Tier 1, Tier 2, and Tier 3 greywater irrigation systems shall be designed and installed to meet the minimum horizontal setback requirements specified in Table I.
Table I
Minimum Horizontal Setbacks | | From edge of subsurface irrigation components | From tank and other system components |
| Building foundations | | | | |
| | Down-gradient1: | 10 ft. | | N/A | |
| | Up-gradient: | 2 ft. | | N/A | |
| Property or easement line | 2 ft. | | 2 ft. | |
| Pressurized water supply line/public water main | 10 ft. | | 10 ft. | |
Interceptor/
curtain drains/drainage ditches | | | | |
| | Down-gradient: | 30 ft. | | N/A | |
| | Up-gradient: | 10 ft. | | N/A | |
| In-ground swimming pool | 10 ft. | | 5 ft. | |
| Spring or surface water measured from the ordinary high-water mark2 | 100 ft. | | 50 ft. | |
| Well or suction line | 100 ft. | | 50 ft. | |
| Public drinking water well | 100 ft. | | 100 ft. | |
| Public drinking water spring measured from the ordinary high-water mark | 200 ft. | | 200 ft. | |
| Decommissioned well (decommissioned in accordance with chapter 173-160 WAC) | 10 ft. | | 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 | |
| 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 | |
| On-site sewage system primary and reserve areas | 10 ft. | | N/A | |
| 1 | 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. |
| 2 | If surface water is used as a public drinking water supply, the greywater system must be located outside of the required source water protection area. |
[Statutory Authority: RCW 90.46.015. 11-02-011, ยง 246-274-405, filed 12/28/10, effective 7/31/11.]