bld20110196-Panera-E1.pdf
DATE: April 1, 2011
TO: Eric Morff
emorff@core-eng.com
FROM: Jeanie McConnell, Engineering Program Manager
Jerry Shuster, Stormwater Program Manager
RE: Application #: bld20110196
Project: Panera Bread New Restaurant
Project Address: 7929 Lake Ballinger
The following comments are provided as a very preliminary review of only the drainage portion of the
Panera Bread project proposal. The intent for providing these comments ahead of the entire project
review is to provide specific direction on the design and layout of the storm system and outline the
requirements necessary to address the downstream drainage issues.
Once a revised plan submittal has been received in response to these comments, the Engineering
Division will perform a complete review of the project.
Pursuant to Edmonds Community Development Code (ECDC) 18.30.050, the proposed project is
classified as a Small Site Project. The project will further be classified as Category 1 if it creates less than
5,000 square feet of new, replaced, or new plus replaced impervious area or Category 2 if it creates more
than 5,000 square feet of new, replaced, or new plus replaced impervious area.
1)Please confirm the calculations for the proposed development for both new and replaced impervious
surface area and provide site specific information in the following table format on the plans.
Line Type Area (square feet)
1. Non-Regulated
Exempt Regulated
2. Replaced
3. New (Post 1977) +
Total Regulated Impervious Area
=
4.
Mitigation required if in excess of 2000sf
-
5. Total Area Mitigated by Existing Stormwater Management System(s)
=
6. Regulated Area Not Yet Mitigated
=
7. Area Proposed to be Mitigated by Low Impact Development Techniques
=
8. Area Proposed to be Mitigated through Conventional SWM Techniques
bld20110196-Panera-E11 Page 1 of 2
Please refer to City handout E72 and/or the Stormwater Supplement for additional information related
to new and replaced impervious surface area.
2)The subject site falls within the Lake Ballinger drainage basin. This basin is overwhelmed and onsite
runoff from development further increases the flooding problems in Lake Ballinger. Where feasible, it
is recommended that low impact development techniques be implemented.
3)In addition to the larger Lake Ballinger drainage basin issues, the stormwater conveyance system that
currently conveys runoff from the site to the north , has limited capacity and also creates localized
flooding issues for the neighborhood properties even in small storm events. The existing on-site
detention system currently discharges to this system to the north and contributes to the local flooding.
As a mitigation measure, the existing stormwater detention system should be re-routed so it discharges
to the east potentially to the existing catch basin (State 77) as shown on the map below.
Apparently, there is an 8 stub from this basin that may drain an existing yard drain on the site. If it is
determined in the downstream analysis that the existing system, the 8 stub and storm system up to ¼
mile downstream of the site, would provide sufficient capacity, then it is likely this line would not
need to be replaced. I have put a message through to WSDOT staff to determine if their approval is
necessary to connect to the existing 8 stub or to upsize the 8 line should that be necessary. As soon
as I hear from them Ill let you know.
4)For those impervious areas that cannot be mitigated through low impact development techniques, an
on-site storm detention system designed to meet all required small site minimum requirements will be
acceptable. This detention system will also need to drain to the east potentially to the existing
catch basin (State 77) as shown on the map below.
Please contact me at 425-771-0220 or by e-mail at mcconnell@ci.edmonds.wa.us if you have specific
questions regarding these plan corrections.
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