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IDEM Releases TPH Guidance and Revised RISC Default Closure Tables


In a pair of announcements made in May and July, 2009, the Indiana Department of Environmental Management (“IDEM”) released revised RISC Default Closure Tables including the addition of new Default Closure Levels (“DCLs”) for three compounds and Total Petroleum Hydrocarbon (“TPH”) guidance with revised TPH DCLs.

Revised RISC Default Closure Tables

On May 1, 2009, the IDEM revised the RISC Default Closure Level Table (Table A), the Chemical/Physical Properties Table (Table B) and the Human Health Toxicity Parameters Table (Table F) in the 2006 RISC Technical Resource Guidance Document (“Technical Guide”) Appendix 1 to include revised and new DCLs. As part of these changes, the IDEM made the following revisions to Appendix 1 of the Technical Guide:

  • Added DCLs for ethylene glycol, propylene glycol monomethyl ether, and trichlorofluoromethane;
  • Eliminated DCLs applicable to bis(2-chloroisopropyl)ether;
  • Revised the RISC Default Closure Tables to reflect changes made in August 2006 revising the DCLs applicable to certain polycyclic aromatic hydrocarbons (acenaphthene, anthracene, benzo(b)fluoranthene, benzo(k)fluoranthene, chrysene, fluoranthene, fluorene, indeno(1,2,3-cd)pyrene, and pyrene);
  • Revised the RISC Default Closure Tables to reflect the November 2006 adoption of the proposed toxicity value for trichloroethylene (“TCE”) and posted additional information regarding the revised TCE DCLs at; and
  • Corrected the construction closure level for vinyl chloride.

TPH Guidance

On July 16, 2009, the IDEM announced substantial updates to the TPH DCLs and to site closure procedures. The July 16, 2009 announcement summarized the conclusions of a workgroup organized by the IDEM in cooperation with the Midwest States Environmental Consultants Association (“IDEM Workgroup”) to address challenges related to determining the nature and extent of TPH-ERO contamination in ground water. Among other actions, the IDEM Workgroup established revised TPH DCLs and developed a “weight of evidence approach” for closure of sites with TPH-DRO contaminated ground water.

The IDEM workgroup developed revised TPH DCLs through the substitution of revised toxicological surrogates used to calculate the closure levels. The result of the IDEM Workgroup’s use of updated toxicological surrogates was a substantial increase in the TPH DCLs. The following revised TPH DCLs were developed by the IDEM Workgroup:

Residential Soil Migration to Ground Water
Residential Ground Water (mg/l)
Soil Migration to Ground Water
Industrial Ground Water (mg/l)
Gasoline Range Organics
Diesel Range Organics
High End Hydrocarbon Oils

According to the IDEM, the revised TPH DCLs became effective immediately upon release of the IDEM’s announcement.

In addition to the revised TPH DCLs, the IDEM workgroup developed a “weight of evidence approach” for closure of sites with TPH-DRO contaminated ground water. The "weight of evidence" approach may be used to obtain closure for sites not representing a serious threat where all chemicals of concern (“COC”) in soil and groundwater are below residential default closure levels (“RDCL”), except TPH-DRO in groundwater. The weight of evidence approach can be used if: (1) TPH-DRO is the only diesel COC that exceeds RDCL in groundwater but is below the industrial default closure level ("IDCL"); (2) TPH-DRO in soil is below the residential migration to groundwater level (230 mg/kg for residential in the new guidance); and (3) Groundwater samples are from a properly constructed and developed monitoring well using low flow sampling.

IDEM also announced it will be posting guidance on TPH background levels from shale and crude oil in soils.

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