway required in subsection (i)(6) of this section, unless otherwise directed by the executive director.

Source Note: The provisions of this §350.75 adopted to be effective September 23, 1999, 24 TexReg 7436; amended to be effective March 19, 2007, 32 TexReg 1526