United States
                       Environmental Protection
                       Agency
 Office of Water
 Washington, D.C.
EPA 832-F-00-073
September 2000
                       Collection  Systems
                       Technology  Fact  Sheet
                       Sewers,  Lift  Station
DESCRIPTION

Wastewater lift stations are facilities designed to
move wastewater from lower to higher elevation
through pipes.  Key elements of lift stations include
a wastewater  receiving well  (wet-well),  often
equipped  with a screen or  grinding to remove
coarse materials; pumps and piping with associated
valves; motors;  a  power  supply  system;   an
equipment control and alarm system; and an odor
control system  and ventilation system.

Lift station equipment and systems are  often
installed in an enclosed structure.   They can  be
constructed on-site  (custom-designed)  or  pre-
fabricated.  Lift  station capacities  range from
76 liters per minute (20 gallons per minute) to more
than 378,500 liters per minute (100,000 gallons per
minute). Pre-fabricated lift stations generally have
capacities of up to 38,000 liters per minute (10,000
gallons per minute).   Centrifugal  pumps  are
commonly used in lift stations.  A trapped air
column, or bubbler system, that senses pressure and
level is commonly used for pump station control.
Other control alternatives include electrodes placed
at cut-off levels, floats, mechanical  clutches, and
floating mercury switches. A more sophisticated
control operation involves the use of variable speed
drives.

Lift stations are typically provided with equipment
for easy pump removal.  Floor access hatches or
openings above the pump room and an overhead
monorail beam, bridge crane, or portable hoist are
commonly used.

The two most common types of lift stations are the
dry-pit or dry-well and submersible lift stations.  In
dry-well lift stations, pumps and valves are housed
in a pump room (dry pit or dry-well), that is easily
accessible.  The wet-well is a separate chamber
attached or located adjacent to the dry-well (pump
room) structure. Figures 1 and 2 illustrate the two
types of pumps.
Source: Qasim, 1994.

       FIGURE 1 DRY-WELL PUMP

Submersible lift  stations do not have a separate
pump  room;  the  lift station header  piping,
associated valves, and flow meters are located in a
separate  dry vault  at grade  for  easy  access.
Submersible lift stations include sealed pumps that
operate submerged in the wet-well.  These are
removed to the surface periodically and reinstalled
using guide rails  and a hoist.  A key advantage of
dry-well lift stations is that they allow easy access
for routine visual inspection and maintenance.  In
general, they are  easier to repair than submersible
pumps. An advantage of submersible lift stations is
that they typically cost less than dry-well stations
and operate without frequent pump  maintenance.
Submersible lift  stations do  not usually  include

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                              Hoist
   Discharge
Source: Qasim, 1994.

   FIGURE 2 WET-WELL SUBMERSIBLE
large  aboveground structures and tend to blend in
with their surrounding environment in residential
areas.  They require less space and are easier and
less expensive to construct for wastewater flow
capacities of  38,000 liters per minute  (10,000
gallons per minute) or less.

APPLICABILITY

Lift stations are used to move wastewater from
lower to higher elevation,  particularly where the
elevation of the source is not sufficient for gravity
flow and/or when the use of gravity conveyance
will result in excessive excavation depths and high
sewer construction costs.

Current Status

Lift  stations  are  widely  used  in  wastewater
conveyance systems.  Dry-well lift stations have
been used in the industry for many years. However,
the current industry-wide trend is to replace dry-
well  lift  stations  of  small and  medium  size
(typically less than 24,000 liters per minute or 6,350
gallons per minute) with submersible lift stations
mainly because of lower costs, a smaller footprint,
and simplified  operation and maintenance.

Variable speed pumping is  often used to optimize
pump  performance  and  minimize  power use.
Several types of variable-speed pumping equipment
are  available,  including  variable  voltage  and
frequency drives,  eddy  current  couplings,  and
mechanical variable-speed drives.  Variable-speed
pumping can reduce the size and cost of the wet-
well and allows the pumps to operate at maximum
efficiency under  a variety  of flow conditions.
Because variable-speed pumping allows lift station
discharge to match inflow, only nominal wet-well
storage volume is required and the well water level
is  maintained  at  a  near  constant  elevation.
Variable-speed  pumping may allow a given flow
range to be achieved with fewer pumps  than a
constant-speed alternative. Variable-speed stations
also minimize the number of pump starts and stops,
reducing mechanical  wear.   Although there is
significant energy saving potential for stations with
large friction losses, it may not justify the additional
capital costs unless the cost of power is relatively
high.  Variable speed equipment  also requires more
room within the lift station and may produce more
noise and heat than constant speed pumps.

Lift  stations are complex facilities with  many
auxiliary systems. Therefore, they are less reliable
than gravity wastewater conveyance. However, lift
station reliability can be significantly  improved by
providing stand-by equipment (pumps and controls)
and emergency power supply systems. In addition,
lift station reliability is improved by using non-clog
pumps suitable for the particular wastewater quality
and by  applying emergency  alarm and automatic
control systems.

ADVANTAGES AND DISADVANTAGES

Advantages

Lift stations are used to reduce  the capital  cost of
sewer system construction. When gravity  sewers
are installed in trenches deeper than  three meters
(10  feet),  the cost  of  sewer line  installation
increases significantly because of the more complex
and costly excavation equipment and trench shoring
techniques required. The size of the gravity sewer
lines is dependent on the minimum pipe slope and
flow. Pumping wastewater can convey the same
flow using smaller pipeline size at shallower depth,
and thereby, reducing pipeline costs.

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Disadvantages
Wet-well
Compared  to  sewer lines where  gravity drives
wastewater flow, lift stations require a source of
electric power.  If the power supply is interrupted,
flow conveyance is discontinued and can result in
flooding  upstream of the  lift station, It can also
interrupt the normal operation of the downstream
wastewater  conveyance and treatment facilities.
This limitation is typically addressed by providing
an emergency power supply.

Key disadvantages of lift stations include the high
cost to construct and maintain and the potential for
odors and noise.   Lift stations also  require  a
significant  amount  of  power, are  sometimes
expensive to  upgrade,  and  may  create  public
concerns and negative public reaction.

The low cost of gravity wastewater conveyance and
the  higher  costs  of  building, operating,  and
maintaining lift stations means that wastewater
pumping  should  be  avoided,  if  possible  and
technically feasible. Wastewater pumping can be
eliminated or reduced by selecting alternative sewer
routes or extending a gravity sewer using direction
drilling or other state-of-the-art deep excavation
methods.  If such  alternatives are  viable,  a  cost-
benefit analysis can determine if a lift station is the
most viable choice.

DESIGN CRITERIA

Cost effective  lift stations  are  designed  to: (1)
match pump capacity, type, and configuration with
wastewater  quantity  and  quality; (2)  provide
reliable and uninterruptible operation; (3) allow for
easy operation and maintenance of the installed
equipment;  (4) accommodate  future  capacity
expansion;   (5)  avoid   septic  conditions  and
excessive release of odors in the collection system
and at the lift station; (6) minimize environmental
and  landscape  impacts   on  the  surrounding
residential and commercial developments; and (7)
avoid  flooding of the  lift  station   and  the
surrounding areas.
Wet-well design depends on the type of lift station
configuration (submersible or dry-well)  and the
type of pump controls (constant or variable speed).
Wet-wells are typically  designed large enough to
prevent rapid pump  cycling but small enough to
prevent a long detention time and associated odor
release.

Wet-well  maximum detention time  in  constant
speed pumps is  typically 20 to 30 minutes. Use of
variable frequency drives for pump speed control
allows wet-well detention time reduction to 5 to 15
minutes.  The  minimum recommended wet-well
bottom slope is to 2:1 to allow self-cleaning and
minimum  deposit of debris.  Effective volume of
the  wet-well  may  include  sewer  pipelines,
especially  when variable speed  drives are used.
Wet-wells should always hold some level of sewage
to minimize odor release.  Bar screens or grinders
are often installed in or upstream of the wet-well to
minimize pump clogging problems.

Wastewater Pumps

The number of wastewater pumps and associated
capacity should  be selected to provide  head-
capacity characteristics that correspond as nearly as
possible to wastewater quantity fluctuations.  This
can be accomplished by preparing pump/pipeline
system head-capacity curves showing all conditions
of head (elevation of a free surface  of water) and
capacity under which the pumps will be required to
operate.

The number of pumps to be installed  in a lift station
depends on the  station capacity, the range of flow
and  the regulations.   In  small  stations,  with
maximum inflows of less  than 2,640 liters per
minute (700 gallons per minute), two pumps are
customarily installed, with each unit able to meet
the maximum influent rate.  For larger lift stations,
the size and number of pumps should be selected so
that the range of influent flow rates  can be  met
without starting and stopping pumps  too frequently
and without excessive wet-well storage.

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Depending on the system, the pumps are designed
to run at  a reduced rate.   The pumps may also
alternate to equalize wear and tear.  Additional
pumps may provide intermediate capacities better
matched to typical daily  flows.   An alternative
option is to provide flow flexibility with variable-
speed pumps.

For pump stations with high head-losses, the single-
pump flow approach is usually the most suitable.
Parallel pumping  is  not  as  effective  for  such
stations because two pumps operating together yield
only slightly higher flows  than one pump.  If the
peak flow is to be achieved with multiple pumps in
parallel, the lift station must be equipped with at
least three pumps: two duty pumps that together
provide peak  flow and  one  standby  pump for
emergency  backup.   Parallel peak pumping is
typically used in large lift stations with relatively
flat  system head  curves.    Such  curves  allow
multiple pumps to  deliver substantially more flow
than a single pump. The use of multiple pumps in
parallel provides more flexibility.

Several types  of centrifugal pumps are  used in
wastewater lift  stations.    In the  straight-flow
centrifugal pumps, wastewater does not change
direction as it passes through the  pumps and into
the discharge pipe.  These pumps are well suited for
low-flow/high head  conditions.    In angle-flow
pumps, wastewater enters the impeller axially and
passes through the volute casing at 90 degrees to its
original direction (Figure 3). This type of pump is
appropriate for pumping against low or moderate
heads.  Mixed flow pumps are most  viable for
pumping large quantities of wastewater at low head.
In these pumps, the outside diameter of the impeller
is less than an ordinary centrifugal pump, increasing
flow volume.

Ventilation

Ventilation  and  heating  are required if the lift
station  includes  an area  routinely entered by
personnel.  Ventilation is particularly important to
prevent the collection  of toxic and/or explosive
gases.   According to the  Nation Fire Protection
Association (NFPA) Section 820, all continuous
ventilation systems should be fitted with  flow
detection  devices connected to alarm systems to
                                t
                 Impeller
           Suction line
                                   Discharge line
                                    Casing
Source: Lindeburg, revised edition 1995.

 FIGURE 3 CENTRIFUGAL ANGLE-FLOW
                    PUMP

indicate  ventilation  system  failure.    Dry-well
ventilation codes typically require six continuous
air changes per hour or 30 intermittent air changes
per hour. Wet-wells typically require 12 continuous
air changes per hour or 60 intermittent air changes
per hour.  Motor control  center  (MCC) rooms
should  have a ventilation  system  adequate to
provide six air changes per hour and should be air
conditioned to between 13 and 32 degrees Celsius
(55 to  90 degrees F).   If the  control  room is
combined with an MCC room, the temperature
should not exceed 30 degrees  C or 85 degrees F.
All  other spaces  should be designed for 12  air
changes  per hour.   The minimum temperature
should be 13 degrees C (55 degrees F) whenever
chemicals are stored or used.

Odor Control

Odor control is frequently required for lift stations.
A relatively simple and widely used odor control
alternative is minimizing wet-well turbulence. More
effective  options  include   collection of  odors
generated at the lift  station and treating them in
scrubbers or biofilters  or  the addition  of odor
control chemicals to the sewer upstream of the lift
station.  Chemicals typically used for odor control
include  chlorine,  hydrogen peroxide, metal salts
(ferric chloride and ferrous sulfate) oxygen, air, and
potassium permanganate.   Chemicals should be

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closely monitored to avoid affecting downstream
treatment processes, such as extended aeration.

Power Supply

The reliability of power for the pump motor drives
is a basic design consideration.  Commonly used
methods of  emergency  power  supply  include
electric  power feed from two independent power
distribution lines; an on-site standby generator;  an
adequate portable generator with quick connection;
a stand-by engine driven  pump; ready access to a
suitable portable  pumping unit and  appropriate
connections; and availability of an adequate holding
facility for wastewater storage upstream of the lift
station.

PERFORMANCE

The overall performance of a lift station depends on
the  performance of the pumps.  All pumps have
four common performance characteristics: capacity,
head, power, and overall efficiency. Capacity (flow
rate) is  the quantity of liquid pumped per unit of
time,  typically  measured as  gallons  per  minute
(gpm) or million gallons  per day (mgd).  Head is
the  energy supplied to  the  wastewater per unit
weight, typically expressed as feet of water. Power
is the energy consumed by a pump per unit time,
typically measured as kilowatt-hours.   Overall
efficiency is the ratio of useful  hydraulic work
performed to actual work  input. Efficiency reflects
the  pump  relative  power losses and  is  usually
measured as a percentage of applied power.

Pump performance  curves (Figure 4)  are used to
define and compare the operating characteristics of
a pump and to identify  the best combination  of
performance  characteristics  under  which a  lift
station pumping system will operate under typical
conditions  (flows  and heads).   Pump  systems
operate at 75 to 85 percent efficiency most of the
time, while overall pump efficiency depends on the
type of installed pumps, their control system, and
the fluctuation of influent wastewater flow.

Performance  optimization  strategies  focus   on
different  ways to  match  pump  operational
characteristics  with  system   flow  and  head
requirements.   They may include the following
Source: Adapted from Roberson and Crowe, 1993.

 FIGURE 4 PUMP PERFORMANCE CURVE

options:  adjusting system  flow paths installing
variable  speed  drives;  using  parallel   pumps
installing pumps of different sizes trimming a pump
impeller; or putting a two-speed motor on one or
more pumps in a lift station.  Optimizing  system
performance may yield significant electrical energy
savings.

OPERATION AND MAINTENANCE

Lift station operation is usually automated and does
not require continuous on-site operator presence.
However, frequent inspections are recommended to
ensure normal functioning and to identify potential
problems. Lift station inspection typically includes
observation  of  pumps, motors and  drives for
unusual noise, vibration, heating and leakage, check
of pump suction and discharge lines for valving
arrangement and leakage,  check of control panel
switches  for  proper  position,  monitoring  of
discharge pump rates  and  pump  speed,  and
monitoring of the pump  suction  and discharge
pressure.    Weekly  inspections  are  typically
conducted, although the frequency  really depends
on the size of the lift station.

If a lift station is  equipped with grinder bar screens
to remove coarse materials from the wastewater,
these materials  are collected  in  containers and
disposed of to a sanitary landfill site as needed. If
the lift  station has a scrubber system  for  odor
control,  chemicals are supplied and replenished
typically every three months.  If chemicals are
added for odor control ahead of the lift station, the

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chemical feed stations should be inspected weekly
and chemicals replenished as needed.

The  most labor-intensive task  for lift stations is
routine  preventive maintenance.  A well-planned
maintenance  program  for  lift  station  pumps
prevents  unnecessary   equipment  wear   and
downtime.  Lift station operators must maintain an
inventory of  critical spare  parts.  The number of
spare parts in the inventory depends on the critical
needs of the unit, the rate at which the part normally
fails, and the  availability of the part.  The operator
should tabulate each pumping element in the system
and its recommended spare parts. This information
is  typically  available from the  operation  and
maintenance manuals provided with the lift station.
COSTS

Lift station costs depend on many factors, including
(1) wastewater quality, quantity, and projections;
(2) zoning and land use planning of the area where
the lift station will be located; (3) alternatives for
standby  power  sources;   (4)  operation  and
maintenance needs and support; (5) soil properties
and underground conditions; (6) required lift to the
receiving (discharge) sewer line; (7) the severity of
impact of accidental sewage spill  upon the local
area; and (8) the need for an odor control system.
These  site and system specific factors must be
examined  and  incorporated  in  preparing  a  lift
station cost estimate.
         Construction Costs

         The most important factors influencing cost are the
         design lift station capacity and the installed pump
         power.   Another  cost factor is the lift station
         complexity.  Factors which classify a lift station as
         complex include two or more of the following: (1)
         extent of excavation; (2) congested site and/or
         restricted access; (3) rock excavation; (4) extensive
         dewatering requirements, such as cofferdams; (5)
         site conflicts, including modification or removal of
         existing facilities; (6)  special foundations, including
         piling; (7) dual power supply  and on-site switch
         stations and emergency power generator; and (8)
         high pumping heads (design heads in  excess of
         200 ft).

         Mechanical,  electrical,  and control  equipment
         delivered to a pumping station  construction site
         typically  account for 15 to 30  percent of total
         construction costs. Lift station construction has a
         significant  economy-of-scale.   Typically,  if the
         capacity of a lift station is increased 100 percent,
         the construction cost  would increase only 50 to 55
         percent.  An important consideration is that two
         identical lift stations will cost 25 to 30 percent more
         than a single station of the same combined capacity.
         Usually, complex  lift stations cost two to three
         times more than more simple lift stations with no
         construction complications.

         Table 1 provides examples of complex lift stations
         and associated construction costs in 1999 dollars.
                     TABLE 1  LIFT STATION CONSTRUCTION COSTS
           Lift Station
Design Flowrate
    (MGD)
Construction Costs
    (1999$US)
Cost curve data1
Cost curve data1
Cost curve data1
Valencia, California2
Sunneymead, California2
Sunset/Heahfield, California2
Springfield, Oregon Terry Street
Pumping Station2
Detroit, Michigan2
0.5
1
3
6
12
14
20
750
$134,467
$246,524
$392,197
$1,390,000
$3,320,000
$2,600,000
$5,470,000
$128,800,000
           Source:  1Qasim, 1994 and2 James M. Montgomery Consulting Engineers, 1998.

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Operation and Maintenance Costs

Lift station operation and maintenance costs include
power, labor, maintenance, and chemicals (if used
for odor control).  Usually, the costs for solids
disposal are  minimal, but are included if the lift
station is  equipped with  bar screens to  remove
coarse materials from the wastewater. Typically,
power costs account for 85 to 95 percent of the total
operation and maintenance costs and are  directly
proportional to the unit cost of power and the actual
power used by the lift station pumps. Labor costs
average 1 to 2 percent  of total  costs.   Annual
maintenance   costs  vary,  depending  on  the
complexity of the equipment and instrumentation.

REFERENCES

Other Related Fact Sheets

Small Diameter Gravity Sewer
EPA 832-F-00-038
September 2000

In-Plant Pump Stations
EPA 832-F-00-069
September 2000

Other  EPA  Fact Sheets can be found at the
following web address:
http://www.epa.gov/owmitnet/mtbfact.htm

1.      Casada,  Don.   Pump Optimization for
       Changing Needs.  Operations Forum. Vol.
       9, No. 5, 14-18, May 1998.

2.      Cavalieri R.R. and G. L. Devin. Pitfalls in
       Wet Weather Pumped Facilities Design. In
       Proceedings of  the  Water  Environment
       Federation,   71st  Annual   Conference,
       Orlando, Florida, Vol. 2, 719-729, October
       1998.

3.      Gravette  B. R.    Benefits of  Dry-pit
       Submersible Pump Stations. In Proceedings
       of the Water Environment Federation, 68th
       Annual Conference, Miami Beach, Florida,
       Vol. 3,  187-196, October  1995.
4.      Graham B, I, Pinto T.G., and T. Southard.
       Backyard Pumping Stations - The Low-
       pressure Grinder Systems That Call Old
       Septic Tanks Home. Operations Forum, Vol.
       10, No. 5, 25-29, May 1993.

5.      Jackson  J. K.  Variable Speed Pumping
       Brings   Efficiency  to  Pump  Systems.
       Operations Forum, Vol. 13, No. 5, 21-24,
       May 1996.

6.      James   M.   Montgomery    Consulting
       Engineers,  1988.    "Sewerage  System
       Preliminary Cost Estimating Curves."

7.      Lindeburg, Michael R.  Civil Engineering
       Reference  Manual, 6th ed., Professional
       Publications, Inc., revised edition 1995.

8.      Makovics   J.   S.  and   M.  Larkin.
       Rehabilitating Existing Pumping Systems:
       Trips,  Traps  and Solutions.  Operations
       Forum, Vol. 9, No. 5, 10-17, May 1992.

9.      Metcalf   &   Eddy    Inc.,   Wastewater
       Engineering: Collection and Pumping of
       Wastewater, McGraw Hill Book Company,
       1981.

10.     National  Fire  Protection  Association.
       National Fire Codes.   Volume 7, Section
       820. Quincy, Massachusetts, 1995.

11.     Paschke  N.W.  Pump Station Basics -
       Design Considerations for a Reliable Pump
       Station. Operations Forum, Vol. 14, No. 5,
       15-20, May 1997.

12.     Public Works Journal.   The 1997 Public
       Works Manual. April 15, 1997.

13.     Qasim,  Syed R.   Wastewater Treatment
       Plants - Planning Design, and Operation.
       Technomic  Publishing Company,  Inc.,
       1994.

14.     Russell   Edward.      Screw-Pump
       Preservation. Operations Forum, Vol. 9,
       No. 5, 18-19, May 1992.

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15.     SanksR. L., TchobanoglousG., Newton D.,
       Bosserman, B.E., and Jones, G. M. Pump
       Station Design, Butterworths, Boston, 1998.

16.     Schneller T. M. Pumping it Up? Practical
       Means For Evaluating Lift Station Fitness.
       In Proceedings of the Water Environment
       Federation, 68th Annual Conference, Miami
       Beach, Florida, Vol. 3, 155-166  October
       1995.

17.     Smith  E. C.    Don't Lose  the Pump
       Efficiency Game. Operations Forum, Vol.
       11, No. 7, 18-21, July 1994.

18.     U.S.  Environmental Protection Agency.
       Design Manual.   Odor  and  Corrosion
       Control in Sanitary Sewerage Systems and
       Treatment  Plants.   EPA/625/1-85/018,
       October 1985.

19.     Water Environment Federation.  Existing
       Sewer   Evaluation  and   Rehabilitation.
       Manual of Practice No. FD6, 1994.

20.     Water Environment Federation. Operations
       and Maintenance ofWastewater Collection
       Systems. Manual of Practice No. 7, 1985.

21.     Water   Environment    Federation.
       Wastewater   Collection   Systems
       Management.  Manual of Practice No. 7,
       1992.
Eileen M. White
East Bay Municipal Utility District
P.O. Box 24055
Oakland, CA 94523

Richard R. Roll
City of Niagara Falls
Department ofWastewater Facilities
P.O. Box 69
Niagara Falls, NY 14302

Gary N. Oradat
City of Houston DPW & Engineering
Utility Maintenance Division
306 McGowen Street
Houston, TX 77006

David Jurgens
City of Fayetteville
113 West Mountain Street
Fayetteville, AR 72701

Bruno Conegliano
Water & Wastewater Utility
City of Austin, P.O. Box 1088
Austin, TX 78767

The  mention  of trade  names  or  commercial
products does not  constitute  endorsement  or
recommendations  for use by the United States
Environmental Protection Agency (EPA).
22.    Workman   G.   and  M.D.   Johnson.
      Automation Takes Lift Station  to  New
      Heights.  Operations Forum, Vol. 11, No.
      10, 14-16, October 1994.

ADDITIONAL INFORMATION

Luis Aguiar
Assistant-Director
Miami-Dade Water and Sewer Department
4200 Salzedo Street
Coral Gables, FL 33146
          For more information contact:

          Municipal Technology Branch
          U.S. EPA
          Mail Code 4204
          1200 Pennsylvania Avenue, NW
          Washington, D.C. 20460
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                                                         MUNICIPAL  TECHNOLOGY BRANCH

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