BLD20161426_Tiersma Stormwater Review-1.docx
Stormwater Review
Date of Review: October 28, 2016
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File/Address:BLD20161426, 9213 224 St SW
Reviewer: Robert C. Edwards, PE, Stormwater Engineer, City of Edmonds
Background
This is classified as a Category 2 Small Site Project because it is part of a two-lot short plat with
impervious area exceeding 5,000 SF.
Category 2 Small Site Projects are subject to Small Site Minimum Requirements 1, 2, 3, 4, 5, 6, 7, 8, 9,
10, and 11.
Minimum Requirement #1 – Preparation of Stormwater Site Plan
Comments:
1. Cat 2 Small Site Projects that involve 5,000 SF or more of impervious area must be designed by a
civil engineer. Please have the Stormwater plan stamped by a Professional Engineer, licensed in
the State of Washington in Civil Engineering. Sheet A1 does not meet this requirement.
2. Please provide details, materials, sizes, and inverts of all Stormwater control features, including
catch basins, pipes, drywells, and oil separators.
3. From Sheet A1, it appears that there is a trench drain/CB near the garage. Provide pertinent
information on these features.
4. As shown, the roof/driveway drywell drains to the oil separator, rather than the oil separator
draining to the drywell.
5. The oil separator then drains to a new CB placed in the Right Of Way on the City’s MS4. As this
project has specified LID techniques, this system will be draining water from the drywell
significantly below its top elevation. Is this an overflow? If so, please provide a drainage profile
for this system.
6. Provide locations of footing/roof drains to each drywell. As drawn, it is not clear how the
Stormwater separates north from south to the respective drywells.
7. Provide specific information on catch basin within the Right Of Way, including type, frame,
grate, and connection to the City’s MS4.
Minimum Requirement #2 – Construction Stormwater Pollution Plan
Comments:
1. Provide inlet protection to existing catch basin(s) within Right Of Way adjacent to the project
site.
Minimum Requirement #3 – Source Control of Pollution
Comments:
1. The Drainage Plan states “No extraordinary measures are required….with the project below the
5,000 square feet threshold.” Previous stated, the project exceeds the 5,000 SF threshold.
Minimum Requirement #4 – Preservation of Natural Drainage Systems
Comments: None, as infiltration is specified.
Minimum Requirement #5 – Onsite Stormwater Management
Comments:
1. See comments related to this section from Minimum Requirement #1.
Minimum Requirement # 6 – Runoff Treatment
Comments:
1. See comments related to this section from Minimum Requirement #1.
Minimum Requirement #7 – Flow Control
Comments:
1. LID techniques are specified for this project. Reiterating from previous comments, for Category 2
Small Site Projects, the LID techniques must be designed by a Professional Engineer licensed in
the State of Washington in Civil Engineering.
Minimum Requirement #8 – Wetland Protection
Comments: None
Minimum Requirement #9 – Operation and Maintenance
Comments:
1. The site plan specifies two oil separators. Please provide O&M guidance for these structures with
respect to their oil control function.
Minimum Requirement # 10 – Offsite Analysis and Mitigation
Comments: None, as LID is specified
Minimum Requirement #11 – Financial Liability
Comments: None