HomeMy WebLinkAboutEX05_Drainage_Evaluation
13705 Bel-Red Road · Bellevue, Washington 98005
Phone 425/649-8757 · Fax 425/649-8758
March 25th, 2022 Project No. G-5204
Ms. Karen Lang
212 – S 20th Place
Renton, Washington
Phone: (208) 880-3296
Email: KarenL@SummitLaw.com
Subject: Drainage Evaluation
Backyard Deck
212 – S 20th Place
Renton, Washington
Reference (Email): Lang/Allison Backyard – 212 S. 20th Place, Renton, WA,
addressed to Ms. Karen Lang, from Brittany Gillia, dated
Wednesday, November 24th, 2021.
Per the email referenced above, at Ms. Karen Lang’s request we visited the above site to evaluate
surface drainage of the backyard deck. Our findings pertaining to this evaluation are provided in
the following sections below.
Existing Stormwater Management Evaluation
During our site reconnaissance, we observed the stormwater management system for the
residence consists of five roof downspouts which are eventually or immediately tightlined below
the ground surface, as seen on Plate 1 – Drainage Control Plan. Plans from the initial
construction of the home are unable to be retrieved, therefore, the end discharge location(s) of
the subsurface stormwater pipe network is unknown at this time.
We did not observe evidence that the existing stormwater management infrastructure is adversely
affecting the existing retaining wall, steep slopes, or sensitive areas on or adjacent to the site.
We also did not encounter signs of surface stormwater adversely affecting the existing retaining
wall, steep slopes, or sensitive areas on or adjacent to the site via rutting, channelizing or
EXHIBIT 5
DocuSign Envelope ID: 9BB52EEA-073E-450F-BED8-2B13DFF227B2
March 25th, 2022 G-5204
Ms. Karen Lang | 212 - S 20th Place, Renton, WA Page 2
GEO Group Northwest, Inc.
concentrating flows. The existing stormwater management for the site is effective and does not
adversely affect the above-mentioned areas in our opinion.
Proposed Stormwater Management Evaluation
We understand that there is a 135-square-foot aluminum drainage grating proposed that is to
accommodate 405 square feet of new deck area added. This is acceptable in our opinion,
contingent that the drainage grating be tightlined via gravity flow to the existing stormwater
management system (downspouts), as seen on Plate 1. Drainage should not be allowed to drain
directly below the grating in the retaining wall backfill area.
Closing
In summary, it is our opinion that the existing and proposed stormwater management systems are
acceptable provided that the recommendations above are employed.
Sincerely,
GEO Group Northwest, Inc.
Garrett Dean, G.I.T. William Chang, P.E.
Staff Engineering Geologist Principal Engineer
Attachments:
Plate 1 – Drainage Control Plan
EXHIBIT 5
DocuSign Envelope ID: 9BB52EEA-073E-450F-BED8-2B13DFF227B2