TAG reports: Volume 3, Number 3; July,2001
Brunswick Wood Preserving OU1 Planned Remedy:
We have received for review several documents related to the upcoming Environmental Protection Agency (EPA) public meeting for the Brunswick Wood Preserving Operable Unit 1 remedy. Although these documents discuss several possible remedies this newsletter will focus on just the EPA’s choice of a barrier wall in situ isolation system with a waste mound and cap. Unfortunately, the documents provide very little actual detail on the system, only a broad concept
Background:
The Brunswick Wood Preserving Superfund Site (BWP site or just the “site”) is a former wood treatment facility located next to Burnett Creek west of I-95 in Glynn County, Georgia. The area is heavily contaminated with toxic levels of dioxins, arsenic, PAH (carcinogens) and other chemicals. A large amount of contaminated soil has been removed by the EPA and the Georgia EPD. Much contamination still remains and contaminated groundwater is moving off-site.
Operable
Unit 1:
The remedy proposed by the EPA is to build a permanent toxic waste landfill near the neighborhoods. The waste mounds will likely be always visible from many houses and Perry Lane Road.
The basic plan is to build an underground “barrel” or “silo” shaped container by digging circular trenches surrounding the contaminated pond areas. The trenches would drop all the way from the surface to a limestone layer where the trench would enter a few feet into the limestone (be “keyed” into the rock). The trenches form the sidewall of the barrel or silo and the limestone is the bottom. The trench backfill forming the side would be refilled with a “slurry“of some of the soils dug from the trench, plus other agents such as clay to reduce the permeability. Reducing “permeability” means to reduce the free movement of water between the contents of the silo and outside the silo. Other areas around the site, such as the former outfall pipe area, the CCA mound left over from the emergency removal action, sediment portions of the creek and other spots of contaminated may be placed on top of the pond areas forming a mound. The entire structure—underground silo and mound—would be capped to reduce rainfall soaking.
Remarks
regarding the slurry walls:
It is not clear why the EPA thinks this system will stop underground contamination of groundwater. The walls may only be 2-feet of clay and sand, which is not much of a barrier. The walls described in EPA’s technical memorandum are relatively thin for this much waste and the barrier walls are still slightly permeable. Groundwater will still flow into and out of the contaminated soil, just at a slower rate. We have not seen computer models or other engineering models for the efficiency of the slurry walls. EPA claims that the documentation is unnecessary at this time. The less water that flows across the walls of the slurry the fewer toxins flushed into the environment. However, as the walls become impermeable, the greater the physical pressure from groundwater flow against the outside of the wall. If there is a very high flow, the outer wall can erode since the walls are thin and soft compared to rock. While particles of sand and clay are not dissolved in water, the individual particles can be carried downgradient as silt, degrading the walls. Note also that while the cap may direct water away from entering the structure it cannot be “drier” inside than out, since water diffusion will occur to correct any such imbalance. This remedy does not treat the bulk of the underground contamination to make it exclude water. The only “treatment” is containment or isolation from the direct flow of water.
Slurry wall systems have been employed with apparent success on smaller scales and at old unlined solid waste landfills where there are small point sources of pollution. The ratio of the internal volume to the surface area of the sidewalls at BWP coupled with the high concentration of toxins may limit the successful use of the same system in Brunswick.
The slurry wall should work for at least the first few years. A reduction in off-site plume width and length should be apparent as dilution occurs downgradient from the isolated waste. Over time compaction of the walls, erosion of the matrix to form voids and channels, and exhaustion of the toxin-binding clay particles can result in increased toxin release.
There is apparently no way to inspect the slurry walls for integrity. The first indication of a problem will be presence of toxic waste in groundwater. For residents this means that those homes and businesses downgradient—to the west and southwest of the site—will always have a future risk of a groundwater plume.
The area needs to remain completely free of trees and woody shrubs. Tree roots can easily puncture the thin walls and release toxins. EPA’s details are sketchy, but apparently the ponds will be enclosed by a single barrier wall/mound. If the wall is breached there will be no way to determine where the hole is, and it might not be readily repaired, even if known.
Remarks regarding the mound:
EPA has not given any firm indication on the height of the mound and cap. It will ultimately depend on the amount of waste exhumed elsewhere on the site and the final dimension of the container. Based on experience at other sites, the volume of contamination at BWP, and the “tree-less” design, the mound should be easily visible from the road and from home sites north and east of the site. Although not a safety hazard, the constant visible reminder of the presence of a toxic waste tomb could depress property values in the neighborhoods.
Volume estimates of 1 to 1.2 million cubic yards of waste for this site are still on the low side. The final estimates are driven by the costs for the minimum amount of cleanup to meet commercial-use safety standards. Increasing the amount of contaminated topsoil that is removed increases the safety of the site, but increases the size of the mound.
Final remarks:
The community should note that EPA has elected to clean other similar sites by techniques such as thermal desorption which actually removes waste. It is not clear why EPA has chosen to leave the waste near the neighborhoods rather than remove or treat it.
The community should hold out for a cleanup based on more stringent residential standards of dioxins and arsenic for surface soils
The long-term effectiveness of this “slurry wall” in situ technique is doubtful. Until EPA provides bona fide numbers and models, we remain concerned that this concept can fail.
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