Wetland Assessment Mitigation
Maine Turnpike Westbrook Interchange Wetland Mitigation
An analysis by the Maine Turnpike Authority (MTA) concluded that there was a
need for additional interchanges in order to handle present traffic demands and
anticipated needs in the Greater Portland Area. A new interchange at Westbrook
was selected as one of the preferred alternatives after a variety of
alternatives were evaluated under NEPA and state transportation planning
protocols.
Delineate wetlands, assess wetland impacts, provide regulatory assistance, and
develop a preliminary wetland compensation plan for the proposed interchange.
Development of the wetland compensation plan included identification and
evaluation of prospective sites, selection of candidate sites, presentation of
sites to regulatory agencies, and preparation of a plan to compensate for lost
wetland functions at the preferred site(s).
Wetlands were delineated in the project vicinity in accordance with the 1987
U.S. Army Corps of Engineers manual and regional hydric soils criteria. The
impact analysis determined that approximately 11 acres of compensation would be
required. Functions to be replaced include groundwater discharge, floodflow
alteration, sediment/toxicant retention, nutrient retention/transformation,
production export, wildlife habitat, and visual quality/aesthetics.
Devine Tarbell & Associates, Inc.’s (DTA) staff evaluated approximately 20 sites
in the Greater Portland Area for their potential to replace the wetland
functions and values that will be impacted by the proposed project. A short list
of 10 sites was presented to the agencies, and a preferred site was selected,
with alternate sites identified in the event that the preferred site became
unavailable. The preferred site consists of wetlands and former wetlands that
are presently in active use as a cow pasture. The pasture wetlands are ditched,
and are bisected by a stream that has been channelized to enhance drainage.
Proposed treatments to restore wetlands include fencing to exclude livestock
from sensitive wetland and riparian areas, blocking ditches and dechannelization
of the stream, construction of an earthen weir to impound water and establish a
shallow marsh, and plantings to encourage revegetation.