The Alewife Brook Sediment Study was conducted in May and June of 2024 by Inter-Fluve, Inc. to
(1) characterize accumulated sediment, (2) evaluate the existing aquatic and riparian habitat, and
(3) explore potential sediment management options for Alewife Brook.
Inter-Fluve used RTK-GPS survey equipment and flexible probing rods to survey the elevation of the bottom of the river channel as well as the bottom of the accumulated sediment. We analyzed the survey data and estimate that approximately 22,000 cubic yards of sediment has accumulated in the 1.4-mile reach of Alewife Brook from Rt. 2 to the Mystic River confluence.
The project area was divided into four sub-reaches for evaluation of the geomorphology and
accumulated sediment. (These correspond to segments 2-5 of the Stantec study).
Sub-reach
Description
Approximate Length (ft)
% of total
A
Rt. 2 Bridge to Massachusetts Ave. Bridge
2,100
29
B
Massachusetts Ave. Bridge to Henderson St. Bridge
1,300
18
C
Henderson St. Bridge to Broadway Bridge
1,000
13
D
Broadway Bridge to Mystic River Confluence
2,900
40
The Brook runs in a trapezoidal concrete lined channel through sections A and B until the Henderson St. Bridge. Downstream of Henderson St., the brook flows through a natural channel with concrete walls before transitioning to a natural channel and bank downstream of the Broadway bridge to the confluence
with the Mystic River.
Segment
A
Average Estimated Sediment Volume (yd3)
5,800
Sediment Load (yd3/ft)
2.76
Estimated Sediment
Volume Range (yd3)
B
2,600
2.00
5,000 – 6,600
2,200 – 2,700
C
D
11,400
2,200
2.20
3.93
9,900 – 12,900
1,900 – 2,500
The sediment analysis found elevated levels of concentrations of PCBs, PAHs and Heavy Metals. This is comparable with earlier studies. Overall, the comparison of the results shows that this waterway has been contaminated since testing of Alewife Brook began in 1988.
Accumulated sediment was estimated at 18,500 cubic yards (CY) in the 2005 USGS report for Alewife Brook. This estimate is approximately 3,500 CY less than Inter-Fluve’s 2024 estimate of 22,000 CY. This indicates an average annual increase of approximately 175 CY of material each year. Input sources include but are not limited to leaf litter, upstream inorganic and organic fluvial deposition, stormwater,
Total
22,000
3.01
19,000 – 25,000
Inter-Fluve Summary – Draft 1.docx
and overland flow. More extensive sampling and contaminant testing is needed to verify how the contaminants are distributed across the impoundment and with depth.
Alternative 1: Leave Sediment in Place
Alewife Brook is a heavily engineered stream that has been degrading in ecological health and function since it was first constructed out of the historical marshlands. Contaminants have become trapped in sediment and contaminants continue to flow into Alewife Brook. The stream includes limited aquatic habitat. Terrestrial habitat can be found in the narrow riparian buffer on either side of the stream. The Do Nothing alternative would not remove the accumulated sediment. The status quo of a heavily modified stream channel with limited habitat would remain. The accumulated sediment would remain a potential health hazard to organisms and humans. This alternative would have no construction cost.
Alternative 2: Active Removal and Off-Site Disposal of impounded material.
Active removal and off-site disposal of the accumulated sediment would include mechanical removal of some or all of the accumulated sediment through dredging or excavation and trucking of the sediment to a facility outside of Massachusetts that accepts this material. The benefit of this management alternative is the channel might have improved hydraulic capacity (pending results from the Stantec study). The additional space within the channel would provide additional area for aquatic organisms, such as fish and turtles, to survive, but it would not necessarily provide improved habitat or living conditions. CSOs and stormwater will still be conveying contaminant-laden water in Alewife Brook and a concrete-lined channel does not provide many habitat opportunities for fish or other aquatic organisms.
The financial cost of removing accumulated sediment will vary depending on the chosen extent of removal and the final determination regarding the disposal location. A possible cost range for this sediment removal is from 20 to 80 million dollars. No estimate was provided for removing the concrete channel itself, which would likely be much more.
Conclusion
The accumulated sediments have a number of contaminants at moderate levels common to an urban stream. The sediment depth varies from one to two feet which moderately limits the channel capacity. Leaving this sediment in place would continue with a heavily modified stream channel with limited habitat.
Removing the sediment would remove some hazards and increase flow capacity, but still leave a mostly concrete-lined channel with limited environmental value. Restoration of a natural stream channel could have a number of benefits but was not analyzed in this sediment-focused study.
Inter-Fluve Summary – Draft 1.docx
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8/28/2026