Section NR 110.14 - Sewage lift stations design criteria(1) GENERAL. (a)Applicability. Lift stations may be approved when gravity sewers are not feasible or economical to transport the same design quantities of sewage.(b)Design report. A design report shall be submitted with plans and specifications for all new sewage lift stations as well as the major rehabilitation of existing lift stations. Major lift station rehabilitation may include, but is not limited to, replacing pumps with larger units or changing the type of lift stations. The design report shall comply with the facilities planning requirements of s. NR 110.11, and shall contain the detailed design calculations for the lift station design capacity.(2) DESIGN CONSIDERATIONS. (a)Location.1. Lift stations may be constructed in floodplains provided the floodproofing requirements of ss. NR 116.16 and are 116.17 met.2. Where practical, lift stations shall be located off the traffic way of streets and alleys.3. Lift stations shall be located with a minimum separation distance of 60 meters (200 feet) from community water system well, and a minimum separation distance of 30 meters (100 feet) from a private water well or any other well subject to ch. NR 812. A lesser separation distance from a community water system well may be approved if hydrogeologic information is provided to the department to indicate the lesser separation distance would provide adequate protection of a well from contamination. When a lift station is proposed within 60 meters (200 feet) of a community water system well, or 30 meters (100 feet) of private water wells or any other well subject to ch. NR 812, the location of the well shall be shown on the engineering plans. Gravity or pressure sewers connecting to lift stations shall be separated from water supply wells in accordance with s. NR 110.13(1) (d).(b)Design capacity.1. Pumping rates for lift stations integral to collection systems shall be determined in the same manner as the flows for the sewers contributory to the lift station and in accordance with the provisions of s. NR 110.11(1) (d).2. Pumping rates for lift stations which operate as part of sewage treatment facilities shall be determined in the same manner as the design flow for the treatment facility in accordance with s. NR 110.15(4) (c).3. Where possible, the pumping rate shall be designed to approximate the peak hour influent design flow rate to the lift station. For main lift stations or lift stations associated with treatment facilities, or in cases where large fluctuations of flow are known to occur, the use of variable speed pumps, or multiple constant speed pumps may be required by the department.(3) GENERAL DESIGN REQUIREMENTS. (a)Type. Sewage lift stations in general use fall into 7 types: wet well/dry well, submersible, suction lift, screw pump, pneumatic ejector, grinder pump and septic tank effluent pump.(b)Structural features.1. Dry wells, including their superstructure, shall be completely separated from wet wells. Common walls shall be gas tight.2. Provisions shall be made in all types of lift stations to facilitate removal of pumps, motors, and other mechanical and electrical equipment without entry into the wet well.3. Permanent ladders or steps may not be provided in the wet wells with the possible exception of built-in place lift stations, in which stairways in the wet wells may be approved if there are special maintenance needs or physical conditions that prevent the provision of necessary access by any other reasonable means. A safe means of access shall be provided to dry wells containing equipment requiring inspection or maintenance. If a dry well is over 6 meters (20 feet) deep, an offset shall be made in the entrance ladder with an intermediate landing at approximately mid-depth. Where an intermediate landing is used, the diameter of the landing area shall be at least 1.5 meters (5 feet), or an equivalent landing area shall be provided. Landings shall be provided with a suitable barrier to prevent an individual from falling past the intermediate landing to the lower level.4. A caution sign shall be installed at top of entrances to wet wells. The caution sign shall provide a warning of the potential for hazardous gases in a confined space and indicate that there shall be no entry without proper equipment and supervision.5. A sump pump shall be provided in a dry well to remove leakage or drainage. The sump pump discharge line shall be equipped with a check valve, and shall discharge above the maximum high water level of the wet well. A siphon break shall be provided when the sump pump discharge line enters at the high water level in the wet well. Pump seal water leakage shall be piped or channeled directly to the sump pit.6. All floors and walkways shall be sloped to a point of drainage.7. All wet wells shall be designed based on fill time and minimum pump cycle time. With any combination of influent flows and pumping rate, the minimum pump cycle time shall be greater than or equal to 5 minutes. The total fill time between pump on and off elevations in the wet well, at average design flow, may not exceed 30 minutes to prevent septicity.8. The wet well floor shall have a minimum slope of one to one to the hopper bottom. The horizontal area of the hopper bottom may not be greater than necessary for proper installation and function of suction pipe intake or pump inlet.9. There may not be a connection between any potable water system and sewage lift station which could potentially cause contamination of the potable water system.10. Exteriors of steel factory built lift stations shall be provided with cathodic protection against corrosion.11. Interior of steel wet wells shall be coated with a suitable water proof epoxy coating or water proof painting system or other appropriate methods to protect against corrosion.(c)Ventilation.1. All covered wet wells shall be vented to the atmosphere using an inverted "j" tube or other means. Adequate ventilation shall also be provided for all dry wells. Where the dry well is below the ground surface, permanent mechanical ventilation shall be provided.2. A permanent mechanical ventilation system shall be provided in wet wells and submersible lift stations where routine entrance is required to inspect or maintain equipment. In all other cases, portable mechanical ventilation equipment shall be available for wet wells as required for entry to a confined space.3. There shall be no interconnection between the wet well and dry well ventilation systems. Switches for operation of ventilation equipment shall be marked and conveniently located. All intermittently operated ventilating equipment shall be interconnected with the respective wet well or dry well lighting system. Consideration shall be given to automatic controls where intermittent operation is used. The manual lighting and ventilation switches shall override the automatic controls.4. The fan wheel for ventilating hazardous areas shall be fabricated from nonsparking material.5. Mechanical ventilation for wet wells shall provide at least 12 complete air changes per hour if ventilation is continuous and at least 30 complete air changes per hour if ventilation is intermittent. Air shall be forced into the wet well by mechanical means rather than exhausted from the wet well.6. Mechanical ventilation for dry wells shall provide at least 6 complete air changes per hour if ventilation is continuous and at least 30 complete air changes per hour if ventilation is intermittent. For conserving heat in large lift stations, the department may approve the following 2 exceptions: a. Intermittent ventilation with an initial ventilation rate of 30 complete air changes per hour for 10 minutes and automatic switch over to 6 complete air changes per hour.b. A continuous ventilation system at a rate of 6 complete air changes per hour when the dry well is occupied and at a rate of 2 complete air changes per hour when not occupied.(d)Auxiliary equipment. All of the following auxiliary equipment shall be installed in lift stations: 1. All dry wells shall be equipped with automatic heaters. The department may waive this requirement if it can be demonstrated that the heat output from the pump motors or controls is sufficient to keep equipment in the dry well from freezing.2. The installation of dehumidifiers shall be considered for all underground dry wells.3. Running time meters shall be installed for each pump in all lift stations. Where the department determines that flow measurement is necessary for the proper operation of the collection system or treatment system, suitable devices for measuring, totalizing, and recording flow shall be installed.(e)Electrical equipment. Electrical systems and components including motors, lights, cables, conduits, switchboxes, and control circuits, which will be located in wet wells, or in enclosed or partially enclosed spaces where hazardous concentrations of flammable gases or vapors may be present, shall comply with the NEC requirements for Class 1, Group D, Division 1 locations. In addition, equipment located in the wet well shall be suitable for use under corrosive conditions. Each flexible cable shall be provided with a watertight seal and separate strain relief. A fused disconnect switch or equivalent circuit breaker located above ground shall be provided for the main power feed for all lift stations. When the equipment is exposed to weather, it shall meet the requirements of weatherproof equipment.(f)Duplicate units. At least 2 pumps or pneumatic ejectors shall be provided in each lift station. Each pump or ejector shall be capable of pumping the design pumping rate as determined by sub. (2) (b). If 3 or more pumps are provided, they shall be designed to meet expected flow conditions and shall be capable of pumping the peak hour design pumping rate as determined by sub. (2) (b), with the largest unit out of service. Where the lift station will serve not more than 25 residential units, a single pump or ejector may be used, provided that the station is designed to permit the installation of a future duplicate pump or ejector with no structural changes.(g)Pumps. 1. All pumps, except grinder and effluent pumps, shall be capable of passing spheres of at least 7.6 centimeters (3 inches) in diameter, and pump suction and discharge piping shall be at least 10 centimeters (4 inches) in diameter. The department may allow the use of pumps with a lesser solids handling ability provided the pump is protected by a comminutor, a mechanically cleaned bar screen, or other suitable equipment.2. All pumps shall be nonclogging. Where a potential for clogging exists, protection in the form of manual bar screens, mechanically cleaned bar screens, comminutors or other suitable means shall be provided. Bar screens and comminutors shall be installed in accordance with s. NR 110.16.3. Each pump shall be located so that under normal operating conditions it will operate under a positive suction head. Self- priming or vacuum primed pumps with adequate suction lift capability are exempted from this requirement.(h)Piping.1. Each pump, except submersible, screw, grinder and effluent pumps, shall be equipped with individual suction piping. Suction piping shall be as straight as possible.2. When suction elbows are used, the bell shall be placed above the floor of the wet well at a distance which is not greater than 1/2 nor less than 1/3 the diameter of the bell.3. A suitable shutoff valve shall be placed on each discharge line, except for screw pumps. A shutoff valve shall be placed on each suction line of the dry well pump. A check valve shall be placed on each discharge line between the shutoff valve and the pump, except for screw pumps. Check valves shall be placed in horizontal sections of the discharge pipe, except for ball check valves which may be placed in the vertical run.4. Valves may not be located in wet wells.(i)Controls. 1. Control systems shall be of the air bubbler type, the encapsulated float or displacement type, the ultrasonic type, the pressure transducer type or capacitance probe type.2. The control system shall be located away from the turbulence of incoming flow and pump suction.3. Provisions shall be made to automatically alternate the pumps in use where multiple equivalent capacity pumps are installed.4. All lift stations shall be equipped with an alarm system. The alarm system shall include audible and visual signals. The alarm system shall be activated in cases of power failure, pump failure, and at a predesignated high water level. It is also recommended that alarm systems be activated in the event of unauthorized entry or other lift station malfunction. The department may require that alarm systems be telemetered to responsible authorities for large or main lift stations.(j)Force mains. 1. At the design pumping rate, a cleansing velocity of at least 61 centimeters per second (2 feet per second) shall be maintained.2. A combination automatic air relief and vacuum valve or an automatic or manual air relief valve shall be placed at each high point in the force main to prevent air locking.3. When a force main enters the gravity sewer manhole, it shall discharge at a point not more than 60 centimeters (2 feet) above the spring line of the receiving sewer.4. Friction losses through force mains shall be based on the Hazen and Williams formula or other acceptable method. The roughness coefficient "C" value used for design shall be noted on the design report. Note: When the Hazen and Williams formula is used, the department recommends a "C" value between 100 and 125 be used for all pipe except plastic pipe. A "C" value between 120 and 140 is recommended for plastic pipe. When initially installed, force mains may have a significantly higher "C" value. The lower "C" value (higher coefficient of friction) should be considered when calculating the head at design conditions. The higher "C" value should be considered when calculating the minimum head in the pump operating range power requirements.
(4) SUCTION LIFT PUMPS OR WET WELL MOUNTED LIFT STATIONS .(a)Priming. Suction lift pumps shall be of the self-priming or vacuum primed type and shall comply with applicable requirements of sub. (3), except as modified in this subsection.(b)Lift. The total dynamic suction lift may not exceed 6.0 meters (20 feet), unless the department approves pumps which exceed this specified limit based on certified pump performance curves and detailed calculations which justify the higher heads.(c)Compartment separation. The pump equipment compartment shall be above grade, partially recessed in the ground or offset and shall be isolated from the wet well in a manner which will prevent the humid and corrosive sewer atmosphere from entering the equipment compartment. Wet well access may not be through the equipment compartment and shall be at least 61 centimeters (24 inches) in diameter or equivalent area.(d)Electrical. Float type displacement switches and electronic transducers which are used in wet wells shall comply with the applicable requirements of sub. (5).(5) SUBMERSIBLE LIFT STATIONS. (a)Construction. Submersible pumps and motors shall be designed specifically for raw sewage use, and for total submergence during operation, and shall comply with the applicable requirements of sub. (3), except as modified in this subsection.(b)Pump removal. Submersible pumps shall be readily removable and replaceable without dewatering the wet well or disconnecting any piping in the wet well. Removal of one submersible pump from the lift station may not interrupt the operation of other pumps in the station.(c)Electrical equipment. 1. Electrical supply, control, and alarm circuits shall be designed to provide strain relief appurtenances. All junction boxes containing terminals and connectors shall be protected from corrosion by being located outside the wet well or through the use of a watertight seal. Junction boxes for motor power cable connections and for intrinsically safe control circuits shall meet the requirements of weatherproof equipment.2. The motor control center shall be located outside the wet well and be protected by conduit seals or other appropriate measures meeting the requirements of the NEC to prevent the atmosphere of the wet well from gaining access to the control center. The explosion proof seals shall be located so the pump motor and the level control float switches or transducers can be removed and electrically disconnected at the respective junction box without destroying the seal.3. Pump motor power cables shall be designed for flexibility and serviceability. Ground fault interruption protection shall be provided in accordance with the NEC requirements. Power cord terminal fittings shall be corrosion-resistant and constructed in a manner to prevent the entry of moisture into the cable, shall be provided with strain relief appurtenances, and shall be designed to facilitate field connecting.(d)Explosion prevention. In order to minimize the potential for ignition of explosive gases in submersible lift stations, one of the following requirements shall be met: 1. Low water level controls may be set such that the pump motor will remain totally submerged at all times. The lift station shall be equipped with a low water alarm in addition to meeting the requirements of sub. (3) (i) 4., and which is distinguishable from the high water alarm.2. The pump motor may be rated for compliance with the NEC explosion proof requirements of Class 1, Group D, Division 1 locations.(6) WET WELL AND DRY WELL LIFT STATIONS. (a)Construction. The wet well and dry well lift stations shall be designed specifically for raw sewage use and shall comply with applicable requirements of sub. (3), except as otherwise provided in this subsection.(b)Electrical. When float type displacement switches or electronic transducers are used to control the liquid level in the wet well, they shall comply with the applicable requirements of sub. (5).(7) SCREW PUMP STATIONS. (a)Applicability. Screw pumps may be approved by the department on a case-by-case basis upon submission of appropriate manufacturer's data and the detailed design calculations.(b)Construction. Screw pumps and motors shall be designed specifically for raw sewage use, and shall comply with applicable requirements of sub. (3).(8) PNEUMATIC EJECTOR LIFT STATIONS. (a)Applicability. Pneumatic ejectors may be approved by the department on a case-by-case basis upon submission of appropriate manufacturer's data and the detailed design calculations.(b)Construction. Pneumatic ejectors shall be designed specifically for raw sewage use, and shall comply with the applicable requirements of sub. (3).(c)Compressors. Multiple compressors shall be provided. The compressors shall be sized to handle the maximum hour design flow with the largest compressor out of service.(9) GRINDER PUMP LIFT STATIONS - DUPLEX. The department may approve duplex grinder pump lift stations. All duplex grinder pump lift stations shall be designed specifically for raw sewage use. Submersible duplex grinder pump lift stations shall meet the submersible pump requirements of sub. (5), and the non-submersible type duplex grinder pump lift stations shall comply with applicable requirements of sub. (6), except that each grinder pump shall have a minimum 11/4-inch pump opening and discharge piping. The total motor horsepower requirement for each pump shall be 5 horsepower or less.(10) GRINDER PUMP LIFT STATIONS - SIMPLEX.(a)Applicability. The department may approve simplex or individual grinder pump lift stations if no more than 3 residential units are ultimately served by 1 pump.(b)Construction. All simplex grinder pump lift stations shall be designed specifically for raw sewage use. The submersible grinder pump shall be designed for total submergence during operation. Both the submersible and the non-submersible type simplex grinder pump stations shall comply with all of the following requirements: 1. `Location.' The location of the grinder pump stations and pressure service laterals shall be shown on the plans.2. `Flood proofing.' Grinder pump stations located in the floodplain shall be flood proofed by constructing 2 feet above the 100 year flood elevation or by providing watertight covers.3. `Pump removal.' Grinder pumps shall be readily removable without entry into the wet well or dewatering the wet well.4. `Valving.' a. All valving shall be accessible without entry into the wet well or dewatering the wet well.b. If a grinder pump station discharges to a common pressurized sewer, a redundant check valve shall be provided. All valves including redundant check valves shall be installed at the grinder pump station. If a grinder pump station discharges to a gravity sewer, the redundant check valve is not required.5. `Ventilation.' All grinder pump stations shall be vented to the atmosphere either from the wet well or from the service lateral.6. `Accessibility.' No permanent ladders or steps shall be provided in the wet wells.7. `Pump size.' All grinder pumps shall have a minimum 11/4-inch pump inlet opening and discharge piping.8. `Velocity.' A minimum velocity of 61 centimeters (2 feet) per second shall be maintained in the discharge piping during pump operation.9. `Separation.' A minimum separation distance of 25 feet shall be maintained between the grinder pump lift station and a private well or any other well subject to ch. NR 812. A minimum separation of 200 feet shall be maintained between the grinder pump station and a community water system well in accordance with ch. NR 811.10. `Alarm.' Audible and visual high water alarm system shall be provided.11. `Electrical.' a. The motor control unit shall be located outside the wet well.b. All junction boxes shall be located outside the wet well, and shall meet the requirements of weather proof equipment. Electrical supply, control and alarm circuits shall be designed to allow disconnection at the junction box, without destroying the conduit-seal.c. Level controls using float type displacement switches shall be suspended in the wet well to facilitate maintenance.12. `Explosion prevention.' a. In order to reduce the potential for ignition of explosive gases in submersible grinder pump lift stations, one of the following conditions shall be met: the low water level alarm shall be set such that the pump motor will remain totally submerged at all times; the pump motor shall be rated explosion proof in accordance with NEC requirements of Class I, Group D, Division 1 locations; or the motor shall be listed as safe and appropriate for residential use by the Underwriters Laboratories, Inc.b. In order to reduce the potential for ignition of explosive gases in non-submersible grinder pump lift stations with non-explosion proof pump motors, the pump motor shall be completely isolated from the wet well atmosphere in a separate gas tight housing.(11) EFFLUENT PUMPS. The department may approve the duplex and simplex effluent pump lift stations for septic tank effluent in accordance with the applicable requirements of subs. (9) and (10), respectively.(12) EMERGENCY OPERATION. (a)General. Provisions for emergency operation of lift stations shall be provided to prevent the discharge of raw or partially treated sewage to a surface water or to a ground surface and to prevent sewage backups into basements.(b)Lift station requirements. One of the following provisions shall be made to insure continued operation of each lift station:1. An on-site generator, with automatic switching and starting equipment may be installed. The generator shall have sufficient capacity to meet the total electrical demands of the pumps, controls, and auxiliary equipment.2. An on-site gasoline or diesel engine driven pump, with automatic switching and starting equipment may be installed. The pump shall have a capacity equal to or greater than the lift station peak design pumping rate.3. A portable generator may be available for use at the lift station. The generator shall have sufficient capacity to meet the total electrical demands of the pumps, controls, and auxiliary equipment. Electrical connections shall be accessible without maintenance personnel having to enter the lift station.4. A portable pump with a pumping capacity equal to or greater than the lift station peak design pumping rate may be available for use at the lift station. Quick disconnect fittings shall be used to connect the portable pump to the suction and the discharge line, and shall be accessible without maintenance personnel having to enter the lift station.5. The lift station electrical system may be connected to 2 independent electrical transmission routes which receive power from the same electrical grid network which supplies power to the lift station service area.6. The lift station may be equipped with a holding facility which has a capacity to hold the average design flow for a minimum period of 24 hours.(c)Grinder pump and effluent pump lift stations.1. Emergency operation of duplex grinder pump and effluent pump lift stations which serve more than 3 residential units shall be provided by one of the methods described in par. (b).2. Emergency operation provisions for duplex grinder pump and effluent pump lift stations may be waived for those stations which serve homes with private water supply systems provided it is demonstrated to the department that the lift station wet well has the capacity to hold the residual water volume of the private water system.Wis. Admin. Code Department of Natural Resources NR 110.14
Cr. Register, November, 1974, No. 227, eff. 12-1-74; r. and recr. Register, February, 1983, No. 326, eff. 3-1-83; correction in (2) (a) 3. made under s. 13.93(2m) (b) 7, Stats., Register, September, 1995, No. 477; correction in (2) (a) 3. was made under s. 13.93(2m) (b) 7, Stats., Register, May, 2001, No. 545; CR 09-123: am. (1) (b) and (2) (b) 3., r. and recr. (2) (a) 3. and (3) to (5), renum. (6) and (7) to be (9) and (12) and am., cr. (6) to (8), (10) and (11) Register July 2010 No. 655, eff. 8-1-10.