bld20080847-SWM compliance review.pdf
CITY OF EDMONDS
CIVIL PLAN REVIEW COMMENTS
ENGINEERING DIVISION
(425) 771-0220
City Website: www.edmondswa.gov
DATE:
November 2, 2015
TO:
Barry Talkington–btalkington@barghausen.com
Tom Barghausen –tbarghausen@barghausen.com
FROM:
JeanieMcConnell, Engineering Program Manager
jeanie.mcconnell@edmondswa.gov
Jerry Shuster, Engineering Stormwater Program Manager
Jerry.shuster@edmondswa.gov
RE:
Stormwater Compliance Review –permit #: bld20080847
Project: Willowdale Townhomes
th
Project Address: 20730 –76AveW
The City received a Stormwater Analysis for Willowdale Townhomes,prepared by
Barghausen Consulting Engineers, Inc., and dated October 8, 2015.
As previously discussed, given there is noactive building permit application on file with the
City, review of the report provides no vesting or approvalnow or to any future building
permit application(s).The subject review has been performed in an effort to confirm
Barghausen’s stormwater calculations are consistent with City stormwater codes that are
currently in effect.
The report shows that the existing stormwater can be in made to comply with current
stormwater code requirements as long a number of conditions apply. These include but
are not limited to:
There will be no more than a total of 0.75 acres of impervious surface area for the
total project.
All of the runoff from the 0.75 acres is directed to the detention vault system.
The existing outlet structure for the detention vault system is modified as described
in the report.
No new or replaced pollution generating impervious surface area is added to the
project.
The parameters used in the WWHM2012 modeling are representative of current
conditions or conditions that can be achieved though retrofitting.
A number of the parameters used in the WWHM2012 modeling of the detention vault
system rely on a 2013 “as-built” survey.Please address the following questions regarding
this survey:
For the westernmost vault, the survey says the following: “Bottom vault =431.60
1.
Top of vault = 438.82 Water Level =7.75.”If the waterlevel is at 7.75 ft, it would be
over the top of the vault.Please reconcile.
There is no survey information for the invert of the outlet pipe from the westernmost
2.
vault, therefore, it is not possible to verify that the live storage depth is 4.9 feet as
use in the modeling.
Provide evidence for assuming the easternmost vault has a live storage volume of
3.
4.9 ft.
For the 54” dia. control structure manhole, the survey says: “8 gate valve (out)
4.
433.80±.” Is this the shear gate? Shouldn’t it be 12”?Why doesn’t’ the 18 “ dia.
inlet pipe from north show up on the survey? It is difficult to understand which pipes
are inlets to the control structure and which are outlets. Please reconcile.
Additional comments
Provide the amount of impervious area, if any, thatbypasses the detention system.
5.
Since the control structure will need tobemodified to meet current flow control
6.
standards, use current Engineering Standard Detail E5.4for the new control
structure:http://www.edmondswa.gov/engineering-standards/section-5-storm-
drainage.html
Prior to final approval, all stormwater facilities (filters, CBs, vaults, control
7.
structures, etc.) shall be brought up to current maintenancestandards (2005
Ecology Stormwater Management Manual for Western Washington, Volume V,
Section 4.6).
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