Washington Administrative Code › Title 246 - Health, Department of › SEWER SYSTEMS › Chapter 246-272A - On-site sewage systems › SPECIFIC REQUIREMENTS › Section 246-272A-0210 - Location

Current through Register Vol. 24-14, July 15, 2024
(1) OSS must be
				  designed and installed to meet at least the minimum horizontal separations
				  shown in Table IV:
Table IV
Minimum Horizontal
					 Separations
Items Requiring
								  Setback
From edge of soil dispersal
								  component and reserve area
From sewage tank and distribution
								  box
From building sewer, and
								  nonperforated distribution pipe
Well
100 ft.
50 ft.
50 ft.
Public drinking water well
100 ft.
100 ft.
100 ft.
Nonpublic drinking water well
100 ft.
50 ft.
50 ft.
Public drinking water spring or surface water
								  measured from the ordinary high-water mark
200 ft.
200 ft.
100 ft.
Nonpublic drinking water spring or surface water
								  measured from the ordinary high-water
								  mark1
100 ft.
50 ft.
50 ft.
Nonpublic, in-ground, drinking water containment
								  vessel3
20 ft.
10 ft.
10 ft.
Pressurized water supply line or easement for
								  water supply line
10 ft.
10 ft.
10 ft.
Closed geothermal
								  loop4 or pressurized nonpotable water
								  line
10 ft.
10 ft.
10 ft.
Decommissioned well (decommissioned in accordance
								  with chapter 173-160 WAC)
10 ft.
N/A
N/A
Surface water measured from the ordinary
								  high-water mark
100 ft.
50 ft.
10 ft.
Building foundation/in-ground swimming
								  pool
10 ft.
5 ft.
2 ft.
Property or easement line
5 ft.
5 ft.
N/A
Lined5 stormwater
								  detention
								  pond6
Down-gradient7:
30 ft.
N/A
N/A
Up-gradient7:
10 ft.
N/A
N/A
Unlined8 stormwater
								  infiltration pond6 (up or
								  down-gradient)7
100 ft.
50 ft.
10 ft.
Irrigation canal or irrigation pond (up or
								  downgradient)
100 ft.
50 ft.
10 ft.
Interceptor/curtain drains/foundation
								  drains/drainage ditches
Down-gradient2:
30 ft.
5 ft.
N/A
Up-gradient2:
10 ft.
N/A
N/A
Subsurface stormwater infiltration or dispersion
								  component6
Down-gradient7:
30 ft.
10 ft.
N/A
Up-gradient7:
30 ft.
10 ft.
N/A
Other site features that may allow effluent to
								  surface
Down-gradient2:
30 ft.
5 ft.
N/A
Up-gradient2:
10 ft.
N/A
N/A
Down-gradient cuts or banks with at least 5 ft.
								  of original, undisturbed soil above a restrictive layer due to a structural or
								  textural change
25 ft.
N/A
N/A
Down-gradient cuts or banks with less than 5 ft.
								  of original, undisturbed soil above a restrictive layer due to a structural or
								  textural change
50 ft.
N/A
N/A
Soil dispersal components serving a separate
								  OSS
10 ft.
N/A
N/A
1 If surface water is used as a
					 public drinking water supply, the designer shall locate the OSS outside of the
					 required source water protection area.
2 The item is down-gradient when
					 liquid will flow toward it upon encountering a water table or a restrictive
					 layer. The item is up-gradient when liquid will flow away from it upon
					 encountering a water table or restrictive layer.
3 Any in-ground containment
					 vessel used to store drinking water.
4 A network of underground
					 piping carrying fluid under pressure used to heat and cool a structure.
5 Lined means any component that
					 has the intended function of detaining the stormwater with no intention of
					 dispersal into surrounding soil.
6 OSS components take precedence
					 in cases of horizontal setback conflicts between OSS and stormwater
					 components.
7 Down-gradient means that
					 subsurface water flows toward and is usually located lower in elevation.
					 Up-gradient means subsurface water does not flow toward and generally flat, or
					 flows away from and generally located higher in elevation.
8 Unlined means any component
					 that has the ability to or intended function of infiltrating the
					 stormwater.
(2) When
				  conditions indicate a greater potential for contamination or pollution, the
				  local health officer may increase the minimum horizontal separations. Examples
				  of such conditions include, but are not limited to, excessively permeable
				  soils, unconfined aquifers, shallow or saturated soils, dug wells, and
				  improperly abandoned wells.
(3) The
				  local health officer may allow a reduced horizontal separation to not less than
				  two feet from where the property line, easement line, or building foundation is
				  up-gradient.
(4) The local health
				  officer may require an applicant to demonstrate the OSS meets (a), (b), or (c)
				  of this subsection when determining if a horizontal separation to a minimum of
				  75 feet between an OSS dispersal component and a water well, spring, or surface
				  water that is not a public water source is allowed:
(a) Adequate protective site-specific
				  conditions, such as physical settings with low hydrogeologic susceptibility
				  from contaminant infiltration. Examples of such conditions include evidence of
				  confining layers, an aquatard that separates potable water from the OSS
				  treatment zone, excessive depth to groundwater, down-gradient contaminant
				  source, or outside the zone of influence; or
(b) Design and proper operation of an OSS
				  with enhanced treatment performance beyond that accomplished by meeting the
				  vertical separation and effluent distribution requirements described in Table
				  VI in WAC
				  246-272A-0230; or
(c) Evidence the OSS satisfies the
				  requirements of (a) and (b) of this subsection.