The Wise Report
Henry M. Wise, P.G.
August 31, 2024
The Texas Commission on Environmental Quality (TCEQ, agency, or commission) proposes amendments to §350.76, concerning Approaches for Specific Chemicals of Concern to Determine Human Health Protective Concentration Levels. The purpose of this rulemaking is to amend 30 Texas Administrative Code (TAC) Chapter 350, Texas Risk Reduction Program (TRRP) rule §350.76, pertaining to the chemical-specific approaches used for developing and demonstrating attainment of the critical human health protective concentration levels (PCLs) for dioxins/furans and dioxin-like polychlorinated biphenyls (PCBs).
The TCEQ proposes to update the approach for developing soil PCLs for dioxins/furans and dioxin-like PCBs used for residential and commercial/industrial land use under TRRP. The current approach is covered in the TRRP rule in §350.76(d) and §350.76(e), and the current PCLs are specified in the TRRP rule at §350.76(e)(3). The PCLs contained in the existing TRRP rule were based on a then-current 1998 United States Environmental Protection Agency (EPA) policy memo (OSWER Directive 9200.4-26), which described an approach for addressing dioxins in soil. Since that time, the EPA completed a reassessment of this approach and derived an updated reference dose for dioxins. Based on more recent scientific evaluations, the TCEQ can support the use of a reference dose in the range of EPA's updated value, and that value will be reflected in the approach provided in this proposed rule revision. Upon the effective date of the adopted revisions, any activity conducted pursuant to TRRP must comply with the revised approach for developing dioxins/furans and dioxin-like PCBs and the soil PCLs used for residential and commercial/industrial land use under TRRP.
Additionally, the proposed rule revision updates the toxicity equivalency factors (TEFs) related to dioxins/furans and dioxin-like PCBs contained in §350.76(d)(2)(B). Dioxins/furans and dioxin-like PCBs are mixtures of chemical compounds (congeners) with different toxicities. TRRP §§350.76(d) and (e) use TEFs to assess the relative toxicity of the individual congeners compared to the toxicity of the most toxic congener, 2,3,7,8-tetrachlorodibenzodioxin (2,3,7,8-TCDD), within a mixture of dioxins/furans and dioxin-like PCBs. The TEFs are applied as a multiplier of the concentration of each measured congener to calculate a 2,3,7,8-TCDD toxicity equivalency quotient (TEQ) concentration. The resulting 2,3,7,8-TCDD TEQ concentrations for each congener are summed to derive a total 2,3,7,8-TCDD TEQ concentration for the entire mixture. The total 2,3,7,8-TCDD TEQ concentration is then compared to a 2,3,7,8-TCDD PCL to determine the nature and extent of contamination and whether a remedy is required. The TRRP rule provides specific TEFs for various dioxins/furans and dioxin-like PCB compounds and directs persons to use these TEF values when demonstrating attainment of the critical PCL.
Henry M. Wise, P.G.
The Wise Report
8/31/2024