A consultants’ report to the Executive Office of Transportation recommends against any tunneling for the Green Line extension project, saying the additional expense is not warranted and that mitigation for noise and vibration can be provided more cost-
effectively using other means.
The consultants, Vanasse Hangen Brustlin and PB Americas, made the recommendation in a 32-page technical memorandum, “Consideration of Tunnel Alignment Alternatives,” that was posted to the Green Line extension project website on Wednesday.
In the memorandum, the consultants analyzed five tunnel alignment proposals and three tunneling methods — cut and cover, depressed section with decking, and deep bore.
The report estimated tunneling would add the following costs to the project:
+ $400 million to use the decking method from Ball Square to Mystic Valley Parkway, and $760 million to $1 million to use the boring method over that distance
+ $500 million to $600 million to bore a tunnel from Prospect Street to Union Square
+ $620 million to $820 million to bore a tunnel to Union Square under Somerville Avenue
+ $1.5 to $2.1 billion to bore a tunnel from Ball Square to Alewife
+ $2.1 billion to $3 billion to bore a tunnel from Brickbottom to Mystic Valley Parkway
In recommending against all of the tunnel options, the consultants concluded:
“While the tunnel alternatives would reduce surface disruption during construction as well as post-construction noise and visual impacts, these impacts, under the surface alternative, are not expected to be significant and can be mitigated cost effectively.
Therefore, the additional costs of tunnel construction are not warranted.”
The memorandum can be found on the project website, www.greenlineextension.org, under Current Materials, Advisory Group Meeting #10.
EOT undertook the study following suggestions from the Green Line Project Advisory Group and the public that the option of tunneling be evaluated during the Draft Environmental Impact Report, which has been ongoing since September 2007.
The analysis of noise and vibration issues is among several items on the agenda for the next Green Line Project Advisory Group meeting, scheduled for Monday, Dec. 1, at 4 p.m. at the St. Clement Parish Hall, 579 Boston Ave., Medford.