DuBois & King provided site identification and viability, evaluation, planning, and design services for a wetland mitigation site to compensate for impacts associated with a 16.7-mile limited access highway on a new alignment in Chittenden County. The project team located a site adjacent to the planned highway. The identified compensatory area had marginal wetland and wildlife habitat function and values. The D&K team developed a design for the wetland that significantly increased the functions and values of the site. Design for the site resulted in a sustainable ecosystem by:

De-channelizing highway runoff, decreasing energy/erosion potential
Increasing treatment of the highway runoff, improving water quality
Reducing the temperature of runoff, improving water quality
Increasing the diversity of wetland, aquatic, and wildlife habitat
Designing the site to function during periods of drought or flood

The project consisted of converting a 7.7-acre field into a wetland. A diversion channel/level spreader was designed along the upslope of the mitigation site. Drainage from approximately 90 acres of upland area is collected and directed into the level spreader. The result of de-channelizing the runoff and allowing it to sheet flow across the upper reaches of the site sufficiently altered the hydrology in the existing hydric soils to support a scrub-shrub wetland. At the base of the steeper terrain, a 1.1-acre marsh was created through excavation. The marsh varies in depth, with the majority averaging between 12 to 18 inches. A 1/8-acre pool, 4 to 5 ft deep, within the marsh provides winter habitat for wildlife such as frogs and turtles. An outlet channel was designed from the marsh to control water levels and divert runoff to the existing drainage channel and culvert under the Central Vermont Railroad. A complete planting plan was developed to speed up and enhance the wetland conversion. DuBois & King provided supervision of the planting program and inspection services for compliance with Army Corps of Engineers requirements.

Services provided include site selection, topographic survey, subsurface/soils evaluations, groundwater monitoring, hydrologic/hydraulic analyses, impoundment structure design, preparation of construction plans and special provision, landscape design, quantity takeoff, and cost estimates.

In order to mitigate for the wetland impacts associated with the construction of the Bennington Bypass project, DuBois & King assisted the Vermont Agency of Transportation in the identification, selection, and design of a 28 ± acre wetland mitigation complex along Barney Brook in Bennington. The plan entailed the conversion of 6.7 acres of upland to wetland, the enhancement of 5.5 acres of existing wetland, and .9 acres of riparian corridor enhancement.

A hydrologic and hydraulic evaluation was conducted to forecast the altered groundwater and surface water conditions necessary to support wetland hydrology/plantings. The analysis included installation and monitoring of observation wells and the modeling of existing and projected groundwater levels using the “Boss International, Groundwater Modeling System” software. Both the US Army Corps of Engineers and the Vermont Agency of Natural Resources approved the wetland complex design.

D&K assisted VTrans with construction services as a resident inspector and provided services during the five-year monitoring period. Construction phase services included project stakeout, quantity calculations, review of plantings, preparation of bi-weekly payment amounts, daily reports, and recording as-built information.

Assisted the Vermont Agency of Transportation (VTrans) in the identification of environmental resources, assessing potential impacts, and designing and permitting for a wetland mitigation complex to compensate for unavoidable wetland impacts associated with a US Route 9 improvement project. Assisted VTrans in the overall environmental permitting for this project, including the Act 250 and stormwater discharge permit processes. As a part of this process, discussion focused upon the proposed river channel relocation and the desire of resource agencies/special interest groups to redesign the project.

Services included developing strategies to address project impacts, and preparing testimony and attendance at Act 250 and District Environmental Commission hearings. Stormwater services included estimating changes in impervious surface area and documenting existing roadway conditions/treatment of stormwater runoff. Coordinated with Agency of Natural Resources for concurrence on stormwater discharge permit, developed a scope of services to design improvements for the proposed channel relocation in accordance with current restoration practices, and completed a field walk-over of proposed alignment shift to determine presence of wetlands.