OAR 340-071-0295
Conventional Sand Filter Design and Construction

(1) Criteria for sizing. Systems must be sized based on quantities of sewage flow under OAR 340-071-0220 (Standard Subsurface Systems)(2)(a).
(2) Minimum filter area:
(a) A sand filter proposed to serve a single family dwelling must have an effective medium sand surface area of at least 360 square feet. If the design sewage flow exceeds 450 gallons per day, the medium sand surface area must be determined with the following equation: Area = projected daily sewage flow divided by 1.25 gallons per square foot.
(b) A bottomless sand filter following an ATT system must have an effective medium sand surface area of at least 250 square feet. If the design sewage flow exceeds 450 gallons per day, the medium sand surface area must be determined with the following equation: Area = projected daily sewage flow divided by 1.80 gallons per square foot.
(c) Sand filter influent may not exceed concentrations of 300 mg/L BOD5, 150 mg/L TSS, or 25 mg/L oil and grease.
(3) Design criteria.
(a) The interior base of the filter container must be level or constructed at a grade of 1 percent or less to the underdrain piping elevation.
(b) Except for sand filters without a bottom, underdrain piping must meet the requirements in OAR 340-073-0060 (Distribution Boxes, Drop Boxes, and Diversion Valves: Pipe Materials and Construction)(2) and must be installed in the interior of the filter container at the lowest elevation. The piping must be level or on a grade of 1 percent or less to the point of passage through the filter container. The pipe perforations or slots must be oriented in the upright or sideways position.
(c) The base of the filter container with the underdrain piping in place must be covered with a minimum of 6 inches of drain media or underdrain media. Unless the agent waives it, the underdrain media proposed for a sand filter must be sieved to determine conformance with the criteria in OAR 340-071-0100 (Definitions)(170) and a report of the analysis must be provided to the agent. Where underdrain media is used, the underdrain piping must be enveloped in an amount and depth of drain media to prevent migration of the underdrain media to the pipe perforations.
(d) Where drain media is used at the base of the filter, it must be covered by a layer of filter fabric meeting the specifications in OAR 340-073-0041 (Distribution Boxes, Drop Boxes, and Diversion Valves: Filter Fabric). Where underdrain media is used, filter fabric is not required.
(e) A minimum of 24 inches of approved sand filter media must be installed over the filter fabric or underdrain media. The sand filter media must be damp at the time of installation. The top surface of the media must be level. Unless waived by the agent, the sand filter media proposed for each sand filter must be sieve-tested to determine conformance with the criteria in OAR 340-071-0100 (Definitions)(124), and a report of the analysis must be provided to the agent.
(f) A minimum of 3 inches of clean drain or underdrain media is required below the distribution laterals, and sufficient media is required above the laterals to meet or cover the orifice shields to provide a smooth, even cover.
(g) A pressurized distribution system meeting the requirements of OAR 340-071-0275 (Pressurized Distribution Systems)(4) and (5) must be constructed as described in subsection (f) of this section.
(A) Distribution laterals must be spaced a maximum of 30 inches center to center. Orifices must be spaced no more than 30 inches apart.
(B) The ends of the distribution laterals must be designed and constructed to allow flushing of the piping, collectively or individually, using a corrosion-resistant and accessible valve or threaded endcap. The flushed effluent may be discharged to the septic tank or into the sand filter.
(C) The diameters of the distribution manifold and laterals must be at least 1⁄2 inch in diameter.
(D) A sand filter must be dosed at a rate not to exceed 10 percent of the projected daily sewage flow.
(h) The top of the media in which the pressure distribution system is installed must be covered with filter fabric meeting the specifications in OAR 340-073-0041 (Distribution Boxes, Drop Boxes, and Diversion Valves: Filter Fabric).
(i) The top of the sand filter area must be backfilled with a soil cover free of rock, vegetation, wood waste, and other materials that may harm the filter. The soil cover must have a textural class no finer than loam unless otherwise authorized by the agent. The soil cover must be at least 6 inches and no more than 12 inches deep.
(j) All piping passing through the sand filter container must be watertight.
(4) Container design and construction.
(a) A reinforced concrete container with watertight walls and floors must be used where watertightness is necessary to prevent groundwater from infiltrating into the filter or to prevent the effluent from exfiltrating from the filter except as otherwise allowed in this division or OAR chapter 340, division 073. The container structure may require a building permit for construction.
(b) The container may be constructed of materials other than concrete where equivalent function, workmanship, watertightness, and at least a 20-year service life can be documented.
(A) Flexible membrane liner (FML) materials must have properties at least equivalent to 30 mil unreinforced polyvinyl chloride (PVC) described in OAR 340-073-0085 (Non-water-Carried Waste Disposal Facilities, Materials, and Construction: Flexible Membrane Liners for Sand Filters Treating Septic Tank Effluent). For FML materials to be approved for installation:
(i) Field repair instructions and materials must be provided to the purchaser with the liner; and
(ii) The final materials must have factory-fabricated boots suitable for field bonding onto the liner to facilitate the passage of piping through the liner in a waterproof manner.
(B) Where accepted for use, flexible sheet membrane liners must be installed as OAR 340-073-0085 (Non-water-Carried Waste Disposal Facilities, Materials, and Construction: Flexible Membrane Liners for Sand Filters Treating Septic Tank Effluent) requires.
(C) The backfill around the container must be no steeper than a 3:1 slope (3 feet for every vertical foot) unless otherwise authorized by the agent.
(5) Internal pump option. Where a pump is used to discharge effluent from a sand filter to another treatment unit, a distribution unit, or an absorption facility, the design and construction of the filter may include an internal pump station if the following conditions are met.
(a) The location, design, and construction of the pump station must not conflict with design, construction, and operation of the sand filter system.
(b) The design and construction of the pump, discharge plumbing, controls, and alarm must meet the requirements in OAR 340-073-0055 (Distribution Boxes, Drop Boxes, and Diversion Valves: Dosing Assemblies: Effluent Pumps, Controls and Alarms, and Dosing Siphons) except subsections (4)(d) and (4)(h).
(c) The pump and related apparatus must be housed in a corrosion-resistant vault designed to withstand stresses and prevent the migration of drain media, sand, or underdrain media to its interior. The vault must have a durable, affixed floor. The vault must provide watertight access to finished grade with a diameter equal to that of the vault and designed to receive treated effluent from the bottom of the sand filter.
(d) The depth of underdrain media and the operating level of the pump cycle and alarm may not allow effluent to come within 2 inches of the bottom of the sand filter media. The pump off-level may be no lower than the invert of the perforations of the underdrain piping.
(e) The internal sand filter pump must be electrically linked to the sand filter dosing apparatus to prevent effluent from entering the sand filter if the internal sand filter pump fails.

Source: Rule 340-071-0295 — Conventional Sand Filter Design and Construction, https://secure.­sos.­state.­or.­us/oard/view.­action?ruleNumber=340-071-0295.

340‑071‑0100
Definitions 340‑071‑0110
Purpose 340‑071‑0115
Technical Review Committee 340‑071‑0120
Jurisdiction and Policy 340‑071‑0130
General Standards, Prohibitions and Requirements 340‑071‑0135
Approval of New or Innovative Technologies, Materials, or Designs for Onsite Systems 340‑071‑0140
Onsite System Fees 340‑071‑0150
Site Evaluation Procedures 340‑071‑0155
Existing System Evaluation Report 340‑071‑0160
Permit Application Procedures — Construction, Installation, Alteration, and Repair Permits 340‑071‑0162
Permit Application Procedures — WPCF Permits 340‑071‑0165
Permit Denial Review — Construction-Installation, Repair, Alteration Permits 340‑071‑0170
Pre-Cover Inspections 340‑071‑0175
Certificate of Satisfactory Completion 340‑071‑0185
Decommissioning of Systems 340‑071‑0200
Prior Construction Permits or Approvals 340‑071‑0205
Authorization to Use Existing Systems 340‑071‑0210
Alteration of Existing Onsite Wastewater Treatment Systems 340‑071‑0215
Repair of Existing Systems 340‑071‑0220
Standard Subsurface Systems 340‑071‑0260
Alternative Systems, General 340‑071‑0265
Capping Fills 340‑071‑0275
Pressurized Distribution Systems 340‑071‑0280
Seepage Trench System 340‑071‑0285
Redundant Systems 340‑071‑0290
Conventional Sand Filter Systems 340‑071‑0295
Conventional Sand Filter Design and Construction 340‑071‑0302
Recirculating Gravel Filter (RGF) 340‑071‑0310
Steep Slope Systems 340‑071‑0315
Tile Dewatering System 340‑071‑0320
Split Waste Method 340‑071‑0325
Gray Water Waste Disposal Sumps 340‑071‑0330
Nonwater-Carried Systems 340‑071‑0335
Cesspools and Seepage Pits 340‑071‑0340
Holding Tanks 340‑071‑0345
Alternative Treatment Technologies (ATTs) 340‑071‑0360
Absorption Trenches in Saprolite 340‑071‑0400
Geographic Area Special Considerations. 340‑071‑0410
Rural Area Consideration 340‑071‑0415
For Cause Variances 340‑071‑0420
Hardship Variances 340‑071‑0425
Variance Officers 340‑071‑0430
Variance Hearings and Decisions 340‑071‑0435
Variance Permit Issuance, Inspections, Certificate of Satisfactory Completion 340‑071‑0440
Variance Appeals 340‑071‑0445
Variance Administrative Review 340‑071‑0460
Moratorium Areas 340‑071‑0500
Community Systems 340‑071‑0520
Large Systems 340‑071‑0600
Sewage Disposal Service Licenses 340‑071‑0650
Training and Certification Requirements for System Installers and Maintenance Providers 340‑071‑0800
Tables
Last Updated

Jun. 8, 2021

Rule 340-071-0295’s source at or​.us