StormTrap Pushes Stormwater Treatment Into Higher Flow Territory
Stormwater treatment becomes increasingly awkward as drainage areas grow. More runoff has to pass through the system, hydraulic capacity rises, and the space available for treatment rarely expands at the same rate. The conventional response can involve larger structures or multiple treatment units.
StormTrap is addressing that problem with SurgeSettler, a high-flow hydrodynamic separator developed to treat large stormwater flows within a single structure. The system has received verification from the New Jersey Corporation for Advanced Technology (NJCAT) and certification from the New Jersey Department of Environmental Protection (NJDEP), following laboratory testing that StormTrap says included the highest flow rate it has attempted for a hydrodynamic separating device.
NJDEP currently lists both the standard SurgeSettler and a side-outlet configuration as certified manufactured treatment devices with a 50% Total Suspended Solids removal rate. SurgeSettler concentrates that capacity inside one structure, using an enhanced settling pack to increase treatment surface area while shortening the distance suspended particles need to travel. The engineering challenge is maintaining sediment separation as hydraulic throughput rises.
Briefing
- SurgeSettler is designed to treat high stormwater flows within a single hydrodynamic separation structure.
- NJDEP has certified the standard and side-outlet configurations for 50% Total Suspended Solids removal.
- Additional Sediment B testing supports NJCAT verification for 80% TSS removal, according to StormTrap.
- Testing used ASTM methods covering hydraulic characteristics and suspended sediment removal performance.
- An enhanced settling pack increases effective treatment surface area while reducing the distance particles need to settle.
Increasing the Settling Area
Hydrodynamic separators have to reconcile two competing requirements. Water needs to move through the structure at the required rate, while suspended particles need sufficient opportunity to leave that moving water and settle. Increasing flow can make that balance progressively harder as velocities and turbulence change.
SurgeSettler addresses the problem with what StormTrap describes as an enhanced settling pack. Rather than relying solely on the footprint of the chamber to provide settling area, the internal structure increases the available treatment surface and reduces the distance particles must travel before settling. Flow-control components distribute incoming stormwater through the pack before treated water leaves the structure.
The principle is familiar in sedimentation engineering. Particle separation depends on more than the physical volume of a chamber, and internal geometry can be used to create substantially more effective settling area within a constrained footprint. In a manufactured stormwater device, however, that geometry also has to operate across changing flows without creating hydraulic conditions that defeat the separation process.
ASTM C1745 is concerned with the hydraulic characteristics of hydrodynamic separators and underground settling devices, including the relationship between discharge and hydraulic head. ASTM C1746 provides a laboratory method for measuring suspended sediment removal efficiency under defined conditions. The current C1746 standard notes that individual devices have different flow patterns and turbulence characteristics and that performance can vary with discharge, particle-size distribution, particle density and fluid viscosity.
ASTM C1746 does not establish removal efficiency under every field condition. Laboratory testing provides a controlled basis for evaluating and comparing performance, while ASTM also makes clear that completing the test does not itself constitute certification by an authority having jurisdiction.
The New Jersey Test
New Jersey has developed a structured regulatory system for manufactured stormwater treatment devices, with separate NJCAT verification and NJDEP certification processes supported by protocols for hydrodynamic separators and filtration devices.
For SurgeSettler, StormTrap reports that testing was conducted at its research and development facility in Morris, Illinois, using ASTM C1745 and C1746 methods to examine hydraulic characteristics and removal efficiency. The company says the programme involved the highest flow rate it has attempted for a hydrodynamic separating device.
NJDEP lists SurgeSettler as certified for 50% TSS removal. StormTrap also reports that additional testing using Sediment B supports NJCAT verification at 80% TSS removal. Those percentages relate to different testing and verification conditions and should not be treated as interchangeable performance claims.
Stormwater requirements also vary with the application. New Jersey’s current guidance states that redevelopment of existing impervious surfaces generally requires the greater of the existing system’s removal rate or 50% TSS removal, while new impervious surfaces are subject to an 80% requirement where the water-quality provisions apply.
Certification provides an established regulatory basis on which a manufactured device can be considered within the relevant design framework. The eventual system still has to be selected and configured around the drainage area, expected flows, site geometry and applicable stormwater requirements.
Designing for Large Flows
Treating more runoff through a single structure can be useful where drainage areas are large but underground space is constrained. Roads, logistics facilities, commercial developments, industrial sites and other heavily paved areas can generate considerable runoff while simultaneously leaving drainage designers with congested utility corridors and limited space for treatment infrastructure.
If the required treatment flow can be accommodated in fewer structures, there may be fewer excavations, connections and access points to incorporate into the drainage layout. The benefit will depend on the hydraulic requirements and physical constraints of the individual project rather than treatment capacity alone.
StormTrap has also designed SurgeSettler to accommodate site-specific arrangements, including a side-outlet configuration. NJDEP’s current manufactured treatment device register separately lists that configuration at the same 50% certified TSS removal level as the standard arrangement, providing another option where drainage alignments or underground infrastructure constrain the installation.
Maintenance Inside the Structure
Concentrating treatment capacity into a single structure also concentrates maintenance. StormTrap has incorporated three access locations into SurgeSettler: the forebay, outlet bay and a dedicated 2 ft by 2 ft opening through the centre of the enhanced settling pack. The arrangement is intended to allow inspection and sediment removal using conventional vacuum maintenance equipment.
Access can determine whether a treatment system remains practical after installation. Sediment captured by a separator eventually has to be removed, and internal components that improve treatment performance cannot become an obstacle to inspecting or cleaning the structure.
A device designed for larger drainage areas may also accumulate substantial quantities of material over its operating life. Maintenance intervals will depend on the individual site, pollutant loading, drainage characteristics and operating conditions rather than certification performance alone.
Extending Hydrodynamic Separation
SurgeSettler joins StormTrap’s existing StormSettler hydrodynamic separator and the company’s wider range of detention, infiltration, water-quality and water-harvesting systems. The new system is aimed at applications where treatment flow becomes large enough for the size or number of conventional structures to become a significant design consideration.
Nathan Olds, CEO of StormTrap, describes scalability as one of the objectives behind the development:ย โStormwater treatment requirements continue to evolve, and our customers need solutions that deliver both verified performance and scalability.โย
StormTrap says the settling-pack technology is intended to help the system handle higher flows and larger drainage areas while retaining practical construction and maintenance characteristics.
Regulatory verification establishes SurgeSettler’s performance under defined testing conditions rather than predicting removal efficiency across every field installation. What StormTrap has demonstrated is a different approach to the capacity problem: instead of increasing treatment primarily by adding structures, it has engineered more settling area into one of them.
Key Industry Questions
- What is SurgeSettler?ย SurgeSettler is a manufactured hydrodynamic stormwater treatment device developed by StormTrap to separate suspended sediment from stormwater while accommodating relatively high treatment flows within a single structure.
- What TSS removal rate has NJDEP certified?ย NJDEP currently lists both the standard SurgeSettler and its side-outlet configuration at a certified 50% Total Suspended Solids removal rate.
- Why does StormTrap also refer to 80% TSS removal?ย StormTrap states that additional Sediment B testing supports NJCAT verification for 80% TSS removal. This is separate from the NJDEP 50% certification and relates to different test conditions.
- How does the enhanced settling pack work?ย The settling pack increases the treatment surface available inside the structure and shortens the distance suspended particles need to travel before settling. Internal flow-control components are used to distribute stormwater through the pack.
- What does ASTM C1746 testing establish?ย ASTM C1746 provides a controlled laboratory method for measuring sediment removal by hydrodynamic separators under specified conditions. ASTM explicitly states that the method is not intended to determine field removal efficiency.
- What does ASTM C1745 measure?ย ASTM C1745 addresses hydraulic characteristics of hydrodynamic separators and underground settling devices, including the relationship between flow and hydraulic head.
- Why could higher treatment capacity matter on infrastructure projects?ย Accommodating larger treatment flows within fewer structures can be useful where underground space, excavation areas or drainage layouts are constrained. The actual benefit depends on project-specific hydraulic and site conditions.
- How is SurgeSettler maintained?ย The structure has access through the forebay and outlet bay plus a dedicated 2 ft by 2 ft maintenance opening through the settling pack, allowing inspection and sediment removal with conventional vacuum equipment.
Strategic Takeaways
- Increasing effective settling area inside the treatment structure offers a route to greater hydraulic capacity without relying solely on a larger physical footprint.
- NJDEP certification establishes SurgeSettler at 50% TSS removal under the applicable New Jersey framework; additional NJCAT Sediment B verification should be considered separately.
- Hydraulic capacity and sediment removal cannot be considered independently because flow conditions directly influence separator performance.
- Side-outlet configurations broaden the options available where drainage alignments or underground infrastructure constrain the installation.
- Maintenance access becomes increasingly important when treatment capacity and captured sediment are concentrated within fewer structures.
