SECTION 317.3. Lift Stations

(a) Site selection. In the selection of a site for a lift station, consideration shall be given to accessibility and potential nuisance aspects. The station shall be protected from the 100-year flood and shall be accessible during a 25-year flood. All lift stations shall be intruder-resistant with a controlled access. Lift stations should be located as remotely as possible from populated areas.

(b) Design.

(1) Small lift stations. Lift stations designed for a discharge capacity of less than 100 gallons per minute will be reviewed on a case-by-case basis by the commission and shall be used only for institutional use or other locations where it is necessary to pump the sewage from a single building, school, or other measurable source establishment into the sanitary sewer lines. If the location of the discharge does not provide a positive head due to elevation, then a positive pressure control valve shall be provided. Ejectors may be used for this type of lift station. Whenever a lift station handles waste from two or more residential housing units, or from any public establishment, standby pumps shall be provided. In the case of ejectors or eductors, two air compressors shall be provided. Grinder pumps should be used for all small installations.

(2) Dry well sump pump. The following design considerations shall be addressed in providing dry well sump pumps.

(A) Two separate sump pumps should be provided for removal of leakage or water from the dry well floor.

(B) The discharge pipe level from the sump pumps shall be above the maximum liquid level of the wet well. A check valve should be installed on the discharge side of each sump pump.

(C) All floor and walkway surfaces shall have an adequate slope to a point of drainage with sufficient measures taken to maximize traction and safety.

(D) Motors to drive sump pumps shall be located above the height of the maximum liquid level in the wet well. As an alternate, sump pumps may be of the submersible type.

(3) Pump controls. All lift stations shall have automatically operated pump control mechanisms. Pump control mechanisms shall be located so that they will not be affected by flow currents in the wet well. Provisions shall be made to prevent grease and other floating materials and rags in the wet well from interfering with the operation of the controls. When a float tube is located in the dry well, its height shall be such as to prevent overflow of the sewage into the dry well. Pump control mechanisms which depend on a bubbler in the wet well shall be equipped with a backup air supply system. All connections to level controls in the wet well shall be accessible at all times. The circuit breakers, indicator lights, pump control switches, and other electrical equipment should be located on a control panel at least three feet above ground surface elevation. If controls are located in a dry well, the dry well shall be protected from flooding.

(4) Wet wells.

(A) Wet wells and dry wells, including their superstructure, shall be separated by at least a watertight and gastight wall with separate lockable entrances provided to each. Equipment requiring regular or routine inspection and maintenance shall not be located in the wet well, unless the maintenance can be accomplished without entering the wet well.

(B) Based on design flow, wet well capacity should provide a pump cycle time of not less than six minutes for those lift stations using submersible pumps and not less than 10 minutes for other nonsubmersible pump lift stations.

(C) All influent gravity lines into a wet well shall be located where the invert is above the "off" setting liquid level of the pumps, and preferably should be located above the lead pump "on" setting.

(5) Stairways. Stairways with non-slip steps shall be provided in all underground dry wells. Removable ladders may be provided in small stations where it is impractical to install stairways.

(6) Ventilation. Ventilation shall be provided for lift stations, including both wet and dry wells.

(A) Passive ventilation such as gooseneck type or turbine ventilators designed to prevent possible entry of insects or birds shall be provided in all wet wells if mechanical ventilation is not provided. All mechanical and electrical equipment in wet wells should be explosion-proof and spark-proof construction if mechanical ventilation is not provided.

(B) Mechanical ventilation shall be provided for all dry wells below the ground surface. The ventilation equipment shall have a minimum capacity of six air changes per hour under continuous operations. At least a capacity of 30 air changes per hour shall be required where the operation is intermittent. All intermittently operated venting equipment shall be interconnected with the stations lighting system.

(7) Wet well slopes. The bottom of wet wells shall have a minimum slope of 10% to the pump intakes and shall have a smooth finish. There shall be no projections in the wet well which will allow deposition of solids under ordinary operating conditions. Antivortex baffling should be considered for the pump suctions in all large sewage pumping stations (greater than five million gallons per day (mgd) firm pumping capacity).

(8) Hoisting equipment. Hoisting equipment or access by hoisting equipment for the removal of pumps, motors, valves, etc., shall be incorporated in the station design.

(9) Dry wells and valve vault drains. Drains from dry wells or valve vaults to the wet well shall be equipped with suitable devices to prevent entry of potentially hazardous gases.

(c) Pumps.

(1) General. All raw sewage pumps shall be of a non-clog design, capable of passing 2 1/2 inch diameter spheres, and shall have no less than three-inch diameter suction and discharge openings. Inspection and cleanout plates, located both on the suction and discharge sides of each pumping unit, are suggested for all nonsubmersible pumps so as to facilitate locating and removing blockage-causing materials. Where such openings are not provided on the pumps, a hand hole in the first fitting connected to the suction of each pump shall be provided. All pumps shall be securely supported so as to prevent movement during operation. For submersible pumps, rail-type pump support systems incorporating manufacturer-approved mechanisms designed to allow the operator to remove and replace any single pump without first entering or dewatering the wet well should be provided.

(2) Lift station pumping capacity. The firm pumping capacity of all lift stations shall be such that the expected peak flow can be pumped to its desired destination. Firm pumping capacity is defined as total station maximum pumping capacity with the largest pumping unit out of service.

(3) Variable capacity pumps. Lift stations or transfer pumping facilities at a wastewater treatment plant or those discharging directly to the treatment plant where the plant's permitted daily average flow is equal to or greater than 100,000 gallons per day shall be provided with three or more pumps or with duplex automatically controlled variable capacity pumps or other automatic flow control devices. The pumps or other devices shall be adjusted for actual flow conditions and controlled to operate so as to minimize surges in the treatment units. No single pumping unit shall have a capacity greater than the design peak flow of the wastewater treatment plant unless flow splitting/equalization is provided.

(4) Pump head calculations. The engineering design report accompanying the plans shall include system curves, pump curves, and head calculations. Calculations and pump curves at both minimum (all pumps off) and maximum (last normal operating pump on) static heads and for a C value of both 100 and 140 must be provided for each pump and for the combination of pumps (modified pump curves). Where a suction lift is required, the report shall include a calculation of the available net positive suction head (NPSH) and a comparison of that value to the required NPSH for the pump as furnished by the pump manufacturer.

(5) Self-priming pumps. Only self-priming pumps or pumps with acceptable priming systems, as demonstrated by a reliable record of satisfactory operation, shall be used where the suction head is negative. All self-priming pumps shall include a means for venting the air back to the wet well when the pump is priming.

(6) Pump positioning. All raw sewage pumps, other than submersible pumps without "suction" piping and self-priming units capable of satisfactory operation under any negative suction heads anticipated for the lift station under consideration, shall be positioned such that the pumps always experience, during their normal on-off cycling, a positive static suction head.

(7) Grinder pumps. See §317.2(d) of this title (relating to Sewage Collection System).

(d) Piping.

(1) Pump suctions. Each pump shall have a separate suction pipe. Cavitation may be avoided by using eccentric reducers in lieu of typical reducers in order to prevent air pockets from forming in the suction line.

(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.

Source Note: The provisions of this §317.3 adopted to be effective November 26, 2015, 40 TexReg 8341