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HomeMy WebLinkAboutSWP272094(4) i i I W, �Y i 4 f C BROWN AND CALDWELL CONSULTING ENGINEERS 1 1 1 1 1 1 i Drainage Report 1 Metro Treatment Plant at Renton Enlargement III August 15, 1991 1 i 1 i i 1 1 i 1 1 ' INTRODUCTION � ' The Municipality of Metropolitan Seattle (Metro) is enlarging ' its regional wastewater treatment plant at Renton (MTP) 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 secondary treatment facilities at Renton will be retained and new facilities will be added to provide increased treatment capacity and other process improvements to alleviate overflows and plant surcharging. The plant can now provide secondary treatment for 72 million gallons of sewage a day (mgd) . The expanded plant will have the capacity to treat about 108 mgd. Plant expansion from 72 to 108 mgd will be referred to in this document as Enlargement III. Phase A of Enlargement III entails site preparation and perimeter landscaping. ' The Phase A expansion will entail additional paved areas for access roads, parking, and a maintenance trail. Other large ' impermeable areas constructed in Enlargement III will include several open tanks and structures that will drain runoff to the plant sanitary drain system. The sanitary drain system is routed ' through the plant as sewage and is ultimately pumped directly to Puget Sound through a 108-inch diameter force main; the effluent transfer system (ETS) . Because rainwater falling in tanks and on process structures is routed through the plant, the net ' stormwater runoff as a result of Enlargement III will actually decrease. Rain falling on plant grounds and draining to surface waters will be subject to catchments, berms, wetlands, and a ' wetvault, as described at length in this document. This document was prepared to respond to the drainage report content list. This document describes aspects of the existing and proposed stormwater drain system, compliance with applicable core requirements, special requirements, and design criteria of the King County Surface Water Design Manual (SWM Manual) , an ' initial design of a wetvault for water quality control, and variances required. ' PROJECT DESCRIPTION ' Site preparation for the Renton MTP will entail excavating approximately 180, 000 cubic yards of native soil and rock and August 15,1991/t1h Page 2 ' placement of approximately 30, 000 cubic yards of--engineered fill. Excavated material will be stockpiled on-site for use in the ' perimeter landscaping. Excess material will be distributed on- site and graded to drain to the existing storm drain system. The first construction phase (Phase A, Enlargement III) will involve installation of concrete-drilled shafts (space piles) , stone ' columns, a site dewatering system, and approximately 840-feet of 48-inch diameter reinforced concrete pipe. t Perimeter landscaping will involve construction of berms and fences, about 5, 500 lineal feet of impervious maintenance trail, an irrigation system, and extensive tree and shrubbery planting. The perimeter landscaping will use approximately 120, 000 cubic ' yards of material, excavated from the secondary sedimentation area, for construction of the berms. Interior landscaping 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. ' CORE REQUIREMENT 1: DISCHARGE AT THE NATURAL LOCATION Existing System Most of the stormwater collected and concentrated on the ' Renton MTP site drains to the Green River via an on-site stormwater sewer system and a 120-inch outfall diffuser. The wetland collects and stores runoff from 8 . 2 acres of pervious area at the northern site periphery (north of the northern access road) . A retention swale along Longacres Drive collects and stores runoff from the southwest boundary of the site. Runoff from the swale, which accumulates to a depth of 18 inches, drains eastward to the P-1 channel. The narrow areas between the eastern property line and the east access road drain directly to the P-1 channel. Stormwater collected in open vessels and on process buildings drain into the plant process stream for treatment and ultimate transfer to Puget Sound through the ETS. Likewise, runoff from the solids handling facilities and septage unloading areas drains to the plant's sanitary sewer system for ' treatment and ETS disposal. Proposed System ' The existing conveyance system will be slightly modified to collect runoff from the new parking areas and access roads. The existing stormwater sewer system will be augmented with a wetvault immediately upstream of the Green River outfall manhole. The wetvault will contain two sets of pumps to discharge stormwater flows to the Green River, directly to the ETS, or to ' the plant's influent structure for treatment and disposal as sewage. rA A wi m t is,iv9i/c ��. 1 Page 3 A smaller set of pumps, each capable of pumping about one cubic foot per second (cfs) , is designed to pump normal ' dewatering flows; not storm flows. (Dewatering, in this instance, refers to lowering the groundwater table. This is done to keep below-grade concrete tanks, when empty, from floating and ' cracking. ) The wetvault will fill during heavy storms when flow exceeds the capacity of the smaller pumps. The larger pumps, each with a capacity of about 35 cfs, will handle storms and any abnormal flows. If stormwater is to be pumped to the Green ' River, the large pumps will guarantee adequate stormwater discharge for a 100-year flood. In an emergency, for instance if the ETS capacity is exceeded, 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 exercise this option. The ETS system has never exceeded its design capacity, despite recent storms that have surpassed the 100-year hydrograph. CORE REQUIREMENT 2 : OFF-SITE ANALYSIS Upstream Drainage Areas ' The King County Reconnaissance Program has placed the Renton MTP site within the Black River watershed. A vestige of the Black River, the P-1 channel, is indeed located within the confines of the treatment plant. However, except for rainwater falling on or near the banks of the P-1 channel, all site drainage flows either to the stormwater system or the sanitary system. The current stormwater system is routed to the Green River, as described above. The sanitary system is ultimately pumped to Puget Sound. The treatment plant and stormwater outfall are located just upstream of the confluence of the Green ' and Black rivers. 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. 7 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 (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. Problems in the lower Green River, both existing and anticipated, nug�t u,1991/un ] Page 4 1 are clearly development-related. Severe erosion along the basin's steep slopes and valley walls (Grandview Park, Kent ' Highlands Landfill) causes 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. Water quality problems in the Black River basin are described in detail in the King County Basin Reconnaissance Program ' Summary. A map from that document, identifying particularly troublesome areas in the basin, accompanies this report. The remainder of the Reconnaissance Summary is incorporated here by ' reference. A vestige of the Black River intersects the Green River at River Mile 11 and forms the Duwamish River. The Black River used ' 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 I s referred to as both Springbrook Creek and the P-1 Channel. Drainage is impounded in the P-1 pond and pumped into the Black River channel before discharge to 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 county 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 Renton MTP) 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. August 15,1991/tlh ' Page 5 Downstream Drainage Areas z 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 Renton MTP discharges at RM ' 12 . 2 . The lower Green River sites have relatively moderate turbidities and high suspended solids. Water quality in the P-1 Channel generally appears turbid at the point of discharge to the Black River. The Black River, both upstream and downstream of the Renton MTP, is listed among the most degraded streams in the Metro sampling area. ' According to the King County Sensitive Area Map Folios, the treatment site is not in the 100 year flood plain. On-site drainage: The existing on-site drainage system has a capacity of 72 cubic feet per second (cfs) . Full buildout (ultimate ' development) for the Renton MTP under Enlargement III will have a total of 25. 1 acres of impervious surface. The existing impervious area is approximately 23 .9 acres. For site ' preparation and perimeter landscaping impervious area will increase by 1. 31 acres. However, only 0. 4 acres of new impervious area will drain to the stormwater system. The ' remaining impervious areas will drain to the plant' s sanitary system. The areas that will contribute runoff are extensions of existing roadways and parking areas. 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, if even perceptibly, 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 estimated stormwater runoff during a 25-year storm lasting 20 minutes and producing 1. 35 inches of rainfall is 56 . 0 cfs. This estimate is based on the ultimate (buildout) site configuration and is less than the capacity of the existing system. The proposed stormwater system will include a pumping station to guarantee its ability to discharge adequately under 100 year flood conditions. Off-site Drainage ' No stormwater originating off-site drains through the Renton MTP site. All stormwater originating on-site drains to either ' August 15,1991/dh �A � .s ' Page 6 ' the Green River or the_P-1 Channel. Rain falliryg,__on the Renton MTP site therefore does not affect other sites. ' CORE REQUIREMENT 3 : RUNOFF CONTROL ' According to the King County Surface Water Design Manual (SWM Manual) Section 1. 2 . 3 , Core Requirement 3 , all proposed projects t must provide peak rate runoff control, through detention, retention, or infiltration, except under any one of the following situations: * The project includes less than 5, 000 square feet of additional impervious surface, or ' * Stormwater modeling indicates that the proposed project will not increase the 100-year, 24-hour storm peak rate runoff (100-year runoff, or 100-year storm) more than 0 . 5 cfs above ' the calculated runoff for existing runoff conditions, or * 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. Preliminary analyses indicate that the Renton MTP Enlargement III does not meet the first or third exemption criteria. Phase A of Enlargement III will construct over 5, 000 square feet of additional impervious area. Much of this area is a maintenance t trail located just within the site's property line. Also, stormwater from the plant currently discharges into the Green River upstream of River Mile 6, at River Mile 12 . A more rigorous analysis was required to determine compliance with the second exemption criterion. The existing and proposed ' site systems were modeled to determine if the proposed site will increase the peak flow from a 100-year storm by more than 0 . 5 cfs. Modeling results indicate that the peak rate runoff for the 100-year storm would decrease due to the proposed construction: 22 . 99 cfs before development as opposed to 22 . 61 cfs after ' development. The remainder of this section describes the process used to calculate the peak storm flows for the pre- and post- developed site. ' Existing and Proposed Stormwater System Modeling Figures 1 and 2 are schematic diagrams of the existing and ' proposed stormwater drain systems for the Renton MTP. The plans show location, diameter, invert, and node ID used in the computer August 15,1991/t1h ' Page 7 ' 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 106 for the proposed system. ' Water from sludge trucks and the loading area, water from the septage disposal area, and water from chemical storage areas (such as the sodium hydroxide storage tank) is directed into the ' sanitary drain system. The sanitary drains flow into the treatment plant for processing before being discharged into Elliot Bay via the effluent transfer system. ' The proposed stormwater drain system is nearly identical to the existing system. The proposed system will reposition a few catch basins and inlets; due mostly to new landscaping and grading and the realignment of access roads and parking lots. Most of the changes are occurring near the Administration Building. The new grades of the proposed plan will redirect some of the flows to new inlets, thus changing the site hydrology. Areas not served by the stormwater sewer system include the wetlands, the eastern perimeter of the site, and the southwest ' corner of the site. The wetlands accept runoff from the area north of the northern access road (north of the solids handling facilities) . 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. Stormwater from these areas was not included in the modeling effort. Figures 1 and 2 also show the subcatchments that were input into the hydrograph 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 area around the dechlorination building; the secondary control ' facility; the influent pump building; and the area between secondary clarifiers 3-4 and 5-6. According to available plans . August 15,1991/tlh ' Page 8 ' it appears that the roQfs of the sludge dewatering facility, the grit building, the influent pumping building and the administration building drain to the plant's sanitary system. The area around secondary clarifiers 3 , 4, 5 and 6 drain to the chlorine contact channel. Peak Storm Hvdrograph and Flow Modeling: Stormwater modeling involved the following tasks: * Mathematically define the stormwater conveyance system, e.g. , pipe diameter, length, upstream and downstream ' inverts (inverts are bottom elevations, usually expressed in feet above mean sea level) and rim elevations. * Delineate catchbasins 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 catchbasin. * 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. ' Design Storm: The 24-hour design storm hyetograph found in Figure 3 . 5. 1A of the SWM Manual (SCS Type lA Distribution) was used in this analysis. The unit hyetograph was multiplied by the total 100-year, 24-hour precipitation for the Renton MTP site, (3 . 9 inches according to Figure 3 . 5. 1H of the SWM Manual) to produce the design storm hyetograph. Adjustments for snowmelt ' were not required because the site elevation is below 1, 000 feet. The design storm hyetograph was input to the model using 10- minute intervals. ' Models: 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 Santa Barbara Unit Hydrograph method, combined with the Soil Conservation Service curve numbers, to generate runoff hydrographs. HYDRA4 routes the stormwater inflow hydrographs ' through the stormwater drain system. Inputs required to generate runoff hydrographs include: * 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 August 15,1991/dh ' Page 9 ' * The longest mute surface water must £].ow to reach the outlet for the land segment. ' Tables 3 and 4 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 the SWM Manual hydrologic group C. The western landscaped areas may be partly Beausite soils, although ' much of that is also imported topsoil. The wetland area will fall under the Puyallup soil group, which is classified as hydrologic group B but was modeled as soil group C. Curve numbers used in the model were obtained from the HYDRA4 manual: * CN for impervious areas = 98� * CN for open spaces in good condition (grass cover on 75% or more of the area) = 74 * CN for open spaces in fair condition (grass cover on 50 to 750 of the area) = 79 The CN numbers for open fields used in this modeling are ' slightly less in value than CN values in the SWM Manual, and will result in slightly lower storm peak flow rates. However, for determining compliance with the 0 . 5 cfs net increase criterion, HYDRA4 CN values should produce conservative results because of the additional impervious area to be constructed in Enlargement III. An example of open spaces in good condition is the open field northwest 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. 1 K values were used to calculate the time of concentration. K values for subbasins were calculated by taking a weighted average based on contributing area. K values used in the modeling were as follows: * K for short pasture and lawn = 7 ,b * K for nearly bare ground = 1,0 13 ' * K for paved areas = r -) The peak flow rate through //the 120-inch outfall diffuser to the Green River was used to compare before and after development. Flow through the outfall was assumed to be unhindered by the Green River surface elevation. 6,1V f Tioe C l� Zw,fic,r�� -vI/ 5-Li vvv August 15,1991/tlhct rrL� 1 Page 10 1 Model Inputs: Tables 1 and 2 are the database files used as inputs to the HYDRA4 model for the pre- and post-development 1 stormwater systems. The database files include information pertinent to the conveyance systems: * Downstream Node ID 1 Downstream Invert Elevation * Downstream Rim Elevation * Pipe Segment Length 1 * 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 1o01 is the outfall junction manhole; nodes between 1001 and 1040 are located along the southern half of the 1 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 3 and 4 . 1 Model 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. Modeling demonstrated that the calculated peak 1 runoff for the 100-year storm after development was less than before development: 22 .99 cfs before development versus 22 . 61 cfs after development; a difference of -0. 38 cfs. Flow hydrographs 1 at the outfall manhole are presented in Figure 3 . These results, upon examination, appear wh justifiable. Construction of the open vessels and the DAF s (which will drain to the sanitary sewer system) will remove about four acres of pervious area that is tributary to the stormwater sewer system. Most of the new impervious area is a maintenance trail that 1 meanders along the perimeter of the site. About one third of the trail passes through areas that either drain directly to the wetlands or to the P-1 Channel. At other locations, the trail is 1 separated from impervious areas that drain directly to the stormwater sewer, and thus runoff from the trail must flow over impervious areas to reach a stormwater inlet. Without the maintenance trail, impervious surfaces directly connected to the 1 stormwater sewer system will only increase by about 9 , 000 square feet, or 0. 26 acres. Most of this increase will be the new access road to the DAFT complex and the parking lot near the 1 electrical substation. August 15,1991/eh 1 ' Page 11 Tables 5 and 6 present the flow quantities and velocities through each stormwater pipe segment for the 106-year 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 ' this design storm. 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. Exemption Eligibility Stormwater modeling indicates that the proposed project will not increase the 100-year, 24-hour storm peak rate runoff more than 0. 5 cfs above the present conditions. In fact, the peak runoff should decrease. Furthermore the Renton MTP site is not in a Critical Drainage Area as defined by the SWM Manual. Thus, the proposed project is exempt from Core Requirement #3 of the SWM Manual and no peak rate runoff control measures are necessary. CORE REQUIREMENT 4 : CONVEYANCE SYSTEM All proposed projects must show that a conveyance system exists, or will be constructed, to adequately convey runoff for a 100-year storm. This compliance condition includes runoff originates on the project site plus any that will be conveyed ' through the site. Surcharging is acceptable for demonstrating the adequacy of the conveyance system, provided that all runoff is contained within the conveyance system and does not inundate ' roadways. The Renton MTP conveyance system was analyzed using the ' procedure described in "Core Requirement 3 : Runoff Control. " HYDRA4 , a sewer analysis program available on Brown and Caldwell's GIS package, was used to calculate conveyance system performance under varying rainfall patterns. HYDRA4 uses the ' Santa Barbara Unit Hydrograph method combined with the Soil Conservation Service curve numbers to generate runoff hydrographs. HYDRA4 simulates the stormwater inflow hydrographs ' through the mathematically defined stormwater system. Modeling results indicate that the existing and proposed conveyance system is adequate to convey the 100-year storm. The results of the modeling effort are presented in Tables 5 and 6. These tables report the flows and velocities through each stormwater pipe segment for the 100-year storm for pre- and post- development. The tables show that flow between the northern and southern 30-inch drain lines is equally split. Only one pipe August 15,1991/tih t/ 1 Page 12 ' segment, the 30-inch pipe at node 1004, was surcharged during the storm simulation. Peak flow at Node 1004 was a5out 102% of ' capacity for both pre- and post-development conditions. The system was adequate for containing all stormwater under all conditions tested. Stormwater did not overflow any manhole covers. CORE REQUIREMENT 5: EROSION/SEDIMENTATION CONTROL PLAN ' All engineering plans, for projects that propose to construct new or modify existing drainage facilities, shall include an erosion and sedimentation control plan (ESP) to prevent sediment- laden runoff from leaving the site during construction. ' This project complies with all requirements in Section 1. 2 . 5 of the SWM Manual. A temporary erosion and sedimentation control plan (TESCP) was prepared for Enlargement III. The TESCP was published as Addendum One of the contract drawings and specifications. The TESCP was submitted to the City of Renton July 11, 1991, certified by the City of Renton, and submitted to the Hearing Examiner on July 16, 1991. Subsequently, the TESCP was revised in response to City of Renton review comments. These revisions are currently being incorporated into the contract drawings. tSPECIAL REQUIREMENT 5: SPECIAL WATER QUALITY CONTROL ' In addition to the Core Requirements, the proposed project must also comply with twelve Special Requirements. Each special requirement identifies threshold criteria which projects must meet to gain approval. Based on the threshold criteria, the Renton MTP Enlargement ' III is exempt from all Special Requirements except Special Requirement #5: Special Water Quality Control. Because the proposed project will add more than one acre of impervious ' surface subject to vehicular use, a wetpond, wetvault, or water quality swale is required. ' Wetpond vs. Wetvault Although the SWM Manual recommends wetponds wh never feasible, site constraints, best engineering pract ce, and ' efficient operation indicate a wetvault to be the best water quality control method for the Renton MTP. A wetvault will easily meet or surpass the water quality control objectives of ' the SWM Manual. Furthermore, a wetvault will fit within the site constraints of the Renton treatment plant, require less energy August 15,1991/tlh ' Page 13 J ' for pumping, and eliminate critical failure mod%x from further consideration. Either a wetpond or wetvault will require about 11, 000 square feet of water surface area. However, with the additional area required to build berms for separate pond cells, adequate side slopes and outfall structures, a wetpond will occupy a much larger area. Such a facility would be difficult to locate on- site because of the extensive landscaping proposed for this project. The landscaping has been designed to screen industrial structures from view, improve plant grounds apparent to passersby, and maintain open areas on the interior grounds for ' future wastewater process expansions. A pumping station will be required to lift stormwater from the junction manhole to the wetpond. The confluence of all storm drains in the junction manhole is about 25 feet below grade. Pumps serving a wetpond must be sized to handle the peak, as Opposed to the average, storm flow. Pump failure would be catastrophic, not only for wetpond operation but also for the plant structures drained by the stormwater system. A pumping station of adequate size and redundancy would be a complex and ' costly facility to construct and maintain in addition to the wetpond. The wetpond would rely completely on the pumping station to receive flow and provide treatment. ' A wetvault avoids the site constraints and potential pumping problems inherent in a wetpond for this site. A wetvault can be constructed below grade at the manhole's storm drain invert ' elevation. At this elevation (101 feet) , the wetvault can operate by gravity during most storms. Only during flood stage in the Green River will pumping be necessary to discharge ' stormwater from the wetvault. This design is not only more energy-efficient, but is inherently less likely to fail or require maintenance. The pumps could be sized for less than the ' peak stormwater flows because of the storage capacity of wetvault. The wetvault will be designed with pumps and piping to allow discharge to either the wastewater treatment plant, The ETS, or the Green River. ' Wetvault Sizing ' The size of the wetpond or wetvault is determined as follows: * The 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 volume shall be at a minimum the total runoff volume ' from the proposed tributary sub-basin from one-third of the two-year, 24-hour storm. August 15,1991/tlh ' Page 14 ' Surface Area: The plant's ultimate buildout -ander Enlargement III will result in 25. 1 acres of -impervious surfaces, 40.2 acres of grass and landscaped area, 8.2 acres of wetland, and 11. 0 acres of tanks that do not contribute to the stormwater system. Thus, the surface area of the wetvault must be a minimum 0. 251 acres, or 11, 000 square feet. Volume: Volume requirements of the wetvault were calculated based on Chapter 3 of the SWM Manual. Table 3 . 5. 2B was used to ' determine SCS curve numbers. The curve number for the pervious surfaces surrounding the existing facilities and the western landscaped areas is assumed to be 90. This is the CN value for open spaces in fair condition under soil classification C. The CN value for the wetland areas, assumed to be Hydrologic Group B, and open space in good condition, is 80. The curve number for impervious areas is 98. ' Based on the formulas from Chapter 3 of the SWM Manual and a 2-year, 24-hour precipitation of 0. 67 inches for the Renton site, t the impervious area should produce a total runoff depth of 0. 475 inches. of this, 0. 129 inches is from the landscaped areas and . 0108 inches is from the wetland area. Multiplying the surface area by the runoff depth and converting to cubic feet, the total ' runoff volume would be 62 , 375 cubic feet (467, 000 gallons) . With a surface area of 11, 000 square feet, the wetvault must have an active average depth of approximately six feet. ' Wetvault Desian The Wetvault was designed in accordance with Section 4 . 6.2 ' (Wetponds and Wetvaults) and Section 4 . 4 . 6 (Vaults) of the SWM Manual. Figure 4 is a schematic of the wetvault which illustrates its hydraulic pathways. Figures 5 through 9 are ' design development plans and sections of the Stormwater Control Wetvault proposed for this project. ' Design Criteria: Sections 4 . 6 . 2 and 4 .4 . 6 of the SWM Manual describe all the criteria that must be met in the design of a wetvault. Several criteria of special importance are given below: ' * Depth of permanent pool shall be 3 to 6 feet plus one foot of dead storage for sediment. ' * The length to 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 cell about 45% of the design surface area. ' August 15,1991/t1h Page 15 ' * Flows above the- 2-year, 24-hour peak storm flow must bypass 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. 1 ' Criteria Compliance: The wetvault was designed as two parallel tanks to allow one half of the structure to be taken off-line for maintenance and cleaning. Each tank has two passes: ' 137 . 5 feet long and 20 feet wide. This produces a length to width ratio of 13 . 75 : 1 which is far greater than the minimum ratio of 3 : 1 required by the SWM Manual. The total surface area of the tanks is 11, 000 square feet as required by Special ' Requirement #5. Chamber baffles with orifices are located at 10% of the total volume and 50% of the tank volume to divide the tanks into three cells as required by the SWM Manual. Two scum baffles with bottom invert elevations of 108. 0 feet are located in each tank at the middle and end of the second pass. The inlet and outlet of the tanks were designed to maximize travel time through the facility. Water enters the tanks through ' two 30-inch square inlet openings at invert elevation 109 . 0 and exits the tanks through V-notch weirs at an invert elevation of 112 . 0. The inlet openings will maintain a minimum water surface elevation at 109 . 0 feet. With the tank bottom at elevation ' 105. 0, this provides one foot of dead storage for sediment and three feet of permanent pool as required by the SWM Manual. An overflow weir (invert elevation 113 . 5) , located between the first flush chamber and the stormwater discharge chamber, creates a bypass for peak stormwater flows. This bypass inhibits ' peak flows from flushing accumulated sediments from the wetvault. Square bypass sluice gates are located between the first flush chamber and the discharge chamber. These 48-inch sluice gates, which have an invert elevation of 105. 0 feet, will bypass flows directly to the discharge chamber during cleaning and maintenance. These sluice gates effectively take the wetvault "off-line. " ' The overflow weir fully complies with the requirement to bypass flows greater than the 2-year, 24-hour storm peak flow. The sluice gates comply with the requirement that the wetvault be capable of isolation. High capacity pumps, sized to handle 35 cfs each, will discharge tank overflows to the treatment plant, the ETS, or the Green River. August 15,1991/uh ' Page 16 ' 24-inch drain sluice gates (invert elevatiorL-:103 . 0) are located between the tanks and the first flush chamber. These ' gates allow the contents of the tanks to drain to the first flush chambers. Low capacity pumps located in the first flush chamber capable of pumping 1. 5 mgd each will drain the 500, 000 gallon content of the tanks in four hours. Thus, this design complies with the requirement to drain the wetvault within four hours. A wetvault equipment access room will be constructed above ' the stormwater vault. This room will be about 50 feet long, 24 feet wide and 12 feet high and have a floor elevation of 116. 0. The room will house the sluice gate operators and access hatches for pump removal. Eight 36-inch watertight manholes provide access to each wetvault chamber. Thus, 12 access points are provided to the active vault area. The manholes for access will be provided with standard Metro access capability. A control ' platform will be located along the northwest wall. Entrance to the equipment access room from the surface is gained through two stairwells. A 5- by 6-foot hatch will be located in the new road off Monster Road. Access to the stairwells will be on either side of the new road. Construction of the wetvault structure will consist of secant piles for excavation sheet piling and concrete pilings for the structural foundation. All walls, floors and ceilings will be cast-in-place concrete with waterstops at all construction joints. The design of the wetvault structures complies with all the requirements of Section 4 . 4 . 6 except for the maximum 20 foot ' depth to the vault invert. The wetvault's invert must be located at such a low elevation to allow the stormwater sewer system to drain by gravity to the wetvault. A variance will be required ' from this design criterion. VARIANCE REQUIREMENTS ' The proposed stormwater plan as designed with a water quality ' wetvault complies with all the Core Requirements, Special Requirements and design criteria of the SWM Manual except for the following: t * Discharge at the Natural Location: Core Requirement 01, Section 1. 2 . 1 ' * Biofiltration Requirement: Core Requirement #3 , Section 1. 2 . 3 ' * Use of Pumps: Core Requirement #4 , Section 1. 2 . 4 v lc C1�1 August 15,1991/t1h Page 17 ' * Wetpond Requirement for Water Quality CqA rol: special Requirement 15, Section 1. 3.5 * Minimum Access Requirements for Vaults: Section 4.4. 6 Variances will be required for each of these requirements and ' criteria. Variances, as discussed in Section 1. 4 of the SWM Manual, may be granted based on a demonstration that such variances are in the public interest and that the objectives of ' safety, function, appearance, environmental protection and maintainability, based upon sound engineering judgement, are fully met. ' These variances involve two site-specific constraints, namely: ' * The deep invert elevation of the storm drains at the junction manhole and ' * The lack of available surface area. Because of these site constraints, a wetvault is considered the best way to provide water quality control. Pumping facilities will be necessary to discharge stormwater to the treatment plant or the Green River. These pumps will also serve to protect the treatment plant from flooding during heavy storms. ' Discharge at the Natural Location: A variance from this requirement is necessary because some stormwater will be diverted away from its natural discharge and into the treatment plant. This diversion will improve water quality. All water entering the plant's existing stormwater sewer ' system eventually drains to the Green River through a 120-inch outfall diffuser. The proposed system will construct a wetvault below grade at invert elevation 103 . 0. The wetvault will be ' fitted with two sets of pumps. Low capacity pumps (1. 0 cfs) located in the wetvault are designed to handle groundwater dewatering flows discharged to the stormwater system. During storm flows, these pumps will lift mixed runoff and dewatering ' flows to the plant, thus diverting this flow from the Green River. The second set of pumps will drain the stormwater system to the Green River during periods of heavy rainfall. This will be necessary for two reasons. First, at flood stage, the water surface in the Green River is higher than the Renton MTP ' stormwater manhole invert. Second, if stormwater is allowed to accumulate on-site, it could jeopardize treatment processes and structures. These larger pumps (35 cfs) may also be used to pump ' stormwater into the treatment plant if the stormwater does not satisfy water quality standards for the Green River. Thus, the ' August 15,1991/tlh 1 ' Page 18 ' high-capacity pumps may divert natural discharge;from the Green River. ' Diversion of stormwater from the Green River is the preferred method of discharge according to the State DOE and the City of Renton. The State DOE has stated that stormwater can be ' discharged to the Green River as long as the water quality standards of the Green River are not violated. ' On-Site Biofiltration Reouirement: A variance from this requirement is necessary because the proposed project will produce runoff from over 5, 000 square feet of impervious surfaces subject to vehicular use and chemical storage. Problems associated with constructing a biofiltration facility on the Renton site are similar in scope to the problems ' associated with constructing a wetpond. Biofiltration facilities must be located at ground elevation. With the area requirements for treatment, check dams, adequate side slopes, freeboard and outfall structures, a biofiltration facility will occupy a large area. Such a facility would be difficult to locate on-site because of the extensive landscaping proposed for this project to screen the site and the need to maintain open areas for future ' wastewater expansions. A pump station would be required to pump stormwater from the junction manhole to the surface-located biofiltration facility. The outfall manhole, which is the confluence of all stormwater drains, is about 25 feet below grade. Pumps serving a wetpond would need to be sized to handle the peak storm flow. This would ' be a large facility to construct and maintain in addition to the biofiltration facility. Also, the biofiltration facility would totally rely on the pumping station to receive flow and thus ' provide treatment. The reliability of a wetvault system will be much greater than a wetpond since the wetvault will continue to provide treatment during power outages. ' The purpose of biofiltration facilities is to improve stormwater quality using vegetated channels or land strips i.e. , "land application techniques. " The quality of stormwater which flows through the wetvault, a water quality control method, and through the wastewater treatment plant, should provide a similar if not superior level of treatment than biofiltration. An ' additional degree of reliability is provided by the State DOE NPDES permit with which the plant must comply. Biofiltration systems are not subject to such stringent standards. Use of Pumps: According to Section 1. 2.4 of the SWM Manual, a variance is required because the proposed project will use pumps in the stormwater drainage system. Pumps are required to ' raise stormwater from the deep invert elevation of the stormwater junction manhole to either the treatment plant or the Green ' August 15,1991/tlh ' Page 19 ' River. The wet vault X ll contain two sets of pimps: one set of low capacity pumps and one set of high capacity pumps. The low ' capacity pumps will discharge dewatering flows to the treatment plant for treatment. The high capacity pumps are required to drain the stormwater collection system under flood river stage to avoid flooding treatment plant structures. ' The pumps will be designed in accordance with the criteria described in the SWM Manual, and be maintained by Metro staff, who are well experienced in pump station operation and maintenance. The pumps, though not necessary for the operation ' of the wetvault, provide Metro with several options for discharge in case of stormwater contamination, flooding in the Green River, or capacity restrictions in the treatment plant. ' Wetpond Requirement: Special Requirement 5 in the SWM Manual mandates a wetpond because the proposed project will result in more than one acre of impervious surface that will be subject to vehicular use or chemical storage, and runoff from the project will discharge into the Green River, a Type 1 stream. However, the requirement allows for a wetvault or water quality swale to be used if a wetpond is not feasible. Because a wetpond would be an impractical solution to providing water quality control for this project, a variance is requested. ' A wetvault is the best water quality control method for the proposed project. While meeting the water quality control objectives of the SWM Manual, it better fits the site constraints ' of the Renton treatment plant. Both a wetpond or wetvault will require significant water ' surface area, about 11,000 square feet. However, with the additional area required to provide berms to separate pond cells, adequate side slopes and outfall structures, a wetpond will ' occupy a significantly large area of ground. Such a facility would be difficult to locate on-site because of the extensive landscaping proposed for this project to screen the site and the need to maintain open areas for future wastewater expansions. tAlso, a pump station would be required to pump stormwater from the junction manhole to the surface-located wetpond. The ' outfall junction manhole which is the confluence of all stormwater drains is about 25 feet below ground. A wetpond on the surface would require construction of a pumping station to discharge stormwater to the wet pond. Pumps serving the wetpond ' must be sized to handle the peak storm flow. This would be a significantly large facility to construct and maintain in addition to the wetpond. Also, the wetpond would totally rely on ' the pumping station to receive flow and thus provide treatment. August 15,1"1/tlh 1 ' Page 20 ' The wetvault solves the problems associated nth minimal land area and pumping, and can be constructed fully below ground at ' the junction manhole invert elevation 101.0. At this elevation, the wetvault can fully operate by gravity during most storm events. Only during flood stage in the Green River will pumping be necessary to discharge stormwater from the wetvault. The ' wetvault will be designed with pumps and piping to allow discharge to either the wastewater treatment plant or the Green River. Also, the pumps could be sized for less than the peak ' stormwater flow because of the storage capacity of wetvault. Metro has a ready staff of well qualified personnel to operate and maintain the wetvault and the associated pumping facilities. ' Minimum Access Requirement: A variance is requested from the requirement for a maximum depth to the vault invert of 20 feet. The proposed vault invert will be about 25 feet below grade. The ' deep invert elevation is required to allow the stormwater sewers to drain by gravity into the wetvault. Even with this deep depth, adequate access has been provided for maintenance and ' general operation. A stormwater wet vault equipment access room is proposed to be built atop the wetvault. Required access is provided to both the equipment access room from the surface and to the wetvault. The depth from the equipment access room to the ' wetvault invert will be between 10 and 11 feet. This vault will be designed according to Metro specifications. 1 1 August 15,1991/tlh 2—YEAR and 100—YEAR DESIGN STORM IIYDROGRAPHS 25 20 ■ 100 year pre—development + 100 year post—development 15 2 year post—development c f 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 hours " ,, \ .. ,�,• �,„ ""T it J .:c"?: i BLACK RIVER BASIN , .w Basin Boundary _. . Subcatchment Boundary � 9 •� s t O Collection Point 1 og, Stream F+ ' 000s Tributary Number 00301 Proposed Project �- ~ 1/ 1g July,1997 once!°" .. -•$ _ it \.VJ..' I I• J �tp �1 •� � u rP ,.onn 'Y•Oes Waves � n wrw.v f,c �•`� — — � - � a Y�} r ., rn � I o I � ♦ � r t-r z �w„�- �Q I a =Lou` 53 �� • ''. �l � '-"� —�,+��� r I \ y h u N 11l I , � • . 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Plan at Elevation 125.0 Consultants Cl IL - :r7RhiN 14 1 1 {� + _ �l: .ql CESS MN:._ 1 _ i I - ILL �--r-----�- - Du 1 i mRm'WP.'MK WET vAULTI i • y ACCESS: -_ ,ROOM_ i -- i 1- -tt ATC l; - -TI G14T T E-]4-1 ► i-- - iL -- - — , _ _. } o _TOP Dk At�I=SS N13DZES�` - - - T v-ti P�AN AT -1 s D.pjaN ELEVATION : 11 Stco) NOit (� I �- _ . - - { -� — — - -t-1 I� -SSA _— Ot S. 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I I ; Ir � � , i I II Figure 9. Sect on I ' rC ' j I I !, I I 11 II I i ivi I L f r } I IACCk`�., {j' DQQRS I o tZ STAIRi i3o it FL s YI I�d RhI f�I , I` .il - lQ �Qvlp iwd� + � IA Il I E, QL x d NU, I I}}t .4 ECHAt26£I . CINIA f3E2 I ( DISC.HPYZ6� ' g; N , ET VAULLT 3.5 t4 I I D Rf' 01 �M t!t 6YPA D IfI}d I I ���ii t G RAV ITyIm ACCESS Cn 111k1 ORmWA_TEi2 - i I `7 I TO 9�OR�t,�/(j R_ t fFW '. 'A FA ti. 1 S F SH C I f I 1I i I�t F RST L6SH G B ^ ' � n '. , I , -. I , , •.i_ I �I_ 1 i � I > I. i �-I •-'.. � I I I I I I ll— ' I I I I . , I ! 1 � it i' III M I �� ' IEAVS- [NG 30" v i I i � ' l i tl `. I l " .i l f l � . I } I 4 + f t GRAVITY sTORMWA(TER C Y I , 1 I I ' ! I i I ,. i - 1 i FIA GATES 1 t ' t m I } � � i I � I : j I ' I { j rl r � t , _ t � I ## O z � � �Y l I ' 1 (h r M t I r j .. j 1 a�Li.4 , OT) Y O W ; if I ' Tablel. Existing Conveyance System Parameters Downstream U stream Elevations Pi Dimensions Elevations Node ID Invert Manhole Rim Len th Diameter Node ID Invert Manhole Rim I 1DOD 89.00 99.00 999.9 120 1001 89.75 129.00 1001 89.75 129.00 71.0 3D 1002 102.73 128.00 1002 102.73 128.00 112.0 30 1003 112.95 127.50 10D3 102.95 12750 102.0 30 1004 103.46 126.00 1 10D4 1D3.46 126.00 482.0 30 1006 104.35 125.50 1006 120.90 125.50 150.0 30 1007 121.50 12550 1007 104.70 125.50 284.0 30 1DOB 105.24 125.60 1008 105.24 125.60 160.0 30 1009 105.56 125.50 1D09 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 3D9.0 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 106.68 125.94 1015 106.60 125.94 63.0 10 1016 109.08 126.20 1016 122.84 126.20 217.0 10 1017 124.58 128.58 1018 107.D0 125.50 245.0 18 102D 107.44 125.50 102D 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 Z_.5.0 18 1018 107.00 125.50 1008 105.24 125.60 128.0 15 1024 1 D7.80 123 M 1024 107.80 123.30 96.0 15 1025 110.50 123.30 1025 11050 123.30 12B.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 1252D 220.0 12 1030 12025 124.25 102D 116.00 12520 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 121.60 125.50 40.0 12 1022 121.70 125.50 1022 121.70 125.51 244.0 12 1023 123.00 129.80 1006 105.35 125.50 80.0 12 1038 106.50 128.60 1038 119.00 126.00 100.0 8 1039 120.20 126.00 1038 119.50 126^A 120.0 12 1040 120.20 126.00 1040 12020 126::> 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.DD 125.50 1001 102.59 129.00 136.0 18 10" 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 123.39 127.95 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 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 149.20 156.00 1052 105.01 129.00 252.0 30 1055 105.85 126.00 1055 105.85 126.00 325.0 30 1056 106.50 125.25 1056 1 107.00 125.25 276.0 24 1058 1 108.20 125.25 Tablel. Existing Conveyance System harameteri Downstream U stream Elevations Pi Dimensions Elevations Node ID Invert Manhole Rim Len th Diameter Node ID Irnert Manhole Rim 1058 108.20 125.25 107.0 24 1059 108.67 125.25 105D 108.67 125.25 191.0 24 1060 109.53 125.25 1080 109.63 125.25 155.0 24 1061 110.19 126.50 1061 120.10 126.50 38.0 12 1062 120.25 126.25 1 1056 110A0 125.25 100.0 6 1057 111.00 126.00 1061 110.44 126.50 383.0 21 1063 111.78 125M 1063 112.28 125M 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.D0 1056 1D6.50 125.25 320.0 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 12525 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 12525 290.0 30 1077 107.35 125.25 1077 120.65 12525 103.0 12 1078 120.98 125.50 1078 120.98 12550 100.0 12 2079 121.78 128.B0 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 120.9E 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 12325 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 1068 1 D4.12 125.35 1088 104.12 125.35 153.0 8 1089 113.50 11554 1089 105.04 115.64 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 1D92 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 1D95 106.39 114.24 1095 106.39 114.24 77.0 12 1096 106.95 119.20 1083 111.25 125.25 108.0 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 12950 180.0 10 3001 122.25 126.10 1006 120.70 125.50 140.0 12 1005 121.40 12420 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 121.00 125.50 207.0 12 2076 1 123.60 125.60 .�� < o �) ` b �� 1 r � � � � � � � � r �r � � � � � � � r ' Table 3. Hydrograph Input Paramters:Pre-Development 1 Node Total Area Fraction of CNlmper CNPery K Slope Distance Acres imperv.Area Ft 1101 1.12 0.123 98.0 74.0 8.6 0.03 220 1100 0.72 0.118 98.0 74.8 9.0 0.03 180 ID99 0.64 0.269 98.0 77A 12.0 0.021 200 1098 ' 1097 1096 0.23 0.884 98.0 74.0 18.5 0.02 300 1095 0.26 0.309 98.0 74.0 11.0 0.054 Bo 1094 0.49 0.507 98.0 75.3 14.0 0.07 160 1093 0.52 0b75 98.0 75.6 14.9 0.148 220 1092 0.35 0.748 98.0 79.0 17.5 0.012 100 1091 0.08 OA17 98.0 74.0 12.4 0.07 60 1090 0.15 0.344 98.0 74.0 11.5 0.07 60 1089 0.28 0.361 08.0 77.1 12.9 0.066 200 1088 0.11 1.000 98.0 75.0 20.0 0.0013 160 1087 0.25 0.661 98.0 79.0 16.6 0.107 70 1086 0.24 0.732 98.0 74.0 16b 0.01 6o ' 1085 1084 0.19 1.000 88.0 74.0 20.0 0.0067 240 1083 2.76 0.000 98.0 74.0 7.0 0.0115 320 1082 1081 0.06 1.000 98.0 74.0 20.0 0.008 50 1080 0.10 1.000 98.0 74.0 20.0 0.0036 160 1079 1.62 0.000 96.0 74.0 7.0 0.012 220 1078 0.55 0.091 98.0 74.0 8.2 0.003 260 1076 0.49 0.000 98.0 74.0 7.0 0.0035 170 1075 0.64 1.000 98.0 74.0 20.0 0.014 260 1074 0.10 1.000 98.0 74.0 20.0 0.03 210 1073 2.41 0.095 98.0 74.0 8.2 0.015 160 1072 0.06 0.000 98.0 74.0 7.0 0.33 40 1071 0.14 1.000 98.0 74.0 20.0 0.005 100 1070 0.33 0.533 98.0 76.8 14.7 0.009 145 1069 0.11 0.813 98.0 74.0 17.6 0.003 90 1068 1087 0.30 0.504 98.0 74.0 13.5 0.011 150 1066 0.20 0.884 98.0 74.0 18.5 0.007 140 1 1065 1064 0.11 0.780 98.0 74.0 17.1 0.01 65 1063 1.02 0.111 98.0 74.0 8.4 0.004 180 1062 0.04 1.000 98.0 74.0 20.0 0.021 90 1061 Assumed no inlet at this node. HYDRA4 Input Files 1 Hydrograph Parameters Pre-Development Renton III ' Node Total Area Fraction of CNlmper CNPery K Slope Distance Acres Im rv.Area Ft 1060 3.46 0.110 98.0 74.0 8.5 0.08 400 1050 0.54 0.000 98.0 74.0 7.0 0.045 180 1058 0.66 0.231 98.0 74.0 10.0 0.045 8o 1 1057 : 1056 1055 1 '054 : 1053 1052 1 1051 0;05 1.00D 98.0 74.o 20.0 0.002 60 loco 1049 1048 3.62 0.000 98.0 74.0 7.0 0.0002 380 1047 0.67 1.000 98.0 74.0 20.0 O.OD65 200 1046 0.22 1.000 98.0 74.0 20.0 0.01 220 104 1044 1021 0.43 0.7o6 98.0 74.0 16.2 0.006 270 1020 0.20 0.765 98.0 74.0 16.9 O.DO3 160 1019 0.11 0.857 98.0 74.0 18.1 OA05 115 1018 0.21 0.564 98.0 74.0 14.3 0.003 135 1017 0.54 0.879 98.0 74.0 18.4 0.005 120 ' 1016 1015 0.39 0S20 98.0 75.2 14.1 0.0065 170 1014 0.44 0.301 98.0 76.8 12.1 0.006 200 1012 1.20 0.149 98.0 78.8 11.4 0.005 12D 1011 0.10 1.000 98.0 74.0 20.0 0.005 110 1010 1009 0.34 0.827 98.0 74.0 17.7 0.005 100 1036 0.48 0.168 98.0 75.4 9.9 O.OD44 90 1035 0.20 1.ODO 98.0 74.0 20.0 0.005 100 ' 1034 0.16 0.280 98.0 74.0 10.6 ODDS 180 1033 0.06 0.155 98.0 74.0 9.0 0.086 5o 1032 0.09 0.667 98.0 74.0 15.7 0.0017 90 _ 1031 0.39 0.000 98.0 74.0 7.0- 0.008 80 1029 0.65 0.690 98.0 76.9 16.5 0.005 160 1028 1027 0.23 0.000 98.0 74.0 7.0 0.006 80 1026 0.33 0.341 98.0 75.9 12.2 0.005 130 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) im rv.Area ! Ft 1025 0.31 0.323 98.0 74.0 11.2 0.005 100 1024 1008 1023 0.19 0.576 98.0 76.3 15.1 0.011 150 1022 0.17 0.232 98.0 74.0 10.0 0.005 90 1037 0.18 0.640 98.0 74.0 15.3 0.005 130 1007 ' 1042 0.58 1.000 98.0 74.0 20.0 0.01 150 1041 1040 1.18 0.730 98.0 74.0 16.6 0.0114 420 ' 1039 0.21 1.000 98.0 74.0 20.0 0.012 280 1038 0.34 0.669 98.0 74.0 15.7 0.005 150 1006 1005 0.45 0.656 08.0 74.0 15.5 0.01 190 1004 0.34 0.557 98.0 74.0 14.2 0.016 170 1043 0.71 0.849 98.0 74.0 18.0 0.026 160 1003 1002 1001 1000 'Assumed no Inlet at this node. ' Table 4. Hydrograph Input Parameters: Post-Development Node Total Area Fracdon of CNlmper CNPery K Slope I Distance Acres Im rv.Area Ft I 1101 0.72 D.191 98.0 74.0 9.5 0.03 220 ' 1100 0.72 0.118 98.0 74.8 9.0 0.03 180 1099 0.73 0.396 98.0 77.4 12.9 0.021 200 1 D98 ' 1097 1096 0.20 1.000 98.0 74.0 20.0 0.02 300 1095 0.08 1.000 98.0 74.0 20.0 0.054 60 ' tO94 0.49 OA16 98.0 75.3 12A 0.07 160 1093 0.66 0.593 98.0 75.6 14.7 0.148 220 1002 0.43 0.654 98.0 79.0 16.5 0.012 10D 1091 0.08 0.417 98.0 74.0 12.4 0.07 60 1D90 0.15 o.344 98.0 74.0 11.5 0.07 60 1089 0.28 0.361 98.0 77.1 12b 0.066 200 1088 0.11 1.000 98.0 75.0 20.0 0.0013 160 1087 025 0.661 98.0 79.0 16.6 0.107 70 1086 0.99 0.445 98.0 74.0 12.8 0.01 60 I 1085 1084 0.19 1.000 98.0 74.0 20.0 0.0067 240 1083 2.50 0.000 98.0 74.0 7.0 0.0115 320 ' 10811 10811 0.06 1.000 98.0 74.0 20.0 0.008 50 1080 0.10 1.000 98.0 74.0 20.0 0.0036 160 1079 1.62 0.000 98.0 74.0 7.0 0.012 220 1078 0.19 0.267 98.0 74.0 10.5 0.003 260 1077 2076 1.03 0.000 0 74 7.0 0.001 400 1076 0.49 0.000 98.0 74.0 7.0 0.0036 170 1075 0.64 1.DDo 98.0 74.0 20.0 0.014 260 1074 0.10 1.000 98.0 74.0 20.0 0.03 210 1073 2.41 0.141 98.0 74.0 8.8 0.015 160 1072 0.06 0.000 98.0 74.0 7.0 0.33 40 1071 0.14 1.000 98.0 74.0 20.0 0.005 100 1070 0.33 0.533 98.0 76.8 14.7 0.009 145 1069 0.11 0.813 98.0 74.0 17.6 0.003 90 1068 1067 0.30 0.504 98.0 74.0 13.5 0.011 150 1066 0.20 0.884 98.0 74.0 18.5 0.007 140 1065 1064 0.11 0.780 98.0 74.0 17.1 0.01 65 1063 1.02 0.111 98.0 74.0 8.4 0.004 180 Assumed no inlet at this node. ' HYDRA4Input Fles_ Hydrograph Parameters Post- Development Renton III ' Node Total Area Fraction of Mlmper CN ry K Slope Distance Acres Impem.Area Ft) 1062 0.04 1.000 96.0 74.0 20.0 0.021 90 1061 1060 2.92 0.236 98.0 74.0 10.1 0.08 400 1059 0.54 0.000 98.0 74.0 7.0 0.045 180 ' 1058 2.49 0.061 98.0 74.0 7.8 0.045 300 1057 1056 105 1054 1053 1052 1051 0.05 1.000 98.0 74.0 20.0 0.002 60 1050 ' 1049 1048 0.29 0.000 98.0 74.0 7.0 0.0002 380 1047 0.74 0.034 98.0 74.0 7.4 0.051 300 2047 1.54 0.061 96 74 7.6 0.05 400 1046 0.22 1.000 98.0 74.0 20.0 0.01 220 1045 1044 2021 2.47 0.000 0.0 74.0 7.0 0.005 350 1021 0.43 0.706 98.0 74.0 16.2 0.006 270 1020 0.20 0.765 98.0 74.0 16.9 0.003 160 1019 0.11 0.857 96.0 74.0 18.1 0.005 115 1018 0.21 0.564 98.0 74A 14.3 0.003 135 1017 0.23 0.711 98.0 74.0 16.2 0.005 120 1016 1016 0.39 0.520 98.0 75.2 14.1 0.0065 170 1014 0.44 0.301 96.0 76.8 12.1 0.006 200 I 1012 1.20 0.149 98.0 78.8 11.4 0.005 120 1011 0.10 1.000 98.0 74.0 20.0 0.005 110 1010 1009 0.34 0.827 98.0 74.0 17.7 O.005 100 1036 0.42 0.194 98.0 75.4 9.6 0.0044 90 1035 0.20 1.000 98.0 74.0 20.0 0.005 100 1034 0.74 0.135 98.0 74.0 8.8 0.047 150 1033 0.06 0.155 98.0 74.0 9.0 0.086 50 1032 0.09 0.802 98.0 74.0 17.4 0.0017 90 1031 0.39 0.000 98.0 74.0 7.0 0.008 80 1029 0.65 0.729 98.0 76.9 16.9 0.005 160 Assumed no Inlet at this node. r HYDRA4 Input Rles- _ Hydrograph Parameters Post- Development Renton III Node Total Area Fraction of CNlmper CNPery K Slope Distance Acres Im rv.Araa (F7 1028 ' 1027 0.23 0.086 98.0 74.0 8.1 0.006 80 1029 0.33 1.000 98.0 75.9 20.0 0.01 120 1025 0.31 0.323 98.0 74.0 11.2 0.005 100 1024 1008 1023 0.19 0.576 98.0 76.3 15.1 0.011 150 ' 1022 0.17 0.232 98.0 74.0 10.0 0.005 90 1037 0.18 0.640 98.0 74.0 15.3 0.D05 130 1007 1042 0S8 1.000 98.0 74.0 20.0 0,01 150 1041 1040 1.23 0.781 98.0 74.0 17.2 0.0114 420 1039 0.21 1.000 98.0 74.0 20.0 0.012 280 1038 0.34 0.669 98.0 74.0 15.7 0.005 150 1006 1005 0.45 0.656 98.0 74.0 15.5 0.01 190 1004 0.34 0.616 98.0 74.0 15.0 0.016 170 1043 0.60 0.822 98.0 74.0 17.7 0.026 160 1003 1002 1.24 0.100 98 74 8.3 0.011 400 1001 1000 Assumed no inlet at this node. r r r r r r Table 5. Results of 100 year Storm Modeling Pre-Development Total Contributing Area = 48.47 Acres Peak Flow = 22.99 cfs r Link Node Length Downstream Elevation Diameter Area DesQ DesVel Time LaImig Sysi-ong ID (it) Rim Invert in Acres cfs min n ft 1 1101 290 126.9 119.5 8 1.12 0.56 3.28 1.48 290 290 2 1100 58 126.21 119 8 1.84 029 3.18 0.3 348 348 3 1099 106 12621 119 8 0.64 0.45 2.51 0.7 105 105 4 10% 324 125.25 113.19 15 2.48 1.31 4.23 1.28 42D 777 5 1097 We 125.25 111.25 15 2.48 1.24 4.16 0.43 537 885 6 1096 77 114.24 106.39 12 0.23 0.26 202 0.63 77 77 7 1095 40 111 106 12 0.49 0.43 2.56 0.26 117 117 1 8 1094 70 109.9 105.44 12 O.Ge 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 11554 105.04 8 0.15 0.11 1.53 0.85 78 78 13 1099 153 12525 104.12 6 0.51 0.39 4.96 0.51 153 303 14 1088 30 110.68 103.94 6 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 110 111.6 103.24 18 2.96 2.66 1.92 0.95 110 908 17 1085 140 125.25 121 14 2.96 255 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 105 125.26 108.36 30 8.38 4.81 5.65 021 105 2145 20 1082 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 10D 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 72 125.25 107.36 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 2.56 025 2.77 1.18 403 403 29 1075 77 125.25 118.38 12 0.64 0.77 2.82 0.46 77 77 r 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 32D 125.25 106.5 30 16.48 7.76 1.61 3.3 403 4211 r 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 0.63 287 287 35 1069 172 125 112.77 15 0.58 0.56 1.81. 1.58 459 459 ' 36 1067 170 125M 112.28 15 0.88 0.77 1.89 1.5 629 629 37 1066 43 125.5 118.7 12 0.2 023 5.18 0.14 43 43 38 1 10M 59 125.5 117 12 0.2 0.23 3.39 1 0.26 96 96 r ' Storm Water Modeling Results Hydra & SCS: Brown and Caldwell GIB 1 Pre-Development Conditions Renton III 100 yr - 24 hr storm Link Noce Length Downstream Elevation Diameter Area DesO DwVel Time Lati-ong Sys Long ID ft Rim Invert in (Acres) (cfs min (ft) (ft 39 1064 65 125.33 112.86 12 0.31 0.34 4.86 0.22 161 161 40 1063 383 126.5 110.44 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 1080 191 125.25 108.67 24 5.71 3.01 3.12 1.02 384 1557 44 1059 107 125.25 108.2 24 6.25 3.09 3.13 0.57 491 1664 45 1058 276 12525 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 0.26 360 380 49 1048 302 130.1 119.79 15 3.67 1.04 2.86 1.76 682 682 50 1D47 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 1 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 0.68 320 320 55 1021 908 125.5 107 18 3.71 1.48 2.52 2.04 628 62B 56 1020 245 125.5 107 18 3.91 1.62 1.96 2.08 873 873 57 1019 217 125.5 107 8 021 0.18 4.55 0.8 217 217 58 1018 255 125.94 106.68 18 4.33 1.86 1.99 2.14 472 1345 59 1017 217 126.2 122.84 10 O.54 0.61 2.68 1.35 217 217 60 1016 63 125.94 106.6 10 0.54 0.68 4.62 0.23 280 280 61 1015 83 126S 106.27 21 5.26 2.52 2.86 0.48 363 1708 1 62 1014 280 1265 106.27 6 0.44 0.28 4.24 1.1 280 280 63 1012 309 126A 117.52 8 1.2 0.75 2.94 1.75 309 309 64 1011 47 1265 117.14 8 1.3 0.81 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 0.27 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 3.04 027 254 254 73 1032 125 123.5 116.54 12 0.99 0.7 3.01 0.69 379 379 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 6.38 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 1 1025 96 123.3 107.8 15 3.13 1.9 1 5.51 1 029 1093 1413 ' Storm Water Modeling Results Hydra&SCS: Brown and Caldwell GIS Pre-Development Conditions Renton III 100 yr-24 hr storm Llnk Node Lenp Downstream Elevation Diameter Area Deso DesVel Tare LatLong SysLong ID tt Rim Invert in Acres cfs min (tt) (ft 80 1024 128 125.6 105.24 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 a 0.18 0.17 8.D4 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 3.21 0.62 437 437 87 1039 100 126 119 8 0.21 0.25 2.42 0.69 100 100 68 1036 80 125.5 105.35 12 2.31 224 4.76 0.28 180 617 W 1005 140 125.5 120.7 12 0.45 0.42 1.97 1.18 140 140 90 1056 325 125 105.85 30 23.39 11.03 3A 1.59 325 6476 91 1055 252 129 105.01 30 23.39 10.82 4.03 1.04 577 6728 92 1052 305 120 102.59 30 23.39 10.64 5.45 0.93 882 7033 93 1008 284 125.5 1D4.7 30 10.47 5.54 2.71 1.75 284 4434 94 1007 150 125.5 120.9 30 11.01 5.84 3.56 0.7 434 4913 95 1006 482 126 103.46 30 13.77 8.D4 3 2.68 916 6152 96 10D4 102 127.5 102.95 30 14.11 8.19 4.29 D.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 12s 102.73 30 17.1 9.27 3.2 0.58 164 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 6 Results of 100 year Storm Post-Development 1 Total Contributing Area - 43.65 Acres Peak Flow = 22.61 cis Link Node Length Downstream Elevation Diameter Area DesQ DesVel Time Lati-ong SysLong ID tt Rim Invert in Acres cis f min tt (it) ' 1 1101 290 126.9 119.5 8 0.72 oA 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 o.64 105 105 4 1098 324 125.25 113.10 15 2.17 1.29 4.21 1.28 429 777 5 1097 108 125.25 11125 15 2.17 1.22 4.15 0.43 537 885 6 1096 77 114.24 106.39 12 02 0.24 1.99 0.64 77 77 7 1096 40 ill 106 12 028 0.34 2.43 0.27 117 117 8 1094 70 100.9 105.44 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 10 1092 95 110.75 103.92 12 1.86 1.76 3.6 0." 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 1B3 333 15 1087 88 110.75 103.42 12 0.87 0.77 2.52 0.58 271 421 16 loss to 111.5 1113.24 18 3.12 2.79 1.95 0.94 110 908 17 1085 140 125.25 121 14 3.12 2.68 4A2 0.53 250 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 7.98 424 5.66 0.31 105 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 too 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 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 o.34 2.68 1.29 207 207 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 2.26 129 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 12525 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 2.66 0.83 287 287 35 1069 172 125 112.77 15 0.58 0.56 1.81 1.58 459 459 36 1067 170 125.33 112.2E 15 0.88 o.77 1.89 1.5 629 629 37 1066 43 125.5 118.7 12 1 0.2 1 0.23 1 6.18 1 0.14 43 43 1 ' Storm Water Modeling Results Hydra & SCS Post-Development Conditions Renton III 100 yr • 24 hr storm LJnk Node length Downstream E1eva5w Diameter Area DesO DesVel Time Latong $yslong ID ft Rim Invert n Acres Cis min ft ft 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 1265 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 3" 1657 44 1059 107 125.25 108.2 24 5.71 3.13 3.14 0.57 491 16U 1 45 1058 276 125.25 107 24 821 4.15 3.43 1.34 767 1940 46 1051 160 136 131 6 0.05 0A6 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 o.26 380 380 49 1046 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 15 022 0.23 2.6 o.79 420 420 54 1044 136 129 10259 18 2.84 1.26 8.77 026 556 1605 55 2021 320 128.8 108.22 a 2.47 021 5.41 0.99 32D 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 lip 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 28D 62 1015 83 126.5 10627 21 4.04 1.65 2.57 0.54 363 1708 63 1014 28D 126.5 106.27 8 0.44 0.28 4.24 1.1 280 280 64 1012 309 126.4 117.52 a 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 1255 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 100 123.5 119.96 12 0.42 024 2.36 0.71 100 100 71 1035 14 123A 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 50 129 117.89 12 1.42 0.85 3,13 0.25 254 254 74 1032 125 123.5 116.54 12 1.61 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 5.58 0.04 449 7e9 77 1028 320 124 114 15 2.78 1.84 2.96 1.8 769 1089 78 1027 100 123.3 113.8 15 1 3.01 1 1.6 1 2.17 1 0.77 1 869 1189 1 Storm Water Modeling Results . Hydra& SCS Post-Development Conditions t Renton III 100 yr- 24 hr storm Unk Node Length Downstream Elevation Diameter Area Deso Desvel Time LatLong SysLong ID ft Rim Invert in Acres ofs f s min ft (ft 79 1026 128 123.3 110.5 15 3.34 2.16 5.55 0.38 997 1317 ' 80 1025 96 123.3 107.E 15 3.65 L33 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 96 1041 169 126 120.2 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 8s 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 325 125 105.85 30 22.89 11.36 3.43 1.58 325 $476 92 1055 262 129 105.01 30 22.89 11.18 4.07 1.03 577 6728 93 1052 305 129 102.59 30 22.89 11.01 5A9 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 1255 120.9 30 10.31 5.52 3.5 0.72 434 4913 1 96 1006 482 126 103.46 30 13.12 7.79 2.97 2.71 916 6162 97 1004 102 127.5 102.95 30 13.46 7.99 4.26 0.4 102 6254 98 3001 12D 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 10D 2043 160 125.5 117.5 10 1.01 0.4 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 9.2 16.45 0.07 415 6669 104 1001 999.9 99 89 120 43. 55 22.61 2.62 6.36 1414.9 16462.9 1 ' Paget of 2 King County Building and Land Development Division TECHNICAL INFORMATION REPORT (TIR) WORKSHEET PART 1 PROJECT OWNER AND PART2 PROJECTLOCATION I AND DESCRIPTION PROJECT ENGINEER ' Owner Metro PrOjectName Enlargement III Project Address 821-2nd Ave. , Seattle Location T23N 664-2100 Township Phone Range R4E ' Project Engineer Jack Warburton Section 24 Brow 85 n and Caldwell ` 85 Company Project Size AC Address Phone 281-4000 Upstream Drainage BasinSize 28 MZ AC — 1 ' [] Subdivision = DOF/G HPA Shoreline Management Short Subdivision = COE 404 Rockery ® Grading = DOE Dam Safety (] Structural Vaults ' Commercial FEMA Floodplain C] Other (] Other l] COE Wetlands HPA . r Community Renton Drainage Basin Black River CHARACTERISTICSPART 6 SITE ® River Black, Green Rivers Floodplain Not 100-year ' ® Stream P-1 Channel �i Q � � Wetlands Yes, north end (] Critical Stream Reach U O Seeps/Springs (] Depressions/Swales 0 High Groundwater Table ' Lake No (] Groundwater Recharge Steep Slopes No Other Lakeside/Erosion Hazard PART7 SOILS ' Soil Type Slopes Erosion Potential Erosive Velocities ' Puyallup Level - 2% Moderately low nc�nci tp 'IS - "40% ModPrat�1v high 1 - Additional Sheets Attatched 1/90 Page 2 of 2 ' King County Building and Land Development Division TECHNICAL INFORMATION REPORT MR) WORKSHEET ' PART 8 DEVELOPMENT LIMITATIONS REFERENCE LIMITATION/SITE CONSTRAINT Ch.4-Downstream Analysis No major construction limitations 0 Wetland Protection No construction activity allowed within25 feet; fenced. ' 0 0 0 ' 0 Additional Sheets Attatched rosion secilmen a ion on ro t PART 9 ESC REOUIREMENTS MINIMUM ESC REQUIREMENTS MINIMUM ESC REQUIREMENTS ' DURING CONSTRUCTION FOLLOWING CONSTRUCTION a Sedimentation Facilities ® Stabilize Exposed Surface ® Stabilized Construction Entrance © Remove and Restore Temporary ESC Facilities ' © Perimeter Runoff Control [7-1 Clean and Remove All Silt and Debris ® Clearing and Grading Restrictions ® Ensure Operation of Permanent Facilities a] Cover Practices © Flag Limits of NGPES_ ' ® Construction Sequence Other Other PART 10 SURFACE WATER SYSTEM 1 ® Grass Lined Channel = Tank = Infiltration Method of Analysis ' Depression HYDRA and SCS � Pipe System � Vault 0 P Open Channel = Energy Dissapator x0 Flow Dispersal Compensation/Mitigabon = Dry Pond © Wetland = Waiver of Eliminated Site Storage = Wet Pond = Stream 0 Regional Detention ' Brief Description of System Operation Gravity flow to wet vault, Vault pumos or m roencv overflow. ' Facility Related Site Limitations Additional Sheets Attatched Reference Facility Limitation PART 11 STRUCTURAL ANALYSIS PART 12 EASEMENTSrrRACTS (May require special structural review) t Drainage Easement ® Cast in Place Vault 0 Other 0 Access Easement ' 0 Retaining Wall Native Growth Protection Easement Rockery>4'High Tract Structural on Steep Slope Other ' PART 14 SIGNATURE OF PROFESSIONAL ENGINEER I 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 sy.s-a.r. here 19 accurate. 1/90 t Drainage Basins-Proposed Development C d E as Arba/Basin Acres to W 1 . Tributary to P-1 Channel 3.57 c 2. Tributary to Wetlands 7.72 *• a a. Oakesdale 1 .16 a: = 3. Tributary to Longacres Swale 2.33 w 4. Septage Unload 0.19 o. 5. Sludge Dewatering 2.93 E 6. Direct to Treatment Plant 17.00 F 7. Tributary to Stormwater Sewer [49.66 w a. Pervious Area 30.75 b. Impervious Area 18.85 d c (Subject to Vehicles & Chemical Storage) 12.00 Total 84.50 5400248A Permit/Code Requirements - Stormwater Control C 0 E v" ❑ Water Quality Treatment W • Required: >1 Acre Impervious Area Vehicular Traffic 0 a Chemical Storage W! 5 • Design Criteria z w Swale: Op = 2 Year - 24 Hour Storm = 10.2 CFS d C Wet Pond/Vault: Op = 1/3 of 2 Year - E 24 Hour Storm = 1 .5 CFS Bypass: Q > Qp ❑ Flow Rate Control - Peak Attenuation 0 d • Not Required: Op < 0.5 CFS • Model Results: Op = -0.3 CFS • Full Compliance 54002480 Water Quality Options-Stormwater Control of E 0 ❑ Pump - 10.2 CFS • Thru Swale - 200 Feet Long/5 Acre Impervious Area W To Green River c To Wetlands - P-1 Direct to P-1 oC C ❑ Pump - 1.5 CFS • Thru Plant • Thru Wetpond e To Green River E To Wetlands - P-1 SA = 1% Impervious Area Volume = 1/3 of 2 Year-24 Hour Storm Total Runoff o • To Future Plant Facility, Le., Primary Sedimentation Tank ❑ No Pump - 1 .5 CFS • Thru Wetvault d Same Design as Wetpond To Green River 5400248a Enlargement Ill-Drainage Options C O E Alternative Discharge Location Variance Requirements IM g a C CL p 1. Pumol=Onflons 0 1A. Gross Swale Adjacent Green R. Green R. P-1 Yes No Yes Yes No No Monster Rd. C IB. Wet Pond NW of Watland, P-1 Green R. P-1 Yes No No You Yes No C RoutedThrough Wetland C iC.Wet Pond NW of Wetland, P-1 Green R. P-1 Yes No No Yss! No No C LBypass Watland E1 D. Route Through Puget Green R. P-1 Yes No Yes Yes No No }O Treatment Plant Sound !" 1E. Future Plant Facilities Green R. Green R. P-1 Yes No Yes Yes No No W 2. Non-Pumolnp Optbna C O 2A. Wet Vault Green R. Green R. P-1 No No Yes Yes No No 3. Flooding Issues 3A. Gravity to P-1 P-1 Yes a Yea 3B. Pump to Green River Green R. g Stormwater Regulatory Requirements C E Wet Pond Wet Pond Treatment Fut.Proeess II Requirements Swale Bypass Wetland Thru Wetland Wet Vault Plant Facilities s. W Water Quantity 102 CFS 1.5 CFS 1.5 CFS 1.5 CFS 1.5 CFS 1.5 CFS C Detention NA 210,000 Gal. 210,000 Gel. 210,000 Gel. NA 210,000 Gal. W ■ Space 200/tJ5 Acre 1% Impervious 1% Impervious 1% Impervious NA 1% hnperolous C (Impervious Area-8215 Area-8215 Area-8215 Area-8215 ,r Road)460 H. Sq FT.Total Sq Ft. Total Sq Ft Total Sq FL Total dTreatment Pumping Req. Yes Yes Yes No Yes Yes Overflow Pumping Req. No No No Yes No No C Discharge Level >117.5-P-1 >117.5-P-1 >117.5-P-1 >117.5-Green >117.5-P4 >117.5-P-1 4a <117.5-Green <117.5-Green <117.5-13-1 <117.5-Green <117Z-Green <117.5-Green C W Swale-Green Wet Pond-P-1 Wetland-P-1 Wet Vault-Green TP-Puget Sound FPF-Green d' Costs C i:s or 00 C Pumping Station $350,000 p� $250,000 $250,000 NA $250,000 $M,000 E P.S. Overflow $718,000{`1°i•°')$716,000 $718,000 NA $718,000 $718,000 W Other $250,000 $250,000 VW,000 $3,000,000 NA $3,000,000 F 88 Total $1,318,000 $1,218,000 $1,218,000 $3,000,000 $9 ,00 $3,90,000 Ej Variance Required Yes (Process Yes Yes (Pumping Yes (Process) Yes (Process Yes (Process C &Pumping) (Pumping) 3 Wetland Use) &Pumping) S Pumping) 01 EIS Impact Possible Possible Yes No Possible Yes Future Site Use Impact Minimum Moderate None Minimum None None EJdsting Construction Moderate Moderate Moderate Major Minimum Major Impact Cf 5400248A • � ` Wj Ir ��� 11%% � . \, .X , � . \ . 1, o / ,/ / , \� I- __ . ;, �` , 1: �.._. ,/ ; , , r If_ � o ./ q . _ ; D f I f' \ F \ rn r!iltEq 0r N (%' o :i z o ; ' z -T-1 /` '� � J (�3 :�: . ; -1 0, 1/ � \ r` , v 0 '' '4 . o ':1,4 Q 1 o Y , J Q I / 1 ,: I i / 1 ", 4 I , i i I i \ .I I_.;,. I f !. ' ?'.1 %% - r 12" 1061. l�Y ,t r. w� 1�J 21 " 1063 15" 15" I / ,...,, / ,. a-. �.. . N ` 1 . r j r— ' If � ° i. , ' 7 � 1064 1 � � r � , . � � ; � I � . 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