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Impaired Surface Waters

When receiving waters do not meet their intended use due to a specific pollutant(s), additional standards for the Stormwater Discharges to that water body become required. In the Town of Williston, our stormwater is received by seven surface water bodies which include the Allen Brook, Johnnie Brook, Lake Iroquois, Muddy Brook, Shelburne Pond, Sucker Brook, and the Winooski River. Of these seven water bodies the following are impaired or have elevated concentrations of pollutant sources as determined by the State of Vermont; Allen Brook, Muddy Brook, and Lake Iroquois.                                                                                                                                                                                                                                             

Allen Brook                                                                                                                                                            The Allen Brook is a 10-mile stream located within the Town of Williston which feeds into Muddy Brook just before reaching the Winooski River. Allen Brook is a Class B water body, as defined by the State of Vermont, which is intended to be a high-quality aquatic habitat. Studies have shown that segments of the Allen Brook do not meet the criteria for this classification, and as a result the stream segments are listed on the  “State of Vermont 303(d) List of Impaired Waters – Part D: Waters Assessed as Impaired and have Completed and EPA-Approved Total Maximum Daily Loads (TMDL’s)”. More information about the TMDL is available here or through the Allen Brook Total maximum Daily Load link below.

What does this mean for the Town’s stormwater program? The “State of Vermont MS4 General Permit (VTR040000) Part 8: TMDL Implementation” requires the Town of Williston to adopt a Stormwater Flow Restoration Plan to address the impacts stormwater discharges are having on the Allen Brook. The required plan was developed and approved by the State in 2016. Additional information about the Allen Brook, including studies performed and projects completed, can be found at the end of this page. 

Allen Brook Flow Monitoring Live Feed
In partnership with the State of Vermont Department of Environmental Conservation, Stone Environmental, and Fitzgerald Environmental Associates LLC, live monitoring of the Allen Brook is available through the following link. This information is used to observe how well stormwater treatment practices are working to reduce peak flows during precipitation events.                                                                                                                                                                                             


Lake Iroquois                                                                                                                                                           Lake Iroquois is a 229-acre reservoir that was created in 1867 and is bordered by the towns of Hinesburg, Richmond, and Williston. Use of the lake includes a variety of recreational activities such as boating, fishing, swimming, and more.  Since its first discovery in 1990, the lake has experience abundant growth of the invasive aquatic species Eurasian watermilfoil (EMW). The abundance of this invasive species has resulted in the lake being listed on the “State of Vermont 303(d) List of Impaired Waters – Part E: Surface Waters Altered by Aquatic Invasive Species.” Since its discovery there have been extensive efforts to eradicate the species from the lake with mixed results. Additional information about the lake and efforts to address the EMW can be found on the Lake Iroquois Association’s website.



Muddy Brook                                                                                                                                                           Tributary #4 and the Tributary to Tributary #4 of the Muddy Brook have been identified as impaired for Chloride. These segments are in areas of commercial development with high volumes of runoff received from parking lots and other impervious surfaces where salts are commonly used for de-icing activities during the winter months. At this time, the Muddy Brook is listed on the “State of Vermont 303(d) List of Impaired Waters – Part A” which identifies waters that do not meet Vermont’s Water Quality Standards, and a Total Maximum Daily Load has not yet been implemented.


Lake Champlain                                                                                                                                                       While Lake Champlain does not directly receive discharges from the Town of Williston, the Allen Brook, Muddy Brook and Winooski River are all tributaries of Lake Champlain. Due to the hydraulic connectivity with the lake the Town of Williston is required by the State of Vermont MS4 General Permit to develop a plan to reduce the overall Phosphorus loads being contributed to the main lake. To meet this requirement, the Town is working with Fitzgerald Environmental to conduct a baseline analysis of current phosphorus loads from municipally owned parcels and use that information develop a Phosphorus Control Plan. A draft of the plan is expected to be available for review by the end of 2020.  

A Phosphorus Control Plan (PCP) was developed to meet the Total Maximum Daily Load (TMDL). The plan has been submitted to Vermont Agency of Natural Resources, and published for public comment. Please contact the Stormwater Program with any questions, comments, or concerns related to the proposed PCP. 


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