Virginia Administrative Code › Title 9 - ENVIRONMENT › Agency 25 - STATE WATER CONTROL BOARD › Chapter 790 - VIRGINIA POLLUTANT DISCHARGE ELIMINATION SYSTEM (VPDES) PERMIT REGULATION › Part III - Manual of Practice for Sewerage Systems and Treatment Works › Article 2 - Sewage Pump Stations › Section 9VAC25-790-380 - Sewage pumping

Current through Register Vol. 40, No. 24, July 15, 2024
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.