(1) The design engineer shall design the LOSS and verify it is installed in compliance with the minimum horizontal setbacks shown in Table 3 of this section.

(2) The design engineer shall increase the separation distance between the LOSS and a public drinking water well, spring, or surface water supply if required by the water purveyor's source water protection program, prepared under chapter 246-290 WAC, Group A public water supplies.

(3) The department may require greater horizontal setbacks than the minimum values shown in Table 3 when needed to protect public health and the environment. Such areas include, but are not limited to, those with:

(a) Highly permeable soils;

(b) Unconfined aquifers;

(d) Shallow soils;

(e) Saturated soils; and

(f) Hand-dug or improperly abandoned wells.

(4) The department may approve a sewer line placed less than ten feet from a water line only:

(a) With the written approval of the owner of the water line; and

(b) When the water line is protected from leakage and contamination consistent with the department of ecology "Criteria for Sewage Works Design," August 2008, or the department of ecology and department of health publication "Pipeline Separation Design and Installation Reference Guide," July 2006.

Table 3: Minimum Horizontal Setbacks

Items requiring setback		From edge of drainfield and reserve area	From sewage tank and distribution box	From building sewer, and nonperforated distribution pipe
Well or suction line		100 ft.	50 ft.	50 ft.
Public drinking water well		100 ft.	100 ft.	100 ft.
Spring used as a drinking water source		200 ft.	200 ft.	100 ft.
Surface water (measured from ordinary high water mark)		100 ft.	50 ft.	10 ft.
Pressurized water supply line		10 ft.	10 ft.	10 ft.
Decommissioned well: Decommissioned according to chapter 173-160 WAC		10 ft.	N/A	N/A
Lined stormwater pond located:			.
•	Down-gradient from LOSS component:	75 ft.	10 ft.	10 ft.
•	Up-gradient from LOSS component	30 ft.	10 ft.	10 ft.
Unlined stormwater pond (up or down-gradient from the LOSS component)		100 ft.	50 ft.	10 ft.
Building foundation and in-ground swimming pool located:
•	Down-gradient from LOSS component	30 ft.	5 ft.	2 ft.
•	Up-gradient from LOSS component	10 ft.	5 ft.	2 ft.
Property or easement line		5 ft.	5 ft.	N/A
Interceptor, curtain drains, foundation drains, lined drainage ditches located:
•	Down-gradient from LOSS component	30 ft.	5 ft.	N/A
•	Up-gradient from LOSS component	10 ft.	N/A	N/A
Other site features that may allow effluent to surface located:
•	Down-gradient from LOSS component	30 ft.	5 ft.	N/A
•	Up-gradient from LOSS component	10 ft.	N/A	N/A
Down-gradient cuts or banks with at least 5 ft. of original, undisturbed soil above a restrictive layer		25 ft.	N/A	N/A
Down-gradient cuts or banks with less than 5 ft. of original, undisturbed, soil above a restrictive layer		50 ft.	N/A	N/A
Down-gradient subsurface stormwater infiltration or dispersion component		30 ft.	N/A	N/A
Up-gradient subsurface stormwater infiltration or dispersion component		100 ft.	N/A	N/A
Other adjacent drainfields, including individual OSS beds or dispersal sectors		10 ft.	N/A	N/A

PDFWAC 246-272B-06050

Horizontal setbacks.