New Bedford Harbor Superfund Liner and Cover

ERDC TN-DOER-C18

August 2000

reinforcement. The sections were heat welded in the field. The membrane

was laid directly on the inside face of the dike using a roller arrangement

mounted on a barge (see Figure 6). As the barge was moved along the inside

face of the dike, the membrane was fed from the roller. Stones were used to

anchor the membrane in place as the work progressed.

To view figure

larger, click here

Observations of fluctuating lake levels during and following construction

indicated that the liner was ineffective in retarding flow of water through the

Figure 6

dike section (there was no appreciable lag in lake water level fluctuations inside

the dike). A dye study showed that the liner was perforated randomly throughout its length due to

tears or punctures during placement. These tears likely resulted from random punctures from the

angular limestone core underneath or the armor stone placed on top of the liner.

Several corrective actions were considered, including grouting and slurry walls. The selected

corrective action was placement of a sand blanket along the inside face of the dike. Sandy material

was excavated directly from the lake bottom within the CDF and placed on the inside dike face at

a 1V on 3H slope. The sand was initially dredged from within the CDF via a small crane barge.

Later, because the sand above the water line was eroded by rainfall, additional sand was hauled in

from an outside source and placed with a "creter crane" from the top of the CDF dike. The creter

crane is a conveyor that could be boomed out over the designated sand fill areas. This equipment,

normally used to place concrete, is mobile and has a large conveyor feed box into which trucks

dumped the sand after backing along the dike to the crane. Following placement of the sand blanket,

comparison of water level fluctuations within the CDF with lake levels indicated that the blanket

was effective in retarding flow through the dikes. Short-term fluctuations were retarded, but the

water level in the CDF followed long-term lake level fluctuations with a lag.

Subsequent to placement of the sand blanket, the Chicago District placed

fine-grained dredged material along the inside face of the dike using a chute

arrangement (Figure 7) to further seal the dike. The dredged material was

To view figure

re-handled from barges using a clamshell and placed on the chute, sliding down

larger, click here

to the inside face of the dike at the water level. As the work progressed, the

chute was moved laterally along the dike until the work was completed.

Figure 7

New Bedford Harbor Superfund Liner and Cover. A 7,600-cu-m CDF with a synthetic liner

and a synthetic cover was used for containment of PCB-contaminated sediments removed from the

"hot spot" of this Superfund site (PCB = polychlorinated biphenyl). The CDF had been previously

constructed along the New Bedford shoreline to contain the contaminated sediments removed during

an earlier pilot study of dredging equipment. The facility was modified and used again during the

hot spot remedial action. The modifications included dividing the facility into three cells to facilitate

the water treatment process, installation of a high density polyethylene geomembrane liner, and

installation of a floating cover over the large cell into which the dredged material was initially

pumped to control volatilization. The purpose of the liner was to contain excess water produced

during hydraulic dredging and leachate during storage of the dredged material. Groundwater

monitoring around the site has not detected any contaminant leakage. The cover for the site was

installed because of concerns over volatilization of PCBs during filling. Dredged material was