New Bedford, MA 2004

A.49 New Bedford, MA 2004

A.49.1 Summary

Environment:	Harbor
Scale:
Contaminants of Concern:	PCBs Lower harbor: 100ppm. Upper Harbor: 50,000 ppm.
Final Remedy:	Two hydraulic cutterheads were used. A 5-acre dewatering facility was created on site for dredged sediments. 4 CDFs were created near shore. Once most of the water has been eliminated from the slurry, it is then sent off site to a TSCA disposal facility in Michigan via rail or truck.

A.49.2 Site Description

The New Bedford Harbor Superfund site is located in Bristol County, Massachusetts (USEPA 2010; USACE 2005). PCB levels in the upper harbor sediments currently range from below detection to greater than 10,000 ppm. PCB levels in the lower harbor sediments range from below detection to approximately 1,000 ppm. Sediment PCB levels in the outer harbor are generally lower. Operable Unit 1 covers the upper and lower harbor, with a 1998 Record of Decision (ROD) that selected dredging of sediment above cleanup goals below:

Upper harbor subtidal and mudflat areas: 10 ppm PCBs
Lower harbor subtidal and mudflat areas: 50 ppm PCBs

The OU 1 ROD has been modified by three Explanations of Significant Differences (ESDs) in 2001, 2002, and 2010. Based upon additional sampling conducted since the original ROD, the estimated of quantities of material requiring dredging and disposal has increased 95 percent to approximately 900,000 cy3. The OU 1 remedy now, includes removal of roughly 900,000 cy3 (approximately 260 acres) of PCB-contaminated sediment, and disposal of this sediment both off site and in 3 shoreline CDFs in the upper harbor.

Operable Unit 2 addressed the hot spot sediments covering a 5-acre area near the Aerovox mill defined by PCB levels above 4,000 ppm. The hot spot ROD was issued in 1990, an amended ROD in 1999, and the hot spot remedy was completed in 2000. All OU 2-contaminated sediments were disposed of in a licensed off-site disposal facility.

Hydraulic dredging with a rotary auger has been conducted in the harbor for several years. Hydraulic dredging was selected at this site because (Gaynor et al., 2010):

It was believed to be more cost efficient than mechanical dredging for high sediment volumes.
It was capable of drawing 18–30 inches of water, which facilitates dredging within shallower intertidal areas.
It is an efficient method of pumping sediment to central, but distant onshore handling facilities.
It was expected to provide uniform removal of material at predetermined cut depths.

The pump on each dredge delivers 1,500–3,000 gallons per minute (gpm) of slurry with a solids content of up to 20 percent. Two dredges operating by turn in two different tidal zones provide a constant flow of dredged material for the dewatering systems downstream to operate uninterrupted.

Year: 2004-present

Lower harbor ranges from: 6-12 ft

Shipping channel: 30–50 ft

Sediment is silty sand.

Upper harbor near the bridge

Width: 250 ft

Depth: 2–6 ft

Under the bridge

Width: 110 ft

Depth: 18 ft

Target Volume: Not available

Initial ROD, Upper Harbor: 433,000 yd³, Lower Harbor: 17,000 yd³, amendment: Total: 867,000 yd3

A.49.3 Remedial Objectives

Goals for area average basis:

Upper harbor: 10 ppm PCB

Lower harbor: 50 ppm PCB

Intertidal areas with residential: 1 ppm PCB

Intertidal areas with public access: 25 ppm PCB

Salt marsh areas with no access: 50 ppm

Contaminated sediment area: 170–190 acres

A.49.4 Remedial Approach

Two hydraulic cutter head dredges—one for each tide. Verification sediment samples after dredging. Initiation of long-term local seafood sampling program to track PCB levels in seafood. Periodic water quality monitoring following dredging.

A.49.5 Monitoring

Silt curtains abandoned. Best management practices reduced turbidity impacts due to sediment scour from workboats, prop-wash, and pipeline groundings, and turbidity caused by silt curtains when in contact with sediment during low tide in shallow water. PCB and toxicity data, along with in situ water quality measurements, confirm that dredging is ecologically protective, while allowing remediationThe act or process of abating, cleaning up, containing, or removing a substance (usually hazardous or infectious) from an environment. efforts to progress.

Performance:

Dredging is still in progress. There is still 700,000+ yd³ to be dredged. Each year an average of 20,000 yd³ of sediment is removed and disposed.

Residuals:

2009 PCB levels in top 2cm of sediment:

Upper harbor: 75 ppm

Lower harbor: 5.1 ppm

A.49.6 References

EPA Superfund Record of Decision: New Bedford EPA ID: MAD980731335. Sep 1998. http://www.mass.gov/eea/docs/eea/oceans/serth/p1002bmf.pdf.

USEPA Superfund Explanation of Significant Differences: New Bedford EPA ID: MAD980731335. Aug. 2002. http://www.epa.gov/superfund/sites/rods/fulltext/e0102019.pdf.

USEPA. First Five-Year Review Report for the New Bedford Harbor Superfund Site. SDMS DocID 237034. Sep 2005. http://www.epa.gov/superfund/sites/fiveyear/f05-01005.pdf.

USEPA. Second Five-Year Review Report for the New Bedford Harbor Superfund Site. SDMS DocID 470549. Sep 2010. http://www.epa.gov/region1/superfund/sites/newbedford/470549.pdf.

Major Contaminated Sediment Sites Database; Sept. 2004 as updated 2008. http://www.smwg.org/MCSS_Database/MCSS_Database_Docs.html.

Publication Date: August 2014

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