Handbook of Solvents - George Wypych - ChemTech - Ventech!

23.1 Natural attenuation of chlorinated solvents 1603
The data in the HGDB were broken into two groups: the chlorinated ethenes, where
one or more of the chlorinated ethenes (PCE, TCE, DCE, or VC) was reported to be the major
contaminant, and other chlorinated solvent sites, where all other chlorinated solvents besides
the ethenes (e.g., TCA, DCA, chlorobenzene) were lumped together. As shown in
Table 23.1.10, the median length of the 75 chlorinated ethene plumes was 1000 ft, with one
site reporting a plume length of 13,200 ft. These median lengths are longer than those reported
for fuel hydrocarbon plumes and this may be attributed to the competition for hydrogen
during halorespiration.
Table 23.1.10. Characteristics of chlorinated solvent plumes from HGDB database
Chlorinated ethenes (e.g.,
PCE, TCE, etc.)
Maximum
75 th percentile
Median
25 th percentile
Minimum
n
Other chlorinated solvents
(e.g., TCA, DCA)
Maximum
75 th percentile
Median
25 th percentile
Minimum
n
Plume
length, ft
13,200
2,500
1,000
600
50
75
18,000
2,725
575
290
100
24
Plume
width, ft
4,950
1,000
500
200
15
75
7,500
1,000
350
188
100
24
Vertical
penetration, ft
500
100
40
25
5
78
150
51
35
24
8
24
Highest
concentration, mg/L
28,000
72
8.467
0.897
0.001
81
2,500
13.250
3.100
0.449
0.016
28
Note: Highest concentration for chlorinated ethenes (28,000 mg/L) was for TCE, which is above the solubility
limit. The highest concentration for “other chlorinated solvents” (2500 mg/L) was for chloromethane and toluene.
[From T.H. Wiedemeier, H. S. Rifai, C. J. Newell and J.T. Wilson, Natural Attenuation of Fuels and Chlorinated
Solvents in the Subsurface, after reference 88. Copyright © 1999 John Wiley & Sons, Inc. Reprinted by
permission of John Wiley & Sons, Inc.]
The other category, “other chlorinated solvent sites,” had shorter plumes, with a median
plume length of 575 ft compared to 1000 ft for the chlorinated ethene sites. Twelve of
the 24 plumes were comprised of TCA, which is degraded biologically via halorespiration
and other mechanisms and abiotically by hydrolysis (half life of 0.5 to 2.5 years). Despite
the degradability of TCA, the TCA plumes had a median length of 925 ft. The shorter
plumes in this database of 24 sites were reported to be comprised of either a general indicator,
such as Total Organic Halogens, or individual compounds such as 1,1-dichloroethane,
dichloromethane, or chlorobenzene. The median highest concentration at these “other chlorinated
solvent sites” was 3.1 mg/L (see Table 23.1.10).
Data compiled from 17 Air Force sites using the AFCEE (Air Force Center for Environmental
Excellence) natural attenuation protocol 107 showed a median plume length of 750
ft (based on 14 plumes). There were significant differences in plume length for different
plume classes, with Type 1 plumes (sites with available man-made fermentation substrates
such as BTEX) being shorter than Type 3 plumes (sites without available fermentation substrates).
Twelve of the sites exhibiting Type 1 plumes had a median plume length of 625 ft,