Loading...
HomeMy WebLinkAboutRS_G-5204 Karen Lang Drainage Eval_v1 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 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 SCALE AS DIMENSIONED DRAWN BY GD CHECKED BY WC DATE 3/25/2022 PROJECT NO.G-5204 PLATE 1 DRAINAGE CONTROL PLAN BACKYARD DECK 212 - S 20TH PL RENTON, WASHINGTON Geotechnical Engineers, Geologists, & Environmental Scientists GEO Group Northwest, Inc. EXISTING STORMWATER MANAGEMENT PROPOSED STORMWATER MANAGEMENT