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July 10, 2019

The first neighborhood-scale Green Stormwater Infrastructure (GSI) project used to mitigate combined sewer overflows in Vermont has been installed and recently won an ACEC-VT Engineering Excellence Award. Green Stormwater Infrastructure projects are used to reduce flooding from storms and treat and/or store stormwater runoff.

The Oak Street Neighborhood Project in St. Johnsbury was completed in 2018 in collaboration with the Town of St. Johnsbury, lead engineers from Stone Environmental Inc. and Dufresne Group, and with grant support coordinated by the Caledonia County Natural Resources Conservation District (CCNRCD) through the VT Department of Environmental
Conservation (DEC)’s Ecosystem Restoration Program.

The Oak Street Neighborhood Project started as traditional utility improvements to reduce combined sewer overflows to the Passumpsic River in St. Johnsbury. The original project was a “grey” infrastructure project and included water main replacement and new sewer and stormwater collection systems. During the design phase for this work, a Stormwater Master Plan was also developed by CCNRCD and the Town of St. Johnsbury, with support from Stone Environmental and funding from the Ecosystem Restoration Program. With construction for the neighborhood slated for the near future, and much of the neighborhood underlain by sandy soils, the opportunity presented itself to consider a larger scale installation of green infrastructure practices while the neighborhood was under construction. CCNRCD approached the Town of St. Johnsbury with the concept, and after grant funding was secured, Stone Environmental joined forces with Dufresne Group to combine design plans for the neighborhood.

The GSI improvements to the neighborhood included bioretention swales sited in the green space along roadways, with road grading directing flow towards the swales. The bioretention swales installed treat runoff from 7.5 acres, including over 2 acres of impervious rooftops, driveways, and roads. The 22 GSI practices provide 5,550 CF of storage and treatment capacity—almost 300% of the “first inch” Water Quality Treatment Standard on a project where water quality treatment was not required by the Vermont Stormwater Management Rule. Through CCNRCD’s and Stone’s work in securing grants and providing engineering support, the town was able to install GSI at no cost but at great benefit by reducing stormwater runoff in the Oak Street drainage area to the Passumpsic River.

In June, Stone Environmental and Dufresne Group accepted an Engineering Excellence Merit Award from the American Council of Engineering Companies of Vermont (ACEC-VT) for an innovative green stormwater infrastructure design and implementation project for the Oak Street drainage area. The Engineering Excellence Awards, created to commemorate outstanding examples of engineering excellence in projects completed in Vermont, were awarded to recipients whose projects were substantially complete and ready for use between January 2017 and December 2018. Recipients were judged on their ability to meet or exceed client needs, new applications of existing techniques, originality, and/or innovation, social or economic benefit, complexity, and technical value to the profession.