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HomeMy WebLinkAboutSWP272094(2) Short Plat (SHPL REQUEST FOR PROJECT 9 Prelim. Plat (PP# _ ) [" CAGH To: Technical Services Date z ' I �- -+ 3 WOk 87435 Grcen# 9sys From: Plan Review/Project Manager p a h II&I Ca rev Project Name M e,4rD Re,eio ,, p' n "I" Li y u d S+re ZnP uy P�1 to - I (70 d'arahers max) SZ Description of Project: C Irm,s'�e-t t tier, to [n. root�S v Gti r ` r d f u-�Ier re lh �¢�s btu) '4V- Vku � J i��/a d /n {trn�� O�rein�it �inll Circle Size of Waterline: 8" 10" 12" Circle One: New or Extension Circle Size of Sewerline: 8" 101, 12" Circle One: New or Extension Circle Size of Stormline: 9' 15" 18" 24" Circle One: New or xtension Address or Street Name(s) M pr7s fEr R o.o/ S kl Dvlpr/Contractor/Owner/Cnslt: _ /fIrrIe 0� / ,grow., e (1►��ect��� (70 dwaaas soaz) Check each discipline involved in Project Ltr Drwg N of sheets per discipline O Trans-Storm _Black R_%Vtr �r,irugL B�Jivr _✓ _� (Roads Y/Drainne) (Off site unpmvc tsxindude basin (include TESC sheets) O Transportation (Signaliurion,Cha m lization,Lighting) 7 O Wastewater (Sanitary serer Main)(Include basin name) O Water (Maim,Valves,Hydrmts) (IMlude composite&Horizontal Oft sheets) TS Use Only 7�n— SCU/o —SO - oo9ef Lef�e� �.reQe� r9-`P'3 Approved by TSM Date: r0tm4/misd97-090.DOC/CD/bh 1 ' MUNICIPALITY OF METROPOLITAN SEATTLE (METRO) ENLARGEMENT III OF METRO TREATMENT PLANT AT RENTON APPLICATION AND REQUEST FOR MODIFICATIONS PURSUANT TO ORDINANCE NO. 4342 IN CONJUNCTION WITH DRAINAGE PLAN APPROVAL ' MARCH 25, 1992 I . INTRODUCTION The Municipality of Metropolitan Seattle (Metro) has ' prepared a stormwater management program consistent with the City of Renton (City) drainage requirements and with Condition 7 of the building permit issued by the City for Phase A of the Metro treatment plant Enlargement III project in Renton. The program ' is described in detail in the Drainage Plan prepared by Brown and Caldwell, consulting engineers (attached) . Metro worked closely with Randall Parsons, City of Renton Stormwater and Wastewater Utility Engineering Supervisor, to develop this program. The City of Renton Municipal Code requires the preparation ' of a drainage plan in conformance with the Core and Special Requirements contained in sections 1. 2 and 1. 3 of chapter 1, and chapters 3 , 4 , and 5 of the King County Surface Water Design Manual .(SWM) and City of Renton standard drafting and design ' requirements . Metro ' s proposed program, which utilizes wetponds and swales, is consistent with applicable drainage requirements and provides adequate protection of water quality. In order to implement the program, however, Metro must obtain approval to deviate from certain technical requirements in the SWM. Metro ' previously obtained variances from the Renton Hearing Examiner (Hearing Examiner) with respect to some of these requirements. Metro is now requesting modifications for the other requirements ' pursuant to Renton Ordinance No. 4342 , enacted February 3 , 1992 and effective March 9, 1992 . ' This document constitutes Metro's application and request for modifications. ' II . SUMMARY OF PROPOSED STORMWATER PROGRAM The proposed stormwater facilities will consist of ' biofiltration swales located adjacent to newly constructed roadways and parking lots, a pump station to lift and transport stormwater, and a series of oversized wetponds. The pump station ' and wetponds will have three times the capacity required in the SWM. These facilities are designed to treat stormwater associated with all new impervious surfaces subject to vehicular use or storage of chemicals. 1 ' Under the proposed stormwater program, stormwater will continue to drain to the Green River outfall manhole west of the Administration Building and just east of Monster Road. The existing system will be augmented with a pump station at the outfall manhole. This pump station is necessary to lift stormwater flows to the wetpond facilities located on the ' surface. Flows in excess of the pump capacity, which is three times the capacity required by the SWM, will overflow into the Green River via the existing 120-inch outfall diffuser. ' Stormwater will be pumped to wetponds for water quality treatment. The wetponds will be a series of ponds located near existing wetlands on-site. The ponds will be terraced to allow ' gravity flow between the wetponds. Ultimately, the wetponds will drain to the P-1 Channel. This avoids the need for another pumping station to discharge flows directly to the Green River. ' The pump station and biofiltration swales are planned to be constructed as part of the Phase A construction contract during summer of 1992 . The wetpond facility is scheduled to be ' constructed during Phase C, which is planned to begin in 1994 . In the interim--while these facilities are being designed and constructed--the pump station will pump stormwater flows to the ' headworks of the wastewater plant for treatment and discharge to Puget Sound via the Effluent Transfer System (ETS) . Stormwater pumping will be redirected to the wetpond facility when it becomes. operational . ' In the Drainage Plan that accompanies this modification request, Metro has identified preliminary locations for the ' wetponds in the northern portion of the site in the vicinity of the wetland area. Metro is continuing to explore wetland enhancement opportunities in this area, which could utilize and incorporate some of the wetponds. Metro will obtain approval from Renton' s Stormwater and Wastewater Utility Engineering Supervisor if the final location of the wetponds is different from the preliminary location identified at this time. III . PREVIOUS VARIANCE REQUEST BEFORE RENTON HEARING EXAMINER ' Metro sought variances from the following SWM requirements in an application submitted to the Director of Public Works on September 16, 1991 and in a public hearing before the Renton ' Hearing Examiner on October 1, 1991, pursuant to Renton Code 4- 22-16: ' • Core Requirement 1: Discharge at the Natural Location To allow interim discharge of stormwater runoff through ' the treatment plant for treatment and discharge directly to Puget Sound through the ETS rather than to 2 1 ' the Green River. To allow permanent discharge of stormwater from wetponds, and rare emergency flows, into the P-1 Channel rather than to the Green River. ' • Core Requirement 3 : Runoff Control To allow interim discharge of stormwater runoff through the treatment plant for treatment rather than on-site biofiltration facilities for all of the new impervious surface areas subject to vehicular use or storage of ' chemicals. To allow some new areas of impervious surface subject to vehicular use or storage of chemicals to not have biofiltration treatment on a ' permanent basis, but to instead provide wetpond water quality treatment up to the water quality design storm event for most of the site's new and existing impervious surface subject to vehicular use or storage ' of chemicals. • Core Requirement 4 : Conveyance System tTo allow the use of , a pump system for stormwater conveyance along with a variance from the standard size ' criteria for a pump storage facility (wet-well) . • Core Requirement 5 : Special Water Quality Controls To allow interim discharge of stormwater runoff through the treatment plant for treatment and discharge directly to Puget Sound through the ETS rather than ' treatment by a wetpond for the new impervious surface areas subject to vehicular use or storage of chemicals. In the Hearing Examiner 's Decision, issued on October 14 , 1991, he stated: The variance to release storm water to the treatment ' plant and discharge it to the Effluent Transfer System is approved for an interim until permanent facilities are constructed, but in no event shall this variance exceed four (4) years. Any extension of the time period shall be subject to a new application for variance relief. The variance to permit the use of three linked wetponds instead of biofiltration swales is approved. ' Decision at 8 . In response to a request for reconsideration, the Hearing ' Examiner stated: 3 ' [T)his office did not intend to limit Metro' s interim use of the existing facility and its non-standard (in terms of the current requirements) use of the pump and ' effluent transfer system. As an interim proposition, the use of the existing facility is appropriate while the system is brought up to current standards. . . . This ' office intended to limit the determination of the pump variance to the permanent facilities that Metro proposes to meet the city's current stormwater ' requirements. Letter from Fred J. Kaufman, Renton Hearing Examiner, to Gregory Bush, Metro Manager of Environmental Compliance at 1-2 (November ' 5 , 1991) . Thus, Metro has already obtained approval to: (1) deviate ' from Core Requirement 1 (Discharge at the Natural Location) during the interim by discharging via the treatment plant and the ETS to Puget Sound; (2) deviate from Core Requirement 3 (Runoff Control) by not utilizing biofiltration in the interim and by ' treating stormwater runoff from all new impervious surface areas (subject to vehicular use or storage of chemicals) on a permanent basis using oversized wetpond facilities rather than ' biofiltration; (3) deviate from Core Requirement 4 (Conveyance System) during the interim to allow the use of a pump system to convey stormwater to the treatment plant; and (4) deviate from ' Special Requirement 5 (Special Water Quality Controls) by treating stormwater from new impervious surface areas (subject to vehicular use or storage of chemicals) on an interim basis through the treatment plant. ' In order to implement the proposed program, Metro must still obtain approval to: (1) deviate from Core Requirement 1 ' (Discharge at the Natural Location) in order to permanently discharge stormwater from the wetponds, and rare emergency relief flows, into the P-1 Channel rather than to the Green River; (2). deviate from Core Requirement 4 (Conveyance System) on a ' permanent basis in order to use a pump system (and a smaller than required wet-well) for stormwater conveyance to the wetponds. ' IV. MODIFICATION REQUEST ' Renton recently amended its stormwater variance process to provide for administrative, rather than Hearing Examiner, approval and to replace the variance criteria with a different standard. Renton Ordinance No. 4342 , enacted on February 3 , 1992 ' and effective on March 9 , 1992 , allows the Director of Public Works to approve "modifications" to requirements of the Storm and Water Drainage Code under certain circumstances. It provides: 4 1 ' Modifications. Whenever there are practical difficulties involved in carrying out the provisions of (the Storm and Water Drainage Code) , the (Director of Public Works] may ' grant modifications for individual cases provided he/she shall first find that a special individual reason makes the strict letter of this code impractical, that the modification is in conformity with the intent and purpose of this code, and that such modification: 1 . Will meet the objectives of safety, function, ' appearance, environmental protection and maintainability intended by the Drainage Code requirements, based upon sound engineering judgment; ' and 2 . Will not be injurious to other property(s) in the vicinity. Metro requests a modification from the following requirements of the SWM, because they create practical t difficulties that make compliance with the strict letter of the SWM impractical : • Core Requirement 1 : Discharge at the Natural Location To allow permanent discharge of stormwater from the wetponds, and rare emergency relief flows, into the P-1 Channel rather than to the Green River. • Core Requirement 4 : Conveyance System To allow the use of a pump system for stormwater conveyance along with a modification from the standard size criteria for a pump storage facility (wet-well) . ' Modification of these requirements is discussed in detail below. ' A. Core Reauirement #1 (Discharge at Natural Location) : Core Requirement #1 provides that All surface and storm water runoff from a proposed project that proposes to construct new, or modify existing drainage facilities must be discharged at the natural location so as not to be diverted onto, or away from the adjacent downstream property. SWM 1. 2 . 1. Metro requests a modification from this section in order to allow stormwater, and emergency relief flows, from the site to drain to the P-1 Channel, rather than to the Green River. 5 ' There are practical difficulties carrying out the provisions of Core Requirement #1. Due to the location of existing sewage treatment facilities and given the public need to preserve ' certain land area for potential future sewage treatment purposes, the only practical and reasonable location for the wetpond facilities is in the northern part of the site near the on-site ' wetlands. The plan shows that stormwater that has been treated in these wetponds will drain by gravity to the P-1 Channel, which borders the northern portion of the site. Strict compliance with the SWM means that treated stormwater flows would have to be conveyed from the proposed wetponds back to the Green River at the other end of the site. This would ' involve the additional expense of discharge of stormwater by gravity flow or pumping through a separate conveyance system. This approach presents the following practical difficulties: (1) Discharge of normal flows would require the construction of a separate conveyance system which would take the storm water flows from the ponds to the Green River. This would add considerably to the public expense and would use additional property that has ' been set aside for sewage treatment facilities. (2) Discharge to the Green River is prohibited when the River is at flood stage. This means that peak flows would either have to go to the P-1 ' Channel or be allowed to back up and flood the treatment plant property, which from a health and safety perspective is not acceptable. The proposed modification meets the objectives of safety, function, appearance, environmental protection, and maintainability, consistent with the Storm and Water Drainage ' Code. From an engineering standpoint, the discharge of flows to the P-1 Channel is workable, maintainable, and preferred to re- routing flows back to the Green River. Aesthetically, the discharge to the P-1 is an element of the landscaped, terraced wetpond facility, and potentially could be incorporated into a . future wetland enhancement. ' With respect to environmental protection, discharge of treated stormwater and emergency overflow to the P-1 Channel will produce no significant quantity or quality impacts to the P-1 Channel, Black River Pumping Station or forebay. A hydraulic modeling analysis requested by Renton concluded that the 100-year 24-hour flood flow from the site would raise the level of the Black River forebay only 0 . 07 feet (about one inch) assuming very ' conservative conditions. A one-inch rise in the forebay will not significantly impact any of the surrounding property or habitat. t Similarly, an analysis of the potential water quality impacts was addressed by Metro' s consultant Adolfson & Associates, who concluded that Metro ' s proposed stormwater ' discharge is not anticipated to have any discernible impacts on the P-1 Channel in the short or long term. Reasons for this 6 conclusion include Metro's relatively small contribution of flow quantitatively, the likely high water quality of Metro' s treated stormwater, and the degraded water quality of the P-1 Channel. Discharge to the P-1 Channel, rather than to the Green River, also is consistent with the directives of the Green River Management Agreement (July 18 , 1985) , entered into by King County, and the Cities of Renton, Tukwila, Kent, and Auburn. While that agreement permits the discharge of additional ' stormwater flows to the Green River, it encourages that those flows be controllable, and it prohibits discharge of stormwater flows when the river is at flood stage. By discharging stormwater to the P-1 Channel, Metro's stormwater flows are ' subject to control at the P-1 pump station and make use of this regional retention facility. Under Metro's proposal, no stormwater flows will be discharged to the Green River when it is ' at flood stage. The modification will not be injurious to other property in the vicinity. As noted above, a one-inch rise in the forebay as a result of Metro's discharge will not significantly impact any of the surrounding property. In addition, rain falling on-site does not drain to other properties. ' Finally, it should be noted that approving a modification for discharge to the P-1 Channel is consistent with the historical natural drainage. Since the construction of the railroad tracks located west of the site (long before Metro arrived) , the natural drainage of the site has been generally toward the P-1 Channel . As part of site development for the ' treatment plant, the topography was altered to contain runoff on- site and stormwater was discharged with the treated wastewater effluent to the Green River. Thus, Metro ' s proposal to discharge stormwater to the P-1 Channel will merely restore the natural drainage that existed at the time Metro occupied the site. The SWM provides that where diversion of stormwater "will correct an existing problem, " the diversion should be considered as a variance. SWM 1. 2 . 1. For all of these reasons, we believe a modification from the natural drainage requirement is appropriate. ' B. Core Requirement #4 (Conveyance System) : Core Requirement #4 provides that ' Pump systems (includes the pumps, force mains, electrical equipment, structures and appurtenances) are not allowed on storm drain systems in King County. A ' variance (see section 1. 4) from this requirement . . . 7 ' may be requested. Any pump system [is required to meet certain] minimum conditions. . . . SWM 1.2 .4 . Metro is seeking a modification to allow pumping for two reasons: (1) in order to implement the SWM's preferred method of water quality treatment--wetponds--and, (2) to utilize ' the existing and extensive system of underground piping at the site. There are site-specific reasons that make compliance with ' the strict letter of Core Requirement #4 impractical. The site contains an existing underground stormwater sewer system. The network of underground pipes was originally designed to allow ' stormwater to drain by gravity to the Green River. For hydrologic reasons at the site, the sewer pipes are located relatively deep underground. The outfall manhole (the confluence of the stormwater sewer system before discharge to the Green ' River) is located about 26 feet below existing grade. In the stormwater treatment system as proposed, a pump system is required to lift the stormwater flows from this manhole and to ' convey the flows to the wetponds located on the ground surface. The pump will be designed and operated in accordance with Metro standard specifications. ' If Metro does not obtain approval to pump the stormwater, then it would be unable to implement the proposed wetpond facility which is the preferred method of treatment. Instead, Metro likely would have to construct a large underground wetvault at the location of the outfall manhole. This would create practical difficulties because the area that would be needed to ' construct a wetvault would involve valuable property that potentially could be used in the future for additional sewage treatment facilities. In addition, the construction of a wetvault would not be consistent with the SWM' s preference for ' wetponds (therefore requiring a modification) and would be very large and costly. ' The modification meets the objectives"of safety, function, appearance, environmental protection, and maintainability, consistent with the Storm and Water Drainage Code. As noted ' above, the pump station will be designed and operated in accordance with Metro standard specifications. The pump station is a wet-well type with submersible dual pumps, each with a capacity of 4 . 5 cfs. The wet-well will be 12 ' 10" in diameter ' and about 40 feet deep. A 48-inch overflow at Elevation 113 . 0 will bypass flows to the existing outfall diffuser in the Green River. A backflow prevention check valve will be installed on the 48-inch overflow. New emergency overflow weirs and relief sewers will bypass flows when the storm sewer backs up to Elevation 118 . 0 8 ' The SWM allows a variance for use of a pump system when certain specified conditions are met. See SWM 1. 2 . 4 . Metro ' s proposed pump system complies with Conditions 1, 2 , 4 , 5, and 6. ' Condition 3 requires a storage facility (wet-well) sized to hold 25% of the total volume of runoff for the developed tributary drainage area for the two year, 24-hour duration design storm ' event. According to modeling results for the site, a total storage volume of 314 , 000 gallons is required. The proposed wet- well and stormwater sewers are estimated to have a storage ' capacity of about 200, 000 gallons when stormwater reaches the relief overflow weirs (i.e. , about two-thirds of the required capacity) . The proposed deviation from the required storage volume is addressed through adequate safeguards incorporated into ' the design of the pumping station, as discussed below. The condition requiring a large wet-well for the pump is ' presumably intended to provide a degree of safety for the pump station and the stormwater conveyance system in the event that the pump fails. Metro requests a modification from this Condition for such a large storage facility. Metro ' s proposed ' pump system accounts for pump failure without the need for such a large storage facility. The safety and integrity of the pump station is provided by dual pumps, an isolation gate, an overflow ' weir, emergency relief sewers, a 24-hour a day on-site maintenance staff, and 200, 000-gallon storage volume in the wet- well where the pump system is located and in the stormwater ' sewers . These measures are consistent with the intent of Condition 3 for pump systems in section 1. 2 . 4 . It is our opinion that construction of a large storage facility in addition to these measures is unnecessary and impractical. Metro therefore ' requests that the minimum storage requirement be modified so that the proposed pump system can be utilized. ' V. CONCLUSION Metro requests a modification from Core Requirement #1 (Discharge at the Natural Location) , and #4 (Conveyance System) of the SWM in order to implement the stormwater management system described in the Drainage Plan. Metro's proposed Drainage Plan will result in a level of control and treatment that meets or exceeds the requirements of the SWM. These modifications do not compromise the quantity or quality of stormwater control or ' treatment at the regional wastewater treatment facility site and are protective of the environment and surrounding property. By implementing this design rather than one which adheres strictly to the SWM, Metro will be able to preserve valuable public property which has been dedicated to potential future sewage treatment facilities and save the ratepayers considerable expense now and in the future. By utilizing the proposed design, Metro will be able to preserve the option of incorporating the 9 wetpond concept into an art/wetland enhancement project for future public benefit. ' For all of the reasons set forth in this application, Metro respectfully requests that the modifications described above be granted. t ' 10 1 Drainage Plan ' Metro Treatment Plant at Renton Enlargement III ' April 29, 1992 1 1 1 1 1 DRAINAGE PLAN ' MUNICIPALITY OF METROPOLITAN SEATTLE (METRO) ENLARGEMENT III OF METRO TREATMENT PLANT AT RENTON TABLE OF CONTENTS ' INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 ' CONSTRUCTION PHASE A, ENLARGEMENT III : SITE PREPARATION AND PERIMETER LANDSCAPING . . . . . . . . 4 CORE REQUIREMENT NO. 1 : DISCHARGE AT THE NATURAL LOCATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Existing System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Proposed System 6 Underground Stormwater Sewer System . . . . . . . . . . 6 Stormwater Pump Station . . . . . . . . . . . . . . . . . . . . . . 6 ' Emergency Relief Sewers 7 Stormwater Quality Treatment . . . . . . . . . . . . . . . 7 ' CORE REQUIREMENT NO. 2 : OFF-SITE ANALYSIS . . . . . . . . . . . . . . . 9 Upstream Drainage Areas . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 ' Downstream Drainage Areas 10 On-site Drainage 11 Off-site Drainage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 CORE REQUIREMENT NO. 3 : PEAK RATE RUNOFF CONTROL . . . . . . . . . 13 Peak Rate Runoff Control Requirements . . . . . . . . . . . . . 13 Stormwater Modeling Results 14 Biofiltration Requirements 15 Proposed Biofiltration Plan . . . . . . . . . . . . . . . . . . . . . . . 15 ' CORE REQUIREMENT NO . 4 : CONVEYANCE SYSTEM ADEQUACY . . . . . . 17 Adequacy of the Proposed Conveyance System . . . . . . . . 17 ' Proposed Pumping Station . . . . . . . . . . . . . . . . . . . . . . . . . . 18 CORE REQUIREMENT NO. 5 : TESCP . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 1 1 MTPR Drainage Pl all/RFp,,rt/Drainp ' TABLE OF CONTENTS, continued ' SPECIAL REQUIREMENT NO. 5 : SPECIAL WATER QUALITY CONTROL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 1 Stormwater Quality Treatment Plan . . . . . . . . . . . . . . . . . 22 Minimum Requirements for Wetpond Facilities . . . . . . . .22 ' Proposed Oversized Wetpond Facilities 23 SWM Wetpond Design Criteria 24 Compliance with SWM Design Criteria . . . . . . . . . . . . . . . 24 ' MODIFICATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 APPENDICES Appendix A: Hydraulic Impacts of Redirecting Stormwater Runoff to the P-1 Channel ' Appendix B: Water Quality Impacts of Redirecting MTPR Stormwater Runoff into the P-1 Channel ' Appendix C : Technical Support for Attaining Equivalent Treatment with Oversized Wetponds Appendix D: Stormwater System Modeling: Hydrologic and Conveyance Capacity Analyses ' Appendix E : Technical Information Report (TIR) Form and Black River Basin Schematic 1 1 MTPR Drainage Plan/Report/DrainpL�.doc/RC[i LIST OF TABLES Table 1 . Drainage Basins - Proposed Development Table 2 . Results of 100 year Storm Modeling : Pre-Development ' Table 3 . Results of 100 year Storm Modeling : Post-Development ' Table D1 . Hydrograph Input Parameters : Pre-Development Table D2 . Hydrograph Input Parameters : Post-Development ' Table D3 . Existing Conveyance System Characteristics Table D4 . Proposed Conveyance System Characteristics 1 1 MTPR Drainage Plan/Report/Dra inpin.doc/Rrg LIST OF FIGURES ' Figure 1 . Design Storm Hydrographs : 100 year and 1/3 of 2 year storms . ' Figure 2 . Site Plan Figure 3A. Stormwater Pumping Station Plan and Section ' Figure 3B: Stormwater Pumping Station Site Plan Figure 4 . Wetpond Facilities Schematic Figure D1 . Existing Conveyance System ' Figure D2 . Proposed Conveyance System 1 MTPR Drainaga Plan/Report/Clrainp Li.b�,/F.rP DRAINAGE PLAN ' MUNICIPALITY OF METROPOLITAN SEATTLE (METRO) ENLARGEMENT III OF METRO TREATMENT PLANT AT RENTON INTRODUCTION ' The Municipality of Metropolitan Seattle (Metro) is enlarging its regional wastewater treatment plant in Renton (MTPR) to ' provide treatment capacity for increased wastewater flows . These increased flows are the result of growth in the plant ' s service area and the transfer of flows from adjacent service areas . The proposed enlargement is a component of Metro ' s Comprehensive ' Water Pollution Abatement Plan for the Seattle-King County Metropolitan area, which implements Metro ' s Wastewater Management Plan for the Lake Washington-Green River Basins . ' The existing Metro treatment facilities in Renton will be retained and upgraded to optimize their capacity. New facilities ' will be added to further increase treatment capacity. The existing plant has the capacity to provide secondary treatment for 72 million gallons of sewage a day (mgd) . The expanded plant will have the capacity to treat 108 mgd. The expansion from 72 ' to 108 mgd is referred to as Enlargement III . Phase A of Enlargement III entails site preparation and perimeter landscaping. Phase B is the liquid and solids stream upgrade and ' expansion. Phase C includes final landscaping and cleanup . The Drainage Plan also addresses the construction and operation of four new additional secondary clarifiers and a new additional 115-feet diameter anaerobic sludge digester. These facilities originally were part of Metro ' s Enlargement III project and were evaluated in the Final Supplemental ' Environmental Impact Statement for the Phase III Enlargement (May 24 , 1991) . Construction of these facilities subsequently has been delayed for budget reasons but are still part of the ' original enlargement proposal . New impermeable areas to be constructed in Enlargement III include paved areas for access roads, parking, a maintenance ' foot-trail, open channels, tanks and process structures . Most roadways and parking areas will drain to the existing underground storm sewer system which discharges to the Green River . Parking ' areas used to unload septage, load dewatered sludge and load grit will drain stormwater runoff to the plant ' s sanitary drain system. The sanitary drain system is routed through the plant ' for treatment and is ultimately pumped to Puget Sound through a 108-inch diameter force main - the effluent transfer system (ETS) . Rainwater falling into open channels and tanks, onto MTPR Drainage Plan/Report/Drainpin.doo/kc6 2 ' covered channels and tanks , and onto process structures will be routed through the wastewater treatment plant . ' This drainage report was prepared in accordance with Paragraph 4 . 22 . 8 of The City of Renton Code . It describes the physical aspects of the existing and proposed stormwater drain system to demonstrate compliance with applicable Core Requirements (CR) , Special Requirements (SR) , and design criteria of the King County Surface Water Design Manual (SWM) . All ' stormwater facilities to be constructed at MTPR are sized to treat stormwater for all of the Enlargement III development, i . e . , eight new secondary clarifiers , two new dissolved air ' flotation tanks (DAFTS) , one new aeration tank, four new primary clarifiers and one new anaerobic sludge digester . Future access roads planned for the middle of the site (to the north of the aeration tanks and between the new aeration tank and new ' secondary clarifiers) were considered in the calculation of peak storm runoff and stormwater quality requirements . Detention/retention facilities will not be required for Enlargement III since peak stormwater runoff will actually decrease . Biofiltration facilities and water quality control ' facilities will be required. Biofiltration swales will be located adjacent to newly constructed roadways and parking lots where sufficient pervious area is available. A stormwater pump station will be constructed at the confluence of the underground stormwater sewer system to lift stormwater to a stormwater wetpond facility located on the ' surface. The capacity of the wetpond facility and pump station will be three times that required by the King County Surface Water Design Manual (SWM) for wetponds . The wetpond facility will be oversized to compensate for new impervious areas which ' will not receive treatment via, biofiltration swales . Metro anticipates that the oversized wetpond facility will attain pollutant removals equal to or greater than removals attainable ' with a wetpond facility sized according to minimum requirements in series with the required biofiltration swales . Treated stormwater will drain from the wetponds to the P-1 channel . Two ' new 30-inch emergency relief overflow sewers , which will also drain to the P-1 channel, will provide flood protection and stormwater treatment bypass during extreme flood conditions in the Green River . ' The stormwater pump station and biofiltration swales will be designed and constructed as part of Phase A. The wetpond ' facilities, associated outfall piping and the emergency relief sewers are scheduled for design and construction during Construction Phase C . Until the time when the oversized wetpond facilities are in operation, stormwater will be pumped to the wastewater treatment plant for treatment and discharge to Puget Sound. Since the pump station is planned to be in operation MTPR Drainage Pian/Report/Drainpin.doc/RCB ' 3 ' during Phase A, " interim" stormwater treatment is planned to begin during the winter of 1992-1993 . ' In this Drainage Plan, Metro has identified preliminary locations for the wetponds in the northern portion of the site in ' the vicinity of the wetland area . Metro is continuing to explore wetland enhancement opportunities in this area, which could utilize and incorporate some of the wetponds . Metro will obtain approval from Renton ' s Stormwater and Wastewater Utility ' Engineering Supervisor if the final location of the wetponds is different from the preliminary location identified at this time. ' Metro ' s proposal deviates from certain technical requirements in the SWM. Metro proposes to (1 ) discharge, on an interim basis, stormwater runoff through the treatment plant for treatment and discharge to Puget Sound through the ETS rather ' than to the Green River, and then to permanently discharge stormwater from the wetponds , and rare emergency flows, into the P-1 channel rather than to the Green River (SWM CR1) ; (2 ) oversize the on-site wetpond facility because of the limited pervious area available to locate the required minimum number of biofiltration swales (SWM CR3 ) ; (3 ) operate a pumping system for ' stormwater conveyance and to use a pump storage facility (wet- well) with less than the minimum required storage volume (SWM CR4) ; and (4) discharge, on an interim basis , stormwater runoff through the treatment plant for treatment and discharge directly ' to Puget Sound through the ETS rather than treatment by the wetpond (SWM SR5) . ' Metro previously requested and obtained approval from the City of Renton Hearing Examiner for variances with respect to items (2 ) and (4) , and a portion of (1) allowing interim discharge of stormwater to the treatment plant . Pursuant to ' Renton Ordinance No . 4342 , effective March 9 , 1992 , Metro is requesting, concurrent with this Drainage Plan, approval ( "modification" ) from the Renton Director of Public Works for ' item (1) to permanently discharge stormwater to the P-1 channel, and item (3 ) to use a pump and smaller storage volume . See Request for Modifications , attached to this Drainage Plan. The Technical Information Report (TIR) Worksheet required with each drainage plan is attached at the end of this document in Appendix E . MTPR Drainage Plan/fteport/D,a inpLi.do c/RCB 4 CONSTRUCTION PHASE A, ENLARGEMENT III : SITE PREPARATION AND PERIMETER LANDSCAPING ' Construction Phase A of Enlargement III includes site preparation for construction of process facilities in Phase B, civil site work including new utilities, roads and parking areas, and perimeter landscaping (grading and plantings) to allow vegetation to mature during the subsequent phases of ' construction. Site preparation will include excavating approximately ' 180, 000 cubic yards of native soil and rock and placement of approximately 30, 000 cubic yards of engineered fill . Excavated material will be stockpiled on-site for use in perimeter ' landscaping. Excess material will be distributed on-site and graded to drain to the existing underground stormwater sewer system. This first construction phase will also involve installation of concrete-drilled shafts (secant piles) , stone ' columns, a site dewatering system, and approximately 840-feet of 48-inch diameter reinforced concrete pipe. ' Perimeter landscaping will involve construction of perimeter berms and fences, about 5 , 500 lineal feet of impervious maintenance trail , an irrigation system, and extensive tree and shrubbery planting. Approximately 120 , 000 cubic yards of material excavated from the secondary sedimentation area will be used for berm construction . Interior civil sitework will include approximately 150, 000 square feet of new and replaced asphalt ' roads and parking lots, and 6 , 500 lineal feet of new and replaced concrete curb and gutter. 1 1 ' MTPR Drainage Plan/Report/Drainp Li.doc/RCR 5 CORE REQUIREMENT NO. 1 : DISCHARGE AT THE NATURAL LOCATION Core Requirement No . 1 requires all surface and stormwater runoff from a proposed project that proposes to construct new, or modify existing drainage facilities must be discharged at the natural location so as not to be diverted onto, or away from, the adjacent downstream property. Discharge from the project must produce no significant adverse impacts to downhill property. Diversion which will correct an existing problem will be considered as a variance. This project will modify existing and construct new drainage facilities . Most of these new drainage facilities are required to comply with the SWM. This project proposes to divert surface and stormwater runoff from it ' s present discharge location, the Green River, to the P-1 Channel . Discharge of stormwater from the MTPR site into the P-1 Channel will not significantly impact downstream property, including the Black River Pumping Station and it ' s forebay. The interim and permanent treated stormwater discharge will be diverted from the existing outfall in the Green River . The project proposes to pump stormwater to the treatment plant with subsequent disposal to Puget Sound during the " interim^ phase of construction. When the wetponds are operational, stormwater will be pumped to the wetponds and will ultimately drain to the P-1 channel . Bypass stormwater will drain to the P-1 channel via new emergency overflow relief sewers when the Green River is at extreme flood stage . Metro has obtained a variance from CR1 for discharging stormwater to the treatment plant on an interim basis . Metro is applying for a modification of CR1 to discharge ' stormwater and emergency relief flows to the P-1 channel on an permanent basis . Existina System The total MTPR site has an area of about 84 . 5 acres . The existing on-site underground stormwater sewer system collects drainage from about 50 acres of impervious and pervious area. The collected stormwater drains by gravity to the Green River via a 120-inch outfall diffuser . Stormwater collected in open ' channels and tanks and on some process buildings, passes into the ' plant process stream for treatment and disposal in Puget Sound through the ETS . Runoff from the solids treatment and handling tanks, the dewatering sludge parking area and the septage unloading areas, about 3 acres in area, also drains to the plant ' s sanitary sewer system for treatment and discharge via the ETS . Wetlands at the northern end of the site collect and store runoff from about 8 acres of pervious area . A section of 1 ' ' ' MTPR Drainage Plan/Report/Dra inp ln.doc/RCP 6 Oakesdale Drive on the northern border of the MTPR site constitutes about 1 . 2 acres of the site. Runoff from Oakesdale Drive enters the City of Renton stormwater system. A grassy swale along Longacres Drive collects and stores runoff from the southwest boundary of the site, about 2 . 5 acres . The swale drains eastward to the P-1 channel . A narrow 3 . 5 acre pervious strip between the eastern property line and the east internal access road drains directly to the P-1 channel . Proposed System The proposed Enlargement III site plan includes 49 . 6 acres of pervious (30 . 75 acres) and impervious (18 . 85) area draining to the underground stormwater sewer system. About 17 additional acres will drain, either directly or via the plant ' s sanitary sewer system, to the wastewater treatment plant . Table 1 presents the area of the various drainage areas of the Enlargement III site. Underaround Stormwater Sewer System. The existing stormwater sewer system will be modified and extended to collect runoff from regraded landscaped areas, realigned roadways, and proposed new parking areas and roadways . The total drainage area tributary to the stormwater sewer system will not be increased in Enlargement III . Modifications to the underground storm sewer system basically consist of relocating existing catch basins to drain realigned roadways and parking lots . Realigned roads and parking lots requiring the repositioning of catch basins are as follows : the internal roads extending from the new entrance off Monster Road, roads extending from the 7th Avenue entrance and around the N Dewatering building, the road realigned around the base of water tower hill , the repositioned parking lot north of the Administration Building, and the new parking lot south of the existing 12 KVA Substation. The stormwater sewer system will be extended to the new roads and parking lots serving the new DAFT complex and anaerobic 't sludge digester. Stormwater from these areas will drain to the plant ' s sanitary sewer system. In the proposed enlargement, stormwater draining to the grit loading ramp will be pumped to ' the plant sanitary sewer system in a manner similar to that ' serving the dewatered sludge loading area . Only when the capacity of the pumps is exceeded, such as during an extreme storm event like the 100-year storm, will stormwater from the ' grit area drain to the stormwater sewer system. Stormwater Pump Station . The existing underground stormwater sewer system will be augmented with a stormwater pump system at the storm sewer junction manhole . The pump station is necessary to lift stormwater flows requiring treatment from the underground 1 ' MTPR Drainage Plan/Report/Drainpin.duc/RCB 7 storm sewer to water quality facilities located on the surface. This pump station will have the capacity to pump three times the required design storm peak flow rate for wetponds, i . e . , 4 . 5 cfs (2 . 9 MGD) . Flows in excess of the pump capacity will bypass the pump station and drain to the Green River via the existing 120- inch outfall diffuser. The proposed system will retain the flap gates located at the outfall manhole to prevent the influx of the Green River into the stormwater sewer system during extreme flood stage in the Green River . Emergency Relief Sewers . Two new 30-inch emergency relief overflow sewers, one to serve each of the two stormwater sewer branches, are proposed for the underground stormwater sewer system. Stormwater entering these overflow sewers will discharge to the P-1 Channel . These overflow sewers will provide relief to the plant ' s stormwater sewer system during extreme flood stage in the Green River, and allow flows to bypass the stormwater water quality facilities as required by the SWM. Also, these sewers will alleviate the need for another pump station while satisfying the goals of the Green River Management Group regarding discharge into the Green River during extreme flood stage. The relief sewers take advantage of the elevation difference between the Green River and P-1 channel during extreme flood events, i .e. , Elevation 121 and Elevation 114, respectively, during the 100-year flood event . Emergency overflow weirs will be set at Elevation 118 . 0 and be located near the eastern end of the 30-inch pipe branches . Stormwater flowing over the weirs will flow by gravity to the P-1 channel through 30-inch pipe . Both emergency relief sewers will be supplied with a flap gate to prohibit water in the P-1 channel from entering the on-site stormwater system. The emergency relief overflow sewer plan will satisfy the goals of the Green River Management Group. The Green River Management Group manages the Green River Drainage Basin and controls the influx of flows to the Green River . For example, the Black River Pumping Station must start to throttle pumping when the Green River reaches 9000 cfs and must stop once the flow in the Green River reaches 12000 cfs, i . e. , about the 100-year flood stage. Overflowing MTPR' s storm sewer system to the P-1 channel allows the Black River pumping station to regulate the ' discharge of stormwater to the Green River, a preference of the ' Green River Management Group. Also, the stage of the Green River will automatically throttle MTPR stormwater bypass flow draining to the Green River via the outfall diffuser . Stormwater Ouality Treatment . Both biofiltration and water quality control facilities are required for this project in accordance with SWM CR3 and SRS . Biofiltration swales will be constructed alongside new roadways and parking lots where sufficient pervious area is available . Runoff from about 33% of 1 ' ' MTPR Drainage Plan/Report/Drainpin.d... RCB 8 the proposed new roadway and parking lot surface area will be treated with swales . Biofiltration swale effluent will subsequently drain to the stormwater sewer system from which it will be pumped to the water quality control facility. The swales will be constructed in accordance with Sections 1 . 2 . 3 , 4 . 6 .3 , and 4 . 3 . 6 of the SWM. Because not all new roadways and parking areas can be treated by localized biofiltration due to site limitations , the required minimum volume and surface area of wetpond will be increased to three times that required by the SWM SR5 . The oversized wetpond facility will impart equivalent or better treatment than biofiltration of all new impervious roads and parking lots in conjunction with wetponds sized for the minimal acceptable criteria . The wetponds will be a series of three ponds located near the existing on-site wetlands . The ponds will be terraced to allow gravity flow between the wetponds, ultimately draining to the P-1 channel . The wetpond facility will be designed and constructed in accordance with SWM Sections 1 . 3 . 5, 4 . 6 .2 and 4 . 4 . 4 . In this Drainage Plan, Metro has identified preliminary locations for the wetponds in the northern portion of the site in the vicinity of the wetland area . Metro is continuing to explore wetland enhancement opportunities in this area, which could utilize and incorporate some of the wetponds . Metro will obtain approval from Renton ' s Stormwater and Wastewater Utility Engineering Supervisor if the final location of the wetponds is different from the preliminary location identified at this time. The proposed stormwater pump station, the force main to the treatment plant , and the biofiltration swales will be constructed as part of Phase A Construction . The pump station should be operational for the winter of 1992-1993 . The wetponds and the emergency relief overflow sewers are planned for design and construction during Phase C . Phase C design is scheduled to commence in late 1994 . In the interim, the pump station will pump stormwater to the headworks of the wastewater plant for treatment and subsequently discharge to Puget Sound via the ETS . In the event of an emergency, stormwater will be routed ' directly to the Green River outfall . Metro currently holds a ' NPDES permit to discharge sewage to the Green River in such an emergency, but has never needed to do so. Also, Metro does not currently need an NPDES permit to discharge stormwater to the Green River . Stormwater pumping will be redirected to the wetpond facility when it becomes operational . I ' MTPR Drainage Plan/Re�,im'V DCG iI1P LL dqc/FCB 9 CORE REQUIREMENT NO. 2 : OFF-SITE ANALYSIS Core Requirement No . 2 requires that all proposed projects must identify the upstream tributary drainage area and perform an analysis of the drainage system downstream from the proposed project . This analysis includes a Level 1 analysis of on-site and off-site drainage systems for the minimum distance prescribed in the SWM. This analysis also includes hydraulic and qualitative assessments of diverting MTPR 100-year 24-hour stormwater flows into the P-1 Channel . Both assessments concluded that the impacts of diverting MTPR stormwater into the P-1 Channel were insignificant . Upstream Drainage Areas The King County Reconnaissance Program has placed the MTPR site within the Black River watershed. Appendix E contains a schematic of the Black River Drainage Basin . A vestige of the Black River, the P-1 channel runs along the eastern boundary of the treatment plant . Except for rainwater falling on or near the banks of the P-1 channel , all site drainage flows either to the stormwater or sanitary sewer systems . The current stormwater sewer system drains to the Green River. The sanitary sewer system discharges to the wastewater treatment plant . The treatment plant and stormwater cutfall are located just upstream of the confluence of the Green River and Black River . The Green River and Black River combine to form the Duwamish River. The Green-Duwamish River drains approximately 483 square miles of south and southwest King County. Flow in the main river below River Mile 64 . 5 is controlled by release from Howard A. Hanson Dam. The mean annual flow at Auburn is 1366 cfs (1986) . The upper drainage of the Green-Duwamish system is fed by rains and snowmelt . The lower drainage - Big Soos Creek and Newaukum Creek, the two main tributaries - are fed by rain and groundwater . The northern portion of the lower Green River basin is dominated by the commercial areas of Southcenter, surrounding commercial and light-industrial land uses, three major traffic arterials , and the shopping district north of Sea-Tac Airport . ' Existing and anticipated problems in the lower Green River are ' clearly development-related . Severe erosion along the basin ' s steep slopes and valley walls (Grandview Park, Kent Highlands Landfill) results in downstream sedimentation that reduces channel capacity and degrades water quality . Continued rapid development in this basin, without installation of adequate runoff controls, will exacerbate existing problems . A vestige of the Black River intersects the Green River at River Mile 11 and forms the Duwamish River . The Black River used MTPR Drainaga Plan/Report/Deg inp ln.doc/RCF 10 to be the primary drainage for Lake Washington before the Lake Washington Ship Canal was dug in 1917 . Now the Black River originates from storm drainage and groundwater in the center of Renton and flows west 2 . 65 miles to its confluence with the Duwamish. Springbrook Creek (also known as the P-1 Channel) drains about 12 miles along the east valley hillside . The Black River basin has extensive areas of impervious surface and is almost wholly contained within the cities of Tukwila, Renton, and Kent . The P-1 Channel conveys drainage from the Southcenter area north of I-405 into the former Black River channel . The channel generally follows the former path of Springbrook Creek and thus is referred to as both Springbrook Creek and the P-1 Channel . Drainage is impounded in the P-1 pond (The Black River Pumping Station Forebay) and pumped into the Black River channel before confluence with the Green River . The P-1 channel joins the former Black River south of a forested wetland area, at the P-1 Pond, behind the Black River Pumping Station. Problems in the Black River basin stem partly from high runoff velocities from developing areas . Steep slopes and saturated soils in the ravines, garbage disposal along riverbanks , and commercial and industrial runoff have all contributed to visibly poor water quality, sedimentation, decimated fish habitat , and other complications . The King County Basin Reconnaissance Program Summary notes that Springbrook Creek, where it flows under the SW 16th Street bridge just east of Longacres (and just upstream of the MTPR) is one of the worst examples of surface water degradation in the area . Problems with this channel will continue unless storm flows are controlled where they originate, steep valley walls are protected from erosion and landslides, garbage dumping is checked, and sediment transport into the valley floor is reduced. Downstream Drainage Areas Water quality in the Duwamish up to River Mile (RM) 11 is designated "Class B" (good) due to, and in full consideration of, its industrial nature. The navigable portion of the Duwamish Waterway, below RM 5 . 2 , is dredged almost every year to alleviate the river ' s heavy sediment load. The Green River from the mouth ' of the Black River (RM 11) to RM 42 . 3 is designated "Class A" ' (excellent) . Stormwater from the MTPR discharges at RM 12 .2 . The lower Green River sites have relatively moderate turbidities and high suspended solids . According to the King County Sensitive Area Map Folios , the treatment site is not in the 100- year flood plain. ' Discharge of treated stormwater and emergency overflow from ' MTPR to the P-1 channel will produce no significant quantity or MTPR Drainage Yla n/Report/DCa Snpin.doclkCB 11 quality impacts to the P-1 channel, Black River Pumping Station or forebay. A hydraulic modeling analysis requested by the City of Renton concluded that the 100-year 24-hour flood flow from the MTPR site would raise the level of the Black River forebay only 0 . 07 feet (about 1-inch) assuming very conservative conditions . A one-inch rise in the forebay will not significantly impact any of the surrounding property or habitat . Appendix A contains a letter describing the results of the hydraulic/hydrologic analysis . Similarly, an analysis of the potential water quality impacts of MTPR stormwater on the P-1 channel was addressed in a letter from Adolphson and Associates to Metro. Water quality in the P-1 Channel generally appears turbid at the point of discharge to the Slack River. The Black River, both upstream and downstream of the MTPR site, is listed among the most degraded streams in the Metro sampling area . Considering the degraded water quality of the P-1 channel, the likely higher water quality of MTPR' s treated stormwater, and MTPR ' s relatively small contribution of flow quantitatively, the conclusion is reached that " . .no discernible impacts to the P-1 Channel are anticipated in the short or long term future . " This letter is attached in Appendix B. On-site Drainage Table 1 presents the tributary drainage areas of the proposed Enlargement III . Of a total site area of 84 . 5 acres, only 49 . 6 acres will be tributary to the site ' s stormwater sewer system. The 49 . 6 acres will consist of about 30 .7 acres of pervious surface and about 18 . 9 acres of impervious surfaces . Of the 18 . 9 acres of impervious surfaces, only 12 . 0 acres will be subject to vehicular use or chemical storage. About 3 . 6 acres of the site will drain directly to the P-1 channel, about 7 . 8 acres will drain to the wetlands, about 2 . 93 acres will drain to the sanitary system from the Sludge Dewatering Facility (during non- extreme storm events) and about 17 . 0 acres of the site will be open tanks and channels or will drain to treatment process tanks . The existing site impervious area is approximately 16 . 5 acres . Enlargement III will increase the total impervious area ' by 2 .4 acres to 18 . 9 acres . Only 0 . 4 acres of this new ' impervious area will drain to the stormwater system. The remaining impervious areas will drain to the plant ' s sanitary system. Realignments of existing roads will not significantly increase the area of impervious surfaces draining to the I , stormwater sewer system. Surfaces that will significantly contribute higher stormwater flows are the new road and parking lots serving the new DAFT complex, the new parking lot for the 12 ' ' MTPR Drainage Plan/Report/Drainp Li..7oc/RCB ' 12 KVA Substation, and the proposed roadways providing access to the new secondary clarifiers and aeration tank . However, stormwater eminating from the roads and parking areas serving the DAFTS will be pumped to the sanitary sewer . Only when the capacity of the pumps are exceeded will runoff from the DAFTS enter the stormwater sewer. The perimeter trail, which is about 5, 500 feet long and between four and six feet wide, constitutes about 0 . 8 acres of impervious surfaces . This trail is hydraulically disconnected from the stormwater sewer system and should not significantly alter the existing drainage conditions along the trail . The trail will drain to the surrounding land, including the wetland, thereby receiving treatment by way of infiltration. The peak stormwater runoff during the 100-year 24-hour design storm (3 . 9 inches of rainfall) for Enlargement III is estimated to be 23 . 0 cfs . The post-development 100-year 24-hour peak storm runoff rate at the outfall manhole is estimated to be 22 . 6 cfs, or 0 .4 cfs less . The existing on-site stormwater sewer system has the capacity to handle the 100-year 24-hour storm. Off-site Drainage No stormwater originating off-site drains through the MTPR site . All stormwater runoff originating on-site drains to either the Green River, the P-1 Channel, or to the treatment plant via open vessels or the plant ' s sanitary sewer system. Rain falling on the MTPR site therefore does not affect other sites . Rain falling on other sites does not flow through the MTPR site. MTPR Drainage F1sn/Repo rt;Drainpin.90 c/HC[+ 13 CORE REQUIREMENT NO. 3 : PEAK RATE RUNOFF CONTROL King County SWM Section 1 . 2 . 3 , CR3 requires that all proposed projects must provide runoff control through a combination of peak rate runoff control and on-site biofiltration measures . Peak rate runoff control is provided through detention, retention or infiltration. This project will not be required to provide peak rate runoff control, i . e . , detention, retention or infiltration. Stormwater modeling indicates that the proposed Enlargement III project will not increase the peak rate runoff resulting from the 100-year 24- hour storm more than 0 . 5 cfs . In fact , modeling indicates that the peak rate runoff from the 100-year 24-hour storm will decrease . This proposed project will be required to provide biofiltration to stormwater before the stormwater leaves the site since over 5000 square feet of new impervious area subject to vehicular use or chemical storage will be constructed. The proposed plan is to construct localized biofiltration swales adjacent to new roadways and parking lots where sufficient pervious area is available . About 33% of the new roads and parking lots will be served by five biofiltration swales . Not all of the new roadways and parking areas will receive biofiltration. A wetpond facility will be oversized to compensate for the inability to provide the minimum biofiltration swales . Metro has obtained a variance from CR3 to use this approach. Peak Rate Runoff Control Requirements All proposed projects must provide peak rate runoff control except for any of the following conditions : The project includes less than 5, 000 square feet of additional impervious surface ' * Stormwater modeling indicates that the proposed project will not increase the peak rate runoff resulting from a 100-year, ' 24-hour storm more than 0 . 5 cfs above the peak rate runoff ' for existing runoff conditions * The proposed project will discharge surface and stormwater runoff directly to: a regional facility; below River Mile 6 . 0 of the Green-Duwamish River; a lake; a wetland; or a closed depression . � i MTPR Drainage Plan/Report/Drainp L�.doc/R�'H 14 ' Stormwater Modelina Results ' The existing and proposed stormwater sewer systems were modeled to establish whether the proposed construction will increase the peak flow resulting from a 100-year storm by more than 0 . 5 cfs . Appendix A describes the methodology used to ' determine the peak storm runoff rates for the pre- and post- developed site. Modeling demonstrated that the calculated peak runoff for the 100-year 24-hour storm after development is less ' than before development -- 22 . 99 cfs before development vs . 22 . 61 cfs after development . Flow hydrographs at the outfall manhole are presented in Figure 1 . ' Because modeling indicated that the peak rate runoff for the 100-year 24-hour storm after development is less than before development, and because the MTPR site is not in a Critical ' Drainage Area, the proposed project is exempt from Core Requirement No . 3 with respect to peak rate runoff control . ' The modeling results are consistent with changes in drainage that will be brought about by Enlargement III . The new additional channels, tanks, DAFTs and anaerobic digester will be constructed on over four acres of pervious area that is currently ' tributary to the stormwater sewer system. Stormwater from these new facilities will be directed to the wastewater treatment plant and will subsequently drain to Puget Sound via the ETS . Proposed new impervious areas will increase the storm sewer tributary impervious area by 2 . 3 acres, from 16 . 6 to 18 . 9 acres . ' Some of the new net impervious area is a maintenance trail that meanders along the perimeter of the site. Most of the trail is separated from the impervious areas that drain directly to the stormwater sewer. Therefore, runoff from the trail must flow over pervious areas to reach a stormwater inlet . Considering that model conditions inherently assume pervious areas to be saturated or nearly saturated, the relatively small net increase ' in impervious area does not appear to be sufficient to offset the removal of more than four acres of pervious area from the drainage basin. ' Tables 2 and 3 present the flow quantities and velocities for each storm sewer pipe segment for the 100-year 24-hour storm for pre- and post-development , respectively. The tables show that ' flow between the northern and southern 30-inch drain lines is fairly equal . Only one pipe segment, the 30-inch pipe at node 1004, experienced flow greater than its rated capacity during t this design storm. Though the peak flow at node 1004 was about 102 percent of capacity for both pre- and post-development conditions, no overflows occurred in any part of the sewer system during this hypothetical storm. Thus, the proposed stormwater ' sewer system is capable of conveying the peak flows generated by the 100-year 24-hour design storm. ' MTPR Drainage Plan/Report/Diainpin.�7oc/RCB ' 15 ' Biofiltration Reauirements ' Biofiltration processes runoff from impervious areas subject to vehicular use or chemical storage . Biofiltration must take place prior to discharge from the project site and be designed as described in SWM Section 4 . 6 . 3 . Biofiltration facilities are ' designed based on the peak flow rate from the 2-year 24-hour storm event . ' One option for meeting the biofiltration requirements is to pass all of the site ' s stormwater through biofiltration after collection and conveyance to the storm sewer outfall manhole . ' This option, though meeting the intent of the SWM, bestows some practical difficulties which can be avoided with another treatment option. Most of these difficulties have to do with the capacity of the pump system, its construction and the required ' and available power sources and force main piping. For instance, the pump station must be sized to pump 10 . 2 cfs to the bioswale, i .e. , the 2-year 24-hour peak storm flow at the storm sewer ' outfall manhole. A wetwell could be designed to attenuate the peak flow rate . However, any increase in the size of the pump station will significantly impact the design and cost of the facility due to the extreme depth of the pump station. (The ' invert of the pump station wet well will be about 25 feet below ground surface . ) Also, a pump station with a capacity of 10 .2 cfs would require an additional source of emergency power and ' deny Metro the use of the to-be-abandoned 12-inch city water main . ' Proposed Biofiltration Plan The proposed method of providing the required biofiltration is to construct swales adjacent to new roadways and parking lots ' where sufficient pervious area is available and to pump stormwater from the outfall manhole to an "oversized" wetpond facility. ' A total of five biofiltration swales will be constructed. New impervious surfaces which will be served by local swales ' include the access road that starts at Monster Road and winds around water tower hill , the new parking lot north of the Administration Building, the new parking lot south the 12 KVA Substation, and the east-west road just south of the Sludge ' Dewatering Building. These local swales will serve 33% of the new impervious surfaces subject to vehicular use, but over 75% of the net increase in impervious road surfaces . ' The proposed swales will be constructed in Phase A in conjunction with the new roadways and parking lots that they will serve . The swales will be designed to handle the peak flow from the 2-year 24-hour storm event for the tributary area . All the swales will receive the 100-year 24-hour storm from the tributary ' MTPR Drainage Plan/Report/D ra i lip I loci R,'P 16 ' area . Treated effluent from the swales will drain to the stormwater sewer system. Roadways and parking areas not treated by localized biofiltration because of site constraints will still satisfy the requirements of SWM Section 1 . 2 . 3 . Figure 2 shows the location of the five biofiltration swales planned for the Enlargement III project . ' The proposed oversized wetpond facility, which will be three times the minimum area and volume suggested by Section 1 .3 . 5 of the SWM, along with the locally constructed biofiltration swales, will provide equivalent or better treatment than a minimum sized wetpond facility and biofiltration facility. Over an entire ' year, it is anticipated that an equivalent or greater mass of pollutants will be removed by the oversized wetpond facility and local swales than by a minimum required wetpond facility and biofiltration facility . (See Appendix C which contains a letter from Metro ' s Technical Staff referencing technical studies of wetponds and stormwater treatment . ) 1 ' MTPR Drainage Plan/Repurt/Urainpin..i...R"F ' 17 CORE REQUIREMENT NO. 4 : CONVEYANCE SYSTEM ADEQUACY Core Requirement No. 4 pertains to the conveyance system' s composition and adequacy, pumping stations, drainage easements, ' interception of interflow (near-surface groundwater) and outfall construction . CR4 only allows pumping systems on storm drainage by variance, and only if certain minimum requirements are met . The stormwater drainage and treatment plan proposed in this ' document requires a pump system to utilize wetponds for treatment . Thus, a variance will be required from CR4 to operate the proposed pumping system. The pump system will only have ' about 67% of the minimum required storage due to practical difficulties . Adeauacy of the Proposed Conveyance System All proposed projects must show that a conveyance system exists, or will be constructed, to adequately convey the runoff from the 100-year 24-hour design storm. This compliance condition includes runoff that originates on the project site plus any existing runoff that will be conveyed through the 1 project site . Surcharged conditions for pipe systems is acceptable for demonstrating the adequacy of the conveyance system provided that all runoff is contained within the conveyance system elements and does not inundate the crown of the roadway . Modeling results indicate that the existing and proposed ' conveyance system is adequate to convey the 100-year design storm without producing overflows . Tables 2 and 3 present flows and velocities through each stormwater pipe segment for the 100-year 24-hour storm event for pre- and post-development, respectively. ' Flow between the northern and southern storm sewer branches is fairly equally split . Only one pipe segment , the 30-inch pipe at node 1004 , was surcharged during the design storm simulation. ' Though peak flow at Node 1004 was about 102% of capacity for both pre- and post-development conditions, nowhere in the system did stormwater overflow a manhole cover . The conveyance system was ' analyzed using the procedure described in the section titled Core Requirement No . 3 . During the 100-year flood event, bypass flows are planned to discharge to the P-1 Channel via the emergency overflow relief sewers . Assuming the overflow relief sewers are about 300-foot in length and the P-1 discharge invert will be Elevation 115 , the ' capacity of the relief sewers is estimated to be about 25 cfs each. These sewers will have sufficient capacity to handle the overflow from each of the main 30-inch storm sewer branches . ' Proposed Pumping Station MTPR Drainage Plan/RNporU Dra inp Li. i�,/F'.'P ' 18 ' The proposed stormwater treatment system includes a pumping station. The pumping station is needed to lift stormwater to the 1 ground surface and then to convey the stormwater to the treatment plant during the interim period and to the wetpond facility once the wetponds are constructed . Metro has obtained a variance from ' CR4 for use of a pumping station during the interim. Metro is requesting a modification of CR4 to operate the pumping station on a permanent basis . The pumping station allows Metro to utilize the existing and extensive system of underground piping at the MTPR site and to implement SWM' s preferred method of water quality treatment -- wetponds . The site ' s network of underground storm sewer pipes were originally designed to allow stormwater to drain by gravity to the Green River. The sewer pipes are located relatively deep underground because of the physical barriers created by the ' process facilities . For example, the depth of the ground cover at the outfall manhole (the confluence of the stormwater sewer before discharge to the Green River) is about 26 feet . ' A profile and plan of the proposed pumping station is presented in Figure 3A. A site plan showing the location of the 1 pumping station and valave vault is shown in Figure 3B. The pumping station is a wet well type with submersible dual pumps , each with a capacity of 4 . 5 cfs . The wet well will be 12 feet 10 inches in diameter and about 40 feet deep. The invert of the pumping station will be at Elevation 92 . 2 . An adjacent valve vault will house the pump controls and valve operators to direct flow to either the treatment plant or the wetponds . A 48-inch overflow at Elevation 113 . 0 will bypass flows to the existing outfall diffuser in the Green River. A backflow prevention check valve will be installed on the 48-inch overflow. New emergency overflow weirs and relief sewers, to be constructed in ' Construction Phase C, will bypass flows when the storm sewer backs up to Elevation 118 . 0 . ' The pump system has been designed to allow the stormwater sewer to drain completely during normal operational and hydrologic conditions . Bypass of the pumping station will not ' occur until the water elevation in the wet well reaches 113 . 0 . Emergency overflows will not occur until the water elevation in the storm sewer reaches 118 . 0 . ' Metro ' s proposed pump system complies with all the SWM minimum requirements to allow a pumping station on a stormwater system but one - a storage facility sized to hold 25% of the ' total volume of runoff for the developed tributary drainage area for the 2-year, 24-hour duration design storm event . According to modeling results , a total storage volume of 314 , 000 gallons is ' required. The wetpit and stormwater sewers are estimated to have a storage capacity of about 200 , 000 gallons when stormwater reaches the relief overflow weirs, i . e . , about two-thirds of the MTPR Drainage Plan/Rport/Dra in�. l n.�]oc,k'H ' 19 ' required capacity . The deviation from the required storage volume is addressed through adequate safegurads incorporated into ' the design of the pumping system, as discussed below. Considering the topography of the site and the depth of the existing stormwater sewer system, an underground well would ' probably be required to provide the additional required wet well volume . This wet well would be similar in construction to a wetvault and carry the same practical difficulties given the depth of the stormwater sewer system. Based on the apparent purpose of the storage volume requirement, i . e . , to provide flood protection in case of power outage or a mechanical failure, ' Metro suggests that the proposed stormwater pumping station, together with other measures, will satisfy the intent of the requirement . In addition to the proposed storage capacity inherent in the wet well and proposed storm sewer, the following safeguards will provide additional protection to surrounding property from flooding in case of an emergency situation such as a power outage or a mechanical failure : ' * Gravity overflow in excess of the pump capacity to the P-1 channel during extreme storm events . ' * Gravity overflow in excess of the pump capacity to the Green River during non-extreme storm events . ' * An emergency power supply and dual power feeds to the treatment plant . ' * External controls as well as external alarms . * A 24 hour a day on-site monitoring, operations and maintenance staff . ' * Flap gates to prohibit the influx of the Green River into the pumping station during extreme flood stage . Metro is requesting a modification from the required wetwell volume . If Metro cannot obtain modifications for its proposed pump system, then it likely will need to construct a large underground vault at the location of the outfall manhole. A wetvault would not be consistent with SWM' s preference for wetponds , would require a modification from SR5, and would be very costly. Constructing a wet vault would create practical difficulties, for example the depth of ground cover at the outfall manhole will be about 30 feet . Such a large structure would deprive Metro from reasonable use and development of its property; the area needed to construct a wetvault is currently dedicated to future sewage treatment purposes . Because a modification would allow Metro to implement the preferred method of water quality treatment, it MTPR Drainage P laNkeporVDra i np ln.dcna RCi; zo will not be detrimental to the public welfare or injurious to other property in the vicinity . 1 1 1 MTPR Drainage Plan/kap.,r[/D[a Lip ln. lu.]/RCP t21 ' CORE REQUIREMENT NO. 5 : TESCP All engineering plans for proposed projects that propose to construct new, or modify existing drainage facilities shall include an temporary erosion and sedimentation control plan (TESCP) to prevent sediment-laden runoff from leaving the site during construction . ' Enlargement III meets the requirements of Section 1 . 2 . 5 of the SWM. A temporary erosion and sedimentation control plan (TESCP) has been prepared for the proposed project . The TESCP is included in Addendum No. l of the Contract Drawings and Specifications . The TESCP was submitted to the City of Renton on July 11, 1991 , certified by the City of Renton, and submitted to the Hearing Examiner on July 16, 1991 . Subsequently, the TESCP ' has been revised in response to City of Renton review comments . These comments were incorporated into the contract drawings . MTPR Drainage Plan/Repo r[/Dra inp Li %,c/RCE ' 22 SPECIAL REQUIREMENT NO. 5 : SPECIAL WATER QUALITY CONTROL In addition to the Core Requirements, the proposed project has also been assessed for compliance with twelve Special ' Requirements of the SWM. Each special requirement identifies "Threshold" criteria to assess the compliance of the proposed project with the Special Requirements . ' Based on the threshold criteria, the proposed project is exempt from all the Special Requirements but one -- SR5 : Special Water Quality Control . Because the proposed project will result ' in more than one acre of impervious surface that will be subject to vehicular use and runoff from the project will discharge into the P-1 channel and the Green River, a Type 1 stream, a wetpond, wetvault or water quality swale is required for water quality ' control . The wetponds will be designed and constructed during Phase C. In the interim, stormwater requiring treatment will be pumped to the wastewater treatment plant . A variance has been obtained to use the wastewater treatment plant , rather than wetponds, for ' treatment during the interim period. Stormwater Ouality Treatment Plan ' This project proposes to provide water quality treatment to stormwater via an oversized wetpond facility. The proposed wetpond facility will be oversized three times the required minimum surface area, volume and peak flow rate. Metro believes this treatment scheme will provide equivalent or better treatment than a minimally sized wetpond and biofiltration facility. (See Appendix D. ) The wetpond facility will receive stormwater from ' the proposed stormwater pumping station. The preliminary location of the wetponds will be near the wetlands . Stormwater will flow by gravity through the cells of the wetpond and effluent will drain by gravity to the P-1 channel . Minimum Requirements for Wetoond Facilities ' The size of the wetpond is determined as follows in accordance with SWM Section 1 . 3 . 5 : ' * The design water surface area shall be a minimum of one percent of the impervious surface area in the drainage sub-basin contributing to the facility . ' * The design volume shall be as a minimum the total runoff volume from the proposed tributary sub-basin ' using the total precipitation equal to one-third of the 2-year, 24-hour total precipitation . 1 ' MTPR Drainage Plan/Report/Drainpin.,9oc/RCB ' 23 ' Enlargement III will result in a total of 18 . 9 acres of impervious surfaces as shown in Table 1 . Thus, the minimum ' required water surface area of the wetponds is 1% of 18 . 9 acres or 8200 square feet . ' The minimum volume requirements for the wetpond facility were calculated based on SWM Chapter 3 and as described in the section Core Requirement No. 3 : Runoff Control . The required wetpond volume was calculated using one-third of the total precipitation ' resulting from the 2-year 24-hour storm event, i .e 33% of two inches, or 0 . 67-inches . Based on the modelling results, the minimum required wetpond volume is 210 , 000 gallons . With a ' minimum required surface area of 8200 square feet, the wetpond must have an active depth of 3 . 4 feet . This depth satisfies the requirement to maintain a permanent pool in a wetpond between three to six feet (Section 4 . 6 .2) . An additional one foot of ' dead storage must also be provided for sediment storage, for a total depth of 4 . 4 feet . ' The wetponds must be designed to bypass flows greater than the peak flow resulting from the one-third of the 2-year 24-hour storm (Pt-wq design storm) for developed conditions (Section ' 4 . 6 .2) . The peak flow resulting from the Pt-wq design storm under developed conditions is 1 . 5 cfs based on the HYDRA4 model . All flows greater than 1 . 5 cfs must bypass the wetpond facilities . The pumps at the outfall manhole will be sized to ' only pump the required peak flow. Flows in excess of the design peak flow rate will drain by gravity to the Green River. ' Proposed Oversized Wetpond Facilities The wetpond facilities will be sized to be three times the minimum SWM requirements . The wetponds are being oversized to ' attain a mass removal of pollutants equivalent to, or greater than, that which can be attained with a minimum sized wetpond in series with a bioswale . Oversized wetponds with localized ' biofiltration swales will reduce the required pump size and will allow the use of existing on-site services (pipe, emergency power supply, etc . ) , thus avoiding the hardship of having to install ' new piping, additional emergency power capacity and flow bypass structures at the water quality facility. The oversized wetpond facility will be designed for a peak ' flow rate of 4 . 5 cfs and a volume of 630, 000 gallons . The total water surface area will be at least 24, 600 square feet, and the permanent pool depth will be between three and six feet with one ' more foot for dead storage for sediment (Section 4 . 6 .2) . The active depth will depend on the actual surface area, the slopes of the dikes, surface contours, and whether concrete walls are ' used in place of dikes . The stormwater pumping station will have a capacity of 4 . 5 cfs with flows in excess of this rate draining to the Green River . For comparison, the average 24-hour runoff ' MTPR Drainage Plan/RPporc/Drainpin.doC/RCB 24 ' flow resulting from the 2-year 24-hour storm from the entire site is about 5 cfs . SWM Wetpond Design Criteria The wetpond will be designed in accordance with SWM Sections 4 . 6 .2 and 4 . 4 . 4 . Section 4 . 6 . 2 controls the design if discrepancies exist between the two sections . Figure 4 is a schematic of a three celled oversized wetpond facility at its ' preliminary location near the wetlands on the north end of the site. Figure 2 shows the preliminary location of the proposed wetpond facility on the site plan. ' In this Drainage Plan, Metro has identified preliminary locations for the wetponds in the northern portion of the site in the vicinity of the wetland area . Metro is continuing to explore ' wetland enhancement opportunities in this area, which could utilize and incorporate some of the wetponds . Metro will obtain approval from Renton ' s Stormwater and Wastewater Utility ' Engineering Supervisor if the final location of the wetponds is different from the preliminary location identified at this time. t Design criteria of specific note are reproduced: * Depth of permanent pool shall be 3 to 6 feet plus one foot of dead storage for sediment . * The length:width ratio at the design surface area shall be no less than 3 : 1 (preferably 5 : 1) . * The facility will be divided into three cells . The first cell shall contain about 10% of the design surface area, the second and third cells about 45% each of the design surface area . * Flows above the 2-year 24-hour peak storm flow must by- pass the facility . A mechanism must be provided to take the facility off-line. * A gravity drain one foot above the facility bottom shall drain the facility in less than four hours . ' Compliance with SWM Design Criteria The wetpond facility will be designed as three cells , the first cell having about 10% of the total water surface area and the other two cells with about 45% each of the total water surface area . Each cell will have a length to width ratio greater than 3 : 1 . The total water depth will be at least 4 feet ' in each cell , one foot of dead storage for sediment and at least 3 feet of permanent pool . The inlet and outlet of the tanks will be designed to maximize travel time through the facility . The ' inlet will be designed to prevent scouring of the bottom sediments and promote sedimentation . MTRR Drainage Plan/Repo rc/Dra inpin. 7oc/RCP. ' 25 ' The capacity of the stormwater pumps (4 . 5 cfs) prevents flows any greater than three-times the design storm peak flow rate from ' entering the wetponds . Thus, the pumping station will act as the required overflow system to control discharge of the 100-year 24- hour design storm and the required emergency overflow spillway to ' safely pass the 100-year 24-hour storm. A gravity drain for maintenance will be installed on each cell . The drain shall maintain one foot of depth and will drain the facility in less than four hours . The outlet drains will be controlled by valves in a control manhole (s) . Berm embankments shall be constructed as recommended by a geo-technical engineer following the criteria described in Section 4 . 4 . 4 of the SWM. Retaining walls may be used instead of berms . These walls will be designed by a structural engineer registered in the State of Washington and in accordance with ' Section 4 . 4 . 6 . Access to the wetponds will be provided for maintenance and public viewing . If located near the wetlands, the perimeter trail can serve as the necessary access . Signs ' will be designed, installed and located so at least one is clearly visible and legible from all adjacent streets and paths . MTPR Drainage Plan/Repoa/D rai nk>1 ri. 4oc/RCB ' 26 ' MODIFICATIONS ' See attached Request of Modifications : Pursuant to Ordinance No . 4342 , March 23 , 1992 . 1 1 MTPR Drainage Plan/Neporc/Dea inFLi.doc/R'P Figure { 2—YEAR and 100—YEAR DESIGN STORM HYDROORAPIIS 25 20 ■— 100 year pre—development 15 100 year post—development c 2 year past—development If s 10 5 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 V' N iv �n in �n �n rn 1� [O-n v� :5 n OO Oi O CV � V � tU of CV M hours Table 1 Drainage Basins-Proposed Development C d E 0 vM Area/Basin Acres L W 1 . Tributary to P-1 Channel 3.57 c 2. Tributary to Wetlands 7.72 d a. Oakesdale 1 .16 cC C 3. Tributary to Longacres Swale 2.33 M 4. Septage Unload 0.19 5. Sludge Dewatering 2.93 E 6. Direct to Treatment Plant 17.00 7. Tributary to Stormwater Sewer 49.60 a. Pervious Area 30.75 a b. Impervious Area 18.85 c (Subject to Vehicles & Chemical Storage) 12.00 !a Total 84.50 i 540024RA 1 ' Table 2. Results of 100 year Storm Modeling Pre-Development Total Contributing Area = 48.47 Acres Peak Flow= 22.99 cfs ' Link Node Length Downstream Elevation Diameter Area DesO DesVel Time LatLong Sys Long ID (ft) Rim Invert (in) (Acres) cfs) (fps) (min) (ft) (ft) 1 1101 290 126.9 119.5 8 1.12 0.56 3.28 1.48 290 290 2 1100 58 12621 119 8 1.84 0.89 3.18 0.3 348 348 3 1099 105 12621 119 8 0.64 0.45 2.51 0.7 105 105 4 1098 324 12525 113.19 15 2.48 1.31 4.23 1.28 429 777 ' 5 1097 108 12525 111.25 15 2.48 1.24 4.16 0.43 537 885 6 1096 77 114.24 106.39 12 0.23 0.26 2.02 0.63 77 77 7 1095 40 111 106 12 0.49 0.43 2.56 0.26 117 117 ' 8 1094 70 109.9 105.44 12 0.98 0.86 2.91 0.4 187 187 9 1093 95 110.1 104.68 12 1.5 1.33 3.3 0.48 282 282 10 1092 95 110.75 103.92 12 1.85 1.69 3.55 0.45 377 377 ' 11 1091 72 115.54 105.04 8 0.08 0.06 1.32 0.91 72 72 12 1090 78 115.54 105.04 8 0.15 0.11 1.53 0.85 78 78 13 1089 153 125.35 104.12 8 0.51 0.39 4.96 0.51 153 303 ' 14 1088 30 110.68 103.94 8 0.62 0.51 2.36 0.21 183 333 15 1087 88 110.75 103.42 12 0.87 0.77 2.52 0.58 271 421 16 1086 110 111.5 103.24 18 2.96 2.66 1.92 0.95 110 908 ' 17 1085 140 125.25 121 14 2.96 2.55 4.35 0.54 250 1048 18 1084 107 125.25 121 12 0.19 0.22 2.88 0.62 107 107 19 1083 105 125.25 108.36 30 8.38 4.81 5.65 0.31 105 2145 ' 20 10112 210 125.25 107.8 30 8.38 4.75 2.9 1.2 315 2355 21 1081 100 125.5 120.98 12 0.06 0.08 1.52 1.1 100 100 22 1080 103 125.25 120.16 12 0.16 0.19 1.94 0.88 203 203 23 2079 100 125.5 120.98 12 1.62 0.59 2.57 0.65 100 100 ' 24 1078 103 125.25 120.65 12 2.17 0.81 2.06 0.83 203 203 25 1079 72 125.25 107.35 30 8.54 4.68 3.91 0.31 72 2630 26 1077 290 125.25 106.61 30 10.71 5.35 2.99 1.62 362 3123 ' 27 2076 207 125.5 121 12 2.07 0.69 3.16 1.09 207 207 28 1076 196 125.25 119.62 12 2.56 0.85 2.77 1.18 403 403 29 1075 77 125.25 118.38 12 0.64 0.77 2.82 0.46 77 77 ' 30 1074 205 125.25 116.74 12 3.3 1.56 3.46 0.99 282 685 31 1073 83 125.25 118.73 12 2.41 1.15 3.15 0.44 83 83 32 1072 320 125.25 106.5 30 16.48 7.76 1.61 3.3 403 4211 ' 33 1071 160 125.02 114.92 8 0.14 0.17 3.19 0.84 160 160 34 1070 127 125 113.76 10 0.47 0.46 2.56 0.83 287 287 35 1069 172 125 112.77 15 0.58 0.56 1.81 1.58 459 459 ' 36 1067 170 125.33 112.28 15 0.88 0.77 1.89 1.5 629 629 37 1066 43 125.5 118.7 12 0.2 0.23 5.18 0.14 43 43 38 1065 53 125.5 117 12 0.2 0.23 3.39 1 0.26 96 96 1 Storm Water Modeling Results Hydra & SCS: Brown and Caldwell GIS ' Pre-Development Conditions Renton III 100 yr- 24 hr storm ' Link Node Length Downstream Elevabon Diameter Area DesQ DesVel Time LatLong SysLong ID h Rim Invert in (Acres) cle) (fps) (min) H ft ' 39 1064 65 125.33 112.86 12 0.31 0.34 4.86 0.22 161 161 40 1063 383 126.5 110." 21 2.21 1.49 2.36 2.7 5" 1173 41 1062 38 126.5 120.1 12 0.04 0.05 1.05 0.6 38 38 42 1061 155 125.25 109.53 24 2.25 1.39 2.54 1.02 193 1366 ' 43 1060 191 125.25 108.67 24 5.71 3.01 3.12 1.02 394 1557 44 1059 107 125.25 108.2 24 6.25 3.09 3.13 0.57 491 1664 45 1058 276 125.25 107 24 6.91 3.44 3.23 1.43 767 1940 ' 46 1051 160 136 131 8 0.05 0.06 5.16 0.52 160 160 47 1050 177 133 121.62 10 0.05 0.06 2.85 1.04 337 337 48 1049 43 126 122 6 0.05 0.06 2.77 0.26 380 380 49 1048 302 130.1 119.79 15 3.67 1.04 2.86 1.76 682 682 50 1047 227 130.1 119.79 8 0.67 0.8 3.81 0.99 227 227 51 1046 296 129.42 121.73 15 0.22 0.27 0.93 5.31 296 296 ' 52 1045 124 130.1 119.79 15 0.22 0.23 2.6 0.79 420 420 53 10" 136 129 102.59 18 4.56 1.83 9.55 0.24 556 1465 54 2021 320 128.8 108.22 8 3.28 1.16 6.04 0.88 320 320 ' 55 1021 308 125.5 107 18 3.71 1.48 2.52 2.04 628 628 56 1020 245 125.5 107 18 3.91 1.62 1.96 2.08 873 873 57 1019 217 125.5 107 8 0.21 0.18 4.55 0.8 217 217 ' 58 10111 255 125.94 106.58 18 4.33 1.86 1.99 2.14 472 1345 59 1017 217 126.2 122.84 10 0.54 0.61 2.68 1.35 217 217 60 1016 63 125.94 106.6 10 0.54 0.58 4.62 0.23 280 280 61 1015 83 126.5 106.27 21 526 2.52 2.86 0.48 363 1708 62 1014 280 126.5 106.27 8 0.44 0.28 4.24 1.1 280 280 63 1012 309 126.4 117.52 8 1.2 0.75 2.94 1.75 309 309 64 1011 47 126.5 117.14 8 1.3 0.61 3.02 0.26 356 356 ' 65 1010 105 125.5 106.06 24 7 3.48 2.47 0.71 461 2449 66 1009 160 125.6 105.24 30 7.34 3.72 2.44 1.1 621 2609 67 2028 100 125.2 116 12 0.1 0.05 1.46 1.14 100 100 68 1030 220 125.2 116 12 0.13 0.11 2.3 1.6 220 220 69 1036 100 123.5 119.86 12 0.48 027 2.42 0.69 100 100 70 1035 14 123.4 119.51 12 0.68 0.51 3.84 0.06 114 114 ' 71 1034 90 123.3 118.5 12 0.84 0.6 2.92 0.51 204 204 72 1033 50 123 117.89 12 0.9 0.63 3.04 o.27 254 254 73 1032 125 123.5 116.54 12 0.99 0.7 3.01 0.69 379 379 t 74 1031 55 125.2 116 12 1.38 0.84 3.09 0.3 434 434 75 1029 15 125 115.55 15 2.26 1.6 5.38 0.05 449 769 76 1024 320 124 114 15 2.26 1.59 2.83 1.88 769 1089 ' 77 1027 100 123.3 113.8 15 2.49 1.55 2.07 0.8 869 1189 78 1026 128 123.3 110.5 15 2.82 1.73 5.19 0.41 997 1317 79 1025 96 123.3 107.8 15 3.13 1.9 1 5.51 0.29 1093 1413 Storm Water Modeling Results Hydra & SCS: Brown and Caldwell GIS ' Pre-Development Conditions Renton III 100 yr- 24 hr storm Link Node Length Downs m El treaevation Diameter Area Des(] DesVel Tlme LatLorg SysLong ID ft Rim Invert in Acres cra (f min (ft (ft) ' 80 1024 1211 125.6 105.24 15 3.13 1.88 4.87 0.44 1221 1541 81 1023 244 125.51 121.7 12 0.19 0.17 1.63 2.5 244 244 82 1022 40 125.5 121.5 12 0.36 0.26 1.76 0.38 284 284 83 1037 45 125.5 104.7 8 0.18 0.17 8.04 0.09 45 45 ' 84 1042 148 125.5 121.61 8 0.58 0.72 2.87 0.86 148 148 85 1041 169 126 120.2 12 0.58 0.69 2.74 1.03 317 317 86 1040 120 126 119.5 12 1.76 1.73 321 0.62 437 437 ' 87 1039 100 126 119 8 0.21 0.25 2A2 0.69 100 100 88 1038 80 125.5 105.35 12 2.31 2.24 4.75 028 180 617 89 1005 140 125.5 120.7 12 0.45 0.42 1.97 1.18 140 140 ' 90 1056 325 126 105.85 30 23.39 11.03 3.4 1.59 325 6476 91 1065 252 129 105.01 30 23.39 10.82 4.03 1.04 577 6728 92 1052 305 129 102.59 30 23.39 10.64 5A5 0.93 882 7033 ' 93 1008 284 125.5 104.7 30 10.47 5.54 2.71 1.75 284 4434 94 1007 150 125.5 120.9 30 11.01 5.94 3.56 0.7 434 4913 95 1006 482 126 103.46 30 13.77 8.04 3 2.68 916 6152 ' 96 1004 102 127.5 102.95 30 14.11 8.19 429 0.4 102 6254 97 3001 156 129.5 118.91 10 3.42 1.47 4.91 0.53 156 156 98 1043 72 127.5 115.5 12 2.99 1.65 3.36 0.36 72 72 ' 99 1003 112 128 102.73 30 17.1 9.27 3.2 0.58 184 6438 100 1002 71 129 89.75 30 17.1 9.24 16.47 0.07 255 6509 101 1001 999.9 99 89 120 48.47 22.99 2.63 6.33 1254.9 16162.9 1 1 Table 3. Results of 100 year Storm Post-Development ' Total Contributing Area= 43.65 Acres Peak Flow = 22.61 cfs ' Link Node Length Downstream Elevation Diameter Area Desa DesVel Time LatLong Sys Long ID ft Rim Invert (in) Acres cfs min It ft) ' 1 1101 290 126.9 119.5 8 0.72 0.4 2.97 1.63 290 290 2 1100 58 126.21 119 8 1.44 0.74 3.01 0.32 348 348 3 1099 105 126.21 119 8 0.73 0.58 2.72 0.64 105 105 4 1098 324 125.25 113.19 15 2.17 1.29 4.21 1.28 429 777 5 1097 108 125.25 111.25 15 2.17 1.22 4.15 0.43 537 885 6 1096 77 114.24 106.39 12 0.2 0.24 1.99 0.64 77 77 ' 7 1095 40 111 106 12 0.28 0.34 2.43 0.27 117 117 8 1094 70 109.9 105.44 12 0.77 0.73 2.75 0.42 187 187 9 1093 95 110.1 104.68 12 1.43 1.34 3.31 0.48 282 282 t 10 1092 95 110.75 103.92 12 1.86 1.76 3.6 0.44 377 377 11 1091 72 115.54 105.04 8 0.08 0.06 1.32 0.91 72 72 12 1090 78 115.54 105.04 8 0.15 0.11 1.53 0.85 78 78 ' 13 1089 153 125.35 104.12 8 0.51 0.39 4.96 0.51 153 303 14 1088 30 110.68 103.94 8 0.62 0.51 2.36 021 183 333 15 1087 88 110.75 103.42 12 0.87 0.77 2.52 0.58 271 421 16 1086 110 111.5 103.24 18 3.12 2.79 1.95 0.94 110 908 17 1085 140 125.25 121 14 3.12 2.68 4.42 0.53 250 1048 18 1084 107 125.25 121 12 0.19 0.22 2.88 0.62 107 107 ' 19 11183 105 125.25 108.36 30 7.911 4.84 5.66 1131 105 2145 20 1082 210 125.25 107.8 30 7.98 4.78 2.91 1.2 315 2355 21 1081 100 125.5 120.98 12 0.06 0.08 1.52 1.1 100 100 22 1080 103 12525 120.16 12 0.16 0.19 1.94 0.88 203 203 23 2079 100 125.5 120.98 12 1.62 0.59 2.57 0.65 100 100 24 1078 103 125.25 120.65 12 1.81 0.69 1.96 0.87 203 203 25 1079 72 125.25 107.35 30 8.14 4.71 3.92 0.31 72 2630 ' 26 1077 290 125.25 106.61 30 9.95 5.28 2.97 1.63 362 3123 27 2076 207 125.5 121 12 1.03 0.34 2.68 129 207 207 28 1076 196 125.25 119.62 12 1.52 0.51 2.36 1.39 403 403 29 1075 77 125.25 118.38 12 0.64 0.77 2.82 0.46 77 77 30 1074 205 125.25 116.74 12 2.26 1.29 3.27 1.04 282 685 31 1073 83 125.25 118.73 12 2.41 1.24 3.23 0.43 83 83 32 1072 320 125.25 106.5 30 14.68 7.38 1.61 3.31 403 4211 33 1071 160 125.02 114.92 8 0.14 0.17 3.19 0.84 160 160 34 1070 127 125 113.76 10 0.47 0.46 2.56 0.83 287 287 ' 35 1069 172 125 112.77 15 0.58 0.56 1.81 1.58 459 459 36 1067 170 125.33 112.28 15 0.88 0.77 1.89 1.5 629 629 37 1066 43 125.5 118.7 12 0.2 1 0.23 5.18 1 0.14 43 43 Storm Water Modeling Results Hydra & SCS ' Post-Development Conditions Renton III 100 yr- 24 hr storm ' Link Node Length Downstream Elevation Diameter Area DesQ Desvel Time LatLong Sys Long ID k Rim Invert in (Acres) cfs (min) (R) f[ 38 1065 53 125.5 117 12 0.2 0.23 3.39 0.26 96 96 ' 39 1064 65 125.33 112.86 12 0.31 0.34 4.86 0.22 161 161 40 1063 383 126.5 110.44 21 2.21 1.49 2.36 2.7 544 1173 41 1062 38 126.5 120.1 12 0.04 0.05 1.05 0.6 38 38 42 1061 155 125.25 109.53 24 2.25 1.39 2.54 1.02 193 1366 43 1060 191 125.25 108.67 24 5.17 3.04 3.13 1.02 384 1557 44 1059 107 125.25 108.2 24 5.71 3.13 3.14 0.57 491 1664 45 1058 276 125.25 107 24 8.21 4.15 3.43 1.34 767 1940 46 1051 160 136 131 8 0.05 0.06 5.16 0.52 160 160 47 1050 177 133 121.62 10 0.05 0.06 2.85 1.04 337 337 ' 48 1049 43 126 122 6 0.05 0.06 2.77 0.26 380 380 49 1048 302 130.1 119.79 15 0.34 0.15 1.77 2.84 682 682 50 1047 140 132.2 121.79 8 0.74 0.31 2.56 0.91 140 140 ' 51 2047 227 130.1 119.79 8 2.28 0.95 3.26 1.16 367 367 52 1046 296 129.42 121.73 15 0.22 0.27 0.93 5.31 296 296 53 1045 124 130.1 119.79 15 0.22 0.23 2.6 0.79 420 420 ' 54 10" 136 129 102.59 18 2.84 1.28 8.77 026 556 1105 55 2021 320 128.8 108.22 8 2.47 0.81 5.41 0.99 32.0 320 56 1021 308 125.5 107 18 2.9 1.13 2.31 2.22 628 628 ' 57 1020 245 125.5 107 18 3.1 1.26 1.83 2.23 873 873 58 1019 217 125.5 107 8 0.11 0.12 4.15 0.87 217 217 59 1018 255 125.94 106.58 18 3.42 1.46 1.85 2.3 472 1345 ' 60 1017 217 126.2 122.84 10 0.23 0.23 2.02 1.79 217 217 61 1016 63 125.94 106.6 10 0.23 0.21 3.58 0.29 280 280 62 1015 83 126.5 106.27 21 4.04 1.85 2.57 0.54 363 1708 63 1014 280 126.5 106.27 8 0.44 0.28 4.24 1.1 280 280 64 1012 309 126.4 117.52 8 1.2 0.75 2.94 1.75 309 309 65 1011 47 126.5 117.14 8 1.3 0.81 3.02 0.26 356 356 66 1010 105 125.5 106.06 24 5.78 2.81 2.33 0.75 461 2449 67 1009 160 125.6 105.24 30 6.12 3.05 2.3 1.16 621 2609 68 2028 100 125.2 116 12 0.1 0.05 1.46 1.14 100 100 69 1030 220 125.2 116 12 0.13 0.11 2.3 1.6 220 220 ' 70 1036 100 123.5 119.86 12 0.42 0.24 2.36 0.71 100 100 71 1035 14 123.4 119.51 12 0.62 0.49 3.78 0.06 114 114 72 1034 90 123.3 118.5 12 1.36 0.83 3.22 0.47 204 204 ' 73 1033 50 123 117.89 12 1.42 0.85 3.33 0.25 254 254 74 1032 125 123.5 116.54 12 1.51 0.93 3.31 0.63 379 379 75 1031 55 125.2 116 12 1.9 1.07 3.32 0.28 434 434 76 1029 15 125 115.55 15 2.78 1.84 5.68 0.04 449 769 77 1028 320 124 114 15 2.78 1.84 2.96 1.8 769 1089 78 1027 100 123.3 113.8 15 3.01 1.8 2.17 1 0.77 869 1189 Storm Water Modeling Results Hydra & SCS t Post-Development Conditions Renton III 100 yr- 24 hr storm Link Node Length Downstream Elevation Diameter Area Deso DesVel Time LatLong Sys Long ID tt Rim Invert in Acres cfs s (min) tt ft 79 1026 121 123.3 110.5 15 3.34 2.16 5.55 0,38 997 1317 8o 1025 96 123.3 107.8 15 3.65 2.33 5.86 0.27 1093 1413 81 1024 128 125.6 105.24 15 3.65 2.3 5.22 0.41 1221 1541 82 1023 244 125.51 121.7 12 0.19 0.17 1.63 2.5 244 244 83 1022 40 125.5 121.5 12 0.36 0.26 1.76 0.38 284 284 84 1037 45 125.5 104.7 8 0.18 0.17 8.04 0.09 45 45 85 1042 148 125.5 121.61 8 0.58 0.72 2.87 0.86 148 148 86 1041 169 126 1202 12 0.58 0.69 2.74 1.03 317 317 87 1040 120 126 119.5 12 1.81 1.83 3.26 0.61 437 437 88 1039 100 126 119 8 0.21 0.25 2.42 0.69 100 100 ' 89 1038 80 125.5 105.35 12 2.36 2.34 4.82 0.28 180 617 90 1005 140 125.5 120.7 12 0.45 0.42 1.97 1.18 140 140 91 1056 325 126 105.85 30 22.89 11.36 3.43 1.58 325 6476 ' 92 1055 252 129 105.01 30 22.89 11.18 4.07 1.03 577 6728 93 1052 305 129 102.59 30 22.89 11.01 5.49 0.93 882 7033 94 1008 284 125.5 104.7 30 9.77 5.19 2.66 1.78 284 4434 ' 95 1007 150 125.5 120.9 30 10.31 5.52 3.5 0.72 434 4913 96 1006 482 126 103.46 30 13.12 7.79 2.97 2.71 916 6152 97 1004 102 127.5 102.95 30 13.46 7.99 4.26 0.4 102 6254 98 3001 120 129.75 119.75 10 1.39 1.52 4.91 0.41 120 120 99 3002 36 127.5 118.91 10 1.61 1.65 5.14 0.12 156 156 100 2043 160 125.5 117.5 10 1.01 OA 3.65 0.73 160 160 ' 101 1043 72 127.5 115.5 12 1.61 1.07 2.94 0.41 232 232 102 1003 112 128 102.73 30 15.07 8.71 3.14 0.59 344 6598 103 1002 71 129 89.75 30 16.31 92 16.45 0.07 415 6669 t104 1001 999.9 99 89 120 43.65 22.61 2.62 6.36 1414.9 16462.9 1 ' KEY: ----- CITY LIMITS 0 100 200 400 _ _ _- - - PROPERTY LINE SCALE IN FEET ANNEL e — - � ', , SHORELINE BOUNDARY NEW 30"0 P1 CHANNEL ' EMERGENCY RELIEF T I O NEW FACILITIES OVERFLOW SEWER - / (INCLUDING ROADS -'---•--- AND PARKING) - .. i NEW BIOFILTRATION / _____ i( 4 I I SWALE 6 I �Q �. ,/' �I FACILITIES (INCLUDING ' I 1 1 ', , �:-=, . -�• (INCLUDIDI NG ROADS AND PARKING) NEW 18" 0 P1 •/ / / I i CHANNEL STORMWATER OUTFALL 1 4t I 1 - ' _ _- = EASEMENTS EXISTING STORM GRAINS EXISTING 12"0 CITY WATER PIPELINE /� j I I j -•-•-•- FENCE UNE (TO REMAIN) EXISTING WATER LINE NEW STORMWATER I 1 TREATMENT WET % I tOFILTRATION ' PONDS r'' +.' i I I f - \ •-- �� NEW 20"0 WASHINGTON ' NATURAL GAS PIPELINE � I EXISTING 20"0 WASHINGTON \-S - NATURAL PIPELINE (TO EXISTING 12"0 CITY BE ABANDONED) WATER PIPELINE T\.• 1 _ '�-� TO BE ABANDONED) CAN BE USED BY NEW 12"0 CITY METRO TO TRANSPORT WATER PIPELINE 4.5 CFS OF STORMWATER TO NEW WET PONDS) �" �I �� / OFILTRATION SWALE ol / / NEW 4.5CFS (2000GPM) STORMWATER PUMPING STATION \ INCLUDES: •CONNECTION TO ABANDONED WATER TO PIPELINE CONVEY- ANCE WE PONDS % SON N j •CONNECTION TO INFLUENT SEWER oll FOR TEMPORARY MTPR TREAT- ' BVR .% -MENT OF STORM WATER FIGURE E SITE PLAN /.,/ Be METRO REGIONAL TREATMENT PLANT IN RENTON ,y T F=T R O ENLARGEMENT tll SgppF}pp 111CIW STORMWATER TREATMENT FACILTIES SEE PLAN FIR OPERATOR 1B' SO T] Y1 BUR-WELD. COAL AS PER KEY fY PD Is �ORIENTAM]N EL IJx-50 FIELD KRIFY NOTE IS AFTER FABRICATION 4 LOCATION G-IO 22 6 PILE CAP BEAR �EL 1]1.Sf 1, tY PO 15 �EL 1310 ELEL 1]O.Bt� SG 24400] 6 Jf— `• , EL IJI.S u / v 1 /. N 999.80 / / N x3 7 r / -lF-lf-- •. S E 1095.75 P 244002 EL ❑ODE �t -JL-ji iI PRECAST CONCRETE VAULT,SEE S ' P 2E4001 j - O- -�---- — I 1 B POSITION ORAWINGI ATTACHEDN VAULT / \ A SEEN n 1� .` I AM CATS p ._x_J EL 127.50 /�'� RAISED a NR - SLOPE 1/4'YTT J" DR ME EXEC DAG U AMS IL FL 123.50 TRAIN! VAULT ACCESS I.tOOER 4 SEE ACC VAULT DAG B STRUCTURAL BAIXFML PUMP UFIWC IF REQUIRED BY ENGINEER —` i0 - RAILS AS REM 1 1) �_ BY MFG I KEY NOTES: 4 ,ro- QA SlE1E O SLEEVE TYPO CXWE1J. M PIPE CR EQUAL. TYPICAL ORO .il STYLE ]B. ROtltwELL TYPE 118. OR EaAL PdOVE STOP FROM 1] 18' STORM MAN (mI SHALL BE REINFORCED COHgIFEE MIDDLE RING RESTRAIN COUPUNO M ACCORDANCE AM AYEWA LAY tll,A IV, ASRI C76, RUBBER GASKETS PER RE•\ ,I 16 • /, I I AIL PARAGRNM 1110. TABLES 1Y7 AND 1}7, AND FIGURE U (3)-]' LENGTHS C PIPE AWAY FROM STRUCTURE 86011E N 1 UYWG STANOAIi0 IFNCM PIPE ^ IS IY PD SYSTEM T-I CORE ANT, MI AND TENSION RODS 1 W OEN50 \ \ ^ II1111, I /' V I I I SYSTEM R A PRIMER ANTI TA$E COAE3, OR EQUAL It WA% TAPE 14 FPRCSSURE ROM UN TS AM SMALL BE PHENCUC NX ETA SM BOURDON'TUBED PRIMER COAT AND Fl WAX TAPE FINISH, OR EWAI_ �U Q PROVIDE LANCED BY PLAIN END STEEL COAT PEA KEY NOTE IS ELEMENTS 270'MIUED STAINLESS STEEL MOVEMENES AND ' CAGE SHAUL BE PROVIDED '\ I - 11 10 I I I PIPE EMBEDDED M WNCFEIE PILE. ATM7111/2'�CLASSEWINDOWS,VAL Y ANDERSON. GREENWOOD- PROVIDE O PROVIDE 3•I.D. PIPE STANCHION WHERE INOCATED. WELD HOLE 21 O1 OR EQAL 2 I, IQ' SQUARE X 1/2• STEEL STANCHION BASE PLATE TO 3' STANCHION. DRILL BASE PLATE FOR s41 3/4-CIA BOLTS ON W 15 ALL EID'G Tt ANO/OR 9JBUERCED %PING M WEIWELL AND CENTERS STANCHION FOR 1/4 A VENT HIMDRILL 1/2' VALVE VAULT SMALL BE COATED AM CON, TAR EPDXY, 20 T OR \ 2 I 17 I I I ABOVE BASE PULE 960RE DOING ANY WEEDING PROVIDE (1) YIL CRY FEM THICKNESS, KOPPERS. GLIOIDE N OR POtMF1 3/4" DIA SS EXPANSION AN HORS IN CONCRETE FLOOR OF VAULT. APPLY PER MANUFACTURERS RECOMENDADONS PROVIDE LEVELING NUTS AND WASHERS UNDER BASE PLATE TO 16 IXIRE MPCUGH IEAAI CONCRETE PINE AND INSTALL DRAIN. = 1 I PROVIDE PIPE AUGNUENT CAPABLTY. DOUBLE NUT.OIOVE BASE O SEAL VAIN UNK-SEAL'. R I t I I TYPICAL. I 10 I DPLAIP CM. AIRR ALVAHH ZE ENMEIGDA SEEM(BL�Y.KGR0.1T UNDER BASE PU1E FOR S 1^ 12•PD I ' hII 1 WEEIIMENT AND ANCHOR STRUCTURAL DRANNGS J X I I © WELD 4• X 13• X J/8• STEEL LIE SADDLE TO TT OF T ID STREET _ 11 TIACAL I CHECK VALVE SHAPE BADGE LEE TO MATCHREGARDING ING GA gNIZI OF OPROVIDE u F_---_-- __ 1 CHECK VALVE BODY. SEE NET HOLE ] RECASTING GALVANIZING 18 "NR (2) IS- LONG BE11 APE PIPES, RESiRNNfD JOMES 9 _- -- --___--_- I I O PROVIDE SAIDENUE F RSADOI3/4' IA TYPE IN DRILL L, LOCK STANCHION 19 BF31 x BELL 43'ELBOW, RESTRAINED JOINT. 1 __ .Nib Ei--•-I __� I 12 I PIPE ANNDDNNut.F ICUNSTNL SADDLE AFTER GALVANIZING 1 1\ i I SEE KEY NOTE J REGARDING CALVAN➢NG ®D BELL X BELL 11.0 ELBOW, RESTRAINED •IGIMT. 1 16• x iC SLUICE GALE ' I •••3 1\I] 4 4 SG 3H�] I O 7 ME AME1FAw gRgRM CPENMC., COAL TM 8• 21 PE:PE W LgIC SPOOL \ / _ ,I �• \III I 1 I P iH003 EPDXY COATC. BUTT UP AGAINST A JY ® SEE gCTION B/S2 FOR SUIIFZ GATE THIMBLE. 14 PRESSURE GAGE I 1 I I I I SPEC 11347 LONG(INCLUDING BELL). IB• DAMETFR, q.A55 IV, A31Y C78 RCP RUBBER CASKET MJ X MJ 4Y DOWN. EIEVARCH b MATCH CONNECTION JOINT PPE FRONT ASSEMBLY IN PLAGL 1 IY PD 11 EL IOD50 PONT FOR PWC 19 12• Pp. ' 1 _I B - I 'I OP BY PUMP O1AM I O PROVIDE UIDES WITH EE CUTE ANCHOR Ott © ALLI .B•-0 NLAII FRAME. BITUMINOUS BRCO TYPE JD-JAL 1/!• ALUMINUM. 19 1 1 — BY PIIYP YFR i SZE AS SPED ED BY SLICE AGAR NEXTI M CONCRER- HINGED ON 6'`SUMTING S TNNLEESS IFAIOE MANUFACTURER. HARDWARE THROUGHOUT• TAKE DRAINAGE M WTSDE VAULT, 31 --F-PUMP ON O PROVIDE TOP CAM STEM DUCE AND UFT TYPICAL 4 DOORS. 2 2 - - - 1 THRUST ASS WBLY. INSTALL AM SS N N INV AT WALL 8 10 ANCHOR BOLTS SIZE AS SPECIFIC BY ® ALUMINUM X B•-0 FRAME. BLCC TYPE COATING 1/4' AME EXY, it I -- ] J - I\-- i IB EL Ims0 6 I EL 1�'� YANUFACRXIER. PRDME VALVE BOX IN ALUMINUM ONCRE BITUMINOUS O W SIDE ON FRAME EXEEAIOE NEXT i0 CONCRETE HINGED ON 6' SOE 3TAINlEs6 TOP SUB FOR OPERATING NUT ACCESS HARDWARE TWRWCHOUT, TAKE DRAINAGE M OUTSIDE VAULT. BOO. E DRAIN M CLOW F2E I PRESSURE GAGE 14 I I O a" P VAULT ®ULT PROOVIDE(2) CCNGNEIE EXPANSION EYE BOLTS FOR UFTINO EL 98.00 I \ / ( I I \ /I I 8• j I �_ J3120 DIE EQUAL DUCTILE IRON=AND ® CAS.RON Sql PIPE. ASEM A14. COMPRE390N JOINT AM SLAB. R0011 DRAIN SNAl BE.N)SA4 TMI I PUMP OFF CUTLET To MATCH PIPE. GROUT DRAIN AND RUBBER CASKET. OR HUBIE33 CAST IRON SYSTEM. EL 926E �/'CLum FLOOR DRAM M S AR WPM NON-SHRINK ® 12• ECCENTRIC PLUG VALVE. SE Y2 FOR SPECIFICATION. 1 I I CIRCLE. SLOPE SLAB TO DRAIN AM '•\ i i TOPPING MINISTER WPM 1/2' MIN ' 1Y PD 1 Ih MIIXHESS ©9 12• SANG CHECK VALVE SEE YI FOR SPECIFICATION- IFqP MRRMETXATE SUPPORTS FOR VERRGl ® SLUICE CATS SNNl BE OF HEAVY DUTY CAST RON I SECTION 6 PUMP DISCHARGE AND W CONS1R1E F WITH NLL METAL WEDGES. LT FRAME 1 I BUBBLER PIPING. SEE STRUCTURAL .z I I EL 921E DRAWINGS AND ME F , FL IHIUME. cNEE SHALL E K X c� INTEGRAL OPEN UP, RUSH ABU F NEOPRENE SLATING ELECTRICAL APPARATUS 11 GALVANIZID SCHEDULE w S1FII PIPE HEEERAL FRASLUICE . TE SHALL FOR 21. OF AWWA C ( I I I I SLEEVE EMBEDDED IN CONCRETE WALL BY NERD. SWCE W1E SHAH COMPLY ON AWWA CSO. I MI SE EEEC TWO U VAULT MFG, TYPICAL PROVIDE HOCULM GATE SHALL BE BUST CLEANED (SSPC-5) AND COAEED u 1 AECHANIWL EJPAHMO RUBBER SEAL-UNK WITH COAL TAR EPDXY TO PROVIDE A 20 MIL DRY f11N STORM WATER PUMP STATION SEAL OR EQUAL. PICAL- MIIXNESS SWIGS GAR yAI1 BE ROD HEY ANT, O N wATERMAN, OR EQUAL- PLAN _4 X ' AT ELEVATION 130.5 z RUMP GUIDE SUPPORTS AS REOD BY SECTION / 1 \ PUMP MANUFACTURER- SCALE: 3/8'�1'-D' s L J e-1'-0' MI o.L DATUM NOW. n[s ,EN/BEI'R 'ii^ ' 'E T R a ' xAWAREGIONAL YuvblpUtf RT YalmpRUlWn 9W.fW MM /992 / A Tuw „�,ppqo�m i�wyI,,w[, y (.1 £ �✓! Esc..RAIMx61m Hn �y oKa[N. �", iM xP Bru Brown and Caldwell l { METRO'S REGONEN TRI��wTiMA IN RENTON w w°nrtw}¢"lm°��01 n5EAW0 GRN STURUWATER PUMPING STATION Consultants Wx Seattle, Washington ' '�,.�`' o[�xxFxa[R AN ND,FD PLAN AND SECTION M1 ' .R xTVMw ~ 7 In' QArt [MXeF N dG R cox WC 161 wUAr xa 6 a A B C D E F G H E • 9 C 9 3 "ST 11•a.LP 141 •I CUT El sS g lY PIPE AND II _ \.\ \ \^ \ , \� \ \\, r - ♦ V t \ SEE DIET NEW 12• Po. 1 ' - •• 1 __ - 1 - SEE DEfwI A/31R CT EACH 0f 9 JIS. I 11 \ \ \ \. \� +y \ "!�\.,, \F.>� , 1__� f OEQLLOBINAnoN FAf22 /. pPw+oK 1a• ,1 _ \ - I '\ \\ \ '°�_ Nnzz ' , ✓ -3 '` r 12'PO SLOPE UWOR;&Y , -\ Y1e7213 MI37221 I .....�_ \�/ \ `. ,^ .:.��'`'• 1 \ �\ -( M1_t7zm NI 87216 M187222 _ %� _'� \. :�` ` \ I M1 B7219 \ l \ 'c I _-_�� \mow 87220 � N10721) YIb)223 � JL �! MI�___ ' ♦ /'( i 14 / 1( 1 \ Y1 e7213 M107224 6] ♦ IX ?,- I . Y131B MIBT223 U157220 CONNECT 10• m TO E12ST MN2 EL 101.0 ; \ \\ t '_ A .� L-?_• - _�_ ,� `� 1 I(, i 1s•eEu,aE7:E,nss' '\u9fT uwlHaE LaenoN '�T'� / I •``,\.i \- / 12•PEIPE 39 1G �/ i' 1 y--..`I i E (;InFn L MT 6 �` ,Ix• bf11aBELL'43 / /Ff / \ \ �;� .i e 1 ('f i1� B.wK. "ST L \ \ 1 \ 1 \ 11 NIB7R13 YIB]2Is -'`. �}�•C,\-•\ ,^ / r ye \ NNPE 6• SEMA '' \.\ I 1 ~' - �{I 7 1F � �\'�` We]216 YIb7219 X;� 1 '\` �•. ')� 1' !� - `.\ � 1 .i' � _ 3 YIb721] MI0]xR0 I .\ � ,• � I \ /gF., —_ !' ' \ r � ELECT DUCT BAHI(CONNfaf To1.4 MH29, {`to-%a'-o % ++ 0 9 k i I CONNECT NEW ELECTRICAL /^a i I I / / ➢-���j ^-� U7B.ITY'VAUL}CG`GT IN�A W7�:. o G - WCT BANK TO FASTING ` Y157213Efabl uYl44.-37?PL�\f\ _ AT Na3o/Ellzb �eisley--� U \ I — -- _ i� F•I NNI1E faRDE 12AIN WLNSiHUCNPE 1. 4 7 '>bi }AI.I -n Y1e7219 ,\ I! _ CLY BY OMEAa � r x{Po 015(?IAP4E �. � biMEPs _ ELECTRICAL DUCT -I �.1 .i e eN073 bcTRI NTu ' •s \ -; // _� - >� — \.: x tor]a Hb7e — -t WP♦ %�1` LIB.-3 I = FU VAWO-•`'"—H STALDICWAL1'E�VA([f 21 t - 1 i\:_ - -� "^ 1041.00 :] E,T03257 PCI C -NAw CL2 _ _- -� t Ill(1 DIYFRSIOfl E1� '_��_jaY. w.EccTDR vAULT`_ \ ;-P�. _>: ti r�,�,Exs) . - u'w« i--=� x`ttr- - _ • �� J� / R (BT OIHEAS) `'-� L '•pRa°[k- LX}'_�... (wiERUPB,w N)I / ._.,WQ_ x♦•wW .- ' / d .�L f ,i ; `!�<----"-- -a"cxlP- -. NOT pWiSIDN E71L-' ♦/ __,_-`__�� _ _ c_ - - _ OY-01Md5)- —_ �_+ T t (eYatHEes (INTERRUNBAw TY) 1 NOTES: / i-� LEGEN©:-� -:� ,is� -�-� / '�, _.� N abo.2x -- >� I.r REFEIIENCE.hI WORK •eT OMFWb• YEARS WGRK I 51194E'7-OONTpUL yWiRTdNt� _ .J r 7� T--1�\g 2E \PI.WNEO,NN PWCIa. 1 TW1CK All aRAWNR .. • •,\ ' _ J �• I DUCTEF BT� BE W.PIPE -_• HriwAUl1C BAw110 WEll` < ;�_ -�� •2- -;_ ' c_ \•1_ r �-"��-- h♦ �, �PD PIPING sNA11.H}WIT1'Af91RNNFHiAw15. _y - ��))� (NBW/) �y \ �__� �'�-. �_ `•\ \' � \ \\�1— _`t%� `__- /• �� `.�:� •- lSQ wxx-enxE QTTI L%S91ALL-�G1-I]PE H CN1191[D daA �� =_ al e•REnwooD pE�nExsr O^ISk lb -D RO p J ZZ -t. �+ �.�/ �' }\ ./` _F - -� _„\._.-ten ."'--� ��`_ l,L `• _ 62 DAfUY NaIE: fwn :,:METR0 MMWcIPW17 al Y.IroPaUW S..IW 4 f_Y- 1.l 'x°Y.1 inu�io�wc jS G NENNAH 49 uAR 199z e Avh oifu(R YUF:Brown and Caldwell �� uE1PD'S REGONAL rPEATYENr Pl1JIT w RFNiON. Consultants " K" " �a Stt Mw T[n�UMPPNIG STATIM. SaatMe, Washington • ' SITE PLAN. G1 ' xa x[Vsax a1 wR •wAa.n WM 37-91 LM1II nn a EOa[f Yt1I PM 2e 1 a C O E F c N 1 ' 0 20 40 80 SCALE IN FEET / _ i `� ' 3 ) (-� r r .. �` `r.. __ f 3 a �f rr Y6' ED SiFiUCTICN FENCE POND 8 / r r f �. ,• t o3 a ,6700 aq FT % t y/' W8 EL 110f� \ r ; POND 2 f' rroP 18;'200 oq FT I ;W8 EL 120 E WETLAND 'B' r o 3 POND 1V It 6800 In FT r eD.108 me W8 EL 125 + % \_ ;{ PUMPED STORM WA7D; 4.5 ........ 0 i 1 , t r ' � 1 `1, 9 ? 1 r ..;:'•-•---'• ,•-=---' NEW 12- CITE{ WATER PIPELINE •, - �� �;� j \`� 1 FIGURE 4: SCHEMATIC '� C T ® EMETRO REGIONAL NLARGEMENT III �EATMENT PLANT IN RENTDN IV 4' 6® y� yp� riETPOfJO FACILITIES APPENDIX A (Hydraulic Impacts of Redirecting Stormwater Runoff to the P- 1 Channel : 100-year Flood Hydraulic Analysis by RW BECK) 1 MTPR Drainage Plan/keport/�rainp L .d�c/RC'5 7ZcJAN-2`-'92,WED 15:21 ID:F,£NTON CDIJSTR TRAILR TEL ND: (206) 910' P02 R.W. BECK_ AND ASSOCIATES s.ti...� ' Fm,th end Blanchard Bultut.Suite 600■1101 Fwnh Annus■Seenle,wuhingem 98121.2375■USA Telephme(206)441.7500•I=(206)4y1.4962 T46K 49QM2 BECKSEA WW-1421-AAl-AA January 22, 1992 3023 ' Mr,' Randall Parsons, Utility Supervisor Storm Water/Waste Water Utility Systems Division City of Renton ' 200 Mill Avenue South Renton, WA 98955 ' Dear Randall:t Subject: Metro Treatment Plant Expansion Wuju;;t ' Review of Storm Water Diverslun at the } Metru Treatsneat Plant in Renton ' We are pleased to submit the =ults of the Task 1 work for the subject project. The analysis was performed by Northwest Hydraulic Consultants(NHC)and reviewed by our office. Copies of their calculations and analvsis are attached. The purpose of the work was to estimate the lucrease hi runoff volume received at the Black River Pump Station(BRPS)forebay resulting from the proposed Metro diversion during an extreme high Crccn River flow condition- The analysis included using the HSPV hydrology, developed as a part of the ESGRW Plan. More spcaifically, the simulation included the local 100-year flood control storage event under current land use conditions in coincidence with high Green River flows. ' Based on the work by NIIC, the predicted increase in forebay elevations would be 0.07 feet(approximately 1 inch). This rise in elevation corresponds to an increase in volume received ' at the forebay of approximately'1,5 ac-ft during a period in which the forebay is filled to approximately elevation 6 (storage .IS2 aaft). We do not believe that performing the work under Task 2 would be benefkW. Performing a detailed simulation using ESPF/FEQ would t more accurately estimate the elevation in the forebay, however the relative change in elevation and the increase in runoff volume at the forebay from the Metro diversion would be nearly the same as predicted by the HSPF analysis. Al.5G.OZ5 ' &imro MA a L`dambo.NE.Damsr,CA.indsnapell.,IN.M[ ..,,h,,MN Neshvlllw TN.Odemlo,FL s Phomlx,A2 s CA I E,sldr.WA .: .A n....�...<F�... p F=93% Yt�N'4I'-did GONSTR TRAI LP. 01-22-92 03: 24PM P002 tt36 '- JJAN-22-192 WED 15:22 ID:RENTON CONSTP TRAILR TEL NO: (206) GB4-2489 Via! P03 l4.4 tt Jt •i-��'bG HCU' � W CC�A FifIL' hiJbVl.1HtCJ YHA NV. BUG 4til'0% ' W. Randall Parsons, Utility Supervisor Storm WaterlWaste water 2 January 22, 1992 ' We would be happy to meet with you to discuss the results of the analysis, If you have ' any questions, please contact our office. ' Very truly yours, R. W. BECK AND ASSOCIATES ' MAx GisebutE Project Engineer MU-.cs ' Enclosure. c: doe Fernandes, Manager ' Metro Treatment Plant Expansion nssc.oa l R.W.BECK AIM A86D(aAlEB A PZw,- b:d Poop*14dKt R=93h RENTON CONSTR TRAILR 01-22-92 03: 24PM P003 r3s 1 ' APPENDIX B (Water Quality Impacts of Redirecting MTPR Stormwater Runoff into the P-1 Channel : Analysis by Adolphson and Assoc . ) 1 1 1 MTPR Drainage Pla❑/Repbet/Drain}' ln.iluc/H<�g ' September 24, 1991 � L J I; ' Ms. Laurie Endiich METRO 821 Second Avenue ' Seattle, Washington 98104-1598 RE: Runoff impacts to the P-1 Channel from the Metro Treatment Plant at Renton ' Dear Ms. Endlich: ' As requested, I have evaluated the potential impact to water quality in the P-1 Channel resulting from discharge of stormwater runoff from the Metro Treatment Plant (MTP) at ' Renton. I have reviewed information including the Drainage Report Metro Treatment Plant at Renton. Enlargement III, September 16, 1991 Draft to City (Brown and Caldwell, 1991); and subsequent revisions of proposed wetponds developed by Brown and ' Caldwell. I have also reviewed preliminary modeling results by the City of Renton (personal communication, R. Straka, City of Renton, September 23, 1991). Water Quantity Imp For this evaluation, I assumed that peak stormflows in the P-1 channel at the point of discharge from the MTP are approximately 90% of the flows at the forebay of the Black River Pumping Station, where modeling results are available. This ' assumption was based upon the estimate (utilized for modeling by the City of Renton) that existing peak storm flows in Springbrook Creek under 1-405 are between 82% and 90% of the flows at the Pumping Station Forebay, depending upon the intensity and ' return frequency of the storm. For existing conditions, estimated peak storm flows in the P-1 Channel for a 2-year 24-hour storm is approximately 604 cis. Peak discharge from the MTP stormwater system during the 2-year 24-hour storm is 4.5 cfs, or approximately t 0.7% of peak stormflow in the P-1 Channel. Under future conditions (full buildout under existing adopted comprehensive plans), the peak flow contributed by the MTP will represent approximately 0.6% of peak flow in the P-1 Channel. This increased flow will have minimal impact to peak flows in the P-1 Channel under both existing and future ' flows. ' Water Quality Impacts. The proposed wetpond facilities have been designed to provide maximum pollutant removal efficiency, in excess of minimum requirements for wetponds promulgated by King County Surface Water Management Division. Based upon generally- accepted levels of treatment removal for wetponds, upwards of 80% of settleable particulates can reasonably be expected to be removed from influent stormwater entering the wetpond facility. 1 ' ADOLFSON ASSOCIATES, INC. Environmental Analysis 600Afain Street Edmonds, WA98020 (206) 778-4273 ' E1V(206) 771-5053 1 1 page 2 of 3 ' Stormwater from the MTP will drain from rooftop areas and paved roadways and parking areas. Although vehicle traffic on the MTP roadways will be lower than a typical public ' roadway, there will be some deposition of vehicular byproducts, including metals and petroleum products. The site runoff will be treated by routing this runoff through biofiltration swales (33% of proposed new roadways and parking lot areas will be routed ' through biofiltration swales) and the wetpond facilities. Because most of the metals commonly detected in urban runoff are associated largely with particulates (e.g., lead, copper, and zinc), these constituents by sedimentation can be significantly reduced by ' the wetpond facility. Regular maintenance of the facilities will ensure that deposited sediments are not flushed out of the treatment facilities and into the P-1 channel. Other parameters which are typically associated with particulates will be significantly removed ' by the treatment facilities, including: (to some degree) total and fecal coliform; and total phosphorus. Petroleum products will be removed to an unknown extent, largely by the ' biofiltration swale. Currently, water quality in the P-1 Channel is degraded, with low dissolved oxygen levels, ' high temperatures, high fecal coliform counts, high turbidity, and high total phosphorus and ammonia levels. The peak storm flow contributed by the MTP represents less than 1% of the total peak storm flow in the P-1 Channel, as described above. The quality of ' stormwater discharged from the MTP stormwater treatment facilities will likely be higher than receiving water quality for numerous parameters, and is expected to be less turbid. Because the stormwater discharged from the MTP is such a low percentage of total flow ' in the P-1 Channel and the quality of discharged runoff is expected to be as high as can be provided using accepted state-of-the-art treatment technology, no discernible impacts to the P-1 Channel are anticipated in the short or long term future. To determine the treatment effectiveness of the facilities, as well as an optimal maintenance schedule, I recommend that stormwater monitoring be conducted at the facilities. I would recommend monitoring influent and effluent stormwater during three or four storms annually following implementation of the facilities. ' If you have any questions or comments, please contact me at (206) 778-4273. Thank you. ' Very truly yours Zollyiolf�sc,n President \ ' ADOLFSON ASSOCIATES, INC. 1 page 3 of 3 1 cc: Mr. Rick Butler, Brown and Caldwell ✓ Mr. Jack Warburton, Brown and Caldwell Mr. Render Denson, Brown and Caldwell 1 1 1 1 1 , 1 1 ' APPENDIX C (Technical Support for Attaining Equivalent Treatment with Oversized Wetponds) 1 1 1 1 MTPR Drainage Plan/Report/D[s in�' ln.ilo:i RCE 'A ETRO ' Municipality of Metropolitan Seattle Exchange Building • 821 Second Ave. • Seattle,WA 98104-1598 (206)684-2100 1 September 19, 1991 Ms. Lynn Guttmann ' Renton Public Works Department Municipal Building 5t1" 2 d 200 Mill Avenue South Renton, WA 98055 Dear Ms. Guttmann: This letter is to provide technical back up for Metro's letter of September 16, 1991, requesting a variance to some of the specific requirements of the King County Surface Water Design ' Manual (KCSWDM) which has been adopted by Renton for stormwater management. Metro's proposed stormwater management system for the Renton Treatment Plant site was developed to meet the water quality objectives of the KCSWDM, and provide water quality ' performanace equivalent to that expected from the core requirements. Metro's proposed design involves less reliance on grassy swales than specified by the core requirements, but compensates by oversizing the on-site detention wet pond. As explained in our application, this flexibility is sought because Metro is providing treatment for existing runoff as well as for the proposed expansion. The existing site drainage pipes are ' placed very deep, which will necessitate pumping the water to the surface for treatment. Because of site constraints and the opportunity to use an existing line for stormwater conveyance, ' biofiltration would be very costly to implement over the entire site. In brief, the system we are proposing involves providing biofiltration for exterior roadways and some parking areas, a constructed wetland for an isolated parking area, and treatment of the remaining stormwater in an oversized wet detention pond. ' About 2/3 of the new impervious area, as well as drainage from the existing site, would be treated via the detention pond. ' Metro believes an oversized wet pond designed to treat the full 2 year-24 hour storm flow will perform significantly better than one sized for 1/3 that flow, as the KCSWDM currently requires. ' Data to support this argument are taken from the Nationwide Urban Runoff Program (NURP) , which studied the performance of wet detention ponds throughout the country (USEPA, 1983) . Walker later analyzed the NURP data, relating water quality performance to engineering design criteria (Walker, 1986) . Four specific design predictors were used in the EPA and Walker reports. They 3 are as follows: 1 ' Ms. Lynn Guttman September 19 , 1991 ' Page 2 1) The ratio of pond surface area to the surface area of ' the drainage, SA/SD; 2) The ratio of pond volume to the mean storm runoff volume, VB/VR; 3) The surface overflow rate during the mean storm; and ' 4) Mean hydrualic residence time. ' In addition, pond configuration and the prevention of short circuiting are important considerations, although no quantitative indices have been developed. ' Each of these areas will be addressed in turn. Attachments provide numerical backup for the stated removal rates of the proposed pond. Ratio of pond surface area to surface area of the drainage. In general, the pond surface area should be about 1% of the ' contributing drainage area to achieve good pollutant removal efficiency. Modeling done for Metro in support of the Lake Sammamish Management Plan suggests that with a pond depth of about 1 meter, almost 90% removal of total suspended solids (TSS) could be expected. NURP data shows that detention ponds with surface areas greater than 1% of the watershed area achieved TSS removals of from 60% to 90%. Removal of heavy metals was also ' superior to that seen in smaller ponds. The proposed detention pond at the Renton site has a surface area of 1. 1% of the site drainage area. ' Ratio of pond volume to mean storm runoff volume. Ponds having the ratio of pond volume to mean storm runoff volume greater or equal to 1 show better removal efficiencies than ponds in which the ratio is less than one. Metro' s proposed pond has a ratio of 2 . 3 , which corresponds to TSS removals of 60% to 90% in the NURP data. ' Surface overflow rate. This design predictor is the ratio of the mean storm runoff rate to the pond surface area. In the NURP ' study, ponds with overflow rates less than about 0. 1 ft/hr performed best in terms of TSS and metal removals. Metro's proposed pond has an overflow rate of 0. 07 ft/hr. ' Ms. Lynn Guttman September 19 , 1991 ' Page 3 Hvdraulic residence time. The longer storm flows are detained, ' the greater treatment provided, both for TSS as well as for the nutrients nitrogen and phosphorus. In part, nutrient removal in wet ponds is due to biological activity in the water column, a ' process which is time dependent. Walker estimates that for phosphorus removal of up to 80%, a detention time in excess of 14 days is required. For about 50% phosphorus removal, detention ' times of 7 - 14 days would be required. TSS removals of 60% to 80% have been seen with detention times of between 6 and 7 days, according to data from NURP and Martin & ' Smoot (1986) . As currently designed, with an active pool volume of about 1 meter, the proposed pond has a detention time of 7 days. Since the receiving waters (P-1 channel and Green River) ' are not particularly phosphorus sensitive in the reaches downstream of the Treatment Plant, detention times of greater than 7 days would not seem necessary. However, if determined ' otherwise, it would be possible to achieve a 15 day detention time by increasing the pond depth to 2 meters. Pond configuration. A laboratory scale model studied by Horner ' 1 and Kortenhof (1987) , found that long, narrow pond configurations l with two cells achieved longer residence times than single cell configurations. The proposed detention pond design provides ' three cells, as per the KCSWDM, and a very elongate configuration. Use of three cells and the long, narrow configuartion serves to maximize the travel path of storm water introduced into the pond, and increase the residence time over ' that projected on the basis of engineering parameters alone. The attached Table indicates a range of expected annual pollutant removal effectiveness for Metro's proposed enlarged pond size, ' and the smaller pond size required in the Manual. The Table also gives preliminary data about the removal efficiencies of biofiltration swales. (Biofiltration data was collected this summer as part of an inter-agency project to monitor the pollutant removal effectiveness of grassy swales, and is as yet unpublished. ) ' The expected pollutant removal performance is given as a range to indicate the variability seen in different parts of the country ' with different pond treatment systems. In general, a much higher annual average level of pollutant removal is expected from large ponds with design characteristics as described previously. ' Ms. Lynn Guttman September 19 , 1991 ' Page 4 These data indicate that with an enlarged detention pond sized as proposed, water quality performance equal to or better than that expected from a smaller pond plus biofiltration can be achieved. ' Metro appreciates your willingness to consider our request for flexibility in the manner the requirements and water quality objectives of the KCSWDM can be met. If you have questions about ' the data presented, please contact me at 684-1551 or Louise Kulzer, at 684-2063 . Additional background information can be found in Metro' s publication "Considerations for the Use of Wet Ponds for Water Quality Enhancement. " References cited in this ' letter are appended. ' Very truly ours, ' ohn F. Spencer Director ' Water Pollution Control Department JFS: lkk ' Enclosures 1 ' References Cited in Letter Considerations for the Use of Wet Ponds for Water Quality ' Enhancement. 1989 . Office of Water Quality, Metro, Seattle, WA 98104 . ' Martin, Edward H. and James L. Smoot. 1986. Constituent-load Changes in Urban Stormwater Runoff Routed Through a Detention Pond-Wetlands System in Central Florida. U.S.Geological Survey, ' Water Resources Investigation Report 85-4310. Walker, William Jr. 1986. Phosphorus Removal by Urban Runoff Detention Basins. "Lake and Reservoir Management: Influences of Nonpoint Source Pollutants and Acid Precipitation" 6th Annual International Symposium, North American Lake Management Society, Portland, Oregon. November 5 - 8 , 1986. ' US Environmental Protection Agency, 1983 . Results of the Nationwide Urban Runoff Program. Volume 1 - Final Report. Water Planning Division, US EPA, Washington D.C. 20460 . 1 . } 1 ' Pollutant Removal Performance of Large and Small Detention Ponds and Grassy Swales ' Pollutant Percent Removal Observed ' Large ponds Smaller ponds Grassy swales (average of 4 storms) ' Total dissolved 60 - 90% neg. - 30% 80% ' solids (TSS) Total ' phosphorus 3 - 80% neg. - 30% 5% ' Total Kjeldahl ^ nitrogen neg - 60% neg. - 20% neg. ' Total lead 80 - 90% 10 - 60% 70% Total zinc neg. - 70% 0 - 10% 60% Notes: Detention pond data is from NURP, USEPA, 1983 . ' Grassy Swale data is from Biofiltration Phase II, unpublished. Large ponds and small ponds are defined as follows: Large ponds Small ponds ----------- ----------- SA/SD > 1 SA/SD < 1 ' VB/VR > 1 VB/VR < 1 Overflow rate < 0.1 ft/hr Overflow rate > 0. 1 ft/hr Hydraulic resedence time Hydraulic resedence time > 14 days < 14 days ' Legend: ^ Data for grassy swales is NO2 + NO3 rather than Kjeldhel Nitrogen # Lead removals were inferred from data on iron, since lead behaves simialrly in water, and lead was below detection. ' Design Parameters for Detention Pond Water Quality Improvement (after Walker, 1986) . I. Pond surface area / Drainage surface area > 1% Renton TP Site: Pond area = 0. 57 acres (0. 23 ha) ' Total site area = 49. 6 acres (20 ha) SA/SD II. Pond volume / Mean storm runoff volume > 1 Mean storm runoff volume = watershed area (ha) ' X runoff coefficient X mean storm size (cm) Renton TP Site: Pond volume = 0.23 ha X 100 cm = 2300 cubic meters ' Mean storm size = 1.22 cm Site runoff coefficient = 0.4 (40% impervious) ' Mean storm volume = 20 ha X .4 X 1. 22 cm = 976 cubic meters '.� VB/VR Ratio = 2300 cubic meters / 976 cubic meters = 2.36 III . Overflow rate < 0. 1 ft/hr Overflow rate = mean runoff rate / pond surface area _ (mean storm size(cm) X runoff coefficient X drainage ' area(ha) ) / (mean storm duration(hr) X pond area(ha) ) Renton TP Site: Assumptions: Mean storm size = 1. 22 cm ' Site Runoff Coefficient = 0. 4 Mean storm duration = 20 hours Overflow rate = (1.22 cm X 0.4 X 20 ha) / (20 hr X 0.23 ha) = 2. 12 cm / hr = 0 . 07 ft / hr ( 1 ft = 30.48 cm) t ' IV. Hydraulic detention time > 14 days for 80o Phosphorus removal. ' = 100 X pond area(ha) X pond depth(m) / Drainage area X runoff coefficient X mean storm size / length of season (yr) 1 Renton TP Site: Assumptions: length of season = 9 mo = .75 yr ' Hydraulic residence time = 100 (0. 23 ha) (1 m) (0 . 66 yr) / 20 ha (0.4) (106 cm) = 0. 019 yr = 7 days 1 1 1 1 1 ' APPENDIX D (Stormwater System Modeling : Hydrologic and Conveyance Capacity Analyses) 1 1 1 1 MTPR Drainages Plan/RepurV Dcu npl!i. i.ci 3�B 1 ' STORMWATER SYSTEM MODELING ' Figures D1 and D2 are schematic diagrams of the existing and proposed stormwater drain systems for MTPR. The plans show location, diameter, and node ID used in the computer modeling. ' Two 30-inch storm sewers, one serving the north and the other serving the south part of the plant , carry most runoff to an outfall manhole west of the Administration Building. Two smaller ' lines also discharge into the outfall manhole : an 18-inch line that drains the parking lot north of the administration building and the impervious areas around the grit handling facility, and a 10-inch line that accepts runoff through catch-basins located on ' the northern entrance road near Monster Road. The locations of the existing stormwater sewer system are based on construction drawings and inspection surveys . About 101 pipe segments were used to model the existing system; about 108 for the proposed system. Stormwater from the dewatered sludge truck loading area, the septage disposal area, and chemical storage areas (such as the sodium hydroxide storage tank) is directed into the sanitary drain system. The sanitary drains flow to the treatment plant ' for processing before being discharged into Elliot Bay via the effluent transfer system. In the proposed enlargement , stormwater draining to the grit loading ramp will also be pumped to the plant sanitary sewer system in a manner similar to that serving the dewatered sludge loading area . Only when the capacity of the pumps is exceeded, such as during an extreme storm event, will stormwater from these areas drain to the stormwater sewer system. Both the sludge loading area and the grit loading area were assumed to flow into the stormwater sewer system for the 100-year 24-hour storm event . ' In the proposed stormwater sewer system, several existing catch basins and inlets will be relocated to drain newly landscaped areas and realigned access roads and parking lots . Most of the realignment changes will occur near the Administration Building and the Dewatering Building . The new grades of the proposed plan will redirect some of the flows to ' new inlets, thus changing the site hydrology . New extensions of the stormwater system will be required to serve the new proposed roads and parking lots of the new DAFT complex and the new secondary clarifiers . Areas that do not drain to the stormwater sewer system ' include the wetlands , the eastern perimeter of the site, the southwest and southeast corners of the site, open process tanks and sludge processing tanks . The wetlands accept runoff from the MTPR Drainaye Plan/ReJ­Lt/DCa i i,pin. 1, -:,R,'P. 1 area north of the northern access road . The P-1 channel receives flow from the eastern perimeter of the site . A swale located ' just north of Longacres Drive receives stormwater from pervious areas along the southwest corner of the site . The swale operates like a retention pond, draining east to the P-1 Channel when the water accumulates to a depth of about 18 inches . Changes proposed in these areas for Enlargement III are minimal and will not significantly alter the drainage patterns or peak flow rates . Stormwater from these areas were not included in the modeling effort as agreed to by the City of Renton ' s Surface and Stormwater Division . ' Figures D1 and D2 also show the subcatchments used in the model . These subcatchments were delineated based on the contours of the site maps . The following areas do not contribute runoff to the stormwater sewer system: open vessels such as the aeration tanks , RAS channel , mixed liquor channel, chlorine contact channels, and secondary clarifiers ; the primary clarifiers ; solids area structures such as the DAFTs, the anaerobic digesters, and the sludge blending tank; the secondary control facilities; the influent pump building; and the area between secondary clarifiers 3-4 and 5-6 . About half of the roof of the sludge dewatering building drains to the plant ' s sanitary system; the other part drains to the stormwater sewer system. The area around secondary clarifiers 3 , 4, 5 and 6 drain to the chlorine contact channel . ' Modelina Methodolocry The methodology used to model peak storm runoff rates and route storm flows through the stormwater sewer system complies with the requirements of the SWM. Modeling involved the following tasks : * Mathematically define the stormwater conveyance system, e .g. , pipe diameter, length, upstream and downstream ' invert and rim elevations . * Delineate catch basins for each stormwater inlet . * Calculate the pervious and impervious areas ' contributing to a stormwater inlet . * Determine the SCS curve numbers, K value, conveyance slope, and characteristic length for each catch basin. * Define the 100-year, 24-hour design storm hydrograph. ' Run simulation runs for both pre- and post-developed site conditions . * Compare the peak flow rates to the 0 . 5 cfs exemption criterion . ' The 24-hour design storm hyetograph found in Figure 3 . 5 . 1A (SCS Type 1A Distribution) of the SWM was used in this analysis . The unit hyetograph was multiplied by the total 100-year, 24-hour MTPR Diainag, P13n/Re�o rC/Dtiainpin.dcc:FCR ' precipitation for the MTPR site, 3 . 9 inches according to Figure 3 . 5 . 1H of the SWM, to produce the design storm hyetograph. ' Adjustments for snowmelt were not required because the site elevation is below 1 , 000 MSL. The design storm hyetograph was input to the model using 10-minute intervals . HYDRA4, a sanitary and stormwater sewer analysis program available on Brown and Caldwell ' s GIS package, was used to calculate conveyance system response to storms . HYDRA4 uses the Soil Conservation Service (SCS) hydrograph method modified with the Santa Barbara Unit Hydrograph algorithm to generate runoff hydrographs . HYDRA4 routes the stormwater inflow hydrographs ' through the stormwater drain system. This methodology complies with Section 3 . 2 of the SWM, "Computation Methods" . Inputs required to generate runoff hydrographs included the following: * Total area in acres ' * Proportion of impervious surfaces * SCS curve number for impervious areas * SCS curve number for pervious areas ' * overland flow characteristics factor "K" * Slope of the overland conveyance system * The longest route surface water must flow to reach the outlet for the land segment . 1 Tables D1 and D2 present the data used by HYDRA4 to generate runoff hydrographs for pre- and post-development stormwater systems . Soil Group C was used for all subcatchments . The majority of the pervious surfaces on the plant site are imported topsoil . These soils fall under SWM hydrologic group C. The ' western landscaped areas may be partly Beausite soils, although much of that is also imported topsoil . The wetland area is also considered to be Puyallup soil, which is classified as hydrologic ' group B, but was modeled as soil group C . Curve numbers used in the model were as follows : * CN for impervious areas = 98 * CN for open spaces in good condition (grass cover on 75% or more of the area) = 86 * CN for open spaces in fair condition (grass cover on 50 to 75% of the area) = 90 An example of open spaces in good condition is the open field north of the Administration Building. An example of an open field in fair condition is the landscaped area lining the road ' just south of the solids handling facilities . ' MTPR Drainage Plan/Report/Dra i npin.loci RCF 1 ' K values used to calculate the time of concentration were weighted averages based on contributing area . K values used in ' the model were as follows : * K for short pasture and lawn = 11 * K for nearly bare ground = 13 * K for paved areas = 27 The peak flow rate at the storm sewer outfall manhole was used to compare before and after development (Node 1001) . Flow through the outfall was assumed to be unhindered by the Green River surface elevation. Tables D3 and D4 present the databases used in the HYDRA4 model for the pre- and post-development stormwater systems . The ' database files contain physical information about the conveyance systems : ' * Downstream Node ID * Downstream Invert Elevation * Downstream Rim Elevation * Pipe Segment Length ' * Pipe Diameter * Upstream Node ID * Upstream Invert Elevation * Upstream Rim Elevation ' Node IDs and pipe diameters are presented on the site plans . To orient the reader, node 1000 is the Green River outfall diffuser; node 1001 is the outfall junction manhole; nodes between 1001 and 1040 are located along the southern half of the site, and nodes between 1044 and 1101 are located on the northern half of the site. Node 1055 is the overflow drain from the ETS Surge Tank west of the site. Input parameters required to ' produce the storm hydrographs are presented in Tables D1 and D2 . 1 ' MTPR Drainage P1aniReportiDrainpin.duci R<-P Table D1. Hydrograph Input Paramters: Pre-Development 86 11 90 98 13 27 ' Node Total Area Fraction 01 CNlmper CNPery K Slope Distance (Acres) Im rv.Area (Ft) 1101 1.12 0.123 96.0 $6.0 13.0 0.03 220 1100 0.72 0.118 98.0 86.7 13.2 0.03 180 1099 0.64 0.269 98.0 88.7 16.3 0.021 200 ' 109 1097 1096 0.23 0.884 98.0 86.0 25.2 0.02 300 1095 0.26 0.309 98.0 86.0 15.9 0.054 80 ' 1094 0.49 0.507 98.0 87.1 19.4 0.07 160 1093 0.52 0.575 98.0 87.3 20.5 0.148 220 1092 0.35 0.748 98.0 90.0 23.5 0.012 100 1091 0.08 0.417 98.0 86.0 17.7 0.07 60 1090 0.15 0.344 98.0 86.0 16.5 0.07 60 1089 0.26 0.361 98.0 88.5 17.6 0.066 200 1 1088 0.11 1.000 98.0 #DIV/01 27.0 0.0013 160 1087 0.25 0.661 98.0 90.0 22.2 0.107 70 1086 0.24 0.732 98.0 86.0 22.7 0.01 60 ' 1085 1094 0.19 1.000 98.0 #DIV/0! 27.0 0.0067 240 1083 2.75 0.000 98.0 86.0 11.0 0.0115 320 ' 1082 1081 0.06 1.000 98.0 #DIV/01 27.0 0.008 50 1080 0.10 1.000 98.0 #DIV/01 27.0 0.0036 160 1079 1.62 0.000 98.0 86.0 11.0 0.012 220 1078 0.55 0.091 98.0 86.0 12.5 O.t103 260 1076 0.49 0.000 98.0 86.0 11.0 0.0035 170 ' 1075 0.64 1.000 98.0 #DIV/0! 27.0 0.014 260 1074 0.10 1.000 98.0 #DIV/01 27.0 0.03 210 1073 2.41 0.095 98.0 86.0 12.5 0.015 160 ' 1072 0.06 0.000 98.0 86.0 11.0 0.33 40 1071 0.14 1.000 98.0 #DIV/01 27.0 0.005 100 1070 0.33 0.533 98.0 88.2 20.0 0.009 145 1069 0.11 0.813 98.0 86.0 24.0 0.003 90 ' 1068 1067 0.30 0.504 98.0 86.0 19.1 0.011 150 1066 0.20 0.884 98.0 86.0 25.2 0.007 140 ' 1065 1064 0.11 0.780 98.0 86.0 23.5 0.01 65 1063 1.02 0.111 98.0 86.0 12.8 O.tb4 180 ' 1062 0.04 1.000 98.0 #DIVro! 27.0 0.021 90 1061 Assumed no inlet at this node. 1 HYDRA4 Input Files ' Hydrograph Parameters Pre-Development Renton III ' Node Total Area Fraction of CNlmper CNPery K Slope Distance (Acres) Im erv.Area (Ft) ' 1060 3.46 0.119 98.0 86.0 12.9 0.08 400 1059 0.54 0.000 98.0 86.0 11.0 0.045 180 1058 0.66 0.231 98.0 86.0 14.7 0.045 80 1057 1056 1055 1054 ; 1053 1052 1051 0.05 1A00 98.0 #DIV/01 27.0 0.002 60 1050 1049 ' 1048 3.62 0.000 98.0 86.0 11.0 0.0002 380 1047 0.67 1.000 98.0 #DIV/0! 27.0 0.0065 200 1046 0.22 1.000 98.0 #DIV/0! 27.0 0.01 220 1045 1044 1021 0.43 0.706 98.0 86.0 22.3 0.006 270 1020 0.20 0.765 98.0 86.0 23.2 0.003 160 1019 0.11 0.857 98.0 86.0 24.7 0.005 115 1018 0.21 0.564 98.0 86.0 20.0 0.003 135 ' 1017 0.54 0.879 98.0 86.0 25.1 0.005 120 1016 1015 0.39 0.520 98.0 86.9 19.6 0.0065 170 ' 1014 0.44 0.301 98.0 88.3 16.6 0.006 200 1012 120 0.149 98.0 89.8 15.0 0.005 120 1011 0.10 1.000 98.0 #DIV/01 27.0 0.005 110 1010 ' 1009 0.34 0.827 98.0 86.0 24.2 0.005 100 1036 0.48 0.168 98.0 87.1 14.2 0.0044 90 1035 0.20 1.000 98.0 #DIV/01 27.0 0.005 100 1034 0.16 0.280 98.0 86.0 15.5 0.006 180 1033 0.06 0.155 98.0 86.0 13.5 0.086 50 1032 0.09 0.667 98.0 86.0 21.7 0.0017 90 1 1031 0.39 0.000 98.0 86.0 11.0 0.008 80 1029 0.65 0.690 98.0 88.3 22.4 0.005 160 1028 / 1027 0.23 0.000 98.0 86.0 11.0 0.006 80 1026 0.33 0.341 98.0 87.5 16.9 0.005 130 4_ 'Assumed no inlet at this node. ' HYDRA4 Input Files Hydrograph Parameters Pre-Development Renton III ' Node Total Area Fraction of CNlmper CNPery K Slope Distance Acres Imperv.Area Ft ' 1025 0.31 0.323 98.0 86.0 16.2 0.005 100 1024 1008 1023 0.19 0.576 98.0 87.8 20.6 0.011 150 ' 1022 0.17 0232 98.0 86.0 14.7 0.005 90 1037 0.18 0.640 98.0 86.0 212 0.005 130 1007 ' 1042 0b8 1.000 98.0 #DIV/01 27.0 0.01 150 1041 1040 1.18 0.730 98.0 86.0 22.7 0.0114 420 ' 1039 0.21 1.000 98.0 #DIV/01 27.0 0.012 280 1038 0.34 0.669 98.0 86.0 21.7 0.005 160 1006 1005 0.45 0.656 98.0 86.0 21.5 0.01 190 1004 0.34 0.557 98.0 86.0 19.9 0.016 170 1043 0.71 0.849 98.0 86.0 24.6 0.026 160 1003 1002 1001 1000 'Assumed no inlet at this node. ' Table D2. Hydrograph Input Parameters: Post-Development 86 11 90 13 27 Node Total Area Fraction of CNlmper CNPery K Slope Distance (Acres) Im rv.Area (Ft) 1101 0.72 0.191 98.0 86.0 14.0 0.03 220 1100 0.72 0.118 98.0 86.7 13.2 0.03 180 1099 0.73 0.396 98.0 87.7 17.9 0.021 200 1098 ' 1097 1096 0.20 1.000 98.0 86.0 27.0 0.02 300 1095 0.08 1.ODO 98.0 86.0 27.0 0.054 80 1094 0.49 0.416 98.0 86.0 17.7 0.07 160 1093 0.66 0.593 98.0 86.0 20.5 0.148 220 1092 0.43 0.654 98.0 90.0 22.2 0.012_ 100 ' 1091 0.08 0.417 98.0 86.0 17.7 0.07 60 1090 0.15 0.344 98.0 86.0 16.5 0.07 60 1089 0.28 0.361 98.0 88.5 17.6 0.066 200 1088 0.11 1.000 98.0 86.0 27.0 0.0013 160 1087 0.25 0.661 98.0 90.0 22.2 0.107 70 1086 0.39 0.445 98.0 86.0 18.1 0.01 60 ' 1085 1084 0.19 1.000 98.0 86.0 27.0 0.OD67 240 1083 2.50 0.000 98.0 86.0 11.0 0.0115 320 1082 1081 0.06 1.000 98.0 86.0 27.0 0.008 50 1080 0.10 1.000 98.0 86.0 27.0 0.0036 160 ' 1079 1.62 0.000 98.0 86.0 11.0 0.012 220 1078 0.19 0.267 98.0 86.0 15.3 0.003 260 1077 ' 2076 1.03 0.000 0 86.0 11.0 0.001 400 1076 0.49 0.000 98.0 86.0 11.0 0.0035 170 1075 0.64 1.000 98.0 86.0 27.0 0.014 260 1074 0.10 1.000 98.0 86.0 27.0 0.03 210 ' 1073 2.41 0.141 98.0 86.0 13.3 0.015 160 1072 0.06 0.000 98.0 86.0 11.0 0.33 40 1071 0.14 1.000 98.0 86.0 27.0 0.005 100 1070 0.33 0.533 98.0 88.2 20.0 0.009 145 1069 0.11 0.813 98.0 86.0 24.0 0.003 90 1068 1067 0.30 0.504 98.0 86.0 19.1 0.011 150 1066 0.20 0.894 98.0 86.0 25.2 0.007 140 1065 ' 1064 0.11 0.780 98.0 86.0 23.5 0.01 65 1063 1.02 0.111 98.0 86.0 12.8 0.004 180 Assumed no inlet atthis node. A(- ' HYDRA4 Input Files Hydrograph Parameters ' Post- Development Renton III ' Node Total Area Fraction of CNlmper CNPery K Slope Distance (Acres) Im erv.Area Ft ' 1062 0.04 1.000 98.0 86.0 27.0 0.021 90 1061 1060 2.92 0.236 98.0 86.0 14.8 0.08 400 1059 0.54 0.000 98.0 86.0 11.0 0.045 180 1058 2.49 0.061 98.0 86.0 12.0 0.045 300 1057 1056 1055 1054 1053 ' 1052 1051 0.05 1.000 98.0 86.0 27.0 0.002 60 1050 ' 1049 1048 0.29 0.000 98.0 86.0 11.0 0.0002 380 1047 0.74 0.034 98.0 86.0 11.5 0.051 300 ' 2047 1.54 0.061 98 86.0 12.0 0.05 400 1046 0.22 1.000 98.0 86.0 27.0 0.01 220 1045 1044 2021 2.47 0.000 0.0 86.0 11.0 0.005 350 1021 0.43 0.706 98.0 86.0 22.3 0.006 270 ' 1020 020 0.765 98.0 86.0 23.2 0.003 160 1019 0.11 0.857 98.0 86.0 24.7 0.005 115 1018 0.21 0.564 98.0 86.0 20.0 0.003 135 ' 1017 0.23 0.711 98.0 86.0 22.4 0.005 120 1016 1015 0.39 0.520 98.0 86.9 19.6 0.0065 170 1014 0.44 0.301 98.0 88.3 16.6 0.006 200 1012 1.20 0.149 98.0 89.8 15.0 0.005 120 1011 0.10 1.000 98.0 86.0 27.0 0.005 110 1010 ' 1009 0.34 0.827 98.0 86.0 24.2 0.005 100 1036 0.42 0.194 98.0 86.0 14.1 0.0044 90 1035 0.20 1.000 98.0 86.0 27.0 0.005 100 ' 1034 0.74 0.135 98.0 86.0 13.2 0.047 150 1033 0.06 0.155 98.0 86.0 13.5 0.086 50 1032 0.09 0.802 98.0 86.0 23.8 0.0017 90 ' 1031 0.39 0.000 98.0 86.0 11.0 0.008 80 1029 0.65 0.729 980 88.1 22.9 0.005 160 Assumed no inlet at this node. i 1 HYDRA4 Input Files Hydrograph Parameters Post- Development Renton III Node Total Area Fraction of CNlmper CNPery K Slope Distance Acres lmperv.Area Ft) 1028 ' 1027 0.23 0.086 98.0 86.0 12.4 0.006 80 1026 0.33 1.000 98.0 86.0 27.0 0.01 120 1025 0.31 0.323 98.0 86.0 16.2 0.005 100 ' 1024 1008 1023 0.19 0.576 98.0 87.8 20.6 0.011 150 1022 0.17 0.232 98.0 86.0 14.7 0.005 90 1037 0.18 0.640 98.0 86.0 21.2 0.005 130 1007 ' 1042 0.58 1.000 98.0 86.0 27.0 0.01 150 1041 1040 1.23 0.781 98.0 86.0 23.5 0.0114 420 ' 1039 0.21 1.000 98.0 86.0 27.0 0.012 280 1038 0.34 0.669 98.0 86.0 21.7 0.005 150 1006 ' 1005 0.45 0.656 98.0 86.0 21.5 0.01 190 1004 0.34 0.616 98.0 86.0 20.9 0.016 170 1043 0.60 0.822 98.0 86.0 24.2 0.026 160 1003 7002 1.24 0.100 98 86.0 12.6 0.011 400 1001 ' ow 'Assumed no inlet at this node. G . y° 1 1 1 1 Table D3. Existing Conveyance System Parameters ' Downstream Upstream Elevations Pi a Dimensions Elevations Node ID Invert Manhole Rim Length Diameter Node ID Invert Manhole Rim ' 1000 89.00 99.00 999.9 120 1001 89.75 129.00 1001 89.75 129.00 71.0 30 1002 102.73 128.00 1002 102.73 128.00 112.0 30 1003 112.95 127.50 1003 102.95 127.50 102.0 30 1004 103.46 126.00 1004 103.46 126.00 482.0 30 1006 104.35 125.50 1006 120.90 125.50 150.0 30 1007 121.50 125.50 1007 104.70 125.50 284.0 30 1008 10524 125.60 1008 105.24 125.60 160.0 30 1009 105.56 125.50 ' 1009 106.06 125.50 105.0 24 1010 106.27 126.50 1010 117.14 126.50 47.0 8 1011 117.52 126.40 1011 117.52 126.40 309.0 8 1012 120.00 125.74 1010 106.27 126.50 280.0 8 1014 120.00 125.50 ' 1010 106.27 126.50 83.0 21 1015 106.58 125.94 1015 106.60 125.94 63.0 10 1016 109.08 126.20 1016 122.84 12620 217.0 10 1017 124.58 128.58 1018 107.00 125.50 245.0 18 1020 107.44 125.50 ' 1020 107.00 125.50 308.0 18 1021 108.22 128.80 1018 107.00 125.50 217.0 8 1019 124.88 128.80 1015 106.58 125.94 255.0 18 1018 107.00 125.50 ' 1008 105.24 125.60 128.0 15 1024 107.80 123.30 1024 107.80 123.30 96.0 15 1025 110.50 123.30 1025 110.50 123.30 128.0 15 1026 113.80 123.30 1026 113.80 123.30 100.0 15 1027 114.00 124.00 ' 1027 114.00 124.00 320.0 15 1028 115.55 125.00 1029 116.00 12520 220.0 12 1030 120.25 124.25 1029 116.00 125.20 55.0 12 1031 116.54 123.50 1031 116.54 123.50 125.0 12 1032 117.89 123.00 ' 1032 117.89 123.00 50.0 12 1033 118.50 123.30 1033 118.50 123.30 90.0 12 1034 119.51 123.40 1034 119.51 123.40 14.0 12 1035 119.86 123.50 1035 119.86 123.50 100.0 12 1036 121.00 123.50 ' 1007 104.70 125.50 45.0 8 1037 123.36 125.46 1007 121.50 125.50 40.0 12 1022 121.70 125.50 1022 121.70 125.51 244.0 12 1029 123.00 128.80 1006 105.35 125.50 90.0 12 1038 106.50 128.80 ' 1038 119.00 126.00 100.0 8 1039 120.20 126.00 1038 119.50 126.00 120.0 12 1040 120.20 126.00 1040 120.20 126.00 169.0 12 1041 121.60 125.50 1041 121.61 125.50 148.0 8 1042 122.75 125.50 ' 1003 115.50 127.50 72.0 12 1043 116.00 125.50 1001 102.59 129.00 136.0 18 1044 119.79 130.10 1044 119.79 130.10 124.0 15 1045 121.73 129.42 ' 1045 121.73 129.42 296.0 15 1046 122.00 129.42 1044 119.79 130.10 227.0 8 1047 123.39 127.65 1044 119.79 130.10 302.0 15 1048 122.00 126.00 1048 122.00 126.00 43.0 6 1049 124.00 133.00 t 1049 121.62 133.00 177.0 10 1050 131.00 136.00 1050 131.00 136.00 160.0 8 1051 175.00 189.80 1001 102.59 129.00 305.0 30 1052 105.01 129.00 1052 105.01 129.00 191.0 12 1053 106.20 129.00 1053 106.20 129.00 339.6 12 1054 14920 156.00 1052 105.01 129.00 252.0 30 1055 105.85 126.00 foss 105.85 126.00 325.0 30 1056 106.50 125.25 1056 107.00 12525 276.0 24 1058 108.20 125.25 1 1 ' Table D3. Existing Conveyance System Parameters ' Downstream Upstream Elevations Pipe Dimensions Elevations Node ID Invert Manhole Rim Length Diameter Node ID Invert Manhole Rim ' 1058 108.20 125.25 107.0 24 1059 108.67 125.25 1059 108.67 125.25 191.0 24 1060 109.53 125.25 1060 109.53 125.25 155.0 24 1061 110.19 126.50 1061 120.10 126.50 38.0 12 1062 120.25 12525 1056 110.00 125.25 100.0 6 1057 111.00 126.00 1061 110.44 126.50 393.0 21 1063 111.78 125.33 1063 112.28 125.33 170.0 15 1067 112.77 125.00 1067 112.77 125.00 172.0 15 1069 113.34 125.00 ' 1063 112.86 125.33 65.0 12 1064 117.00 125.50 1064 117.00 125.50 53.0 12 1065 118.70 125.50 1065 118.70 125.50 43.0 12 1066 123.21 125.00 1056 106.50 125.25 320.0 30 1072 106.61 125.25 ' 1072 118.73 125.25 83.0 12 1073 119.39 125.39 1072 116.74 125.25 205.0 12 1074 118.38 125.25 1074 119.62 125.25 196.0 12 1076 121.00 125.50 1074 118.38 125.25 77.0 12 1075 119.00 125.25 ' 1072 106.61 125.25 290.0 30 1077 107.35 125.25 1077 120.65 125.25 103.0 12 1078 120.98 125.50 1078 120.98 125.50 100.0 12 2079 121.78 128.80 ' 1077 107.35 125.25 72.0 30 1079 107.80 125.25 1079 120.16 125.25 103.0 12 1080 120.98 125.50 1080 120.98 125.50 100.0 12 1081 121.78 128.80 1079 107.80 125.25 210.0 30 1082 108.36 125.25 ' 1082 108.36 125.25 105.0 30 1083 110.00 125.25 1083 121.00 125.25 107.0 12 1084 123.25 125.30 1083 121.00 125.25 14.0 14 1085 95.50 111.50 1085 103.24 111.50 110.0 18 1086 103.36 110.75 ' 1086 103.42 110.75 88.0 12 1087 103.94 110.68 1087 103.94 110.68 30.0 8 1088 104.12 125.35 1088 104.12 125.35 153.0 8 1089 113.50 115.54 1089 105.04 115.54 78.0 8 1090 105.52 111.00 ' 1089 105.04 115.54 72.0 8 1091 105.47 111.00 1086 103.92 110.75 95.0 12 1092 104.68 110.10 1092 104.68 110.10 95.0 12 1093 105.44 109.90 1093 105.44 109.90 70.0 12 1094 106.00 111.00 ' 1094 106.00 111.00 40.0 12 1095 106.39 114.24 1095 106.39 114.24 77.0 12 1096 106.95 119.20 1083 11125 125.25 108.0 15 1097 113.19 125.25 1097 113.19 125.25 324.0 15 1098 119.00 126.21 ' 1098 119.00 126.21 105.0 8 1099 119.84 124.94 1098 119.00 126.21 58.0 8 1100 119.50 126.90 1100 119.50 126.90 290.0 8 1101 123.56 128.11 ' 1069 113.76 125.00 127.0 10 1070 114.92 125.02 1070 114.92 125.02 160.0 8 1071 120.00 124.92 1001 118.91 129.50 180.0 10 3001 122.25 126.10 1006 120.70 125.50 140.0 12 1005 121.40 124.20 1028 115.55 125.20 15.0 12 1029 116.00 125.20 1021 108.22 128.80 320.0 8 2021 122.10 124.10 1029 116.00 125.20 100.0 12 2028 117.00 124.00 1076 1 121.00 125.50 207.0 12 2076 123.60 125.60 1 ' Table D4. Proposed Conveyance System Parameters .........................................._.........._........... ._._......_._._.._._...._._.,._...._._._._.........._._._..........._....................; ..Downstream........ . . . . N.............. .Upstream........_....._..............; _._........_. Elevations ._.Pipe Dimensions_.; ......_.Elevations................ Node ID Invert '.Manhole Rim Length ;Diameter •.Node ID r Invert Manhole Rim i ' 1000 89 00 9900 999.9 120 ' 1001 89.75 129.00 iRRi B�iS :I1$§DD 9i0 i'�0 'if}02 1rJ273 12800 i €ooe ::. R�73 12e �.;ifilNKt '�a0295 � : 12750 .: 1020 30 .1W4` 1fl3A& 12saR !' 1o0451008 YOg35 1551i . 1006 120.90 125.50 150.0 30 i 1007 121.50 125.50 i €1!9$ .10524 :125,$0 :1S0p :3411149 'Y :56 :.Y259¢�;' 1010 11714 126.50 47.0 8 j 1011 117.52 126.40 1011 117.52 126.40 309.0 8 i 1012 120.00 i 125.74 i ' 1010 106.27 126.50 280.0 8 1014 120 00 125 50 Y010 .10627 :12650 8S0 21 105 'lilfi56 .'125:84 .' #015 106$0 :AZ 94 63 R !.10 1016 1i7B 08 ::1'ffi!20 .:i ' 1016 122.84 126.20 217.0 10 1017 124.58 128.56 10t$ 10?00 1286�1 ?A"�0 I ,1$ � 1az0 10734 Y"�,:5tr 342.0 :iR70U : 12550 : 3R8,0 I '.16 iQ21 tu922 €2gb4 .? 1018 107.00 125.50 217.0 8 i 1019 124.88 128.80 i #015 10858 12594 2550 I -19 1£!18 10�O15 12550 :? €008 ":IR524 112560 '. 128R !15 1t124 Yt�FBIt Y29:94 3 702Q: a0�R0 .-:12330 960 -15 . :1425 11t]:50 123;30 : ii 1025 ':':40 w. '.:129 30 126.0 ::15 Yi)26 113 i}R Y 23 9R : 1027 11400 124.00 320.0 15 1028 115.55 125.00 i 1029 116.00 125.20 220.0 12 i 1030 12025 124.25 I 1029 116.00 125.20 55.0 12 i 1031 116.54 123.50 1031 116.54 123.50 125.0 ! 12 1032 117.89 123.00 1032 117.89 123.00 50.0 12 1033 118.50 123.30 1033 118.50 123.30 90.0 12 1034 119.51 123.40 ' 1034 119.51 123.40 14.0 12 1035 119.86 123.50 1035 119.86 ! 123.50 100.0 12 i 1036 121.00 123.50 1007 104.70 125.50 45.0 8 1037 123.36 125.46 1007 121.50 125.50 40.0 12 1022 121.70 125.50 ' 1022 121.70 125.51 244.0 1 12 : 1023 123.00 128.80 €006 R585 12556. ..: 800 : 12 :iti861095i3 1ZA8R:.:. � 1038 119.00 126.00 100.0 8 1039 120.20 126.00 1038 119.50 126.00 120.0 12 i 1040 120.20 126.00 1040 120.20 126.00 169.0 12 1041 121.60 125.50 1041 121.61 125.50 148.0 8 ; 1042 122.75 125.50 1043 117.50 125.50 160.0 10 i 2043 121.70 129.50 1003 115.50 127.50 72.0 12 1043 116.00 125.50 ' 1001 102.59 129.00 136.0 i 18 1044 119.79 130.10 1044 119.79 130.10 124.0 15 1045 121.73 129.42 1045 121.73 129.42 296.0 '�, 15 i 1046 122.00 129.42 1044 119.79 130.10 227.0 8 1047 123.39 127.65 ' 1044 119.79 130.10 302.0 !: 15 i 1048 122.00 ',, 126.00 j 1044 121.79 132.20 227.0 ! 8 I 2047 119.79 130.10 1048 122.00 126.00 43.0 6 1049 124.00 ! 133.00 ' 1049 121.62 133.00 177.0 10 1050 131.00 136.00 i 1050 131,00 136.00 1600 8 ' 1051 175.00 189.80 i 1DR1 10259 ?129{30 :. . 3R g{ s152 10501 129i40 : ,3 . .. :12....(..1Y�53 _ 1i'tfi 2D Y'LyOR t Table D4. Proposed Conveyance System Parameters Downstream Up stream Elevations PIPO Dimensions i EG Node I D wert !Manhole Rim Node ID 1;werlt7=ole Rim-1 1000 8900 99.00 999.9 1 120 1001 89.75 129.00 ........... ...... ..... .. 6 1006 12090 125.50 150.0 30 1007 121.50 125.50 ....1044V..d.:. iw 6 .......... ::: d. :�: :� -: ....... .... ;: : 27 z .1 1 .......... ....... -.1 ........... 1010 117.14 126.50 47.0 8 i 1011 117.52 126.40 1011 117.52 126.40 309.0 a 1012 120.00 125.74 1010 1 D6.27 126.50 280.0 8 1014 120.00 125-50 5o eaQ 1016 122.84 126.20 217.0 10 1017 124.58 128.58 ::12550 :245:0ii 1 :18 125.50 J:,1308 0.:..: .Y6 :::1 1018 107.00 125.50 217.0 8 1019 124.88 128.80 :i�j $ A00s;:: P9i24:. Z:i�i IOiW�i� F. F-11 Z. ::AW :::1 Ox - 0.0 1 * 1, 1027 :: :::�114.00 124.00 320.0 15 1028 115.55 125.00 1029 116.00 125.20 220.0 12 1030 120.25 124.25 1029 116.00 125.20 55.0 12 1031 116.54 123.50 1031 116.54 123.50 125.0 12 1032 117.89 123.00 1032 117.89 123.00 50.0 12 1033 118.50 123.30 1033 118.50 123.30 90.0 12 i 1034 119.51 123.40 1034 119.51 123.40 14.0 12 E 1035 119.86 123.50 1035 119.86 123.50 100.0 12 1036 121.00 123.50 1007 104.70 125.50 450 1 8 1037 123.36 125.46 1007 12150 12550 40.0 12 1022 121.70 125.50 1022 12170 125.51 244.0 12 1023 123,00 128.80 ............. ...... 1038 119.00 126.00 1000 8 i 1039 120.20 126.00 1038 119-50 126.00 1200 12 1040 120.20 126.00 1040 120.20 126.00 169.0 12 i 1041 121.60 125.50 1041 121.61 125.50 148.0 8 1042 122.75 125.50 1043 117.50 125.50 160.0 10 2043 121.70 129.50 1003 115.50 127.50 72.0 12 1043 116.00 125.50 1001 102.59 129.00 136.0i, 18 i 1044 119.79 130.10 10" 119.79 130.10 124.0 15 i 1045 121.73 129.42 1045 121.73 129.42 296.0 15 i 1046 122.00 129.42 1044 119.79 130.10 227.0 8 i 1047 123.39 127.65 15 1048 122.00 126.00 1 1044 119.79 130.10 302.0 1044 121.79 132.20 227.0 8 2047 119.79 13010 1048 122.00 126.00 43.0 6 1049 124.00 133.00 1049 121.62 133.00 177.0 10 i 1050 131.00 136.00 1050 131,00 13600 1600 8 i 1051 175,00 119,110 A .............. 1053 106.20 129.00 339.6 12 1054 149.20 156.00 i W Table D4. Proposed Conveyance System Parameters Downstream Upstream Elevations Pipe Dimensions Elevations Node ID Len 'Diameter Node ID Invert Manhole Rim ............. : IM lw2O.. M K:::::: 01M. 12583 7�7 . ..25. .......--. ... .............. ........... .................. ............. 1061 120.10 126.50 38.0 12 1 1062 120.25 125.25 Ow ........ ............. ................... ......... .......... ...... ........ ..... ........... ..... .......... 1057 . ..YO&3 11#.... 12.33..... Ni Id :::. .- goo:: 1063 112.86 125.33 65.0 12 j 1064 117.00 125.50 1064 117.00 125.50 53.0 12 I 1065 118.70 125.50 1065 118.70 125.50 43.0 i 12 I 1066 123.21 125.00 074; 106 1072 118.73 125.25 83.0 12 1073 119.39 125.39 1072 116.74 125.25 205.0 12 1074 118.38 125.25 1074 119.62 125.25 196.0 12 i 1076 121.00 125.50 1074 118.38 125.25 77.0 12 1075 119.00 125.25 167 120.65 125.25 103.0 12 1078 120.98 125.50 1078 12098 125.50 100.0 12 2079 121.78 128.80 ....... .... si #677 :72A.:. -...I - Wm- -36 7;Ii ............ 1079 120.16 125.25 103.0 12 1080 120.98 125.50 1080 1.20.98 125.50 100-0 12 1081 121.78 . 128.80 ...... ...... :A 1083 12100 125.25 107.0 12 1084 12325 125.30 14 ON. .:.:10336 110:74:. .#0If6...... 88.. : .. 3D0........ ..... 25;36 . ..... i :Z::::::A IV: . A .......... 1d91 105:41 111AO: 109.96,::to I-: ji�ii .................................... 3R. il qf� l w 95i i� Ow ....... 24. . 1097 113.19 125.25 324.0 j 15 i 1098 119.00 126.21 1098 119.00 126.21 105.0 8 i 1099 119.94 124.94 1098 119.00 126.21 58.0 8 11100 11950 126.90 1100 119.50 126.90 290.0 8 1101 123.56 128.11 1069 113.76 125.00 127.0 10 1 1070 114.92 125.02 1070 114.92 125.02 160.0 8 1071 120.00 124.92 3002 119.75 129.75 120.0 10 i 3001 122.25 126.10 3001 118.91 127.50 36.0 10 i 3002 11975 129.75 1006 120.70 125.50 140.0 12 1005 121.40 124.20 1028 115.55 125.20 15.0 12 i 1029 116.00 125.20 1021 108.22 128.80 320.0 8 2021 12210 124.10 1029 116.00 125.20 1000 12 i 2028 11700 124.00 1076 121.00 125.50 207.0 12 i 2076 1 123.60 125.60 1 1 1 1 ' APPENDIX E (TIR and Black River Basin Schematic) 1 1 t MTPR Drainage Plan/Report/Drainpin.doc/RCR ' Page 1 of 2 King County Building and Land Development Division TECHNICAL INFORMATION REPORT (TIR) WORKSHEET PART 1 PROJECT OWNER AND PART 2 PROJECT LOCATION PROJECT ENGINEER AND DESCRIPTION ' ProjectOwner Metro Project Name Enlargement III Address 821-2nd Ave. , Seattle Location 684-2100 Township T23N Phone R4E ._._.__. Project Engineer Jack Warburton Range 24 Brown and Caldwell Section Company Project Size 85 AC 85 Address Phone 281-4000 Upstream Drainage Basin Size 28 M C APPLICATIONPART 3 TYPE OF PERMIT OTHER ' Subdivision 0 DOF/G HPA Shoreline Management Short Subdivision (] COE404 0 Rockery ' © Grading = DOE Dam Safety Structural Vaults Commercial = FEMAFloodplain C] Other Other 0 COE Wetlands HPA ' PART 5 SITE COMMUNITYAND DRAINAGE BASIN Renton Drainage Basin Black River PART 6 SITE CHA ' Black, • River Floodlain ACTERISTICS Green Rivers p Not 100-year � � ' ® Stream P-1 Channel 0 Wetlands Yes, north end C] Critical Stream Reach O Seeps/Springs Depressions/Swales 0 High Groundwater Table ' Lake No Groundwater Recharge Steep Slopes No Other (] Lakeside/Erosion Hazard PART 7 SOILS Soil Type Slopes Erosion Potential Erosive Velocities ' Puyallup Level - 2% Moderately low B ausi te 15 - 3096 Moderately high ' Additional SheetsAttatched ' 1/'90 Page 2 of 2 ' King County Building and Land Development Division TECHNICAL INFORMATION REPORT (TIR) WORKSHEET ' • REFERENCE LIMITATION/SITE CONSTRAINT ' Ch.4-Downstream Analysis No major construction limitations Wetland Protection No construction activity allowed within 25 feet; fenced. ' o a Additional Sheets Attatched rosion a amen a ion on ro REQUIREMENTSPART 9 ESC MINIMUM ESC REQUIREMENTS MINIMUM ESC REQUIREMENTS , DURING CONSTRUCTION FOLLOWING CONSTRUCTION © Sedimentation Facilities ® Stabilize Exposed Surface ® Stabilized Construction Entrance ZI Remove and Restore Temporary ESC Facilities Fx Perimeter Runoff Control ® Clean and Remove All Silt and Debris ® Clearing and Grading Restrictions ® Ensure Operation of Permanent Facilities ® Cover Practices ® Flag Limits of NGPES ' ® Construction Sequence Other Other PART 10 SURFACE WATER SYSTEM Grass Lined Channel 0 Tank = Infiltration Method of Analysis ' Qx Pipe System IS1 Vault 0 Depression HYDRA and SCS 0 Open Channel = Energy Dissapator O Flow Dispersal Compensation/Mitigation 0 Dry Pond ® Wetland (] Waiver of Eliminated Site Storage ' Wet Pond Stream Regional Detention Brief Description of System Operation Gravity flow to wet vault vault pumps for emeroencv overflow. , Facility Related Site Limitations O Additional Sheets Attatched Reference Facility Umitation PART 11 STRUCTURAL ANALYSIS PART 12 EASEMENTSITR ACTS (May require 1 special 0 Drainage Easement ® Cast in Place Vault [=1 Other = Access Easement ' = Retaining Wall = Native Growth Protection Easement = Rockery>4'High Tract = Structural on Steep Slope OtherPART 14 SIGNATURE ( ' OF PROFESSIONAL • • 1 or a civil engineer under my supervision have visited the site. Actual ' site conditions as observed were incorporated into this worksheet and the attatchments. To the best of my knowledge the information provided here is accurate. _ 1/90 ' ' Page 2 of 2 King County Building and Land Development Division TECHNICAL INFORMATION REPORT (TIR) WORKSHEET DEVELOPMENTPARTS REFERENCE LIMITATIOWSITE CONSTRAINT ' Ch.4-DownstreamAnalysis No major construction limitations Q Wetland Protection No construction activity allowed within 25 feet; fenced. 0 a 0 Additional Sheets Attatched rosion a amen a ion on ro REQUIREMENTSPART 9 ESC ' MINIMUM ESC REQUIREMENTS MINIMUM ESC REQUIREMENTS DURING CONSTRUCTION FOLLOWING CONSTRUCTION [91 Sedimentation Facilities ® Stabilize Exposed Surface ® Stabilized Construction Entrance X7 Remove and Restore Temporary ESC Facilities Fx-1 Perimeter Runoff Control ® Clean and Remove All Silt and Debris ' ® Clearing and Grading Restrictions ® Ensure Operation of Permanent Facilities © Cover Practices ® Flag Limits of NGPES ® Construction Sequence Other Other PART t SURFACE WATER SYSTEM ' ED Grass Lined Channel = Tank 0 Infiltration Method of Analysis Pipe System Vault = Depression HYDRA and SCS ' 0 Open Channel Energy Dissapator O Flow Dispersal Compensation/Mitigation Dry Pond © Wetland Waiver of Eliminated Site Storage Wet Pond = Stream Regional Detention ' Brief Description of System Operation Gravity flow to we` vault Vault pumps fQr erreraenQy overflow. Facility Related Site Limitations Additional Sheets Attatched Reference Facility Limitation PART 12 EASEMENTS/TRACTS PART 11 STRUCTURAL ANALYSIS ' tructural review) = Drainage Easement ® Cast in Place Vault Other = Access Easement = Retaining Wall = Native Growth Protection Easement ' = Rockery>4'High Tract = Structural on Steep Slope Other ' PART 14. SIGNATURE OF • • I or a civil engineer under my supervision have visited the site. Actual site conditions as observed were incorporated into this worksheet and the ' matchments. To the best of my knowledge the information provided here is accurate. 1/90 i - - BLACK RIVER BASIN Basin Boundary r ~ Subcatchment Boundary q •4 0 1 g Collection Point —' � �, _ $'�''' - -� -�— Stream ooD6 Tributary Number 1 00301 Proposed Project r IIF It �1 g 1 July.1987 0301 30 ti k W ^ r - Ines :— — G �—.. IT ilF, 7- Mt lr r �: .. - 1 •14' n ��L•I 1 � j � 1�� 1 k,✓; 4'r I ,y rey Kam,-r^,i +,�; ! o e d Ot JL3 W jP 16/Z JUNUISanu/punoS yJe-JaIeM ue9/3 a Q Q � LTOT a,� uT1VlU.�O uo?s?n?p suo?}ea?unuzuzoa s,oz}aIN Xq pampw,I Jo spaau at ul t ouill aay� ,,,.�,,. •oJ aaxa?J 'uoputuao3ui ltodai pup luawd?nba lozluoa luia4sXS ®•o��dilt� at14.1041uout}uawaspupw pup lauuosiad aaueualu?euz 'szo}pzado sdlatl}ueld aul}e )laom1au aalnduioa pa}eaps?tldos d-1.zomlau iu nq"V au?lad?d al?tu-001 sl?}nogSnoatp lueld uo}ua?1 aril antas suopels 2u?dumd malinod '+�• auax SMAoui s�?uigj sdaml � ' = -Lua}sXs ia1ndtuo le}ueld aq}ilea lueld k • ;; 'zno}p alnpatlas olio uopeuuo3u?azouz zo3 ti UaUI pat x k (•/}?1?gout pa4nu?1 114?nt asotil } } Ia4em}oq pup}pall uneo sl?am ozd o}tua}sXs XJanoaa.z X2.taua}ua?a a n aze suoao3 algeltp UO U ❑u s �t duo ut a up sa to eaanas un��etu up sasn osle}ueld atiy uza}s�is s;Cuedtuoa spy }u I3 i q fl P it i �Ii uo}ua r a o u? ?sad?d Pup se ez u uo}�u? se plo sxeaX ZI}seal it,aq pinogs otl vt s.iol?s?n ti} } } P D i � N u M •aldoad 0£o}do 3o sdnoi2 ao3}uatu}tnodde o}}1 silas'sxa}sa2?p s,lueld atl}Xq paanpozd u Xq XepsmgjL-Xppsany alqupenu am sinoy r!!' set aueglatu aq4 sgnaas}upld agjL•uo?4sa2?p a$pnls 2uunp paanpoid set aueglatu aq} • r � sala�C J osle Weld luaulleaty uolua21 ally afoul aas Jo k 1Vlo 01 as M' nnalla ., 001 pap�aj i ameas ., slay AZJaUJ •}upld aul u?luauid?nba Xnuatl ow up n daa auuoszad uopeluaturu}su? p pup sue?au}aala'sa?uetiaauz's}s?u?tlaeut •salts 2u?la�faai o}Tani}Aq a�pnls 1ana1-�iatunof'uo?}?ppp u1 ssaaoad}uatuleaz} r • + aril sd?tis uati}oa}aA•aumlon s}?aanpai w = at1}�uunp aileuz pinotis sneaza suo?lezado 'f,s 't y o}a2pnls at1}uzot;as}pat anoutaa sassazd}lag 11 }eql s}uau4sn[pe Aue }uap?s zagutatu of gu?x 3, } pallea saunlautu le?aads'ssaao zd uopsaS?p aril 33e}s dlatl gu?ldutus sail 3o sllnsa21•ssaaoid s _ _ _ _ _ �uimollo3'ie?Ja}ew a?uu2jo aul asodwoaap }uaut}eazl aril 3o sa2els luaanas 2u?anp a2pnls 65,4 situotiouS! °, ' �;,: of e?zalapq a?goaaeue asn q:)1q t'sza}sa2?p se b y uneotnl s�1ue}a}aaauoa ul paleaq s?l?'pala�Dar �u�Td �uaLu��a�,L puu zalen�3o saldtuesup1e} }ueld}uauzleatl :f` ;4 aril t1$norti}�iauzno[sl?sailetu}?su zalpnta}sunt si aSpnls aril aao3ag slaa[ozd ti}sato3 pup a saz�uue els p a a}p}sal suaa? 1i u11oN 3'a t. 'm ' �u?deaspuel'uopptuplaaa 1ios u?l?Su?la�faat uojuall aqJ 01 ul i 33 a i uy u a l� i .. �� pup pa}sal aap 33e}s qe1 luS?a pup aaueuaimeut i {i 'G ;� aainosaa u se-ssaaotd to}e�vta}sung at1}30 Iu %,, �` an ?sat ?os?utas a a� n s s pawl oila 0£ suopwado 0S,aq L �iep e sznoti 1,Z n � p P i ul- p i l Ili y O sl;nis BuJu}oi uo A}?1?au3 uoluag ati}u?e}u?eui Jy� pup a}ezado szagtuatu 33e}s pau?ezy Eat aJIA�aS • uoluaN a Mn3 ` A LaSpnis au} of uo ��ado .�no�-�Z �d suadduu 1ruM r, r � ; sophisticated computer system allows south and east Kin County.The plant will operators to regulate and control this treat 72 million gallons of sewage per day impressive array of pumping stations,tanks through the mid-1990s.A proposed and machinery. enlargement project will allow the plant to The 88-acre site takes in water from 14 handle up to 108 million gallons per day. a _ Metro pumping stations on the east and south This$150 million project,scheduled for sides of Lake Washington-an area covering completion in 1996,will allow the Renton 140 square miles.Using a system of gravityIM plant to treat the increased flows caused by z .�' and pumping,the water flows through 100 rapid population growth.Beginning in 1992, miles of pipeline.From the plant Metro the plant also will receive northeast King pumps the treated water through a 12-mile County sewage diverted from the West Point pipeline into Puget Sound.The water is Treatment Plant. discharged two miles offshore in 580 feet of The original Renton Treatment Plant design water through an award-winning outfall and called for enlargement in phases to handle flows into the 21st diffuser system. growing regional sewage o century.This third enlargement,however,is • needed earlier than expected.The expansion • Keeping pace with project is the result of a Metro population and Reflecting the image of a caring community growing needs flow study that revealed sewage flows are expected to exceed original projections made in 1982.The enlarged facilities are designed to Water. We're made of it. We drink it. We play in it. It reflects our The Renton plant has been expanding to fit within existing plant boundaries. keep pace with rapid population growth in image. That's why concerned citizens in Seattle and King County formed the Municipality of Metropolitan Seattle in 1958. Metro's initial mission was to clean up pollution in Lake Washington and Puget Sound. Metro's initial mission was to clean up 1965,Lake Washington's transparency hit a pollution in Lake Washington and Puget low of 21/2 feet of visibility.By 1977,lake _ Sound. transparency had cleared to 24 feet-better The main cause of this pollution: than it had been in the 1930s. inadequate sewage treatment by many small cities and sewer districts that discharged Renton: recognized wastewater into both water bodies.Nutrients in the wastewater caused algae growth in ` � r Lake Washington that clouded the water and for excellence produced a foul-smelling odor.As population growth pushed some treatment plants beyond The plant is an award-winning example of their capacities,sewage overflows occurred wastewater treatment engineering.Renton and beach closures followed.In Puget Sound, received the Washington State Department of untreated sewage discharged in shallow water Ecology's 1989 Excellence Award and the U.S. made bathing beaches unsafe for swimming. Environmental Protection Agency's 1989 Metro developed a 20-year water-quality National Award for Outstanding Treatment , plan to close small older plants and replace Plant Operation and Maintenance. them with four new facilities,including the The plant brings together state-of-the-art '` Renton plant.The success of this effort was biological,physical,chemical and mechanical clear; Before the Renton facility opened in elements.From one small room,a Renton Treatment Plant How sewage treatment works Renton is a secondary treatment plant,which Finally, the water flows into large tanks that bubble air through the water, means that sewage coming into the plant sedimentation tanks where solids settle to the stimulating the growth of bacteria that consume undergoes two phases of treatment—primary and bottom, forming sludge. Machines skim off any the waste. Secondary sedimentation tanks then secondary. The entire process takes about 12 hours. material left floating on the surface. remove the bacteria and organisms from the The primary process is a series of mechanical At this point, primary treatment is complete wastewater. The final step is disinfecting the steps. and the water is ready for secondary treatment. treated water with chlorine. The water, now 95 First, as the wastewater enters the plant it The goal of secondary treatment is to eliminate percent clean of all pollutants, is ready for its passes through bar screens to catch objects such any remaining waste material before the treated 12-mile pipeline journey to Puget Sound. Metro as rags, sticks and other debris. water is sent into Puget Sound. This waste discharges the treated water through a Next, the water flows through a grit chamber, consumes oxygen that fish and other aquatic life 580-foot-deep pipe—known as an outfall—that allowing sand and gravel to settle to the bottom need for survival. lies about two miles off Alki head in West Seattle. and be removed. Secondary treatment begins in giant aeration The outfall is the deepest in the world. primary secondary bar grit sedimentation aeration sedimentation removal tanks tanks tanks To Puget Wastewater screen Sound enters here P ° 0 influent disinfection effluent PUMP �� PUMP sludge sludge thickening sludge _ Sludge digester �_ management program OP sludge sludge truck dewatering