Engineering and Storm Comments 1-Design Review.pdfDate:
To:
From:
MEMORANDUM
April 13, 2018
Mike Clugston, Associate Planner
Jeanie McConnell, Engineering Program Manager
Zachary Richardson, Stormwater Engineer
Subject: PLN20180014 — Design Review
PLN20180015 — CU for High School Campus
PLN20180016 — Variance for Light Poles
PLN20180017 — Variance for Batting Cage Setback
The comments provided below are based upon review of the application and documents
submitted for the subject application. Additional information is requested from the applicant
at this time. Please ask the applicant to respond to the following.
PLN20180015 —
No Comments
PLN20180016 —
No Comments
PLN20180017 —
No Comments
PLN20180014
— Design Review comments are as follows:
Stormwater Engineer Review:
Refer to attached plan review comments by City Stormwater Engineer, Zachary Richardson.
Please contact Zack directly at 425-771-0220 or by email at
zachary.richardson@edmondswa.gov with any specific questions you may have regarding his
comments.
General Engineering Review:
The following comments are provided by the Engineering Program Manager, Jeanie
McConnell. Please contact Jeanie directly at 425-771-0220 or by email at
Jeanie.mcconnell@edmondswa.gov with any specific questions you may have regarding his
comments.
City of Edmonds Official Street Map shows 216th St SW as a 60-ft right-of-way.
Snohomish County parcel map and the survey provided with the subject applicaton
indicate the Edmonds School District parcel extends into this 60-ft right-of-way. The
survey contains a note stating "No exception for road contained within the description.
City of Edmonds
Certainly a prescriptive easement exists across the public use". Existing 2161h St SW road
and sidewalk improvements appear to built within the "60-ft ROW" and the project
proposal appears to take setbacks from this "ROW" line. As a condition of building
permit approval, a right-of-way dedication should be recorded to clear up any right-of-
way/parcel boundary discrepancy that may exist.
2. Revise plans to show replacement of corner curb ramps at high school driveway approach
off 216th St SW.
3. Please provide a document that clearly shows easements encumbering the property in
order to confirm that none of the improvements proposed extend into the easement areas.
Informaton provided on the survey is difficult to read and it appears there are additional
easements that have not been shown on the survey. Easements referenced on City maps
and/or the survey include the following:
AFN2027844 ST 10'
AFN1994515 SS 10'
AFN1914233 ST 10'
AFN9806030206 — UTILITY and PED
Thank you.
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STO RM WATE R REVIEW COMMENTS
City of Edmonds
Engineering Division
To: Engineering Reviewer
Date: March 28, 2018
Project Name: Woodway High School Field Improvements
Permit Number: PLN2f
Address: 7600:
Review Type: Prelim )ility
Submittal Date: 3/9/2018
Reviewer: Zack Richardson, PE
City of Edmonds, Stormwater Engineer
Recommendation: I recommend that PLN20180014 be withheld until the comments
below are adequately addressed.
Review Comments:
1. It is stated in the report that areas treated with BMP T.13 (amended soils) are not
considered converted vegetative surfaces, but this is not entirely correct as noted
below; update repot/plans as needed to clarify which areas should be considered
converted and correct impacts to the design as needed.
a. For the requirements of MR #5, areas treated with BMP T5.13 do not
require further consideration for that particular requirement; other
minimum requirements, including flow control, must still be designed per
the manual.
b. Therefore, the definition of converted vegetation must be used which
speaks specifically to native vegetation:
i. Areas which are replanted with native vegetation with amended
soils, do not need to be considered converted vegetation.
ii. Any area which is not replanted with native vegetation does need to
be considered converted vegetation and compared to forested
conditions.
c. The report is correct in that run-on areas which are not disturbed by the
project (ie. not within project limits) may be modeled the same for historic
conditions and developed conditions.
2. It is not clear that the application of LID BMPs, per ECDC 18.30.060.5 and MR
#5, has been adequately addressed.
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a. The geotechnical report appears to only provide a qualitative conclusion
that soils are "slow draining"; revise report to include all information
leading to conclusion that infiltration is not recommended
i. Soils grain analysis is discussed in body of report, but results and
data do not appear to have been not been provided
b. Permeable pavements are infeasible if measured rates are below 0.3
inches per hour; provide additional information as needed to verify that
pervious pavement are feasible and should receive modelling credit as
assumed.
i. Expand text as needed to explain why "infiltration is not
recommended" but infiltration via pervious pavements is allowable.
c. As noted below, field condition is not considered application of an LID
BMPs as proposed; accordingly, assess feasibility of bioretention for the
field basin and/or expand description of infeasibility.
3. Remove all references to the field as an LID BMPs "similar to pervious
pavements"; if field is to be used as a BMP, it would need to follow the guidelines
for modelling per Part 1 of Appendix III-C.
4. It is not clear that the project areas fully meet the retrofit requirement of ECDC
18.30.060.5.b.i for MR #5.
a. Provide information and delineation of existing surfaces which may
already be mitigated by existing facilities.
b. Revise plans and report as needed to apply MR #5 to 25% of currently un-
mitigated impervious surface on the site.
5. Provide additional information for how the field detention stage -storage
information was determined for the inputs in MSGS; I understand that the
included spreadsheet calculates the total volume of the system (and is believed
to be correct in that regard), but it is unclear how the stage -storage relationship
was determined from this information.
6. The field basin detention design will retain water up to 416.80 and will result in
occasional standing water above the rim elevations of the CBs 4, 5, & 6. Updated
design as needed or update report to acknowledge and address this condition.
7. Identify each of the control structure details on F-2.5 by the corresponding CB
numbers.
8. The drainage report does not stated what the turf and infill materials will be;
explicitly state what turf and infill material will be used and address potential
water quality impacts of the material.
a. Turf material must be "lead-free", including the paint/coloring.
9. Update Figure 5 (proposed conditions model areas) to:
a. Identify and show limits of all/each bypass basin(s).
b. Identify the roofs with separate hatching and quantities than the field
surface.
c. Identify with appropriate hatching, and provide a quantity for all areas
which are to receive the amended soils treatment per BMP T5.13 (ie.
grass and landscape beds).
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d. Identify and show limits of the run-on areas which do not require
mitigation.
e. Update field footprint acreage to 2.69 (to match SF listed).
Prior Construction Approval:
The following comments were noted by the reviewer as issues that will require revision prior to
construction approval, but do not necessarily required attention prior to feasibility approval.
A. Nyoplast catch basins do not provide man/ladder access and may not be used at
locations where rim to invert measures greater than 5' (unless alternative access
is provided); revise as needed.
B. It unclear why an "underdrain" is provided around the storm chamber system; the
underdrain is connected to the control structure CB so it will detain water and
runoff will backwater the underdrain system, providing no relief from buoyancy.
a. The underdrain cannot bypass the control structure as the current location
configuration would allow flows in the detention system to flow directly to
the under drain, rather than being detained an release through control
structure.
C. The connection to CB #13 appears to have less than 2' of cover to the bottom of
pavement in a traffic rated location; revise as needed to achieve 2' minimum
cover or provide ductile iron piping.
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