340-071-0315 Tile Dewatering System (1) General conditions for approval. Construction permits may be issued for tile dewatering systems if the following requirements can be met: (a) The site has a natural outlet that will allow a field tile installed on a proper grade around the proposed absorption facility to daylight above annual high water. (b) Soils are silty clay loam or coarser textured and drainable. (c) Soils must have a minimum effective soil depth of at least 30 inches in soils with temporary groundwater and at least 72 inches in soils with permanent groundwater unless otherwise authorized by the agent. (d) Slope does not exceed 3 percent. (e) All other requirements for the system, except depth to groundwater, can be met. After the field collection drainage tile is installed, the groundwater levels must conform to the requirements of OAR 340-071-0220(1), 340-071-0265(1), 340-071-0290(2), 340-071- 0302(1), or 340-071- 0345(8). (2) Construction requirements. (a) Field collection drainage tile must be installed on a uniform grade of 0.2 to 0.4 feet of fall per 100 feet. The tile drainage trench must be constructed to the minimum depth required in the approved site evaluation report. (b) A field collection drainage tile trench must be constructed at least 12 inches wide. (c) Maximum drainage tile spacing must be 70 feet center to center. (d) The minimum horizontal separation distance between the drainage tile and absorption facility must be 20 feet. (e) Field collection drainage tile must be rigid, smooth-wall, perforated pipe or other pipe material the agent approves with a minimum diameter of 4 inches. (f) Field collection drainage tile must be enveloped in clean drain media or underdrain media to within 30 inches of the soil surface in soils with permanent groundwater or to within 12 inches of the soil surface in soils with temporary groundwater. Drain media must be covered with filter fabric, treated building paper, or other nondegradable material approved by the agent. (g) Outlet tile must be rigid, smooth-wall, solid Schedule 40 minimum pipe with an interior diameter of at least 4 inches. The agent may require a flap gate or rodent guard. (h) A silt trap with a 12-inch minimum diameter must be installed between the field collection drainage tile and the outlet pipe unless otherwise authorized by the agent. The bottom of the silt trap must be at least 12 inches below the invert of the drainage pipe outlet. (i) The discharge pipe and tile drainage system are integral parts of the system but do not need to meet setback requirements to property lines, wells, streams, lakes, ponds, or other surface waterbodies. (j) Before issuing a final site evaluation report approving the site, the agent may require demonstration that a proposed tile dewatering site can be effectively drained. (k) The absorption facility must use equal or pressurized distribution. Statutory/Other Authority: ORS 454.625 & 468.020 Statutes/Other Implemented: ORS 454.615 & 454.775 History: DEQ 29-2025, amend filed 10/01/2025, effective 01/01/2026 DEQ 15-2017, amend filed 10/31/2017, effective 11/01/2017 DEQ 11-2004, f. 12-22-04, cert. ef. 3-1-05 DEQ 12-1997, f. & cert. ef. 6-19-97 DEQ 27-1994, f. 11-15-94, cert. ef. 4-1-95 DEQ 8-1983, f. & ef. 5-25-83 DEQ 10-1981, f. & ef. 3-20-81