20141217150920396.pdf�n
»n>itiu9�timA111a0rWNa11@m
ImOBBWWIW
ommBttW� 11
Likq.
C"l�
December 16, 2014
Jeanie McConnell, Engineering Program Manager
City of Edmonds, Engineering Division
121 5th Ave North, Second Floor
Edmonds, WA 98020
C&A Proj # 117-002-14
RE: Harter Residence ADU 9630 23811, St SW — Plan Check #BLD20140871
Response to 2nd Plan Review Comments
Dear Ms. McConnell:
This letter presents our response to the Engineering Division Plan Review Comments for the
subject project dated December 81h, 2014. The responses below correspond to each of the
comments in the December 80h letter.
ENGINEERING DIVISION COMMENTS
2. Thank you for including the impervious surface area chart on the plans. Can you please
provide an explanation as to why the entire proposed impervious surface area is not
shown to be mitigated? The chart indicates 2,610sf new impervious surface area and
2,500sf of area being mitigated by LID techniques
Response: The drivewaygrades slope down toward the street. The runoff at the north
end of the driveway is located within the 238th right-of-way, and cannot be captured
and routed to the on-site LID facilities. Therefore this runoff is not mitigated by LID
techniques.
3. Thank you for submitting the infiltration evaluation prepared by Robinson Noble and
dated 11/13/14. The report indicates test pits were excavated to depths of 4.0-6.0 feet
below the ground surface. Test pit 1 looks to have the most suitable soils for infiltration.
Test pits 2, 3 and 4 showed glacial till at varying depths from 2ft-6ft. The Robinson
Noble report recommends infiltration systems be installed at least 1 -foot above the very
dense glacial till, at approximately 3 -feet below the ground surface. Department of
Ecology guidance states the base of all infiltration trenches shall be greater than or equal
to 5 -feet above the bedrock (or hardpan).
In addition, it is noted there are slopes of 15-40% within and adjacent to the site. DOE
guidance states infiltration facilities should be set back from slopes such as this by at
least 50 -feet.
Would it be possible to site the infiltration gallery in the vicinity of Test Pit 1? This
would allow for infiltration in the most suitable soils as well as provide the necessary
separation from the steep slope areas.
Response: The infiltration trenches have been consolidated at the location of Test Pit 1
and will collect and mitigate site and roof runoff for the project. See revised plans.
Harter Residence ADU
Response to 2nd Review Comments 2 December 16, 2014
Based on our email correspondence with you regarding these issues, we understand that our
revisions address your comments. We have submitted revised plans and TIR for your approval.
If you have any questions regarding this response, please call me at (206) 484-3495.
Regards,
Cecil & Associa'tes, LLC '
Roger J. Cecil, P.E.