|
 NASSCO/Southwest Marine Shipyards Feasibility Study Exponent developed and evaluated remedial alternatives
to address impairments of beneficial uses attributable to
shipyard chemicals in sediment (e.g., metals, PAHs, and
PCBs). Site-specific constraints, including physical,
logistical, and biological considerations, played a key role in the development and
comparison of alternatives. Exponent worked closely with the shipyards’ facilities staff
and remedial design consultant to develop realistic remedial alternatives that accurately
reflected these site-specific constraints. Evaluation of the remedial alternatives was
based on criteria related to effects on beneficial uses, technical feasibility, and economic
feasibility. In evaluating technical feasibility, considerable attention was paid to the
numerous site-specific constraints. Exponent developed a semi-quantitative approach
to estimate effects on beneficial uses for evaluating cost versus benefit. Site-specific
measurements of biological effects were used to evaluate the site's current ability to
meet beneficial uses, and its ability under different remedial scenarios. We demonstrated
that beneficial use outcomes were not significantly better for alternatives using active
remedial measures than for a monitored natural attenuation remedy. The feasibility
study concluded that the most appropriate remedial alternative for the shipyards was
monitored natural attenuation.
Preliminary Feasibility Study at Former Explosives and Ordnance Manufacturing Facility Working for the property owner’s insurer, Exponent conducted a preliminary
feasibility study to address perchlorate-affected groundwater in the vicinity of a municipal
drinking water
production well.
The remedial
objectives were
to control
perchlorate
migration and
meet expected
local water
supply needs.
Exponent developed and
evaluated several interim remedial
measures, including wellhead treatment
and/or blending, water rights trading, plume
interception, and in-situ treatment. The preliminary
feasibility study provided a basis for an objective comparison
of the alternatives; eliminated infeasible alternatives from further evaluation; and
identified critical data needs for selecting a preferred alternative.
Probabilistic Cost Estimate of Sediment Remediation In response to a proposed
settlement offer, our client needed a reasonable range of cost estimates for various
sediment remediation alternatives. Exponent developed a Monte Carlo model to provide
probability distributions of costs for the remedial alternatives, and estimated the
uncertainties in the likelihood of selection of the alternative remedies. The client was
able to use the 90th percentile of the estimated remediation cost as a reasonable upperbound
in negotiating the amount of an “early-buyout” for one of the responsible parties.
top | back | next
|
