(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 GWIng ). 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 GWClass 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 GWInh-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 SWEco 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 SWEco 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.
Cont'd...