United StatesEnvironmental ProtectionAgency

Office of WaterWashington, D.C.

EPA 832-F-00-073September 2000

Collection SystemsTechnology Fact SheetSewers, Lift Station

DESCRIPTION

Wastewater lift stations are facilities designed tomove wastewater from lower to higher elevationthrough pipes. Key elements of lift stations includea wastewater receiving well (wet-well), oftenequipped with a screen or grinding to removecoarse materials; pumps and piping with associatedvalves; motors; a power supply system; anequipment control and alarm system; and an odorcontrol system and ventilation system.

Lift station equipment and systems are ofteninstalled in an enclosed structure. They can beconstructed on-site (custom-designed) or pre-fabricated. Lift station capacities range from76 liters per minute (20 gallons per minute) to morethan 378,500 liters per minute (100,000 gallons perminute). Pre-fabricated lift stations generally havecapacities of up to 38,000 liters per minute (10,000gallons per minute). Centrifugal pumps arecommonly used in lift stations. A trapped aircolumn, or bubbler system, that senses pressure andlevel is commonly used for pump station control.Other control alternatives include electrodes placedat cut-off levels, floats, mechanical clutches, andfloating mercury switches. A more sophisticatedcontrol operation involves the use of variable speeddrives.

Lift stations are typically provided with equipmentfor easy pump removal. Floor access hatches oropenings above the pump room and an overheadmonorail beam, bridge crane, or portable hoist arecommonly used.

The two most common types of lift stations are thedry-pit or dry-well and submersible lift stations. In

dry-well lift stations, pumps and valves are housedin a pump room (dry pit or dry-well), that is easilyaccessible. The wet-well is a separate chamberattached or located adjacent to the dry-well (pumproom) structure. Figures 1 and 2 illustrate the twotypes of pumps.

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

Dry Wel l

Wet Wel l

Inlet

Hoist

Discharge

Source: Qasim, 1994.

FIGURE 1 DRY-WELL PUMP

large aboveground structures and tend to blend inwith their surrounding environment in residentialareas. They require less space and are easier andless expensive to construct for wastewater flowcapacities of 38,000 liters per minute (10,000gallons per minute) or less.

APPLICABILITY

Lift stations are used to move wastewater fromlower to higher elevation, particularly where theelevation of the source is not sufficient for gravityflow and/or when the use of gravity conveyancewill result in excessive excavation depths and highsewer construction costs.

Current Status

Lift stations are widely used in wastewaterconveyance systems. Dry-well lift stations havebeen 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 6,350gallons per minute) with submersible lift stationsmainly because of lower costs, a smaller footprint,and simplified operation and maintenance.

Variable speed pumping is often used to optimizepump performance and minimize power use.Several types of variable-speed pumping equipment

are available, including variable voltage andfrequency drives, eddy current couplings, andmechanical variable-speed drives. Variable-speedpumping can reduce the size and cost of the wet-well and allows the pumps to operate at maximumefficiency under a variety of flow conditions.Because variable-speed pumping allows lift stationdischarge to match inflow, only nominal wet-wellstorage volume is required and the well water levelis maintained at a near constant elevation.Variable-speed pumping may allow a given flowrange to be achieved with fewer pumps than aconstant-speed alternative. Variable-speed stationsalso minimize the number of pump starts and stops,reducing mechanical wear. Although there issignificant energy saving potential for stations withlarge friction losses, it may not justify the additionalcapital costs unless the cost of power is relativelyhigh. Variable speed equipment also requires moreroom within the lift station and may produce morenoise and heat than constant speed pumps.

Lift stations are complex facilities with manyauxiliary systems. Therefore, they are less reliablethan gravity wastewater conveyance. However, liftstation reliability can be significantly improved byproviding stand-by equipment (pumps and controls)and emergency power supply systems. In addition,lift station reliability is improved by using non-clogpumps suitable for the particular wastewater qualityand by applying emergency alarm and automaticcontrol systems.

ADVANTAGES AND DISADVANTAGES

Advantages

Lift stations are used to reduce the capital cost ofsewer system construction. When gravity sewersare installed in trenches deeper than three meters(10 feet), the cost of sewer line installationincreases significantly because of the more complexand costly excavation equipment and trench shoringtechniques required. The size of the gravity sewerlines is dependent on the minimum pipe slope andflow. Pumping wastewater can convey the sameflow using smaller pipeline size at shallower depth,and thereby, reducing pipeline costs.

Hoist

Discharge

Source: Qasim, 1994.

FIGURE 2 WET-WELL SUBMERSIBLE

Disadvantages

Compared to sewer lines where gravity driveswastewater flow, lift stations require a source ofelectric power. If the power supply is interrupted,flow conveyance is discontinued and can result inflooding upstream of the lift station, It can alsointerrupt the normal operation of the downstreamwastewater conveyance and treatment facilities.This limitation is typically addressed by providingan emergency power supply.

Key disadvantages of lift stations include the highcost to construct and maintain and the potential forodors and noise. Lift stations also require asignificant amount of power, are sometimesexpensive to upgrade, and may create publicconcerns and negative public reaction.

The low cost of gravity wastewater conveyance andthe higher costs of building, operating, andmaintaining lift stations means that wastewaterpumping should be avoided, if possible andtechnically feasible. Wastewater pumping can beeliminated or reduced by selecting alternative sewerroutes or extending a gravity sewer using directiondrilling or other state-of-the-art deep excavationmethods. If such alternatives are viable, a cost-benefit analysis can determine if a lift station is themost viable choice.

DESIGN CRITERIA

Cost effective lift stations are designed to: (1)match pump capacity, type, and configuration withwastewater quantity and quality; (2) providereliable and uninterruptible operation; (3) allow foreasy operation and maintenance of the installedequipment; (4) accommodate future capacityexpansion; (5) avoid septic conditions andexcessive release of odors in the collection systemand at the lift station; (6) minimize environmentaland landscape impacts on the surroundingresidential and commercial developments; and (7)avoid flooding of the lift station and thesurrounding areas.

Wet-well

Wet-well design depends on the type of lift stationconfiguration (submersible or dry-well) and thetype of pump controls (constant or variable speed).Wet-wells are typically designed large enough toprevent rapid pump cycling but small enough toprevent a long detention time and associated odorrelease.

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

Wastewater Pumps

The number of wastewater pumps and associatedcapacity should be selected to provide head-capacity characteristics that correspond as nearly aspossible to wastewater quantity fluctuations. Thiscan be accomplished by preparing pump/pipelinesystem head-capacity curves showing all conditionsof head (elevation of a free surface of water) andcapacity under which the pumps will be required tooperate.

The number of pumps to be installed in a lift stationdepends on the station capacity, the range of flowand the regulations. In small stations, withmaximum inflows of less than 2,640 liters perminute (700 gallons per minute), two pumps arecustomarily installed, with each unit able to meetthe maximum influent rate. For larger lift stations,the size and number of pumps should be selected sothat the range of influent flow rates can be metwithout starting and stopping pumps too frequentlyand without excessive wet-well storage.

Depending on the system, the pumps are designedto run at a reduced rate. The pumps may alsoalternate to equalize wear and tear. Additionalpumps may provide intermediate capacities bettermatched to typical daily flows. An alternativeoption 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 suchstations because two pumps operating together yieldonly slightly higher flows than one pump. If thepeak flow is to be achieved with multiple pumps inparallel, the lift station must be equipped with atleast three pumps: two duty pumps that togetherprovide peak flow and one standby pump foremergency backup. Parallel peak pumping istypically used in large lift stations with relativelyflat system head curves. Such curves allowmultiple pumps to deliver substantially more flowthan a single pump. The use of multiple pumps inparallel provides more flexibility.

Several types of centrifugal pumps are used inwastewater lift stations. In the straight-flowcentrifugal pumps, wastewater does not changedirection as it passes through the pumps and intothe discharge pipe. These pumps are well suited forlow-flow/high head conditions. In angle-flowpumps, wastewater enters the impeller axially andpasses through the volute casing at 90 degrees to itsoriginal direction (Figure 3). This type of pump isappropriate for pumping against low or moderateheads. Mixed flow pumps are most viable forpumping large quantities of wastewater at low head.In these pumps, the outside diameter of the impelleris less than an ordinary centrifugal pump, increasingflow volume.

Ventilation

Ventilation and heating are required if the liftstation includes an area routinely entered bypersonnel. Ventilation is particularly important toprevent the collection of toxic and/or explosivegases. According to the Nation Fire ProtectionAssociation (NFPA) Section 820, all continuousventilation systems should be fitted with flowdetection devices connected to alarm systems to

indicate ventilation system failure. Dry-wellventilation codes typically require six continuousair changes per hour or 30 intermittent air changesper hour. Wet-wells typically require 12 continuousair changes per hour or 60 intermittent air changesper hour. Motor control center (MCC) roomsshould have a ventilation system adequate toprovide six air changes per hour and should be airconditioned to between 13 and 32 degrees Celsius(55 to 90 degrees F). If the control room iscombined with an MCC room, the temperatureshould not exceed 30 degrees C or 85 degrees F.All other spaces should be designed for 12 airchanges per hour. The minimum temperatureshould be 13 degrees C (55 degrees F) wheneverchemicals are stored or used.

Odor Control

Odor control is frequently required for lift stations.A relatively simple and widely used odor controlalternative is minimizing wet-well turbulence. Moreeffective options include collection of odorsgenerated at the lift station and treating them inscrubbers or biofilters or the addition of odorcontrol chemicals to the sewer upstream of the liftstation. Chemicals typically used for odor controlinclude chlorine, hydrogen peroxide, metal salts(ferric chloride and ferrous sulfate) oxygen, air, andpotassium permanganate. Chemicals should be

Source: Lindeburg, revised edition 1995.

FIGURE 3 CENTRIFUGAL ANGLE-FLOWPUMP

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

Power Supply

The reliability of power for the pump motor drivesis a basic design consideration. Commonly usedmethods of emergency power supply includeelectric power feed from two independent powerdistribution lines; an on-site standby generator; anadequate portable generator with quick connection;a stand-by engine driven pump; ready access to asuitable portable pumping unit and appropriateconnections; and availability of an adequate holdingfacility for wastewater storage upstream of the liftstation.

PERFORMANCE

The overall performance of a lift station depends onthe performance of the pumps. All pumps havefour common performance characteristics: capacity,head, power, and overall efficiency. Capacity (flowrate) is the quantity of liquid pumped per unit oftime, typically measured as gallons per minute(gpm) or million gallons per day (mgd). Head isthe energy supplied to the wastewater per unitweight, typically expressed as feet of water. Poweris the energy consumed by a pump per unit time,typically measured as kilowatt-hours. Overallefficiency is the ratio of useful hydraulic workperformed to actual work input. Efficiency reflectsthe pump relative power losses and is usuallymeasured as a percentage of applied power.

Pump performance curves (Figure 4) are used todefine and compare the operating characteristics ofa pump and to identify the best combination ofperformance characteristics under which a liftstation pumping system will operate under typicalconditions (flows and heads). Pump systemsoperate at 75 to 85 percent efficiency most of thetime, while overall pump efficiency depends on thetype of installed pumps, their control system, andthe fluctuation of influent wastewater flow.

Performance optimization strategies focus ondifferent ways to match pump operationalcharacteristics with system flow and headrequirements. They may include the following

options: adjusting system flow paths installingvariable speed drives; using parallel pumpsinstalling pumps of different sizes trimming a pumpimpeller; or putting a two-speed motor on one ormore pumps in a lift station. Optimizing systemperformance may yield significant electrical energysavings.

OPERATION AND MAINTENANCE

Lift station operation is usually automated and doesnot require continuous on-site operator presence.However, frequent inspections are recommended toensure normal functioning and to identify potentialproblems. Lift station inspection typically includesobservation of pumps, motors and drives forunusual noise, vibration, heating and leakage, checkof pump suction and discharge lines for valvingarrangement and leakage, check of control panelswitches for proper position, monitoring ofdischarge pump rates and pump speed, andmonitoring of the pump suction and dischargepressure. Weekly inspections are typicallyconducted, although the frequency really dependson the size of the lift station.

If a lift station is equipped with grinder bar screensto remove coarse materials from the wastewater,these materials are collected in containers anddisposed of to a sanitary landfill site as needed. Ifthe lift station has a scrubber system for odorcontrol, chemicals are supplied and replenishedtypically every three months. If chemicals areadded for odor control ahead of the lift station, the

0

10

20

30

40

50

60

70

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4

Discharge (m3/s)

Hea

d (

m)

System Curve

Pump Curve

Source: Adapted from Roberson and Crowe, 1993.

FIGURE 4 PUMP PERFORMANCE CURVE

chemical feed stations should be inspected weeklyand chemicals replenished as needed.

The most labor-intensive task for lift stations isroutine preventive maintenance. A well-plannedmaintenance program for lift station pumpsprevents unnecessary equipment wear anddowntime. Lift station operators must maintain aninventory of critical spare parts. The number ofspare parts in the inventory depends on the criticalneeds of the unit, the rate at which the part normallyfails, and the availability of the part. The operatorshould tabulate each pumping element in the systemand its recommended spare parts. This informationis typically available from the operation andmaintenance 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 wherethe lift station will be located; (3) alternatives forstandby power sources; (4) operation andmaintenance needs and support; (5) soil propertiesand underground conditions; (6) required lift to thereceiving (discharge) sewer line; (7) the severity ofimpact of accidental sewage spill upon the localarea; and (8) the need for an odor control system.These site and system specific factors must beexamined and incorporated in preparing a liftstation cost estimate.

Construction Costs

The most important factors influencing cost are thedesign lift station capacity and the installed pumppower. Another cost factor is the lift stationcomplexity. Factors which classify a lift station ascomplex include two or more of the following: (1)extent of excavation; (2) congested site and/orrestricted access; (3) rock excavation; (4) extensivedewatering requirements, such as cofferdams; (5)site conflicts, including modification or removal ofexisting facilities; (6) special foundations, includingpiling; (7) dual power supply and on-site switchstations and emergency power generator; and (8)high pumping heads (design heads in excess of200 ft).

Mechanical, electrical, and control equipmentdelivered to a pumping station construction sitetypically account for 15 to 30 percent of totalconstruction costs. Lift station construction has asignificant economy-of-scale. Typically, if thecapacity of a lift station is increased 100 percent,the construction cost would increase only 50 to 55percent. An important consideration is that twoidentical lift stations will cost 25 to 30 percent morethan a single station of the same combined capacity.Usually, complex lift stations cost two to threetimes more than more simple lift stations with noconstruction complications.

Table 1 provides examples of complex lift stationsand associated construction costs in 1999 dollars.

TABLE 1 LIFT STATION CONSTRUCTION COSTS

Lift StationDesign Flowrate

(MGD)Construction Costs

(1999 $US)

Cost curve data1 0.5 $134,467

Cost curve data1 1 $246,524

Cost curve data1 3 $392,197

Valencia, California2 6 $1,390,000

Sunneymead, California2 12 $3,320,000

Sunset/Heahfield, California2 14 $2,600,000

Springfield, Oregon Terry StreetPumping Station2

20 $5,470,000

Detroit, Michigan2 750 $128,800,000

Source: 1Qasim, 1994 and 2 James M. Montgomery Consulting Engineers, 1998.

Operation and Maintenance Costs

Lift station operation and maintenance costs includepower, labor, maintenance, and chemicals (if usedfor odor control). Usually, the costs for solidsdisposal are minimal, but are included if the liftstation is equipped with bar screens to removecoarse materials from the wastewater. Typically,power costs account for 85 to 95 percent of the totaloperation and maintenance costs and are directlyproportional to the unit cost of power and the actualpower used by the lift station pumps. Labor costsaverage 1 to 2 percent of total costs. Annualmaintenance costs vary, depending on thecomplexity of the equipment and instrumentation.

REFERENCES

Other Related Fact Sheets

Small Diameter Gravity SewerEPA 832-F-00-038September 2000

In-Plant Pump StationsEPA 832-F-00-069September 2000

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

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

2. Cavalieri R.R. and G. L. Devin. Pitfalls inWet Weather Pumped Facilities Design. InProceedings of the Water EnvironmentFederation, 71st Annual Conference,Orlando, Florida, Vol. 2, 719-729, October1998.

3. Gravette B. R. Benefits of Dry-pitSubmersible Pump Stations. In Proceedingsof the Water Environment Federation, 68th

Annual Conference, Miami Beach, Florida,Vol. 3, 187-196, October 1995.

4. Graham B, J., Pinto T.G., and T. Southard.Backyard Pumping Stations The Low-pressure Grinder Systems That Call OldSeptic Tanks Home. Operations Forum,Vol.10, No. 5, 25-29, May 1993.

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

6. James M. Montgomery ConsultingEngineers, 1988. Sewerage SystemPreliminary Cost Estimating Curves.

7. Lindeburg, Michael R. Civil EngineeringReference Manual, 6th ed., ProfessionalPublications, Inc., revised edition 1995.

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

9. Metcalf & Eddy Inc., WastewaterEngineering: Collection and Pumping ofWastewater, McGraw Hill Book Company,1981.

10. National Fire Protection Association.National Fire Codes. Volume 7, Section820. Quincy, Massachusetts, 1995.

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

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

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

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

For more information contact:

Municipal Technology BranchU.S. EPAMail Code 42041200 Pennsylvania Avenue, NWWashington, D.C. 20460

15. Sanks R. L., Tchobanoglous G., Newton D.,Bosserman, B.E., and Jones, G. M. PumpStation Design, Butterworths, Boston, 1998.

16. Schneller T. M. Pumping it Up? PracticalMeans For Evaluating Lift Station Fitness.In Proceedings of the Water EnvironmentFederation, 68th Annual Conference, MiamiBeach, Florida, Vol. 3, 155-166 October1995.

17. Smith E. C. Dont Lose the PumpEfficiency Game. Operations Forum, Vol.11, No. 7, 18-21, July 1994.

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

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

20. Water Environment Federation. Operationsand Maintenance of Wastewater CollectionSystems. Manual of Practice No. 7, 1985.

21. Water Environment Federation.Wastewater Col lec t ion Sys temsManagement. Manual of Practice No. 7,1992.

22. Workman G. and M.D. Johnson.Automation Takes Lift Station to NewHeights. Operations Forum, Vol. 11, No.10, 14-16, October 1994.

ADDITIONAL INFORMATION

Luis AguiarAssistant-DirectorMiami-Dade Water and Sewer Department4200 Salzedo StreetCoral Gables, FL 33146

Eileen M. WhiteEast Bay Municipal Utility DistrictP.O. Box 24055Oakland, CA 94523

Richard R. RollCity of Niagara FallsDepartment of Wastewater FacilitiesP.O. Box 69Niagara Falls, NY 14302

Gary N. OradatCity of Houston DPW & EngineeringUtility Maintenance Division306 McGowen StreetHouston, TX 77006

David JurgensCity of Fayetteville113 West Mountain StreetFayetteville, AR 72701

Bruno ConeglianoWater & Wastewater UtilityCity of Austin, P.O. Box 1088Austin, TX 78767

The mention of trade names or commercialproducts does not constitute endorsement orrecommendations for use by the United StatesEnvironmental Protection Agency (EPA).