[CPEO-MEF] Natural Attenuation Revisited

[petestrauss1@home.com]

Recently, there has been some discussion about impurities and additives
found in most TCE product.  I have just read an article from the
February 1994 National Environmental Journal by Haar, Ferry, Berry and
Lamarre entitled "Case History: Impurities and Additives May Complicate
Site Characterization." This was a study that was done at a Superfund
site (Site 300), where I am the technical advisor. Below are some cogent
facts.

Worldwide, TCE is sold under about 50 different trade names. It is used
primarily as an industrial solvent, and is perhaps the number one
contaminant found in soil and groundwater in the U.S. Some of these
products contain additives that are used as stabilizers - they are added
in the form of antioxidants, and can be up to two percent of the total
weight.  These stabilizers are numerous (38 in all), and no one seems to
have considered them when developing a strategy for natural
attenuation.  I must admit that I also was not aware of this.  Could
this be the MTBE of chlorinated solvents?

Almost more troubling, however, is the list of impurities in TCE.  These
include vinyl chloride, DCE, PCE, carbon tetrachloride, acetone and on
and on.  In most strategies involving natural attenuation, the presence
of daughter products of TCE (vinyl chloride and DCE) is indicative of
natural attenuation. However, if it already exists in the product,  it
is not indicative of anything unless one knows how much they started
with. The article states that it is uncommon for an individual impurity
to be present in excess of 100 parts per million (this is a lot!), or
total impurities to be greater than 1,000 ppm (a lot more!).  

In characterizing a site, it is easy to see how impurities make life
difficult. For example, at Site 300, carbon tet, benzene and PCE are all
present in the soil and groundwater along with TCE.  These all have MCLs
of 5 parts per billion.  In addition, TCE has trace amounts of metals,
some of which are carcinogenic.  One batch of TCE contained the
following: 990 ppm of copper, 380 ppm of zinc, 38 ppm of chromium, and
about ten other metals.  If the TCE had been spilled at Site 300 in the
near surface, "then some metal contamination could result due to
impurities in the TCE after the spilled TCE had volatilized".

In summary, this data tells me that MNA for VOCs has to be looked at
much more carefully than the EPA protocol requires.

Peter Strauss

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