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1. Is emergency power required for a water treatment plant?

Yes in most cases. The requirement is specified in the Arizona Department of Environmental Quality's (ADEQ) Engineering Bulletin No. 10, "Guidelines for the Construction of Water Systems" in Chapter 4, Section A.4.

The only exception would be for:
- A plant that is 100% redundant to another potable water source (e.g. a surface water treatment plant or a groundwater well field) that is capable of meeting the peak day demand for the water distribution area being served and the plant and the redundant potable water source are on separate electrical grids or power supplies.
- A plant that is 100% redundant to another potable water source (e.g. a surface water treatment plant or a groundwater well field) that is capable of meeting the peak day demand for the water distribution area being served and the redundant potable water source has redundant feeds from two different electrical grids or an emergency power supply.
- A plant which serves a water distribution area that has sufficient system storage capacity to meet the peak day demand and it can be demonstrated that the plant can be restored to normal operation within 24 hours after the interruption of service.

Requests for an exception will be reviewed and approved by the MCESD on a case-by-case basis. For more information, please email treatmentplantprogram@maricopa.gov.

2. Is emergency power required for groundwater production facilities?

Groundwater production facilities (typically a groundwater well, reservoir and booster pump station that do not treat the groundwater) usually do not require emergency power. However, emergency power may be required to meet the regulatory requirements for the distribution system. For more information, please email treatmentplantprogram@maricopa.gov.

3. Is emergency power required for distribution system facilities?

The requirement for back-up power for distribution system facilities is driven by 3 Arizona Administrative Code requirements.

4. What are the requirements for equipment and process redundancy for a water treatment plant?

The Arizona Department of Environmental Quality's (ADEQ) Engineering Bulletin No. 10, "Guidelines for the Construction of Water Systems", Chapter 4, Section A.4 states: "Unless the treatment plant can be taken out of service for a period of time for maintenance and repair work, 2 or more of all essential treatment units or items shall be provided. With 1 unit or item out of service, the remaining units or items shall meet the design capacity of the plant. When deciding whether or not to install more than 1 unit, the consequences of failure of that unit should be considered."

An engineering analysis should be performed when designing a new or modifying an existing water treatment plant to determine what process units and types of equipment require redundancy and increased reliability. The analysis should address the impact and the criticality of process interruptions and equipment failure and assess the length of time the process or system would be out of service. For more information, please email treatmentplantprogram@maricopa.gov.

5. What are the requirements related to the rated capacity of a water treatment plant?

The rated capacity of a water treatment plant is based upon the ‘firm capacity’ of the facility. Firm capacity refers to the available capacity of a system or process with the largest unit out of service. Thus, the reliability and redundancy of a water treatment plant's equipment and process units are integral to the plant's firm capacity.

Reliability and redundancy requirements are based on installed redundant equipment and process units. Using analytical or statistical methods such as ‘predicted downtime,' ‘mean time between failure’ or other types of failure mode analysis to justify the reliability of systems or processes within a water treatment plant is not an acceptable means of determining the rated capacity of the plant. A water treatment plant's rated capacity is solely based on its firm capacity.

The rated capacity of a water treatment plant is critical in determining when an expansion of a plant is required. The Arizona Department of Environmental Quality's (ADEQ) Engineering Bulletin No. 10, "Guidelines for the Construction of Water Systems", Chapter 4, Section A.6 states: "Expansion of the plant is indicated when the maximum daily demands of the system approach the rated capacity of the existing plant. As a general rule, steps to provide additional treatment capacity should be taken at least 5 years before present capacity is reached to allow sufficient time for engineering investigations, design, financing and construction." For more information, please email treatmentplantprogram@maricopa.gov

6. 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.

7. What are the design requirements for venting wet wells, clearwells, tanks and reservoirs?

The requirements are specified in the Arizona Department of Environmental Quality's (ADEQ) Engineering Bulletin No. 10, "Guidelines for the Construction of Water Systems", Chapter 6, Section E.9.

In addition to the installation of inverted 'U' type vents, MCESD also allows the use of recent designs such as 'chair' or cross-flow vents provided these vents have an air flow direction change of 90 degrees in the horizontal plane prior to air entering/leaving the containment vessel.

In all cases, vents shall have a 16-mesh corrosion resistant screen installed to prevent the ingress of birds and insects. For more information, please email treatmentplantprogram@maricopa.gov.

8. What are the design requirements for wet well, clearwell, tank or reservoir overflows?

The requirements are specified in the Arizona Department of Environmental Quality's (ADEQ) Engineering Bulletin No. 10, "Guidelines for the Construction of Water Systems", Chapter 6, Section E.6.

In addition to the installation of overflow piping with a 16-mesh corrosion resistant screen, MCESD also allows the use of alternative designs such as the use of counter-weighted flapper valves or self-sealing valves that will open and close automatically when an overflow occurs.

In all cases, overflows shall have a 16-mesh corrosion resistant screen installed or provide a mechanical means of sealing the overflow opening to prevent the ingress of birds and insects.

If the overflow from a storage vessel is not connected to a sewer or storm water system a suitable means on onsite containment must be included in the design. Onsite retention basins with riprap line channels and sides are typically used to contain an overflow and prevent erosion. Care should be taken in the design to insure that underground vaults and access points are not located in close proximity to overflow channels or retention basins. For more information, please email treatmentplantprogram@maricopa.gov.

9. What are the design requirements for entry hatches on wet wells, clearwells, tanks and reservoirs?

The requirements are specified in the Arizona Department of Environmental Quality's (ADEQ) Engineering Bulletin No. 10, "Guidelines for the Construction of Water Systems", Chapter 6, Section E.8.

Entry hatches shall be constructed with seals to prevent the entry of unsafe water, birds and insects into the containment vessel. Typical entry hatch designs include frames with integral curbs and frame overlapping covers with rubber or plastic seals. For more information, please email treatmentplantprogram@maricopa.gov.

10. Can pump seal water be discharged to a pump wet well?

Pump seal water shall only be discharged to a wet well if the seal water is free of contaminants and of equal water quality to the water contained in the wet well. A finished water pump utilizing plant service water for the pump seal water source cannot discharge the seal water into the wet well as this installation would be a cross connection between potable and non-potable water systems. For more information, please email treatmentplantprogram@maricopa.gov.