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HomeMy WebLinkAbout03159 - Technical Information Report - Supplement ;►, _ CITY OF RENTON „u ' Planning/Building/PublicWorks Department Kathy Keolker-Wheeler, Mayor Gregg Zimmerman P.E.,Administrator May 26, 2004 5�-�r `� � s''_� James Jaeger Jaeger Engineering 9419 S. 204th Place Kent, WA 98031 Subject: Demps/Parkview Plat (U040185) Non-compliance with plat condition Dear Mr. Jaeger: In review of your letter dated May 13, 2004 it is noted in your description claiming an exemption to the drainage detention requirement an assumption of using the 1990 manual. Per condition number five issued with the Environmental Review Committee's DNS-Mitigated this plat is subject to the 1998 King County Surface Water Manual, Level 2 Flow Control. This decision was issued June 24, 2002 and included with the Hearing Examiner's conditions in the recommendation of approval to the Renton City Council dated August 13, 2002. No appeals were filed. Given this condition, a new report and design are required before this plat may be considered complete. Please note, the 1998 manual specifically does not allow removing the roof square footage to be infiltrated to determine exemption from detention, only to determine the size of the facility. It is unfortunate that the issue was not caught in the review process, but this in no way relieves the owner from compliance with the plat condition. As the City of Renton is now aware of this issue, the plat cannot be accepted for final approval until the drainage report, design and construction are approved and complete. Any questions and coordination for review should be directed to Arneta Henninger at 425-430-7298. Sincerely, �. ���� Ka r Kittrick Development Engineering Supervisor Public Works Inspections &Permits Development Services Division CC: Arneta Henninger Ron Straka 1055 South Grady Way-R�nton,Washington 98055 R E N T O N �This paper contains 50%recyded material,30%post consumer .4HEAD OF THE CURVE _- -- _ _ _ __ --_ _ ___ __ ___--- _----- .Ronalc'tStraka - Re: Demps Plat Drainage Code Violation Page 1 From: Ronald Straka �-�t;� "2�i -? , i'� To: Kayren Kittrick Date: 05/21/2004 2:30:19 PM Subject: Re: Demps Plat Drainage Code Violation We are not questioning the decision to not require the 1998 vs the 1990 KCSWD Manual for either of the projects (Jacques or Demps). We are ok with the requirement of using the 1990 KCSWD Manual with detention to the 100-yr st�rm plus the 30%factor of safety for both Plats. The issue, as I stated in my previous email message, is that the engineer for the Demps Plat used roof-downspout infiltration to reduce the runoff from the developed site to below the exemption threshold of 0.5 CFS for the 100-yr design storm. The determination if a project is exempt or not from having to provide detention has to be done based upon a comparison of the pre-developed and post-developed runoff conditions (without any flow controi measures such as roof downspout infiltration)to determine the post-developed peak rate of runoff for the 100-yr, 24-hr design storm is greater than or less than 0.5 cfs above the pre-deveioped peak rate of runoff for the 100-yr, 24-hour design storm. If the increase is less than 0.5 cfs then the project is exempt from having to provide detention. If the increase if greater than 0.5 cfs, then detention is required. The Demps Plat engineer has corrected the calculation and it shows that the project does have to provide detention. In fact, the first drainage report for the project showed detention was required, but the engineer later submitted a revised report stating that the project was exempt from having to provide detention, because he used roof downspout infiltration to get below the exemption threshold. I appreciate your desire to maintain the mylar sign off procedures that we have followed for at least the last 15+ years. I feel the system has worked well and is necessary. Our role in the plan review and approval process is to confirm requirements at the green folder stage (code or any special requirements), review sizing calculations for detention, water quality and important conveyance systems to confirm that they are accurate and satisfy City code, and to provide any technical assistance(answer questions) your section needs during the plan review process. The "nuts and bolts" part of the plan review is something that is performed by the staff in your section and I am confident that they are capable of performing this task. I don't see our role as being a waste of our time and it is a necessary role. Especially since the private sector constructs the majority of the public storm systems in this City and we need to make sure growth is not creating new drainage problems that would have to be solved by the expenditure of Utility rate payer funds. This process has worked well, but for some reason there was a break down in communication on this project. I view this case as an unusual occurrence. I prefer that these types of problems be identified well in advance of the mylars for the project are signed off. The only thing that we can do is to work to improve our coordination and communication during the plan review to hopefully avoid these situations. I look forward to continue to work with you and your staff in the review and approval of plan along with resolving the Demps Plat detention requirement. »> Kayren Kittrick 05/19/2004 9:00:07 AM »> As I had not drafted my letter to reply to the referenced letter yet, I will give you the background and provide a forum for you to participate in the response. The Demps Plat(now known as Parkview) is LUA-02-061, reviewed for preapp and green folder by Arneta Henninger with participation from Allen Quynn. It was noted in 2002 that the plat probably complied with 1990 manual but not 1998. The comments from this section to Planning did not include the recommendation for using the 1998 manual, as the Jacques plat directly next door had been required to provide for the 100-year storm plus 30% under the 1990 KCSWDM. The ERC placed the condition of using the 1998 manual, and the Hearing Examiner included the ERC conditions in his recommendation for approval. Neither were appealed. The plat then dropped out of sight for 2 years. 2003-Jacques plat is constructed. With it, I would say about 75-80% of the Demps plat improvements were also constructed as water, sewer and most of the pavement and some of the storm facilities were installed as they were required for the Jacques plat. Still no sign of Demps. _ -------. _ ---- _ __ _----- - ------- -- --- -----_ __— .Ronald•Straka - Re: Demps Plat Drainage Code Violation Page 2 2004- Demps finally applies for construction permit. There was a bit too much trust in the engineer, although we had no indication that he had departed from his usual interpretations of code and manual when in the past he was the one engineer that seemed to most closely align with Surface Water's interpretations and protocols. Admittedly, we missed the 1998 condition in the rush to get the project permitted. That will now be rectified by a letter from me requiring mitigation and compliance. I was not impressed by the reasoning in his letter and have since had Juliana run some rough calculations for me so I can come from a solid understanding of the issues. My nexus will not be the 1998 manual, but rather the condition placed on the plat to comply with it. Mr. Jaeger failed to address the condition, and now the plat is held until it is brought into compliance. The plat owner is under every obligation to comply with the conditions of the plat, and will have to also pay the price for delaying so long rather than participating fully with the Jacques plat which had been offered early on. The solution will most likely be costly, but as they have already benefitted greatly by the construction already in place at no cost to themselves, I think it is really a wash. When the letter is complete I will provide a copy for your information. This instance points out why I am still in favor of having the utilities sign the plans, even though the current trend in thinking is to discontinue the practice as an unnecessary abuse of utilities' time. Thank you for drawing this to our attention and we will take it from here. Kayren Kittrick Development Engineering Supervisor Public Works Inspections & Permits 425-430-7299 _ _---__ __ _ _. _ _ __ __ __ ,Ronald.Straka - Demps Plat Drainge Code Violation Page 1 From: Ronald Straka To: Kayren Kittrick Date: 05/18/2004 11:58:58 AM Subject: Demps Plat Drainge Code Violation I have just reviewed the letter from Jeager Engineering regarding our plan review comments that found an error in the engineers claim that the project was exempt from detention. The engineer James Jeager revised the calculation to properly determine if the project is exempt from detention. The corrected calculations show that the project does not qualify for the detention exemption and detention is required, as we suspected. The engineer claims that the storm system has been constructed, even though this issue was not resolved nor had I signed off on the construction mylars. The engineer claims that his interpertation of the manual allow him to not include roof areas, if roof downspout infiltration is used, in determining if the project is exempt from detention. The Surface Water Utility contends that this is an incorrect interpertation and if you look in Section 1.2 on page 1-36 of the 1998 KCSWDM, it clearly states that roof downspout infiltration cannot be used in determining if the project is exempt from flow control (detention) requirements. In addition, the engineer claims that since this issue was raised so late in the plan review process and the fact that the City issued the construction permit and the storm system has already been constructed (without approved mylars), that it would be too much of a hardship to change the project storm system. The reason this came up so late is due to the fact that the Plan Review project manager did not accurately review the plans nor was the Surface Water Utiliry Engineering Section provided an opportunity to reveiw the calculation until we were request to sign off on the mylars. If we were provided the opportunity to review the drainage calculation earlier in the Plan Review process, we would have been able to address this problem. I am courious how it is that we issued a construction permit,when the maylars have not been signed off nor does the design comply with City code? Why didn't a stop work order or limited construction permit be issued that allowed other parts of the project to be constructed except the storm system until this issue was resolved? Please let me know what your response is to the James Jaeger letter and this situation as soon as you can. Is there anything that we are going to do about this or are we just going to count it as one of our mistakes? Thanks Background Information: The Demps Plat(Parkview Plat)was issued a construction permit and the pre-construction conference was held on April 20, 2004. After receiving the pre-construction notice, the Surface Water Utility staff recently reviewed the Demps Plat Drainage Report for the first time. The Plan Review project manager for the project, Arneta Henniger, had not provided the report to the Surface Water Utility prior to the project permit being issued. The report was initially submitted in May of 2002, and subsequently revised and resubmitted in March of 2004. In the May 2002 report, the engineer proposed a water quality/detention vault for 12 lots. The latest report dated March 18, 2004, revised the previous report by proposing to infiltrate the roof areas for ten (10) lots. In determining whether the project exceeded the 0.5 cubic feet per second (cfs)threshold requiring detention under the 1990 King County Surface Water Design Manual, the engineer incorrectly excluded the roof area from the runoff m�del. As a result, the difference between the 100-yr., pre-developed, and developed condition runoff rates was calculated to be 0.37 cfs, which is less than 0.5 cfs. The engineer concluded in the report that detention was not required for the project. This is incorrect and violates City Code. When evaluating a project for detention requirements, the applicant must use the whole site area, including the roof area to be infiltrated, in the pre-and post-developed runoff rate calculations. Under ---------_ --- _ __ _ __ _ --_ __ — ___ ___ _Ronald�.Straka- Demps Plat Drainge Code Violation Page 2 developed conditions, the roof area must be characterized as impervious. if the project triggers detention, then the roof area can be discounted from the net impervious area used for sizing the flow control facility, if the applicant uses roof downspout infiltration per the established standards. As it stands now, with the currently approved plans and drainage report, the completed project will release 0.21 cfs for the 2-yr. design storm and 0.35 cfs for the 10-yr. design storm, which exceed the 2-yr. and 10-yr. pre-developed runoff rates by 0.16 cfs and 0.26 cfs, respectively. The storm water design for this project does not comply with City Code since the post-developed runoff rates for the project do not match the pre-developed runoff rates for the 2-yr. and 10-yr. design storms. The project construction permit should not have been issued. The project engineer should be required to bring the project into compliance with City Code and provide the detention and water quality treatment, as required. Please advise me with the course of action you will take to correct this. In the future, it is imperative that Surface Water Utility staff be given sufficient time to review projects that involve more complex issues, such as infiltration, and to verify compliance with City Code. In addition, the determination whether a project requires or is exempt from detention must be based upon the pre-developed condition runoff compared to the post-developed condition, without any flow control measures. If detention is then determined to be required, the engineer can use roof downspout infiltration to reduce post-developed runoff rates to match the pre-developed runoff rates, or use it in combination with a detention pond/vault. However, the pre-developed and post-developed runoff rates, with flow control measures, have to match in order to comply with the City Code. CC: Allen Quynn; Lys Hornsby ,�AY-13.-2004 03:21P FROM: T0:4254307300 P: 1�z � - ,.1A��EF: ��IC IIVE�Rt�IC 9419 S. 204 PLA1:E - K�NT,W/1_4HING70N 98031 PHont� (253) 8i`►0-093d FAx (253) 85a-O 155 May 13, 2004 Arneta Henninger City of Ren#on De�elopment Services Divisio i 1055 S. Grady Way Renton, WA. 98055 RE: Demps Plat - Permit N��. U040185 Dear Arneta, As a result of our meeting this morning with Ron 5tratka and Allen Quynn, I performed a revised SBUH an�lysis of the peok drainage flows for the developed and pre-deve(op 3d conditions. The meeting was called by the Surface Water Managerr ent Dept. to discuss the drainage detention exemption that wos shown ir the plat's drainoge colculaiions. A negligible penk flow detentic n exemption was claimed because the 100 yeor developed peak flow w�s only 0.37 CFS greater than the 100 year pre-developed peak flow (0. i CFS mox. for the exemption). In calculpting fihe peak flows, I did not incl��e the roof a�ea of the hew hovses because a recent geotechnical study ndicated that the soils will adequately support individual lof infltrotic�n. Section 4.5.1 of the 1990 KCSWDM states that "where downspout infiltr�tion is used, the roof areo that is infiltrated need not be included in the mpeNious area used to calculote the R/D facility slze". Section 1 .2.3 di,cusses the exemption criteria and states "The propased project slte p��st-developed peak runoff rate or the 100 year, 24 hour design storm is :;alculated to be less than 0.5 CFS more than the peak runoff rate for ihe e xisiing site conditions". I interpret this to mean that tl�e areas that will be infiltrated will not be included in the impervious su face in the post-developed drainage condition. This is how I co{cu ated the post-developed peak drainage for the exemplion analysis. I un<lerstand that the City can interpret this to mean that the infiltration are,� need not be considered impervious for the R/D facility calculations, but not apply to the analysis far the exemption. However, in fihe actual, real !ituation, the infltrated roof drainage will not enter the drainage system a!�d will not be part of the post-developed droinage conditions. As sucl�, I stilf slond by my interpretation. The revised peak flow analys s, including the roof areas as impervious surface, yielded a post-devE oped 100 year flow of 0.86 CFS and a pre- MAY-1�28a4 03:21P FROM: T0:4254307320 P:z�2 i; developed 100 year flow of 0,24 CFS. This is a 0.62 CFS difference ond would not qualify for ihe exer;iption. I could accommodote the City's interpretation of this siivation,;if it wcas noted during the plan review, or even shortly thereafter. The p ans were approved as being exempt from detention and a construction'permit was issued. It should be noted that we are providing water qualit� enhancement using a wet t�nk. The pre- construction meeting was hel,y on April 20th. The contractor hos indicated that the entire drainage syste:n and sanitary sewer system has been instaHed. The sewer system hc;s been tested and passed. If detention were a part of this system, I w��vld have enlarged the wet tank and made it a combination detention ar d wet tank. However, it would be a tremendous hardship to remo're the system that was recenlly instaNed and re-build it_ I don't feel fihc►t it is fair for the City to request this afi this point, because of a code intE rpretation. It should also be noted that the plans and construction were i:xpedited to minimize the impact on the new construclion within the a �jacent Jacques Plat. Please iefi me know if I can help resolve this. Thank �ou for your time. 5incerely, ames Jaeger