340-071-0265 Capping Fills (1) Criteria for approval. Each site approved for a capping fill system must meet all the following conditions: (a) Slope does not exceed 12 percent. (b) Temporary water table is not closer than 18 inches to the ground surface at any time during the year. A 6-inch minimum separation must be maintained between the bottom of the absorption trench and the temporary water table. (c) Where a permanent water table is present, a minimum 4-foot separation must be maintained between the bottom of the absorption trench and the water table. (d) Except as provided in paragraph (e) of this section, where material with rapid or very rapid permeability is present, a minimum 18-inch separation must be maintained between the bottom of the absorption trench and soil with rapid or very rapid permeability. (e) Sites may be approved with no separation between the bottom of the absorption trenches and soil with rapid or very rapid permeability (as defined in OAR 340-071- 0100(150)(a) or (b)), and absorption trenches may be placed into such soil if any of the following conditions occur. (A) A confining layer occurs between the bottom of absorption trenches and the temporary groundwater table and a minimum 6-inch separation is maintained between the bottom of absorption trenches and the top of the confining layer. (B) A layer of non-gravelly (less than 15 percent gravel) soil with sandy loam or finer texture at least 18 inches thick occurs between the bottom of the absorption trenches and the groundwater table. (C) The design flow does not exceed a loading rate of 450 gallons per acre per day. (f) Effective soil depth is 18 inches or more below the natural soil surface. (g) Soil texture from the ground surface to the layer that limits effective soil depth is no finer than silty clay loam. (h) A minimum 6-inch separation is maintained between the bottom of the absorption trench and the layer that limits effective soil depth. (i) The system can be sized according to effective soil depth in Table 4. (2) Installation requirements. The cap must be constructed as the permit requires. Unless the agent requires otherwise, construction must follow this sequence: (a) The agent must examine and approve the soil before placing the cap. The texture of the soil used for the cap must be the same textural class as or one textural class finer than the natural topsoil unless otherwise allowed in this division. (b) Capping fills must be constructed between June 1 and October 1 unless the agent allows otherwise. The upper 18 inches of natural soil must not be saturated or have a moisture content that causes loss of soil structure and porosity when worked. (c) The absorption area and the borrow site must be scarified to destroy the vegetative mat. (d) The system must be installed as specified in the construction-installation permit with a minimum 10-foot separation between the edge of the fill and the absorption facility. (e) Filter fabric must be used between the drain media and the soil cap, unless the agent authorizes otherwise. (f) Fill must be applied to the fill site and worked in so that the two contact layers, native soil and fill, are mixed. Fill material must be evenly graded to a final depth of 10 inches over the drain media for an equal system or 16 inches over the drain media for a serial system to allow for appropriate settled depths. Both initial cap and repair cap may be constructed at the same time. (g) The site must be landscaped according to permit conditions and be protected from livestock, automotive traffic, and other activity that could damage the system. (3) Required inspections. Unless the agent waives it, the following inspections must be performed for each capping fill installed. (a) Inspecting both the absorption area and borrow material before cap construction for scarification, soil texture, and moisture content. (b) Inspecting the installed absorption facility before covering. (c) Inspection after the cap is placed to determine adequate contact between fill material and native soil (no obvious contact zone visible), adequate depth of material, and uniform distribution of fill material. (d) Final inspection after landscaping or other erosion control measures are established. [ED. NOTE: All table s are found in OAR 340-071-0800.] 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 44-2017, minor correction filed 12/14/2017, effective 12/14/2017 DEQ 15-2017, amend filed 10/31/2017, effective 11/01/2017 DEQ 14-2013, f. 12-20-13, cert. ef. 1-2-14 DEQ 11-2004, f. 12-22-04, cert. ef. 3-1-05 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