OAR 340-071-0275
Pressurized Distribution Systems

(1) Pressurized distribution systems receiving residential strength wastewater may be permitted on any site meeting the requirements for installation of a standard onsite system and on other sites where this method of effluent distribution is preferable and the site conditions in this rule can be met.
(2) Except as allowed in OAR 340-071-0220 (Standard Subsurface Systems)(1)(d), pressurized distribution systems must be used where depth to soil with rapid or very rapid permeability as defined in OAR 340-071-0100 (Definitions)(148)(a) and (b) is less than 36 inches and the minimum separation distance between the bottom of the absorption trench and such soil is less than 18 inches.
(3) Pressurized distribution systems installed in soil with rapid or very rapid permeability as defined in OAR 340-071-0100 (Definitions)(148)(a) and (b) in areas with permanent water tables may not discharge more than 450 gallons of effluent per 12 acre per day except where:
(a) Groundwater is degraded and designated as a non-developable resource by the Oregon Water Resources Department; or
(b) A detailed hydrogeological study discloses loading rates exceeding 450 gallons per 12 acre per day would not increase the nitrate-nitrogen concentration in the groundwater beneath the site or at any down gradient location to above 5 mg/L.
(4) Materials and construction.
(a) General.
(A) All materials used in pressurized systems must be structurally sound, durable, and capable of withstanding normal stresses incidental to installation and operation.
(B) Pump wiring must comply with applicable building, electrical, or other codes. An electrical permit and inspection from the Department of Consumer and Business Services, Building Codes Division, or the municipality with jurisdiction, is required for pump wiring installation.
(C) A single compartment dosing septic tank may not be used in a system with pressurized distribution laterals unless the tank is partitioned with a flow-through below the tank’s lowest liquid level. The flow through port must be at 65 to 75 percent of the minimum liquid level and be at least 4" in diameter.
(b) Pressurized distribution piping. Piping, valves, and fittings for pressurized systems must meet the following minimum requirements.
(A) All pressure transport, manifold, lateral piping, and fittings must meet the requirements in OAR 340-073-0060 (Distribution Boxes, Drop Boxes, and Diversion Valves: Pipe Materials and Construction)(3).
(B) Pressure transport piping must be uniformly supported along the trench bottom. The agent may require the piping to be bedded in sand or other material approved by the agent. A minimum 18 gauge, green-jacketed tracer wire or green color-coded metallic locate tape must be placed above piping.
(C) Orifices must be located on top of the pipe, except as noted in paragraph 4(b)(I) of this section.
(D) The ends of lateral piping must be constructed with long sweep elbows or an equivalent method to bring the end of the pipe to finished grade. The ends of the pipe must be provided with threaded plugs, caps, or other devices acceptable to the agent to allow for access to and flushing the lateral.
(E) All joints in the manifold, lateral piping, and fittings must be solvent-welded using the appropriate joint compound for the pipe material. Pressure transport piping may be solvent-welded or rubber-ring jointed.
(F) A shut off valve must be placed on the pressure transport pipe in or near the dosing tank when appropriate.
(G) A check valve must be placed between the pump and the shut off valve when appropriate.
(H) All orifices must be covered by a protective, durable, noncorrosive orifice shield designed to keep orifices from being blocked by drain media or other system components. The shields or piping must be removable for access to the orifices.
(I) The agent may specify alternate orifice orientation and valve arrangements for conditions such as extended freezing temperatures, temporary or seasonal use, or effluent characteristics.
(J) Where operating a pump could result in siphonage of effluent to below the normal off level of the pump, an anti-siphon measure in the form of a non-discharging valve designed for the specific purpose must be used. The anti-siphon valve must be installed and operated under manufacturer’s specifications.
(c) Absorption trench sizing and construction.
(A) A system using absorption trenches must be designed and sized as OAR 340-071-0220 (Standard Subsurface Systems)(2) requires.
(B) Absorption trenches must be constructed using the specifications for the standard disposal trench unless otherwise authorized by the agent.
(C) The trench must contain drain media at least 12 inches deep, with at least 6 inches of media under the pressure distribution laterals and sufficient media above the laterals to meet or cover the orifice shields to provide a smooth, even cover.
(D) The top of the drain media must be covered with filter fabric or other nondegradable material permeable to fluids that will not allow passage of soil particles coarser than very fine sand. In unstable soils, sidewall lining may be required.
(d) Seepage bed construction.
(A) Seepage beds may be used instead of absorption trenches in soil as defined in OAR 340-071-0100 (Definitions)(148)(b) if flows do not exceed 600 gpd.
(B) The effective seepage area must be based on the bottom area of the seepage bed. The area must be at least 200 square feet per 150 gallons per day waste flow.
(C) Beds must be installed at least 18 inches deep (12 inches with a capping fill) but not deeper than 36 inches into the natural soil. The seepage bed bottom must be level.
(D) The top of the drain media must be covered with filter fabric or other nondegradable material that is permeable to fluids but will not allow passage of soil particles coarser than very fine sand.
(E) The bed must contain drain media at least 12 inches deep with at least 6 inches of media under the pressure distribution laterals and sufficient media above the laterals to meet or cover the orifice shields to provide a smooth, even cover.
(F) Pressurized distribution piping must be horizontally spaced not more than 4 feet apart and not more than 2 feet away from the seepage bed sidewall. At least 2 parallel pressurized distribution pipes must be placed in the seepage bed.
(G) A minimum of 10 feet of undisturbed earth must be maintained between seepage beds.
(5) Hydraulic design criteria. Pressurized distribution systems must be designed for appropriate head and capacity.
(a) Head calculations must include maximum static lift, pipe friction, and orifice head requirements.
(A) Static lift where pumps are used must be measured from the minimum dosing tank level to the level of the perforated distribution piping.
(B) Pipe friction must be based upon a Hazen Williams coefficient of smoothness of 150. All pressure piping and fittings on laterals must have a minimum diameter of 2 inches unless submitted plans and specifications show a smaller diameter pipe is adequate.
(C) A minimum head of 5 feet at the remotest orifice and no more than a 10 percent flow variation between the nearest and remotest orifice in an individual unit are required.
(b) The capacity of a pressurized distribution system refers to the rate of flow given in gallons per minute (gpm).
(A) Lateral piping must have discharge orifices drilled a minimum diameter of 18 inch and evenly spaced no more than 24 inches apart in coarse textured soils or no more than 4 feet apart in finer textured soils.
(B) The system must be dosed at a rate not to exceed 20 percent of the projected daily sewage flow.
(C) The effect of back drainage of the total volume of effluent within the pressure distribution system must be evaluated for its impact on the dosing tank and system operation.
(6) Service contracts. The owner of a pressurized distribution system must maintain a contract, under OAR 340-071-0130 (General Standards, Prohibitions and Requirements)(23), with a maintenance provider to serve, maintain and adjust the onsite system. A service contract must be entered before the system is installed and must be maintained until the system is decommissioned.
[Publications: Publications referenced are available from the agency.]

Source: Rule 340-071-0275 — Pressurized Distribution Systems, https://secure.­sos.­state.­or.­us/oard/view.­action?ruleNumber=340-071-0275.

Technical Review Committee
Jurisdiction and Policy
General Standards, Prohibitions and Requirements
Approval of New or Innovative Technologies, Materials, or Designs for Onsite Systems
Onsite System Fees
Site Evaluation Procedures
Existing System Evaluation Report
Permit Application Procedures — Construction, Installation, Alteration, and Repair Permits
Permit Application Procedures — WPCF Permits
Permit Denial Review — Construction-Installation, Repair, Alteration Permits
Pre-Cover Inspections
Certificate of Satisfactory Completion
Decommissioning of Systems
Prior Construction Permits or Approvals
Authorization to Use Existing Systems
Alteration of Existing Onsite Wastewater Treatment Systems
Repair of Existing Systems
Standard Subsurface Systems
Alternative Systems, General
Capping Fills
Pressurized Distribution Systems
Seepage Trench System
Redundant Systems
Conventional Sand Filter Systems
Conventional Sand Filter Design and Construction
Recirculating Gravel Filter (RGF)
Steep Slope Systems
Tile Dewatering System
Split Waste Method
Gray Water Waste Disposal Sumps
Nonwater-Carried Systems
Cesspools and Seepage Pits
Holding Tanks
Alternative Treatment Technologies (ATTs)
Absorption Trenches in Saprolite
Geographic Area Special Considerations.
Rural Area Consideration
For Cause Variances
Hardship Variances
Variance Officers
Variance Hearings and Decisions
Variance Permit Issuance, Inspections, Certificate of Satisfactory Completion
Variance Appeals
Variance Administrative Review
Moratorium Areas
Community Systems
Large Systems
Sewage Disposal Service Licenses
Training and Certification Requirements for System Installers and Maintenance Providers
Last Updated

Jun. 8, 2021

Rule 340-071-0275’s source at or​.us