Civil_Storm Water Comment Response Letter_2019.06.27.pdfJune 27, 2019
Kernen Lien
Environmental Programs Manager
City of Edmonds
121 5t" Avenue North
Edmonds, Washington 98020
kernen.lien@edmondswa.gov
Re: Storm Water Review Comments: Engineering Division
Edmonds Waterfront Re -Development
Application Nos. bld20181654
Type: 28 — Fill/Grade/Excavate
Dear Kernen:
402 15th Avenue East
Seattle WA 98112-4599
206 329 8300
environmental 206 329 5494 fax
WORKS www.eworks.org
Community Design Center
Environmental Works has reviewed the City of Edmonds' list of Storm Water Review Comments
dated February 19, 2019. Attached is the final Bid Set for the project, which includes revisions to
respond to all Civil Plan comments received to date.
Below are comments from the Engineering Division's memorandum with responses in bold.
CIVIL PLAN REVIEW COMMENTS (from Zach Richardson, dated February 19, 2019) &
RESPONSES:
1. General: The reviewer and design engineer have worked through several pipe capacity
and conveyance calculation concerns which were addressed after these documents were
formally submitted for review; ensure all previously coordinated revisions are incorporated
into documents included with the resubmittal.
Previously coordinated revisions are included in resubmittal documents.
General: It is still unclear how the edge of pavement and bioretention walls will interact;
the detail and plan view do not appear entirely consistent on location of wall/limits of
paving, curbing appears to be used inconstantly along this edge of pavement, and curb
cuts are not currently called out but curb appears (in detail) to create a barrier to surface
flowing entering the system. Update or clarify as needed.
Curb cut call outs added and clarified on drawings CS2.0 and CS4.0.
General: Bio-retention areas #1 & #2 were modelled as a full depth for a width of 4' but
are only shown with a 3' bottom that extends to full depth; update calculations or detail, or
provide additional support to ensure modelling matches actual proposed BMP
configuration as appropriate.
Detail revised to show full bottom width that matches bottom width shown on CS4.0 and
calculations.
4. CS2.0: List top of wall elevations for the bioretention walls (and any curb cuts) and
ensure positive drainage and 6" freeboard can be maintained.
Top of wall elevations for bioretention walls are to be 6 inches above adjacent surface
grade shown on CS2.0. Curb cut elevations shown on CS2.0.
5. CS2.0: Add callout for top of rock/boulder elevation for the boulders projecting above
the walkway near the north beach.
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Sheet note #2 added. Boulders along ramp to project min 12 inches above promenade
walkway surface.
6. CS2.0: It appears that line work for the top of bioretention area #3 may not be the 3'
minimum to provide a 3:1 slope for 1' of rise, but it appears the surrounding grain may
be sufficient to contain the bioretention volume. Update line work or provide addition
grading points to confirm that grading for the bioretention area can achieve the 6"
freeboard at 3:1 max slope.
Line work updated to show 3:1 slope limits
7. CS2.0: Show line work for top/grading associated with bioretention area # 4.
Line work updated to show 3:1 slope limits. Additional grading points added for
clarification.
8. CS2.0: A slope of T.6%" is shown south-west of the north driveway which
would be lower than typical minimum for asphalt surfacing, but it appears the
slope is not aligned to the low point and may be sufficient when correctly
aligned; update grading or correct slope callout as needed.
Slope arrow and associated slope revised.
CS3.0: Add a callout for the actual, or minimum, separation at the water service
crossing near 11+78
Minimum separation callout added.
10. C4.0: For each bioretention area:
a. Provide an identifying number (corresponding with those used in the
drainage report)
Identifying number matching drainage report added.
b. List a minimum bottom area
Minimum bottom area added for each bioretention location.
c. List a minimum top elevation
Minimum top elevation added for each bioretention location.
11. CS4.1: Modify bioretention planter detail to:
a. Revise the 12" max dimension to 12" min, and adjust freeboard line to
correct location at curb cuts (or where surface flow enters).
Shown 12" max dimension is correct. Water ponding depth is shown as 6"
and the required 6" of freeboard will result in a maximum depth of 12" for
the bioretention.
b. Address concerns for erosion from the potential 1' drop of entering
surface flows.
Standard curb cut detail includes splash pad of streambed cobbles. Note
added to CS4.0 referencing standard detail and increasing splash pad to
2'x2', min 12" thick.
c. Specify, or provide additional direction to the contractor, sufficient
information for them to purchase and install "bioretention soil mix".
Bioretention soil mix specified in landscaping technical specifications.
d. Show or reference a planting plan
Note added to reference planting plan.
12. CS4.1: Revise tide gate detail to be proportional (12" pipe is huge compared to
manhole, which should be 60" diameter).
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Detail revised to be proportional.
13. CS4.1: Revise tide gate manhole to be a typical Type 2 manhole with sump;
reviewer has concern that the channelized configuration will obstruct the gate
movement too easily and that allowing for some accumulation of sediment in
the sump is a necessity for long-term operation of the gate.
Tide gate manhole revised to Type 2 catch basin, 60" diameter.
14. CS4.1: It appears an additional concrete block is needed within the manhole to
mount the tide gate as proposed; consider alternate mounting configuration or
revise detail to specify the material of the blocking, any reinforcing required,
and the proposed method for adjoining the block to the basin wall (dowel bars,
epoxy, etc.)
Detail revised to specify blocking material and joining method to basin wall (dowel
bars & epoxy).
15. CS4.1: If allowable by permit, lower the rip -rap section in outfall pipe protection
detail in order to allow for some sediment/sand/debris accumulation without
impacting hydraulics, and show a minimum slope (away from the pipe) on the
rip- rap surfacing.
Rip -rap detail revised to show 2 inches of allowance for sediment/sand/debris
accumulation. Min slope added.
16. CS4.1: Provide additional direction or specification (such as minimum helical
head size or material) for the pipe anchoring as needed for the contractor to
install anchoring sufficient for the project needs at this location.
Rip -rap detail revised to show 2 inches of allowance for sediment/sand/debris
accumulation. Min slope added.
17. CS5.0: Show all areas required to be mitigated with BMP T5.13 (amended
soils) and provide detail/specification sufficient enough for the contractor to
install soils meeting the requirement.
See added sheet note on L6.0 Overall Planting Plan.
14. All soils to be applied in landscape areas shall meet BMP T 5.13 per the 2014
SWMMWW (Stormwater Management Manual for Western Washington)
Sincerely,
Nicolas Morin
Director of Landscape Architecture
206.787.1392
nmorin@eworks.org
Attachments:
A. Edmonds Waterfront Redevelopment Land Use Submittal Set with Permit Corrections -12 sheets
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