Section 490. Reliability protection

A. Reliability is a measurement of the ability of a component or system to perform its designated function without failure or interruption of service. Overflow criteria, such as a period of discharge, are utilized solely for the establishment of reliability classification for design purposes and are not to be construed as authorization for or defense of an unpermitted discharge to state waters. The treatment works design shall provide for satisfactory operation during power failures, flooding, peak loads, equipment failure, and maintenance shut-down (in accordance with the requirements of the appropriate reliability class). Such design features include: (i) additional electrical power sources; (ii) additional flow storage capacity; and (iii) additional treatment unit operations, that provide for alternate operation in accordance with the issued certificate permit requirements.

B. Power feed. For Class I Reliability, two separate and independent sources of power feed shall be provided. Each source shall be capable of maintaining continuous treatment works operation at peak design flow during power failures, flooding, or equipment malfunction. Certain Reliability Class I treatment works for which it is feasible to shut down or discontinue treatment works operation during periods of power failure without bypassing or violating effluent limitations may be exempt from the alternate feed requirement.

1. Class I Reliability treatment works that may qualify for the alternate feed exemption can be broadly categorized as (i) those that serve facilities or institutions that could be closed during periods of power failure, such as certain industrial plants, schools, and recreational and park areas; (ii) those equipped with an emergency overflow holding basin with sufficient capacity to retain a minimum of one day of treatment works design flow and having provisions for recycle to the treatment works; and (iii) those with sufficient operational resources for which it can be demonstrated that projected power failures will not result in public health problems, water quality damage, or socio-economic resource losses.

2. Single source power feed is acceptable for Reliability Class II and III systems or works.

C. Power source. Electric power shall be provided by alternate feed from distribution lines that are serviced by alternate feed from transmission lines (e.g., 115KV) where possible. The transmission lines shall have alternate feed from the generating source or sources. The requirement for alternate feed can be satisfied by either a loop circuit, a "tie" circuit, or two radial lines. Where alternate feed lines terminate in the same substation, the substation shall be equipped as follows:

1. Reliability Class I: two or more in-place transformers.

2. Reliability Class II and Class III: one in-place transformer and capability for a connection of a mobile transformer.

On-site power generating equipment may be used as a substitute for alternate utility source feed. The capacity of the back-up power source shall be sufficient to operate all components vital to wastewater treatment operations during peak wastewater flow conditions, together with critical lighting and ventilation.

D. Power systems. External power distribution lines to a Class I Reliability Treatment Works shall be completely independent (i.e., both power lines cannot be carried on the same pole, cannot be placed in the same underground conduit, or cannot cross in their route to the treatment works) where possible. Minimum separation between alternate lines of 75 feet for above ground routes and 25 feet for underground routes shall be maintained. This shall also apply to service connections into the sewage treatment works. Devices should be used to protect the system from lightning.

1. Reliability Class I treatment works shall have a final step down transformer on each electrical feed line with adequate physical separation between them to prevent a common mode failure. In addition, Reliability Class I treatment works shall be provided with separate buses for each power source and separate independent internal power distribution systems up to the transfer switch for all critical components. The electrical power transfer to the alternate source should occur within 10 minutes of the time of failure of the primary power source.

2. Breaker settings or fuse ratings shall be coordinated to effect sequential tripping such that the breaker or fuse nearest the fault will clear the fault prior to activation of other breakers or fuses, to the degree practicable.

3. Where practicable, the electric switchgear and motor control centers shall be housed in a separate room from the liquid processing equipment. All outdoor motors shall be adequately protected from the weather. Motors located indoors and near liquid handling piping or equipment shall be, at least, of splash-proof design. Means for heating motors located outdoors or in areas where condensation may occur should be provided. On-site emergency power generating equipment shall be located above grade and be adequately ventilated. Fuel shall be stored in safe locations and in containers specifically designed for fuel storage.

a. All electrical equipment (motors, controls, switches, conduit systems, etc.) located in raw sewage wet wells or in totally or partially enclosed spaces where hazardous concentrations of flammable liquids, gases, vapors, or dusts may be present shall comply with the National Electrical Code, including the requirements for Class I, Group D, Division 1 locations.

b. Three-phase motors and their starters shall be protected from electric overload and short circuits on all three phases.

c. Large motors shall have a low voltage protection device that, on the reduction or failure of voltage, will cause and maintain the interruption of power to that motor.

d. Consideration should be given to the installation of temperature detectors in the stator and bearings of large motors in order to give an indication of overheating problems.

e. Wires in underground conduits or in conduits that can be flooded shall have moisture resistant insulation identified in the National Electrical Code.

4. The means for starting an on-site emergency power generator shall be completely independent of the normal electric power source. Air-starting systems shall have an accumulator tank or tanks with a volume sufficient to furnish air for starting the generator engine a minimum of three times without recharging. Batteries used for starting shall have a sufficient charge to start the generator engine a minimum of three times without recharging. The starting system shall be appropriately alarmed and instrumented to indicate loss of readiness (e.g., loss of charge on batteries, loss of pressure in air accumulators, etc.).

5. Testing provisions shall be included in the design of essential equipment requiring periodic testing to enable the tests to be accomplished while maintaining electric power to all vital components. Such provisions would involve an ability to conduct tests, such as actuating and resetting automatic transfer switches and starting and loading emergency generating equipment without taking essential equipment off-line. The electric power distribution system and equipment shall be designed to facilitate inspection and maintenance of individual items without interruption of operations.

E. Flow Storage. In combination with provisions for electrical power reliability, the use of flow storage and additional unit operations should be evaluated. Additional flow storage capacity should provide up to a 24-hour detention of the peak design flow. Additional unit operations could involve chemical clarification, filtration, additional disinfection capacity, or use of natural treatment technology for enhancing effluent quality.

F. Alarm systems. An audiovisual alarm system to monitor the condition of equipment whose failure could result in a bypass or a violation of effluent limitations shall be provided for all treatment works. Alarms shall also be provided to monitor conditions which could result in damage to vital components.

1. For continuously manned treatment works, the alarm system shall sound and be visible in areas normally manned and in areas near the equipment being monitored.

2. Treatment works not continuously manned shall have, in addition to a local audiovisual alarm, provisions for transmitting an audible alarm to a central location where personnel competent to receive the alarm and initiate corrective action are available 24 hours per day or during the period of time that the treatment works receives influent flow.

3. The following requirements apply to all treatment works:

a. The on-site alarm system should be designed in such a manner that each announced condition is uniquely identified.

b. A back up power supply, such as a battery pack with an automatic switchover feature, shall be provided for the alarm system (such that a failure of the primary power source would not disable the alarm system), unless an adequate alternate or backup power source is provided.

c. Test circuits shall be provided to enable the alarm system to be tested and verified to be working properly.

Historical Notes

Former 12VAC5-581-550 derived from Volume 18, Issue 10, eff. February 27, 2002; amended and adopted as 9VAC25-790-490, Virginia Register Volume 20, Issue 09, eff. February 12, 2004.

Statutory Authority

§ 62.1-44.19 of the Code of Virginia.