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Avtex Fibers Superfund Site
Front Royal, Virginia
The Avtex Fibers Superfund site is a former rayon manufacturing
facility that poses a unique environmental challenge—namely,
a series of historical disposal basins to which plant waste
was disposed, which have contributed contaminants to groundwater
in the fractured bedrock beneath the site. Three of these
basins contain some 250,000 cubic yards of aged viscose sludge,
which has a water content of 85 percent and a viscous, soft-rubber-like
consistency. These three viscose basins are releasing carbon
disulfide, phenols, and trace metals, forming a groundwater
plume that has sunk through the fractured bedrock aquifer
(it has been detected as deep as 300 feet below the ground
surface) and has moved off site, passed beneath the nearby
Shenandoah River, and affected residential wells in a housing
development across the river from the site. This type of material
has never been remediated before, and its low load-bearing
capacity precludes the use of heavy equipment that would normally
be employed to excavate such a source area. At present, Exponent
is preparing a Feasibility Study for these basins and the
contaminated groundwater. The Feasibility Study will include
developing potential remedial measures and screening these
possibilities to select the most promising approach for site
remediation.
Ketchikan Pulp Company
Ketchikan, Alaska
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Exponent served as RI/FS contractor for the Ketchikan Pulp Company
(KPC), a timber company closing a dissolving sulfite pulp mill
in southeast Alaska. Exponent conducted a focused investigation
of both upland areas and offshore marine sediments, and provided
technical support for the Ward Cove Sediment Remediation Project.
Exponent scientists first reviewed the historical database for
Ward Cove and proposed a phased approach to delineating potential
areas of concern. A key objective of the work was to discriminate
effects due to toxic chemicals from effects due to conventional
variables such as ammonia, sulfide, and oxygen-demanding organic
material. Site-specific sediment chemistry, bathymetry, circulation,
and toxicity data were collected to support site assessment.
We then applied a suite of four sediment toxicity tests representing
a variety of exposure regimes, aeration designs, test species,
and endpoints to allow identification of toxicity designations
based on a preponderance of evidence (rather than the results
of a single test). This approach also differentiated between
potential effects of toxic substances and conventional variables
on sediment toxicity in the cove.
Human health and ecological food web evaluations applied
existing tissue data and sediment data to realistic estimates
of exposure and determined that risks associated with seafood
consumption were within acceptable levels. Additional work
was conducted to assess the severity and causative agents
associated with sediment toxicity to benthic organisms. In
a second phase, more detailed evaluations were conducted in
the areas of concern identified in Phase 1. These studies
identified the vertical extent of substances of concern within
a confined area and better characterized the substances that
are likely responsible for any observed toxicity. The detailed
evaluations included evaluations of pore water, Toxicity Identification
Evaluations (TIEs), and various forms of sediment manipulation.
Problem chemicals were determined to be non-persistent chemicals
(e.g., ammonia, sulfide, 4-methylphenol) that are natural
degradation products of organic matter and woody debris. Modeling
and a case study analysis were conducted to assess the rate
of natural recovery.
The feasibility study focused on development of a practical
remedy for a large volume of low-toxicity sediment, as identified
using site-specific effects thresholds in a weight-of-evidence
approach. The proposed remedy will consist of a combination
of natural recovery, limited maintenance dredging, and capping.
As required under Section 7(c) of the Endangered Species Act,
Exponent is currently conducting a Biological Assessment of
the impacts of the proposed remediation on three endangered
species: humpback whales, peregrine falcons, and Steller sea
lions.
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