7505 SEAWAY BLVD 2022-05-13 - Laserfiche WebLink

Kirk Brooks From: Erik Emerson Sent: Tuesday, February 14, 2017 1:47 PM To: Kirk Brooks Subject: Seaway Transit Center Plan Review Comments Kirk, Here are my comments on the Seaway Transit Center. I have discussed these with the engineer already and they are already working to address some of the more significant comments. General • The City has adopted the 2014 Ecology Stormwater Management Manual as it's stormwater manual. All projects submitted for construction permit review after January 1, 2017 must comply with the requirements in the new manual. The City has also published draft Design and Development Standards and Specifications (DCSS). The draft standards for stormwater facilities (Chapter 4) only have been set as the City's standards. The changes include revisions to the standard plan content and numbering, as well as significant revisions to the text. Your proposed design must comply with the requirements of the revised standard. Drainage Report • Pg. 10 — Requirement #2 The project must address all 13 SWPPP elements since the design includes a rain garden. This also applies to the summary on Page 12 and the formal SWPPP provided in the Appendix. • Pg. 10 — Requirement #5 The report provides insufficient justification for the determination that onsite stormwater management practices are infeasible. Please provide infeasibility documentation in accordance with the current Stormwater Management Manual or apply onsite stormwater management BMPs in accordance with the current manual. • Appendix C- Last page of calcs. Notes that the HGL at CB#12 is 568.85, which is not only higher than the top of the detention vault, but is also higher than the rim of CB#7 and backwaters the treatment and oil control facilities. While it is unlikely that these pipes will ever need to convey an un-detained 100 year flow the concern can likely be addressed by upsizing the three runs of downstream pipe to 18" diameter. The structures are already Type 2 due to their depth, so the difference is minimal. Plans • DR1- CB#3 is shown with 4 pipes coming into a Type 1 structure. It appears that multiple pipes will be connected on the same side which is infeasible for a Type 1 structure. Revise the configuration of the pipes or switch to a Type 2 structure. • DR2 - Per the current Stormwater Management Manual a high flow bypass must be provided for the Oil Water Separator (Volume V, Section 11.6, second bullet) unless it is necessary to locate it offline. It appears that it is feasible to configure the system to bypass high flows. The bypass can be connected directly to the detention vault, or back to the conveyance system as desired. (Note that the 2010 stormwater manual the bypass was mandatory.) • DR2 - It is unclear what the cross section will be for the ditch on the southern side of the site. Provide a ditch section reference. • DD1— Both riser structures shown are called out as 12" risers but the calculations in the drainage report are based on 18 inch risers. Please revise to 18" risers or provide revised calculations. • DD2 —The detention tank must be designed in accordance with Standard Plan 418 of the new DCSS. Notably, connector pipes must be a minimum of 48" diameter and must be set at the same invert as the invert of the detention tank. C/