New Jersey Zinc/Mobil Chemical Site
You are invited to comment on
The Proposed Pland and Other Remedies Considered For
The South Ditch Sediments
Fact Sheet #8
September 2002
DePue, Illinois
 What
is the South Ditch? The South Ditch is a ditch between the plant property
of the New Jersey Zinc/Mobil Chemical Superfund Site and Lake DePue. (For
more information on the site, see page 7.)
Historically, the ditch has received runoff from the former plant property.
Because of the nature of past plant operations, the runoff contained high
levels of metals that contaminated sediments in the ditch. These contaminated
sediments are called "unnatural" sediments.
In 1995, the State of Illinois and the potentially responsible
parties (PRPs) 1 signed an interim consent
order 2. One of the requirements of that order was for
the PRPs to investigate the sediments in the South Ditch and, if necessary,
construct a remedy for the sediments. The PRPs completed the investigation
in 1996.
Alternatives Studied for the South Ditch Sediments
The PRPs studied four main alternatives to remedy the South Ditch sediments.
These alternatives are described on the next two pages. The Illinois EPA
has designated one alternative (4b) as the Illinois EPA proposed plan.
The public is invited to comment on all the studied alternatives as well
as the proposed plan.
Costs are given in 1997 dollars, because the study of alternatives was
conducted in 1997. All alternatives except Alternative 1 include institutional
controls. In the short term, these controls would include "No Trespassing"
signs and limited fencing. Long-term institutional controls could include
restrictions on the deed of the property limiting certain activities such
as excavation, swimming and fishing.
The PRPs studied four main alternatives to remedy the South Ditch sediments.
These alternatives are described on the next two pages. The Illinois EPA
has designated one alternative (4b) as the Illinois EPA proposed plan.
The public is invited to comment on all the studied alternatives as well
as the proposed plan.
Costs are given in 1997 dollars, because the study of alternatives was
conducted in 1997. All alternatives except Alternative 1 include institutional
controls. In the short term, these controls would include "No Trespassing"
signs and limited fencing. Long-term institutional controls could include
restrictions on the deed of the property limiting certain activities such
as excavation, swimming and fishing.
Alternative 1 No Action/Natural Recovery.
This alternative is a passive form of action involving natural processes.
In this case, the natural process of siltation caused by regular flooding
of the Illinois River would gradually cover the "unnatural" sediment.
As long as the Illinois River sediment covered the "unnatural" sediment,
humans and other organisms would not come into contact with the elevated
levels of metals. As developed by the PRPs, this alternative would also
include monitoring.
Estimated cost in 1997 dollars: $429,000 ($0 capital cost and $21,665
estimated annual operation and maintenance [O & M] cost)
Estimated months to construct: 0
Estimated time for sediments to become covered: 30 years
Alternative 2 Enhanced Natural Recovery with Surface Water Diversion.
This alternative would be similar to Alternative 1 in that it would
rely on the natural process of siltation eventually covering the "unnatural"
sediment with a clean layer of silt. The difference is that water currently
flowing into the ditch would be directed around the ditch so that the
water does not wash the "unnatural" sediment into the lake. Then a series
of dams would be constructed across the ditch. The dams across the ditch
would be constructed low enough so that when the Illinois River is in
flood stage, river water (with sediment) would wash over the dams into
the ditch. Low berms would be constructed on both sides of the ditch.
As the floodwaters recede, the sediment from the river water would be
retained behind the dams and berms. This "clean" river sediment eventually
would cover the "unnatural" sediment with a cap.
Estimated cost in 1997 dollars: $1,176,000 ($608,000 capital cost
and $28,662 annual O & M cost)
Estimated months to construct: Less than six months
Estimated time for sediments to become covered: Five to 15 years
Alternative 3 Above-Grade Cap.
This alternative would involve redirection of the surface water that
flows into the ditch so that it would flow into a new drainage ditch.
The sediment would be stabilized by adding kiln dust, fly ash or other
material. A two to three foot cap of compacted clay soils would be placed
on top of a special geofabric that would be laid over the top of the "unnatural"
sediments. The cap would be vegetated, and riprap, such as big rocks,
would be placed on the sides to prevent the sediment from eroding during
rainfall. As long as the cap is intact, it would prevent people or animals
from coming in contact with the "unnatural" sediments. Institutional controls
would be placed on the property to prevent people from digging into or
in other ways damaging the cap.
Estimated cost in 1997 dollars: $1,387,000 ($946,000 capital cost
and $22,330 annual O & M cost)
Estimated months to construct: Less than six months
Alternative 4 Removal of "Unnatural" Sediment.
This alternative is divided into three sub alternatives (4a, 4b and
4c). There are several common elements among the three sub alternatives.
Common Elements of 4a, 4b and 4c
- The sediment would be removed. The "unnatural" sediment would
be removed by a combination of mechanical and hydraulic dredging. The
sediment would be excavated as a semi-solid and/or dredged as a slurry
(suspended in water). The sediments would be transferred to a settling
basin probably located on the south side of the railroad tracks where
the old dump was formerly located. Here the sediment would be allowed
to settle out. Most of the water would be returned to the ditch. Three
ways of disposing of the sediment were considered and are described
on page 3.
- The water now flowing into the ditch, including the spring water
in the ditch, would be temporarily rerouted around the ditch. In
order for the sediments to be removed, the water now flowing through
the ditch would be rerouted around the ditch and discharged into Lake
DePue at another location for the period of dredging. The water could
be temporarily diverted by a combination of interception trenches, shallow
groundwater wells and piping in or near the springs.
Differences in methods of sediment disposal in sub alternatives 4a,
4b and 4c
- Sub alternative 4a. In this sub alternative, the PRPs proposed
to transport the dewatered sediment to a nearby fertilizer plant. The
zinc and copper in the sediment are valued micronutrients and would
be added to the fertilizer being manufactured. The fertilizer plant
withdrew their interest in the South Ditch sediments so this option
was abandoned. The fertilizer plant subsequently closed.
- Sub alternative 4b. In this sub alternative, an interim containment
unit would be constructed on the former plant property site for the
sediment after the sediment has been dewatered in the settling basins
and stabilized with fly ash, kiln dust or other additives. A permanent
remedy for the sediment would be selected later, when the remedy for
the entire site is chosen.
The interim unit would be constructed over an area of contaminated soil
and groundwater on the former plant property. The sediment would be
placed on top of a liner, such as recompacted clay and high-density
polyethylene (HDPE), to prevent the metals in the sediment from being
washed down into the soil below. An aggregate drainage layer such as
gravel would be placed on top of the liner before the sediment is placed
in the containment unit. Water draining through the sediment would be
collected periodically from this drainage layer and sent to the water
treatment plant already constructed and being operated by the PRPs.
The water treatment plant was required by the interim consent decree
and has been constructed by the PRPs to treat water coming off the plant
property so the water meets state and federal regulations before it
is discharged into the Illinois River.
To prevent rain from entering the containment unit, the unit would be
covered with HPDE and a clay layer graded to shed water. The clay layer
would be vegetated. The current thinking is that this containment unit
will be located north of the zinc slag pile toward the west end. The
actual location will be determined during the design phase of the project.
Estimated cost: $1,895,000 ($1,677,000 capital cost and $11,000 annual
O & M cost)
Months to construct: Less than six months.
- Sub alternative 4c. In this sub alternative, the sediment
would be removed from the settling basins after it is dewatered, stabilized
with a material like fly ash or kiln dust and shipped off site for disposal
at a permitted, compliant, non-hazardous waste landfill.
Estimated cost: $2,402,000
Months to construct: Less than six months.
Human and Ecological Risk Assessments of the Ditch Sediments
What is the concern with the sediments? There are two concerns.
One concern is for human health. The second is an ecological concern;
that is, a concern about plants and animals that may be affected by the
ditch sediments. The following evaluation of the risk that the sediments
might pose to human health and the environment is based on the 1996 investigation
results.
- Human Health Risk. The South Ditch is in the annual floodplain
of the Illinois River and unsuitable for residences; therefore, risk
was not considered for residential use. Risk was considered for two
other scenarios. The first scenario is that of a child trespasser; that
is, for a child playing in the South Ditch for four hours per day, 50
days per year for six years. The second scenario is that of a construction
worker who is digging in the ditch sediment for short periods of time.
There are no standards for metals in sediments. Since there are no standards,
the U.S. EPA and the Illinois EPA have calculated screening values to
serve as guidelines in evaluating whether certain concentrations of
chemicals in sediment pose a threat to humans. The Illinois EPA and
U.S. EPA consider exposure to a chemical at concentrations above the
screening value to pose either a potential cancer or potential
non-cancer risk 3. An example of a non-cancer risk is
a concentration of lead that would damage the developing nervous system
of a child. Exposure can be from eating, drinking, breathing or touching
a chemical or, in this case, sediment that contains the chemical.
Conclusion. The maximum levels of arsenic, copper and lead in
South Ditch sediment exceed screening levels for a child trespasser.
The metal concentrations in the South Ditch sediment also exceed the
Illinois EPA arsenic, cadmium, copper, lead and zinc screening levels
for construction workers.
- Ecological Risk. Ecological risk was measured by placing two
benthic organisms (midge larvae and scud) in samples of sediment collected
in eight locations along the length of the ditch. Benthic organisms
are small organisms that would normally live on the bottom of streams.
These organisms are important, because they are food for larger organisms
such as fish and waterfowl.
Conclusion. One hundred percent of the midge larvae died within
four days in sediment from seven of the eight sample locations. In the
eighth sediment sample, 85% of the midge larvae died within four days.
One hundred percent of the scud in all eight samples died within four
days.
For comparison, two sediment samples were collected from nearby Turner
Lake. Within four days, 22 percent of midge larvae died in one sample
and 35 percent died in the other sample. For scud, 22 percent died in
one sample within four days and 23 percent died in the other sample.
Evaluation of Remedy Alternatives
What is the objective of the South Ditch sediment remedy? There
are three main objectives for the South Ditch remedy: (1) to reduce the
potential for flood water or water moving through the ditch to move the
"unnatural" sediment into Lake DePue; (2) to reduce the risk to humans
or sensitive plants or animals coming into contact with the "unnautral"
sediment, and (3) to be compatible with future site-wide remedies.
How are the alternative remedies evaluated? The federal Superfund
Law specifies the following nine criteria for evaluation of remedies.
They are (1) overall protection of human health and the environment, (2)
compliance with applicable or relevant and appropriate requirements (ARARs)
under federal or state laws, (3) long-term effectiveness and permanence,
(4) reduction of toxicity, mobility or volume of contaminants through
treatment, (5) short-term effectiveness, (6) implementability, (7) cost,
(8) support agency acceptance and (9) community acceptance.
Criteria one and two are called threshold criteria, because all remedies
must meet these two criteria. Criteria three through seven are called
balancing criteria, because they are weighed against one another. Criteria
eight and nine are considered modifying criteria.
| Summary of Evaluation of Each Alternative
Against the Nine Criteria |
| Criteria |
Alternative 1
Natural Recovery / No Action |
Alternative 2
Enhanced Natural Recovery with Surface Water Diversion |
Alternative 3
Above Grade Cap |
Alternative 4B
Removal with On-Site Consolidation |
Alternative 4C
Removal with Off-Site Disposal |
| 1 Overall protection of human health and the environment
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| 2 Compliance with ARARs |
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| 3 Long-term effectiveness and permanence |
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| 4 Reduction in toxicity, mobility, or volume through
treatment |
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| 5 Short-term effectiveness |
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| 6 Implementability |
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| 7 Cost |
$429,000 |
$1,176,000 |
$1,387,000 |
$1,895,000 |
$2,402,000 |
| 8 Support agency acceptance |
The USEPA has reviewed the components of Alternative
4-B and supports its acceptance as the recommended alternative pending
review of public comments. |
| 9 Community acceptance |
Community acceptance of the recommended alternative
will be evaluated after the public comment period. |
Fully
Meets Criteria; Partially
Meets Criteria; Does
Not Meet Criteria
1 The Superfund law specifies
that potentially responsible parties are past and present owners and operators
of the site. In this case, the potentially responsible parties are Viacom
International Inc., ExxonMobil Corporation and Horsehead Industries, Inc.
These three companies call themselves the "DePue Group." Since DePue citizens
have expressed confusion about the name "DePue Group," thinking it belongs
to a group of local citizens, this fact sheet will refer to these three
companies as the potentially responsible parties (PRPs). The Illinois
EPA oversees the work of the PRPs to ensure that samples are collected
and other work is conducted as described in the Illinois EPA approved
work plans.
2 A consent order is a legally
binding court order agreed upon by the parties entering into the order.
The order lists the benefits and obligations of all the parties who signed
the order. In this case, the consent order was filed in the 13th Judicial
Circuit Court in Bureau County, Illinois. This order is "interim" because
it covers only investigations, design of the remedy and certain actions
such as the remedy for the South Ditch. A second order will be negotiated
for the implementation of the overall site remedy.
3 For more information on how
risk is calculated, see the Proposed Plan and the study of South Ditch
remedies. These documents are in the project repository at the Selby Township
Library in DePue.
Illinois EPA Proposed Plan
What is the Illinois EPA Proposed Plan? The Illinois EPA Proposed
Plan is Alternative 4b, which is removal of "unnatural" sediment and consolidation
of the sediment in an on-site interim containment unit. The public is
invited to comment on this proposal as well as all alternatives studied.
Why does the Illinois EPA prefer Alternative 4b? Alternatives
4b and 4c are the only alternatives that meet both of the first two criteria.
(See the above table.) In the Agency's opinion, 4b provides the best balance
of criteria three through seven. Criteria 9 will be evaluated after the
end of the public comment period.
Other Questions
How much sediment would be removed? Approximately 8,000 cubic
yards of sediment would be removed. The "unnatural" sediment has characteristics
distinct from the sediment in the surrounding area. For example, the "unnatural"
sediment is much looser and of a different color.
Determination of which sediment will be removed will be based on the
physical characterisitics. In later phases, a comprehensive investigation
of the area surrounding the South Ditch will be conducted.
When is construction planned to begin? If the Proposed Plan is
accepted, treatability studies and design work should be completed in
the summer of 2003. The entire South Ditch remedy is expected to be completed
by the fall of 2004.
The mouth of the South Ditch has moved over time. The Illinois
EPA is aware that the mouth of the South Ditch may have moved over time
and that contamination probably is located in other places in the area
around the ditch. The whole Southeast Area will be investigated in later
stages of the project. If additional remedies are necessary, the Illinois
EPA will submit a Proposed Plan(s) to the public for comment before selecting
an additional remedy(s) for the area.
Who will conduct the South Ditch remedy? The PRPs will construct
the remedy for the South Ditch with Illinois EPA oversight.
Is the remedy implementable? The Illinois EPA's position is that
the Proposed Plan can be implemented. It may be difficult to implement,
but it is possible. The PRPs, at a citizens' advisory group meeting, raised
questions about their ability to meet water quality standards during dredging.
The Illinois EPA's position is that it is highly important to keep additional
contaminated sediment from entering the lake and that every effort must
be made to meet water quality standards. The Agency takes into account
naturally occurring disturbances of the sediment, such as wind and wave
conditions, when considering compliance. But, releases of contaminants
caused by dredging can and should be avoided to the greatest extent practicable.
The Illinois EPA Proposed Plan, however, does allow the PRPs to conduct
treatability studies. If the PRPs demonstrate through treatability studies
that they cannot meet the standards, then the Illinois EPA will reconsider
its position.
Next Steps
How will the final decision about the South Ditch sediments be made?
The Illinois EPA and U.S. EPA will carefully consider all the public
comments made during the public comment period including the oral comments
at the hearing and the written comments submitted to the Illinois EPA
hearing officer. See the enclosed flyer for more information on submitting
comments.
After considering these comments, the Illinois EPA will make a final
decision about the remedy in consultation with the U.S. EPA. The Illinois
EPA will write a Record of Decision, which will include a summary of comments
received during the comment period and the Agencies' response to these
comments. A notification of the Record of Decision will be advertised
in the local newspaper. The complete document will be placed in the Selby
Township Library in DePue.
For More information
Contacts: You may contact Kurt
Neibergall, Illinois EPA Community Relations Coordinator (217) 785-3819,
or Rich Lange, Illinois EPA
Project Manager (815) 447-2125, at 1021 North Grand Ave. East; P.O. Box 19276,
Springfield, IL 62794-9276.
The PRPs have asked that a contact for their group be listed. The PRP
contact is Jim Frank, Frank and Cowles, 7226 N. State Route 29, Springfield,
IL 62707, telephone number 217-487-7686.
Repositories: The Illinois EPA has placed project documents and
fact sheets in the Selby Township Library in DePue for public review (815-447-2660).
Please call for hours.
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