| Clearwater =
has created=20
this webpage to provide background on environmental dredging, =
which is=20
distinctly different from dredging used for navigational and =
construction=20
purposes.
Navigation and Construction Dredging
This technology is used to remove accumulated =
sediment=20
and debris from waterway channels in order to improve navigation =
and also=20
used for construction projects. Large open clamshell dredges fall =
into=20
this category. These dredges are NOT used for cleaning up toxic =
materials=20
like PCBs, as GE has portrayed in its intentionally misleading,=20
multi-million dollar advertising ``blitz=C2=B4=C2=B4.
Environmental Dredging
Environmental=20
dredging is used to remove contamination from targeted areas. This =
technology is very precise and is designed to minimize =
resuspension of=20
small sediment particles that may be contaminated with PCBs, heavy =
metals,=20
or other toxic materials. This process is much more controlled =
than=20
navigational dredging, using technologies like the hydraulic =
dredge, which=20
functions like a large vacuum cleaner to remove contaminated =
sediments=20
with strong suction pumps.
Examples =
of=20
hydraulic dredges include the cutterhead and the eddy pump. Most =
hydraulic=20
dredges have a cutting head to dislodge the contaminated sediment =
which is=20
immediately suctioned into a pipe. This diluted sediment, or =
`slurry=C2=B4, is=20
pumped through a flexible, floating pipe to a covered floating =
barge, or=20
directly to an on-land dewatering facility, where the sediment is =
allowed=20
to settle out of the water. PCBs will then be separated from the =
water by=20
a multi-stage sand and carbon filter system. The purified water is =
released back into the river cleaner than the river water =
itself.
The sediment that accumulates at the bottom of =
the=20
settling basin is removed, dried, immobilized with cement-kiln =
dust, and=20
shipped by rail to a landfill near Buffalo, NY, that has been =
built to=20
specifications outlined in the Toxic Substances Control Act. Some =
of the=20
`hotter=C2=B4 sediments may be treated to remove and destroy PCBs =
before=20
shipment. These processes must occur in an enclosed environment to =
prevent=20
volatilization of PCBs.
Environmental =
dredging=20
is much more precise than navigational dredging. Environmental =
dredges are=20
often fitted with GPS, video and/or sonar equipment to monitor the =
process. During hydraulic dredging the river remains clear enough =
to allow=20
underwater cameras to guide the operations. Multiple water testing =
sites=20
are set up in the vicinity of dredging so that if a problem should =
arise,=20
it will be immediately detected and the operation can be quickly =
shut=20
down. Safety precautions include silt curtains, which are used to =
surround=20
the work area to contain any loose sediment.
There is nothing new, untried, or experimental =
about=20
environmental dredging. Environmental dredges are proven =
effective. EPA=20
has used environmental dredging at many sites around the country, =
and=20
state environmental agencies also make wide use of these =
technologies. One=20
recent success story occurred in Cumberland Bay, part of Lake =
Champlain=20
near Plattsburgh, NY. In a cleanup ordered by the NYS DEC, one =
small=20
dredge boat removed sediment containing 25,000 pounds of PCBs over =
the=20
course of three summers. Two nearby swimming beaches remained open =
and a=20
paper mill process-water intake limited to 2 ppb sediment content =
remained=20
open despite being within 50 feet of the dredging operation. =
Property=20
values in Plattsburgh are reported to be rising. Waterfront =
property=20
owners observed ducks resting on the dredge vessel.
We expect the Hudson River to be another =
success story.=20
There is no data to support GE=C2=B4s contention that the river =
will be closed=20
to swimming or navigation.
These photographs and graphics are examples of =
environmental=20
dredges which will be used in the clean up of the Upper Hudson =
River=20
hotspots. The examples shown are hydraulic cutterhead dredges. =
Once the=20
PCB-containing sediments have been removed by environmental =
dredging,=20
navigational dredges may be used to further open channels to boat =
traffic.=20
Snags, rocks, and sunken logs may have to be removed by=20
clamshell.
Thanks to Jim Gordon for =
his=20
photograph of the dredge used in the Lake Champlain clean-up. More =
details=20
about the Plattsburgh cleanup are available in Jim=C2=B4s article, =
`Dredging =
Works=C2=B4.=20
Thanks also to Keene Engineering, a manufacturer of dredging =
equipment,=20
for allowing use of photos and graphics from their=20
website.
Additional =
diagrams and=20
photographs and a current report on dredging technologies =
entitled,=20
`Results of Contaminated Sediment Cleanups Relevant to the Hudson =
River=C2=B4,=20
technologies are available on the Scenic Hudson=20
website. Descriptions of environmental dredging are =
available=20
on EPA=C2=B4s=20
website.
|
|
![](3D"http://www.clearwater.org/art/JGdredge.jpg"=20)
This little =
dredge boat=20
removed tons of sediment containing 25,000 pounds of PCBs - =
about=20
one quarter the amount to be removed from the Hudson - over =
three=20
summers. The Hudson River cleanup may require several boats =
like=20
this, and a small number of attendant barges - hardly the =
vast=20
destructive armada envisioned by GE. =20
-- Photo by Jim=20
Gordon | |
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Environmental dredge =
graphics=20
courtesy of Keene Engineering![3D"The](3D"http://www.clearwater.org/button/pcbhome.gif")
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