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HomeMy WebLinkAbout2025-1 Hazen High School - Vault Lids & Access Drive - SD Adjustment September 25th, 2025 Renton School District Michael Cato 7812 South 124th Street Seattle, WA 98178 Transmitted via email: Michael.cato@rentonschools.us RE: Hazen High School Modernization (C24005771) – Stormwater Drainage Adjustment Dear Mr. Cato: The City of Renton has completed review of the storm drainage adjustment request for Hazen High school (C24005771) in accordance with the City adopted 2022 City of Renton Surface Water Design Manual (RSWDM). As the applicant, you are requesting an adjustment from the 2022 RSWDM Chapter 5 drainage review and requirements. More specifically, you are requesting an adjustment from section 5.1.3.1 – Access Requirements, for consideration of reducing the requirements of a 5-foot x 10-foot locking panel lid and reducing the limits of a maintenance access road. FINDING OF FACTS (FOF): 1. The modular nature of the StormTrap detention system prohibits the structural ability for a 5-foot by 10-foot removable access hatch to be installed, nor does it allow for side access as verified by the manufacturer. 2. The project proposes to provide an equivalent square footage from three (3) removable 4- foot by 4-foot access hatches. 4-foot by 4-foot access hatch is the maximum allowable size removable lid that StormTrap will accept due to structural constraints. The total surface area of the three access hatches sums up to 48 square feet, which is 2 square feet shy of the required 50 square feet of surface area that the 5-foot by 10-foot access panel provides. Given that the three removable hatches will still provide the proper ventilation and access intended by code, the 2 square feet is negligible in this case. 3. A maintenance access road is unable to be provided all the way up to the detention system at the northwest corner of the property due to a steep slope and trees. The detention system was placed in this location due to unique site circumstances where the threshold discharge area (TDA) is almost entirely being used for geothermal wells and a baseball field. The low point of the TDA drains to the northwest corner where there is a steep slope that prohibits access from Duvall Ave NE. Additionally, maintenance activities from Duvall Recipient Page 2 of 2 September 25, 2025 Ave NE are strictly prohibited because it would require a full lane closure within the city right-of-way. 4. As the vault has been placed at the natural low point of the TDA, installation of an access drive up to the system would require significant grading, retaining walls, and removal of trees along a steep slope in order to sufficiently meet the requirements of the manual. In order to save trees within the vegetative steep slope buffer, the project has alternatively indicated that they are able to provide the necessary maintenance by driving a vactor truck up to the northwest corner of the site and servicing it with 235 feet of hose reach in order to provide an equivalent level of maintainability while also preserving the natural environment to the greatest extent possible. Applicant has verified with CatchAll Environmental that this maintenance plan is achievable. 5. Conformance with RSWDM, Chapter 1, Section 1.4.2, Criteria for Granting Adjustments. Compliance Conformance with Criteria for Granting Adjustments  (see FOFs 1-4) The Storm Drainage Adjustment shall: 1. Produce a compensating or comparable result that is in the public interest, AND 2. Meet the objectives of safety, function, appearance, environmental protection, and maintainability based on sound engineering judgement. DECISION: The storm drainage adjustment request conforms to the storm drainage adjustment criteria; therefore, your request is approved. If you have any questions about this adjustment, please contact Nathan Janders, Development Engineering Manager, at 425-430-7382 or Joe Farah, Surface Water Utility Engineering Manager at 425-430-7248. Sincerely, Nathan Janders, PE Joseph Farah, PE Development Engineering Manager Surface Water Utility Engineering Manager cc: Ron Straka, PE, Utility Systems Director Brianne Banwarth, PE, Development Engineering Director Nathan Nelson, surface water/wastewater/ special projects maintenance manager Nathan Janders 255 S. King Street, Suite 800, Seattle, WA 98104 | 206.426.2600 | JACOBSONENGINEERS.COM September 11, 2025 City of Renton Development Engineering 1055 S Grady Way Renton, WA 98057 Attn: Michael Sippo RE: Hazen High School Improvements (C24005771) Drainage Adjustment Request – StormTrap Detention Facility Access and Maintenance Dear Michael: The Drainage Adjustment Request for Hazen High School (1101 Hoquiam Ave NE, Renton, WA) pertains to the 2022 City of Renton Surface Water Design Manual (RSWDM). The project proposes a StormTrap modular detention vault system, located near the SW corner of the baseball field, to meet Core Requirement #3: Flow Control Facilities – See attached Integrus Architecture Memorandum dated 7/21/25 for information on siting of detention vault. City of Renton comments dated 5/2/25, addressing access, maintenance, and OSHA compliance for confined space entry, have been noted and addressed below. Sheet C203 Comment No.1 For access into StormTrap Vault, comment from City of Renton dated 5/2/25 notes: “For vaults with greater than 1,250 sf of floor area, a 5'x10' removable, locking panel shall be provided. Alternatively, a separate access vault may be provided as shown in figure 5.1.3.1 of the stormwater manual. Access openings shall be positioned a max of 50' from any location within the vault.” Figure 1 – Detention Vault Schematic Figure 5.1.3.A from the RSWDM The StormTrap modular detention vault (model DoubleTrap) is manufactured by StormTrap® and has been well-established and installed on a large number of projects across western Washington. Due to the StormTrap consisting of individual modular units that are then assembled and attached together to form a large vault footprint and not a conventional concrete detention vault, there is not enough 255 S. King Street, Suite 800, Seattle, WA 98104 | 206.426.2600 | JACOBSONENGINEERS.COM concrete in the lid of each modular unit to construct and install a 5’x10’ opening for a removable panel. StormTrap modules also don’t allow access installations from the side to provide the optional access location noted in Figure 5.3.1.A above of the RSWDM – See Figure 2 StormTrap Vault Access Plan. Figure 2 – StormTrap Vault Access Plan The project is proposing instead to provide (3) three 4’x4’ removable access hatches, which is the maximum size that a StormTrap vault module lid can accept, which provides an approximate equivalent hatch area (48 sq ft) to the 5’x10’ (50 sq ft) - See Figure 3 Example Removable Access Hatch for what look of hatch, but will be 48”x48” square. 255 S. King Street, Suite 800, Seattle, WA 98104 | 206.426.2600 | JACOBSONENGINEERS.COM Figure 3 – Example Removable Access Hatch Below each access opening a ladder or steps will be installed adjacent to each hatch that will extend approximately from floor to ceiling. There will also be (2) two standard storm drain manhole access covers installed over each inlet and outlet pipe as noted on the plans, which will also have ladder access to the inside floor of the vault - See Figure 4 StormTrap Riser Detail. Figure 4 – StormTrap Riser/Stair Detail In section 1 page 1 of the StormTrap Operations and Maintenance (O&M) Manual notes: "Prior to entry into any underground storm sewer or underground detention systems, appropriate OSHA and local safety regulations and guidelines should be followed." See Appendix A StormTrap Operations and Maintenance Manual. 255 S. King Street, Suite 800, Seattle, WA 98104 | 206.426.2600 | JACOBSONENGINEERS.COM Removing the (3) three 4’x4’ access hatches and (2) two manhole covers, as well as the cleanout covers for the (6) six 12-inch diameter vent pipes located at corners of vault indicated on Civil Plan C203, will allow for proper ventilation of vault prior to pumping air into it and gaining entry. Once personnel enter the vault, free movement between modules can be achieved via rows connecting each module together and via side pocket windows that allow access to the next row of modules – see Figure 5 StormTrap Construction Schematic. Figure 5 – StormTrap Construction Schematic Sheet C203 Comment No.2 For maintenance access to StormTrap Vault, comment from City of Renton dated 5/2/25 notes: “Vault, water quality facility, and presettling facility do not appear to have vehicular access for maintenance. Discussion is warranted for alternative maintenance measures that can be done with smaller vehicles and maintenance staff. Storm drainage adjustment is likely required.” As previously noted, the top lid of the StormTrap Vault will have (3) three 4’x4’ access hatches and (2) two manhole covers installed to allow for both venting and access as needed to maintain the vault. Each StormTrap module has separate walls with pocket window openings in the walls that allows for flow through of stormwater in the vault while also providing additional structural integrity throughout the vault versus typically only one baffle wall for a conventional concrete vault. Cleaning and maintenance of StormTrap vault would be like that of a cast-in-place vault with a Vactor truck vehicle access nearby with hoses to jet and vacuum any sediment that may have accumulated at the bottom of the vault, without requiring confined space entry. Maintenance is recommended to be performed every 6 to 12 months and consists of system inspection for sediment buildup, and back-flushing. Maintenance costs are expected to be less than or equal to that of a cast-in-place vault. A Contech CDS Separator structure is located upstream of the vault, where it pre-settles solids, debris, and sediments prior to stormwater being conveyed to the vault – see Figure 6 Contech CSD Separator Schematic. Regular maintenance of this structure will minimize the need for frequent upkeep within the vault. See Appendix B Contech CDS Separator O&M Manual included with this drainage adjustment. 255 S. King Street, Suite 800, Seattle, WA 98104 | 206.426.2600 | JACOBSONENGINEERS.COM Figure 6 – Contech CDS Separator Schematic Maintenance and access to the StormTrap vault, water quality and pre-settling facilities will be privately operated and maintained by the Renton School District, who will hire a Vactor truck company to perform the cleaning and maintenance of these structures. Please reference the attached StormTrap Vault Maintenance Access Exhibit located in Appendix C indicating an approximate maximum 235-ft of hose pull to the furthest corner of the inside of the detention vault from the north side of the vault by a Vactor truck. The nearest access hatch will be located roughly 125-ft away from the vactor truck. This has been reviewed with the school district’s maintenance staff & CatchAll Environmental (Vactor truck maintenance company), City of Renton, and the vault manufacturer, StormTrap. See Appendix D CatchAll Environmental StormTrap Access Inspection Letter. In our professional opinion, the StormTrap modular detention vault, coordinated with the manufacturer, will be maintained by the Renton School District, ensuring safe access per Washington State OSHA regulations. Required access points will allow maintenance personnel unobstructed movement within the vault. Given its efficiency and prevalence in western Washington, the StormTrap system is the most feasible solution for this project's tight site constraints while meeting the 2022 RSWDM Flow Control Facilities requirements. 255 S. King Street, Suite 800, Seattle, WA 98104 | 206.426.2600 | JACOBSONENGINEERS.COM Please feel free to reach out to me if there are any questions regarding this drainage adjustment at (206) 293-9134 or sascha@jacobsonengineers.com. I would be happy to have any further discussions or provide additional information. Thank you for your review and consideration of this stormwater drainage adjustment. Regards, Sascha Eastman, P.E., Senior Project Manager Attachments: • Integrus Architecture Memorandum • Appendix A - StormTrap Vault Operations and Maintenance Manual • Appendix B - Contech CDS Separator Operations and Maintenance Manual • Appendix C - StormTrap Vault Maintenance Access Exhibit • Appendix D - CatchAll Environmental StormTrap Access Inspection Letter MEMORANDUM TO: Heather Bray Civil Engineer III for City of Renton, Development Engineering FROM: Alexandra V. Forin Project Manager, Integrus Architecture DATE: 21 July 2025 SUBJECT: Hazen High School Drainage Adjustment Request Hazen High School Modernization City of Renton Civil Construction Permit C24005771 Integrus Project No. 22318.00 The intent of this project is to minimize site disturbance. The field improvements at Hazen High School were designed in 1999 including a track, soccer field, softball field, and baseball field with dugouts and permanent fencing. Permanent batting cages were built out some time thereafter. These improvements occupy the majority of the west portion of the site. The original steam mechanical system, approaching its end of life, is being replaced with a high efficiency ground source mechanical system. This system is located below ground and allows continued use of the fields above by students for athletic activities. The decision to replace the baseball field surfacing with synthetic turf was undertaken once this area was identified as a well field. The stormwater vault required for a synthetic field is configured with the goal of limiting the impacts to the existing tree canopy. The modular system fits into a smaller overall site area than a more traditional precast vault. Overall, the project approach is to focus the district’s budget on modernizing the building, including addressing structural deficiencies, replacing an end-of-life mechanical system, improving security via an entry vestibule and replacing roofing. Other project scopes have been ancillary to or necessitated by these interventions. 117 S MAIN ST, SUITE 100 SEATTLE, WA 98104 206.628.3137 | OFFICE Appendix A StormTrap Vault Operations and Maintenance Manual STORMTRAP MAINTENANCE MANUAL 1. Introduction Regular inspections are recommended to ensure that the system is functioning as designed. Please call your Authorized StormTrap Representative if you have questions in regards to the inspection and maintenance of the StormTrap system. Prior to entry into any underground storm sewer or underground detention systems, appropriate OSHA and local safety regulations and guidelines should be followed. 2. Inspection Schedules for Municipalities StormTrap Stormwater Management Systems are recommended for inspection whenever the upstream and downstream catch basins and stormwater pipes of the stormwater collection system are inspected or maintained. This will economize the cost of the inspection if it is done at the same time the Municipal crews are visiting the area. 3. Inspection Schedules for Private Development StormTrap Stormwater Mangement Systems, for a private development, are recommended for inspection after each major storm water event. At a minimum, until a cleaning schedule can be established, an annual inspection is recommended. If inspected on an annual basis, the inspection should be conducted before the stormwater season begins to be sure that everything is functioning properly for the upcoming storm season. 4. Inspection Process Inspections should be done such that at least 2-3 days has lapsed since the most recent rain event to allow for draining. Visually inspect the system at all manhole locations. Utilizing a sediment pole, measure and document the amount of silt at each manhole location (Figure 1). Inspect each pipe opening to ensure that the silt level or any foreign objects are not blocking the pipes. Be sure to inspect the outlet pipe(s) because this is typically the smallest pipe in the system. It is common that most of the larger materials will be collected upstream of the system in catch basins, and it is therefore important at time of inspections to check these structures for large trash or blockages. Remove any blockages if you can during the inspection process only if you can do so safely from the top of the system without entering into the system. Do not go into the system under any circumstances without proper ventilation equipment and training. Pass any information requiring action onto the appropriate maintenance personnel if you cannot remove the blockages from above during the inspection process. Be sure to describe the location of each manhole and the type of material that needs to be removed. The sediment level of the system should also be measured and recorded during the inspection process. Recording the sediment level at each manhole is very important in order get a history of sediment that can be graphed over time (i.e. years) in order to estimate when the system will need to be maintained next. It is also important to keep these records to verify that the inspection process was actually performed if anyone asks for your records in the future. The sediment level in the underground detention system can be determined from the outside of the system by opening up all the manholes and using a sediment pole to measure the amount of sediment at each location. Force the stick to the bottom of the system and then remove it and measure the amount of sediment at that location. Again, do not go into the system under any circumstances without proper ventilation equipment and training. 5. When to Clean the System Any blockages should be safely removed as soon as practical so that the Stormwater detention system will fill and drain properly before the next stormwater event. The Dry Detention System should be completely cleaned whenever the sediment occupies more than 10% to 15% of the originally designed system’s volume. The Wet Detention System should be cleaned when the sediment occupies more than 30% or 1/3rd of the originally designed system’s volume. NOTE: Check with your municipality in regards to cleaning criteria, as the allowable sediment before cleaning may be more or less then described above. 6. How to Clean the StormTrap The system should be completely cleaned back to 100% of the originally designed storage volume whenever the above sediment levels have been reached. Be sure to wait at least 3 days after a stormwater event to be sure that the system is completely drained (if it is a Dry Detention System), and all of the sediments have settled to the bottom of the system (if it is a Wet Detention System). Do not enter the System unless you are properly trained, equipped, and qualified to enter a confined space as identified by local occupational safety and health regulations. There are many maintenance companies that are in business to help you clean your underground stormwater detention systems and water quality units. Please call your StormTrap representative for referrals in your area. A. Dry Detention System Cleaning Maintenance is typically performed using a vacuum truck. Sediment should be flushed towards a vacuum hose for thorough removal. For a Dry Detention System, remove the manhole cover at the top of the system and lower a vacuum hose into one of the rows of the StormTrap system. Open up the manhole at the opposite end of the StormTrap and use sewer jetting equipment to force water in the same row from one end of the StormTrap row to the opposite side. The rows of the StormTrap are completely open in one contiguous channel from one end to the other for easy cleaning. Place the vacuum hose and the sewer jetting equipment in the next row and repeat the process until all of the rows have been cleaned. When finished, replace all covers that were removed and dispose of the collected material properly. B. Wet Detention System Cleaning If the system was designed to maintain a permanent pool of water, floatables and any oil should be removed in a separate procedure prior to the removal of all sediment. The floatable trash is removed first by using a bucket strainer to capture and remove any floating debris. The floatable oils are then removed off the top of the water by using the vacuum truck to suck off any floatable fluids and liquids. The next step is to use the vacuum truck to gently remove the clarified water above the sediment layer. The final step is to clean the sediment for each row as described above in the paragraph “A. Dry Detention System Cleaning”. For smaller systems, the vacuum truck can remove all of the sediment in the basin without using the sewer jetting equipment because of the smaller space. 7. Inspection Reports Proof of these inspections is the responsibility of the property owner. All inspection reports and data should be kept on site or at a location where they will be accessible for years in the future. Some municipalities require these inspection and cleaning reports to be forwarded to the proper governmental permitting agency on an annual basis. Refer to your local and national regulations for any additional maintenance requirements and schedules not contained herein. Inspections should be a part of your standard operating procedure. Figure 1. During inspection, measure the distance from finished grade to the top of the sediment inside the system. Sample inspection and maintenance log 11 | P a g e Project Owner MODULAR BURIED STORMWATER STORAGE UNITS Project Name 33 46 23 Project # 1 OF 5 StormTrap Guide Specification StormTrap 2 DoubleTrap on Stone Groundwater BELOW Invert Revised 11/21/18 This product guide specification is written according to the Construction Specifications Institute (CSI) 3-Part Format, including MasterFormat, SectionFormat, and PageFormat, contained in the CSI Manual of Practice. The section must be carefully reviewed and edited by the Engineer to meet the requirements of the project and local building code. Coordinate this section with other specification sections and the Drawings. Delete all “Specifier Notes” when editing this section. Section numbers are from MasterFormat 2016 Edition. Update section numbers to versions if required. Specifier Notes: This section covers “StormTrap®” precast concrete, modular, storm water detention. StormTrap is custom designed to meet the specific requirements of the project. Consult StormTrap for assistance in editing this section for the specific application. Project Owner MODULAR BURIED STORMWATER STORAGE UNITS Project Name 33 46 23 Project # 2 OF 5 SECTION 33 46 23 – MODULAR BURIED STORMWATER STORAGE UNITS PART 1 - GENERAL 1.01 SECTION INCLUDES A. StormTrap Precast concrete, modular stormwater detention. 1.02 RELATED SECTIONS A. Section 31 00 00 – Earthwork B. Section 03 40 00 – Precast Concrete 1.03 REFERENCE STANDARDS A. AASHTO – Standard Specifications for Highway Bridges – Seventh (7th) Edition B. ACI 318 - Building Code Requirements for Structural Concrete. C. ASTM A 615/A 615M - Standard Specification for Deformed and Plain Billet-Steel Bars for Concrete Reinforcement. D. ASTM C 857 - Standard Practice for Minimum Structural Design Loading for Underground Precast Concrete Utility Structures. E. ASTM C 858 - Standard Specification for Underground Precast Concrete Utility Structures. F. ASTM C 891 - Standard Practice for Installation of Underground Precast Concrete Utility Structures. G. ASTM C 990 - Standard Specification for Joints for Concrete Pipe, Manholes, and Precast Box Sections Using Preformed Flexible Joint Sealants. H. ASTM A 1064 – Standard Specification for Carbon-Steel Wire and Welded Wire Reinforcement, Plain and Deformed, for Concrete. 1.04 DESIGN REQUIREMENTS A. Precast Concrete Modular Stormwater Detention shall comply with ASTM C858. B. Underground precast concrete stormwater management system shall be sized in accordance with the design requirements provided by the Engineer of Record (EOR) and approved by the reviewing agency. C. The system shall be designed so modules are aligned and have channels that extend to the bottom of the modules allowing for relatively unrestricted fluid flow in both directions. D. Minimum Structural Design Loading: ASTM C 857. 1. Total Cover: a. Minimum: As indicated on the drawings. b. Maximum: As indicated on the drawings. 2. Concrete chamber shall be designed for AASHTO HS-20 wheel load. Project Owner MODULAR BURIED STORMWATER STORAGE UNITS Project Name 33 46 23 Project # 3 OF 5 3. Minimum Soil Pressure: a. DoubleTrap Modules: As indicated on the drawings. 4. Vertical and lateral soil pressures shall be determined using: a. Groundwater: At or below invert of system. b. Lateral soil pressures to be based on Active earth pressure 1) Lateral soil pressure = 35 pcf for 120 pcf backfill unit weight c. Vertical soil pressures 1) Live load = HS-20-44 and Dead load = 120 pcf cover fill unit weight d. Engineer to verify geotechnical requirements 1.05 QUALITY ASSURANCE A. The manufacture of the concrete modules shall be performed at a precast production facility certified by the NPCA or PCI. 1.06 SUBMITTALS A. Comply with Section 01 33 00 - Submittal Procedures, except shop drawings shall be eleven inches (11”) by seventeen inches (17”). B. Product Data: Submit manufacturer’s product data and installation instructions. C. Record Documents: 1. Shop Drawings: a. Submit manufacturer’s shop drawings, including plans, elevations, sections, and details indicating layout, dimensions, foundation, cover, and joints. b. Indicate size and location of roof openings and inlet and outlet pipe openings. c. Indicate sealing of joints. D. Operation and Maintenance Data: Submit manufacturer’s operation and maintenance instructions 1.07 DELIVERY, STORAGE AND HANDLING A. Delivery of Accessories: Deliver to site in manufacturer’s original, unopened containers and packaging, with labels clearly identifying product name and manufacturer. B. Storage of Accessories: 1. Store in accordance with manufacturer’s instructions. 2. Store in clean, dry area, out of direct sunlight. C. Handling: Protect materials during handling and installation to prevent damage. 1.08 WARRANTY A. The Manufacturer shall provide a minimum five (5) year limited warranty. Project Owner MODULAR BURIED STORMWATER STORAGE UNITS Project Name 33 46 23 Project # 4 OF 5 PART 2 - PRODUCTS 2.01 MANUFACTURER A. StormTrap, LLC, 1287 Windham Parkway, Romeoville, Illinois 60446. Phone (877) 867-6872. Fax (331) 318-5347. Website www.stormtrap.com. 2.02 STORMWATER DETENTION A. All material shall meet or exceed all applicable referenced standards, federal, state and local requirements, and conform to codes and ordinances of authorities having jurisdiction. B. Stormwater Detention Modules: 1. Description: Engineered, precast concrete, modular stormwater detention. 2. Module Type: StormTrap DoubleTrap 3. Size: As indicated on the drawings. 4. Concrete: Manufacturer’s Approved Mix design providing a minimum compressive strength of 6,000 psi at 28 days. 5. Reinforcing Bars: ASTM A 615, Grade 60. 6. Reinforcing Mesh: ASTM A 1064, Grade 80. 7. Cover for Reinforcing Bars: ACI 318 2.03 ACCESSORIES A. Joint Tape: 1. ASTM C 990. 2. Seven eights inch (7/8”) diameter, preformed butyl mastic joint sealer. 3. Approved by manufacturer. B. Joint Wrap: 1. Eight inch (8”) wide self-adhesive elastomeric resin bonded woven puncture resistant polymer wrap. 2. Approved by manufacturer. PART 3 - EXECUTION 3.01 EXAMINATION A. Examine area to receive stormwater detention modules. Notify Engineer if area is not acceptable. Do not begin installation until unacceptable conditions have been corrected. B. Verify in field before installation, dimensions and soils conditions, including groundwater and soil bearing capacity. Project Owner MODULAR BURIED STORMWATER STORAGE UNITS Project Name 33 46 23 Project # 5 OF 5 3.02 INSTALLATION A. Install stormwater detention modules in accordance with manufacturer’s instructions and ASTM C 891. B. Install modules plumb, on line, and to proper elevation. C. Install modules with a maximum space of three quarters inch (3/4”) between adjacent modules. If the space exceeds three quarters inch (3/4”), the modules shall be reset with appropriate adjustment made to line and grade to bring the space into compliance. D. DoubleTrap: 1. Place modules on level, six-inch (6”) pad of three quarters inch (3/4”) stone that extends two feet (2’-0”) past the outside of the system as indication on the drawings. E. Joint Tape: 1. Seal perimeter horizontal joint between modules with joint tape in accordance with ASTM C 891, 8.8 and 8.12. 2. Prepare surfaces and install joint tape in accordance with manufacturer’s instructions. F. Joint Wrap: 1. Seal exterior joints between adjacent modules with joint wrap in accordance with ASTM C 891. 2. Prepare surfaces and install joint wrap in accordance with manufacturer’s instructions. G. Field Modifications to the modules is strictly prohibited without prior written consent of StormTrap. H. Excavation and fill shall be as specified in Sections 31 00 00. I. Fill: 1. Backfill material shall consist of a GW, GP, SW, or SP material as defined by the Unified Soil Classification System and that meets the gradation requirements as indicated on the drawings. 2. Native materials shall be separated from backfill materials with a geotextile filter fabric unless the drawings indicate separation is not required. 3. Deposit fill on both sides of modules at same time and to approximate same elevation. 4. Prevent wedging action against structure by stepping or serrating slopes bounding or within area to be backfilled. 5. Do not disrupt or damage joint wrap during backfilling. J. Do not use stormwater detention modules that are damaged, as determined by manufacturer. K. Contractor is responsible for installation in accordance with project plans, specifications, and all federal, state, and local regulations. END OF SECTION 33 46 23 Appendix B Contech CDS Separator Operations and Maintenance Manual CDS Guide Operation, Design, Performance and Maintenance ENGINEERED SOLUTIONS 2 CDS® Using patented continuous deflective separation technology, the CDS system screens, separates and traps debris, sediment, and oil and grease from stormwater runoff. The indirect screening capability of the system allows for 100% removal of floatables and neutrally buoyant material without blinding. Flow and screening controls physically separate captured solids, and minimize the re-suspension and release of previously trapped pollutants. Inline units can treat up to 6 cfs, and internally bypass flows in excess of 50 cfs (1416 L/s). Available precast or cast-in- place, offline units can treat flows from 1 to 300 cfs (28.3 to 8495 L/s). The pollutant removal capacity of the CDS system has been proven in lab and field testing. Operation Overview Stormwater enters the diversion chamber where the diversion weir guides the flow into the unit’s separation chamber and pollutants are removed from the flow. All flows up to the system’s treatment design capacity enter the separation chamber and are treated. Swirl concentration and screen deflection force floatables and solids to the center of the separation chamber where 100% of floatables and neutrally buoyant debris larger than the screen apertures are trapped. Stormwater then moves through the separation screen, under the oil baffle and exits the system. The separation screen remains clog free due to continuous deflection. During the flow events exceeding the treatment design capacity, the diversion weir bypasses excessive flows around the separation chamber, so captured pollutants are retained in the separation cylinder. Design Basics There are three primary methods of sizing a CDS system. The Water Quality Flow Rate Method determines which model size provides the desired removal efficiency at a given flow rate for a defined particle size. The Rational Rainfall Method™ or the and Probabilistic Method is used when a specific removal efficiency of the net annual sediment load is required. Typically in the Unites States, CDS systems are designed to achieve an 80% annual solids load reduction based on lab generated performance curves for a gradation with an average particle size (d50) of 125 microns (μm). For some regulatory environments, CDS systems can also be designed to achieve an 80% annual solids load reduction based on an average particle size (d50) of 75 microns (μm) or 50 microns (μm). Water Quality Flow Rate Method In some cases, regulations require that a specific treatment rate, often referred to as the water quality design flow (WQQ), be treated. This WQQ represents the peak flow rate from either an event with a specific recurrence interval, e.g. the six-month storm, or a water quality depth, e.g. 1/2-inch (13 mm) of rainfall. The CDS is designed to treat all flows up to the WQQ. At influent rates higher than the WQQ, the diversion weir will direct most flow exceeding the WQQ around the separation chamber. This allows removal efficiency to remain relatively constant in the separation chamber and eliminates the risk of washout during bypass flows regardless of influent flow rates. Treatment flow rates are defined as the rate at which the CDS will remove a specific gradation of sediment at a specific removal efficiency. Therefore the treatment flow rate is variable, based on the gradation and removal efficiency specified by the design engineer. Rational Rainfall Method™ Differences in local climate, topography and scale make every site hydraulically unique. It is important to take these factors into consideration when estimating the long-term performance of any stormwater treatment system. The Rational Rainfall Method combines site-specific information with laboratory generated performance data, and local historical precipitation records to estimate removal efficiencies as accurately as possible. Short duration rain gauge records from across the United States and Canada were analyzed to determine the percent of the total annual rainfall that fell at a range of intensities. US stations’ depths were totaled every 15 minutes, or hourly, and recorded in 0.01-inch increments. Depths were recorded hourly with 1-mm resolution at Canadian stations. One trend was consistent at all sites; the vast majority of precipitation fell at low intensities and high intensity storms contributed relatively little to the total annual depth. These intensities, along with the total drainage area and runoff coefficient for each specific site, are translated into flow rates using the Rational Rainfall Method. Since most sites are relatively small and highly impervious, the Rational Rainfall Method is appropriate. Based on the runoff flow rates calculated for each intensity, operating rates within a proposed CDS system are GRATE INLET(CAST IRON HOOD FORCURB INLET OPENING) CREST OF BYPASS WEIR(ONE EACH SIDE) INLET(MULTIPLE PIPES POSSIBLE) OIL BAFFLE SUMP STORAGESEPARATION SLAB TREATMENT SCREEN OUTLET INLET FLUME SEPARATION CYLINDER CLEAN OUT(REQUIRED) DEFLECTION PAN, 3 SIDED(GRATE INLET DESIGN) 3 determined. Performance efficiency curve determined from full scale laboratory tests on defined sediment PSDs is applied to calculate solids removal efficiency. The relative removal efficiency at each operating rate is added to produce a net annual pollutant removal efficiency estimate. Probabilistic Rational Method The Probabilistic Rational Method is a sizing program Contech developed to estimate a net annual sediment load reduction for a particular CDS model based on site size, site runoff coefficient, regional rainfall intensity distribution, and anticipated pollutant characteristics. The Probabilistic Method is an extension of the Rational Method used to estimate peak discharge rates generated by storm events of varying statistical return frequencies (e.g. 2-year storm event). Under the Rational Method, an adjustment factor is used to adjust the runoff coefficient estimated for the 10-year event, correlating a known hydrologic parameter with the target storm event. The rainfall intensities vary depending on the return frequency of the storm event under consideration. In general, these two frequency dependent parameters (rainfall intensity and runoff coefficient) increase as the return frequency increases while the drainage area remains constant. These intensities, along with the total drainage area and runoff coefficient for each specific site, are translated into flow rates using the Rational Method. Since most sites are relatively small and highly impervious, the Rational Method is appropriate. Based on the runoff flow rates calculated for each intensity, operating rates within a proposed CDS are determined. Performance efficiency curve on defined sediment PSDs is applied to calculate solids removal efficiency. The relative removal efficiency at each operating rate is added to produce a net annual pollutant removal efficiency estimate. Treatment Flow Rate The inlet throat area is sized to ensure that the WQQ passes through the separation chamber at a water surface elevation equal to the crest of the diversion weir. The diversion weir bypasses excessive flows around the separation chamber, thus preventing re-suspension or re-entrainment of previously captured particles. Hydraulic Capacity The hydraulic capacity of a CDS system is determined by the length and height of the diversion weir and by the maximum allowable head in the system. Typical configurations allow hydraulic capacities of up to ten times the treatment flow rate. The crest of the diversion weir may be lowered and the inlet throat may be widened to increase the capacity of the system at a given water surface elevation. The unit is designed to meet project specific hydraulic requirements. Performance Full-Scale Laboratory Test Results A full-scale CDS system (Model CDS2020-5B) was tested at the facility of University of Florida, Gainesville, FL. This CDS unit was evaluated under controlled laboratory conditions of influent flow rate and addition of sediment. Two different gradations of silica sand material (UF Sediment & OK-110) were used in the CDS performance evaluation. The particle size distributions (PSDs) of the test materials were analyzed using standard method “Gradation ASTM D-422 “Standard Test Method for Particle-Size Analysis of Soils” by a certified laboratory. UF Sediment is a mixture of three different products produced by the U.S. Silica Company: “Sil-Co-Sil 106”, “#1 DRY” and “20/40 Oil Frac”. Particle size distribution analysis shows that the UF Sediment has a very fine gradation (d50 = 20 to 30 μm) covering a wide size range (Coefficient of Uniformity, C averaged at 10.6). In comparison with the hypothetical TSS gradation specified in the NJDEP (New Jersey Department of Environmental Protection) and NJCAT (New Jersey Corporation for Advanced Technology) protocol for lab testing, the UF Sediment covers a similar range of particle size but with a finer d50 (d50 for NJDEP is approximately 50 μm) (NJDEP, 2003). The OK-110 silica sand is a commercial product of U.S. Silica Sand. The particle size distribution analysis of this material, also included in Figure 1, shows that 99.9% of the OK-110 sand is finer than 250 microns, with a mean particle size (d50) of 106 microns. The PSDs for the test material are shown in Figure 1. Figure 1. Particle size distributions Tests were conducted to quantify the performance of a specific CDS unit (1.1 cfs (31.3-L/s) design capacity) at various flow rates, ranging from 1% up to 125% of the treatment design capacity of the unit, using the 2400 micron screen. All tests were conducted with controlled influent concentrations of approximately 200 mg/L. Effluent samples were taken at equal time intervals across the entire duration of each test run. These samples were then processed with a Dekaport Cone sample splitter to obtain representative sub-samples for Suspended Sediment Concentration (SSC) testing using ASTM D3977-97 “Standard Test Methods for Determining Sediment Concentration in Water Samples”, and particle size distribution analysis. Results and Modeling Based on the data from the University of Florida, a performance model was developed for the CDS system. A regression analysis was used to develop a fitting curve representative of the scattered data points at various design flow rates. This model, which demonstrated good agreement with the laboratory data, can then be used to predict CDS system performance with respect 4 to SSC removal for any particle size gradation, assuming the particles are inorganic sandy-silt. Figure 2 shows CDS predictive performance for two typical particle size gradations (NJCAT gradation and OK-110 sand) as a function of operating rate. Figure 2. CDS stormwater treatment predictive performance for various particle gradations as a function of operating rate. Many regulatory jurisdictions set a performance standard for hydrodynamic devices by stating that the devices shall be capable of achieving an 80% removal efficiency for particles having a mean particle size (d50) of 125 microns (e.g. Washington State Department of Ecology — WASDOE - 2008). The model can be used to calculate the expected performance of such a PSD (shown in Figure 3). The model indicates (Figure 4) that the CDS system with 2400 micron screen achieves approximately 80% removal at the design (100%) flow rate, for this particle size distribution (d50 = 125 μm). Figure 3. WASDOE PSD Figure 4. Modeled performance for WASDOE PSD. Maintenance The CDS system should be inspected at regular intervals and maintained when necessary to ensure optimum performance. The rate at which the system collects pollutants will depend more heavily on site activities than the size of the unit. For example, unstable soils or heavy winter sanding will cause the grit chamber to fill more quickly but regular sweeping of paved surfaces will slow accumulation. Inspection Inspection is the key to effective maintenance and is easily performed. Pollutant transport and deposition may vary from year to year and regular inspections will help ensure that the system is cleaned out at the appropriate time. At a minimum, inspections should be performed twice per year (e.g. spring and fall) however more frequent inspections may be necessary in climates where winter sanding operations may lead to rapid accumulations, or in equipment washdown areas. Installations should also be inspected more frequently where excessive amounts of trash are expected. The visual inspection should ascertain that the system components are in working order and that there are no blockages or obstructions in the inlet and separation screen. The inspection should also quantify the accumulation of hydrocarbons, trash, and sediment in the system. Measuring pollutant accumulation can be done with a calibrated dipstick, tape measure or other measuring instrument. If absorbent material is used for enhanced removal of hydrocarbons, the level of discoloration of the sorbent material should also be identified 5 during inspection. It is useful and often required as part of an operating permit to keep a record of each inspection. A simple form for doing so is provided. Access to the CDS unit is typically achieved through two manhole access covers. One opening allows for inspection and cleanout of the separation chamber (cylinder and screen) and isolated sump. The other allows for inspection and cleanout of sediment captured and retained outside the screen. For deep units, a single manhole access point would allows both sump cleanout and access outside the screen. The CDS system should be cleaned when the level of sediment has reached 75% of capacity in the isolated sump or when an appreciable level of hydrocarbons and trash has accumulated. If absorbent material is used, it should be replaced when significant discoloration has occurred. Performance will not be impacted until 100% of the sump capacity is exceeded however it is recommended that the system be cleaned prior to that for easier removal of sediment. The level of sediment is easily determined by measuring from finished grade down to the top of the sediment pile. To avoid underestimating the level of sediment in the chamber, the measuring device must be lowered to the top of the sediment pile carefully. Particles at the top of the pile typically offer less resistance to the end of the rod than consolidated particles toward the bottom of the pile. Once this measurement is recorded, it should be compared to the as-built drawing for the unit to determine weather the height of the sediment pile off the bottom of the sump floor exceeds 75% of the total height of isolated sump. Cleaning Cleaning of a CDS systems should be done during dry weather conditions when no flow is entering the system. The use of a vacuum truck is generally the most effective and convenient method of removing pollutants from the system. Simply remove the manhole covers and insert the vacuum hose into the sump. The system should be completely drained down and the sump fully evacuated of sediment. The area outside the screen should also be cleaned out if pollutant build-up exists in this area. In installations where the risk of petroleum spills is small, liquid contaminants may not accumulate as quickly as sediment. However, the system should be cleaned out immediately in the event of an oil or gasoline spill. Motor oil and other hydrocarbons that accumulate on a more routine basis should be removed when an appreciable layer has been captured. To remove these pollutants, it may be preferable to use absorbent pads since they are usually less expensive to dispose than the oil/water emulsion that may be created by vacuuming the oily layer. Trash and debris can be netted out to separate it from the other pollutants. The screen should be cleaned to ensure it is free of trash and debris. Manhole covers should be securely seated following cleaning activities to prevent leakage of runoff into the system from above and also to ensure that proper safety precautions have been followed. Confined space entry procedures need to be followed if physical access is required. Disposal of all material removed from the CDS system should be done in accordance with local regulations. In many jurisdictions, disposal of the sediments may be handled in the same manner as the disposal of sediments removed from catch basins or deep sump manholes. Check your local regulations for specific requirements on disposal. 6 Note: To avoid underestimating the volume of sediment in the chamber, carefully lower the measuring device to the top of the sediment pile. Finer silty particles at the top of the pile may be more difficult to feel with a measuring stick. These finer particles typically offer less resistance to the end of the rod than larger particles toward the bottom of the pile. CDS Model Diameter Distance from Water Surface to Top of Sediment Pile Sediment Storage Capacity ft m ft m y3 m3 CDS1515 3 0.9 3.0 0.9 0.5 0.4 CDS2015 4 1.2 3.0 0.9 0.9 0.7 CDS2015 5 1.5 3.0 0.9 1.3 1.0 CDS2020 5 1.5 3.5 1.1 1.3 1.0 CDS2025 5 1.5 4.0 1.2 1.3 1.0 CDS3020 6 1.8 4.0 1.2 2.1 1.6 CDS3025 6 1.8 4.0 1.2 2.1 1.6 CDS3030 6 1.8 4.6 1.4 2.1 1.6 CDS3035 6 1.8 5.0 1.5 2.1 1.6 CDS4030 8 2.4 4.6 1.4 5.6 4.3 CDS4040 8 2.4 5.7 1.7 5.6 4.3 CDS4045 8 2.4 6.2 1.9 5.6 4.3 CDS5640 10 3.0 6.3 1.9 8.7 6.7 CDS5653 10 3.0 7.7 2.3 8.7 6.7 CDS5668 10 3.0 9.3 2.8 8.7 6.7 CDS5678 10 3.0 10.3 3.1 8.7 6.7 Table 1: CDS Maintenance Indicators and Sediment Storage Capacities 7 CDS Inspection & Maintenance Log CDS Model: Location: Water Floatable Describe Maintenance Date depth to Layer Maintenance Personnel Comments sediment1 Thickness2 Performed —————————————————————————————————————————————————————————— —————————————————————————————————————————————————————————— —————————————————————————————————————————————————————————— —————————————————————————————————————————————————————————— —————————————————————————————————————————————————————————— —————————————————————————————————————————————————————————— —————————————————————————————————————————————————————————— —————————————————————————————————————————————————————————— —————————————————————————————————————————————————————————— —————————————————————————————————————————————————————————— —————————————————————————————————————————————————————————— —————————————————————————————————————————————————————————— —————————————————————————————————————————————————————————— —————————————————————————————————————————————————————————— 1. The water depth to sediment is determined by taking two measurements with a stadia rod: one measurement from the manhole opening to the top of the sediment pile and the other from the manhole opening to the water surface. If the difference between these measurements is less than the values listed in table 1 the system should be cleaned out. Note: to avoid underestimating the volume of sediment in the chamber, the measuring device must be carefully lowered to the top of the sediment pile. 2. For optimum performance, the system should be cleaned out when the floating hydrocarbon layer accumulates to an appreciable thickness. In the event of an oil spill, the system should be cleaned immediately. SUPPORT • Drawings and specifications are available at www.ContechES.com. • Site-specific design support is available from our engineers. ©2017 Contech Engineered Solutions LLC, a QUIKRETE Company Contech Engineered Solutions provides site solutions for the civil engineering industry. Contech’s portfolio includes bridges, drainage, sanitary sewer, earth stabilization and stormwater treatment products. For information on other Contech division offerings, visit www.ContechES.com or call 800.338.1122 NOTHING IN THIS CATALOG SHOULD BE CONSTRUED AS A WARRANTY. APPLICATIONS SUGGESTED HEREIN ARE DESCRIBED ONLY TO HELP READERS MAKE THEIR OWN EVALUATIONS AND DECISIONS, AND ARE NEITHER GUARANTEES NOR WARRANTIES OF SUITABILITY FOR ANY APPLICATION. CONTECH MAKES NO WARRANTY WHATSOEVER, EXPRESS OR IMPLIED, RELATED TO THE APPLICATIONS, MATERIALS, COATINGS, OR PRODUCTS DISCUSSED HEREIN. ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND ALL IMPLIED WARRANTIES OF FITNESS FOR ANY PARTICULAR PURPOSE ARE DISCLAIMED BY CONTECH. SEE CONTECH’S CONDITIONS OF SALE (AVAILABLE AT WWW.CONTECHES.COM/COS) FOR MORE INFORMATION. The product(s) described may be protected by one or more of the following US patents: 5,322,629; 5,624,576; 5,707,527; 5,759,415; 5,788,848; 5,985,157; 6,027,639; 6,350,374; 6,406,218; 6,641,720; 6,511,595; 6,649,048; 6,991,114; 6,998,038; 7,186,058; 7,296,692; 7,297,266; related foreign patents or other patents pending. 800-338-1122 www.ContechES.com cds_manual 3/17 PDF ENGINEERED SOLUTIONS Appendix C StormTrap Vault Maintenance Access Exhibit X X E E E E E CO SUB SUB S U B SUB SUB S U B SUB SUB S U B SUB S U B SUB S U B SUB S U B SUB S U B SUB S U B SUB S U B SUB S U B SUB S U B SUB S U B SUB S U B SUB S U B SUB S U B SUB S U B S U B S U B E E E E E E E EEE E EE E E E E E E EE SD DU V A L L A V E . N . E . HO Q U I A M A V E . N . E . N.E. 12TH ST. N.E. 10TH ST. N.E. 11TH PL N.E. 11TH CT N.E. 11TH ST N.E. 10TH PL GR A H A M AV E N . E . FIE L D AV E N . E . NE 10TH ST SCALE 1"=150' 75 150 3000 VACTOR TRUCK (TYP) ACCESS VIA NE 10TH ST THROUGH DOUBLE VEHICLE GATE VACTOR TRUCK ACCESS PATH (TYP) STORMTRAP DETENTION VAULT BASEBALL FIELD TRACK & FIELD GRASS PRACTICE FIELD VACTOR TRUCK HOSE PULL LENGTH (INCLUDES 10' VAULT DEPTH) TO FURTHEST CORNER OF VAULT 235 ' ACCESS VIA HAZEN AVE NE DRIVEWAY 12'-4" EXISTING GRAVEL ACCESS PATH FROM ASPHALT DRIVE TO THE SOUTH - WIDTH VARIES. 12'-0" 13'-0 " 12'- 0 " 20 ' - 0 " 1 2 ' - 0 " 12'-0" 12'- 6 " 13'-0 " ADDITIONAL GRAVEL FOR ACCESS PATH TO BE 12-FT MINIMUM WIDTH NEW GRAVEL ACCESS PATH TO BE 12-FT MINIMUM WIDTH 1 2 ' - 0 " VACTOR TRUCK VACTOR TRUCK HOSE PULL LENGTH (INCLUDES 10' VAULT DEPTH) 235' 4'X4' ACCESS HATCH (TYP) STORMTRAP DETENTION VAULT EXISTING ASPHALT PATH FROM NE 10TH ST TO THE SOUTH HAZEN HIGH SCHOOL 1101 HOQUIAM AVE NE RENTON, WA 98059 DETENTION VAULT MAINTENANCE VACTOR TRUCK ACCESS JULY 30,2025 SCALE 1"=20' 0 10 20 40 125 ' Appendix D CatchAll Environmental StormTrap Access Inspection Letter