Handbook of Solvents - George Wypych - ChemTech - Ventech!

23.1 Natural attenuation of chlorinated solvents 1599
Compound
Carbon
tetrachloride
Mean of field/in-situ
studies
1 st order rate
coefficients,
day -1
halflives,
day
number
studies
used
for
mean
Recommended 1 st order rate
coefficients
low-end high-end
1 st order rate 1 st order rate
coefficients,
day -1
half-lives
day
coefficients,
day -1
half-lives
day
0.37 1.9 9 0.0037 187 0.13 5
Chloroform 0.030 23 1 0.0004 1,733 0.03 23
Dichloromethane 0.0064 108 1 0.0064 108 - -
Trichlorofluoromethane
- - - 0.00016 4,331 0.0016 433
2, 4-Dichlorophenol 0.014 50 2 0.00055 1,260 0.027 26
Comments
Range not appropriate for nitrate-reducing
conditions. Expect lower
limits to be much less
Only one field study available.
Biodegradation under nitrate-reducing
conditions expected
Rate constant reported from a single
field study under methanogenic conditions
All studies with very low concentrations
of this compound
Range may not be appropriate for nitrate
reducing conditions
[From T.H. Wiedemeier, H. S. Rifai, C. J. Newell and J.T. Wilson, Natural Attenuation of Fuels and Chlorinated
Solvents in the Subsurface. Copyright © 1999 John Wiley & Sons, Inc. Reprinted by permission of John
Wiley & Sons, Inc.]
23.1.5 GEOCHEMICAL EVIDENCE OF NATURAL BIOREMEDIATION AT
CHLORINATED SOLVENT SITES
23.1.5.1 Assessing reductive dechlorination at field sites
Assessing biological activity at a field site based on monitoring data can be difficult. However,
there are a number of monitoring parameters that can be indicative of halorespiration.
First, the presence of methane in the groundwater indicates that fermentation is occurring
and that the potential for halorespiration exists. Second, the transformation of PCE and TCE
has been studied intensely and many researchers report that of the three possible DCE isomers,
1,1-DCE is the least significant intermediate and that cis-1,2-DCE predominates over
trans-1,2-DCE. 103-105 Third, because chlorinated ethenes are 55 to 85% chlorine by mass, the
degradation of these compounds releases a large mass of chloride. Therefore, elevated chloride
concentrations also indicate reductive dechlorination.
23.1.5.2 Plume classification schemes
Wiedemeier et a1. 106 proposed a classification system for chlorinated solvent plumes based
on the amount and origin of fermentation substrates that produce the hydrogen that drives
halorespiration. Three types of groundwater environments and associated plume behavior,
Type 1, Type 2, and Type 3, are described below. While the classification system can be
used to represent entire plumes, it can also be used to define different zones within a chlorinated
solvent plume.
23.1.5.2.1 Type 1
For highly chlorinated solvents to biodegrade, anaerobic conditions must prevail within the
contaminant plume. Anaerobic conditions are typical at sites contaminated with fuel hydro-