IDEM’s Changes to TPH Procedures for Ground Water

Written by Steve Henshaw, P.G., President & CEO, EnviroForensics

On June 17, 2010 the Indiana Department of Environmental Management (IDEM) once again adjusted their guidance regarding the regulation of Total Petroleum Hydrocarbons (TPH) and revised pertinent sections of their Risk Integrated System of Closure (RISC) Technical Guidance Document.  A special RISC TPH Work Group has determined that the investigation, delineation and/or remediation of TPH in ground water are no longer warranted, unless protection of drinking water wells is necessary.  This development could significantly impact environmental cleanup projects where releases of petroleum products have occurred. 

The term TPH refers to an accumulation of hydrocarbon compounds that make up a variety of petroleum products.  Not all of the compounds that fall in this category have been researched individually by toxicologists, such that closure levels could be established.  Those that do have closure levels are considered Contaminants of Concern (COCs) at cleanup sites, which are commonly the more toxic compounds and are regulated individually.  The non-specific TPH is also regulated as a COC based on surrogate toxicological data. 

As petroleum products weather and degrade in the subsurface, the individual COCs (e.g. benzene) tend to breakdown first.  At older petroleum release sites there can be elevated TPH levels with essentially no detected individual COCs.  Prior to this latest shift in guidance by IDEM, sites with only groundwater impacts of TPH would require investigation, risk assessment and a closure strategy that may have included active remediation.  Since TPH is no longer a regulated COC in groundwater, many sites will now be eligible for closure, foregoing expensive cleanups. 

The IDEM’s stance on TPH in soil has not changed at this time.  Soils impacted with TPH, solely or in the presence of individual COCs, must be investigated and addressed.  If the levels of TPH in soil are above levels considered protective of groundwater, analysis of individual COCs in groundwater may be required. 

EnviroForensics represents many clients who own sites impacted with TPH in groundwater and will be evaluating how the recent changes in TPH procedures at the IDEM will affect closure requests.  Look for future Blog entries on this topic and read the full IDEM memorandum on this issue on our web site at

Click Here To View a PDF Version of IDEM’s Announcement.