Section 340. Vacuum sewage system

A. Features. Vacuum sewer systems consisting of small diameter pipes that collect sewage delivered through multiple service connection values and deliver that flow under negative pressure to one or more receiving stations will be considered on a case-by-case basis. The design shall include, but not be limited to, the following criteria:

1. Minimum pipe diameter shall be three inches for nonsettled sewage and 1-1/2 inches for settled sewage.

2. Shut-off valves shall be provided at branch connections with lines exceeding 300 feet and at intervals no greater than 2000 feet on main vacuum lines. Valves shall not obstruct the flow path when fully opened for operation. Gate valves and butterfly valves may not be acceptable if the flow path is obstructed during system operation.

3. Access points equal to the vacuum line diameter shall be provided at the end of main and branch lines and at intervals or locations suitable for operation and maintenance of the system. Access or inspection points shall be provided so that a suitable means for shut off of lines can be readily inserted.

4. Provisions for vacuum testing the piping system shall be described and made available to the department.

B. Connection valves. The minimum diameter of vacuum valves for nonsettled sewage shall be such that a sphere of 2-1/2 inches can pass through. For settled sewage a 1-1/2 inches sphere shall pass through the vacuum valve. Vacuum valves shall be capable of operation under severe climatic conditions such as submerged under water or ice conditions. Air vents shall extend above ground to a level up to the 100-year flood elevation, if practical. Air vent design should provide protection against both freezing and physical damage, where possible. Access to valve pits shall be such that valves may be easily removed and replaced. A holding tank of sufficient volume up to 25% or more of the design daily flow shall be provided upstream of the vacuum valve when the location of the vacuum valve alone does not permit proper system operation.

C. Receiving station. A minimum of two sewage and vacuum pumping units shall be provided for receiving stations. The system shall be capable of handling peak sewage and air flow conditions with one unit out of service. In the overall design, consideration shall be given to pump cooling requirements and features required for pumping moist air containing sewer gases. Provisions for odor control such as exhaust air oxidation or deodorization shall be considered in the system design. The design of the pump station should minimize the discharge of air along with the sewage. The capacity of the collecting tanks shall be sufficient to limit the start frequency of all pumps to less than 12 per hour. The number of collection tanks shall be established to account for system reliability and operability.

1. Provisions shall be made to isolate the receiving vacuum collection tank, vacuum pumps, raw sewage influent line, and raw sewage discharge pumps.

2. The raw sewage pumps shall meet all applicable requirements of this chapter. The negative head created by the vacuum pumps shall be considered in calculating Net Positive Suction Head (NPSH).

D. Service. Adequate service arrangements shall be provided for routine and emergency maintenance and operation. The arrangements shall include:

1. Right of access.

2. Adequate spare valves, spare parts, and service tools.

3. Monitoring, alarm system to locate vacuum loss or valve failure.

E. Operability. The vacuum collection system is to be operated in a manner to prevent the discharge of raw sewage to any waters and to protect public health and welfare by preventing back-up of sewage and subsequent discharge to basements, streets, and other public and private property.

1. Provisions for maintaining interim household service and preventing sewage overflows during system malfunction shall be described and submitted with design information in accordance with this chapter.

2. An alarm system shall be provided capable of alerting maintenance personnel of operational and safety problems in case of malfunction in the collection system.

Historical Notes

Former 12VAC5-581-400 derived from Volume 18, Issue 10, eff. February 27, 2002; amended and adopted as 9VAC25-790-340, Virginia Register Volume 20, Issue 09, eff. February 12, 2004.

Statutory Authority

§ 62.1-44.19 of the Code of Virginia.