Before diving into the technical specifications of the City of Asheville Water Resources Manual, watch this 2-minute overview of the essential water resource requirements for small retail developments.
This video covers:
- The Administrative Path: Understanding when a Letter of Commitment (LOC) is required for your project.
- Demand Modeling: A quick look at using fixture unit analysis to calculate peak domestic demand.
- Fire & Pressure Standards: The critical ’20 PSI rule’ during fire flow and the 40 PSI requirement for domestic peak flow.
Watch below for a high-level summary before reading our deep dive into the engineering details.“
Designing a small retail site requires a clear understanding of both administrative procedures and technical standards to ensure a reliable water supply for domestic and fire protection needs. While our introductory video gave you a high-level overview, this post dives into the specifics every civil engineer needs to know when working within the City of Asheville’s jurisdiction.
1. The First Hurdle: The Letter of Commitment (LOC)
For most commercial retail projects, the process begins long before a shovel hits the ground. You must apply for a Letter of Commitment (LOC) through the Water Engineering Division. This is mandatory if your project requires a water meter larger than 1-inch or if the service involves a fireline connection along with domestic service.
The LOC application must include a fixture unit analysis to determine peak domestic water demand and a sketch plan showing the desired location and size of connections.
2. Calculating Demand: The Fixture Unit Method
For commercial projects, “guestimating” water demand isn’t an option. The manual requires a fixture unit analysis based on the North Carolina Administrative Code.
- Weighted Values: Different fixtures (sinks, water closets, etc.) are assigned specific “weights”.
- Peak Flow: These weights are then converted into an estimated demand in Gallons Per Minute (GPM) using standard demand curves.
- Meter Sizing: The City reviews these calculations to ensure the selected meter is the smallest size capable of handling both minimum and maximum expected flow rates to maintain accuracy.
3. Fire Flow and Pressure Standards
Fire protection is often the most demanding aspect of water resource design.
- Minimum Fire Flow: For non-single-family uses, the base fire flow is typically 1000 GPM, though the specific Fire Marshal may require more.
- The 20 PSI Rule: You must demonstrate through hydraulic calculations that the system can maintain a minimum residual pressure of 20 PSI during fire flow conditions.
- Domestic Pressure: Under peak domestic demand (without fire flow), the system must maintain at least 40 PSI at the highest point.
4. Infrastructure Fundamentals
When extending or modifying the water system, several physical standards must be met:
- Pipe Diameter: The standard size for water mains is 8 inches. A 6-inch main is only permitted in limited local distribution areas where demand is fully defined, and it cannot exceed 2,000 feet if it is a dead-end.
- Material: All mains must be ductile iron pipe rated for a working pressure of at least 350 PSI for pipes 12 inches or smaller.
- Separation: To protect public health, water mains must maintain a 10-foot lateral separation from sanitary sewers and storm drains. If they must cross, a vertical separation of 18 inches is required.
5. Metering and Backflow Prevention
For commercial retail applications, the City typically requires combination fire and domestic water service.
- Master Meter Vaults: These assemblies are usually installed in below-ground vaults located outside of travel areas.
- Backflow Prevention: Because commercial sites are considered a potential hazard, backflow prevention assemblies are required on all connections.
- High Hazard Risks: Irrigation systems or certain fire suppression setups are classified as “high hazard” and require Reduced Pressure Zone (RPZ) assemblies, which must be installed in above-ground, heated enclosures to prevent freezing.
Final Thoughts
Success in the design phase relies on early coordination. The manual emphasizes that fire hydrant locations must be approved by the Fire Official and coordinated with parking and street design. By integrating these Asheville-specific standards into your early site plan, you can avoid costly revisions during the official plan review.
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For the full manual, refer to the City of Asheville Water Resources Design & Construction Manual.