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RULE §217.98Vacuum Sewer Systems

(a) A vacuum sewer system is a non-conforming technology. The executive director may review a vacuum sewer in accordance with §217.7(b)(2) of this title (relating to Types of Plans and Specifications Approvals) and the criteria described in this section.

(b) On-Site Component Design.

  (1) A building lateral must be constructed using pipe material that has performance characteristics at least equivalent to American Society for Testing and Materials (ASTM) D 2241 Class 160 polyvinyl chloride (PVC) pipe.

  (2) A building lateral must use a screened auxiliary vent no less than 4.0 inches in diameter and located no closer than 10.0 feet to a vacuum valve.

  (3) A vacuum valve control must be in a tamper-resistant, watertight, and corrosion-resistant structure.

  (4) A vacuum valve pit must be watertight to prevent surface and groundwater inflow.

  (5) A control mechanism that uses a pressure differential must use atmospheric air supplied by a screened breather on the lateral line.

  (6) A vacuum valve must have a minimum capacity of 30 gallons per minute.

  (7) A service pipe must be at least 3.0 inches in diameter.

  (8) The performance characteristics of a service pipe must meet or exceed the performance characteristics of ASTM D 2241 Class 200 PVC pipe.

  (9) A service pipe joint must be made using either vacuum-rated elastomeric gasket or solvent welding.

  (10) A vacuum valve and a main pipe must be separated by at least 5.0 feet of service pipe.

  (11) If there is a vertical profile change in a service pipe, the vacuum sewer system must have at least 5.0 feet between the vacuum valve and the first profile change, and between the last profile change and the main pipe.

  (12) A service pipe must have a minimum slope of 0.2%.

  (13) The connection of a service pipe to a main pipe must use a wye and a long radius elbow, oriented so that the invert of the service pipe is higher than the crown of the collection pipe, and must not be located within 6.0 feet of a collection pipe vertical profile change.

(c) Vacuum Sewer System Design.

  (1) The performance characteristics of a pipe in a vacuum sewer must meet or exceed the performance characteristics of ASTM D 2241 Class 200 PVC pipe.

  (2) A pipe joint must have a vacuum-rated rubber gasket or be solvent welded.

  (3) A pipe in a vacuum sewer must be at least 4.0 inches in diameter. A service pipe must be at least 3.0 inches in diameter.

    (A) The length of a 4.0 inch diameter vacuum pipe must not exceed 2,000 feet.

    (B) The maximum length of a pipe larger than 4.0 inches in diameter must be determined by the amount of friction and lift head loss.

  (4) The total available head loss from the farthest input point in a system is 18 feet, consisting of five feet to operate the vacuum valve and 13 feet available for wastewater transport.

  (5) A vacuum sewer system must be laid out in a branched pattern designed to balance pressures within the system. A pipe must have a saw-tooth profile that slopes toward a vacuum station.

  (6) The design of an upgrade main line transport pipe must reduce the risk of blocking a pipe with trapped sewage.

  (7) A collection pipe that is depressed in order to avoid an obstruction must have at least a 20 foot segment centered on the obstruction.

  (8) An intersection of collection pipes must include a division valve at both sides of a watercourse crossing, at both sides of an area of unstable soil, and at intervals of no more than 1,500 feet.

    (A) A division valve must be either a plug valve or a resilient-seated gate valve capable of sustaining a vacuum of 24 inches of mercury.

    (B) A gauge tap must be located downstream of each division valve.

(d) Vacuum station design. The vacuum pump capacity must be the greater of the capacities calculated using the following equations, but not less than 150 gallons per minute:

Attached Graphic

(e) Vacuum Pumps.

  (1) A vacuum pump must be capable of evacuating the system to restore the design vacuum pressure in less than 180 seconds.

  (2) The vacuum system must include duplicate vacuum pumps. Each vacuum pump must be capable of delivering 100% of the required airflow and be capable of operating continuously.

  (3) A vacuum pump may be either liquid-ring or sliding-vane type. Liquid-ring pumps must be sized at least 15% larger than the necessary vacuum pump capacity.

  (4) The transfer pipe must have an electrically or pneumatically controlled plug valve between the collection tank and the reservoir to prevent carryover of liquid into the pump.

(f) Duplicate discharge pumps.

  (1) Duplicate discharge pumps are required and must have the capacity to deliver the peak flow with one pump out of service.

  (2) A discharge pump must be:

    (A) designed for vacuum sewage duty;

    (B) equipped with equalizing pipes;

    (C) capable of passing a 3.0 inch sphere; and

    (D) constructed from corrosion-resistant material.

  (3) A discharge pump must use double mechanical shaft seals and have shut-off valves on both the suction and discharge pipes.

  (4) The total dynamic head calculation must include the head attributed to overcoming the vacuum in the collection tank.

  (5) The available net positive suction head must be greater than the required net positive suction head for the expected vacuum operating range.

  (6) The pump suction pipe must be sized 2.0 inches larger than the discharge pipe to prevent wastewater from forming a vortex in the collection tank.

  (7) The pump design calculations and pump curves must be included in the engineering report.

(g) Vacuum Reservoir.

  (1) A vacuum system that requires a collection tank of 1,600 gallons or more must also include a vacuum reservoir tank with a capacity of at least 400 gallons.

  (2) Liquid from a vacuum pump must be piped to the top of the vacuum reservoir tank.

  (3) A vacuum reservoir tank must include internal access for periodic cleaning and inspection.

  (4) All main pipes must connect to the collection tank.

  (5) The wastewater pump suction pipe must lie at the lowest point on the collection tank and away from the main pipe inlet.

  (6) The main pipe must enter at the top of the collection tank with the inlet elbows inside the tank turned at an angle away from the pump suction opening.

  (7) The collection tank must include probes for liquid level sensing for operation of the discharge pumps.

  (8) A vacuum pump must include automatic vacuum switch controls, which must operate based on the liquid level in the reservoir tank.

  (9) The collection tank and low system vacuum must include an audiovisual alarm for high liquid level.

(h) An owner shall include a description of the alternative collection system's anti-corrosive protection in the engineering report.

Source Note: The provisions of this §217.98 adopted to be effective August 28, 2008, 33 TexReg 6843; amended to be effective December 4, 2015, 40 TexReg 8254

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