Oregon Administrative Rules › Chapter 340 - DEPARTMENT OF ENVIRONMENTAL QUALITY › Division 71 - ONSITE WASTEWATER TREATMENT SYSTEMS › Section 340-071-0220 - Standard Subsurface Systems

Current through Register Vol. 63, No. 7, July 1, 2024
(1)
			 Criteria For standard subsurface systems. Each site must meet all of the
			 conditions in this section to be approved for a standard subsurface system.
(a) Effective soil depth must extend 30
			 inches or more below the ground surface as shown in Table 3. [NOTE: All tables
			 are found in OAR 340-071-0800.] A minimum 6-inch separation must be maintained
			 between the layer that limits effective soil depth and the bottom of the
			 absorption facility.
(b) Water
			 table levels must be predicted using standards in OAR 340-071-0130(23).
(A) The permanent water table must be at
			 least 4 feet below the bottom of the absorption facility, except in defined
			 geographic areas where DEQ has determined through a groundwater study that less
			 separation will not degrade groundwater or threaten public health. In these
			 exception areas, the permanent water table must be at least 24 inches below the
			 ground surface.
(B) A temporary
			 water table must be 24 inches or more below the ground surface. An absorption
			 facility may not be installed deeper than the top of the temporary water table.
(C) A groundwater interceptor may
			 be used to intercept or drain water from an absorption area on sites with
			 adequate slope to permit proper drainage. An agent may require a demonstration
			 that the site can be de-watered before issuing a site evaluation report
			 approving the site. Where required, groundwater interceptors are an integral
			 part of the system but do not need to meet setback requirements to property
			 lines, wells, streams, lakes, ponds, or other surface water bodies that are
			 required for the wastewater absorption area.
(c) Except as subsection (d) of this section
			 provides, soil with rapid or very rapid permeability must be 36 inches or more
			 below the ground surface. A minimum 18-inch separation must be maintained
			 between soil with rapid or very rapid permeability and the bottom of absorption
			 trenches.
(d) Sites may be approved
			 with no separation between the bottom of absorption trenches and soil with
			 rapid or very rapid permeability as defined in OAR 340-071-0100 (148)(a) and (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 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 nongravelly (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 projected daily sewage
			 flow does not exceed a loading rate of 450 gallons per acre per day.
(e) Slopes do not exceed 30
			 percent or the slope/effective soil depth relationship described in Table 3.
			 [NOTE: All tables are found in OAR 340-071-0800.]
(f) The site has not been filled or the soil
			 has not been modified in a way that would, in the agent's opinion, adversely
			 affect the system's functioning.
(g) The site is not on an unstable land form
			 that might adversely affect operation of the system.
(h) The site of the initial and replacement
			 absorption facility is not covered by asphalt or concrete or subject to
			 vehicular traffic, livestock, or other activity that would adversely affect the
			 soil.
(i) The site of the initial
			 and replacement absorption facility will not be subjected to excessive
			 saturation from artificial drainage of ground surfaces, driveways, roads, roof
			 drains, or other circumstances.
(j)
			 Setbacks in Table 1 except as modified by this subsection can be met.
(A) Surface waters setbacks. Setback from
			 streams or other surface waters must be measured from bank drop-off or mean
			 yearly high water mark, whichever provides the greatest separation
			 distance.
(B) Lots created before
			 May 1, 1973. For lots or parcels legally created before May 1, 1973, the agent
			 may approve installing a standard or alternative system with a setback from
			 surface waters of less than 100 feet but not less than 50 feet if all other
			 applicable provisions of this rule can be met.
(C) Water lines and sewer lines. Effluent
			 sewer and water line piping constructed of materials that are approved for use
			 within a building in the 2000 Edition of the Oregon State Plumbing Specialty
			 Code may be run in the same trench or may cross. Where the effluent sewer pipe
			 material is not approved for use in a building, it may not be run or laid in
			 the same trench as water pipe unless:
(i) The
			 bottom of the water pipe at all points is set at least 12 inches above the top
			 of the sewer pipe; and
(ii) The
			 water pipe is placed on a solid shelf excavated at one side of the common
			 trench with a minimum, clear, horizontal distance of at least 12 inches from
			 the sewer pipe.
(D)
			 Septic tank setbacks. The agent must encourage placing septic tanks and other
			 treatment units as close as feasible to the minimum separation from the
			 building foundation to minimize clogging the building sewer.
(E) Pressure transport pipe setback to well.
			 Notwithstanding the setback distance in Table 1, the agent may allow the
			 separation distance between a pressure transport pipe and a well to be less
			 than 50 feet but no less than 25 feet when [NOTE: All tables are found in OAR
			 340-071-0800.] :
(i) The pressure transport
			 pipe is PVC Sch. 40 or heavier pressure-rated piping meeting ASTM Specification
			 D-2241;
(ii) The pressure transport
			 pipe is placed within a larger diameter PVC or ABS Sch. 40 or heavier
			 encasement pipe, with the pipe ends located at least 50 feet away from the
			 well; and
(iii) All pipe joints in
			 the pressure transport pipe and encasement pipe are solvent-welded.