GSI Construction Inspection Requirements

The City of Seattle requires special inspections for bioretention facilities installed in the public right-of-way that will become assets of the City.

This page describes the special inspection program for such facilities and explains the responsibilities of the applicant, their contractor, and their Bioretention Facilities Special Inspector(s).

Special Inspectors inspect components of bioretention facilities that are critical to:

  • Safety
  • Function
  • Performance

They also make sure bioretention facilities comply with Street Improvement Permitting (SIP) plans approved by the Seattle Department of Transportation (SDOT).

The applicant selects and pays the Special Inspector, but the Special Inspector provides inspection information to the City as an authorized deputy of Seattle Public Utilities’ Inspectors.

Special inspections for non-bioretention facility elements shown on the SIP plans are not included here. For construction inspection of other green stormwater infrastructure (GSI), including rain gardens and/or pervious concrete sidewalks in the right-of-way, contact the SDOT Street Use Inspector.

The following steps outline the process for special inspection of bioretention facilities in the public right-of-way and transfer of the constructed facilities to the City of Seattle:

Step 1: The Bioretention Facilities Special Inspector reviews this Client Assistance Memo (CAM) for qualifications and responsibilities of all parties, reporting requirements, monitoring requirements, close out letters, and fees and charges.

Step 2: During construction, the Bioretention Facilities Special Inspector compiles, observes, documents and reviews construction activities to complete the documentation noted in Step 3.

Step 3: When construction is complete, the Special Inspector submits to the SDOT Street Use Inspector:

Step 4: The SDOT Street Use Inspector forwards documentation noted in Step 3 to SPU Asset Management

Step 5: Upon SPU’s approval of Step 3 documentation and in coordination with SDOT’s final closeout of the Street Improvement Permitting (SIP) plan, the bioretention facility asset is transferred to the City.

Depending on the size and type of the bioretention facility requiring inspection, Bioretention Facilities Special Inspectors may include a civil engineer, landscape architect (LA) and/or geotechnical engineer/hydrogeologist (Geotech).Special Inspectors must have relevant professional qualifications and experience to perform the inspections.

Civil, Landscape, and Geotechnical/Hydrogeologist Special Inspectors must be licensed in the State of Washington and have:

  • At least four years of employment as a licensed professional in their discipline
  • At least four years of experience with design and/or construction of bioretention facilities

The Civil Special Inspector must be the Engineer of Record (EOR) for the SIP plans for the project. The on-site Civil Inspector may be an Engineer-in-Training (EIT) or other experienced inspection professional working under the direct supervision of the Civil Special Inspector.

The Landscape Special Inspector must be the Landscape Architect of Record for the SIP plans for the project. The on-site Landscape Inspector may be a landscape designer or other experienced inspection professional working under the direct supervision of the Landscape Special Inspector.

Geotechnical/Hydrogeologist Special Inspectors must be the Geotechnical Engineer of Record or the Hydrogeologist of Record for the project, respectively. The on-site Geotechnical/Hydrogeologist Special Inspector may be an Engineer-in-Training (EIT), Geologist-in-Training (GIT) or other experienced inspection professional working under the direct supervision of the Geotechnical/Hydrogeologist Special Inspector.

When special inspections are required for the bioretention facilities shown on the SIP plans, the SDOT SIP reviewer notifies the applicant during the SIP plan review/permit application process.

  • Contracting with and paying the Bioretention Facilities Special Inspectors to perform inspections during construction (see section Checklist of Elements for Special Inspection of Bioretention Facilities).*
  • Notifying the Bioretention Facilities Special Inspectors of the schedule for the SDOT SIP pre-construction meeting and for construction activities that require special inspection
  • Ensuring that the Special Inspectors perform the required inspections (in the event that the applicant has designated the contractor or another representative to provide notification)

* To prevent a conflict of interest, Special Inspectors may not be employed or paid by the contractor unless the applicant is also the contractor.

The applicant’s contractor is responsible for:

  • Attending the SDOT SIP preconstruction meeting
  • Knowing which special inspections are required for the project
  • Performing the work according to SDOT-approved SIP plans
  • Coordinating with the applicant to notify the Special Inspectors when inspections are needed
  • Making the area or items to be inspected available to the Special Inspectors

General Responsibilities
Each Bioretention Facilities Special Inspector is responsible for:

  • Knowing the contents of the approved plans in their discipline
  • Understanding which elements they are responsible for reviewing during construction as described in the section Checklist of Elements for Special Inspection of Bioretention Facilities
  • Attending the SDOT SIP pre-construction meeting with the applicant, the lead design professional, the contractor, and SPU and SDOT representatives

The purpose of the SDOT SIP pre-construction meeting is to discuss aspects of the construction that may:

  • Pose particular risks
  • Need special attention
  • Cross the lines of separate disciplines

Each Special Inspector should be prepared to highlight the most critical issues in their area of inspection during the pre-construction meeting.

Inspection and Reporting Requirements
The Special Inspector must:

  • Observe the construction
  • Confirm compliance with the SDOT-approved SIP plans

The Geotechnical Special Inspector must also observe the construction for compliance with the recommendations in the geotechnical report.

The Special Inspector(s) must report all irregularities, substitution of materials and code violations to:

  • The contractor for correction
  • The responsible registered design professional
  • SPU

The SDOT SIP permit number must be included on all reports and project correspondence with SDOT and SPU.

Final Letter for Closing Out Special Inspections upon Construction Completion
When construction is complete, the Bioretention Facilities Special Inspectors must each submit a letter that:

  • States that the completed project substantially complies with SDOT-approved SIP plans and permit requirements.
  • Highlights any issues that were encountered during construction, along with their resolution.

The level of detail in the letter depends on the complexity of the project and the number of elements that were inspected (as identified in the section Checklist of Elements for Special Inspection of Bioretention Facilities).

If the project included a Geotechnical/Hydrogeologist Report, then the letter from the Bioretention Facilities Special Inspector responsible for reviewing the soil conditions must also confirm that the completed project substantially complies with recommendations in the Geotechnical/Hydrogeologist Report, as applicable.

The final letters must be signed and stamped by the responsible Bioretention Facilities Special Inspectors and then submitted to SDOT Street Use Inspector, who will forward letters to SPU.

SDOT Street Use Inspectors will not approve the project until SPU reviewers have approved the final letters.

The Bioretention Facilities Special Inspectors must be paid by the project owner or the owner’s agent, not the contractor. SPU will not enforce the terms of any contract between the Special Inspectors and the project owner.

This table outlines a checklist of information that shall be reviewed by the Bioretention Special Inspector during construction of bioretention facilities. The column titled “Possible Discipline(s) Qualified to do Inspection” denotes which licensed professional (with past design/construction experience) could do the inspection. If changes are made during construction from the approved plans, the Special Inspector must document reason for change and obtain approval of the change from SDOT and SPU.

Description of Elements for Bioretention Special Inspection Visible Discipline(s) Qualified to do Inspection
EOR LA Geotech
Temporary Erosion and Sediment Control (TESC) measures were in place during construction to protect bioretention facilities from offsite erosion or sedimentation from start of excavation through completion of construction. X X X
Native and subsurface soil conditions are as expected, consistent with assumptions used for the facility’s design (e.g., soil bearing, no or minimal perched groundwater seepage), and consistent with the findings from the Geotechnical Design Report. No design modifications were needed to address soil conditions.     X
Native soil infiltration rate and/or conditions (based on observations and/or review of field tests as applicable) are consistent with design assumptions for providing shallow infiltration or deep infiltration (as applicable to project design).     X
Location of bioretention facility is consistent with plan.
  • Maximum design ponding depth of bioretention cell is consistent with plan.
X X  
Bioretention cells adhere to the following:
  • Graded side slopes not steeper than noted on plans.
  • Cells shape, lengths, bottom widths are in accordance with plan.
  • A level area width (adjacent to curb/sidewalk edge) exists at top of cell slope, as in plan.
X X  
Presettling zone/cell adheres to description in plan. The area draining to presettling zone/cell is consistent with design assumptions or has been adjusted to accommodate changes made during construction. X X  
Pipes daylighted into bioretention cell adhere to plan:
  • Pipe type and location is consistent with plan.
  • Pipe outlet is consistent with plan (e.g., precast pad, cobbles, boulders, if applicable).
  • Pipe end is beveled as shown on plan.
Plant palettes:
  • Planting zones and palettes (including species) adhere to plan.
  • Placement of new street trees within or adjacent to bioretention cell was consistent with plan.
Bioretention swales drain down as expected per design based on observations and/or review of tests.
  • If stagnant water was observed during construction (such as water not draining after cell was watered/irrigated or after rain had stopped), confirm that a cause was determined and addressed (for example, observe if bioretention soil was remediated for over compaction and/or was removed, replaced, and replanted).
If bioretention systems were contaminated with construction stormwater/debris during construction, confirm that drain system was remediated or reconstructed. X X X
Storm drain structures adhere to plan:
  • Structures are set at correct elevations and location, per plan.
  • Type matches the type shown on plan.
  • Grate and frame match what is shown on plan.
  • Maintenance-access opening is oriented as described in plan.
Flow into and out of bioretention cell is not impeded:
  • Drain curb cut type is as it is described in plan, and follows details.
  • Plants and trees do not block drain curb cuts.
  • Cobbles do not block drain curb cuts.
  • Miscellaneous utilities/structures (e.g., irrigation heads, meter boxes, valves, etc.) do not impede flow through drain curb cut.
  • Positive grade is provided through curb cut and along flow path (e.g., the cobbles are set low).
  • Overflow/outlet is constructed as per plan.
  • Special Inspector observed the flow tests through drain curb cuts to ensure water in gutter/street sheet flows towards the curb cut and into cell, and does not bypass curb cut.
Underdrain System
  • Pipe material is per plan
  • Alignment of pipe slots is per plan.
  • Location of slotted and solid wall pipe is per plan.
  • Underdrain pipe maintenance access structure (MH, CB or Cleanout) is installed per plan.
  • Bedding and backfill is per plan.
  • Observation Port cleanout is per plan.
X   X
  • Liner is installed according to plan (e.g. accurate extents, anchored ends and sides, overlapped seams, welded seams if liner should be water tight, etc.).
  • Material matches what is shown on plan.
X   X
  • Material matches what is shown on plan.
  • Location, elevations, and dimensions is consistent with plan.
X X  
Deep infiltration systems (such as screen wells, drilled drains, pit drains, dug drains, infiltration trenches, and associated deep infiltration infrastructure) have been installed and tested per specifications and plans, and are ready to accept infiltration.     X
Temporary Flow Diversion measures removed post-establishment
  • Street and sidewalk adjacent and upstream of cells have been cleared of debris.
  • Pipes conveying flow to cells are not capped.
  • Blockage at curb cuts has been removed.
X X  

Public Utilities

Andrew Lee, General Manager and CEO
Address: 700 5th Avenue, Suite 4900, Seattle, WA, 98104
Mailing Address: PO Box 34018, Seattle, WA, 98124-5177
Phone: (206) 684-3000

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Seattle Public Utilities (SPU) is comprised of three major direct-service providing utilities: the Water Utility, the Drainage and Wastewater Utility, and the Solid Waste Utility.