1997 CPEO Military List Archive

From: Don Zweifel <zweifel@chapman.edu>
Date: 10 Jun 1997 04:09:08
Reply: cpeo-military
Subject: A "novel" soil standard for TCE
 
The potential problem is in applying Henry's Constant as it is utilized to
translate the maximum contaminant levels (MCL) of priority pollutants to
generate a target clean-up goal in soil by exclusively measuring
"soil-gas" concentrations. We believe this hypothesis should receive
exceedingly close scrutiny. 

The definition of Henry's theoretical constant: It is the partial pressure
of a component divided by its molar mass fraction in solution. In other
words it is utilized to estimate the ostensible "concentration" of a
compound in solution and/or its vapor pressure at 25 degrees C.

A case in point being at Marine Corps Air Station, El Toro, Ca. The Dept.
of the Navy (DON) proposes to implement soil vapor extraction (SVE) of
contaminated soil in the vadose zone at site 24. Their attempt at a new
precedent setting criterian is essentially to use a soil-gas analysis to
achieve a lower soil clean-up standard. Specifically to adopt 27
micro-grams per liter or 27 ppb (by soil-gas) as a new benchmark for
trichloroethylene or TCE as an "MCL." 

TCE's toxicity characteristics for contaminated substances in the TCLP or
leachate test is a maximum RCRA-mandated concentration of 0.5 mg/liter or
500 ppb. Can we accept a toxicity level of up to 10 mg of TCE per kg (2.21
lbs) in the soil?

What about the ambitious goal of "clean closure" with no deed
restrictions?

Your comments, criticisms or witticisms would be greatly appreciated.

P.S.: Engineers refer to TCE as having a Henry's Constant of 1.17 times 10
to the minus 2. This is a dimensionless number and herein lies the rub.
I believe this constant is not applicable because it refers to a "partial
pressure" of a component in solution not a "concentration."

Note: The vapor pressure of TCE is 77 mm of mercury at 25 degrees C.

TCE specification source: USEPA Risk Reduction Engineering Lab (RREL) in
Cincinnati, Ohio

 Don Zweifel
 CalEPA DTSC Adv Grp rep

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