Environmental Engineering Reference
In-Depth Information
~25 Months Post-Flush
~28 Months Post-Flush
C7
C7
C3
C3
C4
C4
18 mg/L
MW-512
MW-513
MW-512
MW-513
MW-514
MW-514
C2
C2
MW-505
MW-505
16 mg/L
C1
C1
14 mg/L
MW-506
MW-506
MW-509
MW-510
MW-511
MW-509
MW-510
MW-511
12 mg/L
MW-507
MW-507
10 mg/L
8 mg/L
~31 Months Post-Flush
6 mg/L
4 mg/L
2 mg/L
C7
0 mg/L
C3
C4
MW-512
MW-513
MW-514
C2
MW-505
C1
MW-506
MW-509
MW-510
MW-511
MW-507
Figure 5.46
Methane contour plots over the groundwater monitoring period (18 mg/l
= 1.12 m
M
).
test and 1 and 2 years after the test are being analyzed to determine the
changes in microbial ecology that may have occurred. These samples are
currently being analyzed and the data are not available at this time.
5.5.4 Ethanol toxicity assessment
The effects of continuous and transient exposure of ethanol on subsurface
microbial populations were evaluated in laboratory microcosms and in terms
of available field data. Ethanol oxidation, as evidenced by concentration
decreases, was observed at up to 1% (v/v) concentrations for transient expo-
sure and 0.1% in continuous exposure microcosms (Table 5.5). Analysis of
field ethanol concentration data yielded a first-order degradation rate of 0.3/
year. Laboratory rates appeared to be much faster, ranging from 13 to 90/
year (Table 5.6). We feel this is a reflection of the toxic effect of higher ethanol
concentrations in the source area and that the observed field rates are
impacted by limitations on the size and location of bioactive zones. The
observed acetate and methane formation rates are insufficient to account for
ethanol losses and indicate the presence of other electron sinks, such as
dechlorination and sulfate reduction. Examination of PFLA
profiles in lab-
oratory microcosms suggests that higher concentrations of ethanol (at or
above 5%) reduced microbial populations and that the decrease in biomass
was influenced by exposure time (data not shown).
