A.27 Housatonic River, MA
A.27.1 Summary
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Environment: |
Freshwater |
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Scale: |
Full |
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Contaminants of Concern: |
PCBs, NAPLs |
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Final Remedy: |
Cofferdam/sheet piling was in place to dewater contaminated sediment. Material was excavated and disposed of at an on-site facility. |
A.27.2 Site Description
The Housatonic River in Pittsfield, MA, its sediment, and its associated floodplain are contaminated with PCBs and other contaminants. The USEPA performed a 1½ Mile Reach Removal Action using two excavation techniques costing a total of $84,000,000.
A.27.3 Remedial Approach
Excavation was chosen because the river was too shallow for conventional dredging and had a sandy, rocky bottom. Further, there was free-phase NAPL that could be better controlled and isolated with dry dredging.
The first technique used was a 1,400 ft length sheet pile coffer dam technique which consisted of using sheet pile to construct individual sheet pile installed along the centerline of the riverbed. Then, upstream and downstream sheet pile cut-off walls were installed branching off the centerline sheet pile wall and extending up the riverbank. The river flow was thus diverted around the sheet pile cell. The cell was then dewatered and the sediment and riverbank soil was removed. The cell was then backfilled with clean fill and riprap to the design grade. Next, the two cut-off walls were removed and re-installed on the opposite side of the river creating the next cell to be remediated and restored. Remediation activities proceeded downstream with activities alternating from one side of the river to the other. Standard excavating equipment was used to complete the sediment and soil removal and backfilling. A typical sheet pile cell was approximately 300 ft long and approximately 30 ft wide. Water was removed from each sheet pile coffer dam system down to 6 inches of water above the sediments and directly discharged into the river. The remaining water was subjected to water treatment and then discharged back into the river. Sediments consisted of mostly sand and gravel. Removed sediments were stockpiled within the river cell for gravity dewatering.
The second technique, excavation, involved a gravity-fed bypass system. The bypass system consisted of a temporary river diversion dam installed approximately 1,400 ft downstream from the Lyman Street Bridge. The gravity-fed bypass technique was used in this area because shallow bedrock prevented the use of the sheet pile cofferdam system. The bypass system diverted the river flow into two 54-inch movable high density polyethylene pipes. The pipes were placed along one side of the river channel and the riverbed sediment and soil on the other side were removed and backfilled. The sediment and soil removal and backfilling was accomplished using standard excavation equipment. Once the backfilling was complete, the pipes were moved to the remediated side of the river and the process was repeated. Additional sections of pipe were added to the two 54-inch pipes extending the system as the removal and restoration progressed downstream. The gravity bypass system was used to remediate and restore approximately 3,400 ft of the river channel to a location 400 ft downstream of the Dawes Avenue Bridge.
Dry excavation here was more effective in controlling sediment resuspensionA renewed suspension of insoluble particles after they have been precipitated. than conventional dredging would have been. Limited resuspension occurred during sheet pile installation. In total, approximately 91,700 yd3 of contaminated sediment and riverbank material was removed and disposed of as part of the 1½ Mile Reach Removal Action. Approximately 7,000 yd3 of this material was impacted by NAPL. Approximately 50,750 yd3 of the contaminated material was disposed of at GE's on-plant consolidation areas and the remainder of the contaminated material, including all of the NAPL-impacted material, was disposed of at licensed off-site disposal facilities. The sediment remediationThe act or process of abating, cleaning up, containing, or removing a substance (usually hazardous or infectious) from an environment. action met the cleanup goals.
A.27.4 Additional Areas
Year: 2002
Water Depth: 0–8 feet
Target Volume:
Hotspot: 2,800 yd3
Half mile: 12,100 yd3
Actual Volume Removed:
Hotspot: 7,000 yd3
Half mile: 18,138 yd3
A.27.5 Remedial Objectives for Additional Areas
Hot spot: Area average of > 5 ft depth: 1 ppm, < 5 ft depth: 10 ppm.
Half mile: 1–3 ft depth: 15 ppm
Contaminated sediment area: 0.5 mile segment
A.27.6 Remedial Approach
Hotspot in Silver Lake. First half mile of the river was remediated as well.
An isolation capA covering over material (contaminated sediment) used to isolate the contaminants from the surrounding environment. was installed on areas not dredged. This cap consisted of a geotextile layer, and isolation sand layer, another layer of geotextile and geogrid and stone armor layer.
A.27.7 Monitoring
Sheet piling was in place to contain contaminated sediment area and to dewater it for dry excavation. No suspension measures needed for this site because both areas used dry excavation. The project was slowed by periodic presence of NAPLs.
Dredged areas were backfilled and seeded/ replanted.
A.27.8 References
USEPA, EPA Cleanups: GE-Pittsfield/Housatonic River Site Housatonic River ½ Mile Removal-Reports. http://www.epa.gov/region1/ge/thesite/halfmile-reports.html.
USEPA, EPA Cleanups: GE-Pittsfield/Housatonic River Site Housatonic River 1½ Mile Removal-Reports. http://www.epa.gov/region1/ge/thesite/1andhalfmile-reports.html.
USEPA, EPA Cleanups: GE-Pittsfield/Housatonic River Site Silver Lake-Reports. http://www.epa.gov/region1/ge/thesite/silverlake-reports.html.
Major Contaminated Sediment Sites Database; Sept. 2004 as updated 2008. http://www.smwg.org/MCSS_Database/MCSS_Database_Docs.html.
Publication Date: August 2014