Boston's Sewage Outfall

Palmer, David T.; ,

Boston's Sewage Outfall

by David T. Palmer, (M.ASCE), Asst. Vice Pres.; Parsons Brinckerhoff Quade and Douglas, New York, NY,

Serial Information: Civil Engineering—ASCE, 1991, Vol. 61, Issue 4, Pg. 74-76

Document Type: Feature article

Abstract:

The centerpiece of the Boston Harbor cleanup plan will be the sewage plant on Deer Island, which will treat water from 43 municipalities in the Boston metro area�500 mgd to start. In order to assure adequate dilution of the effluent, it will flow out to Massachusetts Bay through a 9� mile long, 25 ft diameter tunnel, then be dispersed through 55 riser pipe/diffuser combinations. The tunnel/riser project is scheduled to be completed in July 1995 at a cost of $279 million. Design required extensive hydraulic and geotechnical investigations including borings, vibracores, piezocone tests, seismic reflections, seismic refraction, bathymetric surveys, side scan sonar and magnetometer surveys, and a deep digital seismic survey. The deep digital survey was only the second of its type performed at sea. The 2,500 hp tunnel-boring machine (TBM) will cut 100 ft per day with its 18 in. cutter disks. After boring the tunnel will be lined with concrete. The risers will be built of filament wound fiberglass, while the domes containing the diffusers will be rotationallyy-molded, cross-linked high-density polyethylene (HDPEX) and the diffuser ports will have ultrahigh-density polyethylene nozzles. The contractor will drill 60 in. diameter holes for each riser and install a steel casing; crews in the tunnel will locate the riser through a probehole, excavate to the diffuser and install a pipe joining the two. Safety barriers to protect construction crews will include watertight caps on the diffuser nozzles, plugs in the risers and bulkhead in the riser offtakes.

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