Based on the results of
recent studies it appears in situ stabilization can work to protect groundwater from toxic waste at the 009 Superfund
Landfill. The 009 dumpsite is a source of toxic contamination for residents along Spur 25 in
In 1992 the EPA proposed in situ stabilization to
control future toxaphene toxicity at the site. In situ stabilization uses underground mixing of
concrete and buried waste to prevent further spread of toxins. In situ stabilization is an
experimental approach for treating pesticides. Accordingly, in 1993 the EPA required laboratory and field
studies to determine if in situ will work at this site.
The results of these studies show that in situ
can be used at the 009 site. Although not all of the studies provide clear results there was enough
information to conclude that the site will show greater long-term stability with in situ
treatment, and is less likely to impact ground water in future years.
The Hercules 009 Landfill was created out of a
roadbed borrow pit in the mid 1970's using pesticide sludge from manufacturing operations.
Located in Glynn County along the Golden Isles Parkway the site is also bordered by an
elementary school, a neighborhood, and several businesses. The site was closed in 1980 after
toxaphene waste was found in nearby streams. Later studies found very widespread contamination
throughout the adjacent neighborhood and schoolgrounds. The full extent of contamination
in the schoolgrounds and along the highway remains unknown at this time. Local residents and
businesses are now on public water supplies as a precaution against groundwater contamination.
Toxaphene is a carcinogenic pesticide banned in
the United States. Toxaphene is linked to organ (kidney and liver) damage and causes mutation and
cancer under laboratory conditions.
The site became a Superfund in the mid 1980's and
the Environmental Protection Agency (EPA) is the lead agency overseeing the cleanup. The 1993
Record of Decision (ROD) specifies both primary and alternate cleanup methods. The
Responsible Party-- Hercules Incorporated-- tested an experimental procedure called in situ ("in
place") stabilization. In situ is experimental at this site since until recently the technique was not used
for pesticides. If in situ fails then the company must dig up the soil to extract the toxaphene.
Tests Mandated by the Record of Decision
The EPA has seven goals to meet for every
cleanup: overall protection; legal compliance; effectiveness; cost; reduction of toxicity,
mobility or volume; and community acceptance.
During the Feasibility Study for the 009 Site
several alternative technologies were examined and two methodologies were specified: in situ
stabilization and chemical extraction. Chemical extraction provides the best overall protection
since the site will have no long-term toxaphene concern. Extraction has wider community
acceptance for the same reason. The EPA chose in situ stabilization as a primary alternative and
required on-site studies to determine if cleanup goals are met. If waste is not isolated from ground water
flow by underground cement mixing then chemical extraction is required for the site.
The EPA established scientific criteria for the
site studies. Three broad goals must be met using a combination of laboratory and field studies:
determine cements for the highest degree of immobilization; confirm performance under
worse-case environmental conditions; and evaluate long-term permanence for ground water protection.
Specifically, the stabilization must achieve a minimum compressive strength of 50 psi
(pounds-per-square-inch); a permeability of less than 1 X 10-6 cm/sec after stabilization; a 90 percent
reduction in toxaphene mobility; and a treated leachate concentration of less than 0.2 ppm.
Minimum compressive strength: This is the ability
of the ground to support objects and to resist erosion. Both laboratory and field studies show
that cement formulations meet this criteria.
Permeability of less than 10-6 cm/sec:
Permeability is the ability of water to flow through a material. To ensure long-term stability it is
important to reduce ground water flowing into the toxaphene sludge. Toxic waste dumps need a water
tight lining to prevent water flow from entering into the waste disposal area. At the 009
Site studies have failed to establish the presence of a liner or other permanent barrier to the
entry of flowing water. The in situ stabilization process is intended to limit water flow into the
buried waste. The studies show that underground mixing of concrete is homogenous enough to form a
monolith when concentrated cement formulations are used. The resulting monolith
reduces the flow of water through the sludge layers, thus meeting this criteria.
A 90 percent reduction in toxaphene mobility, and
a treated leachate concentration of less than 0.2 ppm: These factors are important only if
water is allowed to interact with site sludge.
Unfortunately, this data is ambiguous due to
problems in analyzing toxaphene in treated water. From the information provided it is not readily
apparent that these criteria are met. However, the permeability data of in situ stabilized
sludge shows that water would not enter the monolith in amounts that would cause leaching concerns.
Studies on Treatability
Over the last three years studies required by the
EPA were performed as mandated in the Record of Decision. These studies are a comprehensive
test of ability of cement to prevent the interaction of toxaphene and groundwater. To test
the cement three kinds of studies were done:
Laboratory "Benchtop" tests, site soil
characterization, and an on site trial of in situ using the cement and equipment that would be used to remedy
the site .
Laboratory studies These studies focused on
choosing a cement formulation for use in the field demonstration. Site soils were taken to a
laboratory and mixed using several different cement formulations. Some of the formulations used
different ratios of cement to soil, ranging from 15% mixtures up to 50% (equal amounts). Some trials
used different kinds of cements or chemical binders to trap toxaphene. All of the resulting
hardened mixtures were tested under simulated environmental conditions for strength, stability,
and reduced water migration. Finally, the solidified cement/soil mixtures were broken up
and the toxaphene extracted. The purpose was to find ratios of cement and soil that were strong,
hardened rapidly, and would limit the flow of groundwater. The higher cement/soil ratios
(around 30%) were the strongest, solidified the fastest, and reduced water flow to the highest
degree. However, all of the cement formulations worked well. Studies showed that there was no
real advantage when using an organic binder.
One problem was prevalent throughout these
studies. The cement formulations leached a material that interfered with Gas Chromatography (GC)
analysis of toxaphene. These studies use the Toxicity Characteristic Leaching Procedure (TCLP)
to determine the degree to which toxaphene leaches from the cement. Hercules' contract lab
worked to prevent this problem, but in the end
there is no firm data on immobilization of
toxaphene using the TCLP protocols. However, in all fairness the TCLP data is less critical in this
case than the water permeability data.
Water permeability findings show that water will
not easily flow through the solidified waste. Leaching is proportional to flow, so reducing
permeability also reduces leaching. Therefore, the TCLP data problem is not very important in making
a decision on proceeding with in situ.
Characterization of Soil
As reported in previous TAR newsletters (Volume
4, Number 2, August 1995) studies conducted at the site revealed deeper toxaphene contamination
than previously thought, and numerous buried objects. The site was tested using metal
detectors and the presence of metallic debris mapped. Several pits were dug into the landfill and the
presence of concrete and other construction debris noted. Also, "grab" samples were taken into the
site at various depths to characterize the waste profile. These studies suggested that in situ
stabilization needed to be deeper than called for in the Feasibility Study. Further, the numerous
buried objects raised concern that the site could not be mixed well enough to thoroughly trap the
On site in situ field trial
The on site in situ trial was designed to test
concrete formulations that showed promise during the Benchtop studies. Also, the process tested
methods of immobilization to ensure that site soils could be treated without interference from buried
objects. The trial was conducted at the 009 Landfill to depths of 20-25 feet underground.
This depth is sufficient to ensure that the main mass of toxaphene will be treated. The studies show
that the concrete mixture may need to be more concentrated at the north end of the site to
compensate for the differences in soil type. Some of the material was removed and tested after
solidifying underground. These tests, demonstrating both strength and low ground water permeability,
indicate a successful experiment. At one time a collar used to guide the underground mixing
augers broke during operations. This may have occurred from encountering underground debris.
After repairs the stabilization continued without further problems. It does not appear that buried
objects significantly interfered with the technology as carried out at this site.
Ground Water Model
The Final Treatability study produced by Hercules
includes an elaborate ground water computer simulation. This study is not required by the EPA
and is not necessary for determining the effectiveness of cement to decrease water/site
soil interactions. The Glynn Environmental Coalition contracted Disposal Safety Incorporated
to review this model with respect to the cleanup objectives for 009. A full copy of this
report (Groundwater Transport Modeling in Hercules' Treatability Study; March 30, 1996) is available
from the Coalition. The discussion is summarized here.
Ground Water Transport Modeling
Memo to the GEC from Disposal Safety Inc.
This memo has been prepared solely for the
guidance of the Glynn Environmental Coalition in interpreting information
available to it. Other users should satisfy themselves independently as to the facts and
conclusions contained herein. In particular, such users should refer to the
original sources of information rather than to this memo. This memo is not intended for
use in any real estate or other transaction, and should not be used or
relied upon for such purposes.
Section 4 of the Treatability Study examines
the potential for toxaphene to migrate from the site via the ground water. However,
EPA's ROD does not require ground water transport modeling, which has limited
relevance to the issue of treatability, so why has Hercules expended a significant
amount of effort to modeling and included it in the treatability study?
The likely answer is contained in the
study's Executive Summary, which states that the purpose of ground water modeling is to:
... evaluate the appropriateness of in situ
technology performance criteria specified in the ROD, and the effectiveness of in situ
stabilization in providing ground water quality relative to other remedial options.
It thus appears that a major purpose of this
section is to support Hercules' arguments against the remedy and performance criteria
specified in the ROD. Although the transport model has little bearing on the
effectiveness of in situ treatment, which makes most of the content of this section
extraneous and irrelevant to the Treatability Study, this work is worth summarizing
because potential toxaphene migration via the ground water is so important.
Hercules' consultant uses mathematical
modeling to predict the potential for the ground water to transport toxaphene from the site
via two mechanisms: transport via sorption to migrating colloid-sized particles and
Colloid transport: As the ground water
travels through the aquifers, particles suspended in the water are often filtered
out by the soil. However, there are cases where very tiny soil particles (called
colloids) can travel through the aquifer along with the water without being filtered out.
Whether this occurs or not is mostly controlled by sizes of soil grains that make
up the aquifer and the size of the colloids suspended in the ground water. Since
toxaphene is known to sorb (or adhere) to soil grains, Hercules' considered the possibility
that toxaphene might be carried through the aquifer as colloids. The Treatabilty
Study used a published mathematical rule of thumb, based on soil and aquifer grain
sizes, to evaluate this possibility. Based on the measured sizes of the grains making up the
toxaphene sludge, the landfill dirt, and the surrounding aquifer Hercules consultant
concluded that colloid transport will not occur.
Dissolved Transport: To predict the rate and
extent to which toxaphene dissolved in the ground water might migrate away from the
landfill, Hercules' consultant used a computer model called AT123D. This model,
first published in 1981, incorporates fundamental properties of the aquifer, the
contaminant, surface soils, and the climate to predict toxaphene migration over time. To
simulate conditions at the 009 Landfill site, Hercules' consultant had to specify
the required input values in to the model. Some of these values were based on
properties measured at the landfill, others were assumed based on the values published in the
Hercules' consultant used the AT123D model
to predict the degree of toxaphene migration 100 years in to the future under
A continuation of current conditions (no
further remedial actions), In Situ treatment of the sludge and soil, and Capping the soil
with a multi-layer cap that is impervious to water.
In all cases, the AT123D model predicts
little or no transport in ground water and toxaphene concentrations that are less than
drinking water standards at the property boundary.
Evaluation: The modeling approach appears to
be generally sound; however, there are some questionable input parameters which
cast doubt on the validity of the exact predicted transport distances. For example,
Hercules' consultant assumes a toxaphene solubility in water of 0.55 mg/L and a Koc
of 210,000 ml/g (Koc is a measure of a chemicals tendency to sorb to organic
carbon, which can be related to its tendency to migrate in dissolved form through aquifer).
These values are somewhat different from other published sources. For example, the
Groundwater Chemicals Desk Reference (Montgomery and Welkom, 1990) lists a Koc
value that is 140 times smaller than that used by Hercules' consultant (the lower the
value, the more readily a chemical can move). Also, the Reference lists a range of
published water solubilities (0.4, 0.74, 1.75, 3 and 3 mg/L) that yield an average
value of 1.78 mg/L. This value is nearly three times higher than that used by Hercules
consultant (the higher the value, the greater the solubility of toxaphene in ground
water). As shown in the sensitivity study (Appendix Q), the AT123D model is most
sensitive to these two parameters.
Despite these problems, the fundamental
conclusion that toxaphene migrates very slowly in the dissolved form is likely to be
correct. This conclusion, however, is neither new nor surprising, since in 1992
Hercules had already stated in the Remedial Investigation report (page 4-15) that the
chemical characteristics of toxaphene indicate that it will be largely immobile in
soils and groundwater. The transport modeling merely restates this same finding
in a more quantitative way. Furthermore, past and present ground-water monitoring has
not shown compelling evidence of a toxaphene plume.
Despite Hercules' argument to the contrary
the recent transport modeling results do not appear to be significant enough to compel a
reconsideration of the soil/sludge treatment remedy chosen by the EPA. As shown
by the 1993 Record of Decision, in which the EPA repeatedly cites the lack of a
toxaphene plume in support for no immediate action on groundwater remediation,
EPA has already factored into its remedy selection the low expectation for
toxaphene transport by ground water.
Furthermore, data collected in the
Treatability Study support EPA's cautious approach to remediation. As shown in Figures E-1
through E-3 of Appendix E, soil samples collected from different depths show
numerous instances in which clear toxaphene "hits" were recorded as much 14 feet into
the undisturbed native soil. This is as much as 20 feet below the observed toxaphene
sludge layer. Although it is possible that these "hits" were caused by the coring
equipment dragging down contamination from above (which would indicate sloppy
technique), it could also indicate that toxaphene does exhibit slightly more than the expected
mobility in the aquifer. ---Steven Amter,
Senior Hydrologist, Disposal Safety
Will in situ make the landfill safe?
Probably, yes. The main concern with toxaphene is
mutagenicity and carcinogenicity. However, toxaphene is a mixture of many
different chemicals and the actual cancer and mutation causing chemicals are not known. The model for movement
of toxaphene chemicals in the environment is based on testing a few of the chemicals and it is
not known if the cancer-causing chemicals move at the same speed, or slower or faster. The
safest long-term remedy is the soil extraction option.
Considering how little is known about toxaphene
and the ambiguity in many of the site studies the community is justified in asking for the soil
In situ stabilization will decrease water flow in
the dumpsite soil and greatly decrease any potential future movement of the toxaphene
chemicals. The dumpsite will be safer with in situ stabilization than without it.
Are there any options besides in situ
stabilization and extraction?
No. The EPA considered several capping options
during the feasibility study and Hercules has proposed reopening the ROD to reconsider capping.
Placing a cap over the landfill only prevents occurrence of any more erosion spills such as
those that occurred in the early 1980's. Capping does not reduce ground water flow throughout the dump.
Complete removal is the appropriate treatment for carcinogenic compounds in contact
The EPA has asserted in situ as a compromise
between the communities desire for full removal and Hercules' preference of inexpensive
The 009 landfill is in the heart of Brunswick's
expanding commercial and residential areas. Nearly 20,000 tons of pesticide residue with a long
environmental fate is buried in an unlined pit in contact with the shallow ground water. This waste
will remain toxic for centuries. Local residents impacted by the pollution and a majority of the
community preferred that the toxaphene waste be removed. Removal costs are quite high due to
the problems of moving a toxic waste dump in such an urbanized area. Since it is well known
that toxaphene dissolves poorly in water the Environmental Protection Agency promoted in situ
stabilization as a remedy for this site. In theory, the underground mixing of concrete and
contaminated soil would form a relatively water tight mass that protects the aquifer for
generations and produces no fugitive toxins that might trouble neighbors. The community agreed to abide
by the findings of a scientific study to determine if toxaphene contaminated soils would
form a water resistant monolith using in situ stabilization.
The results of this study do indicate that in
situ is a practical treatment for this waste. Unfortunately, Hercules has used the Treatment
Study to advance a plan that would leave buried waste untreated. It is unclear at this time if
treatment will actually begin, or if more studies and models will be attempted.
The Environmental Protection Agency is urged to
ignore challenges to the Record of Decision and complete this cleanup in a timely manner.
Written by R. Kevin Pegg, Ph.D.; edited by Dr. Mary S. Saunders. Copies of
the report are available from the GEC, at the Glynn County library, or
at www.enviro-isues.net on the Internet.
"This project has been funded wholly or partly by the U.S. Environmental
Protection Agency under Assistance Agreement Number V994050-92-0 to The
Glynn Environmental Coalition, Inc. The contents of this document do not
necessarily reflect the views and policies of the U.S. Environmental
Protection agency, nor does mention of trade names or commercial products
constitute endorsement or recommendation for use."