B09 Amendment 3 Yellowstone Mammoth Project Report 0003.pdf
Posted: Sept. 2, 2026
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Summary
This **Chapter 3 Permit to Construct Design Report**, prepared by **Stantec Consulting Services, Inc. for the National Park Service and Wyoming Department of Environmental Quality**, addresses potable-water, fire-suppression, and sanitary-sewer improvements supporting four new modular employee-housing units in Yellowstone National Park’s Mammoth Government Area, with construction anticipated to begin in fall 2026.
The project is located in Park County, Wyoming, in the southeast quarter of Section 30 and northeast quarter of Section 31, Township 58 North, Range 114 West. The report supports permitting under Wyoming DEQ Water Quality Rules and Regulations Chapters 11 and 12 and documents compliance with the 2023 Wyoming Public Works Standard Specifications.
The proposed water work consists of installing approximately 35 linear feet of 2-inch HDPE water and fire-service piping for each of the four modular units, connected to the existing Mammoth distribution system and certified to AWWA C901. No new water storage, pumping, or treatment facilities are proposed.
Hydraulic modeling using EPANET evaluated peak-hour, maximum-day, and fire-flow conditions, including:
- Average daily demand: 1,500 gallons per day
- Maximum daily demand: 4,080 gallons per day
- Peak-hour demand: 11.3 gallons per minute
- Automatic fire-suppression demand: 55 gallons per minute
- Site fire flow: 1,000 gallons per minute for one hour
The modeled system maintains at least 20 psi during fire-flow conditions, with residual pressures of 33.90 psi at Hydrant M1 and 23.26 psi at Hydrant M3. Peak-hour dynamic pressures range from 85.99 to 100.3 psi, although the report notes an additional 7.5-psi meter-and-pit loss at 55 gallons per minute.
Sanitary-sewer improvements include:
- Replacing approximately 400–430 linear feet of existing 8-inch vitrified-clay sewer with 8-inch SDR 26 bell-and-spigot PVC
- Installing two new 48-inch manholes
- Abandoning the existing sewer segment during construction
- Adding new services to the housing units:
- 4-inch gravity services for three units
- 2-inch force service for one unit
The replacement sewer will use slopes ranging from 2.0 to 3.5 feet per 100 feet and has calculated full-flow capacities of approximately 589 to 775 gallons per minute, demonstrating adequate capacity for the proposed connections.
Yellowstone National Park will own and maintain the modified water and sewer infrastructure. The existing Mammoth wastewater treatment system, designed for 1.2 million gallons per day with 2025 average inflows below 0.1 million gallons per day, is reported to have sufficient remaining capacity.
The project is located in Park County, Wyoming, in the southeast quarter of Section 30 and northeast quarter of Section 31, Township 58 North, Range 114 West. The report supports permitting under Wyoming DEQ Water Quality Rules and Regulations Chapters 11 and 12 and documents compliance with the 2023 Wyoming Public Works Standard Specifications.
The proposed water work consists of installing approximately 35 linear feet of 2-inch HDPE water and fire-service piping for each of the four modular units, connected to the existing Mammoth distribution system and certified to AWWA C901. No new water storage, pumping, or treatment facilities are proposed.
Hydraulic modeling using EPANET evaluated peak-hour, maximum-day, and fire-flow conditions, including:
- Average daily demand: 1,500 gallons per day
- Maximum daily demand: 4,080 gallons per day
- Peak-hour demand: 11.3 gallons per minute
- Automatic fire-suppression demand: 55 gallons per minute
- Site fire flow: 1,000 gallons per minute for one hour
The modeled system maintains at least 20 psi during fire-flow conditions, with residual pressures of 33.90 psi at Hydrant M1 and 23.26 psi at Hydrant M3. Peak-hour dynamic pressures range from 85.99 to 100.3 psi, although the report notes an additional 7.5-psi meter-and-pit loss at 55 gallons per minute.
Sanitary-sewer improvements include:
- Replacing approximately 400–430 linear feet of existing 8-inch vitrified-clay sewer with 8-inch SDR 26 bell-and-spigot PVC
- Installing two new 48-inch manholes
- Abandoning the existing sewer segment during construction
- Adding new services to the housing units:
- 4-inch gravity services for three units
- 2-inch force service for one unit
The replacement sewer will use slopes ranging from 2.0 to 3.5 feet per 100 feet and has calculated full-flow capacities of approximately 589 to 775 gallons per minute, demonstrating adequate capacity for the proposed connections.
Yellowstone National Park will own and maintain the modified water and sewer infrastructure. The existing Mammoth wastewater treatment system, designed for 1.2 million gallons per day with 2025 average inflows below 0.1 million gallons per day, is reported to have sufficient remaining capacity.
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