2026: Additional Nutrient Fate Modeling

Prepared by WGM Group on behalf of GCCWSD

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This study expanded earlier analysis of how nutrients move through the ground and water, using modeling software to help support the project's goal of reducing nutrient pollution. Even under cautious assumptions, the modeling shows that a centralized wastewater treatment system for the canyon service areas would substantially cut the amount of nitrogen reaching the aquifer and the Gallatin River. Across the whole canyon, this approach is projected to reduce nitrogen loading to the river by about 23% (41% within the specific project planning area). While local conditions can affect how efficiently nitrogen is broken down naturally, moving from individual septic systems to one monitored, centralized system offers a more dependable and adaptable way to manage nutrients long-term.

2026: Phase 1 Discharge Permit Application and Supplements

Prepared by WGM Group on behalf of GCCWSD

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The district has submitted an application for a groundwater discharge permit covering Phase 1 of the canyon sewer project, and it is currently under review by DEQ. DEQ will soon begin a formal environmental assessment of the proposed discharge, with a public comment period expected to open in late 2026. The included table of contents outlines what's in the supporting documents.

2025: Water Quality Sampling and Groundwater Modeling

Prepared by the Montana Bureau of Mines and Geology (MBMG)

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MBMG gathered and analyzed water resource data to build a groundwater model showing how water moves through the area's underground aquifer. This data and modeling have since been incorporated into ongoing sewer project planning, design and discharge permit documents.

2025: Go-It-Alone Preliminary Study

Prepared by WGM Group and AE2S on behalf of GCCWSD

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This analysis provide an evaluation of costs to construction a wastewater treatment plant in the canyon area (aka “Go-It-Alone”). The findings supported continuing down the preferred project path of connecting to the BSCWSD (aka “Co-Solution”) as identified in the 2021 Wastewater PER.

2025: 60% Design and Cost Estimates

Prepared by WGM Group and AE2S on behalf of GCCWSD

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In 2025, the project team developed design plans, reports, specifications, and a cost estimate reflecting the project at 60% design completion, representing the most current design progress and planning extent to date.

2025: Water Preliminary Engineering Report (PER)

Prepared by WGM Group on behalf of GCCWSD

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A preliminary engineering report evaluated the canyon's existing water system, current and future needs, and long-term options. Water quality is generally acceptable, but the study identified concerns about system capacity, reliability, and firefighting capability. It recommends a centralized water system for the canyon.

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While GCCWSD does not plan to pursue a water project until after the sewer project is complete, evaluating both needs together now helps identify where the two projects should coordinate. One key idea from this study: using treated wastewater return flow to help supply firefighting capacity.

2024: Financial Analysis Memorandum

Prepared by WGM Group on behalf of GCCWSD

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This analysis found that GCCWSD could reasonably finance about $5 to $10 million of the project through debt, based on projected income from user rates. The remaining $20 to $25 million needed, beyond the grant funding already secured, could come from a mix of Tax Economic Development District (TEDD) funding, public-private partnerships, Big Sky Resort Area District (BSRAD) funding, and other grants.

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While GCCWSD initially began pursuing a TEDD for this purpose, BSRAD is now leading a similar effort with broader reach across the community. If approved, it would help fund both the Canyon Sewer Project and other Big Sky infrastructure needs. GCCWSD continues to evaluate other grant opportunities and is beginning conversations about private funding.

2024: Baseline Environmental Analysis

Prepared by WGM Group on behalf of GCCWSD

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This analysis built on an earlier environmental assessment, incorporating updates from the 30% canyon design. It found no significant change in the project's anticipated environmental impact.

2023: Sampling and Analysis Plan (SAP)

Prepared by WGM Group on behalf of GCCWSD

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As the first step in preparing the discharge permit application, the team developed a Sampling and Analysis Plan. This plan guided fieldwork and ensured data was collected and reported accurately, following standard operating procedures.

2023: The Gallatin River Is Listed as Impaired,

Triggering a Pollution Study

From MT DEQ and EPA

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Following a rise in excess algae growth beginning in 2018, the middle segment of the Gallatin River was added to the state's official list of "impaired" waters under section 303(d) of the Clean Water Act. This triggered additional studies to identify the sources of pollution behind the algae growth and to determine safe pollutant limits, known as Total Maximum Daily Loads (TMDLs), for the river.

This is a multi-year process not expected to be complete until 2028 or later. A TMDL sets a pollution "budget" for the river and specifies how much each major pollution source needs to reduce its contribution. Once that's determined, a Watershed Restoration Plan is developed with community watershed groups to guide water quality improvements. Improved wastewater management in the canyon is expected to be a recommended part of that plan.

2022: Canyon Inventory and Prioritization Study

Prepared by WGM Group on behalf of the Gallatin River Task Force

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This study created an updated inventory of existing septic systems throughout the canyon and identified which areas are contributing the most nutrient pollution to the Gallatin River, as well as which systems pose the greatest health risk to nearby drinking wells. The findings have helped guide project phasing and priority connection areas, and confirmed that the sewer project can achieve a net reduction in nutrient pollution.

2022: Environmental Assessment (Montana Coal Endowment Program)

Prepared by WGM Group on behalf of GCCWSD

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As part of applying for a Montana Coal Endowment Program (MCEP) grant, the project underwent a required environmental assessment, including two public meetings for community discussion and comment. The assessment found no long-term adverse effects; other potential effects will be addressed through permitting or are expected to have no impact. The review also identified a range of potential benefits from the project.

2021: Gallatin Canyon Sewer Preliminary Engineering Report (PER)

Prepared by WGM Group on behalf of GCCWSD

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After GCCWSD was formed in December 2020, one of its first steps was commissioning this report to evaluate solutions to existing and future wastewater problems and reduce nutrient pollution reaching the Gallatin River. Building on an earlier feasibility study, it recommended a combined approach: building a sewer collection system in the canyon, phasing out existing septic systems, and pumping the collected wastewater up Highway 64 to be treated at BSCWSD's newly upgraded treatment plant. Treated water would then be piped back down the canyon for disposal through a combination of groundwater infiltration and irrigation.

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While some details have been refined since, the core project concept hasn't changed. This report was used to apply for the project's initial funding.

2020: Upper Gallatin Nutrient Assessment and Reduction Plan

Prepared by WGM Group on behalf of the Gallatin River Task Force

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This report examined the sources of nitrogen pollution in the West Fork and Upper Gallatin watersheds. In order from largest to smallest, the main human-related sources were found to be wastewater irrigation, individual septic systems, equestrian and grazing operations, stormwater and erosion, and domesticated animals.

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Since this report, upgrades to the BSCWSD water resource recovery facility have significantly reduced pollution from wastewater irrigation. The canyon sewer project is designed to address the remaining load from septic systems and prevent it from growing over time.

2020: Voters Approve 1% Resort Tax,

Securing $12 Million for a Canyon Sewer

Coordinated by BSRAD, the Gallatin River Task Force, and BSCWSD

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In May 2020, Big Sky voters approved a ballot measure adding an additional 1% infrastructure resort tax, bringing the total local resort tax to 4%. The measure was designed to raise up to $12 million to build a lift station near the Highway 191/64 intersection and the pipelines needed to carry wastewater from the canyon to the BSCWSD treatment plant, including a force main running alongside Highway 64 to the treatment plant, and a second pipeline to carry treated water back to the canyon for disposal through groundwater infiltration. These funds are managed through an agreement between BSRAD and BSCWSD and began being put to use in 2026.

2020: Feasibility Study

Prepared by WGM Group and AE2S on behalf of the Gallatin River Task Force

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This initial study evaluated wastewater management options for the canyon and helped establish that existing septic systems are a significant source of nitrogen pollution reaching the Gallatin River during low-flow periods.

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Recommendations from this study led directly to the formation of the Gallatin Canyon County Water & Sewer District (GCCWSD) and a renewed push for a canyon sewer system.

2008: Initial Canyon Preliminary Engineering Report (PER)

Prepared by DOWL on behalf of BSCWSD

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One of the first formal assessments of sewer options for the Gallatin Canyon area, this report aimed to protect the Gallatin River while allowing for continued economic growth. Nearly 20 years later, that goal remains the same, but the river's health has continued to decline, making nutrient reduction more urgent than ever.