(a) In all cases, the toxicity factors used must be protective of human health and the environment. The person shall use the chronic human toxicity factors taken from the following hierarchy of sources (unless otherwise specified in §350.76 of this title (relating to Approaches for Specific Chemicals of Concern to Determine Human Health Protective Concentration Levels)) unless the specific provision contained in subsection (b) of this section applies. The person shall use the source in paragraph (1) of this subsection and only if the relevant chronic human toxicity factor is not available in that source, proceed to the source in paragraph (2) of this section and, only if the toxicity factor is not available in that source, proceed in the same fashion through sources in paragraphs (3) - (7) of this subsection. The chronic human toxicity factors, in order of hierarchy of sources in paragraphs (1) - (7) of this subsection, which are most current as of the submittal date of the SIN or the RAP are presumed to be protective of human health and the environment, unless a person rebuts this presumption by published credible authority. In addition, the executive director may determine during review of the RACR that a change in a toxicity factor since the submittal of the SIN or RAP has been of such a magnitude that the PCLs previously developed for a COC would clearly not be protective of human health and the environment, then the adequacy of the response action must be reevaluated. Likewise, if the executive director determines at any time that a subsequent change in a toxicity factor is of such a magnitude such that the proposed response action is no longer warranted to protect human health and the environment, then a response action based on that previous chronic toxicity factor consideration shall no longer be required.
  (1) United States Environmental Protection Agency (EPA) Integrated Risk Information System (IRIS);
  (2) EPA Provisional Peer Reviewed Toxicity Values (i.e., Superfund Health Risk Technical Support Center;
  (3) EPA Health Effects Assessment Summary Tables;
  (4) EPA National Center for Environmental Assessment (i.e., Superfund Technical Support Center);
  (5) the TCEQ Chronic Remediation-Specific Effects Screening Levels;
  (6) Agency for Toxic Substances and Disease Registry; and
  (7) other scientifically valid sources as approved by the executive director.
(b) The executive director may direct a person to use a chronic human toxicity factor from a source other than that selected in accordance with the source hierarchy list provided in subsection (a) of this section in cases where the executive director has determined it to be necessary to use a more scientifically valid chronic human toxicity factor than that from the source identified in accordance with subsection (a) of this section.
(c) If the executive director determines that it is necessary to evaluate COCs which do not have any human chronic toxicity factors provided in the sources listed in subsection (a) of this section, then the executive director will provide chronic toxicity factors. The person may provide toxicological information to the executive director for consideration in the derivation of the chronic toxicity factors. The person shall provide all toxicological data from any toxicological studies conducted for the person when such information is requested by the executive director. The person shall use the TCEQ Chronic Remediation-Specific Effects Screening Level value as the reference concentration in evaluating the inhalation pathway for both residential and commercial/industrial land use in accordance with §350.75(i)(3), (6) and (8) of this title (relating to Tiered Human Health Protective Concentration Level Evaluation), and all chronic inhalation exposure pathways for which PCLs are established in accordance with §350.75(i)(5) and (11) of this title, but only in cases where neither an EPA unit risk factor nor an EPA reference concentration is available for that COC from the hierarchy list provided in subsection (a) of this section, and the executive director has not directed the person to use a toxicity factor in accordance with subsection (b) of this section.
(d) Unless prior approval is provided by the executive director in accordance with §350.74(j)(2) of this title (relating to Development of Risk-Based Exposure Limits) to use a subchronic exposure duration (i.e., < nyears) for a commercial/industrial property, the person shall not use subchronic toxicity factors.
(e) In the situation where different reference doses have been established for a COC based on water ingestion and food consumption, the person shall use the reference dose for water ingestion for the water ingestion exposure pathway and the reference dose for food consumption for all soil exposure pathways.
(f) The person shall use the COC chemical/physical parameter values for COCs provided in the following figure to calculate PCLs, unless the executive director approves the use of a more representative alternative value in accordance with paragraphs (1) and (2) of this subsection. For those COCs not included in the figure in this subsection, the person may provide chemical/physical information to the executive director for consideration in developing appropriate chemical/physical parameters.
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  (1) For Tiers 2 and 3, the person may determine property-specific soil pH in order to account for the high pH dependence of the soil-water partition coefficient (Kd ) of inorganic compounds and the organic carbon-water partition coefficient (Koc ) of ionizing organic compounds. Once the property-specific pH is determined, the person shall apply subparagraphs (A) - (C) of this paragraph as applicable to determine pH-dependent Kd and K oc values unless another appropriate method is approved by the executive director. The executive director may also approve the use of data from appropriately-conducted tests in determining a site-specific Kd or Koc .
    (A) For aluminum and lead, the person shall select a Kd from the following figure in accordance with the pH range and the total weight percent of clay, organic matter, iron, and aluminum oxyhydroxide representative of the affected property soils.
Attached Graphic
    (B) The person shall use the following figure to determine the pH-dependent Koc value for the ionizing organic COCs listed.
Attached Graphic
    (C) The person shall use the following figure to determine the pH-dependent Kd value for the inorganic COCs listed.
Attached Graphic
  (2) For Tiers 2 and 3, the person may establish alternate soil-to-plant biotransfer factors (Brabg and Br bg ) by establishing the pH of the soil and the soil type, and then identifying a biotransfer factor in the published literature appropriate for those soil conditions. Alternatively, the person can measure the biotransfer factor in accordance with procedures acceptable to the executive director.

Source Note: The provisions of this §350.73 adopted to be effective September 23, 1999, 24 TexReg 7436 ; amended to be effective March 19, 2007, 32 TexReg 1526