Section 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.

Historical Notes

Former 12VAC5-581-490 derived from Volume 18, Issue 10, eff. February 27, 2002; amended and adopted as 9VAC25-790-430, Virginia Register Volume 20, Issue 09, eff. February 12, 2004.

Statutory Authority

§ 62.1-44.19 of the Code of Virginia.