It is likely that the eventual cleanup of the Housatonic River will include a variety of strategies and remediation
technologies, due to the changing character of the river as it flows south, especially between the General Electric facility and the Connecticut border.
The cleanup will also involve the 250-acre GE site (see Brownfields on page 10) and
Silver Lake, a 30-acre pond at the southern edge of the site, containing as much PCB contamination as the entire river south of GE. PCBs are not known to have migrated from Silver Lake.
The EPA has identified five distinct stretches of river as described below:
The upper reach . . .
that extends from the GE facility to New Lenox Road in Lenox, changes from north to south. The northern stretch is characterized as relatively straight, swiftly moving and shallow, flowing over cobbles and coarse sand, with relatively little silt or clay present. In this section, river banks are well defined and flows are turbulent in many areas. In the southern section of this reach, the river widens, deepens and is slower moving. The river bottom contains more clay and silt. Meanders and oxbow backwaters are present. Some areas are heavily wooded and a portion lies within the Housatonic Valley Wildlife Management Area, owned and managed by the Massachusetts Division of Fisheries and Wildlife.
Within this stretch of river, recent sampling found "hot spots" at the GE facility
(Building 68) which had average concentrations of 2,000 ppm in the sediment, with individual concentrations reported as high as 54,000 ppm in river sediment and 104,000 ppm in the soil of the adjacent riverbank. This is the highest PCB level found to date. GE will be removing this contamination this summer.
In the downstream reach . . .
from New Lenox Road to the headwaters of Woods Pond, the Housatonic River be-
comes a wetland floodplain with backwater areas characterized by an abundance of aquatic vegetation. Much of the lower portion is within the Housatonic Valley Wildlife Management Area. PCB levels as high as 270 ppm have been found in this area.
The Woods Pond reach . . .
the next section, including a 50-acre open-water mill pond. Woods Pond is a manmade impoundment created when Woods Pond dam was constructed. A large wetland is present, wildlife habitat abounds.routine visitors. Woods Pond functions as a sedimentation basin because of the dam. PCB concentrations range from below detection (0.05 ppm) to 220 ppm. GE estimates that 95,000 cubic yards of sediment contain PCBs of 10 ppm or more.
From Woods Pond Dam south . . .
to the Connecticut border, PCB concentrations generally continue to decline as the Housatonic River flows south. Higher concentrations are found behind dams in both Massachusetts and Connecticut sections of the Housatonic River as far south as the Stevenson Dam.
In Connecticut . . .
from Falls Village to New Milford, the
Housatonic is a free flowing erosional habitat where PCB levels in fish respond directly to increases or decreases in the transport of contaminated sediments from Massachusetts. Lake Lillinonah and Lake Zoar, with their respective impoundments, serve as sediment traps which have protected the estuary and Long Island Sound from significant PCB contamination.
CLEANUP OPTIONS
There are a variety of technologies that could be considered for PCB cleanup, ranging from highly experimental, to field-proven methods, all with varying degrees of potential success. The technologies currently being evaluated for the Housatonic River include:
Natural recovery, or the "no-action" alternative, is the gradual silting over of PCB contaminated sediments with cleaner sediments which reduce the mobility of and potential exposure to PCBs. This may be the option used for most of the floodplain areas and areas of low PCB concentration in the river. The drawback associated with this method is that the PCBs would still be in the river system.
Biodegradation, a natural process that uses bacteria to speed up the natural breakdown
of PCBs, is currently unproven in a river system. The few pilot studies which have been done have not produced any significant results.
Armoring is a method whereby PCB contaminated sediments are capped with layers of clean materials. It is generally not used where depths are greater than 10 feet. Armoring eliminates natural vegetation and aquatic habitat, and may alter flow velocities and flood storage capacity. It will most likely destroy river and wetland ecology for an undetermined amount of time wherever it is used.
Dredging technologies, including mechanical, pneumatic, and hydraulic, have been used in other PCB contamination sites, and will also cause the complete destruction of river and wetland ecology
wherever they are used. Dredging removes
aquatic and benthic ecosystems and vege-
tation, destroys wetlands, fish and waterfowl by disrupting their natural habitat. No
dredging technique exists that will remove
100 percent of the PCB contamination.
Dredging may cause sediment resuspen-
sion and downstream transport of PCBs and may
cause contaminant release during handling or transport. Dredging at other sites has not resulted in reducing PCB levels to the point where the water system is once again fishable. This, combined with the high cost of removing, treating, disposing of contaminated sediments, and impacts to the river, make dredging a challenging option.However, failure to remove PCBs from the sediment, will result in continued resuspension and downstream transport of PCBs from severe flood events such as a 50-year storm.
Treating dredged sediment
Wherever dredging is used, sediments will have to be treated and disposed of. A variety of treatment options exist:
Thermal treatment, by either high or low temperature methods, heats the soil to destroy PCBs.
Nucleophilic substitution is a dechlorina-
tion process that can be used after thermal
desorption to destroy the remaining PCBs.
Soil washing is a separation and volume reduction techniques that involves mechanically scrubbing soil with a water solution to remove contaminants for subsequent recovery from the wash water.
Other disposal options
If sediment cannot be adequately treated
and remains contaminated, one of the following disposal options may be used:
Confined Aquatic Disposal, (creating an
in-river cell for disposal) is unlikely to be acceptable due to regulatory limitations
under the Clean Water Act, local hydrogeo-
logy, shallow depth to groundwater, perme-
able soils, proximity to aquifer recharge
areas and drinking water supplies and pub-
lic health concerns. This method is especially unacceptable for areas with higher PCB concentrations, if the goal is to remove them from the river system entirely.
Local Upland Disposal may be feasible from an engineering standpoint, however past studies indicate there may be no site that meets all of the siting criteria. There may be reluctance on the part of local communities to host such a facility. Dredged sediments need to be dewatered; the water must then be treated to remove suspended PCBs before upland disposal. Long term monitoring and treatment of potentially PCB contaminated leachate is essential.
Off-Site Disposal, where the material is taken away from the site to a licensed hazardous waste landfill or disposal facility, may be seriously considered as a preferred disposal option, regardless of the higher transportation and disposal costs associated with it.
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