Environmental Engineering Reference
In-Depth Information
to dredge the contaminated sediment and dispose of the material in a con-
tainment facility to prevent release and further environmental damage. The
responsible party saw this as a bad idea because: (1) the natural resource was
diminished in environmental value prior to the contamination due to his-
toric use and continued future industrial/commercial use (it was estimated
at only 60% of the value of a similar resource in a less industrialized area); (2)
it would be a severe drain on the available funds allocated for environmental
issues (estimated cost was $25 million) and addressing more immediate and
serious problems would be delayed; and (3) the physical dredging in similar
situations had been shown to cause extensive habitat destruction and release
to adjacent clean areas. However, if no direct actions were taken, with only
reliance on natural processes to address the issue, there would be a signifi-
cant net environmental deficit of 4000 service acre years (SAYs) which was
the chosen and negotiated NEBA currency (Figure 7.12).
Based on NEBA currency and the extensive studies and predictions used
to calculate the benefit, the preferred alternative of dredging all contami-
nated sediment would only worsen the situation (Figure 7.13). There had
been substantial historic damage and even an extensive dredging operation
could not remove all the contamination, thus there would be a 2000-SAY
debit from this alternative. In addition, the dredging would alter the benthic
physical habitat, requiring a period to recover, and some contaminated mate-
rial would be released to adjacent habitat. These two activities would result
in an additional 1600-SAY debit for a total net benefit of negative 3600 SAY.
Given this loss of benefit and the high price tag, the responsible party was in
search of a better way.
100
80
Benef its = 0
Baseline
services
60
Deficit = -4000 SAYs
with natural recovery
40
20
Start
Full recovery
Years
FIGURE 7.12
Environmental deficit from contaminated sediment with no active remediation.
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