Water Treatment Facilities

Is Emergency Power Required for Distribution System Facilities?

The requirement for back-up power for distribution system facilities is driven by three Arizona Administrative Code (AAC) requirements as follows:
  • R18-5-502.B - A potable water distribution system shall be designed to maintain and shall maintain a pressure of at least 20 pounds per square inch at ground level at all points in the distribution system under all conditions of flow.
  • R18-5-503.A - The minimum storage capacity for a CWS [community water system] or a non-community water system that serves a residential population or a school shall be equal to the average daily demand during the peak month of the year. Storage capacity may be based on existing consumption and phased as the water system expands.
  • R18-5-503.B - The minimum storage capacity for a multiple-well system for a CWS [community water system] or a non-community water system that serves a residential population or a school may be reduced by the amount of the total daily production capacity minus the production from the largest producing well.
Conformance with item 1 is usually implemented by the construction of one or more reservoirs to provide storage capacity for a distribution system service area. Properly designed reservoirs located at the high water elevation of a service area can provide hydraulic head to maintain a nominal system pressure of 20 psi. In some cases, isolated service areas may be fed by redundant supply sources instead of using reservoirs to maintain system pressure.

Conformance with items 2 and 3 is implemented by sizing the reservoirs to provide sufficient capacity to meet the required capacity for peak and fire flow demands in combination with redundant supply sources feeding a distribution system service area such as surface water treatment plants, groundwater wells, booster pump stations and pressure reducing valve stations.

Emergency power may be required for groundwater wells, booster pump stations and pressure reducing valve stations acting as a source of supply to isolated service areas. For example, a service area with insufficient storage capacity fed by two other service areas via booster pump stations that are on the same electrical grid would not conform to the AAC requirements as loss of power would result in a loss of pressure in the distribution system.

An engineering analysis of the distribution system should be performed when adding new or modifying existing groundwater wells, booster pump stations and pressure reducing valve stations to determine if emergency power is required at these facilities. The analysis should calculate the required minimum storage capacity for peak demand and fire flows and address the impact of system wide interruptions due to loss of power, major transmission pipeline ruptures and equipment failure.

What Are Some Key Issues When Converting a Groundwater Production Facility to a Water Treatment Plant?

A number of key issues need to be addressed when converting an groundwater production facility to a water treatment plant:
  • Physical Space Limitations - A typical groundwater production facility consists of a well, reservoir and booster pump station. The addition of treatment process equipment may exceed the physical size of the existing site.
  • Access and Visibility - Access to an existing site may be constrained or limited. Sites in residential areas may have to be accessed only during daylight hours and may require architectural features to provide a level of aesthetics compatible with the neighborhood.
  • Noise and Lighting - Noise associated with new treatment equipment may be an issue if the site is located in a residential neighborhood or has neighbors in close proximity. Lighting may have to be muted as compared to what is typical for a water treatment plant.
  • Special Use Permit - For facilities located in unincorporated areas of the County a special use permit is required to be obtained from the Maricopa County Planning and Development Department. Similar types of permits may be required for facilities located in incorporated areas of the County by the city or town which has jurisdiction.
  • Waste Streams - Treatment processes typically generate solid and/or liquid waste streams. Storage and the disposal of these streams can be problematic. Storage basins may have to be covered to provide vector control.
  • Emergency Power - Emergency power is required for water treatment plants. See the very first question on top for additional details.
  • Reliability - Reliability may have to be increased when converting a groundwater production facility to a water treatment plant.
  • Operator Certification - Groundwater production facilities are operated by Water Distribution certified operators. Water treatment plants must be operated by Water Treatment certified operators.