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Brunswick Wood Preserving Superfund Site
TECHNICAL ASSISTANCE REPORT

Volume 6, Number 1                                                                               December 2004

 
 
Brunswick Wood Preserving Remedial Design
 
 

Overview

   We received for review the Brunswick Wood Preserving Site Final Design Report dated October 14, 2004. This document discusses in detail the planned project for remediating the Brunswick Wood Preserving Site.

   The Design follows previous models for incorporating toxic site soils, and the remaining toxic waste piles, into two caps for reducing rainwater movement.  The caps would be placed on top of old pond areas where contamination remains in contact with groundwater. Barrier-wall impoundments would be constructed around underground waste to slow release of site contaminants into groundwater.

   In addition to the Design this document includes the results of recent studies at the site, and previously unavailable discussion of the site groundwater and underlying geology. The document provides the most complete view of the site yet released.

   The Environmental Protection Agency stated in the Record of Decision and at a formal Public Meeting that the limestone layer beneath the site would act as a fully confining floor for the proposed barrier walled impoundments. It appears from the actual data this presumption was too optimistic and the limestone layer is not full protection for the lower aquifers.  

Site History

   The Brunswick Wood Preserving Superfund site (“BWP” or the “site”) is an old wood treatment facility. The plant produced creosote and CCA (copper-chromium-arsenate) soaked wood products from local timber. A large contaminated area includes heavy metals, aromatic hydrocarbons (some are known to cause cancer) and dioxins. Cleanup operations by both the U.S. Environmental Protection Agency (EPA) and the State of Georgia left considerable toxic waste at the site. Two toxic plumes of groundwater flow underground from the site. Toxic releases into adjacent Burnett Creek are still common.  There have been numerous studies and meetings for this site. A Record of Decision (ROD) and Public Meeting were held earlier to discuss the remedy.

Overview of the Proposed Remedy

   There are six basic parts to the remedy proposed in the ROD:

1) Construction of two underground confining areas in the old ponds by digging trenches down to a limestone layer and backfilling with a slurry of materials to form barrier “walled” impoundments;

2) Consolidating contaminated on-site surface ground materials onto the top of the confined pond impoundments;

3) Digging out areas of contaminated creek sediments from Burnett Creek and placing them within the consolidated areas on top of the old pond impoundments;

4) Placing a rainwater-shedding cover on top of the impoundment mounds;

5) Treating remaining groundwater areas outside of the impoundments; and,

6) Long-term monitoring and site maintenance.

 

Overview of the Design Report

   The Brunswick Wood Preserving site is not stable: there are groundwater contamination plumes spreading west and south from the site; dense non-aqueous layers (DNALs) are sinking and moving beneath the site; there is surface runoff into Burnett Creek; there are groundwater releases to Burnett Creek; there are contaminated materials in Burnett Creek moving downstream; and, trespassers are exposed to site contamination through faulty security.

   The proposed barrier wall impoundments will confine a large percentage-- but certainly not all-- of the waste within the borders of the former pond areas. This will reduce, not end, the release of toxins into the surrounding groundwater. This is not a treatment. The toxins will still be present, but over time it may reduce the amount of waste release. It is not practical with the information provided to determine how much waste will continue to enter the system or how soon residents will see a difference.

   Building a rainwater-reducing cap over the impoundments will somewhat reduce water movement. However, the cap is too small to really change the amount of rainwater adding to the groundwater, so flow will not be impacted significantly. Further, the Dense Non-Aqueous Layers of pollutants are moving as a result of gravity, not driven by groundwater flow. The cap should have no impact on that material.

   Consolidating the surface soils is not a cleanup, merely moving waste from one part of the site to another provides no real advantage. There may be some benefit to animals using the site, although EPA has done a poor job quantifying environmental exposure.

   The proposed cleanup of Burnett Creek is by far the best part of the Design. The actual removal of waste from this stream can have big impact on the health of area waters.

The in situ treatment of organic wastes in groundwater is beneficial to reducing the off-site plumes that now extend under the highway and beneath adjacent properties. Combined with the slurry wall impoundments used to reduce wastes the in situ treatment has the potential to reduce off-site contamination. However, this is a future benefit; there will be no short-term reduction in the footprint of site contamination.

   Throughout the history of this site there have been reports the EPA was unable or unwilling to maintain the integrity of site fences, post effective signage, and control access. The proposed long-term site security plan requires more work to build genuine barriers to entry.

 

Findings

   The Design provides additional information on groundwater flow, toxin movements and the geological makeup of the site that was not previously available during the Remedial Investigation phase.

Plumes:

   The plumes of contamination that originate in the former ponds extend much further than previous documents indicated. One plume originates in the IM-1/IM-2 pond area and the second plume begins in the IM-4/IM-5 area.  The larger of the two plumes is the Eastern Plume that starts in the IM-4/IM-5 pond area and moves easterly towards Perry Lane Road and Burnett Creek. This plume contains significant amounts of polycyclic aromatic hydrocarbons (“PAH”’) a mixture of many chemicals, some of which are known carcinogens.  The plume from the IM-1 area reaches Burnett Creek, but apparently does not pass it. The best explanation for the data is that the toxins enter Burnett Creek. At this time there are two few observations to provide velocity of contaminates to the creek or to estimate chemical mass calculations.

Barrier Wall Construction:

   The purpose of the barrier walls (often called slurry walls) is to prevent the horizontal plume movement of toxins in groundwater. The old ponds are the source of toxins in groundwater plumes. Hydrocarbons (the oils in the creosote used to waterproof the logs) and toxins (a variety of chemicals were added to reduce rotting) left in the ground are moving both downward by the pull of gravity and moving away from the site in the groundwater currents flowing under the site. The downward vertical migration will not be stopped by the building of barrier walls or caps. However, the horizontal movement in groundwater could be stopped by creating large circular containment walls underground.

   To produce a slurry wall, a trench is dug from the surface down to a limestone layer beneath the ponds. The trench would be 3 feet (about 1 meter) wide and form a complete ring around the waste. There would be two such trenches, one around the ponds in the IM1/2 areas, the other around the IM4/5 areas. The dimensions of the walls for the IM1/2 impoundment are unchanged from the Record of Decision phase. For that impoundment, the critical eastern boundary was defined by proximity of Perry Lane and could not be expanded. For the IM4/5 ponds the wall was moved further outward to better enclose high concentrations of groundwater contaminates.

   The slurry material poured into the trench to form the wall would be fill dirt mixed with clays, such as bentonite. Fine clays have a high surface area and are not very wettable—they do not take up water easily. Material that becomes stuck to the surface of clay tends to stay attached and clay particles neither shrink nor swell. Properly constructed man-made clay-containing walls are known to be stable for generations.

   The entire design calls for a rainwater-shedding cap over the impoundments after construction of the underground walls. The thought by the EPA is that with little rainwater entering the impoundment there should be little water leaving the impoundment; accordingly, there should be no release of toxins to the environment. However, rainwater and horizontal groundwater flow are not the only potential sources of water that could enter the impoundments. The floor of the impoundment will allow movement of water into and out of the impoundments—unless there is a perfect seal between the upper and lower aquifers. The data provided by EPA suggests that the limestone layer is not such a perfect seal. In a best case scenario voids and areas of high permeability within the limestone floor would allow water to migrate upwards into the impoundment container, and then slowly out through the walls of the impoundment. This would greatly reduce influx of contaminates into the upper aquifer, probably at the levels where natural dilution would render them harmless.  A worse-case scenario is that water from the lower aquifer would slosh up and down with fluctuations within the impoundment, exchanging clean groundwater with contaminated groundwater and resulting in a deep plume within the lower drinking water aquifer. A scientifically constructed monitoring system with independent oversight is needed to assure the public that this remedy works and is safe for the long-term.

Treatment of Hazardous Plume Material:

   After the slurry walls are complete and the areas beneath the ponds are no longer sources of contamination there will still be toxic materials in groundwater outside of the slurry wall impoundments. This material will continue to flow off-site for the foreseeable future. The Design states the groundwater toxicity will be reduced by injecting treatments into the groundwater. This discussion remains unchanged from previous statements in the ROD and at the public meeting. The rate at which pollutants would be removed would depend on how aggressive the treatment is; the more injection points and the higher the concentration of treatment reagents the faster the plumes would be reduced to non-toxicity. Unfortunately, the Design does not provide specific details on the treatment chemicals and concentrations, or where injection pumps may be placed, or how many pumps would be used, or what flow rates will be used. However, although the Design document does not allow estimates of how fast the groundwater may be cleaned, underground treatment of this type of toxin is a mature technology and should work.

DNAL Containment:

   It would be fair to say that the success of this remedy relies on the ability of the bottom of the containment impoundments to retain toxins. According to the ROD, when a barrier walls is entrenched into the limestone layer that forms the floor it should act like a giant bucket, with the consolidation and cap forming the lid. There is little doubt the slurry walls can be built as described, and landfill caps are well known technology. However, there is no engineering to the bottom of the “bucket”, it either works or it does not.

   The Design document describes nine geological layers, numbered from the surface down about 75 feet below the surface. Each “layer” is a collection of sands, gravels, clays, rocks, and/or solid limestone that is characteristic for the layer. The first six layers are not relevant to this discussion since the bottom of the slurry wall could not form a seal in any of those layers. For example, stratum 6 (layer 6) is described as dark sand (with) little to some fine gravel, shell fragments (ancient mollusk shells), and trace to little fines. Trenching into this sandy layer and backfilling with slurry would have little effect on waste mobility, groundwater would flow into the “impoundment” under the wall, and toxins would just continue to flow out. Ideally, the stratum used for the containment should be like cement, and should be like cement over the entire impoundment.

   Stratum 7 is the layer described as ideal in the Record of Decision. However, further studies show this layer is not consistently thick. Further, stratum 7 in some areas is two layers and in others a single layer. EPA has designated some areas to have layers 7a and 7b, where 7b is more like hard limestone and 7a is limestone “weathered” to the consistency of gravel. Some areas studied lack a stratum 7b. For example, on Design Sheet BW-3 there is no layer 7b at the boring BRU-GT-3, only the weathered limestone layer 7a, and it is not especially thick either, only a few feet thick there, and even thinner at nearby boring BRU-GT-4. Note also that even the limestone of Stratum 7b is described as having voids (open spaces with water) and areas of imbedded sand, gravel and clay—it is not always solid rock. It is clear the weathered limestone layer described in the Record of Decision is not adequate protection as an impound floor.

   To get around the problems with the limestone layer, EPA states the barrier wall will pass through the limestone into layer 8, a stratum of mixed sands and clays. Laboratory studies on the clays indicate this layer is a low permeability layer, similar to material proposed for the slurry walls. If the layer was thick enough and consistent enough it would form an effective bottom to the slurry wall impoundment “buckets.” However, data casts doubt on this for the IM4/5 impoundment, which raises questions regarding the sufficiency of this layer for the entire project. In the IM4/5 impoundment footprint some areas of stratum 8 are too thin and the layer contains sands and materials that can conduct water. In these regions the barrier walls might not form a good seal with the strata. It is important to note that it is not just the intersection of the barrier wall and bottom layer that results in a stable impoundment. Rather, the entire floor must be free of channels, gravels, sands and other artifacts. Water follows the path of least resistance underground as on the surface and the entire base must have water resisting features or there will be movements of water into and out through the impoundment floor.  The variability of the strata and the large size of the areas to be confined indicate that neither stratums 7 or 8 are sufficient to guarantee waste confinement.

   The Design plan calls for the engineer to make judgment calls during slurry wall construction, ending it in either layer 7 or layer 8 depending on results of the digging. In the Record of Decision and at the Public Meeting there was no mention of such guesswork, the public was told unequivocally the limestone layer was more than adequate and would work unconditionally.

   It is likely the impoundments will be only a first step, and some form of technology will be necessary to actually treat material within the impoundments. EPA notes the possibility that additional treatment could be needed, but the Design documents lack specific information on further treatments or monitoring criteria that would trigger a decision to begin treatment within the impoundments.

Burnett Creek Cleanup:

   During and after plant operation toxic material washed into Burnett Creek. Some of this material has detoxified by natural processes—dilution, biological degradation, photochemical breakdown, and similar processes. Some “pockets” of contaminated sediment remain and must be removed. The estimates provided in the Design documents indicate that 300 cubic yards must be dug out of the creek and returned to the site for processing.  This amount is probably low. For reference, a small “dumpster” trash bin is about 2 cubic yards, so the removal of 300 cubic yards is not a large volume of sediment considering the length of the creek. However, that amount would aid the creek’s recovery when combined with the site no longer being a source of continued contamination.

Soil Consolidation:

   This section is little changed from the Record of Decision. Essentially, contaminated surface and subsurface soils from areas on site and some sediment from Burnett Creek will be “consolidated” (dug up) and placed on top of the slurry wall impoundments. There is no net decrease in total toxicity at this site, and the waste is not “clean” in any way after consolidation. However, areas that were highly contaminated at the surface will be less so after consolidation. Consolidation could reduce toxic runoff to Burnett Creek. Consolidation’s main benefit would be to wildlife and trespassers that are exposed from activities on the site. Both groups are poorly quantified by the EPA, so the degree of potential benefit is hard to estimate.

Cap Construction:

   After soil consolidation, the pond areas will have a grade that is higher than the surrounding landscape—they will no longer be ponds they will be low mounds. The purpose of the landfill caps is to reduce or prevent rainwater from entering the impoundments through the consolidated soil mounds. If the impoundments are successfully constructed, they will act like buckets buried in the ground. If significant amounts of water were allowed to enter from the top, the impoundment would fill and spill over, causing the consolidated material on top to become unstable and possibly erode. Caps placed on top of the impoundments should shed water—this would not decrease or increase plume movements-- merely keep the impoundments from catching rainfall. Rainfall would continue to be diverted to Burnett Creek through surface channels. The scenarios provided all should work to shed water as described.

Monitoring/Institutional Controls:

   Long-term monitoring is required to know if the remedy is working. Monitoring includes checking chemical concentrations and movements within the groundwater plumes outside of the impoundments. These chemical levels would be expected to diminish over time. If the remedy is successful, the plumes extending off site should withdraw from their present tracks, and then dissipate. Deep monitoring outside of the impoundments is needed to ensure the impoundments retain toxins and are not leaking to the deeper aquifers.

   Monitoring inside the impoundments would expect to show stability-- no diminishment over time. It will be very important to monitor fluctuations in water levels within the impoundments. Each impoundment will need multiple measuring devices and the readings should be monthly for the first five years.

   The height and side slopes of the consolidation and cap should settle during the first few years, and then become stable. Burnett Creek monitoring should show no contamination after a few years. Institutional controls include fences to restrict access, repair of the cap from weather erosion—and there will be weather erosion-- and landscaping to control destructive vegetation on the caps.

Conclusions

   The geological layers underneath the areas proposed for the slurry walled impoundments do contain some regions that can block toxin movements; however, it is also clear some areas will not provide a continuous “floor” to the impoundments. Just as a bucket with a single hole will eventually leak all of its contents these impoundments will not hold material indefinitely. Using the bucket analogy, the rate at which the contents leak depends on the number and size of the holes in the bottom. There is insufficient information in the Design to predict with accuracy how well the impoundments will work.

   It can be agreed that the walls will be effective if properly constructed; three-foot wide walls of high content clay material can be effective chemical barriers. The notion that excluding rainwater will improve DNAL migration is not supported by scientific studies at other sites. The DNAL migration is driven by physical interactions and gravity, not by rainwater intrusion or flow. If anything, the DNAL movement may speed up when the slurry walls are in place since lateral groundwater movement would cease.

   The Design lacks sufficient detail on the monitoring system envisioned for the interior of the impoundments. Annual monitoring of a single well within the impoundments would be grossly inadequate. Multiple monitoring wells at several points within each impoundment are needed, and the wells should be sampled monthly for at least the first few years to assure stability within the impoundments.

   Since it now seems likely technology will be needed to treat material within the slurry walled impoundments there should be a thorough discussion of the types of technologies that would be employed. A decision mechanism needs to be added to the Design for implementation of treatment if water levels within the impoundments are seen to be changing, of if monitoring within the deep groundwater indicates migration of contaminants. Specific legal language should be added to the Record of Decision and Scope of Work documents regarding the limestone and deeper layers to be used as the floor of the impoundments, since these are not as described to the public.

   Cleanup of Burnett Creek appears limited in scope. However, removal of even 300 cubic yards is a big improvement over the current condition. Consolidation of toxic surface materials on-site provides no advantages in terms of reduction of waste, removal would be better. It will improve the quality of life for wildlife that accesses the site. Trespassers continue to enter the site. Site security and signage needs to be better defined than currently described in the Design.

   Studies on the geological layers indicate there really are no options if the trenching fails to find a secure layer to act as a solid base. Those sections of the wall inadequately keyed to limestone or clay will simply leak waste at that spot.

   This is a remedy with no margins for error on a geology marginally suited for the technology.

In the long-term, the safety of this Design is invested in the natural floor of the impoundments and the security of the fences. Neither is adequately defined in this Design.

 

Written by R. Kevin Pegg, Ph.D.; edited by Dr. Mary S. Saunders. Copies of the newsletter are available from the GEC, at the Glynn County library, or at www.enviro-issues.net on the Internet.

"This project has been funded wholly or partly by the U.S. Environmental Protection Agency under Assistance Agreement Number 1984482-98-0 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."

 

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