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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