Environmental Engineering Reference
In-Depth Information
followed an identical first-order decay curve with a kinetic coefficient of
0.04749 ppm/month (r
2
= 0.96209). The half-life of PAHs in the LTUs was
14.7 months.
Removal of PAHs from the LTUs during the study was not due to
volatilization from tilling because no effect was seen when the cultivation
frequency was changed after the first 6 months. The conclusion is that tilling
was not a driving factor in PAH degradation. A plateau period in contami-
nant removal was observed in both LTUs that coincided with colder winter
weather in the second year of operation. However, during the first winter,
there was no decrease in the removal rate, which would seem to indicate
the involvement of another variable. PAH concentration continued to decline
from mid-May through mid-August of 2000. There was unusually extended
high temperatures and drought during this time. High temperatures and
low soil moisture do not appear to adversely affect PAH degradation. Reduc-
tion in the concentration of the BaP toxic equivalent homologues over time
is shown in Figure 7.24 and Figure 7.25 for LTUs 1 and 2, respectively.
The extent of reduction of PAH homologues varied depending on the
compound (i.e., number of rings and molecular weight) and the soil treat-
ment, as shown in Table 7.15. The compounds acenaphthylene and
benzo(g,h,i)perylene, and the BaP toxic equivalent homologues indeno
(1,2,3-c,d)pyrene and dibenzo(a,h)anthracene, are not shown in Table 7.15
because although they were present, the concentrations were below the
300
Initial
6 months
13 months
22 months
30 months
250
200
150
100
50
0
BaP Toxic Equivalent PAH Homologues
Figure 7.24
LTU 1 BaP toxic equivalent homologues.
