North Main stormwater improvements

Challenge

Lamoille River is an important recreational, economic, and scenic resource for Northern Vermont. The river, which is a tributary to Lake Champlain, is over 85 miles in length and has a drainage area of around 706 square miles. In a 2012 stormwater mapping exercise, the Town of Hardwick and Vermont Department of Environmental Conservation recognized that they could improve their water quality by developing a stormwater treatment system for part of the Village, which drained untreated into Lamoille River by pre-filtering contaminates in the stormwater.

Two existing storm drainage systems collected runoff from parking lots, roads, and rooftops in the town and used to discharge to the Lamoille River at a private property on North Main Street. The parking area of the private property, between a stone masonry retaining wall and the property’s mixed-use building was identified as the highest value location for the system, but sensitivities around the businesses on the property and the community’s needs had to be addressed before construction could begin.

Solution

SLR’s Water Resource Engineering team was engaged to help the Town of Hardwick to design, update, and construct the underground infiltration system. Additional soil information was collected, and the design was updated to meet state criteria from the 2017 Vermont Stormwater Management Manual. The specified treatment system was updated to reflect the latest technology and best practices in stormwater treatment, so the town implemented the most modern system possible.

In August 2022, the underground infiltration system was installed. Within the new system, flow from existing stormwater pipes is intercepted, pre-treated, and directed to infiltration units via swirl separators. Each separator within the infiltration system includes a high-level overflow with a discharge to the river.

This project integrated needs of the landowners with a design that fits the floodplain context and maximized treatment potential. Local floodplain permitting was completed. Paving over the system and backflow preventors on outfalls were included to protect the system from possible high floodwaters. Impact to the foundation of the adjacent building and retaining wall were considered in the design, as was limited space for the required construction techniques.

Construction was managed to retain access to a yoga studio, mechanic garage, veterinarian office, and residential units on the property and surrounding areas. Construction was completed in a sequential manner with all layers of the underground system installed in a short period of time to limit the footprint of the excavation and maximize available working area. The project was completed on schedule and within the revised grant budget.

Impact

This water quality improvement project was beneficial for the landowners, the public, and the environment. The project helps move the Lamoille River towards meeting the nutrient load reduction for the Lake Champlain TMDL. This is a successful example of a public-private partnership that will be needed across the state to meet water quality goals. The landowner, the NRCD (i.e., client), the town (i.e., the system owner responsible for maintenance) and the funders were pleased with the project outcome.

It’s very satisfying to shepherd a complex project like this from start to finish, where all of the pieces have to come together just right. It’s really a testament to the Town of Hardwick and ‘landowner’, that they were excited to work with us to complete this project that has real benefits in terms of reduced pollution to the Lamoille River and Lake Champlain.

Emily Finnegan, Caledonia County NRCD