Most importantly, we, environmental professionals, protect our society from being exposed to toxic chemicals.  It is easy to lose track of this in the practice of Phase I Environmental Site Assessments, as you spend time talking about real estate transactions, collateral, and environmental liability.  But all of these important real estate matters are ultimately underpinned by the protection of human health and the environment.

A recognized environmental condition as defined by ASTM 1527-2005 is “the presence or likely presence of any hazardous substances or petroleum products on a property under conditions that indicate an existing release, a past release, or a material threat of a release of any hazardous substances or petroleum products into structures on the property or into the ground, ground water, or surface water of the property.”   In this blog, I will focus on the term “threat to human health.”   Our job as engineers is easy when the government gives us an action level.  The rub is what if the government gives us a bunch of vague guidance, much of it contradicting itself.  

Consider how trichloroethylene (TCE) is regulated as a case in point.  And for the sake of this blog assume that the primary data set is in the form of soil vapor (see blog on soil vapor versus soil matrix).  Federal OSHA publishes Permissible Expose Limits (PELs) which dictate the level of chemicals allowed in air in a work environment.  The PEL for TCE is 100 ppm or 537,000 ug/m^3.   In California the closest thing to a government published action level to the PEL is the CHHSL.   Compare the PEL with the California Human Health Screening Level (CHHSLs) published by the California Office of Environmental Health Hazard Assessment (OEHHA).   The CHHSL of TCE in air in an industrial setting is 2.04 ug/m^3.    

While PELs and CHHSLs are not trying to do exactly the same thing, they are very relevant government published levels on indoor air quality and the federal government and the state of California are differ by a factor of over 250,000! 

The environmental professional practicing Phase I Environmental Site Assessments must opine on what is safe in the soil.   When a Phase I finds that a historical release or an off-site release has resulted in on-site soil vapor of TCE above the CHHSL, then the consultant must opine on whether this level of contamination is a “threat to human health”. 

The easy way to do this is to compare them to government published look-up tables.  California published the aforementioned CHHSLs for sub-slab soil gas too.   Oregon, Hawaii, New Jersey, and New York are among the states who also publish safe soil vapor levels.   If the site is in California and the soil vapor concentration is above the CHHSLs, then there appears to be a health risk.  The rub is that the CHHSLs are super conservative and many sites fail even sites that had received closure as recently as 10 years ago.   If the site is in a state without published action levels, then the profession is tempted to use the levels from California.  

The more time consuming way to address risks represented by soil vapor levels is by creating a risk model such as the Johnson & Ettinger Model.  These models consider the chemical’s volatility and toxicity and building features such as slab thickness and air exchange.   The most important input in these models is what the safe levels for indoor air.  I typically use the CHHSLs in California; however, I have peer reviewed risk assessments which use the 250,000 times more lenient PELs.   The indoor air CHHSLs and PELs plugged into a risk model result in sub-slab soil vapor action levels 2500,000 times apart from each other.   This gulf is too large; however, this is where our government leaves the environmental professional.  

Happy New Year Everyone!