bld20140871-Harter-ADU-E2.pdf
CITY OF EDMONDS
PLAN REVIEW COMMENTS
ENGINEERING DIVISION
(425) 771-0220
City Website: www.edmondswa.gov
DATE:December 8, 2014
TO:Riverside Architecture
Jeff Price
jeff@riverarch.net
FROM:Jeanie McConnell
Engineering Program Manager
RE:Plan Check #:BLD20140871
th
Project& Address :Harter –9630–238St SW
During review of the above noted application, it was found that the following information,
corrections, or clarifications are needed. Please redline plans or submit three (3) sets of revised
plans/documents with a written response to each of the items below to a Permit Coordinator.
City of Edmonds handouts and standard details can be referenced on the City website under Permit
Assistance.
Review 1 –September 24, 2014
Review 2 –December 8, 2014
1)ok
December 8, 2014 –Thank you for including the impervious surface area chart on the plans. Canyou
2)
please provide an explanation as to why the entireproposed 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.
9/24/2014 comment -Please provide the impervious surface calculations as shown on the plans in
the table format provided below.
3)ok
December 8, 2014 –Thank you for submitting the infiltration evaluationprepared by
4)
Robinson Nobleand dated 11/13/2014.The report indicates test pits were excavated to
depths of 4.0-6.0 feet below the groundsurface. Test pit 1looks to have the most suitable
soils for infiltration. Test pits 2, 3 and 4showed 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 belowthegroundsurface.
Department ofEcology 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.
Woulditbe possible to site the infiltration gallery in thevicinity of Test Pit 1? This would
allow for infiltration in the most suitable soils as well as provide the necessary separation
from thesteep slope areas.
9/24/2014 comment -The proposed improvements appear to create more than 2000 square feet
of new impervious surface area. City stormwater regulations went into effect in 1977. Per
Edmonds Community Development Code 18.30, sites that create 2000sf or more impervious
surface area from 1977 forward shall provide stormwater management. Please refer to the
City’s stormwater handouts (E72 series)found in the Stormwater Management
section on the
City website.
a.Low impact development techniques are encouraged to be used whenever feasible.
b.Stormwater management systems designed for impervious surface areas greater than
5000sf shall be designed by a licensed engineer.
c.Two downspout infiltration systems have been shown on the plans, but design
calculations, including infiltration pit test information, has not been provided to support
the sizing.
d.Indicate on the plans how on site impervious surface areas will be collected and
discharged to the stormwater management system(s).
5)ok
6)ok
7)ok
8)ok
Please contact me at 425-771-0220 or by e-mail atJeanie.mcconnell@edmondswa.govif you have
specific questions regarding these plan corrections.
Page 2of 2