Projects | Water & Sewer District

Gallatin Canyon Sewer Project Environmental Benefits

Protecting the Gallatin River While Supporting Responsible Growth

The Gallatin Canyon Sewer Project is a long‑term investment in water quality, public health, and community sustainability. The project replaces aging septic systems with centralized wastewater treatment to reduce nutrient loading to the Gallatin River and its underlying aquifer, while supporting smarter development in the canyon corridor. Connecting to central sewer is not just an infrastructure upgrade, it is a direct investment in the health of our water, our rivers, and our community.

Increasing Nutrient Loads and Population Growth

The Gallatin River is experiencing excessive summer algae blooms linked to excess nitrogen.
Gallatin River nitrogen concentrations roughly double in the canyon during summer low flows
While only about 8% of nutrient loading in the Upper Gallatin watershed is human‑caused, that addition beyond background is a problem.
Onsite wastewater systems (septics) are a major part of the human-caused load in the canyon.
Planned development and area growth trends indicate that this problem will only increase without intervention

Gallatin Canyon Sewer Project

The Gallatin River Task Force, Big Sky Resort Area District and a few

landowners were instrumental in initial studies and establishing the

GCCWSD to pursue centralized sewer. The project replaces numerous

individual septic systems with centralized wastewater collection,

treatment, and disposal, allowing:

Consistent operation and maintenance
Professional monitoring and regulatory oversight
Improved nutrient removal through treatment

and natural attenuation

Better separation of waste disposal and drinking water wells
Leverage of private development funds to help address existing issues

Protects Drinking Water

By reducing contaminants entering the aquifer

Environmental & Public Health Benefits

Protecting Water Quality Through Central Sewer

Measurable Reductions in Nitrogen Pollution

Connecting homes and businesses to a modern, centralized sewer system is one of the most effective ways to protect local groundwater and rivers, including the Gallatin River and its tributaries. While human sources make up a relatively small portion of nutrient loading across the entire watershed, providing a centralized alternate to septic systems is one of the main tools we have to reduce loads.

Existing onsite systems in the sewer planning area currently contribute about 3,500 pounds of nitrogen per year to the Gallatin River. The sewer project is expected to reduce this load by 25% - 50% by abandoning septic systems and connecting those properties to centralized treatment. The more existing properties that connect, the bigger the impact. This net nutrient reduction is achieved while serving the expected growth in the canyon and disposing of of some of BSCWSD's effluent in addition to existing canyon uses. Central sewer significantly lowers nutrient pollution overall and on a per‑person basis.

This is achieved with advanced treatment paired with a strategic mix of groundwater discharge and irrigation with treated effluent. Process reliability is also greatly improved in centralized versus small private systems.

Cleaner Effluent

The Membrane Bioreactor (MBR) treatment plant is designed to produce a maximum of 5 mg/L total nitrogen. This is cleaner discharge than most other public groundwater and surface water dischargers in the state and many times better than the average nitrogen coming out of existing systems in the canyon.

Effluent will also be disinfected - a major reduction to public health risks.

Environmental Benefits of Reuse Irrigation

A key part of the system’s environmental strategy is reuse irrigation with treated wastewater during summer, which offers several benefits:

Further reduces nutrient loading to surface water by limiting discharge
Conserves groundwater by offsetting irrigation pumping
Provides a reliable, no‑cost water source for irrigated lands

By carefully managing where and how treated water is reused, the system minimizes groundwater interaction and maximizes environmental protection.

Improved Operations

The central sewer will replace many small systems with one larger one. DEQ will require careful planning and monitoring and operation by certified personnel for the proposed system. This will help ensure that standards are being met and that the system is working as planned. This is a major improvement upon septic systems which have almost no regulatory oversight once built are rarely properly maintained.

Turning Growth into an Asset

Funding for the project is a significant barrier to project feasibility with the existing customer-base. Population growth will help to fund this project protecting public health and the river.

Sewer will also enable denser development, mitigating the current patter of sprawl and providing the opportunity for much needed work-force housing.

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Why This Project Matters

Protecting the Gallatin River While Supporting Responsible Growth

The Gallatin Canyon Sewer Project is a long‑term investment in water quality, public health, and community sustainability. The project replaces aging septic systems with centralized wastewater treatment to reduce nutrient loading to the Gallatin River and its underlying aquifer, while supporting smarter development in the canyon corridor.

Gallatin Canyon is experiencing two converging challenges:

Increasing nutrient impacts

to the river and aquifer, including algae growth

Ongoing growth pressure

in an

environmentally sensitive

corridor

The sewer project addresses both by managing wastewater more effectively, protecting drinking water sources, and reducing long‑term environmental risk. The sewer will create net nutrient reduction, even with the expected growth.