by Compass Vermont

The weekend’s Compass piece reported that agriculture contributes roughly 41% of Vermont’s phosphorus load to Lake Champlain — by far the largest sector. Compass readers responded with a question that came up repeatedly on Facebook, in email, and in the comments: what about sewers? What about all that municipal wastewater that periodically pours into our rivers and lakes when storms hit?

It’s a fair question, and one with an honest answer that’s more complicated than the question.

Vermont’s wastewater treatment facilities contribute about 4% of the phosphorus load entering Lake Champlain from the Vermont side. That’s the smallest of the state’s five major source sectors — agriculture is roughly ten times larger, streambank erosion five times larger, urban runoff and forests each four times larger. By that measure alone, sewage looks like a footnote in the cleanup story.

But the measure is misleading.

Where the 4% number comes from

The 2016 Lake Champlain Total Maximum Daily Load, or TMDL — the EPA-approved phosphorus pollution budget governing Vermont’s cleanup obligations — divides the state’s load into five sectors. Of the 631 metric tons per year EPA modeled as Vermont’s base period load, agriculture accounts for 261 tons (41%), streambank erosion 130 tons (21%), developed land 114 tons (18%), forests 101 tons (16%), and wastewater 25 tons (4%).

The 4% wastewater figure covers the 59 municipal wastewater treatment facilities discharging into the Lake Champlain watershed. These plants operate under federal NPDES permits with phosphorus limits set by the 2016 TMDL and applied through subsequent permit reissuances. According to the Lake Champlain Basin Atlas, wastewater phosphorus loads have declined dramatically over the past 25 years, driven by treatment plant upgrades and the early phosphorus-detergent bans. A peer-reviewed analysis of long-term Lake Champlain monitoring data found that phosphorus detergent laws were in place basinwide by 1978, and that those laws together with phosphorus removal at large treatment facilities reduced wastewater phosphorus loads to Lake Champlain by 86% between the 1970s and 2010. The Lake Champlain Committee led the campaign that produced the Vermont detergent ban.

Wastewater is, in other words, one of the success stories of long-term phosphorus regulation in Vermont. That’s the part of the answer Vermonters angry about sewage in the lake may not have heard.

What the 4% number doesn’t include

Here is where the accounting gets strange.

A combined sewer overflow, or CSO, is what happens when an older municipal system that uses the same pipes for sewage and stormwater gets overwhelmed by a heavy rain. Rather than back the mixture up into people’s basements, the system is engineered to discharge it — partially treated or untreated — into the nearest waterway. Burlington’s CSOs discharge into Lake Champlain. Rutland’s into Otter Creek. Hartford-Quechee’s into the Ottauquechee River.

The TMDL accounting treats nearly all of these CSO discharges as nonpoint source pollution, lumped in the same category with agricultural runoff and streambank erosion — not as wastewater. Only the CSO at Burlington’s Main Plant is counted as a wastewater point source. According to DEC’s own TMDL FAQ, “estimated annual phosphorus loads from untreated CSOs were included as part of the TMDL’s Load Allocation (non-point sources), therefore, any reductions or eliminations of CSOs would be credited toward Load Allocation reductions, not Waste Load Allocations.”

So when a 15-million-gallon discharge of partially treated sewage entered the Ottauquechee on December 28, 2025 — one of the largest single overflows logged in Vermont’s public sewage overflow inventory in recent months — that volume of phosphorus did not, by federal accounting, count toward the wastewater sector.

This is not a clerical detail. It means the 4% wastewater figure understates the visible, episodic discharge of sewage into Vermont’s waters. The actual physical contribution from CSOs is small in basin-wide phosphorus terms — the LCBP Basin Atlas reports that nonpoint sources together contribute roughly 95% of the total phosphorus load to Lake Champlain — but the public health stakes of CSOs are not measured in phosphorus alone.

What’s in a CSO besides phosphorus

Sewage carries pathogens — bacteria, viruses, parasites — at concentrations that pose immediate health risks to anyone in contact with it. It carries pharmaceuticals, microplastics, household chemicals, and industrial residues. It carries a smell, and it produces visible discoloration of waterways for hours or days after a discharge.

This is why Vermont maintains beach water quality monitoring and drinking water intake protections in the first place. A 4% phosphorus contribution does not translate to a 4% public health concern. The visible, concentrated, episodic nature of CSO discharges is the reason readers asked the question they asked. They were not wrong to ask it. They were responding to something real.

The state’s overflow inventory, and what it shows

Vermont maintains a real-time Sewage and Wastewater Overflow Inventory that logs every reportable discharge with location, volume, cause, and treatment status. Recent April 2026 entries include St. Johnsbury, Vergennes (multiple), Rutland (multiple), Barre City, West Rutland, and Woodstock. Volumes range from a few thousand gallons to several million.

The inventory is searchable by date and town. Vermonters who want to know what’s discharging into their local waterways can subscribe to the alert system directly through DEC. Compass encourages readers to do so. Knowing what’s happening in the watershed where you live is the first step toward holding the system accountable.

What Vermont is doing about CSOs

Vermont’s Combined Sewer Overflow Rule, effective September 15, 2016, treats elimination as the default policy. The rule superseded the state’s 1990 CSO Control Policy. Municipalities operating combined systems must implement what’s known as the Nine Minimum Controls — a federally defined set of engineering and operational practices to minimize CSO frequency and volume — and submit Long Term Control Plans showing how they will eventually phase combined systems out.

In April 2024, Governor Phil Scott and DEC announced $29.25 million in American Rescue Plan Act grants to 11 Vermont municipalities for CSO reduction and elimination work. The recipients were Burlington, Enosburg Falls, Hartford, Middlebury, Montpelier, Newport, Northfield, Rutland, St. Albans, St. Johnsbury, and Vergennes. Each project is at a different stage of construction.

Burlington runs the largest and longest-standing CSO program in the state. According to the city’s own CSO program documentation, starting in 1988, all three of Burlington’s wastewater treatment plants — Main, North, and East — were upgraded and significant portions of the combined sewer system were disconnected. The Main Plant collects the largest portion of combined sewer area in the city and was designed with dedicated wet-weather treatment for that reason. Burlington has reduced annual CSO volumes substantially over four decades, but eliminating the system entirely will take longer still. The work is bounded by what’s physically possible to build during construction seasons in a fully developed urban environment.

This is the sewage version of the timeline problem Compass wrote about last week with agriculture. The work is real. The progress is real. The pace is set by the size of the problem and the cost of fixing it, not by how quickly Vermonters want it fixed.

Climate is making it harder

The same climate intensification that’s reshaping the agricultural phosphorus problem is also reshaping the sewage problem. Combined sewer systems were engineered for the rainfall patterns of the 20th century. Vermont’s 21st-century rainfall — wetter growing seasons, more rain-on-snow events, more high-intensity storms — pushes those systems past their designed capacity more often.

The July 2023 floods triggered widespread wastewater treatment failures and CSO discharges across the state. Hardwick’s facility was inundated five feet above the first floor of its main building, knocking out power and treatment capacity for days. Ludlow’s plant was rendered inoperable for weeks, and a year later much of the damage at the facility remained unresolved. The 15-million-gallon Hartford-Quechee discharge from December 28, 2025 occurred during a heavy rain event. As storms get bigger and more frequent, the wet-weather scenarios CSO engineers have been planning for are arriving faster than the elimination work can be completed.

Two problems, one lake

Sewage and agriculture are different problems sharing the same lake. Agriculture is the larger phosphorus contributor by an order of magnitude. Wastewater is smaller and shrinking. CSOs are smaller still in phosphorus terms, but they carry public health stakes that pure phosphorus accounting can’t capture.

Both problems are being addressed. Both are running on long timelines. Both are running against climate change.

The honest answer to readers who asked what about sewage is that Vermont is not ignoring it. The 1978 detergent ban, the wastewater plant upgrades, the 2016 CSO Rule, the 2024 ARPA grants, Burlington’s four-decade program — these are the work being done. None of it is finished. None of it is fast. And the most visible kind of sewage discharge, the CSO that pours from an overwhelmed system into a swimming hole or a river or the lake itself, is the kind that climate change is making harder to prevent.

That is not a reason for Vermonters to stop asking the question. It is a reason for Vermonters to ask it more precisely.