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HomeMy WebLinkAboutExhibit G - Preliminary TIR-08.18.2022 Approved by: Sheri H. Murata, P.E. Prepared by: Christian R. Vanderhoeven, E.I.T. and Katie E. Lane, E.I.T. Date: 7/6/21, 3/23/22, 7/21/22, 8/18/22 Core No: 21159 Preliminary Technical Information Report FOR THE SUMMIT AT STEEL LAKE PARCEL NO. 0521049033 FEDERAL WAY, WASHINGTON 98003 8/18/22 Core Design, Inc. THE SUMMIT AT STEEL LAKE Page i Table of Contents 1. Project Overview ................................................................................................................................. 1-1 2. Conditions and Requirements Summary ............................................................................................. 2-3 2.1. Core Requirements ............................................................................................................... 2-3 2.1.1. Core Requirement # 1: Discharge at the Natural Location ......................................... 2-3 2.1.2. Core Requirement # 2: Off-Site Analysis ..................................................................... 2-3 2.1.3. Core Requirement # 3: Flow Control ........................................................................... 2-3 2.1.4. Core Requirement # 4: Conveyance System ............................................................... 2-3 2.1.5. Core Requirement # 5: Erosion and Sediment Control ............................................... 2-3 2.1.6. Core Requirement # 6: Maintenance and Operations ................................................ 2-3 2.1.7. Core Requirement # 7: Financial Guarantees and Liability ......................................... 2-4 2.1.8. Core Requirement # 8: Water Quality ......................................................................... 2-4 2.1.9. Core Requirement # 9: Flow Control BMPs ................................................................. 2-4 2.2. Special Requirements............................................................................................................ 2-4 2.2.1. Special Requirement # 1: Other Adopted Area-Specific Requirements ...................... 2-4 Critical Drainage Areas (CDAs) ...................................................................................................... 2-4 Master Drainage Plan (MDPs) ................................................................................................ 2-4 Basin Plans (BPs) ..................................................................................................................... 2-4 Salmon Conversation Plans (SCPs) ......................................................................................... 2-5 Stormwater Compliance Plans (SWCPs) ................................................................................. 2-5 Lake Management Plans (LMPs) ............................................................................................ 2-5 Flood Hazard Management Plan (FHMPs) ............................................................................. 2-5 Shared Facility Drainage Plans (SFDPs) .................................................................................. 2-5 2.2.2. Special Requirement # 2: Floodplain/Floodway Delineation ...................................... 2-5 2.2.3. Special Requirement # 3: Flood Protection Facilities .................................................. 2-5 2.2.4. Special Requirement # 4: Source Control .................................................................... 2-5 2.2.5. Special Requirement # 5: Oil Control .......................................................................... 2-5 3. Off-Site Analysis ................................................................................................................................... 3-1 4. Flow Control, Low Impact Development (LID) and Water Quality Facility Analysis and Design ......... 4-1 4.1. Performance Standards ........................................................................................................ 4-1 4.2. Hydrologic Modeling ............................................................................................................. 4-1 4.3 Existing Conditions Summary.................................................................................................. 4-1 4.4 Developed Conditions Summary............................................................................................. 4-2 4.5. Flow Control System Analysis and Design ............................................................................. 4-3 4.6. Water Quality System and Analysis ....................................................................................... 4-5 4.7. BMP Feasibility ....................................................................................................................... 4-5 5. Conveyance System Analysis and Design ............................................................................................ 5-8 6. Special Reports and Studies ................................................................................................................ 6-1 7. Other Permits ...................................................................................................................................... 7-1 8. CSWPP Analysis and Design ................................................................................................................. 8-1 9. Bond Quantities, Facility Summaries and Declaration of Covenant ................................................... 9-1 Core Design, Inc. THE SUMMIT AT STEEL LAKE Page ii 10. Operations and Maintenance Manual .............................................................................................. 10-1 Figures Figure 1-1. Vicinity Map Figure 4-1. MGS Flood – Existing Conditions Figure 4-2. MGS Flood –Developed Conditions Tables Table 1-1. Parcel Information Table 4-1. Existing Land Cover Table 4-2. Proposed Land Cover Appendices Appendix A Runoff Model Reports Appendix B Biopod Appendix C Soil Map Core Design, Inc. THE SUMMIT AT STEEL LAKE Page 1-1 1. Project Overview The project site is located at S 304th St & 11th Ave S in the City of Federal Way. The site is bordered by single family residential homes on the west, north, and east; S 304th St borders the site to the south. The King County tax parcel ID number for the parcel involved is shown in Table 1-1 below Table 1-1: Parcel Information KC Parcel # Site Area (AC) 0521049033 5.94 The project site is approximately 5.94 acres in size and currently completely forested. Large trees, tall grass, and thick bush cover are found throughout the site. The entire site drains west towards an unnamed creek which flows into Puget Sound. See section 3 for full detail on downstream analysis. Proposed development of the property will include constructing 24 new single-family residences with associated roadways, utilities, open spaces, and stormwater management on the site. See Figure 1-1: Vicinity Map, provided below. The project will be designed using the guidelines and requirements established in the 2021 King County Surface Water Design Manual (2021 KCSWDM), the City of Federal Way Addendum to the 2021 KCSWDM and the King County LID Technical Guidance Manual for Puget Sound. The project is subject to Conservation Flow Control requirements and Enhanced Basic Water Quality requirements. Core Design, Inc. THE SUMMIT AT STEEL LAKE Page 1-2 Figure 1-1: Vicinity Map Core Design, Inc. THE SUMMIT AT STEEL LAKE Page 2-3 2. Conditions and Requirements Summary The proposed project is classified as requiring “Full Drainage Review” per the 2021 KCSWDM. Therefore, all nine core requirements and five special requirements will be addressed per Section 1.1 of the 2021 KCSWDM. 2.1. Core Requirements 2.1.1. Core Requirement # 1: Discharge at the Natural Location This project will discharge into the existing conveyance system associated with 10th Avenue South, will be directed to the Unnamed Creek which is located west of the project site. The natural discharge location will be preserved. Detention will be implemented to mitigate discharge requirements 1-3. 2.1.2. Core Requirement # 2: Off-Site Analysis This core requirement is addressed in Section 3 of this report. 2.1.3. Core Requirement # 3: Flow Control The detention pond is designed for Conservation Flow Control (Level 2). This requires that the developed condition discharge durations match the existing condition durations from 50% of the 2-year to the 50-year storm events and that the developed 2-year and 10-year peak discharge rates do not exceed the historic 2-year and 10-year peak discharge rates, respectively. See section 4 for details. 2.1.4. Core Requirement # 4: Conveyance System The proposed Conveyance Systems, both on-site and off-site, have been analyzed and designed to meet the requirements listed under KCSWDM 1.2.4. to provide protection against overtopping, flooding, erosion, and structural failure. See Section 5 for additional information. 2.1.5. Core Requirement # 5: Erosion and Sediment Control The project will clear, grade, or otherwise disturb portions of the site, and therefore, will provide construction stormwater pollution prevention measures that meet the requirements listed under KCSWDM 1.2.5 in order to prevent transporting sediment from the site to downstream drainage facilities, water resources, and adjacent properties. Both temporary and permanent erosion and sediment control measures will be implemented and meet the requirements listed under KCSWDM 1.2.5. See Section 8 for additional information. 2.1.6. Core Requirement # 6: Maintenance and Operations Property owners shall be responsible for maintenance and operation of all drainage facilities, unless an easement, tract, or right-of-way is granted to the City of Federal Way. The City of Federal way must assume maintenance and operation of the facility as described in Section 1.2.6 of the KCSWDM. Core Design, Inc. THE SUMMIT AT STEEL LAKE Page 2-4 Drainage facilities will be maintained and operated in compliance with the City of Federal Way maintenance standards. See Section 10 for additional information. 2.1.7. Core Requirement # 7: Financial Guarantees and Liability The project will comply with the financial guarantee and liability requirements listed in Section 1.2.7 of the KCSWDM. See Section 9 for additional information. 2.1.8. Core Requirement # 8: Water Quality Due to the site being located within the Basic Enhanced Water Quality treatment area as shown in the Federal Way Addendum Water Quality Applications Map, and as required by section 1.2.7 of the KCSWDM, the project will provide an ecology approved technology to treat stormwater that meets, at a minimum, Enhanced Basic Water Quality Area standards. A Biopod is proposed which has General Use Level Designation (GULD) Approval for enhanced treatment from the Department of Ecology. See Section 4 for additional information. 2.1.9. Core Requirement # 9: Flow Control BMPs The project is required to implement Flow Control BMPs where feasible per the Large Lot BMP Requirements in the 2021 KCSWDM. Refer to Section 4 of this report. 2.2. Special Requirements The project site is subject to Full Drainage Review; therefore, Special Requirements 1-5 apply per Section 1.1 of the 2021 KCSWDM. 2.2.1. Special Requirement # 1: Other Adopted Area-Specific Requirements The following list of area-specific requirements are items addressed per section 1.3.1 by the 2021 KCSWDM. Critical Drainage Areas (CDAs) Not applicable, the project is not located within a critical drainage area. Master Drainage Plan (MDPs) Not applicable. Basin Plans (BPs) This project is located within the Lower Puget Sound drainage basin and is subject to the Lower Puget Sound Basin Plan. Core Design, Inc. THE SUMMIT AT STEEL LAKE Page 2-5 Salmon Conversation Plans (SCPs) Not applicable. Stormwater Compliance Plans (SWCPs) Not applicable. Lake Management Plans (LMPs) Not applicable. Flood Hazard Management Plan (FHMPs) Not applicable. Shared Facility Drainage Plans (SFDPs) Not applicable. 2.2.2. Special Requirement # 2: Floodplain/Floodway Delineation This project is not located within the 100-year floodplain. Refer to the FEMA Flood Map included in the Appendix. 2.2.3. Special Requirement # 3: Flood Protection Facilities The developed site is not protected by levees, revetments, or berms that require a high level of confidence in their structural integrity and performance, nor is the project proposing to modify existing flood protection facilities, therefore, flood protection facility requirements do not apply. 2.2.4. Special Requirement # 4: Source Control The site is proposed as a residential development, and therefore, is not subject to source control requirements. 2.2.5. Special Requirement # 5: Oil Control A “high-use site” is a commercial or industrial site that typically generates or is subject to runoff containing high concentrations of oil due to high traffic turnover, on-site vehicle or heavy or stationary equipment use, or the frequent transfer of liquid petroleum or coal derivative products. The site is proposed as a residential development and does not have “high-use” characteristics, nor is it a redevelopment of a high-use site, and therefore, is not subject to oil control requirements. Core Design, Inc. THE SUMMIT AT STEEL LAKE Page 3-1 3. Off-Site Analysis Site Description The project site is located at S 304th Street & 11th Avenue S in the city of Federal Way. The site is bordered by single family residential homes on the west, north, and east; S 304th Street borders the site to the south. The King County tax parcel ID number is 0521049033 for the project site. The project proposes to construct 24 single-family homes with corresponding access roads. Upstream The general trend of the project site and surrounding area slopes from east to west at moderate to steep slopes. The topography of the project site also indicates two hills on site that serve as local highpoints in the neighborhood. The only upstream flow onto the site comes from the collection of houses directly east of the project site on 13th Avenue S. The upstream flow enters the project site via sheet flow. Downstream Date of Field Inspection: Wednesday, June 15, 2021 Weather Conditions: Partly Cloudy, approximately 63 degrees Fahrenheit The site consists of a single parcel of approximately 5.94 acres. The site is undeveloped and consists of thick forest cover throughout. Large trees, thick bushes, and tall grass are found throughout the parcel. Small openings of trees are found in the center of the parcel, and the overall site is not easily traversable by foot. The entire site is located within the Lower Puget Sound drainage basin. There is a general northwesterly direction of flow on the site. Runoff leaves the site along the west and north and enters one of four flow paths. Path 1: Flow is moved southwest along the steep boundary of the project site (southern boundary of site). The steep hill creates sheet flow along the northern edge of S 304th Street. That flow is directed west until it reaches the catch basin on the corner of 10th Avenue S and S 304th Street. It is then conveyed north until reaching the catch basin which directs flow west towards 9th Avenue S (shown on downstream map), where it then is conveyed west underneath houses to Dash Point Road. At this point it exits an open culvert into the creek shown on the map where it will flow beyond the ¼ mile extent of the analysis. Path 2: Flow is collected along the western edge of the parcel and enters a culvert exiting the site. That culvert pipes out to the street west of the project site (10th Avenue S). It enters the catch basin shown on the downstream map where it is moved across to the western side of the street and directed south along 10th Avenue S. Runoff flows south until entering the direction changing catch basin shown on the map. Runoff is piped west to 9th Avenue S, where it rejoins Flow Path 1 described above Path 3: Flow exiting the site sheet flows onto properties northwest of site. That flow is directed into S 302nd Street where it is collected at intersection of 10th Avenue S and S 302nd Street. The flow continues north until reaching the intersection of S 301st Street. The flow continues west until reaching S Dash Core Design, Inc. THE SUMMIT AT STEEL LAKE Page 3-2 Point Road. From there, the flow is piped south along the eastern side of S Dash Point Road. The flow continues for approximately 1,000 feet before its outlets into the creek and joins the first two flow paths. Path 4: Flow is piped out north from the site to the catch basin shown on S 302nd Street. The flow then is conveyed north along 11th Place S. From there it is moved west along S 301st Street until reaching the intersection of S 301st Street and 10th Avenue S. At this point, Flow Paths 3 and 4 have combined and follow the flow path described above. The entire site is within a single drainage basin as all flow paths enter the creek shown on the map within ¼ mile of the project site. After flowing northwest in the creek for approximately 600 feet the flow path has reached the ¼ mile extent and the analysis is terminated. See downstream map for details. Core Design, Inc. THE SUMMIT AT STEEL LAKE Page 4-1 4. Flow Control, Low Impact Development (LID) and Water Quality Facility Analysis and Design 4.1. Performance Standards This project is subject to “Full Drainage Review” per the 2021 King County Surface Water Design Manual. Flow control and water quality requirements apply to the project. This section discusses the existing conditions and proposed conditions. Per the 2021 KCSWDM, Level 2 Flow Control is implemented to 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. Also match developed peak discharge rates to predeveloped peak discharge rates for the 2- and 10- year return periods. Assume historic site conditions as the predeveloped condition. Per KCSWDM 6.1.2 The Enhanced Basic Water Quality menu is applied where an enhanced level of treatment is required for those development sites with land uses that generate the highest concentrations of metals in stormwater runoff and drain by surface flows to a fish-bearing stream. Metals including but not limited to copper and zinc are toxic to fish and other aquatic biota. The project proposes a two-facility treatment train. The proposed two-facility treatment train shall be comprised of a wetpond and a Biopod biofilter. The Biopod Biofilter manufactured by Oldcastle has General Use Level Designation (GULD) Approval for enhanced treatment by the Department of Ecology. This combination will serve to match the treatment goal in terms of dissolved copper and zinc removal. 4.2. Hydrologic Modeling A hydraulic analysis of the predeveloped and developed land cover was conducted using an approved continuous simulation model, MGS Flood. See section 4.5 below for flow frequency calculations. 4.3 Existing Conditions Summary The site is currently undeveloped. The parcel consists of thick forest cover throughout. The general topography of the site is characterized by two highpoints; one found in the center of the parcel and the other found along the southern boundary. Slopes travel downhill generally in a northwest direction. See table 4.1 below for a summary of the existing sites land cover. Table 4.1 Existing Land Cover Surface Type Area Units Notes Till Forest 258,746 SF Undeveloped Total 258,746 SF Core Design, Inc. THE SUMMIT AT STEEL LAKE Page 4-2 The following figure shows the summary of areas used in MGS Flood for the existing condition. Figure 4-1: MGS Flood – Existing Conditions 4.4 Developed Conditions Summary The project proposes to subdivide the existing parcel into twenty-four lots with associated roadways, tracts, and detention pond. Each parcel will contain a single-family home Refer to Table 4.2 below for the proposed impervious areas. Impervious area calculations were determined based the project site plan. Per Section 3.2.2.1 of the KCSWDM, the engineer can use maximum impervious allowed by code or an assumed maximum lot coverage of 4,000 square feet per lot, whichever is less. Maximum impervious coverage allowed by code is 60% of the lot areas, which will be greater than 4,000 square feet for all proposed lots. As such, an assumed coverage of 4,000 square feet of impervious per lot will be assumed for all proposed lots. Per Table 3.2.2.B of the 2021 KCSWDM, the surface of the proposed pond is considered to be impervious for modeling purposes. Table 4.2 Proposed Land Cover Surface Type Area Units Till Grass 102,066 SF Pervious Subtotal 102,066 SF Lots 96,000 SF Road 33,114 SF Sidewalk 7,495 SF Pond 20,071 SF Impervious Subtotal 156,680 SF Total 258,746 SF The following figure shows the summary of areas used in MGS Flood for the developed condition. Per Section 7.2 of the 2012 LID Technical Guidance Manual for Puget Sound, all areas subject to soil amendment can be entered into the model as pasture rather than grass. As such, all impacted pervious areas, which are subject to soil amendment, have been modeled as pasture. Figure 4-2: MGS Flood – Developed Conditions Core Design, Inc. THE SUMMIT AT STEEL LAKE Page 4-3 4.5. Flow Control System Analysis and Design The project proposes a combined detention and wetpond facility within Tract A to mitigate the developed flows. Refer to the developed conditions exhibit for the proposed location of the detention pond and conveyance system. A summary of the MGS Flood release rates and flow durations chart from the pond is located below. A summary of the MGS Flood release rates and flow durations chart from the vault is also located below. According to the model, the required volume of the pond is 74,817 cubic feet. Refer to Appendix A for the full MGS Flood report. Core Design, Inc. THE SUMMIT AT STEEL LAKE Page 4-4 Core Design, Inc. THE SUMMIT AT STEEL LAKE Page 4-5 4.6. Water Quality System and Analysis The proposed water quality treatment system was designed to meet the requirements of the Enhanced Basic Treatment Menu along with the requirements of the Federal Way Public Works development Standard Section 2.1.1.B. The 2021 KCSWDM provides three options to meet the Enhanced Basic treatment requirement: large sand filter, stormwater wetland, or two-facility treatment train. This project has opted to use a two- facility treatment train consisting of a wetpond and Biopod filter to meet this requirement. Per MGS Flood, the Basic Wetpond Volume for 91% exceedance was found to be 17,614 cubic feet and the 2-year discharge rate from the pond is 0.076 cubic feet per second. 4’ of dead storage is proposed to be provided at the bottom of the pond. A BPU-48IB Biopod Biofilter Underground Vault by Oldcastle will be provided. The BPU-48IB has a maximum treatment flow of 0.086 cubic feet per second, which is greater than the required treatment flow of 0.076 cubic feet per second so the Biopod is adequately sized. 4.7. BMP Feasibility Per Section 1.2.9.3.1 of the 2021 KCSWDM, the proposed project is a road improvement project that is within the UGA or is on a site/parcel less than 5 acres in size. Then flow control BMPs for plat infrastructure improvements of these projects shall meet the requirements described in Section 1.2.9.3.2 for “Small Road Improvement and Urban Road Improvement Project BMP Requirements.” Implementation of flow control BMPs required for the individual lots of the subdivision may be deferred until a permit is obtained for construction on each lot. 1. The feasibility and applicability of full dispersion as detailed in Appendix C, Section C.2.1 must be evaluated for all target impervious surfaces. If feasible and applicable, full dispersion must be implemented as part of the proposed project. Response: Full dispersion is considered infeasible for the project site. Due to the inability of providing a vegetated flow path segment of at least 100 feet in length. 2. All target impervious surfaces not mitigated by Requirement 1 above, must be mitigated to the maximum extent feasible using one or more BMPs from the following list. Use of a given BMP is subject to evaluation of its feasibility and applicability as detailed in Appendix C. Infeasible BMPs are not required to be implemented. The BMPs listed below may be located anywhere on the site/lot subject to the limitations and design specifications for each BMP. These BMPs must be implemented as part of the proposed project. · Full Infiltration per Section C.2.2, or per Section 5.2, whichever is applicable · Limited Infiltration per Appendix C, Section C.2.3, Core Design, Inc. THE SUMMIT AT STEEL LAKE Page 4-6 · Bioretention per Appendix C, Section C.2.6, sized as follows: o Inside the UGA (Rainfall region SeaTac 1.0 and less): In till soils, provide bioretention volume based on 0.6 inches of equivalent storage depth; in outwash soils provide bioretention volume based on 0.1 inches of equivalent storage depth o Inside the UGA (Rainfall regions greater than SeaTac 1.0): In till soils, provide bioretention volume based on 0.8 inches of equivalent storage depth; in outwash soils, provide bioretention volume based on 0.4 inches of equivalent storage depth, o Outside the UGA: In till soils, provide bioretention volume based on 1.9 inches of equivalent storage depth; in outwash soils provide bioretention volume based on 1.0 inches of equivalent storage depth, · Permeable Pavement per Appendix C, Section C.2.7, Response: Per the Geotech report, “Native soils encountered during our fieldwork were characterized primarily as medium dense to very dense Vashon till. The Vashon till is not considered an ideal geologic feature to accommodate infiltration facilities, especially when encountered in a dense, compact state (hardpan). In our opinion, infiltration is not feasible on this site from a geotechnical standpoint.” 3. All target impervious surfaces not mitigated by Requirements 1 and 2 above, must be mitigated to the maximum extent feasible using the Basic Dispersion BMP described below. Use of Basic Dispersion is subject to evaluation of its feasibility and applicability as detailed in Appendix C. Infeasible BMPs are not required to be implemented. Basic Dispersion BMPs may be located anywhere on the site/lot subject to the limitations and design specifications cited in Appendix C. The BMPs must be implemented as part of the proposed project. · Basic Dispersion per Appendix C, Section C.2.4 Response: Sheet flow dispersion may be feasible in some areas to discharge stormwater on site. This BMP will be evaluated further during final design. 4. The soil moisture holding capacity of new pervious surfaces must be protected in accordance with KCC 16.82.100 (F) and (G). KCC 16.82.100(F) requires that the duff layer or native topsoil be retained to the maximum extent practicable. KCC 16.82.100(G) requires soil amendment to mitigate for lost moisture holding capacity where compaction or removal of some or all of the duff layer or underlying topsoil has occurred. The amendment must be such that the replaced topsoil is a minimum of 8 inches thick, unless the applicant demonstrates that a different thickness will provide conditions equivalent to the soil moisture holding capacity native to the site. The replaced topsoil must have an organic content of 5-10% dry weight and a pH suitable for the proposed surface vegetation (for most soils in King County, 4 inches of well-rotted compost tilled into the top 8 inches of soil is sufficient to achieve the organic content standard.) Core Design, Inc. THE SUMMIT AT STEEL LAKE Page 4-7 The amendment must take place between May 1 and October 1. The specifications for compost for soil amendment can be found in Reference 11-C. Response: 8 inches of soil amendment as described here will be applied to all disturbed pervious surfaces as part of this project. Individual Lot BMP Requirements The project is proposed on a site larger than 22,000 square feet, therefore it must demonstrate compliance with the LID performance standard or apply the BMPs from the large lot BMP requirements from Section 1.2.9.2.2 of the 2021 KCSWDM. The project elects to apply the BMPs from the list provided in the SWDM and will evaluate this with the building permits. Since no BMPs have been accounted for with the plat, no credits have been taking in sizing the flow control facilities. Core Design, Inc. THE SUMMIT AT STEEL LAKE Page 5-8 5. Conveyance System Analysis and Design Conveyance calculations will be submitted at the time of final design. Core Design, Inc. THE SUMMIT AT STEEL LAKE Page 6-1 6. Special Reports and Studies The reports listed are provided under separate cover.  Geotechnical Report Prepared for: The Summit at Steel Lake Prepared by: Keven D. Hoffman, PE and Raymond A. Coglas, PE Dated: November 13, 2018 Earthwork Solutions NW, LLC 1805 136th Place NE, Suite 201 Bellevue, WA 98005 Core Design, Inc. THE SUMMIT AT STEEL LAKE Page 7-1 7. Other Permits Additional permits include the following: · Right-Of-Way Use Permit Core Design, Inc. THE SUMMIT AT STEEL LAKE Page 8-1 8. CSWPP Analysis and Design CSWPP Analysis will be included with final design Core Design, Inc. THE SUMMIT AT STEEL LAKE Page 9-1 9. Bond Quantities, Facility Summaries and Declaration of Covenant Bond quantity worksheet will be provided during final design. Core Design, Inc. THE SUMMIT AT STEEL LAKE Page 10-1 10. Operations and Maintenance Manual The Operations and Maintenance Manual will be included upon final design. Appendix A Runoff Model Reports ————————————————————————————————— MGS FLOOD PROJECT REPORT Program Version: MGSFlood 4.57 Program License Number: 200210008 Project Simulation Performed on: 08/15/2022 3:08 PM Report Generation Date: 08/15/2022 3:13 PM ————————————————————————————————— Input File Name: 21159 Detention Pond (update).fld Project Name: Summit at Steel Lake Analysis Title: Comments: ———————————————— PRECIPITATION INPUT ———————————————— Computational Time Step (Minutes): 15 Extended Precipitation Time Series Selected Climatic Region Number: 15 Full Period of Record Available used for Routing Precipitation Station : 96004005 Puget East 40 in_5min 10/01/1939-10/01/2097 Evaporation Station : 961040 Puget East 40 in MAP Evaporation Scale Factor : 0.750 HSPF Parameter Region Number: 1 HSPF Parameter Region Name : Ecology Default ********** Default HSPF Parameters Used (Not Modified by User) *************** ********************** WATERSHED DEFINITION *********************** Predevelopment/Post Development Tributary Area Summary Predeveloped Post Developed Total Subbasin Area (acres) 5.940 5.940 Area of Links that Include Precip/Evap (acres) 0.000 0.000 Total (acres) 5.940 5.940 ----------------------SCENARIO: PREDEVELOPED Number of Subbasins: 1 ---------- Subbasin : Subbasin 1 ---------- -------Area (Acres) -------- C, Forest, Mod 5.940 ---------------------------------------------- Subbasin Total 5.940 ----------------------SCENARIO: POSTDEVELOPED Number of Subbasins: 1 ---------- Subbasin : Subbasin 1 ---------- -------Area (Acres) -------- C, Pasture, Mod 2.343 ROADS/FLAT 3.597 ---------------------------------------------- Subbasin Total 5.940 ************************* LINK DATA ******************************* ----------------------SCENARIO: PREDEVELOPED Number of Links: 0 ************************* LINK DATA ******************************* ----------------------SCENARIO: POSTDEVELOPED Number of Links: 1 ------------------------------------------ Link Name: New Structure Lnk1 Link Type: Structure Downstream Link: None Prismatic Pond Option Used Pond Floor Elevation (ft) : 432.00 Riser Crest Elevation (ft) : 437.00 Max Pond Elevation (ft) : 438.00 Storage Depth (ft) : 5.00 Pond Bottom Length (ft) : 120.0 Pond Bottom Width (ft) : 101.0 Pond Side Slopes (ft/ft) : Z1= 2.00 Z2= 2.00 Z3= 2.00 Z4= 3.50 Bottom Area (sq-ft) : 12120. Area at Riser Crest El (sq-ft) : 17,990. (acres) : 0.413 Volume at Riser Crest (cu-ft): 74,817. (ac-ft) : 1.718 Area at Max Elevation (sq-ft) : 19296. (acres) : 0.443 Vol at Max Elevation (cu-ft): 93,456. (ac-ft) : 2.145 Hydraulic Conductivity (in/hr) : 0.00 Massmann Regression Used to Estimate Hydralic Gradient Depth to Water Table (ft) : 100.00 Bio-Fouling Potential : Low Maintenance : Average or Better Riser Geometry Riser Structure Type : Circular Riser Diameter (in) : 18.00 Common Length (ft) : 0.000 Riser Crest Elevation : 437.00 ft Hydraulic Structure Geometry Number of Devices: 4 ---Device Number 1 --- Device Type : Circular Orifice Control Elevation (ft) : 432.00 Diameter (in) : 1.19 Orientation : Vertical Elbow : No ---Device Number 2 --- Device Type : Circular Orifice Control Elevation (ft) : 434.80 Diameter (in) : 1.44 Orientation : Horizontal Elbow : Yes ---Device Number 3 --- Device Type : Circular Orifice Control Elevation (ft) : 435.70 Diameter (in) : 1.88 Orientation : Horizontal Elbow : Yes ---Device Number 4 --- Device Type : Circular Orifice Control Elevation (ft) : 436.40 Diameter (in) : 2.00 Orientation : Horizontal Elbow : Yes **********************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: New Structure Lnk1 ********** Link WSEL Stats WSEL Frequency Data(ft) (Recurrence Interval Computed Using Gringorten Plotting Position) Tr (yrs) WSEL Peak (ft) ====================================== 1.05-Year 433.722 1.11-Year 433.827 1.25-Year 434.125 2.00-Year 434.861 3.33-Year 435.214 5-Year 435.540 10-Year 436.049 25-Year 436.446 50-Year 436.650 100-Year 436.748 ***********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: Subbasin 1 1024.489 _____________________________________ Total: 1024.489 Total Post Developed Recharge During Simulation Model Element Recharge Amount (ac-ft) ----------------------------------------------------------------------------------------------- Subbasin: Subbasin 1 381.472 Link: New Structure Lnk1 0.000 _____________________________________ Total: 381.472 Total Predevelopment Recharge is Greater than Post Developed Average Recharge Per Year, (Number of Years= 158) Predeveloped: 6.484 ac-ft/year, Post Developed: 2.414 ac-ft/year ***********Water Quality Facility Data ************* ----------------------SCENARIO: PREDEVELOPED Number of Links: 0 ----------------------SCENARIO: POSTDEVELOPED Number of Links: 1 ********** Link: New Structure Lnk1 ********** Basic Wet Pond Volume (91% Exceedance): 17614. cu-ft Computed Large Wet Pond Volume, 1.5*Basic Volume: 26421. cu-ft 2-Year Discharge Rate : 0.076 cfs 15-Minute Timestep, Water Quality Treatment Design Discharge On-line Design Discharge Rate (91% Exceedance): 0.53 cfs Off-line Design Discharge Rate (91% Exceedance): 0.29 cfs Infiltration/Filtration Statistics-------------------- Inflow Volume (ac-ft): 1897.52 Inflow Volume Including PPT-Evap (ac-ft): 1897.52 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): 1897.25 Secondary Outflow To Downstream System (ac-ft): 0.00 Volume Lost to ET (ac-ft): 0.00 Percent Treated (Infiltrated+Filtered+ET)/Total Volume: 0.00% ***********Compliance Point Results ************* Scenario Predeveloped Compliance Subbasin: Subbasin 1 Scenario Postdeveloped Compliance Link: New Structure Lnk1 *** 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 0.127 2-Year 7.609E-02 5-Year 0.206 5-Year 0.115 10-Year 0.278 10-Year 0.186 25-Year 0.352 25-Year 0.245 50-Year 0.450 50-Year 0.289 100-Year 0.487 100-Year 0.306 200-Year 0.759 200-Year 0.327 500-Year 1.123 500-Year 0.356 ** 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%): -29.7% PASS Maximum Excursion from 50%Q2 to Q2 (Must be Less Than or Equal to 0%): -0.6% PASS Maximum Excursion from Q2 to Q50 (Must be less than 10%): -11.8% PASS Percent Excursion from Q2 to Q50 (Must be less than 50%): 0.0% PASS ------------------------------------------------------------------------------------------------- MEETS ALL FLOW DURATION DESIGN CRITERIA: PASS ------------------------------------------------------------------------------------------------- Appendix B ISOMETRIC VIEW BPU-IB C US Patents Pending THIS DOCUMENT IS THE PROPERTY OF OLDCASTLE INFRASTRUCTURE, INC. IT IS SUBMITTED FOR REFERENCE PURPOSES ONLY AND SHALL NOT BE USED IN ANY WAY INJURIOUS TO THE INTERESTS OF SAID COMPANY. COPYRIGHT © 2020 OLDCASTLE INFRASTRUCTURE, INC. ALL RIGHTS RESERVED. BioPod f Biofilter Underground Vault with Internal Bypass dOldcastle dOldcastle dOldcastle Bioretention/ Biofiltration A PLAN VIEW A SECTION A-A BPU-IB C US Patents PendingSAUDFI1325-0510USAXXXXTHIS DOCUMENT IS THE PROPERTY OF OLDCASTLE INFRASTRUCTURE, INC. IT IS SUBMITTED FOR REFERENCE PURPOSES ONLY AND SHALL NOT BE USED IN ANY WAY INJURIOUS TO THE INTERESTS OF SAID COMPANY. COPYRIGHT © 2020 OLDCASTLE INFRASTRUCTURE, INC. ALL RIGHTS RESERVED. MODEL VAULT SIZE 1 (ID) VAULT FOOTPRINT 1 (OD) TREATMENT FLOW CAPACITY (GPM/CFS) A DIM B DIM C DIM A1 DIM B1 DIM 1.6 GPM/SF (WA GULD2) 1.8 GPM/SF (NJCAT3) BPU-46IB 4'6'1.5'5'7'25.6 / 0.057 28.8 / 0.064 BPU-48IB 4'8'1.5'5'9'38.4 / 0.086 43.2 / 0.096 BPU-412IB 4'12'1.5'5'13'64.0 / 0.143 72.0 / 0.160 BPU-66IB 6'6'1.5'7'7'38.4 / 0.086 43.2 / 0.096 BPU-68IB 6'8'1.5'7'9'57.6 / 0.128 64.8 / 0.144 BPU-612IB 6'12'2'7'13'91.2 / 0.203 102.6 / 0.229 BPU-812IB 8'12'2'9'13'121.6 / 0.271 136.9 / 0.305 BPU-816IB 8'16'2'9'17'172.8 / 0.385 194.4 / 0.433 BioPod f Biofilter Underground Vault with Internal Bypass fFIDSAUXXXXUSADFI11540010FIDSAUXXXXUSADFI11540010 SITE SPECIFIC DATA Structure ID Model Size Orientation (Left or Right) Treatment Flow Rate (cfs) Peak Flow Rate (cfs) Rim Elevation Pipe Data Pipe Location (Front or Side)Pipe Size Pipe Type Invert Elevation Inlet Outlet Notes: 1 All Dimensions are nominal, ID=Inside Dimension, OD=Outside Dimension. 2 Treartment flow capacity at 1.6 gpm/sf media surface area based on an WA Ecology GULD Approval for Basic, Enhanced & Phosphorus. 3 Treatment flow capacity at 1.8 gpm/sf media surface area based on an NJCAT Verification & NJ DEP Certification. Bioretention/ Biofiltration Appendix C Soil Map—King County Area, Washington Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 5/25/2021 Page 1 of 3524201052420305242050524207052420905242110524213052421505242170524219052422105242230524201052420305242050524207052420905242110524213052421505242170524219052422105242230551340551360551380551400551420551440551460551480551500 551340 551360 551380 551400 551420 551440 551460 551480 551500 47° 19' 53'' N 122° 19' 14'' W47° 19' 53'' N122° 19' 5'' W47° 19' 46'' N 122° 19' 14'' W47° 19' 46'' N 122° 19' 5'' WN Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 10N WGS84 0 50 100 200 300 Feet 0 15 30 60 90 Meters Map Scale: 1:1,160 if printed on A portrait (8.5" x 11") sheet. Soil Map may not be valid at this scale. MAP LEGEND MAP INFORMATION Area of Interest (AOI) Area of Interest (AOI) Soils Soil Map Unit Polygons Soil Map Unit Lines Soil Map Unit Points Special Point Features Blowout Borrow Pit Clay Spot Closed Depression Gravel Pit Gravelly Spot Landfill Lava Flow Marsh or swamp Mine or Quarry Miscellaneous Water Perennial Water Rock Outcrop Saline Spot Sandy Spot Severely Eroded Spot Sinkhole Slide or Slip Sodic Spot Spoil Area Stony Spot Very Stony Spot Wet Spot Other Special Line Features Water Features Streams and Canals Transportation Rails Interstate Highways US Routes Major Roads Local Roads Background Aerial Photography The soil surveys that comprise your AOI were mapped at 1:24,000. Warning: Soil Map may not be valid at this scale. Enlargement of maps beyond the scale of mapping can cause misunderstanding of the detail of mapping and accuracy of soil line placement. The maps do not show the small areas of contrasting soils that could have been shown at a more detailed scale. Please rely on the bar scale on each map sheet for map measurements. Source of Map: Natural Resources Conservation Service Web Soil Survey URL: Coordinate System: Web Mercator (EPSG:3857) Maps from the Web Soil Survey are based on the Web Mercator projection, which preserves direction and shape but distorts distance and area. A projection that preserves area, such as the Albers equal-area conic projection, should be used if more accurate calculations of distance or area are required. This product is generated from the USDA-NRCS certified data as of the version date(s) listed below. Soil Survey Area: King County Area, Washington Survey Area Data: Version 16, Jun 4, 2020 Soil map units are labeled (as space allows) for map scales 1:50,000 or larger. Date(s) aerial images were photographed: Jul 6, 2020—Jul 20, 2020 The orthophoto or other base map on which the soil lines were compiled and digitized probably differs from the background imagery displayed on these maps. As a result, some minor shifting of map unit boundaries may be evident. Soil Map—King County Area, Washington Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 5/25/2021 Page 2 of 3 Map Unit Legend Map Unit Symbol Map Unit Name Acres in AOI Percent of AOI AmB Arents, Alderwood material, 0 to 6 percent slopes 5.5 100.0% Totals for Area of Interest 5.5 100.0% Soil Map—King County Area, Washington Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 5/25/2021 Page 3 of 3