Current through Register Vol. 41, No. 3, September 23, 2024
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.
Statutory Authority
§ 62.1-44.19 of the Code of Virginia.
