Environmental Engineering Reference
In-Depth Information
Table 5.3
PCE Removal Effectiveness Calculated by Different
Techniques
Preflushing
(mg/l)
Postflushing
(mg/l)
Removal
Effectiveness
Technique
RW (n = 6)
17.2 ± 25.9
16.5 ± 13.5
0.04
IW (n = 3)
54.5 ± 46.3
0.6 ± 0.5
0.99
RW and IW (n = 9)
29.6 ± 36.1
11.2 ± 13.2
0.62
Core material
0.65
Partitioning tracer
0.62-0.63
This calculation compares well with estimates of the amount of PCE removed
during the cosolvent flushing test by two techniques explained in more detail
in Jawitz et al. (2000). Comparison of core material collected prior to and
following the cosolvent flushing test indicated a removal effectiveness of
0.65. The overall removal effectiveness for the recovery wells calculated from
the partitioning tracer data was 0.62 to 0.63, but it varied significantly at
individual recovery wells, depending upon the technique used for analysis.
The hydraulic containment system was adequate to maintain capture
within the testing zone. Groundwater elevations measured during the course
of the pilot test showed an inward gradient from the outer monitoring wells
(MW-505, MW-506, MW-507, and MW-509) toward the recovery wells.
DNAPL PCE migration was not observed during the test, and ethanol was
detected in only two of the outer monitoring wells following the test. In the
first sampling event following the cosolvent flushing test, the ethanol con-
centration in MW-505 was 4620 mg/l, and in MW-506 was 0.74 mg/l.
MW-506 is located upgradient from the targeted area, and MW-505 is located
to the north. Neither well is located downgradient of the direction of ground-
water flow.
Analysis of the partitioning tracer data by Jawitz et al. (2000) estimated
42 l of PCE was removed by the cosolvent flushing test. Remaining PCE
DNAPL was estimated to be 26 l. Approximately 92% of the 34 kl of injected
alcohol was recovered at the end of the hydraulic containment so that 2.72
kl of ethanol remained in the subsurface as an electron donor for enhance-
ment of the microbial processes.
The cosolvent extraction demonstration at the Sage's site was a suc-
cessful demonstration of the removal of a significant mass of DNAPL
contaminant from a selected zone. Improvement in removal effectiveness
could be obtained by selection of a remedial cosolvent with a higher cosol-
vency property and by increased volume of cosolvent pumped through
the system. This test demonstrated the capability of this technology to be
utilized at other Florida DEP DSCP sites. Information obtained from this
test will aid in the design of a full-scale technology implementation for the
Sage's site.
