Clearances and setbacks

No power pole within bioretention cell or rain garden.

5-foot (radius) level area around power poles.
No plantings except ground cover/sod within level area.

If section of underdrain pipe is slotted then provide minimum 5-foot horizontal separation between new street tree and slotted underdrain pipe.

If section of underdrain pipe is solid wall then provide minimum 3-foot horizontal separation between new street tree and underdrain pipe.

Service may be located within the bioretention cell or rain garden footprint but prefer outside due to future maintenance.

Minimize locating bioretention cell or rain garden over water service piping that would require full replacement of the water service pipe (e.g. existing galvanized iron or plastic pipe) from the meter to the water main.

Meter shall be relocated to the back of walk in a landscape area within the right-of-way (preferred) or into the sidewalk.

Provide minimum depth of cover per SPU water.

If there is an underdrain, service may be above underdrain pipe as long as minimum depth of cover is provided.

Maintain standard clearance from other utilities per Standard Plans and Specifications.

Meter/vault shall be located outside bioretention cell and rain garden.

Provide cover for water main pipe per Standard Plan 030.

Horizontal setback distance from the water main (measured from the edge of the pipe to the edge of any bioretention cell*) must be minimum of 3.5′ for water mains up to and including 12″∅ water mains. Water mains larger than 12″∅ must be evaluated and approved on a case by case basis by Seattle Public Utilities. If soil within setback is disturbed, a support plan and soil re-compaction to 95% min compaction will be required. Zone of influence of the water main is a plane form the spring line of the pipe extending down and away from the main at a 1 to 1 slope. Exceptions to the minimum 3.5′ horizontal setback must be approved by Seattle Public Utilities plan review section and water quality division.

*Bioretention cells shall be located in Landscape/Furniture Zone – the area between the roadway curb face and the front edge of the pedestrian clear zone. See 3.2 Sidewalks Design Criteria for additional guidance.

Provide settlement monitoring if construction impact is closer than 10′ to any cast iron water main and more than 5′ to any ductile iron water main. Construction impact includes breaking up pavement with heavy equipment.

See reference to requirements with SPU water department.

Provide minimum 3 feet of cover over pipe to hydrant.

Provide 4-foot level area (4-foot radius from center of hydrant).

No plantings except ground cover/sod within 4 feet of hydrant.

Not allowed within footprint of bioretention cell or rain garden.

Minimize locating bioretention cells and rain gardens at locations that would require relocating a fire hydrant since this will increase project costs.  Relocating hydrants typically requires full replacement of hydrant lateral piping to the water main.

May be located within the bioretention cell, rain garden or permeable pavement footprint but shall maintain clearances from underdrain pipes if included in the design. Maintain standard cover and clearances.

Avoid locating infiltrating bioretention cells, rain gardens and permeable pavements over existing side sewers unless the side sewer is replaced since the stormwater could flow into the pipe at a crack or joint in the side sewer.

For non-infiltrating bioretention cells or rain gardens over existing side sewers, the bioretention cell or rain garden section (including underdrain if used) shall be above side sewer.

Lined Bioretention Cells must be designed for compatibility with street tree planting standards. New bioretention cells shall not be located within 5’ of a standard proposed street tree location or within the dripline of an existing tree to be retained.

For additional guidance to locate trees within bioretention facilities, see SPU GREEN STORMWATER INFRASTRUCTURE details BTP-1 through BTP-7.

See SPU’s GREEN STORMWATER INFRASTRUCTURE Tree Lists for trees allowed by both SDOT and SPU for use in bioretention facilities.