A recent Consumer Affairs ranking put Vermont in the top five greenest states in the US. That’s no surprise to those of us that live and work here; and a team of engineers led by Burlington-based Senior Technical Engineer Kirstin DiPietro Worden are underway with designing stormwater management practices that will further reduce pollution of our local streams, wetlands and Lake Champlain.

Five of those projects have already begun providing municipalities – and commercial and private landowners such as homeowner associations – with stormwater practices that will satisfy requirements of the state’s Three-Acre Stormwater Rule, further protect our wetlands, aquatic ecosystems and waterbodies and help conserve water resources.

What is the Three-Acre Rule?

In 2020, the Vermont Department of Environmental Conservation (VTDEC) released the Three-Acre Stormwater General Permit 3-9050, which fulfils a requirement of Vermont’s 2015 Clean Water Act. This was noted as a necessary step in Vermont’s efforts to improve water quality and meet Lake Champlain cleanup goals.

On Vermont’s Agency of Natural Resources page, “The Permit requires landowners with more than three acres of impervious surfaces to develop and implement projects to treat runoff to remove phosphorus, sediment and other pollutants.” Vermont has identified multiple Three-Acre Sites across the state, over 650 of which are within the Lake Champlain basin.

VTDEC offers extensive assistance and information on the Three-Acre Rule, as well as information on funding available for all phases of stormwater management upgrades. Hoyle Tanner is experienced in the design and implementation of Best Management Practices (BMPs) to meet stormwater management objectives, and routinely assists clients with the next steps.

Three-Acre Project Steps

A process timeline for the three-acre stormwater rule

Step 1 – Notice of Intent (NOI):

The property owner of the three-acre site must submit an application notifying the state of intent to apply for an Individual Stormwater Discharge Permit (INDS). The first step in this process is to submit an Initial Notice of Intent (INOI) with basic information about the three-acre site. For a three-acre sites which need to comply with a Stormwater General Permit 3-9050, Hoyle Tanner prepares and submits the initial NOI on behalf of the property owner(s) in accordance with state requirements.

Step 2 – Engineering Feasibility Analysis (EFA):

Hoyle Tanner then performs a detailed analysis of all existing stormwater practices located on each project site, and evaluates whether the existing practices meet the requirement of the Vermont Stormwater Management Manual (VSMM). The analysis includes recommendations of additional measures or retrofits that can be implemented to improve treatment and/or bring the practice into compliance with the VSMM, and/or Flow Restoration Plans if applicable, and identify all natural resource impacts of the recommended project. Step 2 concludes with preparation of an EFA Report. Based on results from the EFA, compliance with the Stormwater General Permit 3-9050 will be determined. Projects not in compliance will advance into final design phase (Steps 3-5).

Step 3 – Establish Existing Conditions:

Early stages of design rely on information provided through site survey, soil evaluation and infiltration testing, utility location and wetland screening and delineation – all performed by a team of local partners including Watershed Consulting, Vermont Compliance Monitoring, Gilman & Briggs Environmental, Inc. and Vermont Survey and Engineering, Inc.

Step 4 – Preliminary Design for Permitting Purposes:

Following buy-in of the conceptual design from all stakeholders ((property owner(s) and municipality)), each project advances into preliminary design for identification of all required permits. AutoCAD and a preliminary HydroCAD model are used to advance the design; a preliminary cost estimate is completed at this stage; and a list of applicable permits is provided.

Step 5 – Final Design:

At the final design stage, Hoyle Tanner prepares final plans and specifications of the proposed stormwater practice and contract documents for use in bidding and construction, as well as our engineer’s opinion of probable construction costs. Permit applications are prepared and submitted, and a final NOI application is submitted to the state on behalf of the three-acre property owner(s).

Once the project advances from final design, projects enter the implementation phase during which Hoyle Tanner offers bid-phase services, construction administration, and inspection services to ensure the stormwater management system design is constructed in accordance with the contract documents and the requirements of the Three-Acre Rule.  A final construction inspection report to demonstrate the Three-acre site’s compliance with the Stormwater General Permit 3-9050 is prepared and submitted on behalf of the property owner(s).


The Stormwater Three-Acre Rule is just another tool to help our environment; by complying with the requirements of the Rule, we can keep untreated stormwater runoff and nutrients such as phosphorus out of our streams, rivers and lakes, keeping our water systems cleaner and safer for the public and the ecosystem. We have a team of knowledgeable environmental engineers experienced with water quality and stormwater management projects throughout New England. Do you have a question or concern about your community? Reach out to me!

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