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Home My WebLink AboutRS_Drainage_Report_Fire_Station _15_1South_170922_v1 Fire Station 15 1404 N 30th St, Renton, WA Technical Information Report September 22, 2017 Prepared by: LPD Engineering, PLLC 1932 1st Avenue Suite 201 Seattle, WA 98101 Contact: Laurie J. Pfarr, P.E. (206) 725-1211 Prepared for: Schreiber Starling Whitehead Architects 901 5th Avenue #3100 Seattle, WA 98164 Contact: Keith Schreiber, AIA (206) 682-8300 Fire Station 15 Technical Information Report September 22, 2017 FIRE STATION 15 TABLE OF CONTENTS Section 1 – Project Overview ...................................................................................................................................... 1 Section 2 – Conditions and Requirements Summary ............................................................................................ 2 Section 3 – Offsite Analysis .......................................................................................................................................... 4 Section 4 – Flow Control and Water Quality Facility Analysis and Design .................................................... 6 Section 5 – Conveyance Systems Analysis and Design ......................................................................................... 9 Section 6 – Special Reports and Studies ..................................................................................................................10 Section 7 – Other Permits ..........................................................................................................................................10 Section 8 – CSWPPP Analysis and Design .............................................................................................................10 Section 9 – Bond Quantities, Facility Summaries, and Declaration of Covenant ........................................11 Section 10 – Operations and Maintenance Manual ..............................................................................................11 FIGURES Figure 1: TIR Worksheet Figure 2: Vicinity Map Figure 3: Soils Map Figure 4: Existing Conditions Figure 5: Proposed Conditions Figure 6: Downstream Drainage Course APPENDICES Appendix A – Design Drawings Appendix B - Design Calculations Appendix C - Stormwater Pollution Prevention and Spill Plan Report Appendix D – Operations and Maintenance Manual Page 1 Fire Station 15 Technical Information Report September 22, 2017 FIRE STATION 15 PRELIMINARY TECHNICAL INFORMATION REPORT SEPTEMBER 22, 2017 SECTION 1 – PROJECT OVERVIEW This Technical Information Report (TIR) is for the construction the new fire station 15 for the City of Renton. Refer to Figure 1: TIR Worksheet for basic site information. The project is west of I-405, located at 1404 N 30th Street on parcel #3342103245. The site is in Section 32, Township 24, Range 5, 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 2016 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 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 2016 RSWDMA. The current property is proposed to be subdivided into two lots. The northern lot will be for the development of a new water storage reservoir serving the 320-pressure zone. The project in the northern lot will be on a similar timeline for design and construction and will be permitted separately. The southern lot will be the extent of the proposed project improvements addressed in this report. Existing Site The total existing parcel area is 47,538.4 SF (1.09 acres). The project limit of work within the southernmost subdivided lot totaling 31,173 SF (0.72 acres). The site and bounded by two gas stations to the east and west, single-family residences to the north, and N 30th St to the south. The property is located in the Kennydale neighborhood on a vacant, city-owned parcel. See Figure 4 – Existing Conditions. Topographically the site generally slopes downward from northeast to southwest, a vertical elevation change of 12.5 feet. According to the USDA Natural Resources Conservation Service, the site soils in the project area are mapped as Indianola loamy sand (InC) with 5 to 15 percent slopes. Refer to Figure 3 – Soils Map. HWA GeoSciences, Inc. prepared a preliminary study for the northern portion of the parcel dated November 10, 2016. Field investigation included three boring samples. In general, the borings indicated one to two feet of topsoil underlain with recessional outwash to approximately 5-feet in depth. Underneath the recessional outwash is medium dense silty sand. In the geotechnical engineer’s preliminary study, it was determined that the soils underneath the first 5-feet form finished grade may be suitable for infiltration. However, none of the boring locations were within the proposed on-site stormwater management facilities on the project site and HWA will need to conduct a PIT test to determine the infiltration rate. In this preliminary TIR drainage report, LPD has assumed the existing soils are no conducive for infiltration until further investigation has been conducted by the geotechnical engineer. A survey of the site has been prepared by Duane Hurtmant & Associates, Inc. on October 21st, 2016. According to the survey, there are no existing drainage facilities on the property. It appears the Page 2 Fire Station 15 Technical Information Report September 22, 2017 majority of the stormwater runoff from the project site sheet flows southwest towards an existing inlet within in N 30th St. There is a 12-inch public storm main flowing west within the north portion of N 30th Street. The site is located in the East Lake Washington drainage basin. According to the City of Renton GIS maps, the site is located within a Wellhead Protection Area Zone 2. Along the eastern property line of the site, a relatively small area has been designated as a regulated slope (>15% and ≤ 25%). There do not appear to be any other critical areas on the site. Proposed Site Improvements Proposed improvements include a new fire station with 11 standard parking stalls on-site and one ADA stall with ADA accessible walkways to the front entrance. An asphalt drive access will be constructed along the west side of the property to be shared with the northern subdivided water reservoir lot. A second drive on the eastern portion of the property that will be for fire truck exit only out of the 2-bay garage. Runoff from the pollution generating surfaces will be treated via a permeable pavement facility as well as StormFilter cartridges. On-site stormwater management will be implemented via a bioretention pond and the permeable pavement facility. The majority of the project site run-off will be routed to a shallow detention facility before discharging from the site. Refer to Section 4 – Flow Control and Water Quality Analysis and Design for further information on the storm drainage design. Also refer to Figure 5 – Proposed Conditions. Improvements will be made to the frontage along N 30th Street to accommodate the two proposed drive entrances per City of Renton standards. An 11-foot dedication along the site frontage has been requested by the City to allow for future right-of-way (ROW) expansion to N 30th Street. SECTION 2 – CONDITIONS AND REQUIREMENTS SUMMARY This section addresses the Core Requirements (Section 1.2) and Special Requirements (Section 1.3) requirements set forth by 2016 RSWDMA. Core Requirement 1 - Discharge at the Natural Location (1.2.1) The proposed conditions will maintain the natural drainage patterns within its basin. All stormwater runoff will be routed to the existing catch basin inlet within N 30th Street discharging to the 12-inch public storm main. Core Requirement 2 - Off-site Analysis (1.2.2) An offsite analysis is required for this project and can be referred to in Section 3 below. A field investigation and assessment will be conducted for the final draft of this report. 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 a Peak Rate Flow Control Standard (Existing Site Conditions) area. Therefore, flow control facilities must be provided to match the existing site’s peak discharge rates for the 2- year, 10-year, and 100- year return periods at the point of discharge from the site. 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. Page 3 Fire Station 15 Technical Information Report September 22, 2017 Core Requirement 4 - Conveyance System (1.2.4) A preliminary conveyance design analysis for the project has been completed and is included within Section 5 of this Report. Core Requirement 5 - Erosion and Sedimentation Control (1.2.5) A Temporary Erosion and Sediment Control (TESC) plan for the project is included with this submittal. 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 clearing, grubbing, or construction of proposed improvements. Core Requirement 6 - Maintenance and Operations (1.2.6) The maintenance and operations guidelines for all of the proposed stormwater facilities will be included with the final drainage report. Core Requirement 7 – Financial Guarantees and Liability (1.2.7) Financial guarantees and liability are not anticipated to be required since the Owner is a public agency. Core Requirement 8 – Water Quality (1.2.8) The project proposes more than 5,000 SF of pollutant generating impervious surface (PGIS) and therefore requires the project to provide water quality treatment. Basic WQ Treatment of the pollution generating impervious surfaces will be provided with a proprietary cartridge treatment system and permeable pavement surfaces. For further information regarding the water quality design requirements, refer to Section 4 of this report. Core Requirement 9 – On-site BMP’s (1.2.9) The project is required to provide onsite flow control best management practices (BMP’s) to mitigate the impacts of stormwater runoff generated by the new plus replaced impervious surface to the maximum extent feasible. Per section 1.2.9.2 of the 2016 RSWDMA, the project is larger than 22,000 SF; therefore, the project will apply the large lot BMP requirements. For further information regarding the on-site BMP’s, refer to Section 4 of this report. Special Requirement 1 – Other Adopted Area-Specific Requirements (1.3.1) • Master Drainage Plans (MDPs) – Project is not within an area covered by an approved Master Drainage Plan. • Basin Plans (BPs) – The project is located in the East Lake Washington drainage basin. The Renton Municipal Code does not provide any more stringent flow control or water quality requirements than that of the current code. • Salmon Conservation Plans (SCPs) – The applicable SCP is the Water Resource Inventory Area (WRIA) 8 for the Lake Washington/Cedar/Sammamish Watershed. Within the large watershed, our project is in the Lake Washington. The SCP does not appear to have stormwater management requirements more stringent than Renton Municipal Code. • Stormwater Compliance Plans (SWCPs) – The project is not within an area governed by a SWCP. Page 4 Fire Station 15 Technical Information Report September 22, 2017 • Flood Hazard Reduction Plans (FHRPs) –The project site is not within a designated flood hazard area. • Shared Facility Drainage Plan (SFDPs) – The proposed project is not within an area with a SFDP. Special Requirement 2 – Flood Hazard Area Delineation (1.3.2) The project site is not located within or adjacent to a designated flood hazard area Special Requirement 3 – Flood Protection Facilities (1.3.3) The project does not rely on an existing flood protection facility, nor will a new flood protection facility be constructed; therefore, this requirement is not applicable. Special Requirement 4 – Source Control (1.3.4) In the proposed conditions, there will be no applicable activities matching those listed within the 2016 King County Stormwater Pollution Prevention Manual (KCSPPM) that will require the use of source control measures. 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. Special Requirement 6 – Aquifer Protection Area (1.3.6) Per the city of Renton Aquifer Protection Area (APA) map, the project site is within Zone 2, which may require some open flow control and water quality treatment facilities as well as open conveyance systems to be constructed with a liner. The proposed does not include these facilities. SECTION 3 – OFFSITE ANALYSIS The following is the Level 1 downstream analysis for the proposed project. Refer to Figure 6 - Downstream Drainage Map. The following resources have been reviewed for the project area: Basin Summary King County’s Watershed Map locates the project site in the East Lake Washington – Renton drainage basin. Floodway Map A FEMA flood insurance rate map (53033C0664F) is included in Appendix B, illustrating the FEMA flood zone designations for the site. The site is located within zone X, which are areas outside the 0.2% annual chance floodplain. Sensitive Areas The sensitive areas within one-mile upstream and downstream of the subject property were examined using the King County iMAP application. According to iMAP, the following are the sensitive area designations for the project site and within one mile downstream of the site: Page 5 Fire Station 15 Technical Information Report September 22, 2017  SAO Erosion Hazard – The project site is not located within an erosion hazard area. There is an erosion hazard area identified on iMAP approximately 900 LF east of the site which is not downstream of the site.  SAO Seismic Hazard – There are no seismic hazard areas on the site on within one mile of the site.  SAO Landslide Hazard – There are no landslide hazard areas on the site on within one mile of the site.  SAO Coal Mine –There are no known coal mines on the site or within one mile of the site.  SAO Stream – There are no sensitive streams located within the project site or within a mile downstream of the project site.  SAO Wetland – There are no wetlands located within the project site or within one mile downstream of the project site.  Groundwater Contamination – The project area is not located within an area designated as being susceptible to groundwater contamination.  Sole Source Aquifer – The project area is not within a sole source aquifer area.  Channel Migration Hazard – There are no channel migration hazards for the site. Topographic Map The Topographic information for the project area is shown on the Design Drawings in Appendix A of this report. 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. King County Soils Survey As stated previously, according to the USDA Natural Resources Conservation Service, the site soils in the area of proposed work are mapped as Indianola loamy sand (InC). Refer to Figure 3: Soils Map. Migrating River Studies According to King County’s iMAP program, the project site is not located within a channel migration hazard. 303d List of Polluted Waters According to Washington State Department of Ecology’s Water Quality Assessment map, the project site does not contain any polluted water. The southeast area of Lake Washington, the immediate receiving water for the downstream system, is designated as a Category 5-303d water for bacteria (Listing ID 12193). There are no Water Quality Improvement Projects identified as part of the 303d listing. Water Quality Problems According to King County’s iMAP program, the project site is not within a designated King County water quality problem area. Page 6 Fire Station 15 Technical Information Report September 22, 2017 Field Inspection and Problem Descriptions A field inspection will be conducted for the final draft of the TIR drainage report. Drainage System Description As stated previously, there are no existing drainage facilities on the property. It appears the majority of the stormwater runoff from the project site sheet flows southwest towards existing inlet within in N 30th Street. Refer to Figure 6 – Downstream Drainage Course for the continuation of the downstream flow path. The remaining downstream course is as follows: 1. The flow continues west within the 12-inch system along N 30th Street for approximately 1,000 feet. 2. The system continues west through 18-inch line in N 30th Street, between Park Ave N and Burnett Ave N, about 300 feet before crossing the ¼-mile point downstream from the site. 3. Stormwater discharges into existing catch basin located at the intersection of N 30th Street and Burnett Ave N. Flow continues north through 18-inch pipe to an existing catch basin near the intersection of Burnett Ave N and N 33rd Street. 4. A 24-inch storm line exits the existing catch basin and continues north for about 530 feet to a catch basin at the intersection of Burnett Ave N and N 34th Street. 5. Flow continues west before discharging to existing catch basin at the intersection of Lake Washington Blvd N and N 34th Street. 6. A 24-inch storm line exits the catch basin and continues southwest for about 120 feet. 7. The system continues west through 24-inch line, eventually outfalling to Lake Washington. SECTION 4 – 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. Proposed 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, Section 5 – Conveyance Systems Analysis, and the Flow Control System, Water Quality, and On-site BMP sections of this report for a brief description of the required standards applicable to this report. Flow Control System As stated in Section 3 of this report, the project site is located within a Peak Rate Flow Control Standard (Existing Site Conditions) area. Therefore, flow control facilities must be provided to match the existing site conditions peak discharge rates for the 2- year, 10-year, and 100- year return periods at the point of discharge. Based on the RSWDMA definition, the ‘existing site conditions’ are those that existed at the site prior to May 1979 as determined from aerial photographs, unless a drainage plan for land cover changes has Page 7 Fire Station 15 Technical Information Report September 22, 2017 been approved by the city since May 1979 as a part of a city permit or approval. Based on the city’s records, there have been no drainage plans for permitted land cover changes by the City since 1979. Based on available historical aerials from King County’s map vault, a 1954 and 1965 map show two residential building with a gravel driveway and grassed-landscape on-site. Based on Renton’s record documents, the previous owners sold the deed of the property to the City in 2001. In the year 2005 the house was demolished according to Google aerial maps. Currently, the site is a grassed vacant lot with a few large trees. For the modeled pre-developed conditions, instead of calculating the amount of existing impervious area constructed before 1979 based on aerial photos, the redeveloped area will be considered as “grass” for conservative flow calculations. Please refer to Figure 4 – Existing Conditions for the referenced aerial images has been included in Appendix B. For the stormwater threshold analysis, MGSFlood was used to model the pre-developed and developed conditions within the project site area. A summary of areas for the site can be found in Appendix B of this report and are also referred in Figure 5 – Proposed Conditions. The project proposes approximately 20,835 SF of new plus replaced impervious surface. The majority of the site which includes the asphalt access drive, walkways, and roof will be modeled to route directly to the detention facility and are considered to be 100% impervious surfaces. For the purposes of this preliminary report, the permeable pavement facility within the parking lot will be under-drained and considered 100% impervious until further infiltrative testing has been conducted. The surfaces considered pollution-generating will be treated by a water quality facility preceding the detention system. For more information, see the Water Quality section below in this report. A portion of the roof will be routed to a bioretention cell west of the proposed fire station building, which will be credited as an on-site BMP for stormwater mitigation. The target surfaces within the 11- foot dedication area associated with the ROW cannot physically be routed to the detention facility and will be modeled as target surfaces bypassing the detention facility in the developed conditions. The bypass areas on site will sheet flow the northern gutter line along N 30th Street into the existing inlet where the detention facility will also connect to before discharging into the existing 12-inch public main. The MGSFlood output for the peak flow rates for the developed project area are included in Table 1 below, and in Appendix B of this report. Table 1 – Net Peak Flow Rates for Discharge from Project Work Area Peak Runoff Rates for Project Work Area Storm Event Existing Conditions Proposed Conditions Delta 2-yr 0.0671 cfs 0.0655 cfs 0.0016 cfs 10-yr 0.169 cfs 0.187 cfs 0.018 cfs 100-yr 0.365 cfs 0.302 cfs 0.063 cfs The required storage volume of detention facility totals 1,100 CF of live storage. The detention facility is a Brentwood StormTank Module system that will consist of approximately 200 polypropylene modules with a total dimension of 42-feet long by 21-feet wide and 2-feet deep. A 12-inch layer of angular stone backfill will cover all sides of the facility and separated from the subgrade by geotextile fabric. The overall dimensions of the facility will be 44-feet long by 23-feet wide and 3-feet deep. The facility will outflow to a flow control structure located west of the facility to restrict the flows entering the public storm system. Page 8 Fire Station 15 Technical Information Report September 22, 2017 On-site BMPs Flow Control BMPs have been applied in accordance with Section 1.2.9 of the RSWDMA. 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. The project site is more than 22,000 SF and will have an impervious coverage greater than 65% on the buildable portion of the site. Therefore, the site is categorized under the Large Lot BMP Requirements and on-site BMPs will be applied to at least 20% of the target impervious surfaces. Based upon the site size, the total area required to be mitigated by BMP facilities is 4,170 SF. Refer to Figure 5 – Proposed Conditions and Area Summary spreadsheet for the calculated impervious coverage and area calculations for BMP implementation. Per the following summary, the total area mitigated is currently greater than what is required due to the potential to infiltrate. If infiltration is not feasible, the permeable pavement surface may be eliminated and the water quality aspect of the facility replaced with an additional StormFilter. Full dispersion is not feasible to be used as BMP due to the limited downstream vegetative flow path. The use of infiltration facilities has not yet been determined, the final drainage report will reflect the results of site infiltration testing that will conducted by the geotechnical engineer. Per Requirement #3 of Section 1.2.9.2.2 of the RSWDMA, the following is a list of BMPs that have been evaluated and applied to the proposed target surfaces: • Bioretention: Approximately 4,975 SF of roof will be directed to a bioretention cell west of the proposed building. Per the King County Rainfall Regions map, the project site falls within the rainfall region Seatac 1.0. In outwash soils, the bioretention volume is based on 0.1 inches of equivalent storage depth by the square footage of the target surface area serve. Therefore, the required storage volume of the bioretention pond is 42 CF of required storage. The project proposes a 6-inch ponding bioretention cell with a total designed volume of 122 CF. The bioretention area consists of 18-inches of bioretention soil mix underlain by 18-inches of drain rock over the native subgrade. A 6-inch slotted underdrain will extend the entire length of the bottom of the bioretention area. • Permeable Pavement: Permeable asphalt pavement has been proposed for the parking area located north of the proposed fire station. The permeable pavement facility will include a 6- inch layer of sand filter media to address water quality treatment requirements referred to in the Water Quality System section of this report. The total permeable pavement area proposed for the project is approximately 4,180 SF. Water Quality System The project proposes approximately 8,965 SF of pollution-generating impervious surfaces and therefore requires the project to provide water quality treatment for the proposed access drive and parking lot. The driveway on the southeast side of the proposed building and the drive apron on the north side of the building are restricted to fire truck access only are not considered pollution-generating surfaces. Page 9 Fire Station 15 Technical Information Report September 22, 2017 Stormwater runoff from the asphalt access drive will be treated by a Stormfilter catch basin system. A Stormfilter analysis will be conducted by Contech Stormwater Solutions for the final drainage report, using the project’s flow rates calculated in MGSFlood stormwater modeling. The StormFilter structure will have ZPG media (zeolite, perlite, granular activated carbon). Per Section 6.5.5.1 of the KCSWDM manual, the Stormfilter sizing is based on water quality design flow and a mass loading method. The water quality design flow is based on 35% of the developed two-year peak flow rate, modeled with 15- minute time steps when the facility is preceding the detention. The resulting size of StormFilter Structure is estimated to be (2) 18-inch cartridge in a catch basin structure. The MGSFlood output for the water quality analysis and the calculations by Contech for the StormFilter will be provided for the final draft of the drainage report. The parking lot will be constructed with a heavy-duty concrete permeable pavement designed for fire truck loading. Stormwater runoff will percolate through the permeable surface layer into the free- draining base and storage reservoir. These aggregate layers will be underlain with 6-inch of sand filter med to be treated for water quality. SECTION 5 – CONVEYANCE SYSTEMS ANALYSIS AND DESIGN The proposed conveyance system will be designed to convey the 25-year peak flow rate of the developed site. The system is allowed to overtop during the 100-year peak flow provided that it does not create or aggravate a severe flooding problem. The entire project site was considered 100% impervious for conservative calculations. A conveyance analysis was performed for one pipe run. The 8-inch storm line is the ultimate discharge point, receiving flow from the entire site at a minimum 0.5% slope. The tributary flows were calculated using MGS Flood with the 158-year, 5-minute time series and were compared to the full flow capacity of the conveyance pipe calculated by the Manning’s equation. The pipe analyzed was determined to have adequate capacity to convey the 25-year peak flow for the tributary area. Attached is the complete output from MGS Flood and Conveyance Analysis Spreadsheet. Page 10 Fire Station 15 Technical Information Report September 22, 2017 SECTION 6 – SPECIAL REPORTS AND STUDIES There are no additional special reports or studies associated with this project. The final geotechnical report will be provided under separate cover. SECTION 7 – OTHER PERMITS An NPDES permit from the Washington State Department of Ecology will not be required for the project disturbs less than one (1) acre of land. There are no additional permits required from other agencies for this project. SECTION 8 – CSWPPP ANALYSIS AND DESIGN An Erosion Sediment Control (ESC) plan has been prepared for the project and is included within the Design Drawings included in Appendix A of this report. The construction storm water pollution prevention plan (CSWPPP) consists of the site preparation plan and a Stormwater Pollution Prevention and Spill (SWPPS) plan (to be provided in the final report). The Contractor will be responsible for implementing all TESC measures and upgrading as necessary. The TESC facilities will be in place prior to any clearing, grubbing or construction. Anticipated minimum ESC and stormwater pollution prevention measures are as follows: • Mark Clearing Limits/Minimize Clearing – Clearing limits will be defined by erosion control components and areas of proposed grading. Clearing will be minimized to the maximum extent practicable. No existing trees will be removed. • Minimized Sediment Tracked Offsite – A stabilized construction entrance for vehicle access to minimize the tracking of public roads. The temporary construction access is shown on the ESC plan. If necessary, sediment shall be removed from roads by shoveling or pickup sweeping and shall be transported to a controlled sediment disposal area. • Install Sediment Controls – Runoff from disturbed areas must pass through a sediment control measures to prevent the transport of sediment downstream until the disturbed area is fully stabilized. Sediment will be controlled using perimeter siltation control which includes silt fencing. In addition catch basin inlet protection will be installed on any existing catch basin within and surrounding the project area. • Stabilize Exposed Soils –It is possible that some of the earthwork and grading may occur in wet weather conditions. The site must be stabilized and no soils will be allowed to remain unstabilized for more than two days between October 1 and April 30. From May 1 through September 30, cover measures must be installed to protect disturbed areas that will remain unworked for seven days or more. By October 8, seed all areas that will remain unworked from October 1 through April 30. Mulch all seeded areas. Exposed slopes will be protected by DOE-approved coverage measures, such as mulching, nets and blankets, plastic covering, seeding, and sodding per Section C.3 of the KCSWDM will be used to stabilize onsite soils during construction. See Erosion and Sedimentation Control Notes on the plans in Appendix A • Control Pollutants – Sediment is the only pollutant expected from the proposed project. Limiting the duration of disturbance of the site soils provides the first level of protection for pollution control, and perimeter measures on the edges of the disturbed areas will mitigate the remaining pollutants. Page 11 Fire Station 15 Technical Information Report September 22, 2017 • Control De-watering – De-watering is not expected to be required. If perched groundwater is encountered and de-watering is necessary, a temporary pump will be used to remove water from the trenches. Pumped water will be routed to perimeter undisturbed areas or other approved location prior to discharge from the project site. • Maintain BMPs – The BMPs will be maintained regularly in accordance with the Erosion and Sedimentation Control Plan and Notes. • Manage the Project – The Contractor will maintain a daily presence on the site and will assign a contact person for erosion and sedimentation control issues. SECTION 9 – BOND QUANTITIES, FACILITY SUMMARIES, AND DECLARATION OF COVENANT A Bond Quantities Worksheet is not expected to be required since the owner is the City of Renton, which is a public agency; no bonding is required. A Facility Summary and Declaration of Covenant will be provided in the final drainage report submittal. SECTION 10 – OPERATIONS AND MAINTENANCE MANUAL The operations and maintenance guidelines will be provided in the final drainage report submittal. Fire Station 15 Technical Information Report September 22, 2017 FIGURES Figure 1: TIR Worksheet Figure 2: Vicinity Map Figure 3: Soils Map Figure 4: Existing Conditions Figure 5: Proposed Conditions Figure 6: Downstream Drainage Course engineering pllc 1932 1st Ave, Suite 201, Seattle, WA 98101 p. 206.725.1211 f. 206.973.5344 www.lpdengineering.com FIRE STATION 15 2VICINITY MAP engineering pllc 1932 1st Ave, Suite 201, Seattle, WA 981041 p. 206.725.1211 f. 206.973.5344 www.lpdengineering.com FIRE STATION 15 3SOILS MAP MAP UNIT SYMBOL KING COUNTY AREA, WASHINGTON (WA633) InC Indianola Loamy Sand, 5% to 15% slopes MAP UNIT NAME PROPERTY AREA 1932 1st Ave,Suite 201,Seattle, WA 98101p. 206.725.1211f. 206.973.5344www.lpdengineering.comengineering pllc2017 LPD Engineering PLLC©FIRE STATION 154EXISTING CONDITIONS 1932 1st Ave,Suite 201,Seattle, WA 98101p. 206.725.1211f. 206.973.5344www.lpdengineering.comengineering pllc2017 LPD Engineering PLLC©FIRE STATION 155PROPOSED CONDITIONS engineering pllc2017 LPD Engineering PLLC©FIRE STATION 1561932 1st Ave,Suite 201,Seattle, WA 98101p. 206.725.1211f. 206.973.5344www.lpdengineering.comDOWNSTREAMDRAINAGE MAPPROPERTYAPPROXIMATELY 1/4 MILEDOWNSTREAM FROM SITEAPPROXIMATE LOCATION OFLAKE WASHINGTON OUTFALLDISCHARGE POINTFROM PROPERTY12" SD SYSTEM18" SD SYSTEM24" SD SYSTEM Fire Station 15 Technical Information Report September 22, 2017 APPENDIX A Design Documents (To Be Provided in Final Drainage Report) Fire Station 15 Technical Information Report September 22, 2017 APPENDIX B Design Calculations Fire Station 15 Area Summary 9/22/2017 Existing Areas (SF) (AC) North Subdivided Lot 16,495 0.38 South Subdivided Lot 31,045 0.71 Grand Total Area 47,540 1.091 On‐Site to Bio Pond (SF) (AC) Roof 4,975 0.114 Total On‐Site to Bio 4,975 0.114 On‐Site Driect to Vault (SF) (AC) PGIS 4,135 0.095 Fire Access Only 2,440 0.056 Pervious Pavement 4,180 0.096 Walk 755 0.017 Roof 2,780 0.064 Landscape 2,420 0.056 Total Impervious On‐Site to Vault 14,290 0.328 Total Pervious On‐Site to Vault 2,420 0.056 On‐Site Bypass Area (SF) (AC) PGIS 650 0.015 Fire Access Only 400 Walk 520 0.012 Landscape 7,790 0.179 Total Impervious On‐Site 1,570 0.036 Total Pervious On‐Site 7,790 0.179 Total Target Impervious 20,835 0.478 Total Pervious 10,210 0.234 Total Basin Modeled 31,045 0.713 Percentage of Target Impervious 67.11% 20% of Target Surface 4,167 Proposed Areas ————————————————————————————————— MGS FLOOD PROJECT REPORT - FLOW CONTROL ANALYSIS Program Version: MGSFlood 4.40 Program License Number: 201410003 Project Simulation Performed on: 08/21/2017 6:38 PM Report Generation Date: 08/21/2017 6:38 PM ————————————————————————————————— Input File Name: DD Detention with approx. bypass.fld Project Name: FS 15 Analysis Title: Detention Comments: ———————————————— PRECIPITATION INPUT ———————————————— Computational Time Step (Minutes): 15 Extended Precipitation Time Series Selected Climatic Region Number: 0 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 : 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) 0.713 0.707 Area of Links that Include Precip/Evap (acres) 0.000 0.006 Total (acres) 0.713 0.713 ----------------------SCENARIO: PREDEVELOPED Number of Subbasins: 1 ---------- Subbasin : Pre-dev Basin ---------- -------Area (Acres) -------- Till Grass 0.713 ---------------------------------------------- Subbasin Total 0.713 ----------------------SCENARIO: POSTDEVELOPED Number of Subbasins: 3 ---------- Subbasin : Direct to Det ---------- -------Area (Acres) -------- Till Grass 0.050 Impervious 0.328 ---------------------------------------------- Subbasin Total 0.378 ---------- Subbasin : Bypass ---------- -------Area (Acres) -------- Till Grass 0.179 Impervious 0.036 ---------------------------------------------- Subbasin Total 0.215 ---------- Subbasin : Roof to Bio ---------- -------Area (Acres) -------- Impervious 0.114 ---------------------------------------------- Subbasin Total 0.114 ************************* LINK DATA ******************************* ----------------------SCENARIO: PREDEVELOPED Number of Links: 1 ------------------------------------------ Link Name: New Copy Lnk1 Link Type: Copy Downstream Link: None ************************* LINK DATA ******************************* ----------------------SCENARIO: POSTDEVELOPED Number of Links: 3 ------------------------------------------ Link Name: Det Systm Link Type: Structure Downstream Link Name: New Copy Lnk2 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) : 20.0 Pond Bottom Width (ft) : 18.0 Pond Side Slopes (ft/ft) : L1= 0.00 L2= 0.00 W1= 0.00 W2= 0.00 Bottom Area (sq-ft) : 360. Area at Riser Crest El (sq-ft) : 360. (acres) : 0.008 Volume at Riser Crest (cu-ft) : 1,080. (ac-ft) : 0.025 Area at Max Elevation (sq-ft) : 360. (acres) : 0.008 Vol at Max Elevation (cu-ft) : 1,296. (ac-ft) : 0.030 Massmann Infiltration Option Used Hydraulic Conductivity (in/hr) : 0.00 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 : 103.00 ft Hydraulic Structure Geometry Number of Devices: 2 ---Device Number 1 --- Device Type : Circular Orifice Control Elevation (ft) : 100.00 Diameter (in) : 0.95 Orientation : Horizontal Elbow : No ---Device Number 2 --- Device Type : Circular Orifice Control Elevation (ft) : 102.15 Diameter (in) : 0.85 Orientation : Vertical Elbow : No ------------------------------------------ Link Name: New Copy Lnk2 Link Type: Copy Downstream Link: None ------------------------------------------ Link Name: Bio Pond Link Type: Bioretention Facility Downstream Link Name: Det Systm Base Elevation (ft) : 100.00 Riser Crest Elevation (ft) : 100.50 Storage Depth (ft) : 0.50 Bottom Length (ft) : 100.0 Bottom Width (ft) : 2.5 Side Slopes (ft/ft) : L1= 3.00 L2= 3.00 W1= 3.00 W2= 3.00 Bottom Area (sq-ft) : 250. Area at Riser Crest El (sq-ft) : 567. (acres) : 0.013 Volume at Riser Crest (cu-ft) : 316. (ac-ft) : 0.007 Infiltration on Bottom and Sideslopes Selected Soil Properties Biosoil Thickness (ft) : 1.50 Biosoil Saturated Hydraulic Conductivity (in/hr) : 2.50 Biosoil Porosity (Percent) : 30.00 Maximum Elevation of Bioretention Soil : 102.00 Native Soil Hydraulic Conductivity (in/hr) : 0.00 Underdrain Present Orifice NOT Present in Under Drain Riser Geometry Riser Structure Type : Circular Riser Diameter (in) : 6.00 Common Length (ft) : 0.000 Riser Crest Elevation : 100.50 ft Hydraulic Structure Geometry Number of Devices: 0 **********************FLOOD FREQUENCY AND DURATION STATISTICS******************* ----------------------SCENARIO: PREDEVELOPED Number of Subbasins: 1 Number of Links: 1 ----------------------SCENARIO: POSTDEVELOPED Number of Subbasins: 3 Number of Links: 3 ***********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: Pre-dev Basin 87.136 Link: New Copy Lnk1 0.000 _____________________________________ Total: 87.136 Total Post Developed Recharge During Simulation Model Element Recharge Amount (ac-ft) ----------------------------------------------------------------------------------------------- Subbasin: Direct to Det 6.111 Subbasin: Bypass 21.876 Subbasin: Roof to Bio 0.000 Link: Det Systm Not Computed Link: New Copy Lnk2 0.000 Link: Bio Pond Not Computed _____________________________________ Total: 27.986 Total Predevelopment Recharge is Greater than Post Developed Average Recharge Per Year, (Number of Years= 158) Predeveloped: 0.551 ac-ft/year, Post Developed: 0.177 ac-ft/year ***********Water Quality Facility Data ************* ----------------------SCENARIO: PREDEVELOPED Number of Links: 1 ********** Link: New Copy Lnk1 ********** Infiltration/Filtration Statistics-------------------- Inflow Volume (ac-ft): 143.39 Inflow Volume Including PPT-Evap (ac-ft): 143.39 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): 143.39 Secondary Outflow To Downstream System (ac-ft): 0.00 Percent Treated (Infiltrated+Filtered)/Total Volume: 0.00% ----------------------SCENARIO: POSTDEVELOPED Number of Links: 3 ********** Link: New Copy Lnk2 ********** Infiltration/Filtration Statistics-------------------- Inflow Volume (ac-ft): 264.07 Inflow Volume Including PPT-Evap (ac-ft): 264.07 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): 264.07 Secondary Outflow To Downstream System (ac-ft): 0.00 Percent Treated (Infiltrated+Filtered)/Total Volume: 0.00% ***********Compliance Point Results ************* Scenario Predeveloped Compliance Link: New Copy Lnk1 Scenario Postdeveloped Compliance Link: New Copy Lnk2 *** 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 6.708E-02 2-Year 6.558E-02 5-Year 0.115 5-Year 0.146 10-Year 0.168 10-Year 0.186 25-Year 0.256 25-Year 0.218 50-Year 0.331 50-Year 0.275 100-Year 0.363 100-Year 0.293 200-Year 0.400 200-Year 0.358 ** Record too Short to Compute Peak Discharge for These Recurrence Intervals Fire Station 15 9/22/2017 Conveyance Analysis Spreadsheet Gravity Discharge Pipe Run Size Mannings N Plan Slope Qfull Tributary Basins Tributary Area Impervious Grass Qtrib (25yr-5min) % Full (25yr) #(inches)(ft/ft)(cfs)(acres)(acres)(acres)(cfs) 1 Pipe Connecting to Point of Discharge 8 0.011 0.005 1.01 Entire Project Site 0.716 0.716 0.000 0.687 68% ————————————————————————————————— MGS FLOOD PROJECT REPORT- CONVEYANCE ANALYSIS Program Version: MGSFlood 4.40 Program License Number: 201410003 Project Simulation Performed on: 08/21/2017 5:48 PM Report Generation Date: 08/21/2017 5:49 PM ————————————————————————————————— Input File Name: Conveyance Calcs.fld Project Name: FS 15 Analysis Title: Conveyance Comments: ———————————————— PRECIPITATION INPUT ———————————————— Computational Time Step (Minutes): 5 Extended Precipitation Time Series Selected Climatic Region Number: 0 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 : 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) 0.713 0.713 Area of Links that Include Precip/Evap (acres) 0.000 0.000 Total (acres) 0.713 0.713 ----------------------SCENARIO: PREDEVELOPED Number of Subbasins: 1 ---------- Subbasin : Pre-dev Basin ---------- -------Area (Acres) -------- Till Grass 0.713 ---------------------------------------------- Subbasin Total 0.713 ----------------------SCENARIO: POSTDEVELOPED Number of Subbasins: 1 ---------- Subbasin : Subbasin 1 ---------- -------Area (Acres) -------- Impervious 0.713 ---------------------------------------------- Subbasin Total 0.713 ************************* LINK DATA ******************************* ----------------------SCENARIO: PREDEVELOPED Number of Links: 1 ------------------------------------------ Link Name: New Copy Lnk1 Link Type: Copy Downstream Link: None ************************* LINK DATA ******************************* ----------------------SCENARIO: POSTDEVELOPED Number of Links: 0 **********************FLOOD FREQUENCY AND DURATION STATISTICS******************* ----------------------SCENARIO: PREDEVELOPED Number of Subbasins: 1 Number of Links: 1 ----------------------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: Pre-dev Basin 87.076 Link: New Copy Lnk1 0.000 _____________________________________ Total: 87.076 Total Post Developed Recharge During Simulation Model Element Recharge Amount (ac-ft) ----------------------------------------------------------------------------------------------- Subbasin: Subbasin 1 0.000 _____________________________________ Total: 0.000 Total Predevelopment Recharge is Greater than Post Developed Average Recharge Per Year, (Number of Years= 158) Predeveloped: 0.551 ac-ft/year, Post Developed: 0.000 ac-ft/year ***********Water Quality Facility Data ************* ----------------------SCENARIO: PREDEVELOPED Number of Links: 1 ********** Link: New Copy Lnk1 ********** Infiltration/Filtration Statistics-------------------- Inflow Volume (ac-ft): 143.41 Inflow Volume Including PPT-Evap (ac-ft): 143.41 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): 143.41 Secondary Outflow To Downstream System (ac-ft): 0.00 Percent Treated (Infiltrated+Filtered)/Total Volume: 0.00% ----------------------SCENARIO: POSTDEVELOPED Number of Links: 0 ***********Compliance Point Results ************* Scenario Predeveloped Compliance Link: New Copy Lnk1 Scenario Postdeveloped Compliance Subbasin: Subbasin 1 *** 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 8.601E-02 2-Year 0.333 5-Year 0.159 5-Year 0.437 10-Year 0.214 10-Year 0.535 25-Year 0.326 25-Year 0.687 50-Year 0.427 50-Year 0.836 100-Year 0.559 100-Year 1.034 200-Year 0.570 200-Year 1.134 ** Record too Short to Compute Peak Discharge for These Recurrence Intervals Fire Station 15 Technical Information Report September 22, 2017 APPENDIX C Stormwater Pollution Prevention and Spill Plan (SWPPS) (To Be Provided in Final Drainage Report) Fire Station 15 Technical Information Report September 22, 2017 APPENDIX D Operations and Maintenance Manual (To Be Provided in Final Drainage Report)