Under state, federal and local law, typical regulations require new or redeveloped sites of one or more acre, to develop and implement a SWQ Plan to the maximum extent practicable. After construction has been completed and the site permanently stabilized, the BMP must reduce the average annual total suspended solids (TSS) loadings by 80%.
The most popular Structural Control for SWQ is a detention or retention pond. It is hard to construct a pond on a one acre site, hence a StormTrooper is the solution for the cases, where land space is too small or too valuable to obtain treatment with a pond.
The permittee will be required to complete a Stormwater Quality Management Plan (SWQMP) to obtain a permit. Most cities will accept some variation of the following steps:
If you have trouble with any steps call your stormwater professional at ParkUSA.
Post-Construction Stormwater Interceptors are typically sized utilizing the “First Flush” principle of stormwater management. Pollutants deposited on to exposed areas can be dislodged and entrained by the rainfall-runoff process. Usually the stormwater that initially runs off an area will be more polluted than the stormwater that runs off later, after rainwater has ‘cleansed’ the catchment. The stormwater containing this high initial pollutant load is called the ‘First Flush’.
As a result, many cities have adopted the Rationale Method (Q=ciA) for sizing First Flush for stormwater interceptors by requiring a runoff coefficient typical of Residential or Commercial properties and rainfall intensity typical of the first 30 minutes or first ½ inch of a storm event. Use the StormTrooper Sizing Tool (in tab SWQMPs) to find out which StormTrooper size is recommended.
StormTrooper “First Flush” flows into the inlet of the Control Manhole and is then diverted from a bypass weir into the interceptor. Debris, Suspended Solids, and Oils are filtered and separated through the Coalescing Media Pak inside the interceptor. We call this “Enhanced Gravity Separation” which means StormTrooper can filter and separate more particles in a smaller interceptor through the use of the coalescing plates.
During ‘High Flow’, stormwater runoff flows over the inlet weir of the control manhole. Large trash and debris is still captured in the control manhole by a custom designed debris screen.
ParkUSA also offers a “Full-Treatment” stormwater interceptor Model SWAQ in lieu of the ‘First Flush’ based system.
Note! It is helpful to search on websites to see if stormwater interceptors are approved for the ‘First Flush’ in your area. Different regulations have different names for interceptors. The most popular name for stormwater interceptors is “Manufactured Systems".
Here are other interceptor names that typically mean some style of "Manufactured Systems".
- Wet Vaults
- Hydrodynamic Systems (gravity or Vortex Separators)
- Sand Grit Interceptors
- Oil Grit Separator
- Oil Water Separators
- Passive Interceptors
- Proprietary Systems
- Sediment Traps
- Filtration Systems
- Chemical Treatment Systems
- Packaged Treatment Systems
In this section you find tools to assist in writing a Stormwater Quality Management Plan (SWQMP).
Use the interactive module to calculate the StormTrooper size electronically.
- A - For each stormwater discharge outfall enter size of the acreage
- C - Houston areas typically use .80 coefficients for commercial property and .55 coefficients for residential property.
Note! There are exceptions to this standard.
- I – Houston areas use .27 for Rainfall Intensity. Check with ParkUSA for Rainfall Intensities in other cities.
- Q in cfs and gpm will be provided automatically.
A chart with StormTrooper sizes will appear, when clicking on the "View StormTrooper Sizing Chart" button.
Punch Chat or call ParkUSA, 888-611-Park, for information on other city’s SWQMP requirements.
StormTrooper Sizing Tool
To see which StormTrooper Model is recommended, please insert your numbers for the area size (acres), the runoff Coefficient and the rainfall intensity in the below fields and hit the calculate button.
Flowrate (cfs) =
|Most cities accept:
Commercial: .80 | Residential: .55 | All Pavement: .95
Flowrate (gpm) =
StormTrooper Interceptors are available in two standard models. Cylindrical sizes are available from 500 gallon (SwST 05C) to 6,000 gallons (Swst 60C). Rectangular sizes are available from 500 gallon (SwST 05) to 15,000 (Swst 150). Typically, clients prefer Cylindrical designs in softer soil conditions due to the smaller footprint. Low profile Rectangular designs are handy in rocky soil conditions where digging deep gets expensive.
ParkUSA also offers other sizes and special designs to fit your jobsite conditions.
Below you will find the specifications for the StormTrooper categorized in different sectins. Please click on the section name to expand the tab.
- A Stormwater Interceptor shall be provided and installed as indicated on plans. System shall be Park Environmental Equipment Company, StormTrooper® Model SwST-XX. The system shall be installed in strict accordance with the manufacturer's recommendations. Manufacturer shall have been in business for 10 years in the design and manufacturing of wastewater products. Manufacturer shall provide a one-year limited warranty. Manufacturer shall provide proof of third party testing by an independent applied engineering and physical sciences testing organization.
- The Stormwater Interceptor shall be provided with installation, operation & maintenance manuals that contain clear and concise descriptions.
- Contractor shall submit required copies of manufacturer's equipment specification for engineer's review. Shop drawings shall include the following:
- Detailed manufacturer's data including installation plan/elevation drawings, rebar layout drawings, buoyancy calculations, and site specific coalescing plate performance analysis for TSS & TPH, all certified by a registered professional engineer.
- Manhole frame/cover specifications.
- Joint Sealant specifications.
- Coatings and/or concrete additives specifications.
- Stormwater Interceptor design shall conform to criteria set forth by the International Association of Plumbing and Mechanical Officials (IAPMO), the American Petroleum Institute, and all other governing state and local code requirements.
- Contractor shall field verify all dimensions for piping inverts and interceptor excavation depth.
- Concrete: The Stormwater Interceptor tank shall be constructed of precast concrete having a 28 day minimum compressive strength of 4500 PSI using a Type I Portland Cement.
- Steel Reinforcement: The Stormwater Interceptor shall be designed for H-20-44 traffic loading as defined by AASHTO 14th ED. 1989 using a 30% impact factor. Structural reinforcement placement shall be in accordance to ACI. All reinforcement steel shall comply with ASTM A615 grade 60 or ASTM A706 Grade 60. Bar bending shall comply with latest ACI standards. Lifting inserts to be installed for handling and be installed per manufacturer's requirements.
- Manhole Access: Interceptor shall have adequate manhole access covers and frames to permit access for cleaning all areas of the interceptor. Each manhole access shall be minimum 24” diameter clear opening. Cast iron frame and covers shall conform to ASTM A48-83 Class 30. Fabricated steel access covers shall be ASTM A36 steel construction and hot-dipped galvanized after fabrication. All access covers shall be traffic duty. Access covers shall be placed at grade elevation by using concrete extensions.
- Pipe Material: All pipe and fittings shall be of materials approved by engineer.
- Coalescing Media: The oil coalescing media pak shall be fabricated of an oleophillic polypropylene plastic material and assembled into modules with 304 stainless steel materials. Media assembly shall be self-cleaning and removable.
- The Stormwater Interceptor shall be equipped with a system to control by-pass manhole to control unusually high rainfall. The control manhole system shall prevent re-suspension and scouring of the storm water interceptor. The control by-pass system shall be equipped with an adjustable weir and stainless steel debris screen.
C. Interceptor Performance
- The interceptor shall be sized to treat the flow generated by the design rainfall intensity of the Harris County area, which is based on 0.27-inch per hour. Using 0.27-inch per hour rainfall intensity, the rational formula (Q=CIA) shall be used to determine the design flow rate for impervious (C=0.80) commercial drainage areas.
- The Interceptor shall be capable containing and treating a wide variety of concentration and loads of floatable and non floatable constituents such sand, sediments, oil, grease, grit and trash debris to the acceptable loadings of EPA and local authorities.
- Influent Characteristics - The interceptor shall be designed for intermittent and variable flows of water, oil, or any combination of non-emulsified sediment/oil/water mixtures ranging from zero to 2,400 gpm (adjust number accordingly). Operating temperatures of the influent storm water shall range from 40F to 60F. The specific gravities of the hydrocarbons shall range from .68 to .95 at operation temperature and have a concentration of 400 PPM or less.
- Effluent Characteristics – The total petroleum hydrocarbon (TPH) concentration of the interceptor effluent shall not exceed 10 mg/l. The system shall be capable of removing a minimum of 80% of the total suspended solids (TSS).
- The Interceptor manufacturer shall provide recommended maintenance and operations instructions that comply with EPA, county and local monitoring requirements.
- The Interceptor shall be installed in strict accordance with the manufacturer's recommendations and according to plans and specifications. The manufacturer shall have representation during the setting procedure to insure proper installation.
- The Stormwater Interceptor shall be installed on level, undisturbed soil or an approved compact fill with a load bearing capacity of minimum 2000 PSF.
- The interceptor shall be backfilled after placement with an approved backfill material. Backfill of all sides of structure shall be performed simultaneously to prevent unbalanced lateral pressures during construction.
- All joints shall be made watertight. Manufacturer shall seal joints with a plastic flexible gasket conforming to AASHTO M-198-75 for bitumen gasket.
- All interceptor inlet/outlet/vent piping shall be installed in accordance to manufacturer’s recommendations and project specifications.
- Interceptor shall be filled with clean water prior to start-up of system. Follow manufacturer’s recommendations for testing and start-up.
Testing and Certification
Each StormTrooper becomes a unique design with custom specification drawings which include unit sizes, orientations, risers, hatchways, weights, excavation depths, flowline and top of rim elevations. The engineer and contractor should have everything necessary for a smooth transition from approval of a project through installation.
Each StormTrooper Production Drawing begins with an analysis of the number of coalescing media plates needed to handle the TSS and TPH treatment for a particular size. This analysis is based on Stokes’s Law for laminar flows between the plates and Stokes’s Law for particle rise (see CMP description, TSS & TPH analysis). Certified Buoyancy Calculations are completed when requested or when necessary for structural considerations (see Buoyancy PDF example).
StormTrooper is a Patented Design (Patent No.: US 7,470,361 B2), that was independently 3rd party tested and certified by Southwest Research Institute, San Antonio, Texas in 2002. Tests were conducted utilizing Test Method EPA 162 for TSS and Test Method EPA 1664 for TPH (see SwRI letter & Test protocol).
|CMP||Coalescing Media Pack|
|Patent 7470361||Patent 7470361|
|SwST Test & Approval||SwST Testing Approval Letter|
|SwAQ Test & Approval||SwAQ Testing Approval Protocol|
|TSS & TPH||TSS & TPH Analysis|
|Buoyancy Example||Buoyancy Example|