1326_001May 20, 2019
Strobl Design
Jacob Strobl
PO Box 20764
Seattle, WA 98102
Jacob@strobldesign.com
(206)661-3622
Zach Richardson, PE
Stormwater Engineer
City of Edmonds
(425) 771-0220
Re: Plan Check: BLD2019-0116
Engineering Review Comments
Dear Zach,
Please see the below responses to the correction notice dated March 5, 2019 for 9527 190th PI SW, plan
check number BLD2019-0116.
Correction 41 Through #4
Response:
See response from civil engineer.
These items resolve the plan corrections for the project. Please let me know if you have any questions.
Best Regards,
Jacob Strobl
C GM
ENGINEERING
May 30, 2019
Zach Richardson
City of Edmonds
121 5th Ave N
Edmonds, WA 98020
civil & structural
engineering & planning
RE: Permit Number: BLD20190116
Project Name: Aw Residence
Project Address: 9527 190th PL W
Dear Mr. Richardson,
Itemized below is our response to the review comments dated March 5, 2019 for the above referenced
project. Our response appears in bold.
Stormwater Review:
Review Comments
General: It is not clear that sufficient testing was done to establish a measured infiltration rate as
required by ECDC 18.30 and 2014 SWMMWW; review Edmonds Addendum Appendix B and revise
geotechnical information as needed to ensure infiltration rate is measured and adjusted consistent
with the requirements.
a. It appears that on -site testing was not performed, and grain -size analysis was not performed
and therefore it does not appear that a site -specific infiltration rate was measured.
A stormwater infiltration letter has been provided by Nelson Geotechnical Associates.
NGA performed a small-scale Pilot Infiltration Test and determined a design infiltration
rate. This report can be found in Section V in the drainage report.
b. It is not clear that the stipulated correction factors have been applied to the measured rate.
See Stormwater Infiltration Letter by NGA in Section V of the drainage report.
c. The report does establish a medium SAND at the infiltration layer (EP2 does note gravel but
appears further from the trench than EP1 & EP3 which do not note any gravel) which, per
the prescriptive sizing for downspout full infiltration (Edmonds Checklist #13), would suggest
more like 150' of typical trench is required (75' at the doubled -depth proposed): 4,986 /
1000 X 30 = 150'.
The infiltration trench has been re -designed per the LID Performance Standard with a new
infiltration rate from NGA. See Section III of the drainage report for more about the LID
Standard and Section V for infiltration letter from NGA detailing infiltration rate and soil
logs.
250 4th Avenue South, Suite 200
Edmonds, WA 98020
ph.425.778.8500 1 f.425.778.5536
www.cgengineering.com
Aw Residence
Comment Response
May 30, 2019
Page 2 of 2
2. Report: Update report text to acknowledge the bypass flows from the ROW portion of driveway and
state how they are mitigated (i.e. oversized infiltration trench, etc.).
Report updated. See Section III.
3. C3.1: Show/list the existing invert elevation at the connection CB in the south-west corner.
Existing invert elevation added.
4. C3.1: Label/callout the roof and footing stub connection points (where it joins the lines surrounding
the structure) as "Connect roof drains only" and "Connect footing drain only" as appropriate.
Callouts added.
If you have any questions or comments regarding the responses to this review, please do not hesitate to
call.
Sincerely,
CG En ineering
Jared Underbrink, PE
Project Manager
C 4m
ENGINEERING
250 4th Avenue South, Sulte 200
Edmonds, WA 98020
ph.425.778.8500 1 f.425.778.5536
www.cgengineering.com