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RS_Drainage_Report_TIR_20210108_v1.pdf
Renton Elementary School #16 Preliminary Technical Information Report January 8, 2021 The information contained in this report was prepared by and under the direct supervision of the undersigned: Owner: Renton School District 300 SW 7th St Renton, WA 98057 (425) 204-2300 Contact: Traci Brewer-Rogstad Prepared for: Nicole Hernandez, P.E. LPD Engineering, PLLC 1932 1st Ave, Suite 201 Seattle, WA 98101 (206) 725-1211 Renton School District 300 SW 7th St Renton, WA 98057 (425) 204-2300 Contact: Traci Brewer-Rogstad RENTON ELEMENTARY SCHOOL #16 PRELIMINARY TECHNICAL INFORMATION REPORT TABLE OF CONTENTS Section 1 – Project Overview ................................................................................................. 1 Section 2 – Conditions and Requirements Summary ......................................................... 3 Section 3 – Offsite Analysis ..................................................................................................... 5 Section 4 – Flow Control and Water Quality Facility Analysis and Design ...................... 8 Section 5 – Conveyance Systems Analysis and Design ..................................................... 16 Section 6 – Special Reports and Studies ............................................................................. 17 Section 7 – Other Permits .................................................................................................... 17 Section 8 – CSWPPP Analysis and Design ......................................................................... 17 Section 9 – Bond Quantities, Facility Summaries, and Declaration of Covenant .......... 18 Section 10 – Operations and Maintenance Manual ........................................................... 18 FIGURES Figure 1: TIR Worksheet Figure 2: Vicinity Map (To Be Provided for Building Permit Submittal) Figure 3: Existing Conditions Figure 4: Proposed Conditions Figure 5: Soils Map (To Be Provided for Building Permit Submittal) Figure 6: Downstream Drainage Map (To Be Provided for Building Permit Submittal) APPENDICES Appendix A – Design Drawings (CUP plans included) Appendix B – Design Calculations and Supporting Information Appendix C – Stormwater Pollution Prevention and Spill Plan (SWPPS) & Construction Stormwater Pollution Prevention Plan (SWPPP) Narrative (To Be Provided for Building Permit Submittal) Appendix D – Operations and Maintenance Manual (To Be Provided for Building Permit Submittal) LPD Engineering PLLC Page 1 Renton Elementary School #16 Preliminary Technical Information Report, January 8, 2021 RENTON ELEMENTARY SCHOOL #16 PRELIMINARY TECHNICAL INFORMATION REPORT JANUARY 8, 2021 SECTION 1 – PROJECT OVERVIEW This Technical Information Report (TIR) is for the construction of the new Elementary School #16 for the Renton School District. Refer to Figure 1 – TIR Worksheet for basic site information. The new Elementary School #16 will be constructed on eleven (11) tax lot parcels and two (2) right-of-way (ROW) parcels with a total area of 11.17 acres. The parcels are bounded by NE 12th Street to the north, Duvall Avenue NE to the east, and residential properties to the west and south. The site is located in Section 10, Township 23 North, Range 5 East, Willamette Meridian. Refer to Figure 2 – Vicinity Map. The City of Renton has adopted the 2016 King County Surface Water Design Manual (KCSWDM) with the City’s 2017 Surface Water Design Manual Amendment (RSWDMA). According to Figure 1.1.2.A of the RSWDMA, Flow Chart for Determining Type of Drainage Review Required, the project is subject to a “Full Drainage Review” because the project results in greater than 2,000 SF of new plus replaced impervious surface, and it is not defined as a large project or single-family residential project. Per the “Full Drainage Review” requirements in Table 1.1.2.A, the TIR addresses Core Requirements #1-9 and Special Requirements #1-5 of the 2017 RSWDMA. Existing Site The majority of the parcels contained in the project site previously contained single-family residences which were demolished in January of 2019 and the remaining parcels were undeveloped. See Figure 3 – Existing Conditions. There are two existing wetlands on the site. The City’s Critical Area Map do not identify wetlands on-site; however, a wetland delineation report was performed by The Watershed Company on November 2019 and initially identified three wetlands; Wetlands A, B, C. Further evaluation eliminated Wetland A because it did not meet the criteria for jurisdictional wetlands. Wetland B is located in the northeast portion of the site and Wetland C is along the west property line. The Wetland C, which provides a higher level of function than Wetland B, will be maintained as part of the school development. It is classified as a Type III and requires a 100-ft buffer. Wetland B is considered a Type IV and will be removed and mitigated through a wetland banking system as a part of this project. Topographically, the site sits at a high point relative to the surrounding properties. Generally, the site slopes down from the east to the west with elevations ranging from approximately 438 feet in the southeastern portion of the parcel to approximately 409 feet at the existing west wetland area. The site also has areas which slope from south to north, and a smaller area that slopes towards the southwest. The existing topography divides the site drainage into three basins as described in detail below. LPD Engineering PLLC Page 2 Renton Elementary School #16 Preliminary Technical Information Report, January 8, 2021 The site is located within three drainage basins, denoted as the South Basin, the North Basin, and the Wetland Basin. The areas within the South Basin sheet flow to the southwest. The runoff is collected by the existing catch basins along the east side of Chelan Avenue NE and flows into a 12-inch main. The North Basin discharges into Wetland B which flows offsite to the north via a 12-inch storm line and ultimately discharges into a 12-inch storm pipe within NE 12th Street. The Wetland Basin sheet flows to Wetland C and discharges from the site via a 15-inch CMP that conveys flow to the north and eventually connects into a 15-inch storm pipe within NE 12th Street. The storm system from Chelan Avenue NE and NE 12th Street eventually converge and ultimately discharge to May Creek which outlets to Lake Washington. A subsurface exploration and geotechnical feasibility study were conducted by Associated Earth Sciences, Inc. (AESI). They prepared their findings in a preliminary report dated November 21, 2019. Their field study included fourteen exploration borings across the site. The explorations typically encountered existing fill and recessional outwash sediments underlain by dense, silty Vashon lodgement till sediments. Five exploration borings encountered surficial existing fill to thicknesses of up to approximately 7 feet. Two explorations found shallow Vashon recessional outwash sediments ranging in thickness from approximately 2.5 to 5 feet thick. The northernmost exploration borings terminated in potential lodgement till and advance outwash transition sediments at depths of approximately 20.5 to 21.5 feet. Groundwater was not encountered in any of the explorations completed for this study at the time of exploration. According to AESI’s exploration, the use of potential stormwater infiltration was found to be infeasible due to the extent of dense, silty soils across the site. The existing fill is not a suitable infiltration receptor due to its variable density, silt, and organic content. The recessional outwash found in two of the borings do not have enough vertical depth to support infiltration without adequate separation from the hydraulically restrictive layers. Lodgement till is not a suitable infiltration receptor due to its high silt content. Proposed Site Improvements The project is not considered a redevelopment project based upon the following definition from the KCSWDM: “Redevelopment project means a project that proposes to add, replace, or modify impervious surfaces (for purposes other than a residential subdivision or maintenance) on a site that is already substantially developed in a manner consistent with its current zoning or with a legal non- conforming use, or has an existing impervious surface coverage of 35% or more.” The survey was used in AutoCAD to delineate the existing impervious coverage for the project property. Refer to Figure 3 – Existing Conditions. The existing impervious coverage is less than 35% and therefore the project is considered a New Development. The new Renton Elementary School #16 will include an approximately 46,000 square foot school building with a central outdoor courtyard, natural grass playfield, hard and soft surface play areas, an entry plaza, emergency and fire apparatus access loop, a designated bus loop, parking, and a student loading lane. Refer to Figure 4 – Proposed Conditions. Improvements will be made to the frontage along Duvall Avenue NE to accommodate the three proposed driveways, along with a sidewalk, planter strip, and bicycle/vehicle queuing lane per coordination with the City of Renton. Additionally, Chelan Avenue NE will also be improved to establish a new egress LPD Engineering PLLC Page 3 Renton Elementary School #16 Preliminary Technical Information Report, January 8, 2021 only driveway, with an extension of the existing sidewalk and planter strip to the north through the School District property. The project proposes approximately 238,530 SF (5.48 acres) of new plus replaced impervious surface. In order to preserve the drainage patterns of the existing site, the post-developed grading of the project site has been designed to maintain the existing basin areas, to the extent feasible, which have the same denotation of South Basin, North Basin, and Wetland Basin. For the South Basin, stormwater runoff will be collected in a series of catch basins and routed via pipe conveyance systems to a shallow flow control detention facility. This is currently designed as an ADS StormTech Chamber system, located on the south portion of the site beneath the proposed parking lot. The detention system will have a flow control structure to attenuate flows and will be followed by a water quality treatment facility which is designed as a Modular Wetland vault. The detained and treated discharge will eventually be conveyed to the existing 12-inch main within Chelan Avenue NE. For the North Basin, stormwater runoff will be collected in a series of catch basins and routed via pipe conveyance systems to an ADS StormTech Chamber system, located underneath the play field. Under- drain pipes within the play field subsurface will also discharge into the StormTech system. The detention system will have a flow control structure to attenuate flows and will be followed by a water quality treatment facility which is designed as a Modular Wetland vault. The detained and treated discharge will then discharge into an existing vegetated swale running along the east side of the gravel drive perpendicular to NE 12th Street, before entering the piped conveyance system in the right-of-way. In the Wetland Basin, the project proposes to utilize full dispersion for the majority of the new plus replaced impervious surfaces in this basin which includes a portion of the roof, fire lane, and pedestrian walkways. Runoff from the roof and paved surfaces will be routed to gravel dispersion trenches and overflow into the vegetated wetland buffer zone, eventually discharging into Wetland C. Proposed surfaces that utilize full dispersion are not considered to be target surfaces and thus, do not trigger flow control and water quality requirements. Flow Control Best Management Practices (BMPs) have been evaluated. As stated above, the geotechnical investigation by AESI did not find the site’s soil profile favorable for infiltration. The stormwater strategy will be to utilize Dispersion BMPs as well as a permeable pavement type system for the fire lane within the Wetland Basin. Site constraints do not allow for BMPs to be used for the South and North Basins. Refer to Section 4 – Flow Control and Water Quality Analysis and Design for further information on the storm drainage design. SECTION 2 – CONDITIONS AND REQUIREMENTS SUMMARY This section addresses the requirements set forth by the 2017 Renton SWDM, Core and Special Requirements listed in Chapter 1. Core Requirements Core Requirement 1 – Discharge at Natural Location (1.2.1): The proposed conditions will maintain the existing discharge locations to the maximum extent feasible. The site is divided into three drainage LPD Engineering PLLC Page 4 Renton Elementary School #16 Preliminary Technical Information Report, January 8, 2021 basins, the South Basin, the North Basin, and the Wetland Basin. Flow control detention facilities and BMPs will be implemented, thus attenuating discharge from the project area and creating no adverse impacts on the downstream system. Refer to the Offsite Analysis section of this report for a description of the existing discharge points from the site. Core Requirement 2 – Off-site Analysis (1.2.2): A Level 1 Downstream Analysis will be included in the TIR that is provided with the Building Permit Submittal. Core Requirement 3 – Flow Control (1.2.3): Per the City of Renton Flow Control Application Map, Reference 15-A in the RSWDMA, the project site is located within Flow Control Duration Standard area. Therefore, the flow duration of predeveloped rates for forested (historical) site conditions over the range of flows extending from 50% of 2-year up to the full 50- year flow AND matches peaks for the 2- and 10-year return periods. Per the RSWDMA, flow control facilities must mitigate the runoff from the target surfaces which include new impervious surfaces and new pervious surfaces not fully dispersed. For further information regarding the flow control design, refer to Section 4 of this report. Core Requirement 4 – Conveyance System (1.2.4): Refer to Section 5 of this report for conveyance analysis. Core Requirement 5 – Erosion and Sedimentation Control (1.2.5): A Temporary Erosion and Sediment Control (TESC) plan has been included with the plan set. The TESC plan will be considered the minimum for anticipated site conditions. The Contractor will be responsible for implementing all TESC measures and upgrading as necessary. The TESC facilities will be in place prior to any demolition, clearing, grubbing or construction. Core Requirement 6 – Maintenance and Operations (1.2.6): The Operations and Maintenance Manual for the project will be provided for the Building Permit submittal in Appendix D. Core Requirement 7 – Financial Guarantees and Liability (1.2.7): This project is owned by a public entity, the Renton School District, and therefore the project will not need to comply with Section 1.2.7 of the 2017 RSWDMA. Core Requirement 8 – Water Quality (1.2.8): The project proposes more than 5,000 square feet of pollution-generating impervious surface (PGIS), and therefore this project will require water quality treatment. Per the City of Renton WQ Applications Map, the project is in a Basic Water Quality Treatment area; however, since schools are classified as commercial projects, Enhanced Basic Water Quality is required. For further information regarding the water quality design requirements, refer to Section 4 of this report. Core Requirement 9 – Flow Control BMPs (1.2.9): The project site proposed more than 2,000 SF of new plus replaced impervious surfaces which will require an evaluation of BMP feasibility for all target surfaces. Per section 1.2.9.2 of the 2017 RSWDMA, this project will be subject to Large Lot BMP Requirements since the project site is larger than 22,000 SF. Refer to the Flow Control BMPs evaluation within Section 4 of this report. LPD Engineering PLLC Page 5 Renton Elementary School #16 Preliminary Technical Information Report, January 8, 2021 Special Requirements Special Requirement 1 – Other Adopted Area-Specific Requirements (1.3.1): The City of Renton Surface Water Design Manual is one of several adopted regulations in the City of Renton that apply requirements for controlling drainage on an area-specific basis. Other adopted area-specific regulations include requirements that have a more direct bearing on the drainage design of a proposed project. These regulations include the following: • Master Drainage Plans (MDPs) – The project is not within an area covered by an approved Master Drainage Plan. Project is not a Master Planned Development, a Planned Unit Development, a subdivision that will have more than 100 lots, a commercial development that will construct more than 50 acres of impervious surface, and will not clear more than 500 acres within a drainage sub-basin. Therefore, a Master Drainage Plan is not required. • Basin Plans (BPs) – The Watershed Management Committee Lower Cedar River Basin and Nonpoint Pollution Action Plan, adopted 1997, was reviewed to determine if there are regulations applicable to this site. There are no additional water quality requirements listed by the report. • Salmon Conservation Plans (SCPs) – The project is not within an area governed by SCPs. • Lake Management Plans (LMPs) – The project is not within an area governed by an LMP. • Hazard Mitigation Plan – The proposed project is not within an area with a Hazard Mitigation Plan. • Shared Facility Drainage Plans (SFDPs) – The proposed project is not within an area with an SFDP. Special Requirement 2 – Flood Hazard Area Delineation (1.3.2): According to King County iMap, the project does not contain nor is it adjacent to a Flood Hazard Area. Special Requirement 3 – Flood Protection Facilities (1.3.3): The project does not have existing flood protection facilities, nor does it propose new flood protection facilities. Special Requirement 4 – Source Control (1.3.4): In the proposed conditions, kitchen facilities will involve activity A-8 listed within the 2016 King County Stormwater Pollution Prevention Manual (KCSPPM) that will require the use of source control measures. Activity A-8 includes storage of solid and food wastes (including cooking grease). Therefore, a grease interceptor will be required as a source control measure. Special Requirement 5 – Oil Control (1.3.5): The project will not have high-use site characteristics nor is it an existing high-use site; therefore, oil control is not required. SECTION 3 – OFFSITE ANALYSIS The following is the Level 1 downstream analysis for the proposed project. Refer to Figure 6 - Downstream Drainage Map (to be provided for Building Permit Submittal). The following resources have been reviewed for the project area: LPD Engineering PLLC Page 6 Renton Elementary School #16 Preliminary Technical Information Report, January 8, 2021 Task 1 – Study Area Definition and Maps The school property incorporates eleven parcels (#1023059173, #1023059275, #1023059096, #1023059107, #1023059249, #1023059138, #1023059124, #1023059076, #1023059202, #1023059332, #1023059139), as well as two unopened ROW parcels, totaling approximately 11.17 acres. The downstream analysis for the project area is based upon the following resources: • Site Survey • On-site Investigation (to be provided for Building Permit Submittal) • King County iMap • City of Renton GIS Mapping • A subsurface exploration and geotechnical feasibility study prepared by Associated Earth Sciences, Inc.; dated November 21, 2019 Task 2 – Resource Review Basin Summary According to the site survey and GIS mapping, the project is situated within three drainage basins, denoted as the South Basin, the North Basin, and the Wetland Basin. After the ¼-mile mark of the downstream drainage system, all drainage basins eventually converge and discharge to May Creek which outlets to Lake Washington. Refer to Figure 3 – Existing Conditions, for a layout of the existing basin dividing line. Floodway Map The site is not located within a Floodway or Floodplain per the Washington State Department of Ecology Flood Maps and King County iMap. Sensitive Areas The following is a summary of SAO sensitive areas located within the project area or within the downstream drainage course from the project area. The King County iMap application was used to examine the SAOs. SAO Erosion Hazard – The project site is not located within an erosion hazard area. SAO Seismic Hazard – The project site is not located within a seismic hazard area. SAO Landslide Hazard – There are no landslide hazard areas located within the project site. SAO Coal Mine – There are no coal mines located within the project site. SAO Stream – According to King County iMap, there are no unclassified stream or any waterbodies through the developed school site. SAO Wetland – There are is a wetland located within one mile downstream of the project site. Groundwater Contamination – According to iMap, the project site has no mapped susceptibility to groundwater contamination. Sole Source Aquifer – Per King County iMap, the project site is not located within a sole source aquifer area. LPD Engineering PLLC Page 7 Renton Elementary School #16 Preliminary Technical Information Report, January 8, 2021 Critical Aquifer Recharge Area – The project site is not considered a Critical Aquifer Recharge Area. Channel Migration Hazard – Per King County iMap, the project site is not located within a channel migration hazard zone. Topographic Map The detailed topographic information for the project area is shown on the design drawings. Drainage Complaints According to King County’s iMap program, there have been no drainage complaints within the last 10 years within the project site, upstream area, or downstream area. Soils Survey A published geologic map of the project, Geologic Map of Surficial Deposits in the Seattle 30’ by 60’ Quadrangle, Washington, by J.C. Yount, J.P. Minard, and G.R. Dembroff, indicates that the site is underlain at shallow depths by Vashon lodgement till. The generally consistent with geotechnical engineer’s investigation. Refer to Section 1 of this report and Figure 5: Soils Map for additional soils information. Migrating River Studies According to King County’s iMap program, the project site is not located within or adjacent to a channel migration hazard area. Water Quality Problems Per the 2017 Renton SWDM, King County-identified water quality problems do not apply to the City. Task 3 – Field Inspection (To Be Provided for Building Permit Submittal) Task 4 – Drainage System Description and Problem Descriptions (Additional Information To Be Provided for Building Permit Submittal) Please refer to Section 1- Project Overview and Section 3- Off-site Analysis of this report for a description of the existing drainage system which is based on information from the site survey as well as the City’s GIS stormwater mapping. Task 5 – Mitigation of Existing or Potential Problems (To Be Provided for Building Permit Submittal) Site observations will be conducted prior to the Building Permit submittal. At this time, it is anticipated that proposed project is not expected to adversely impact the downstream system since the stormwater flows from the site will be mitigated per the City’s requirements. LPD Engineering PLLC Page 8 Renton Elementary School #16 Preliminary Technical Information Report, January 8, 2021 SECTION 4 –LOW IMPACT DEVELOPMENT (LID), FLOW CONTROL AND WATER QUALITY FACILITY ANALYSIS AND DESIGN Existing Site Hydrology Please refer to Section 1- Project Overview and Section 3- Off-site Analysis of this report for a description of the existing hydrology. Developed Site Hydrology Please refer to Section 1- Project Overview and the Flow Control System section below in this report for a description of the proposed hydrology. Performance Standards Please refer to Section 2- Conditions and Requirements Summary, and the Flow Control BMPs, Flow Control System, and Water Quality sections of this report for a description of the required standards applicable to this report. Flow Control Facility Standard As stated previously, the project site is located within Flow Control Duration Standard area. Therefore, the flow duration of predeveloped rates for forested (historical) site conditions over the range of flows extending from 50% of 2-year up to the full 50- year flow AND matches peaks for the 2- and 10-year return periods. Per Section 1.2.3.1.B. of the 2017 RSWDMA, below is a description and evaluation of the target surfaces for this project: 1. New impervious surface that is not fully dispersed per the criteria on Section 1.2.3.2.C, as specified in Appendix C. For individual lots within residential subdivision projects, the extent of new impervious surface shall be assumed as specified in Chapter 3. Note, any new impervious surface such as a bridge or boardwalk that spans the ordinary high water of a stream, pond, or lake may be excluded as a target surface if the runoff from such span is conveyed to the ordinary high water area in accordance with Criteria (b), (c), (d), and (e) of the "Direct Discharge Exemption" (p 1-39) Interpretation: New impervious surfaces fully dispersed will not be considered a target surface. This would apply to the impervious surfaces within the North and South Basin. New impervious surfaces that cannot be fully dispersed are considered to be a target surface. Note, the project proposes to utilize full dispersion for the majority of new impervious surfaces within the Wetland Basin. 2. New pervious surface that is not fully dispersed or not farmland dispersed as specified in Appendix C. For individual lots within residential subdivision projects, the extent of new pervious surface shall be assumed to be the entire lot area, except the assumed impervious portion and any portion in which native conditions are preserved by covenant, tract, or easement. In addition, the new pervious surface on individual lots shall be assumed to be 100% grass. Interpretation: The definition of new pervious surface from the 2017 RSWDMA includes the conversion of a native vegetated surface or other native surface to non-native pervious surface (e.g. conversion of forest or meadow to pasture land, grass land, cultivated land, lawn, LPD Engineering PLLC Page 9 Renton Elementary School #16 Preliminary Technical Information Report, January 8, 2021 landscaping, bare soils, etc.), or any alteration of existing non-native pervious surface that significantly increases surface and storm water runoff (e.g., conversion of pasture land, grass land, or cultivated land to lawn, landscaping, or bare soil). Per the definitions above, the play field in the North Basin will be considered as a target surface as a new pervious surface. It should be noted, that the play field will be hydrologically modeled as 50% impervious and 50% grass for flow control mitigation since the field is an underdrain system and will be atop of the proposed detention facility and flow percolate vertically through a sand and aggregate subbase directly to the detention facility below. The detention facility will be an open top system with lining on the bottom and sides. The majority of the landscape improvements will be amended as lawn area which are in areas where the existing site was non-native lawn. 3. Replaced impervious surface that is not fully dispersed as specified in Appendix C on a non- redevelopment project in which the total of new plus replaced impervious surface is 5,000 square feet or more, OR new pervious surface is ¾ acre or more. Interpretation: Replaced impervious surfaces that are not fully dispersed will be considered target surfaces. 4. Replaced impervious surface that is not fully dispersed on a transportation redevelopment project in which new impervious surface is 5,000 square feet or more and totals 50% or more of the existing impervious surface within the project limits. Interpretation: Since the project is not a transportation redevelopment project, this item does not apply to this project. 5. Replaced impervious surface that is not fully dispersed as specified in Appendix C, on a parcel redevelopment project in which the total of new plus replaced impervious surface is 5,000 square feet or more and whose valuation of proposed improvements (including interior improvements and excluding required mitigation improvements) exceeds 50% of the assessed value of the existing site improvements. Interpretation: Since the project is a new development, this item does not apply to this project. As determined above, new plus replaced impervious surfaces, and new pervious surfaces not fully dispersed are considered the “target surface” requiring flow control mitigation and BMPs. Water Quality Treatment Standards The treatment goal for facility options in the Enhanced Basic WQ Menu is to accomplish better removal of heavy metals and potentially other toxic materials than can be achieved by basic treatment, while still meeting the basic treatment goal of 80% TSS removal. The specific target performance is > 30% reduction of dissolved copper and > 60% removal of dissolved zinc. Similarly, to the Flow Control Standards section above, Section 1.2.8.1 of the 2017 RSWDMA states that pollution-generating new plus replaced impervious surfaces, and new pervious surfaces not fully dispersed are considered the “target surface” requiring water quality treatment. Conveyance System Capacity Standards The proposed conveyance systems will be designed to convey at a minimum the 25-year peak flow rate from the tributary developed area. LPD Engineering PLLC Page 10 Renton Elementary School #16 Preliminary Technical Information Report, January 8, 2021 Flow Control BMPs Per Core Requirement #9, the project site proposed more than 2,000 SF of new plus replaced impervious surfaces which will require an evaluation of BMP feasibility for all target surfaces. Per section 1.2.9.2 of the 2017 RSWDMA, this project will be subject to Large Lot BMP Requirements since the project site is larger than 22,000 SF. For each drainage basin, the feasibility of on-site BMPs must be evaluated for each BMP listed in Section 1.2.9.2.2 of the RSWDMA. Due to the fill and glacial till found on the project site, there is no suitable stormwater infiltration receptor for infiltration BMPs. For these reasons, the LID performance standard cannot be achieved. Below is the alternate FCBMP list approach for the site and frontage improvements within all three drainage basins. North and South Basin BMP Evaluation: 1. Full Dispersion: Full dispersion of runoff from target surfaces is not feasible for both the site area and road frontage according to Section C.2.1.1 of the KCSWDM due to the limited native vegetated surface downstream of each of these areas on site. 2. Full Infiltration of Roof Runoff: Per the geotechnical report, the site soils consist of fill and lodgment till. Fill soils are not suitable as a stormwater infiltration receptor. The lodgment till is very dense and silty, and the infiltration potential of lodgment till is very low. Storm water infiltration using lodgment till as the receptor horizon is not recommended by the Geotechnical Engineer. 3. Since the target impervious surfaces could not be mitigated by Requirements 1 and 2 above, the following has been reviewed and implemented where feasible: • Full Infiltration: Full infiltration of runoff from target surfaces is not feasible. As stated above: fill soils are not suitable as a stormwater infiltration receptor; and infiltration with lodgment till as the receptor horizon is not recommended by the Geotechnical Engineer. • Limited Infiltration: As stated above: fill soils are not suitable as a stormwater infiltration receptor; and infiltration with lodgment till as the receptor horizon is not recommended by the Geotechnical Engineer. Therefore, limited infiltration is considered infeasible. • Bioretention: Per Section C.2.6, a bioretention facility without underdrains is considered infeasible as stated above due to: fill soils are not suitable as a stormwater infiltration receptor; and infiltration with lodgment till as the receptor horizon is not recommended by the Geotechnical Engineer. Underdrains are not permitted by the City to meet Core Requirement #9. • Permeable Pavement: Based on other completed field projects in King County, the natural grass turf field surface has been considered to be a flow control BMP since this surface functions similarly to a pervious pavement surface. Rainfall that lands on the field is unable to be collected at the surface since it percolates vertically through the surface into the base permeable aggregate layers. Therefore, the flow control BMP for the field’s surface is the aggregate base layers, which slow the release of stormwater to the point of discharge. The total pervious synthetic field area that is considered a flow control BMP is 34,020 square feet. 4. Basic Dispersion: is not feasible to be used as BMP per Section C.2.4 of the RSWDMA due to the limited vegetative flow path downstream of the target surfaces. Wetland Basin BMP Evaluation LPD Engineering PLLC Page 11 Renton Elementary School #16 Preliminary Technical Information Report, January 8, 2021 1. Full Dispersion: The project proposes to disperse approximately 21,170 SF of impervious surfaces by utilizing gravel dispersion trenches. A fully dispersed surface conforms to the BMP strategy detailed in Appendix C, Section C.2.1 of the RCSWDMA. The design criteria for full dispersion is further described in the Flow Control Analysis and Design section of this report. 4. Permeable Pavement: The fire lane on the west side of the proposed building is proposed as a grass-pave surface totaling 8,550 SF. This modular grid pavement system will have grass planted in the openings within the grid material. The increased water storage provided in the grid soil and base, and the increased evapotranspiration provided by the grass with attenuate runoff. Flow Control Analysis and Design As previously mentioned, the project is required to meet the Level 2 Flow Control standard, for which the project must match developed discharge durations to predeveloped durations for the range of predeveloped discharge rates from 50% of the 2-year peak flow up to the full 50-year peak flow and matches historic 2- and 10-year peaks. Per the RSWDMA, the predeveloped conditions must model the target surfaces as historic site conditions (forested) in order to reasonably anticipate development- induced problems. The majority of the site which includes the asphalt surfaces, concrete surfaces, and roof will be considered to be 100% impervious surfaces. The play field will be considered as 50% impervious and 50% grass. The grass landscape areas will be considered as 100% pervious surfaces. The grass-paved fire lane will be a grass modular grid pavement and will be considered as 100% pervious per the RSWDMA Table 1.2.3.A. Stormwater modeling was conducted using the MGSFlood Version 4, an approved continuous-modeling software by the RSWDMA. The proposed project will be divided into three basins: South Basin, North Basin, and Wetland Basin. Refer to Figure 4 – Proposed Conditions for a clear delineation of drainage basins. South Basin South Basin Target Surfaces to Flow Control Facility The proposed StormTech detention facility will consist of SC-740 chambers within a gravel basin, which will utilize both the storage within the chambers and also the void space within the gravel basin for stormwater detention. The StormTech chambers and gravel basin have a non-uniform change in storage volume as the stage height increases. The StormTech chambers and gravel basin have a non- uniform change in storage volume as the stage height increases. The minimum design standards for the SC-740 chamber require a 30-inch chamber, 6-inches gravel below and 6-inches gravel above the chamber, which were the parameters used in this design. Around the perimeter of the chambers, a 12- inch gravel section will be used, although in some areas there will be extra gravel to accommodate bends, manifolds, and access structures. A flow control structure will be installed that will attenuate stormwater outflow and utilize the storage within the chambers and its surrounding permeable gravel basin. The required storage volume of the detention system was found to be 15,300 cubic feet, with a live storage depth of 2-ft. The designed StormTech Facility will have a slightly larger storage volume to accommodate any minor site changes prior to the Building Permit submittal. A full summary of areas and MGSFlood Output for the South Basin can be found in Appendix B of this report. Please note, the model uses a standard detention pond to conservatively size a Stormtech LPD Engineering PLLC Page 12 Renton Elementary School #16 Preliminary Technical Information Report, January 8, 2021 Facility. A stage-storage elevation table will be used for the Building Permit submittal for a more accurate size. South Basin Bypass Target Surfaces For the South Basin, the project includes bypass areas from both on-site improvements and off-site improvements that cannot be gravity-drained to the detention facility. On-site runoff bypass area includes driveway entry and associated walkways. Offsite runoff includes the sidewalk improvements within Chelan Avenue NE. Bypass area totals 3,055 SF of impervious surface. All criteria per Section 1.2.3.2.E of the King County manual the following criteria has been met for the bypass area. The project proposes to waive the Item #5 requirement of Section 1.2.3.2.E using the following criteria: 1. The existing conditions 100-year peak discharge from the area of bypassed target surfaces is increased by no more than 0.15cfs for the 15-minute time step. MGSflood output for calculations of the bypass area have been provided in Appendix B. Below is a table summarizing the flow rate results: Table 2 – Net Peak Flow Rates for Bypass Area of South Basin Peak Runoff Rates for Project Work Area Storm Event Existing Conditions Proposed Conditions Delta 100-yr 0.144 cfs 0.155 cfs 0.011cfs 2. Flow Control BMPs must be applied to bypass target surfaces per Appendix C. After applying the feasibility to each Flow Control BMP to the bypass target surfaces, all BMPs were found to be infeasible. Refer to the Flow Control BMP section of this report. North Basin North Basin Target Surfaces to Flow Control Facility The proposed StormTech detention facility will consist of MC-350 chambers within a gravel basin, which will utilize both the storage within the chambers and also the void space within the gravel basin for stormwater detention. The StormTech chambers and gravel basin have a non-uniform change in storage volume as the stage height increases. The StormTech chambers and gravel basin have a non- uniform change in storage volume as the stage height increases. The minimum design standards for the MC-3500 chamber require a 45-inch chamber, 9-inches gravel below and 12-inches gravel above the chamber, which were the parameters used in this design. Around the perimeter of the chambers, a 12- inch gravel section will be used, although in some areas there will be extra gravel to accommodate bends, manifolds, and access structures. A flow control structure will be installed that will attenuate stormwater outflow and utilize the storage within the chambers and its surrounding permeable gravel basin. LPD Engineering PLLC Page 13 Renton Elementary School #16 Preliminary Technical Information Report, January 8, 2021 The required storage volume of the detention system was found to be 73,000 cubic feet, with a live storage depth of 4-ft. The designed StormTech Facility will have a slightly larger storage volume to accommodate any minor site changes prior to the Building Permit submittal. A full summary of areas and MGSFlood Output for the South Basin can be found in Appendix B of this report. Please note, the model uses a standard detention pond to conservatively size a Stormtech Facility. A stage-storage elevation table will be used for the Building Permit submittal for a more accurate size. North Basin Bypass Target Surfaces For the North Basin, the project includes bypass areas from both on-site improvements and off-site improvements that cannot be gravity-drained to the detention facility. On-site runoff bypass area includes the three driveway entries accessing Duvall Avenue NE as well as the gravel access maintenance road accessing NE 12th Street. Offsite runoff includes the sidewalk improvements and queueing lane within Duvall Avenue NE. Bypass area totals 10,190 SF of impervious surface. All criteria per Section 1.2.3.2.E of the King County manual the following criteria has been met for the bypass area. The project proposes to waive the Item #5 requirement of Section 1.2.3.2.E using the following criteria: 1. The existing conditions 100-year peak discharge from the area of bypassed target surfaces is increased by no more than 0.15cfs for the 15-minute time step. MGSflood output for calculations of the bypass area have been provided in Appendix B. Below is a table summarizing the flow rate results: Table 2 – Net Peak Flow Rates for Bypass Area of North Basin Peak Runoff Rates for Project Work Area Storm Event Existing Conditions Proposed Conditions Delta 100-yr 0.181 cfs 0.289 cfs 0.11 cfs 2. Flow Control BMPs must be applied to bypass target surfaces per Appendix C. After applying the feasibility to each Flow Control BMP to the bypass target surfaces, all BMPs were found to be infeasible. Refer to the Flow Control BMP section of this report. Wetland Basin Wetland Basin Non-Target Surfaces to be Fully Dispersed A full summary of areas for the Wetland Basin can be found in Appendix B of this report. Full Dispersion: As mentioned previously, in the Wetland Basin, the majority of new and replaced impervious surfaces will be fully dispersed. Full dispersion was evaluated using the minimum design requirements per Section C.2.1 of the 2017 RSWDMA. These requirements are outlined and addressed below: LPD Engineering PLLC Page 14 Renton Elementary School #16 Preliminary Technical Information Report, January 8, 2021 1. The total area of impervious surface being fully dispersed must be no more than 15% of the total area of native vegetated surface being preserved by a City-approved recorded tract, easement, or covenant within the same threshold discharge area. The total area of impervious surface plus nonnative pervious surface being fully dispersed must be no more than 35% of a threshold discharge area. Response: The total native vegetated retention area is approximately 155,520 SF, and the total impervious area being fully dispersed is approximately 21,170 SF, which is equal to 13.6% of the native vegetated surface. This under the required 15% in order to allow for any minor changes during construction. The total impervious plus the replaced non-native pervious surface being fully dispersed is approximately 42,740 SF, which is equal to 27.5% of the total native retention area. Thus, this requirement is met. 2. The runoff from a fully dispersed surface must be discharged using one of the following dispersion devices in accordance with the design specifications and maximum area of fully dispersed surface for each device as set forth in Sections C.2.1.3 through C.2.1.6. Response: Runoff from the fully dispersed surfaces will be discharged using gravel filled dispersion trenches as specified in section C.2.1.5 of the RSWDMA. Dispersion trenches will be 50-ft trenches with notch board. See the design drawings and area calculations of Appendix B for further details of the dispersion trenches. 3. A native vegetated flowpath segment of at least 100 feet in length (25 feet for sheet flow from a non-native pervious surface) must be available along the flowpath that runoff would follow upon discharge from a dispersion device listen in Minimum Requirement 2 above. Response: The native vegetated flowpath will be greater than 100 feet on-site. The average slope of the flow path is not steeper than 15%. The flow path is within the existing western wetland and complies with the minimum spacing requirements. 4. For sites with septic systems, the discharge of runoff from dispersion devices must not be upgradient of a drainfield. Response: There are no septic drainfield areas downstream of the proposed dispersion trenches. 5. Dispersion devices are not allowed in critical area buffers (unless approved by DPER) or on slopes steeper than 20%. Response: No dispersion devices will be located within critical area buffers or slopes steeper than 20%. 6. Dispersion devices are not allowed within 50 feet of a steep slope hazard area, erosion hazard area, or landslide hazard area. Response: Per the King County iMap, there are no steep slope, erosion, or landslide hazard areas located on the site or within 50 feet of the dispersion devices. 7. Dispersion devices proposed on slopes steeper than 15% must be approved by a geotechnical engineer or engineering geologist unless otherwise approved by the CED. Response: The proposed dispersion devices will not be located on slopes steeper than 15%. 8. Dispersion devices proposed near slopes steeper than 15% must be approved by a geotechnical engineer or engineering geologist unless otherwise approved by the DPER staff geologist if the LPD Engineering PLLC Page 15 Renton Elementary School #16 Preliminary Technical Information Report, January 8, 2021 facility is located within a setback from the top of slope equal to the total vertical height of the slope area that is steeper than 15%. The geotechnical analysis must consider cumulative impacts from the project and surrounding areas under full built-out conditions. Response: No dispersion devices will be located within the top of slope setback for slopes steeper than 15%. 9. Dispersion devices that direct runoff toward a slope steeper than 15% may require evaluation and approval of the proposal by a geotechnical engineer or engineering geologist as determined by DPER. The geotechnical analysis must consider cumulative impacts from the project and surrounding areas under full built-out conditions. Response: No runoff from the dispersion devices will be directed towards slopes steeper than 15%. 10. Dispersion devices proposed within 200 feet of a steep slope hazard area, erosion hazard area, or landslide hazard area must be approved by a geotechnical engineer or engineering geologist unless otherwise approved by the DPER staff geologist. The geotechnical analysis must consider cumulative impacts from the project and surrounding areas under full built-out conditions. Response: All dispersion devices will be on-site, and per the King County iMap, there are no steep slope, erosion, or landslide hazard areas located on the site or within 200 feet of the dispersion devices. 11. The dispersion of runoff must not create flooding or erosion impacts as determined by the DPER. If runoff is discharged toward a landslide hazard area, erosion hazard area, or steep slope hazard area, DPER may require evaluation and approval of the proposal by a geotechnical engineer or engineering geologist. The geotechnical analysis must consider cumulative impacts from the project and surrounding areas under full built-out conditions. Response: The dispersion of runoff will not create flooding or erosion impacts. The dispersal of stormwater will flow into a healthy vegetated area that is not within an erosion hazard area and has slopes less than 15%. Thus, it has been determined that full dispersion is feasible. Developed surfaces conforming to this strategy are considered to have a negligible impact downstream, and therefore, may be modeled as forest and are not subject to flow control or water quality facility requirements. Refer to Figure 4 – Proposed Conditions for a visual representation of the proposed dispersion measures. Full dispersion evaluation calculations are attached in Appendix B of this report. Wetland Basin Target Surfaces Flow Control Exception #2 The total on-site improvements not fully dispersed total 4,285 SF. Due to the small amount of target surfaces, the Wetland Basin is not required to provide a flow control facility. Item #2 of Exceptions from Section 1.2.3.1.B states that facility requirements in Flow Control Duration Standard Areas are waived for any threshold discharge area in which there is no more than a 0.15-cfs difference (when modeled using 15-minute time step) in the sum of developed 100-year peak flows for those target surfaces subject to this requirement and the sum of historic site conditions 100-year peak flows (modeled using the same time step unit) for the same surface areas. Based on the amount of new plus replaced impervious surfaces, the modeled condition of basin improvements will meet this exception as shown in Table 1 and will not be required to provide flow control. The MGSFlood output is included in Appendix B. LPD Engineering PLLC Page 16 Renton Elementary School #16 Preliminary Technical Information Report, January 8, 2021 Table 1 – Net Peak Flow Rates for Discharge from Wetland Basin Peak Runoff Rates Storm Event Historic Conditions Proposed Conditions Delta 100-yr 0.273 cfs 0.294 cfs 0.021 cfs Water Quality System As mentioned previously, the project proposes more than 5,000 SF of pollution generating surface in a Basic Water Quality Treatment area, and triggers Enhanced Basic Water Quality. Water quality treatment is required for the play field, bus lane, and parking lot as they are considered to be pollution- generating surfaces by the 2017 RSWDMA. All the other impervious surfaces such as the roof, walkways, and gated fire apparatus are non-pollution generating. The proposed water quality facility will be a Modular Wetland System, which does have General Use Level Designation (GULD) approval by Ecology for enhanced treatment. This approval will be provided for the Building Permit submittal in Appendix B for reference. The project does involve detention facilities, which means that per section 4.1.2 of Volume V of the Ecology Manual, the water quality design flow rate shall be the 2-year flow rate discharged by the detention facility. Therefore, a single Modular Wetland System will be used downstream of both the South Basin detention system as well as the North Basin detention system prior discharge from site. Refer to MGSFlood output in Appendix B for the 2-year release rate from the detention system (water quality design flow). Sizing of the Modular Wetland System will be conducted by the Manufacturer, BioClean for the Building Permit submittal. Details and sizing letter from BioClean will be added as reference in Appendix B for the Building Permit submittal. In addition, the frontage improvement within Duvall Avenue NE will require water quality treatment for drive entrance and extended queueing lane at the southeast corner of the site. Based on preliminary discussions with the City, the City plans to improve the roadway improvements along Duvall Avenue NE. To address water quality treatment, The City plans to install Filterra facilities along the west side of Duvall Avenue NE. Coordination with the City to coordinate the school frontage improvements with the roadway improvements is ongoing. It is assumed the school project will need to provide one Filterra facility for the queueing lane extension for Enhanced Basic Water Quality Treatment. Details and sizing letter from Contech will be added as reference in Appendix B for the Building Permit submittal. SECTION 5 – CONVEYANCE SYSTEMS ANALYSIS AND DESIGN An analysis of the onsite conveyance system was performed for the South Basin and the North Basin. Refer to the Conveyance Analysis Spreadsheet and accompanying MGS Flood reports included in Appendix B. Per section 1.2.4.1 of the 2017 RSWDMA, the conveyance system shall be designed to accommodate the 25-year storm event. Both the 25-year and 100-year peak runoff rates were compared LPD Engineering PLLC Page 17 Renton Elementary School #16 Preliminary Technical Information Report, January 8, 2021 with the full-flow capacity of the conveyance pipe. The peak runoff rates from each of the tributary areas were determined using MGS Flood with 15-minute time steps. The full flow capacity of the conveyance pipe was determined using Manning’s equation. South Basin For the 12-inch outlet from detention (Pipe Run #1), the tributary area to StormTech chamber was entered into the model, as in the flow control model. The 12-inch pipe with Manning’s n value of 0.011, at 0.5% slope yields full-flow capacity of 2.99 cubic feet per second (cfs). The 25-year and the 100-year peak flows from WWHM were found to have adequate capacity. North Basin For the 12-inch outlet from detention (Pipe Run #2), the tributary area to StormTech chamber was entered into the model, as in the flow control model. The 12-inch pipe with Manning’s n value of 0.011, at 0.5% slope yields full-flow capacity of 2.99 cubic feet per second (cfs). The 25-year and the 100-year peak flows from WWHM were found to have adequate capacity. SECTION 6 – SPECIAL REPORTS AND STUDIES A geotechnical report has been prepared by Associated Earth Sciences, Inc. dated November 21, 2019. This report is provided under separate cover. A wetland delineation report has been prepared by The Watershed Company, dated November 26, 2019. SECTION 7 – OTHER PERMITS Coverage under the Construction Stormwater General Permit through the Department of Ecology will be required for the project because it disturbs over one (1) acre of land area. The NOI and public noticing required for this permit will be completed later in the design process, prior to construction. SECTION 8 – CSWPPP ANALYSIS AND DESIGN The construction storm water pollution prevention plan (CSWPPP) consists of the TESC plan in the drawing set and a Stormwater Pollution Prevention Plan narrative (SWPPP) based upon Ecology’s Construction Stormwater General Permit SWPPP Template which will be provided for the Building Permit Submittal. The Stormwater Pollution Prevention and Spill (SWPPS) report will also be provided for the Building Permit submittal. The TESC plan includes temporary sediment settling ponds, sized using the methodology from the 20167 RSWDMA. A copy of the Sediment Facility Sizing Calculations worksheet and the associated output from MGS Flood used for the sediment tank sizing are included in Appendix B. LPD Engineering PLLC Page 18 Renton Elementary School #16 Preliminary Technical Information Report, January 8, 2021 SECTION 9 – BOND QUANTITIES, FACILITY SUMMARIES, AND DECLARATION OF COVENANT A Bond Quantities Worksheet is not expected to be required by the City of Renton, as the owner is the Renton School District, which is a public agency; no bonding is required. SECTION 10 – OPERATIONS AND MAINTENANCE MANUAL The Operations and Maintenance Manual will be provided for the Building Permit submittal in Appendix D of this report. This will include maintenance recommendations associated with the conveyance pipes, catch basins, flow control structure, StormTech chamber detention facility, the Modular Wetland System (water quality facility), and the Filterra (water quality facility). FIGURES Figure 1: TIR Worksheet Figure 2: Vicinity Map (To Be Provided for Building Permit Submittal) Figure 3: Existing Conditions Figure 4: Proposed Conditions Figure 5: Soils Map (To Be Provided for Building Permit Submittal) Figure 6: Downstream Drainage Map (To Be Provided for Building Permit Submittal) KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL TECHNICAL INFORMATION REPORT (TIR) WORKSHEET Part 1 PROJECT OWNER AND PROJECT ENGINEER Part 2 PROJECT LOCATION AND DESCRIPTION Project Owner ___________________________ Phone _________________________________ Address _______________________________ _______________________________________ Project Engineer _________________________ Company ______________________________ Phone _________________________________ Project Name _________________________ DPER Permit # ________________________ Location Township ______________ Range ________________ Section ________________ Site Address __________________________ _____________________________________ Part 3 TYPE OF PERMIT APPLICATION Part 4 OTHER REVIEWS AND PERMITS Landuse (e.g.,Subdivision / Short Subd. / UPD) Building (e.g.,M/F / Commercial / SFR) Clearing and Grading Right-of-Way Use Other _______________________ DFW HPA COE 404 DOE Dam Safety FEMA Floodplain COE Wetlands Other ________ Shoreline Management Structural Rockery/Vault/_____ ESA Section 7 Part 5 PLAN AND REPORT INFORMATION Technical Information Report Site Improvement Plan (Engr. Plans) Type of Drainage Review (check one): Date (include revision dates): Date of Final: Full Targeted Simplified Large Project Directed __________________ __________________ __________________ Plan Type (check one): Date (include revision dates): Date of Final: Full Modified Simplified __________________ __________________ __________________ Part 6 SWDM ADJUSTMENT APPROVALS Type (circle one): Standard / Experimental / Blanket Description: (include conditions in TIR Section 2) ____________________________________________________________________________________ ____________________________________________________________________________________ ____________________________________________________________________________________ Approved Adjustment No. ______________________ Date of Approval: ______________________ 2016 Surface Water Design Manual 4/24/2016 1 KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL TECHNICAL INFORMATION REPORT (TIR) WORKSHEET Part 7 MONITORING REQUIREMENTS Monitoring Required: Yes / No Start Date: _______________________ Completion Date: _______________________ Describe: _________________________________ _________________________________________ _________________________________________ Re: KCSWDM Adjustment No. ________________ Part 8 SITE COMMUNITY AND DRAINAGE BASIN Community Plan : ____________________________________________________________________ Special District Overlays: ______________________________________________________________ Drainage Basin: _____________________________________________________________________ Stormwater Requirements: ____________________________________________________________ Part 9 ONSITE AND ADJACENT SENSITIVE AREAS River/Stream ________________________ Lake ______________________________ Wetlands ____________________________ Closed Depression ____________________ Floodplain ___________________________ Other _______________________________ _______________________________ Steep Slope __________________________ Erosion Hazard _______________________ Landslide Hazard ______________________ Coal Mine Hazard ______________________ Seismic Hazard _______________________ Habitat Protection ______________________ _____________________________________ Part 10 SOILS Soil Type _________________ _________________ _________________ _________________ Slopes _________________ _________________ _________________ _________________ Erosion Potential _________________ _________________ _________________ _________________ High Groundwater Table (within 5 feet) Other ________________________________ Sole Source Aquifer Seeps/Springs Additional Sheets Attached 2016 Surface Water Design Manual 4/24/2016 2 KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL TECHNICAL INFORMATION REPORT (TIR) WORKSHEET Part 11 DRAINAGE DESIGN LIMITATIONS REFERENCE Core 2 – Offsite Analysis_________________ Sensitive/Critical Areas__________________ SEPA________________________________ LID Infeasibility________________________ Other________________________________ _____________________________________ LIMITATION / SITE CONSTRAINT _______________________________________ _______________________________________ _______________________________________ _______________________________________ _______________________________________ _______________________________________ Additional Sheets Attached Part 12 TIR SUMMARY SHEET (provide one TIR Summary Sheet per Threshold Discharge Area) Threshold Discharge Area: (name or description) Core Requirements (all 8 apply): Discharge at Natural Location Number of Natural Discharge Locations: Offsite Analysis Level: 1 / 2 / 3 dated:__________________ Flow Control (include facility summary sheet) Level: 1 / 2 / 3 or Exemption Number ____________ Flow Control BMPs _______________________________ Conveyance System Spill containment located at: _________________________ Erosion and Sediment Control / Construction Stormwater Pollution Prevention CSWPP/CESCL/ESC Site Supervisor: _____________________ Contact Phone: _________________________ After Hours Phone: _________________________ Maintenance and Operation Responsibility (circle one): Private / Public If Private, Maintenance Log Required: Yes / No Financial Guarantees and Liability Provided: Yes / No Water Quality (include facility summary sheet) Type (circle one): Basic / Sens. Lake / Enhanced Basic / Bog or Exemption No. ______________________ Landscape Management Plan: Yes / No Special Requirements (as applicable): Area Specific Drainage Requirements Type: CDA / SDO / MDP / BP / LMP / Shared Fac. / None Name: ________________________ Floodplain/Floodway Delineation Type (circle one): Major / Minor / Exemption / None 100-year Base Flood Elevation (or range): ______________ Datum: Flood Protection Facilities Describe: 2016 Surface Water Design Manual 4/24/2016 3 KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL TECHNICAL INFORMATION REPORT (TIR) WORKSHEET Part 12 TIR SUMMARY SHEET (provide one TIR Summary Sheet per Threshold Discharge Area) Source Control (comm ercial / industrial land use) Describe land use: Describe any structural controls: Oil Control High-use Site: Yes / No Treatment BMP: ________________________________ Maintenance Agreement: Yes / No with whom? ____________________________________ Other Drainage Structures Describe: Part 13 EROSION AND SEDIMENT CONTROL REQUIREMENTS MINIMUM ESC REQUIREMENTS DURING CONSTRUCTION Clearing Limits Cover Measures Perimeter Protection Traffic Area Stabilization Sediment Retention Surface Water Collection Dewatering Control Dust Control Flow Control Protection of Flow Control BMP Facilities (existing and proposed) Maintain BMPs / Manage Project MINIMUM ESC REQUIREMENTS AFTER CONSTRUCTION Stabilize exposed surfaces Remove and restore Temporary ESC Facilities Clean and remove all silt and debris, ensure operation of Permanent Facilities, restore operation of Flow Control BMP Facilities as necessary Flag limits of SAO and open space preservation areas Other ______________________ Part 14 STORMWATER FACILITY DESCRIPTIONS (Note: Include Facility Summary and Sketch) Flow Control Type/Description Water Quality Type/Description Detention Infiltration Regional Facility Shared Facility Flow Control BMPs Other ________________ ________________ ________________ ________________ ________________ ________________ Vegetated Flowpath Wetpool Filtration Oil Control Spill Control Flow Control BMPs Other ________________ ________________ ________________ ________________ ________________ ________________ ________________ 2016 Surface Water Design Manual 4/24/2016 4 KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL TECHNICAL INFORMATION REPORT (TIR) WORKSHEET Part 15 EASEMENTS/TRACTS Part 16 STRUCTURAL ANALYSIS Drainage Easement Covenant Native Growth Protection Covenant Tract Other ___________________________ Cast in Place Vault Retaining Wall Rockery > 4’ High Structural on Steep Slope Other ______________________________ Part 17 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 attached Technical Information Report. To the best of my knowledge the information provided here is accurate. Signed/Date 2016 Surface Water Design Manual 4/24/2016 5 1932 1st Ave,Suite 201,Seattle, WA 98101p. 206.725.1211f. 206.973.5344www.lpdengineering.comengineering pllc2018 LPD Engineering PLLC©RENTON ELEMENTARY SCHOOL #163EXISTING CONDITIONS 1932 1st Ave,Suite 201,Seattle, WA 98101p. 206.725.1211f. 206.973.5344www.lpdengineering.comengineering pllc2020 LPD Engineering PLLC©RENTON ELEMENTARY SCHOOL #164PROPOSED CONDITIONS APPENDIX A Design Drawings (CUP plans included) IN COMPLIANCE WITH CITY OF RENTON STANDARDS IN COMPLIANCE WITH CITY OF RENTON STANDARDS IN COMPLIANCE WITH CITY OF RENTON STANDARDS IN COMPLIANCE WITH CITY OF RENTON STANDARDS IN COMPLIANCE WITH CITY OF RENTON STANDARDS IN COMPLIANCE WITH CITY OF RENTON STANDARDS IN COMPLIANCE WITH CITY OF RENTON STANDARDS IN COMPLIANCE WITH CITY OF RENTON STANDARDS IN COMPLIANCE WITH CITY OF RENTON STANDARDS IN COMPLIANCE WITH CITY OF RENTON STANDARDS IN COMPLIANCE WITH CITY OF RENTON STANDARDS IN COMPLIANCE WITH CITY OF RENTON STANDARDS IN COMPLIANCE WITH CITY OF RENTON STANDARDSSECTION A-ASECTION B-B IN COMPLIANCE WITH CITY OF RENTON STANDARDSSECTION C-C IN COMPLIANCE WITH CITY OF RENTON STANDARDSSECTION D-DMATCHLINE - SEE ABOVEMATCHLINE - SEE BELOW IN COMPLIANCE WITH CITY OF RENTON STANDARDS IN COMPLIANCE WITH CITY OF RENTON STANDARDS IN COMPLIANCE WITH CITY OF RENTON STANDARDS IN COMPLIANCE WITH CITY OF RENTON STANDARDS IN COMPLIANCE WITH CITY OF RENTON STANDARDS IN COMPLIANCE WITH CITY OF RENTON STANDARDS IN COMPLIANCE WITH CITY OF RENTON STANDARDS IN COMPLIANCE WITH CITY OF RENTON STANDARDS IN COMPLIANCE WITH CITY OF RENTON STANDARDS IN COMPLIANCE WITH CITY OF RENTON STANDARDS IN COMPLIANCE WITH CITY OF RENTON STANDARDS IN COMPLIANCE WITH CITY OF RENTON STANDARDS APPENDIX B Design Calculations and Supporting Information RENTON ES #16 TOTAL AREA SUMMARY NORTH BASIN Pervious [SF] Impervious [SF] [AC] Total Impervious 173,410 3.981 Total Pervious (Modeled Grass)78,975 1.813 Total NORTH Basin 5.794 SOUTH BASIN Pervious [SF] Impervious [SF] [AC] Total Impervious 27,975 0.642 Total Pervious (Modeled Grass)15,880 0.365 Total SOUTH Basin 1.007 WETLAND BASIN Pervious [SF] Impervious [SF] [AC] Total Impervious 22,930 0.526 Total Pervious (Modeled Grass)21,570 0.495 Total Pervious (Modeled Forested)155,520 3.570 Total WETLAND Basin 4.592 Total Impervious 224,315 5.150 Total Pervious (Modeled Forested)155,520 3.570 Total Pervious (Modeled Grass)116,425 2.673 252,385 43,855 200,020 RENTON ES #16 Areas Spreadsheet ‐ SOUTH BASIN Modeled Proposed Conditions SOUTH BASIN: Area Summary Pervious [SF] Impervious [SF] [AC] Landscape Area 15,880 0.365 PGIS 25,070 0.576 NPGIS 2,905 0.067 Total Impervious 27,975 0.642 Total Pervious (Modeled Grass)15,880 0.365 Total Basin Disturbed 1.007 SUBBASIN: To Detention and WQ Facility Pervious [SF] Impervious [SF] [AC] PGIS 23,340 0.536 NPGIS 1,580 0.036 Landscape Area 10,195 0.234 Total Impervious 24,920 0.572 Total Pervious (Modeled Grass)10,195 0.234 Total Area 0.806 SUBBASIN: To Chelan Ave NE (Bypass) Pervious [SF] Impervious [SF] [AC] PGIS 1,730 0.040 NPGIS 1,325 0.030 Landscape Area 5,685 0.131 Forest 0.000 Total Impervious 3,055 0.070 Total Pervious (Modeled Grass)5,685 0.131 Total Area 0.201 43,855 35,115 8,740 RENTON ES #16 Areas Spreadsheet ‐ NORTH BASIN Modeled Proposed Conditions NORTH BASIN: Area Summary Pervious [SF] Impervious [SF] [AC] Play Field (50% Grass/50% Impervious)17,010 17,010 0.390 Landscape Area 61,965 1.422 PGIS 45,400 1.042 NPGIS 68,725 1.578 Building Roof 42,275 0.970 Total Impervious 173,410 3.981 Total Pervious (Modeled Grass)78,975 1.813 Total Pervious (Modeled Forested)0 0.000 Total Basin Disturbed 5.794 SUBBASIN: to Detention and WQ Facility Pervious [SF] Impervious [SF] [AC] Landscape Area 28,490 0.654 PGIS 39,920 0.916 NPGIS 62,310 1.430 Building Roof 42,275 0.970 Play Field (50% Grass/50% Impervious)17,010 17,010 0.390 Total Impervious 161,515 3.708 Total Pervious (Modeled Grass)45,500 1.045 Total Area 4.752 SUBBASIN: Duvall Ave NE to WQ Facility Pervious [SF] Impervious [SF] [AC] PGIS 2,235 0.051 NPGIS 2,075 0.048 Landscape Area 1,880 0.043 Total Impervious 4,310 0.099 Total Pervious (Modeled Grass)1,880 0.043 Total Area 0.142 SUBBASIN: Duvall Ave NE Bypass Pervious [SF] Impervious [SF] [AC] PGIS 1,540 0.035 NPGIS 4,340 0.100 Landscape Area 9,435 0.217 Total Impervious 5,880 0.135 Total Pervious (Modeled Grass)9,435 0.217 Total Area 0.352 252,385 6,190 207,015 15,315 SUBBASIN: NE 12th Street Bypass Pervious [SF] Impervious [SF] [AC] PGIS 1,705 0.039 NPGIS 0.000 Landscape Area 22,160 0.509 Total Impervious 1,705 0.039 Total Pervious (Modeled Grass)22,160 0.509 Total Area 0.54823,865 RENTON ES #16 Areas Spreadsheet ‐ WETLAND BASIN Modeled Proposed Conditions WETLAND BASIN: Area Summary Pervious [SF] Impervious [SF] [AC] Grass Pave Fire Lane 100% Pervious 8,550 0.196 Landscape Area 13,020 0.299 Forested 155,520 3.570 NPGIS 9,540 0.219 Building Roof 13,390 0.307 Total Impervious 22,930 0.526 Total Impervious Surface Being Fully Dispersed 21,170 0.486 Total Pervious (Modeled Grass) (Non‐Native Non‐converted Lawn)21,570 0.495 Total Pervious (Modeled Forested)155,520 3.570 Total Basin 4.592 Total Native Growth Retention Area 3.570 Percentage of Impervious Surface Dispersed to Native Retention Area Percentage of Impervious Surface plus Non‐Native Pervious Dispersed to Native Retention Area SUBBASIN: Dispersion Gravel Trench A Two (2) 50 LF Trench with 120‐FT Flow Path Allow Tributary Impervious Surface = 12,000 SF Pervious [SF] Impervious [SF] [AC] Landscape Area 0.000 Grass Pave Fire Lane 1,910 0.000 NPGIS 4,060 0.093 Building Roof 6,660 0.153 Total Impervious 10,720 0.246 Total Pervious (Modeled Grass)1,910 0.044 Total Area 0.290 SUBBASIN: Dispersion Gravel Trench A Two (2) 50 LF Trench with 110‐FT Flow Path Allow Tributary Impervious Surface = 11,000 SF Pervious [SF] Impervious [SF] [AC] Landscape Area 0.000 Grass Pave Fire Lane 1,970 NPGIS 3,720 0.085 Building Roof 6,730 0.000 Total Impervious 10,450 0.240 Total Pervious (Modeled Grass)1,970 0.045 Total Area 0.285 SUBBASIN: Bypass Pervious [SF] Impervious [SF] [AC] Grass Pave Fire Lane 100% Pervious 5,520 0.127 Landscape Area 13,020 0.299 Forested 155,520 3.570 NPGIS 1,760 0.040 Building Roof 0.000 200,020 12,630 12,420 155,520 13.6% 27.5% Total Impervious 1,760 0.040 Total Pervious (Modeled Grass)174,060 3.996 Total Area 4.036175,820 ————————————————————————————————— MGS FLOOD PROJECT REPORT – FC, WQ, and Conveyance Analysis This model uses a standard detention pond to conservatively size a Stormtech Facility. A Stage-Storage Elevation table will be used for the Building Permit submittal for a more accurate size. Program Version: MGSFlood 4.50 Program License Number: 201410003 Project Simulation Performed on: 11/18/2020 4:55 PM Report Generation Date: 11/18/2020 5:02 PM ————————————————————————————————— Input File Name: South Basin Project Name: Renton ES #16 Analysis Title: WQ/Detention - South Basin Comments: ————————————————————————————————— ———————————————— PRECIPITATION INPUT ———————————————— Computational Time Step (Minutes): 15 Extended Precipitation Time Series Selected Climatic Region Number: 16 Full Period of Record Available used for Routing Precipitation Station : 96004405 Puget East 44 in_5min 10/01/1939-10/01/2097 Evaporation Station : 961044 Puget East 44 in MAP Evaporation Scale Factor : 0.750 HSPF Parameter Region Number: 1 HSPF Parameter Region Name : USGS Default ********** Default HSPF Parameters Used (Not Modified by User) *************** ********************** WATERSHED DEFINITION *********************** Predevelopment/Post Development Tributary Area Summary Predeveloped Post Developed Total Subbasin Area (acres) 0.806 0.806 Area of Links that Include Precip/Evap (acres) 0.000 0.000 Total (acres) 0.806 0.806 ----------------------SCENARIO: PREDEVELOPED Number of Subbasins: 1 ---------- Subbasin : South Basin ---------- -------Area (Acres) -------- Till Forest 0.806 ---------------------------------------------- Subbasin Total 0.806 ----------------------SCENARIO: POSTDEVELOPED Number of Subbasins: 1 ---------- Subbasin : To Detention/WQ ---------- -------Area (Acres) -------- Till Grass 0.234 Impervious 0.572 ---------------------------------------------- Subbasin Total 0.806 ************************* LINK DATA ******************************* ----------------------SCENARIO: PREDEVELOPED Number of Links: 0 ************************* LINK DATA ******************************* ----------------------SCENARIO: POSTDEVELOPED Number of Links: 1 ------------------------------------------ Link Name: Detention Vault Link Type: Structure Downstream Link: None Prismatic Pond Option Used Pond Floor Elevation (ft) : 100.00 Riser Crest Elevation (ft) : 103.00 Max Pond Elevation (ft) : 103.50 Storage Depth (ft) : 3.00 Pond Bottom Length (ft) : 85.0 Pond Bottom Width (ft) : 45.0 Pond Side Slopes (ft/ft) : L1= 3.00 L2= 3.00 W1= 3.00 W2= 3.00 Bottom Area (sq-ft) : 3825. Area at Riser Crest El (sq-ft) : 6,489. (acres) : 0.149 Volume at Riser Crest (cu-ft) : 15,309. (ac-ft) : 0.351 Area at Max Elevation (sq-ft) : 6996. (acres) : 0.161 Vol at Max Elevation (cu-ft) : 18,679. (ac-ft) : 0.429 Constant Infiltration Option Used Infiltration Rate (in/hr): 0.00 Riser Geometry Riser Structure Type : Circular Riser Diameter (in) : 18.00 Common Length (ft) : 0.020 Riser Crest Elevation : 103.00 ft Hydraulic Structure Geometry Number of Devices: 2 ---Device Number 1 --- Device Type : Circular Orifice Control Elevation (ft) : 100.00 Diameter (in) : 0.55 Orientation : Horizontal Elbow : No --- Device Number 2 --- Device Type : Vertical Rectangular Orifice Control Elevation (ft) : 102.00 Length (in) : 0.20 Height (in) : 12.00 Orientation : Vertical Elbow : No **********************FLOOD FREQUENCY AND DURATION STATISTICS******************* ----------------------SCENARIO: PREDEVELOPED Number of Subbasins: 1 Number of Links: 0 ----------------------SCENARIO: POSTDEVELOPED Number of Subbasins: 1 Number of Links: 1 ********** Link: Detention Vault ********** Link WSEL Stats WSEL Frequency Data(ft) (Recurrence Interval Computed Using Gringorten Plotting Position) Tr (yrs) WSEL Peak (ft) ====================================== 1.05-Year 101.024 1.11-Year 101.080 1.25-Year 101.241 2.00-Year 101.606 3.33-Year 101.886 5-Year 102.176 10-Year 102.469 25-Year 102.614 50-Year 102.683 100-Year 102.742 ***********Groundwater Recharge Summary ************* Recharge is computed as input to Perlnd Groundwater Plus Infiltration in Structures Total Predeveloped Recharge During Simulation Model Element Recharge Amount (ac-ft) ----------------------------------------------------------------------------------------------- Subbasin: South Basin 153.333 _____________________________________ Total: 153.333 Total Post Developed Recharge During Simulation Model Element Recharge Amount (ac-ft) ----------------------------------------------------------------------------------------------- Subbasin: To Detention/WQ 30.138 Link: Detention Vault 0.000 _____________________________________ Total: 30.138 Total Predevelopment Recharge is Greater than Post Developed Average Recharge Per Year, (Number of Years= 158) Predeveloped: 0.970 ac-ft/year, Post Developed: 0.191 ac-ft/year ***********Water Quality Facility Data ************* ----------------------SCENARIO: PREDEVELOPED Number of Links: 0 ----------------------SCENARIO: POSTDEVELOPED Number of Links: 1 ********** Link: Detention Vault ********** Basic Wet Pond Volume (91% Exceedance): 3026. cu-ft Computed Large Wet Pond Volume, 1.5*Basic Volume: 4539. cu-ft 2-Year Discharge Rate : 0.010 cfs 15-Minute Timestep, Water Quality Treatment Design Discharge On-line Design Discharge Rate (91% Exceedance): 0.09 cfs Off-line Design Discharge Rate (91% Exceedance): 0.05 cfs Infiltration/Filtration Statistics-------------------- Inflow Volume (ac-ft): 344.59 Inflow Volume Including PPT-Evap (ac-ft): 344.59 Total Runoff Infiltrated (ac-ft): 0.00, 0.00% Total Runoff Filtered (ac-ft): 0.00, 0.00% Primary Outflow To Downstream System (ac-ft): 344.53 Secondary Outflow To Downstream System (ac-ft): 0.00 Percent Treated (Infiltrated+Filtered)/Total Volume: 0.00% ***********Compliance Point Results ************* Scenario Predeveloped Compliance Subbasin: South Basin Scenario Postdeveloped Compliance Link: Detention Vault *** Point of Compliance Flow Frequency Data *** Recurrence Interval Computed Using Gringorten Plotting Position Predevelopment Runoff Postdevelopment Runoff Tr (Years) Discharge (cfs) Tr (Years) Discharge (cfs) ---------------------------------------------------------------------------------------------------------------------- 2-Year 2.073E-02 2-Year 1.023E-02 5-Year 3.322E-02 5-Year 1.519E-02 10-Year 4.332E-02 10-Year 2.696E-02 25-Year 5.955E-02 25-Year 3.443E-02 50-Year 7.488E-02 50-Year 3.827E-02 100-Year 7.945E-02 100-Year 4.179E-02 200-Year 0.127 200-Year 4.759E-02 500-Year 0.191 500-Year 5.531E-02 ** Record too Short to Compute Peak Discharge for These Recurrence Intervals **** Flow Duration Performance **** Excursion at Predeveloped 50%Q2 (Must be Less Than or Equal to 0%): -4.7% PASS Maximum Excursion from 50%Q2 to Q2 (Must be Less Than or Equal to 0%): -4.7% PASS Maximum Excursion from Q2 to Q50 (Must be less than 10%): -45.4% PASS Percent Excursion from Q2 to Q50 (Must be less than 50%): 0.0% PASS ------------------------------------------------------------------------------------------------- MEETS ALL FLOW DURATION DESIGN CRITERIA: PASS ------------------------------------------------------------------------------------------------- ————————————————————————————————— MGS FLOOD PROJECT REPORT – North Basin Bypass Analysis Program Version: MGSFlood 4.50 Program License Number: 201410003 Project Simulation Performed on: 11/19/2020 5:11 PM Report Generation Date: 11/19/2020 5:12 PM ————————————————————————————————— Input File Name: South Basin - bypass.fld Project Name: Renton ES #16 Analysis Title: Comments: ———————————————— PRECIPITATION INPUT ———————————————— Computational Time Step (Minutes): 15 Extended Precipitation Time Series Selected Climatic Region Number: 16 Full Period of Record Available used for Routing Precipitation Station : 96004405 Puget East 44 in_5min 10/01/1939-10/01/2097 Evaporation Station : 961044 Puget East 44 in MAP Evaporation Scale Factor : 0.750 HSPF Parameter Region Number: 1 HSPF Parameter Region Name : USGS Default ********** Default HSPF Parameters Used (Not Modified by User) *************** ********************** WATERSHED DEFINITION *********************** Predevelopment/Post Development Tributary Area Summary Predeveloped Post Developed Total Subbasin Area (acres) 0.201 0.201 Area of Links that Include Precip/Evap (acres) 0.000 0.000 Total (acres) 0.201 0.201 ----------------------SCENARIO: PREDEVELOPED Number of Subbasins: 1 ---------- Subbasin : South Basin ---------- -------Area (Acres) -------- Till Grass 0.151 Impervious 0.050 ---------------------------------------------- Subbasin Total 0.201 ----------------------SCENARIO: POSTDEVELOPED Number of Subbasins: 1 ---------- Subbasin : Bypass ---------- -------Area (Acres) -------- Till Grass 0.131 Impervious 0.070 ---------------------------------------------- Subbasin Total 0.201 ************************* LINK DATA ******************************* ----------------------SCENARIO: PREDEVELOPED Number of Links: 0 ************************* LINK DATA ******************************* ----------------------SCENARIO: POSTDEVELOPED Number of Links: 1 ------------------------------------------ Link Name: Basin POC Link Type: Copy Downstream Link: None **********************FLOOD FREQUENCY AND DURATION STATISTICS******************* ----------------------SCENARIO: PREDEVELOPED Number of Subbasins: 1 Number of Links: 0 ----------------------SCENARIO: POSTDEVELOPED Number of Subbasins: 1 Number of Links: 1 ***********Groundwater Recharge Summary ************* Recharge is computed as input to Perlnd Groundwater Plus Infiltration in Structures Total Predeveloped Recharge During Simulation Model Element Recharge Amount (ac-ft) ----------------------------------------------------------------------------------------------- Subbasin: South Basin 19.448 _____________________________________ Total: 19.448 Total Post Developed Recharge During Simulation Model Element Recharge Amount (ac-ft) ----------------------------------------------------------------------------------------------- Subbasin: Bypass 16.872 Link: Basin POC 0.000 _____________________________________ Total: 16.872 Total Predevelopment Recharge is Greater than Post Developed Average Recharge Per Year, (Number of Years= 158) Predeveloped: 0.123 ac-ft/year, Post Developed: 0.107 ac-ft/year ***********Water Quality Facility Data ************* ----------------------SCENARIO: PREDEVELOPED Number of Links: 0 ----------------------SCENARIO: POSTDEVELOPED Number of Links: 1 ********** Link: Basin POC ********** Infiltration/Filtration Statistics-------------------- Inflow Volume (ac-ft): 67.31 Inflow Volume Including PPT-Evap (ac-ft): 67.31 Total Runoff Infiltrated (ac-ft): 0.00, 0.00% Total Runoff Filtered (ac-ft): 0.00, 0.00% Primary Outflow To Downstream System (ac-ft): 67.31 Secondary Outflow To Downstream System (ac-ft): 0.00 Percent Treated (Infiltrated+Filtered)/Total Volume: 0.00% ***********Compliance Point Results ************* Scenario Predeveloped Compliance Subbasin: South Basin Scenario Postdeveloped Compliance Link: Basin POC *** Point of Compliance Flow Frequency Data *** Recurrence Interval Computed Using Gringorten Plotting Position Predevelopment Runoff Postdevelopment Runoff Tr (Years) Discharge (cfs) Tr (Years) Discharge (cfs) ---------------------------------------------------------------------------------------------------------------------- 2-Year 3.666E-02 2-Year 4.200E-02 5-Year 5.225E-02 5-Year 5.814E-02 10-Year 6.622E-02 10-Year 7.273E-02 25-Year 8.825E-02 25-Year 9.289E-02 50-Year 0.114 50-Year 0.123 100-Year 0.144 100-Year 0.155 200-Year 0.147 200-Year 0.157 500-Year 0.150 500-Year 0.158 ** Record too Short to Compute Peak Discharge for These Recurrence Intervals ————————————————————————————————— MGS FLOOD PROJECT REPORT – FC, WQ, and Conveyance Analysis This model uses a standard detention pond to conservatively size a Stormtech Facility. A Stage-Storage Elevation table will be used for the Building Permit submittal for a more accurate size Program Version: MGSFlood 4.50 Program License Number: 201410003 Project Simulation Performed on: 01/07/2021 11:36 AM Report Generation Date: 01/07/2021 11:37 AM ————————————————————————————————— Input File Name: North Basin - Detention.fld Project Name: Renton ES #16 Analysis Title: WQ/Detention - East Basin Comments: Using proposed basin delineation ———————————————— PRECIPITATION INPUT ———————————————— Computational Time Step (Minutes): 15 Extended Precipitation Time Series Selected Climatic Region Number: 16 Full Period of Record Available used for Routing Precipitation Station : 96004405 Puget East 44 in_5min 10/01/1939-10/01/2097 Evaporation Station : 961044 Puget East 44 in MAP Evaporation Scale Factor : 0.750 HSPF Parameter Region Number: 1 HSPF Parameter Region Name : USGS Default ********** Default HSPF Parameters Used (Not Modified by User) *************** ********************** WATERSHED DEFINITION *********************** Predevelopment/Post Development Tributary Area Summary Predeveloped Post Developed Total Subbasin Area (acres) 4.752 4.752 Area of Links that Include Precip/Evap (acres) 0.000 0.000 Total (acres) 4.752 4.752 ----------------------SCENARIO: PREDEVELOPED Number of Subbasins: 1 ---------- Subbasin : North Basin ---------- -------Area (Acres) -------- Till Forest 4.098 Till Grass 0.654 ---------------------------------------------- Subbasin Total 4.752 ----------------------SCENARIO: POSTDEVELOPED Number of Subbasins: 1 ---------- Subbasin : To Detention/WQ ---------- -------Area (Acres) -------- Till Grass 1.045 Impervious 3.707 ---------------------------------------------- Subbasin Total 4.752 ************************* LINK DATA ******************************* ----------------------SCENARIO: PREDEVELOPED Number of Links: 0 ************************* LINK DATA ******************************* ----------------------SCENARIO: POSTDEVELOPED Number of Links: 1 ------------------------------------------ Link Name: Detention Vault Link Type: Structure Downstream Link: None Prismatic Pond Option Used Pond Floor Elevation (ft) : 100.00 Riser Crest Elevation (ft) : 104.00 Max Pond Elevation (ft) : 104.53 Storage Depth (ft) : 4.00 Pond Bottom Length (ft) : 173.0 Pond Bottom Width (ft) : 86.0 Pond Side Slopes (ft/ft) : L1= 3.00 L2= 3.00 W1= 3.00 W2= 3.00 Bottom Area (sq-ft) : 14878. Area at Riser Crest El (sq-ft) : 21,670. (acres) : 0.497 Volume at Riser Crest (cu-ft) : 72,712. (ac-ft) : 1.669 Area at Max Elevation (sq-ft) : 22656. (acres) : 0.520 Vol at Max Elevation (cu-ft) : 84,458. (ac-ft) : 1.939 Constant Infiltration Option Used Infiltration Rate (in/hr): 0.00 Riser Geometry Riser Structure Type : Circular Riser Diameter (in) : 24.00 Common Length (ft) : 0.040 Riser Crest Elevation : 104.00 ft Hydraulic Structure Geometry Number of Devices: 2 ---Device Number 1 --- Device Type : Circular Orifice Control Elevation (ft) : 100.00 Diameter (in) : 1.37 Orientation : Horizontal Elbow : No --- Device Number 2 --- Device Type : Vertical Rectangular Orifice Control Elevation (ft) : 102.28 Length (in) : 0.50 Height (in) : 21.06 Orientation : Vertical Elbow : No **********************FLOOD FREQUENCY AND DURATION STATISTICS******************* ----------------------SCENARIO: PREDEVELOPED Number of Subbasins: 1 Number of Links: 0 ----------------------SCENARIO: POSTDEVELOPED Number of Subbasins: 1 Number of Links: 1 ********** Link: Detention Vault ********** Link WSEL Stats WSEL Frequency Data(ft) (Recurrence Interval Computed Using Gringorten Plotting Position) Tr (yrs) WSEL Peak (ft) ====================================== 1.05-Year 101.398 1.11-Year 101.541 1.25-Year 101.744 2.00-Year 102.293 3.33-Year 102.647 5-Year 102.904 10-Year 103.384 25-Year 103.623 50-Year 103.765 100-Year 103.799 ***********Groundwater Recharge Summary ************* Recharge is computed as input to Perlnd Groundwater Plus Infiltration in Structures Total Predeveloped Recharge During Simulation Model Element Recharge Amount (ac-ft) ----------------------------------------------------------------------------------------------- Subbasin: North Basin 863.835 _____________________________________ Total: 863.835 Total Post Developed Recharge During Simulation Model Element Recharge Amount (ac-ft) ----------------------------------------------------------------------------------------------- Subbasin: To Detention/WQ 134.592 Link: Detention Vault 0.000 _____________________________________ Total: 134.592 Total Predevelopment Recharge is Greater than Post Developed Average Recharge Per Year, (Number of Years= 158) Predeveloped: 5.467 ac-ft/year, Post Developed: 0.852 ac-ft/year ***********Water Quality Facility Data ************* ----------------------SCENARIO: PREDEVELOPED Number of Links: 0 ----------------------SCENARIO: POSTDEVELOPED Number of Links: 1 ********** Link: Detention Vault ********** Basic Wet Pond Volume (91% Exceedance): 19044. cu-ft Computed Large Wet Pond Volume, 1.5*Basic Volume: 28565. cu-ft Infiltration/Filtration Statistics-------------------- Inflow Volume (ac-ft): 2117.45 Inflow Volume Including PPT-Evap (ac-ft): 2117.45 Total Runoff Infiltrated (ac-ft): 0.00, 0.00% Total Runoff Filtered (ac-ft): 0.00, 0.00% Primary Outflow To Downstream System (ac-ft): 2117.15 Secondary Outflow To Downstream System (ac-ft): 0.00 Percent Treated (Infiltrated+Filtered)/Total Volume: 0.00% ***********Compliance Point Results ************* Scenario Predeveloped Compliance Subbasin: North Basin Scenario Postdeveloped Compliance Link: Detention Vault *** Point of Compliance Flow Frequency Data *** Recurrence Interval Computed Using Gringorten Plotting Position Predevelopment Runoff Postdevelopment Runoff Tr (Years) Discharge (cfs) Tr (Years) Discharge (cfs) ---------------------------------------------------------------------------------------------------------------------- 2-Year 0.152 2-Year 7.552E-02 5-Year 0.271 5-Year 0.139 10-Year 0.369 10-Year 0.220 25-Year 0.513 25-Year 0.268 50-Year 0.629 50-Year 0.297 100-Year 0.710 100-Year 0.305 200-Year 0.986 200-Year 0.533 500-Year 1.358 500-Year 0.840 ** Record too Short to Compute Peak Discharge for These Recurrence Intervals **** Flow Duration Performance **** Excursion at Predeveloped 50%Q2 (Must be Less Than or Equal to 0%): -12.1% PASS Maximum Excursion from 50%Q2 to Q2 (Must be Less Than or Equal to 0%): -7.8% PASS Maximum Excursion from Q2 to Q50 (Must be less than 10%): 9.9% PASS Percent Excursion from Q2 to Q50 (Must be less than 50%): 14.0% PASS ------------------------------------------------------------------------------------------------- MEETS ALL FLOW DURATION DESIGN CRITERIA: PASS ------------------------------------------------------------------------------------------------- ————————————————————————————————— MGS FLOOD PROJECT REPORT – North Basin Bypass Analysis Program Version: MGSFlood 4.50 Program License Number: 201410003 Project Simulation Performed on: 12/30/2020 11:22 AM Report Generation Date: 12/30/2020 11:22 AM ————————————————————————————————— Input File Name: North Basin - Bypass Analysis.fld Project Name: Renton ES #16 Analysis Title: North Basin - Bypass Comments: ———————————————— PRECIPITATION INPUT ———————————————— Computational Time Step (Minutes): 15 Extended Precipitation Time Series Selected Climatic Region Number: 16 Full Period of Record Available used for Routing Precipitation Station : 96004405 Puget East 44 in_5min 10/01/1939-10/01/2097 Evaporation Station : 961044 Puget East 44 in MAP Evaporation Scale Factor : 0.750 HSPF Parameter Region Number: 1 HSPF Parameter Region Name : USGS Default ********** Default HSPF Parameters Used (Not Modified by User) *************** ********************** WATERSHED DEFINITION *********************** Predevelopment/Post Development Tributary Area Summary Predeveloped Post Developed Total Subbasin Area (acres) 0.273 0.273 Area of Links that Include Precip/Evap (acres) 0.000 0.000 Total (acres) 0.273 0.273 ----------------------SCENARIO: PREDEVELOPED Number of Subbasins: 1 ---------- Subbasin : North Basin ---------- -------Area (Acres) -------- Till Grass 0.234 Impervious 0.039 ---------------------------------------------- Subbasin Total 0.273 ----------------------SCENARIO: POSTDEVELOPED Number of Subbasins: 1 ---------- Subbasin : Bypass ---------- -------Area (Acres) -------- Impervious 0.273 ---------------------------------------------- Subbasin Total 0.273 ************************* LINK DATA ******************************* ----------------------SCENARIO: PREDEVELOPED Number of Links: 0 ************************* LINK DATA ******************************* ----------------------SCENARIO: POSTDEVELOPED Number of Links: 1 ------------------------------------------ Link Name: Basin POC Link Type: Copy Downstream Link: None **********************FLOOD FREQUENCY AND DURATION STATISTICS******************* ----------------------SCENARIO: PREDEVELOPED Number of Subbasins: 1 Number of Links: 0 ----------------------SCENARIO: POSTDEVELOPED Number of Subbasins: 1 Number of Links: 1 ***********Groundwater Recharge Summary ************* Recharge is computed as input to Perlnd Groundwater Plus Infiltration in Structures Total Predeveloped Recharge During Simulation Model Element Recharge Amount (ac -ft) ----------------------------------------------------------------------------------------------- Subbasin: North Basin 30.125 _____________________________________ Total: 30.125 Total Post Developed Recharge During Simulation Model Element Recharge Amount (ac -ft) ----------------------------------------------------------------------------------------------- Subbasin: Bypass 0.000 Link: Basin POC 0.000 _____________________________________ Total: 0.000 Total Predevelopment Recharge is Greater than Post Developed Average Recharge Per Year, (Number of Years= 158) Predeveloped: 0.191 ac-ft/year, Post Developed: 0.000 ac-ft/year ***********Water Quality Facility Data ************* ----------------------SCENARIO: PREDEVELOPED Number of Links: 0 ----------------------SCENARIO: POSTDEVELOPED Number of Links: 1 ********** Link: Basin POC ********** Infiltration/Filtration Statistics-------------------- Inflow Volume (ac-ft): 137.04 Inflow Volume Including PPT-Evap (ac-ft): 137.04 Total Runoff Infiltrated (ac-ft): 0.00, 0.00% Total Runoff Filtered (ac-ft): 0.00, 0.00% Primary Outflow To Downstream System (ac-ft): 137.04 Secondary Outflow To Downstream System (ac-ft): 0.00 Percent Treated (Infiltrated+Filtered)/Total Volume: 0.00% ***********Compliance Point Results ************* Scenario Predeveloped Compliance Subbasin: North Basin Scenario Postdeveloped Compliance Link: Basin POC *** Point of Compliance Flow Frequency Data *** Recurrence Interval Computed Using Gringorten Plotting Position Predevelopment Runoff Postdevelopment Runoff Tr (Years) Discharge (cfs) Tr (Years) Discharge (cfs) ---------------------------------------------------------------------------------------------------------------------- 2-Year 4.125E-02 2-Year 0.106 5-Year 6.334E-02 5-Year 0.139 10-Year 8.349E-02 10-Year 0.161 25-Year 0.113 25-Year 0.194 50-Year 0.145 50-Year 0.236 100-Year 0.181 100-Year 0.289 200-Year 0.187 200-Year 0.302 500-Year 0.194 500-Year 0.319 ** Record too Short to Compute Peak Discharge for These Recurrence Intervals ————————————————————————————————— MGS FLOOD PROJECT REPORT - WETLAND BASIN FC EXEMPTION Program Version: MGSFlood 4.50 Program License Number: 201410003 Project Simulation Performed on: 01/04/2021 3:55 PM Report Generation Date: 01/04/2021 3:55 PM ————————————————————————————————— Input File Name: Wetland Basin FC Exemption.fld Project Name: Renton ES #16 Analysis Title: Wetland Basin FC Exemption Comments: ———————————————— PRECIPITATION INPUT ———————————————— Computational Time Step (Minutes): 15 Extended Precipitation Time Series Selected Climatic Region Number: 16 Full Period of Record Available used for Routing Precipitation Station : 96004405 Puget East 44 in_5min 10/01/1939-10/01/2097 Evaporation Station : 961044 Puget East 44 in MAP Evaporation Scale Factor : 0.750 HSPF Parameter Region Number: 1 HSPF Parameter Region Name : USGS Default ********** Default HSPF Parameters Used (Not Modified by User) *************** ********************** WATERSHED DEFINITION *********************** Predevelopment/Post Development Tributary Area Summary Predeveloped Post Developed Total Subbasin Area (acres) 0.466 0.466 Area of Links that Include Precip/Evap (acres) 0.000 0.000 Total (acres) 0.466 0.466 ----------------------SCENARIO: PREDEVELOPED Number of Subbasins: 1 ---------- Subbasin : Wetland Basin ---------- -------Area (Acres) -------- Till Grass 0.466 ---------------------------------------------- Subbasin Total 0.466 ----------------------SCENARIO: POSTDEVELOPED Number of Subbasins: 1 ---------- Subbasin : Wetland Basin ---------- -------Area (Acres) -------- Till Grass 0.426 Impervious 0.040 ---------------------------------------------- Subbasin Total 0.466 ************************* LINK DATA ******************************* ----------------------SCENARIO: PREDEVELOPED Number of Links: 0 ************************* LINK DATA ******************************* ----------------------SCENARIO: POSTDEVELOPED Number of Links: 1 ------------------------------------------ Link Name: Basin POC Link Type: Copy Downstream Link: None **********************FLOOD FREQUENCY AND DURATION STATISTICS******************* ----------------------SCENARIO: PREDEVELOPED Number of Subbasins: 1 Number of Links: 0 ----------------------SCENARIO: POSTDEVELOPED Number of Subbasins: 1 Number of Links: 1 ***********Groundwater Recharge Summary ************* Recharge is computed as input to Perlnd Groundwater Plus Infiltration in Structures Total Predeveloped Recharge During Simulation Model Element Recharge Amount (ac-ft) ----------------------------------------------------------------------------------------------- Subbasin: Wetland Basin 60.019 _____________________________________ Total: 60.019 Total Post Developed Recharge During Simulation Model Element Recharge Amount (ac-ft) ----------------------------------------------------------------------------------------------- Subbasin: Wetland Basin 54.867 Link: Basin POC 0.000 _____________________________________ Total: 54.867 Total Predevelopment Recharge is Greater than Post Developed Average Recharge Per Year, (Number of Years= 158) Predeveloped: 0.380 ac-ft/year, Post Developed: 0.347 ac-ft/year ***********Water Quality Facility Data ************* ----------------------SCENARIO: PREDEVELOPED Number of Links: 0 ----------------------SCENARIO: POSTDEVELOPED Number of Links: 1 ********** Link: Basin POC ********** Infiltration/Filtration Statistics-------------------- Inflow Volume (ac-ft): 124.69 Inflow Volume Including PPT-Evap (ac-ft): 124.69 Total Runoff Infiltrated (ac-ft): 0.00, 0.00% Total Runoff Filtered (ac-ft): 0.00, 0.00% Primary Outflow To Downstream System (ac-ft): 124.69 Secondary Outflow To Downstream System (ac-ft): 0.00 Percent Treated (Infiltrated+Filtered)/Total Volume: 0.00% ***********Compliance Point Results ************* Scenario Predeveloped Compliance Subbasin: Wetland Basin Scenario Postdeveloped Compliance Link: Basin POC *** Point of Compliance Flow Frequency Data *** Recurrence Interval Computed Using Gringorten Plotting Position Predevelopment Runoff Postdevelopment Runoff Tr (Years) Discharge (cfs) Tr (Years) Discharge (cfs) ---------------------------------------------------------------------------------------------------------------------- 2-Year 5.316E-02 2-Year 6.364E-02 5-Year 8.750E-02 5-Year 0.101 10-Year 0.123 10-Year 0.135 25-Year 0.173 25-Year 0.185 50-Year 0.232 50-Year 0.241 100-Year 0.273 100-Year 0.294 200-Year 0.287 200-Year 0.306 500-Year 0.306 500-Year 0.321 ** Record too Short to Compute Peak Discharge for These Recurrence Intervals Renton ES 16Conveyance Analysis SpreadsheetGravity DischargePipe Run Size Mannings NPlan SlopeQfull Tributary BasinsTributary AreaImpervious GrassQtrib (25yr)% Full (25yr)#(inches) (ft/ft) (cfs) (acres) (acres) (acres) (cfs)1South Basin ‐ Pipe Outlet to Point of Discharge12 0.011 0.0052.99South Basin ‐ Tributary to Detention 0.806 0.572 0.2340.034 1%2North Basin ‐ Pipe Outlet to Point of Discharge12 0.011 0.0052.99North Basin ‐ Tributary to Detention 4.752 4.098 0.6540.256 9% ————————————————————————————————— MGS FLOOD PROJECT REPORT – TESC Sizing Program Version: MGSFlood 4.50 Program License Number: 201410003 Project Simulation Performed on: 12/30/2020 4:40 PM Report Generation Date: 12/30/2020 4:40 PM ————————————————————————————————— Input File Name: TESC.fld Project Name: Renton ES #16 Analysis Title: TESC Comments: ———————————————— PRECIPITATION INPUT ———————————————— Computational Time Step (Minutes): 5 Extended Precipitation Time Series Selected Climatic Region Number: 16 Full Period of Record Available used for Routing Precipitation Station : 96004405 Puget East 44 in_5min 10/01/1939-10/01/2097 Evaporation Station : 961044 Puget East 44 in MAP Evaporation Scale Factor : 0.750 HSPF Parameter Region Number: 1 HSPF Parameter Region Name : USGS Default ********** Default HSPF Parameters Used (Not Modified by User) *************** ********************** WATERSHED DEFINITION *********************** Predevelopment/Post Development Tributary Area Summary Predeveloped Post Developed Total Subbasin Area (acres) 5.540 5.540 Area of Links that Include Precip/Evap (acres) 0.000 0.000 Total (acres) 5.540 5.540 ----------------------SCENARIO: PREDEVELOPED Number of Subbasins: 1 ---------- Subbasin : Basin ---------- -------Area (Acres) -------- Impervious 5.540 ---------------------------------------------- Subbasin Total 5.540 ----------------------SCENARIO: POSTDEVELOPED Number of Subbasins: 1 ---------- Subbasin : Basin ---------- -------Area (Acres) -------- Impervious 5.540 ---------------------------------------------- Subbasin Total 5.540 ************************* LINK DATA ******************************* ----------------------SCENARIO: PREDEVELOPED Number of Links: 0 ************************* LINK DATA ******************************* ----------------------SCENARIO: POSTDEVELOPED Number of Links: 0 **********************FLOOD FREQUENCY AND DURATION STATISTICS******************* ----------------------SCENARIO: PREDEVELOPED Number of Subbasins: 1 Number of Links: 0 ----------------------SCENARIO: POSTDEVELOPED Number of Subbasins: 1 Number of Links: 0 ***********Groundwater Recharge Summary ************* Recharge is computed as input to Perlnd Groundwater Plus Infiltration in Structures Total Predeveloped Recharge During Simulation Model Element Recharge Amount (ac-ft) ----------------------------------------------------------------------------------------------- Subbasin: Basin 0.000 _____________________________________ Total: 0.000 Total Post Developed Recharge During Simulation Model Element Recharge Amount (ac-ft) ----------------------------------------------------------------------------------------------- Subbasin: Basin 0.000 _____________________________________ Total: 0.000 Total Predevelopment Recharge Equals Post Developed Average Recharge Per Year, (Number of Years= 158) Predeveloped: 0.000 ac-ft/year, Post Developed: 0.000 ac-ft/year ***********Water Quality Facility Data ************* ----------------------SCENARIO: PREDEVELOPED Number of Links: 0 ----------------------SCENARIO: POSTDEVELOPED Number of Links: 0 ***********Compliance Point Results ************* Scenario Predeveloped Compliance Subbasin: Basin Scenario Postdeveloped Compliance Subbasin: Basin *** Point of Compliance Flow Frequency Data *** Recurrence Interval Computed Using Gringorten Plotting Position Predevelopment Runoff Postdevelopment Runoff Tr (Years) Discharge (cfs) Tr (Years) Discharge (cfs) ---------------------------------------------------------------------------------------------------------------------- 2-Year 2.728 2-Year 2.728 5-Year 3.549 5-Year 3.549 10-Year 4.338 10-Year 4.338 25-Year 5.368 25-Year 5.368 50-Year 6.637 50-Year 6.637 100-Year 8.213 100-Year 8.213 200-Year 9.412 200-Year 9.412 500-Year 10.991 500-Year 10.991 ** Record too Short to Compute Peak Discharge for These Recurrence Intervals Sediment Sizing Calculations Per City of Renton Surface Water Design Manual 2016 Section D.2.1.5.1 Project Name: Renton 16 Required Sediment Trap Surface Area (SA): SA =2*Q/Vsed Where: Q = Vsed = Settling Velocity (0.00096 ft/sec) Calculation: multiplier = 2 Q = 3.5490 cfs Vsed = 0.00096 fps Required SA = 7393.8 square feet Equivalent Sediment Trap Volume: Length of Top Surface Area = 86 feet Width of Top Surface Area = 86 feet Surface Area Provided = 7396 square feet Side Slope = 3 (H:1V) Total Depth of Sediment Trap = 3.5 feet Bottom Length of Sediment Trap = 65 feet Bottom Width of Sediment Trap = 65 feet Total pond Volume = 20336.75 cubic feet 152118.89 gallons 5-year developed flow rate from MGS Flood with SPU 158-year 5-minute time series To determine the minimum sediment trap volume, an equivalent sediment trap was sized based upon the required surface area. APPENDIX C Stormwater Pollution Prevention and Spill Plan (SWPPS) & Construction Stormwater Pollution Prevention Plan (SWPPP) Narrative (To Be Provided for Building Permit Submittal) APPENDIX D Operations and Maintenance Manual (To Be Provided for Building Permit Submittal)