SECTION 334.203. Risk-Based Criteria for Establishing Target Concentrations

Owners and operators shall apply the following risk-based criteria to evaluate sites and determine target concentrations:

(1) Plan A site evaluation criteria. The owner and operator should use Plan A established target concentrations to screen sites for closure, or use the Plan A criteria to establish target concentrations for the purposes of establishing a corrective action plan in accordance with §334.81 of this title (relating to Corrective Action Plans), or to evaluate the potential benefit of further site evaluation under paragraph (2) of this section.

(A) The owner and operator shall consider potential exposure to receptors through direct and indirect exposure pathways as required by the agency and determine whether or not such pathways are complete. A pathway is considered complete if there is a source area, a transport mechanism and an existing or potential receptor;

(B) For complete pathways, target concentrations shall be calculated using equations and models, target risk goals, and exposure factors as established by the agency;

(C) Target concentrations shall be based upon chemical property information defined by the agency when such information is provided by the agency;

(D) Target concentrations for indirect or cross-media pathways shall be based upon default media property assumptions defined by the agency when site-specific media property information is not available;

(E) Target concentrations shall be based upon residential land use unless the owner and operator satisfies the requirements of §334.204 of this title (relating to Criteria for Selection of Land Use) to demonstrate commercial/industrial land use is more appropriate.

(F) The owner and operator shall use equations and models as required by the agency to calculate target concentrations;

(G) Target air concentrations shall be evaluated when there is concern of a potential vapor hazard, or known or suspected indoor air exposure to regulated substances. Regulated substance concentrations in soils and groundwater are not to generate vapors in soil, air, utilities, or in the atmosphere which could cause an explosive atmosphere at any surface or subsurface structure. The presence of free product and associated level of vapors and the presence of conduits or pathways such as utility conduits, foundation piers, foundation cracks that may act as a transport pathway should be considered in this determination;

(H) Target surface water concentrations shall be as provided in the Texas Surface Water Quality Standards of Chapter 307 of this title (relating to Supplemental Surface Water Quality Standards) and Chapter 319 of this title (relating to General Regulations Incorporated Into Permits). If those values are not available or appropriate, then federal maximum contaminant levels (MCLs) promulgated under the federal Safe Drinking Water Act (42 Code of Federal Regulations §300f, et seq.) shall apply. If MCLs are not available or appropriate, then the target surface water concentrations are to be based on reasonable maximum exposure expected to occur through human ingestion of the water;

(I) Target groundwater concentration criteria:

(i) the actual beneficial use or potential beneficial use of the affected groundwater shall be considered;

(ii) groundwater with a natural total dissolved solids content of less than 10,000 mg/l and which is capable of yielding useable quantities of water to a well or spring shall be considered to have a potential beneficial use. When no site-specific data is available, the affected groundwater shall be considered to be potentially useable;

(iii) residential groundwater ingestion shall be the default exposure pathway unless the owner and operator can show to the satisfaction of the agency that the documented actual beneficial use of the affected groundwater is for a use other than drinking water purposes;

(iv) the individual carcinogenic risk must not exceed a range of 1 X 10^-6 to 1 X 10^-4 as required by the agency for beneficial use groundwaters. For any carcinogen, if the federally promulgated MCL is a higher value (less stringent), then the MCL may be used;

(v) the hazard quotient for non-carcinogens shall not exceed unity (one) for beneficial use groundwater;

(vi) Only the removal of non-aqueous phase liquid as required pursuant to §334.79 of this title (relating to Removal of Non-Aqueous Phase Liquid) and any subsequent monitoring as required by the agency shall be necessary when the affected groundwater is of no potential beneficial use provided the owner and operator can document to the satisfaction of the agency that the dissolved regulated substance concentrations for such groundwater that is less than 15 feet deep, is protective of potential direct contact by construction workers; that any explosive vapors, adverse affects to subsurface utilities, nuisance conditions, discharge of regulated substances to surface waters at unprotective levels, and plume expansion have been abated and should not occur in the future. When any of these conditions are not met with only the removal of non-aqueous phase liquid, then target groundwater concentrations shall be established by the owner and operator so as to meet these conditions;

(vii) Target groundwater concentrations shall apply throughout the groundwater plume; and

(viii) If remaining groundwater concentrations will discharge to a surface water body or other potentially usable aquifer at an unprotective level, then an additional compliance point shall be established for the point of discharge. The target groundwater concentration to be applied at the additional compliance point(s) shall be based on the applicable target concentration for the receiving water.

(J) Target soil concentration criteria:

(i) ingestion of soils from ground surface to a depth of 15 feet for residential and commercial/industrial land uses unless the owner and operator can provide documentation to the satisfaction of the agency that an alternate depth is more appropriate. Fifteen feet in the opinion of the agency represents a reasonable depth above which soil could be excavated and brought to the ground surface during construction activities;

(ii) inhalation of volatile and particulate emissions for residential and commercial/industrial land uses, when the soil from ground surface to a depth of 15 feet is affected, but not covered with an impermeable surface. If the owner and operator can provide sufficient evidence that the impermeable surface will be maintained and will prevent inhalation exposure, then inhalation from soil contaminants may be dropped from further analysis;

(iii) cross-media affects (e.g., soil leachate to groundwater);

(iv) the target soil concentration shall be the lower concentration of clauses (i), (ii) or (iii) of this subparagraph;

(v) reasonable maximum exposure expected to occur under both current and future land use for either residential or commercial/industrial as appropriate for the site;

(vi) maximum detected concentrations of regulated substances remaining in place;

(vii) the individual carcinogenic risk shall not exceed 1 X 10^-6 for Class A and B carcinogens and 1 X 10^-5 for Class C carcinogens; and

(viii) the hazard quotient must not exceed unity (one) for non-carcinogens;

(K) Target concentrations for soil, air and water shall also take into account other factors such as vegetation effects, sensitive environmental receptors, and aesthetic considerations (e.g., stained surface soils) as appropriate in the final analysis;

(L) The maximum levels of regulated substances remaining in all affected media shall meet the established target concentrations throughout the entire extent of affected area unless the owner and operator can demonstrate to the satisfaction of the agency that such action is technically infeasible and that public health and the environment are otherwise adequately protected;

(M) The owner and operator shall submit reports in accordance with a schedule and in a format established by the agency;

(N) The owner and operator or agency may recommend institutional controls in accordance with §334.205 of this title (relating to Institutional Control Requirements) to reinforce exposure assumptions; and

(O) Any necessary requirements as established by the agency to protect public health, safety, and the environment.

(2) Plan B site-evaluation criteria. The owner and operator may elect to further evaluate a site under Plan B to determine more appropriate target concentrations for affected media which may be used to justify a closure recommendation, or for the purposes of establishing a corrective action plan in accordance with §334.81 of this title.

(A) The owner and operator shall consider potential exposure to receptors through direct and indirect exposure pathways as required by the agency and determine whether or not such pathways are complete or not. A pathway determined to be incomplete in the Plan A evaluation does not need to be reevaluated under this subsection.

(B) For complete pathways, target concentrations shall be calculated using equations, target risk goals, and exposure factors as established by the agency.

(C) Target concentrations shall be based upon chemical property information defined by the agency when such information is provided by the agency.

(D) Target concentrations for indirect or cross-media pathways shall be based upon default media property assumptions and models defined by the agency when site-specific media property information is not available. Use of site-specific media property information is encouraged as part of this evaluation. If the owner and operator wish to use alternative models, prior concurrence from the agency shall be obtained.

(E) The agency may require owners and operators to collect additional site information prior to or after the evaluation of the site under this section to substantiate the conclusions of the evaluation.

(F) For known or suspected carcinogens, the individual and cumulative carcinogenic risk of 1 X 10^-6 to 1 X 10^-4 as required by the agency.

(G) Target concentrations are to be established at concentrations which do not exceed a hazard index of unity (one) for non-carcinogens.

(H) The owner and operator may apply target concentrations for direct exposure pathways calculated under paragraph (1) of this section at reasonable exposure points instead of the source area unless the source area is a reasonable exposure point. All exposure points assumptions are subject to approval by the agency.

(I) The agency may allow use of compliance points to serve as the basis for meeting target concentrations for indirect exposure pathways provided:

(i) the proposed compliance point locations are consistent with the results of the exposure assessment;

(ii) the proposed compliance point locations are upgradient of actual receptors;

(iii) the proposed compliance point locations will not allow unaffected receptors to become affected;

(iv) the proposed compliance point locations are accessible for monitoring/sampling;

(v) karst, fracture controlled, or otherwise highly complex hydrogeologic system is not involved;

(vi) estimates or predictions of compliance point concentrations and degree and rate of transport of regulated substances are verified with site monitoring data. Where site monitoring data and contaminant fate and transport modelling results yield conflicting information, the agency shall place more value on the monitoring data;

(vii) the agency may require the use of specific contaminant fate and transport models; and

(viii) target concentrations shall be met at all points beyond (downgradient of) the compliance point(s).

(J) When the criteria for the use of compliance points as required in subparagraph (I) of this paragraph cannot be met, then the target concentrations for indirect exposure pathways shall be met throughout the plume.

(K) Target concentrations for soil, air, and water shall also take into account other factors such as vegetation effects, sensitive environmental receptors, and aesthetic considerations (e.g., stained surface soils) as appropriate in the final analysis.

(L) The owner and operator, or the agency, may recommend the use of specific institutional controls to control or eliminate potentially viable exposure pathways, and to reinforce exposure assumptions and future land use assumptions.

(M) The owner and operator shall submit reports in accordance with a schedule and in a format established by the agency.

(N) The owner and operator shall meet all requirements imposed by the agency.

(3) Health-based target concentration established pursuant to paragraphs (1) or (2) of this section shall be based upon toxicological information current at the time the report is submitted to the agency. Toxicological information shall be from the following sources in order of listing:

(A) United States Environmental Protection Agency Integrated Risk Information System (IRIS);

(B) Health Effects Assessment Summary Table (HEAST);

(C) United States Environmental Protection Agency Criteria Documents;

(D) Agency for Toxic Substances and Disease Registry (ATSDR) Toxicological Profiles; and

(E) other scientifically valid published sources that are widely accepted.

(4) Target concentrations shall be based on the particular land use (residential or commercial/industrial) as defined in §334.202 of this title (relating to Definitions) of each affected property.

(5) The exposure assessment and determination of target concentrations conducted pursuant to paragraphs (1) or (2) of this section shall consider:

(A) the physical and chemical characteristics of the regulated substance, including its toxicity, persistence, and potential for migration;

(B) the hydrogeologic characteristics of the facility and the surrounding area;

(C) the proximity, quality, and current and future uses of nearby surface water and groundwater;

(D) the potential effects of residual contamination on nearby surface water and groundwater;

(E) an exposure assessment considering exposure pathways as requested by the agency;

(F) any information assembled in compliance with this subchapter; and

(G) any additional considerations as established by the agency.

(6) After receipt of a written statement by the agency that all corrective action regulations have been met and that no further corrective actions are warranted, then the case shall be considered closed unless a substantial change in circumstances results in an unacceptable risk to human health or the environment. A substantial change in circumstance shall include, but is not limited to:

(A) a failure to maintain the obligations of an institutional control as set out in §334.206 of this title (relating to Criteria for Institutional Control Use);

(B) a change in land use from a less sensitive land use to a more sensitive land use, such as commercial/ industrial to residential;

(C) an actual exposure condition is determined to be occurring at levels not protective of human health and safety, or the environment. For purposes of this subchapter, changes in toxicity values or general procedures utilized to determine target concentrations shall not be considered a substantial change in circumstances, unless these changes are of such magnitude to present an unacceptable threat to human health and safety, or the environment when evaluated for future exposure conditions based on site- specific considerations; or

(D) new information indicates that the regulated substances at the facility or affected area were not sufficiently characterized such that an unacceptable threat to human health and safety, or the environment continues to exist.

Source Note: The provisions of this §334.203 adopted to be effective November 8, 1995, 20 TexReg 8800; amended to be effective November 23, 2000, 25 TexReg 11442