Memo for Approved RW Drainage.pdf7936 Seward Park Avenue South
Seattle, WA 98118
p. 206,725. 121 1
C 206,973.5344
on 91 I IDC Ipdengineering.com
P C
Memorandum
DatMay 25, 2011
e:
To: City of Edmonds
Attn: Jennifer Lambert
From: Steve Hatzenbeler, P.E.
V
lProject: Restaurants Unlimited, Scott's Bar and Grill --- -
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LPDProjectNo: 147-10-01
Subject: Connection of Wall Footing Drain to Detention System
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Per our recent phone conversation, this memo provides documentation of stormwater detention storage provided in the
project and assessment of the impact of connecting one of the footing drains to the detention system.
Each proposed wall constructed with the project includes a wall drain to help prevent the build-up ofhydrostatic
pressure behind it. The drawings include various connections from wall drains to the proposed storm drain system
downstream of the detention System. Our understanding is that upon visiting the site to perform the final inspection,
you noticed that the footing drain from the western half of the upper (north/west) retaining wall is connected to the
catch basin in the new parking lot, which discharges to the detention system.
We reviewed the as -built condition with the project's geotechnical engineer and they noted that they did not encounter
any groundwater in their borings when performing their on-site investigation. Their opinion is that, based on the site
topography, location, and their soils investigation, they expect the groundwater flow to, contribute a negligible arnount
of additional water to the detention system.
In addition, we reviewed the project's stoma drainage report and confirmed that the detention system's required storage
capacity per the stormwater modeling is 728 cubic feet; the proposed system includes 752 cubic feet of live storage.
Considering the infonnation above, it is our opinion that the addition of an insignificant amount of groundwater flow
from the western end of the upper retaining wall will not have an adverse impact on the function of the detention
system.
Please feel free to contact us if you have any questions. Thank you.
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