| (2) Valves. Full closing valves shall be installed
on the discharge piping of each pump and on the suction of all dry
pit pumps. A check valve shall be installed on the discharge side
of each pump, preceding the full closing valve. Check valves should
be of a swing check type with external levers. Rubberball check valves
may be used for grinder pump installations in lieu of the swing check
type. Butterfly valves, tilting disc check valves, or other valves
with a pivoted disc in the flow line are not allowed. The design shall
consider surge effects and provide protection where necessary. Surge
relief shall be contained in the system.
(3) Valve position indicators. Gate valves should be
rising-stem valves. If other than rising-stem gate valves and check
valves with external levers are used, the valves shall include a position
indicator to show their open and closed positions.
(4) Lift station piping. Flanged pipe and fitting or
welded pipe shall be used for exposed piping inside of lift stations.
A flexible or flanged connection shall be installed in the piping
to each pump so that the pump may be removed easily for repairs. Provisions
shall be made in the design to permit flexure where pipes pass through
walls of the station. Piping should normally be sized so that the
maximum suction velocity does not exceed five feet per second and
the maximum discharge velocity does not exceed eight feet per second.
(5) Force main pipe selection. Force mains shall be
a minimum of four inches in diameter, unless justified, as with the
use of grinder pumps. In no case shall the velocity be less than two
feet per second with only the smallest pump operating, unless special
facilities are provided for cleaning the line at specified intervals
or it can be shown that a flushing velocity of five feet per second
or greater will occur one or more times per day. Pipe specified for
force mains shall be of a type having an expected life at least as
long as that of the lift station and shall be suitable for the material
being pumped and the operating pressures to which it will be subjected.
All pipe shall be identified in the technical specifications with
appropriate American Society for Testing and Materials (ASTM), American
National Standards Institute (ANSI), or American Water Works Association
(AWWA) specifications numbers for both quality control (dimensions,
tolerances, etc.) and installation (bedding, backfill, etc.). All
pipe and fittings shall have a minimum working pressure rating of
150 pounds per square inch.
(6) Force main tests. Final plans and specifications
shall describe and require pressure testing for all installed force
mains. Minimum test pressure shall be 1.5 times the maximum design
pressure.
(7) Air release valves. Air release valves or combination
air release/vacuum valves suitable for sewage service shall be provided
at all peaks in elevation. The final engineering drawings must depict
all proposed force mains in both plan and profile.
(e) Emergency provisions. Lift stations shall be designed
such that there is not a substantial hazard of stream pollution from
overflow or surcharge onto public or private property with sewage
from the lift station. Options for a reliable power source may include
the following.
(1) Power supply. The commission will determine the
reliability of the existing commercial power service. Such determinations
shall be based on power outage records obtained from the appropriate
power company and presented to the commission. When requesting outage
records for submittal to the commission, it is important to note that
the records be in writing, bear the signature of an authorized utility
employee, identify the location of the wastewater facilities being
served, list the total number of outages that have occurred during
the past 24 months, and indicate the duration of each recorded outage.
The facility will be deemed reliable if the demonstrated wastewater
retention capacity, in the station's wet well, spill retention facility,
and incoming gravity sewer lines, is sufficient to insure that no
discharge of untreated wastewater will occur for a length of time
equal to the longest electrical outage recorded in the past 24 months.
If records for the service area cannot be obtained, a 120 minute worst
case outage duration will be assumed. Provisions for a minimum wastewater
retention period of 20 minutes should be considered even in those
cases where power company records indicate no actual outages of more
than 20 minutes occurred during the past 24 months.
(2) Alternative power supply. If the existing power
supply is found to be unreliable, an emergency power supply or detention
facility shall be provided. Options include:
(A) electrical service from two separate commercial
power companies, provided automatic switchover capabilities are in
effect;
(B) electrical service from two independent feeder
lines or substations of the same electric utility, provided automatic
switchover capabilities are in effect;
(C) on-site automatic starting electrical generators;
(D) reliance on portable generators or pumps. Proposals
for the utilization of portable units shall be accompanied by a detailed
report showing conclusively the ability of such a system to function
satisfactorily. Portable units will be approved only in those cases
where the station is equipped with an auto-dialer, telemetry device,
or other acceptable operator notification device, operators knowledgeable
in acquisition and startup of the portable units are on 24-hour call,
the station is accessible in all weather conditions, reasonable assurances
exist as to the timely availability and accessibility of the proper
portable equipment, and the station is equipped with properly designed
and tested quick connection facilities. This option is usually acceptable
only for smaller lift stations.
(3) Restoration of lift station. Provisions should
be made to restore the lift station to service within four hours of
outage.
(4) Spill containment structures. A spill containment
structure should be considered together with in-system retention in
determining a total wastewater retention time. Because separate spill
retention facilities are not suitable for all locations, engineers
should check with the commission prior to designing such structures.
The design shall provide:
(A) a minimum storage volume of average design flow
from the contributing area and the longest power outage during the
most recent consecutive 24-month period or, if power records are not
available, an assumed 24-hour outage;
(B) an impermeable liner (such as concrete or synthetic
fabric (20 mil thickness)) and should have an energy dissipator at
the point of overflow from the lift station to prevent scour;
(C) a fence with a controlled access; and
(D) a plan for routine cleaning and inspection.
(5) Alarm system. An audiovisual alarm system (red
flashing light and horn) shall be provided for all lift stations.
These alarm systems should be telemetered to a facility where 24-hour
attendance is available. The alarm system shall be activated in case
of power outage, pump failure, or a specified high water level.
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