DNS RESUB1 BLD2023-1391+Applicant_Response+5.3.2024_3.35.56_PM+4236789C �
ENGINEERING
May 3, 2024
civil & structural
engineering & planning
Jerry Shuster
City of Edmonds
1215th Ave N
Edmonds, WA 98020
RE: Response on Drainage Report
Permit Number: BLD2023-1391
Project Name: Mathay Ballinger Park Improvements
Project Address: 24100 78th Place West Edmonds, WA 98026
CG Project Number:23072.001
Dear Mr. Shuster,
Itemized below is our response to the review comments dated December 21, 2023 for the above
referenced project. Our response appears in bold.
It should be noted that the project has been adjusted from the previous review. Originally the plan had
been to prepare documents in two separated phases, constructing a restroom area (under 2,000 square
feet impervious, under 7,000 square feet land disturbing) first and then preparing a Phase II accounting
for all areas, including those of Phase I. The project is now shown in its entirety, with no phasing
anticipated.
Comments on Drainage Resort. Mathv Ballinger Park. C G Eneineerine. Received November 2. 2023.
1. Section I, Page 1, Last paragraph — Remove the last sentence and substitute with a sentence that
says the site resides in the Lake Ballinger watershed; it is more relevant to the City stormwater
requirements.
Added.
2. Section I, Page 2 — It appears that the existing hard surface does not have stormwater controls
and that these hard surfaces will remain after this project is completed. As such the retrofit
requirement per ECDC 18.30.060.D.5.b.i applies.
Retrofit requirement incorporated in drainage sizing.
3. Section I, Page 6, Minimum Requirement #4 — Describe how the runoff currently leaves the site
and if that will change based on the proposed development.
Added.
250 4th Avenue South, Suite 200
Edmonds, WA 98020
ph.425.778.8500 1 f.425.778.5536
www.cgengineering.com
Mathay Ballinger Park Improvements / 23072.001
Comment Response
May 3, 2024
Page 2of2
4. Section III, Page 2- Provide exhibits that show the outline of the various areas (i.e., C, Lawn, flat;
C, Forest, Flat, etc.) used in the WWHM2012 modeling; one for the current condition and one
for the proposed condition.
More detailed area information and modeling is provided.
5. Section III, Page 1— Feasibility Review —
a. The correct citation for this project is ECDC18.30.060.D.5.b.iii.
Roofs and walkways (other hard surfaces) must be evaluated separately using the sub -list
under List No. 2.
c. There is no design information related to the proposed infiltration trenches nor refence to
the geotechnical investigation. A 0.19 in/hr infiltration rate from the geotechinical report is
very low. Infiltration trenches that that uses BMP T5.10A under Minimum Requirement No.
5 shall not be longer than 100 feet (Per Ecology Stormwater Manual) and the infiltration
rate generally should be 0.3 inch/hr or greater (approximate infiltration rate of "Loam").
Both criteria are not met in this report. If an infiltration system is used for the walkway and
other hard surfaces, it must be modeled and include the proposed slope.
The geotechnical report must verify that there is 3 feet or more of permeable soil from the
proposed final grade to the seasonal high ground water table. and at least 1-foot of
clearance from the expected bottom elevation of the infiltration trench to the seasonal high
ground water table.
The gravel infiltration trench for the roof water can be sized using method in BMP T.5.10A in
the Manual if the Geotech information in the previous paragraph is verified and the Geotech
can say the infiltration receptor is coarse sand and cobble, medium sand, fine sand, loamy
sand sandy loam, or loam soil.
Project has been revised with a trench system meeting the LID Performance Standard. The roof
downspout control method is no longer used, it is WWHM sized, and less than 100 lineal feet.
6. Stormwater Comments on the Civil Plans will be deferred until the above comments are
resolved.
Noted.
If you have any questions or comments regarding the responses to this review, please do not hesitate to
call.
Sincerely,
CG Engineering
C -IQ-J-IZ
Jared Underbrink, PE
Senior Project Manager
250 4th Avenue South, Suite 200
Edmonds, WA 98020
ph.425.778.8500 I f.425.778.5536
ENGINEERING www.cgengineering.com