Administrative Code

Virginia Administrative Code

Article 2. Sewage Pump Stations

9VAC25-790-380. Sewage pumping.

Article 2
Sewage Pump Stations

A. Features. Sewage pump stations should be located as far as practicable from present or proposed built-up residential areas, and an all-weather road shall be provided. Stations should have a proper zone of controlled or limited use surrounding them. Within such zones, residential uses or high density human activities or activities involving food preparation should be prevented. Provisions for noise control and odor control, and station architectural design should conform to site requirements. Sites for stations shall be of sufficient size for future expansion or addition, if applicable. All mechanical and electrical equipment which could be damaged or inactivated by contact with or submergence in water (motors, control equipment, blowers, switch gear, bearings, etc.) shall be physically located above the 100-year flood/wave action or otherwise protected against the 100-year flood/wave action damage. All stations shall be designed to remain fully operational during the 25-year flood/wave action.

1. Where it may be necessary to pump raw (untreated) or unsettled sewage prior to grit removal, the design of the wet well shall receive special attention. The discharge piping shall be designed to prevent grit settling in the discharge lines when pumps are not operating.

2. At least two pumping units shall be provided. Where two units are provided, each shall be capable of handling flows in excess of the expected maximum flow or a minimum of 2-1/2 times the average design flow, whichever is greater. Where three or more units are provided, they shall be designed to fit actual flow conditions and must be of such capacity that, with any one unit out of service, the remaining units will have capacity to handle the maximum sewage flow or a minimum of 2-1/2 times the average design flow, whichever is greater. When the station is expected to operate at a flow rate less than one-half times the average design flow for an extended period of time, the design shall address measures taken to prevent septicity due to long holding times of untreated sewage in the wet well.

3. Treatment works pump stations should be designed so that sewage will be delivered to the treatment works at approximately the same rate it is received at the pump station. At least two pumping units shall be provided. Treatment works pump stations are those stations which discharge to sewage treatment works without dissipation of flow through a gravity collection system. Where only two pumping units are to be utilized, they shall be variable speeded and sized so that the pumps deliver from 1/2 to 2-1/2 times the average design flow or the maximum flow, whichever is greater, except where flow equalization is utilized in accordance with this chapter. Where constant speed pumps are to be utilized without equalization, either (i) at least three pumps, each having a capacity of approximately 1-1/4 times the average design flow, or (ii) two pumps, each having a capacity of approximately 1-1/4 times the average design flow, with the third pump having a capacity of 2-1/2 times the average design flow, shall be provided as needed to transfer the maximum flow. Multiple-speed pumps in lieu of variable speed pumps may be considered for specific applications. These criteria for influent flows will not apply to such treatment works where several days' holding capacity is provided, such as in stabilization ponds or in aerated lagoons.

4. Pumps handling raw sewage should be preceded by readily accessible bar racks with clear openings not exceeding 2-1/2 inches, unless pneumatic ejectors are used or special devices are installed to protect the pumps from clogging or damage. Where the size of the installation warrants, a mechanically cleaned bar screen with either a grinder or comminution device is recommended. Where screens are located below ground, convenient facilities must be provided for handling screenings. For the larger or deeper stations, duplicate protection units of proper capacity are preferred. Interceptor or separation basins may be necessary prior to pumps handling raw sewage.

5. Pumps in which the solids pass through the impeller(s) shall be capable of passing spheres of at least three inches in diameter. Pumping equipment having integral screens for preventing solids from passing through the impeller shall be capable of passing spheres of at least two inches in diameter. Pumping equipment preceded by grinding equipment shall be capable of passing the solids discharged from the grinding mechanism.

6. Pumps shall be so placed that under normal start conditions they will start with a positive suction head, except as specified for suction lift pumps. Each pump shall have an individual intake and suction line. Wet well design should be such as to avoid turbulence near the intake. Pump suction and discharge piping shall not be less than four inches in diameter except where design of special equipment allows. The design velocity in pump piping should not exceed (i) six feet per second in the suction piping, and (ii) in the discharge piping, eight feet per second. All pumps should be provided with an air relief line on the pump discharge piping.

7. Control float cages shall be so located as not to be affected by the flows entering the wet well or by the suction of the pumps. Float tubes will not be permitted in either the wet or dry well. Air-operated pneumatic controls are preferred for all sewage pump stations. Provisions shall be made to automatically alternate the pumps in use (which is referred to as lead-lag operation) unless adequate operation and maintenance is to be provided to protect against pump failure.

8. For the purpose of designating liquid levels for alarm requirements, high liquid level in the wet well is defined as a level of sewage in the wet well above normal operating levels such that either: (i) a backup of sewage in the incoming sewer may occur, or (ii) an overflow may occur, or (iii) standby pump(s) may be required to be activated. In the case of a duplex pump station with limited wet well volume, the alarm design should include activation at the time of simultaneous operation of both pumps, initiating when the second alternating pump starts (referred to as the lag pump).

9. Suitable shut-off valves shall be placed on each suction and each discharge line of each pump for normal pump isolation. A check valve is to be placed on each discharge line, between the shut-off valve and the pump. No shut-off valve need be placed on the suction side of suction lift or submersible pumps. Periodic exercising of valves should be specified within the routine maintenance programs.

10. System pump stations should have the provision for installing flow measuring devices when necessary. Consideration should be given to installation of such devices in system pump stations whose flow rate can affect the proper operation of the treatment works.

11. Adequate lighting for the entire pump station shall be provided in accordance with VOSH and other applicable codes and standards.

12. Pump stations shall be designed in accordance with the statewide building code and so as to minimize the adverse effects of vandalism. Pump stations shall be equipped with a secure external disconnect switch located above grade where possible.

B. Ventilation shall be provided in accordance with VOSH requirements and shall comply with this chapter for enclosed spaces within pump stations during all periods when the station is manned. Where the pump is permanently mounted below the ground, mechanical ventilation is required and shall be arranged so as to independently ventilate the dry well.

1. As a minimum, ventilation of the wet well shall be accomplished by the provision of a properly screened vent, with the end either turned downward or provided with a "mushroom" cap. The vent shall be at least four inches in diameter. If screens or mechanical equipment, which might require periodic maintenance and inspection, are located in the wet well, then it shall be mechanically ventilated at the time of access by maintenance personnel.

2. There shall be no interconnection between the wet well exhaust flow and the dry well ventilation systems. In pits over 15 feet deep, multiple inlets and outlets are desirable. Dampers shall not be used on exhaust or fresh air ducts, and fine screens or other obstructions in air ducts shall be avoided to prevent clogging. In climates where excessive moisture or low temperature are problems, consideration should be given to installation of automatic heating and dehumidification equipment.

3. Switches for operation of ventilation equipment shall be marked and conveniently located above grade and near the pump station entrance. Consideration should be given also to automatic controls where intermittent operation is used. The fan drive shall be fabricated from nonsparking material in accordance with applicable codes and standards.

4. Where heat buildup from pump motors may be a problem, consideration should be given to automatic cooling and ventilation to dissipate motor heat.

5. Ventilation of wet wells in accordance with VOSH requirements may be either continuous or intermittent. Ventilation, if continuous, shall provide at least 12 complete air changes per hour; if intermittent, at least 30 complete air changes per hour. Such ventilation shall be accomplished by mechanical means.

C. Water supply. There shall be no cross connection between any potable water supply and a sewage pump station which under any conditions might cause contamination of the potable water supply. Any potable water supply brought to the station shall comply with conditions stipulated in the Virginia Waterworks Regulations (12VAC5-590). Where conditions do not warrant the installation of an approved reduced pressure zone backflow prevention device on the water supply line to the pump stations, other approved devices may be considered on a case-by-case basis.

D. Service. Provisions shall be made to facilitate removing pumps, motors, and other equipment without interruption of system service while providing all necessary worker safety features.

1. In accordance with VOSH requirements, suitable and safe means of access shall be provided to dry wells and wet wells containing equipment requiring inspection or maintenance. Compliance with all applicable VOSH and Uniform Statewide Building Code requirements is recommended. All ladders shall have slip-resistant rungs.

2. If the dry well or wet well floor is more than 10 feet below the entrance, special consideration shall be given to safety features such as harness lifts, ladder cages, spiral stairways, or intermediate landings. Intermediate landings should not exceed 10 foot vertical intervals.

E. Wet wells. Proper design of wet wells is essential to effective pump station operation.

1. The wet wells at major pumping stations and in those located in critical areas should be divided into two sections properly interconnected to facilitate repairs and cleaning.

2. The wet well size and control settings shall be designed and operated so as to avoid heat buildup in the pump motor due to frequent starting and to avoid septic conditions due to excessive detention time.

3. Provisions shall be made to prevent solids deposition. Where used, wet well fillets shall have a minimum slope of one-to-one to the hopper bottom. The horizontal area of the hopper bottom shall be no greater than necessary for proper installation and function of the inlet.

Statutory Authority

§ 62.1-44.19 of the Code of Virginia.

Historical Notes

Former 12VAC5-581-440 derived from Virginia Register Volume 18, Issue 10, eff. February 27, 2002; amended and adopted as 9VAC25-790-380, Virginia Register Volume 20, Issue 9, eff. February 12, 2004.

9VAC25-790-390. Reliability.

A. Purpose. Reliability provisions are based on a measurement of the ability of a component or system to perform its designated function without failure or interruption of service. Overflow criteria, such as a period of discharge, are utilized solely for the establishment of reliability classification for design purposes and are not to be construed as authorization for, or defense of, an unpermitted discharge to state waters.

1. The objective of achieving reliability protection is to prevent the discharge of raw or partially treated sewage to any waters and to protect public health and welfare by preventing backup of sewage and subsequent discharge to basements, streets and other public and private property. Provisions for continuous operability of pumping stations shall be evaluated in accordance with the appropriate reliability classification.

2. For Class I Reliability, alternate motive force sufficient to operate the station at peak flow rates being received shall be operating the station prior to the expiration of an allowable time period. The maximum allowable period will be the time transpiring between the high liquid level alarm and the occurrence of an overflow, or backup and subsequent discharge, at flow rates being received (except when an emergency holding basin is provided to satisfy the requirement for continuous operability). The transpired time to be considered allowable may be the critical (shortest) transpired time (peak flow rates) or a spectrum of transpired times keyed to the 24 individual hours of the day. Certain Reliability Class I pump stations, for which it is feasible to shut down or discontinue operation during periods of power failure without bypassing or overflowing, may be exempted from the continuous operability requirement. Pump stations which may qualify for the exemption can be broadly categorized as those which serve facilities or institutions which would be closed during periods of power failure, such as certain industrial plants, schools and recreational and park areas.

3. For Class II Reliability, alternate motive force sufficient to operate the station at peak flow rates being received shall be operating the station prior to the expiration of a 24-hour period commencing at the time an overflow or discharge subsequent to a backup begins.

4. Reliability Class III pump stations are not limited to a specific period of overflow or discharge, and will be considered on a case-by-case basis.

B. Continuous operability. The owner shall demonstrate, to the satisfaction of the department, that the time allowances for continuous operability will be met on a 24-hour basis. This information shall accompany the plans and specifications when submitted and shall be subsequently modified and resubmitted at any time in the future that the actual allowable time (transpiring between the high liquid level alarm and the time that an overflow or backup and subsequent discharge will occur at flow rates being received) becomes less than the allowable time claimed in the original submission. The demonstration shall include provision of instructions indicating the essentiality of routinely maintaining, and regularly starting and running, auxiliary and reserve units under field conditions. The following means for provision of continuous operability shall be acceptable:

1. Alternate power sources or auxiliary stand-by generator that can operate sufficient pumps to deliver the design peak flow.

2. Alternate drive arrangements whereby all pumps are backed by internal combustion motors with "Y" mechanical couplings to the pump drive shafts or to permanently mounted reserve pumps capable of delivering total peak flows.

3. Portable pump resources in accordance with this chapter.

4. An emergency overflow holding basin with capacity to retain a minimum of one day of station design flow and having provisions for recycling flow to the pump station.

C. Electrical power. The sources of electrical power required to operate pump stations shall be evaluated in accordance with the reliability classification of the pump station.

1. For Class I Reliability, electric power shall be provided by alternate feed from distribution lines which are serviced by alternate feed from transmission lines (e.g., 115 KV) where possible. The transmission lines shall have alternate feed from the generating source or sources. The capacity of each power source shall be sufficient to operate the pumps during peak wastewater flow conditions, together with critical lighting and ventilation. The requirement for alternate feed can be satisfied by either a loop circuit, a "tie" circuit, or two radial lines. Where alternate feed lines terminate in the same substation, the circuit feeding the pumping station shall be equipped with two or more in-place transformers. Where alternate feed is not possible, provision of auxiliary power sources will be considered.

2. External alternate distribution lines shall be completely independent. The two sets of alternate feed distribution lines should not be supported from the same utility pole and, if used, should neither cross over, nor be located in an area where a single plausible occurrence (e.g., fallen tree) could disrupt both lines. A minimum separation of 25 feet for underground routes shall be maintained unless a properly designed and protected conduit bank is utilized. This shall apply to service connections into the pump station. Devices should be used to protect the system from lightning.

3. For Class II Reliability, a single source feed is acceptable. If alternate power sources are provided for a Class II or III station, one in-place transformer and capability for connection of a mobile transformer may be provided where the alternate feed lines terminate in the same substation.

D. Power distribution. The design of power distribution circuitry and equipment provided within pump stations shall be in accordance with the reliability classification of the pump station.

1. Reliability Class I pump stations shall have the following features:

a. Final stepdown transformer on each electric feed line with adequate physical separation to prevent a common mode failure.

b. In addition, Reliability Class I pump stations shall be provided with separate buses for each power source.

c. Each power source shall remain separate and from separate distribution substations up to the transfer switch to preclude a common mode failure of both sources.

2. Reliability Class II and Class III pump stations may be equipped with a single final stepdown transformer, a single bus, a single motor control center, and a single power distribution system.

3. Breaker settings or fuse ratings shall be coordinated to effect sequential tripping such that the breaker or fuse nearest the fault will clear the fault prior to activation of other breakers or fuses, to the degree practicable.

Statutory Authority

§ 62.1-44.19 of the Code of Virginia.

Historical Notes

Former 12VAC5-581-450 derived from Virginia Register Volume 18, Issue 10, eff. February 27, 2002; amended and adopted as 9VAC25-790-390, Virginia Register Volume 20, Issue 9, eff. February 12, 2004.

9VAC25-790-400. Pumping equipment.

A. Proper location. Where practicable, the electric switchgear and motor control centers should be housed above grade and in a separate area from the dry well. All motors and control enclosures shall be adequately protected from moisture from the weather and water under pressure. In cases where equipment may be damaged by flooding from natural events, in such a manner as to cause excessive delays in restoring the pump station to design operating levels, the means of protecting or removing such equipment prior to flooding should be described in the Operation and Maintenance Manual. Motors located indoors and near liquid handling piping or equipment shall be, at least, of-splash-resistant design. Means for heating motors located outdoors or in areas where condensation may occur should be provided. On-site emergency power generation equipment shall be located above grade and be adequately ventilated. Fuel shall be stored in safe locations and in containers specifically designed for fuel storage.

B. Electrical protection. All electrical equipment design (motors, controls, switches, conduit systems, etc.) located in raw sewage wet wells or in totally or partially enclosed spaces where hazardous concentrations of flammable liquids, gases, vapors, or dusts may be present will be evaluated in accordance with the appropriate requirements of the National Electrical Code (e.g., Class I, Group D, Division I for ignitable gases or vapors, etc.) and VOSH requirements.

1. Three-phase motors and their starters shall be protected from electric overload and short circuits on all three phases.

2. All motors shall have a low voltage protection device which, on the reduction or failure of voltage, will cause and maintain the interruption of power to that motor. The low voltage protection device should protect each phase of 3-phase motors.

3. Consideration should be given to the installation of temperature detectors in the stator and bearings of larger motors in order to give an indication of overheating problems.

4. Wires in underground conduits or in conduits that may be flooded shall have moisture resistant insulation as identified in the National Electrical Code.

5. Concrete, metals, control and operating equipment, and safety devices shall, insofar as practical, be designed to protect against corrosion.

6. Electrical power devices or equipment used to convert single phase power to three phase power shall be dedicated to a single specific motor.

C. Testing. Provisions shall be included in the design of equipment requiring periodic testing, to enable the tests to be accomplished while maintaining electric power to all vital components. This requires being able to conduct tests such as actuating and resetting automatic transfer switches and starting and loading emergency generating equipment. The electric distribution system and equipment shall be designed to facilitate inspection and maintenance of individual items without interruption of operations.

D. Generator. The power capacity provided by the on-site emergency generator shall be in accordance with the reliability classification of the pump station. The automatic start system shall be completely independent of the normal electric power source. Air-starting systems shall have an accumulator tank or tanks with a volume sufficient to furnish air for starting the generator engine a minimum of three times without recharging. Batteries used for starting shall have a sufficient charge to permit starting the generator engine a minimum of three times without recharging. The starting system shall be appropriately alarmed and instrumented to indicate loss of readiness (e.g., loss of charge on batteries, loss of pressure in air accumulators, etc.)

E. The specifications shall require that the equipment manufacturers provide to the owner one complete set of operational instructions, equipment and maintenance manuals, with troubleshooting and emergency procedures for each major mechanical and electrical equipment item. The manuals shall contain drawings of equipment and a numbered parts list keyed to a list of components. Tools and such spare parts as may be needed shall also be specified.

Statutory Authority

§ 62.1-44.19 of the Code of Virginia.

Historical Notes

Former 12VAC5-581-460 derived from Virginia Register Volume 18, Issue 10, eff. February 27, 2002; amended and adopted as 9VAC25-790-400, Virginia Register Volume 20, Issue 9, eff. February 12, 2004.

9VAC25-790-410. Portable equipment and diversions.

A. Needs. Portable equipment (pumps or generator sets) shall be acceptable to satisfy the continuous operability requirements where, under critical conditions imposed by rush hour traffic, multiple pumping station failures, etc., the portable equipment transportation, connection and starting can be accomplished within allowable time periods.

1. Portable pumping equipment shall have the following provisions:

a. Pumping units shall have capability to operate between the wet well and the discharge side of the station.

b. Each station served by portable pumping equipment shall facilitate rapid and easy connection of lines.

2. Numbers of portable units and their pumping implementation capabilities that are simultaneously available to service pumping stations, which are provided continuous operability through the use of portable equipment, shall conform to the following, whichever shall yield the greater number:

a. The number shall be the maximum number of pumping stations (dependent on portable equipment for continuous reliability) that are on the same radial extremity (single source feed) of any electrical distribution circuit from the point of the radial extremity's intersection with circuitry that has alternate feed.

b. The number shall be equal to 5.0% of the number of pumping stations (dependent on portable equipment for continuous reliability).

3. Volume and head capabilities (pumps) or power watts (generators) of portable equipment shall be capable, singly or in combination, of operating the largest pump station dependent on portable equipment for continuous reliability.

B. Submittals. Plans and specifications for a pump station submitted to the area engineer proposing to use portable equipment to meet continuous operability requirements shall be accompanied by a completed "Portable Equipment for Sewage Pump Stations" form. A list of this information is included in 9VAC25-790-990.

1. The design submitted for sewerage systems that utilize portable equipment to meet the continuous operability requirements for sewage pump stations shall include the following information: (i) an inventory of the owner's portable equipment (pumps or generators) which lists numbers of units, capacities, storage locations, and assignment of this equipment by the owner; and (ii) an analysis of response times based on geographical locations within the owner's sewerage system service area.

2. The response time analysis should be based upon a work crew responding to an alarm from the pump station during the hour of the day that the peak flow to that station is expected to be received.

C. Controlled diversion. The provision of a high-level wet well-controlled diversion may be considered for pump stations of all reliability classes.

1. If a high-level wet well-controlled diversion is utilized, the overflow elevation shall be such that the maximum feasible storage capacity of the wastewater collection system shall be used before the controlled diversion is used. When a controlled diversion is utilized at a Reliability Class I pumping station, it shall be to a storage detention basin or tank. The storage volume shall be sized in accordance with the pump station's operating conditions and the constraints and conditions applicable to the owner's repair and maintenance capabilities. The storage volume shall provide, without overflow, not less than six hours detention capacity at the anticipated flow diversion rate.

2. Additional storage volume, or provisions for protection against overflows in critical areas, may be required.

Statutory Authority

§ 62.1-44.19 of the Code of Virginia.

Historical Notes

Former 12VAC5-581-470 derived from Virginia Register Volume 18, Issue 10, eff. February 27, 2002; amended and adopted as 9VAC25-790-410, Virginia Register Volume 20, Issue 9, eff. February 12, 2004.

9VAC25-790-420. Alarm systems.

A. The alarm system provided to monitor pump station operation shall meet the appropriate reliability requirements.

B. Class I. For Class I reliability, the alarm system shall monitor the power supplies to the station, auxiliary power source, failure of pumps to discharge liquid, and high liquid levels in the wet well and in the dry well, and shall include a test function. An on-site audio-visual alarm system shall be provided such that each announced alarm condition is uniquely identified. In addition, provisions shall be made for transmitting a single audible alarm signal to a central location where personnel competent to receive the alarm and initiate corrective action are either: (i) available 24 hours per day, or (ii) available during the periods that flow is received at the pump station. A sign indicating notification procedures (responsible persons, telephone numbers, etc.) to be followed in case of alarm actuation shall be displayed conspicuously.

C. Classes II and III. For Class II or III reliability, the alarm system shall monitor high liquid levels in the wet well. An on-site audio-visual alarm signal shall be provided. A sign indicating notification procedures (responsible persons, telephone numbers, etc.) to be followed in case of alarm actuation shall be displayed conspicuously.

D. Backup. A backup power supply, such as a battery pack with an automatic switchover feature, shall be provided for the alarm system, such that a failure of the primary power source would not disable the alarm system. A backup power supply for the alarm system should be provided for a Reliability Class I facility with dual electrical feed sources. Test circuits shall be provided to enable the alarm system to be tested and verified to be working properly.

Statutory Authority

§ 62.1-44.19 of the Code of Virginia.

Historical Notes

Former 12VAC5-581-480 derived from Virginia Register Volume 18, Issue 10, eff. February 27, 2002; amended and adopted as 9VAC25-790-420, Virginia Register Volume 20, Issue 9, eff. February 12, 2004.

9VAC25-790-430. Alternatives.

A. General. Wet well-dry well pump stations shall meet the applicable requirements for both types of systems. Both wet and dry wells shall be separated to prevent leakage of gas into the dry well. A separate sump pump or suitable means shall be provided in the dry well to remove leakage or drainage, with the discharge above the high water level of the wet well. Vacuum ejectors connected to a potable water supply will not be approved. All floor and walkway surfaces shall have an adequate slope to a point of drainage. Drainage shall be unobstructed by conduit, piping, etc., installed on the dry well floor.

B. Suction lift. Suction lift pump installations shall be designed to meet the applicable requirements of this chapter.

1. The capacity of suction lift pump stations shall be limited by the net positive suction head and specific speed requirements as stated on the manufacturer's pump curve under the most severe operating conditions.

2. All suction lift pumps shall be provided with an air relief line on the pump discharge piping. This line shall be located at the maximum elevation between the pump discharge flange and the discharge check valve to ensure the maximum bleed-off of entrapped air. Air relief piping shall have a minimum diameter adequate to purge air during priming. The use of 90° elbows in air relief piping should be avoided. A separate air relief line shall be provided for each pump discharge. The air relief line shall terminate in the wet well or suitable sump and open to the atmosphere.

3. Valving to prevent recycle of flow to the wet well should be provided on all relief lines. The air relief valves shall be located as close as practical to the discharge side of the pump. Automatic operating air relief valves may be used if the design of the particular valve is such that the valve will fail in the open position under varying head conditions. Unvalved air relief piping may lead to air entrainment in the sewage and will materially affect pump efficiency and capacity. Air entrainment shall be considered accordingly by the design consultant.

4. All pumps, connections, shut-off valves, and check valves shall be located in a separate vault either above or outside of the wet well, allowing accessibility to both the wet well and pump/valve vault for inspection, maintenance, etc.

5. Access to the wet well shall not be through a sealed vault. The dry well shall have a gas-tight seal when mounted directly above the wet well.

C. Submersible. Submersible pump station installations shall be designed to meet the applicable requirements of this chapter.

1. Submersible pumps shall be provided with equipment for disconnecting, removal, and reconnection of the pump without requiring personnel to enter the wet well.

2. Owners of submersible pumping facilities shall provide a hoist and accessories for removing the pumps from the wet well.

3. Electrical controls shall be located in a suitable housing for protection against weather and vandalism.

4. The shut-off valve and check valve on the discharge lines of pumps operating at flows greater than 25 gpm shall be located in a separate vault outside of the wet well allowing accessibility for inspection and maintenance.

D. Pneumatic ejectors. Pneumatic ejector stations shall be designed to meet the applicable requirements of this chapter. Pneumatic ejectors should not be directly connected to force mains. The ejector design features should include:

1. Ejector pots shall be vented to the atmosphere in such a manner as to prevent nuisance conditions.

2. Duplicate compressors shall be provided.

3. Pneumatic ejectors may utilize either stored or direct air systems. If a stored air system is utilized, the air storage chamber shall not enclose any piping, valves, or working parts.

4. Duplicate receiver pots shall be provided. The units shall be alternated in operation.

E. Grinder. Grinder pump installations shall be designed to meet the applicable requirements of this chapter.

1. Maintenance and operation service arrangements shall be identified to the division. Acceptable service arrangements shall include:

a. Right of access.

b. Adequate spare parts, spare units and service tools.

2. A single pumping unit for a single home or equivalent flow is acceptable, but the wet well capacity for a single family residence should be a minimum of 60 gallons.

3. Duplex pumping units shall be provided where two houses or equivalent flow are served by a single installation. The wet well or holding tank capacity shall be twice the requirements for a single house.

4. The alarm system should provide notice to residents of pump failure, including excessive high liquid levels. The alarm system should alert the operating staff of the location of pump failure.

5. Pumping equipment shall be capable of delivering flows at the design pressure of the sewer system. Cutter blades shall be driven with a minimum motor size of two horsepower, unless performance data, evaluated by the department, verifies that a smaller motor is suitable.

F. Septic tank effluent pump. Septic Tank Effluent Pumps (STEP) may be located within the effluent end of a single tank or within a separate vault external from the septic tank. The design for STEP facilities is described in published literature, such as the USEPA Technology Transfer Manual "Alternative Wastewater Collection Systems" (EPA/625/1-91/024), which may be used as a reference.

Statutory Authority

§ 62.1-44.19 of the Code of Virginia.

Historical Notes

Former 12VAC5-581-490 derived from Virginia Register Volume 18, Issue 10, eff. February 27, 2002; amended and adopted as 9VAC25-790-430, Virginia Register Volume 20, Issue 9, eff. February 12, 2004.

9VAC25-790-440. Force mains.

A. Capacity. The minimum size of force mains shall be four inches in diameter, except for grinder pumps and septic tank effluent (settled sewage) pumping systems, which shall be provided with a minimum diameter of one inch.

1. At pumping capacity, a minimum self-scouring velocity of two feet per second shall be maintained unless provisions for flushing are made. A velocity of eight feet per second should not be exceeded unless suitable construction methods are specified.

2. Air relief valves shall be placed at the high points in the force main to relieve air locking and shall be periodically exercised and maintained.

B. Connections. Force mains shall normally enter a gravity sewer system at a point no more than one foot above the flow line of the receiving manhole with a curved section to prevent air from traveling up into the force main. The force main should enter the receiving manhole with its center-line horizontal, and shall have an invert elevation which ensures a smooth flow transition to the gravity flow section. Special attention shall be paid to the design of the termination in order to prevent turbulence at this point. Whenever existing force mains are connected within a sewerage system in a manner that results in increased flow rates or pressure increase to the existing force mains, those existing force mains shall be examined by the owner. Existing force mains may be examined by internal visual inspections, flow or pressure testing, or other suitable means to verify hydraulic and structural adequacy to convey the actual or projected flow. The results of such inspections and tests shall be submitted with the design documents.

C. Materials. All pipe used for force mains shall be of the pressure type with pressure type joints. The force main shall be constructed of materials with a demonstrated resistance to deterioration from corrosion, acidity, and other chemical action.

1. Consideration should be given to the use of inert materials or protective coatings for either the receiving manhole or gravity sewer to prevent deterioration as a result of hydrogen sulfide or other chemical attack. These requirements should be provided for all force mains.

2. All force mains shall be tested at a minimum pressure of at least 50% above the design operating pressure for at least 30 minutes. Leakage shall not exceed the amount given by the formula contained in the most current AWWA Standard C-600.

D. Installation. Class A, B or C bedding (ASCE Manuals and Reports on Engineering Practice—No. 36, 1974 and the WPCF Manual of Practice—No. 9, 1970) or AWWA pipe installation conditions 3, 4 or 5 (ANSI/AWWA C600-82) shall be provided for installation of pipelines in excavated trenches. Installation of pipelines of flexible materials shall be in accordance with recognized standards.

Force mains shall be sufficiently anchored within the pump station and throughout the line length. The number of bends shall be as few as possible. Thrust blocks, restrained joints, or tie rods shall be provided where restraint is needed.

Statutory Authority

§ 62.1-44.19 of the Code of Virginia.

Historical Notes

Former 12VAC5-581-500 derived from Virginia Register Volume 18, Issue 10, eff. February 27, 2002; amended and adopted as 9VAC25-790-440, Virginia Register Volume 20, Issue 9, eff. February 12, 2004.

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