bld20140871-Harter-ADU-E3.pdf
CITY OF EDMONDS
PLAN REVIEW COMMENTS
ENGINEERING DIVISION
(425) 771-0220
City Website: www.edmondswa.gov
DATE:January 7, 2015
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
Review 3 –January 7, 2014
1)ok
ok
2)
3)ok
January 7, 2014 –Thank you for relocating the infiltration system into a location with
4)
suitable soils. The proposal includes 4 trenchesside by side, each 2-feet in width. City
handout E72B –Low Impact Development StormwaterBMP’s states “One pipe per
trench. If multiple trenches are used, the spacing shall not be closerthan 10-feet,
measured on center”. According to the City’s stormwater engineer, more recentguidance
would allow for trench spacing at 6-foot on center.Alternatively, the infiltration system
could be modeled by an engineer as an 18’x 8’facility to confirm that it meets standards.
Please reviseand resubmitplans and documents accordingly.
December 8, 2014 –Thank you for submitting the infiltration evaluation prepared by Robinson
Noble and dated 11/13/2014. 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.
9/24/2014 comment -The proposed improvements appear to create more than 2000 square feet
of new impervious surface area. City stormwaterregulations 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 Managementsection 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.
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