Underground BMPs

Underground BMP’s are becoming a more popular option for stormwater management. This guide will provide more information on different types of underground BMP’s to help determine which underground BMP works best for the site conditions. This guide will provide a description of the process utilized by the BMP, the pollutants the BMP aims to remove, and information on the operation and maintenance of the BMP. The underground BMP’s described in this guide will be separated into categories based on the type of BMP it is, which include: bioretention, detention and infiltration, detention and retention, filtration, and hydrodynamic separators.

Bioretention BMP’s

Bioretention BMP’s treat stormwater runoff by passing the runoff through a specially engineered filter media that aims to capture and immobilize pollutants.

Filterra – Contech


Filterra is similar to bioretention in its function and application, but has been optimized for high volume/flow treatment and high pollutant removal. Its small footprint allows it to be used on highly developed sites such as landscaped areas, parking lots and streetscapes. Filterra is exceedingly adaptable and can be used alone or in combination with other BMPs.

Filterra Operation and Maintenance Manual

Filterra Maintenance Steps

The video below shows the process that Filterra uses to remove pollutants from stormwater runoff

Tree Pod Biofilter – Old Castle

BioMod Modular Bioretention System is a modular precast concrete biofiltration cell system that has been developed to add consistency to design and construction, with features to enhance filter performance, structural integrity and reduced construction and ongoing maintenance costs.

No operation and maintenance manuals available.

BioMod Modular Bioretention System – Old Castle

BioMod Modular Bioretention System is a modular precast concrete biofiltration cell system that has been developed to add consistency to design and construction, with features to enhance filter performance, structural integrity and reduced construction and ongoing maintenance costs.

BioMod Maintenance Manual

DeepRoot – Silva Cell


The Silva Cell is a modular suspended pavement system that uses soil volumes to support large tree growth and provide powerful on-site stormwater management through absorption, evapotranspiration, and interception.

DeepRoot Operation and Maintenance Manual

This video shows the various sizes of Silva Cell that can be used and how the system is fits together.

Detention and Infiltration BMP’s

Detention and infiltration BMP’s store stormwater runoff and infiltrate the stored runoff into the ground or release the runoff downstream at a required discharge rate. Detention and infiltration BMP’s can provide flood control measures as well as a reduction in pollutants for stormwater runoff. If filter media that is designed to treat stormwater runoff is the infiltration media the performance of pollutant removal should increase.

CMP Detention and Infiltration – Contech


Contech’s CMP stormwater detention and infiltration systems store stormwater and release it downstream at an allowable discharge rate or allow it to infiltrate into the surrounding soils. Systems can be sized and shaped to meet site-specific needs, and are available fully or partially perforated.
CMP Detention and Infiltration Operation and Maintenance Manual

Contech – Duromaxx Detention Systems


DuroMaxx steel-reinforced polyethylene (SRPE) pipe combines steel and polyethylene (PE) to make an exceptionally strong and durable pipe for stormwater detention and infiltration applications. DuroMaxx is unique as it has fewer joints to assemble on site, can be made watertight, and can be used in applications with corrosive soils.
Duromaxx Detention Systems Operation and Maintenance Manual

Contech – Chambermaxx Detention Systems


The ChamberMaxx corrugated, open-bottom plastic infiltration chamber system allows you to meet stormwater runoff reduction requirements and maximize available land space by providing economic infiltration below grade. ChamberMaxx maximizes storage volume in a small footprint, and its low profile shape is ideal for sites with shallow footprints.
Chambermaxx Detention Systems Operation and Maintenance Manual

Contech – CON/SPAN Detention Systems


CON/SPAN is a modular, precast concrete arch system designed to provide economical, large volume stormwater detention or infiltration below grade. CON/SPAN’s distinctive arch top and vertical side walls maximize storage volume while providing enhanced structural integrity.

No operation and maintenance manual available.

Contech – Terre Arch


Terre Arch is a modular, multi-chambered, precast concrete stormwater storage system engineered for underground installation. Terre Arch’s strength, storage capacity, and fast installation make it the most economical concrete system available.
Terre Arch Operation and Maintenance Manual

This video provides more information and shows the construction of the Terre Arch detention and infiltration stormwater BMP

Detention/Retention BMP’s

Detention and retention BMP’s store and then release stormwater runoff downstream at a allowable discharge rate while reducing pollutant levels in the runoff by letting the sediment settle to the bottom of the system. These systems will build up sediment overtime and this sediment will need to be removed periodically.

Old Castle – Permecapture


PermeCapture system combines the advantages and versatility of StormCapture structural precast concrete underground storage modules with the aesthetics and performance of Belgard permeable interlocking concrete pavers to reduce peak flows and runoff at the source.

PermeCapture requires regular maintenance to prolong the life of the system. Routine maintenance includes periodic sweeping and removal of surface trash and debris. Frequency of maintenance depends on the conditions of the site and performance of the system.

No operation and maintenance manuals available.

Old Castle – Stormcapture – 3 sided


StormCapture PV panel vaults allow for below-grade, large-capacity water storage. Detention vaults are available in a wide range of sizes and configurations. Vault access covers, various baffle configurations and access ladders are available as required.

No operation and maintenance manual available.

The video below describes the design, installation, and the treatment process of 3 Sided Stormcapture BMP

Old Castle – Stormcapture – 6 sided

StormCapture PV panel vaults are a unique solution for building a custom stormwater detention structure. Panel vaults are used in a wide variety of applications, including detention, retention, harvesting and infiltration, and can be modified to meet most any jobsite application.

No operation and maintenance manual available.

Hydro International – Hydro-Brake Optimum

Manage low, moderate and high flows to deliver low-impact drainage from single sites to large networks.

The Hydro-Brake® Optimum vortex flow control provides customized water quantity management for stormwater, foul or combined water across a wide range of flows and for a variety of applications.

Precision engineered to meet site-specific flow, head and storage requirements, only the Hydro-Brake® Optimum leverages more than 30 years of vortex flow control expertise to deliver exceptional flood protection and low-impact drainage.

No operation and maintenance manual available.

The video below shows the formation of the vortex created when water flows through the Hydro-Brake Optimum

Hydro International – Hydro-Brake Flood


Hydro-Brake® Flood provides large-scale protection at the watercourse level, preventing costly stormwater damage and disruption to residents, businesses and essential services.

Using precisely engineered vortex flow control technology, Hydro-Brake® Flood is the only flood protection system to benefit from our unrivaled legacy of engineering excellence and scientific rigor.

No operation and maintenance manual available.

Hydro International – Hydro-Brake Agile

Reduce upstream storage and manage flood risk at sites with stringent discharge consents where space for on-site attenuation is at a premium.

Where adequate on-site infiltration is not possible, flood risks must be mitigated by attenuating stormwater to result in adequate flood storage. The Hydro-Brake® Agile flow control delivers effective flow control for sites with highly constrained storage conditions.

No operation and maintenance manual available.

Hydro International – Hydro-Brake Orifice

Manage moderate flows and deliver sustainable drainage at site and development level.

The Hydro-Brake® Orifice flow control provides water quantity management for stormwater, foul or combined water at sites with generous discharge consents and low storage constraints.

A low-cost, low-complexity flow control, the Hydro-Brake® Orifice is ideal for development-scale low-impact drainage at sites with moderate flows and moderate storage options.

No operation and maintenance manual available.

Rinker – Stormwater Retention/Detention Systems

Rinker Materials designs and manufactures Stormwater Retention/Detention systems for safe storage and controlled release of collected stormwater.

Rinker Stormwater Retention/Detention Systems Operation and Maintenance Manual

Filtration BMP’s

Filtration BMP’s treat stormwater runoff by passing the runoff through filter media which is typically a mixture of sand and organic matter. Filtration BMP’s typically treat catchment areas of 5 acres or less and are effective at treating total suspended solids (TSS), particulate phosphorus, metals, and organics.

Contech – StormFilter



The Stormwater Management StormFilter® uses rechargeable, media-filled cartridges to absorb and retain the most challenging pollutants from stormwater runoff including total suspended solids, hydrocarbons, nutrients, metals, and other common pollutants. StormFilter performance has been verified by the State of Washington Department of Ecology and New Jersey Department of Environmental Protection, as well as numerous other stormwater regulatory agencies.

StormFilter Inspection and Maintenance Procedures
DownSpout StormFilter Operation and Maintenance Manual
Stormfilter CatchBasin Operation and Maintenance Manual

The video below describes the process that the Stormfilter® utilizes to remove pollutants from stormwater.

Contech – JellyFish Filter



The Jellyfish Filter is a stormwater quality treatment technology featuring high flow pretreatment and membrane filtration in a compact stand-alone system. Jellyfish removes floatables, trash, oil, debris, TSS, fine silt-sized particles, and a high percentage of particulate-bound pollutants; including phosphorus, nitrogen, metals and hydrocarbons. The Jellyfish Filter has been tested in the field and laboratory, and is performance verified by the New Jersey Department of Environmental Protection, as well as numerous other stormwater regulatory agencies

JellyFish Filter Maintenance Guide

The video below describes the process that the JellyFish Filter utilizes to remove pollutants from stormwater runoff

Old Castle – Perkfilter Catch Basin

The PerkFilter is a media-filled, cartridge filtration system that removes pollutants such as Total Suspended Solids (TSS), metals, nutrients, gross solids, trash and debris as well as petroleum hydrocarbons to significantly reduce the total downstream pollutant discharge load in stormwater runoff.

The PerkFilter consists of an inlet chamber for high-flow bypass and removal of gross pollutants, a treatment chamber for filtration through media-filled cartridges, and an outlet chamber for flow collection and discharge. A variety of filter media is available to target specific pollutants of concern.

the PerkFilter is available in multiple configurations, including catch basins, concrete vaults, manholes and curb inlets as well as larger custom-designed precast concrete structures.

PerkFilter Inspection and Mainenance Guide

Old Castle – Perkfilter Manhole



The PerkFilter is a media-filled, cartridge filtration system that removes pollutants such as Total Suspended Solids (TSS), metals, nutrients, gross solids, trash and debris as well as petroleum hydrocarbons to significantly reduce the total downstream pollutant discharge load in stormwater runoff.

The PerkFilter consists of an inlet chamber for high-flow bypass and removal of gross pollutants, a treatment chamber for filtration through media-filled cartridges, and an outlet chamber for flow collection and discharge. A variety of filter media is available to target specific pollutants of concern.

PerkFilter Inspection and Mainenance Guide

Old Castle – Perkfilter Vault


The PerkFilter is a media-filled, cartridge filtration system that removes pollutants such as Total Suspended Solids (TSS), metals, nutrients, gross solids, trash and debris as well as petroleum hydrocarbons to significantly reduce the total downstream pollutant discharge load in stormwater runoff.

The PerkFilter consists of an inlet chamber for high-flow bypass and removal of gross pollutants, a treatment chamber for filtration through media-filled cartridges, and an outlet chamber for flow collection and discharge. A variety of filter media is available to target specific pollutants of concern.

PerkFilter Inspection and Mainenance Guide

Hydro International – Up-Flo Filter



Capture sediment, heavy metals, oil and nutrients from stormwater while reducing your site footprint and cutting maintenance costs.

The Up-Flo® Filter is an advanced stormwater treatment system that combines sedimentation and screening with filtration to deliver exceptional surface water pollution removal.

Verified to remove 80% TSS but with demonstrated removal rates up to 98%, only the Up-Flo® Filter was developed in collaboration with the US Environmental Protection Agency

Up-Flo Filter Operation and Maintenance Manual
Stormwater BMP Inspection and Maintenance Services

The video below describes the process that the Up-Flo Filter system utilizes to treat stormwater runoff.

Hydro International – Hydro Dry Screen


Screen and capture stormwater trash, organic matter and sediment, then store it dry to prevent nutrient pollution.

The Hydro DryScreen® is a next-generation baffle box that captures sediment and screens trash and other solids, storing organic materials dry to prevent nutrient leaching.

With a large, blinding-resistant screening capture area and a patented flow diffuser that evenly spreads debris across the entire surface area, only the Hydro DryScreen® can go without maintenance for up to four times longer than conventional screening technologies.

Hydro Dry Screen Operation and Maintenance Manual

The video below describes the process that the Up-Flo Filter system utilizes to treat stotmwater runoff.

BaySaver Technologies – BayFilter


Utilizing concrete vaults, an easy-to-handle cartridge design, a proven mixed media sand filter, and a proprietary spiral wrapped layered construction, BayFilter removes very fine sediment and nutrient pollutants at an astounding maximum flow of 30 GPM per cartridge.

Over 42 square feet of surface area per cartridge assures greater than 80% TSS removal, greater than 50% reduction in total phosphorous, greater than 12% reduction in dissolved phosphorous, and greater than 50% reduction in turbidity*.

Bay Filter Inspection and Maintenance Guide

The link below shows a demo of the process the Bayfilter utilizes to treat stormwater runoff.

BayFilter Operation Demo

Hydrodynamic Separation BMP’s

Hydrodynamic separators are stormwater BMP’s that operate in a flow through setting. As the stormwater flows through a hydrodynamic separator a vortex is generated that sorts sediment, trash, and debris though cyclonic separation. Sediment and pollutants that are removed from the runoff typically settle into a sump chamber that will need to be maintained by removing sediment, trash, and debris regularly. Hydrodynamic separators can be used to treat or pre-treat stormwater runoff.

Contech – CDS


The CDS hydrodynamic separator uses swirl concentration and continuous deflective separation to screen, separate and trap trash, debris, sediment, and hydrocarbons from stormwater runoff. CDS captures and retains 100% of floatables and neutrally buoyant debris 2.4mm or larger, effectively removes sediment, and is the only non-blocking screening technology available in a stormwater treatment device.

CDS Inspection and Maintenance Guide

The video below describes the process utilized by the CDS hydrodynamic separator to remove pollutants from stormwater and describes the required maintenance for the system.

Contech – Vortechs


Vortechs is a hydrodynamic separator that combines swirl concentration and flow controls into a shallow treatment unit that traps and retains trash, debris, sediment, and hydrocarbons from stormwater runoff. Vortechs removes sediment down to 50 microns and is the ideal solution for projects that require a shallow treatment device due to groundwater, utility or bedrock constraints.

Operation and Maintenance:
Maintaining a Vortechs is a simple process that can be easily accomplished using a vacuum truck, with no requirement to enter the unit.
Contech has created a network of Certified Maintenance Providers to provide maintenance on stormwater BMP’s

The video below describes the process that the Vortechs system utilizes to remove pollutants from stormwater runoff.

Contech – Vortsentry HS


The VortSentry HS is a compact stormwater treatment system that uses helical flow technology to enhance gravitational separation of floating and settling pollutants from stormwater. The small footprint of the VortSentry HS makes it an effective stormwater treatment option for projects where space is at a premium.

VortSentury Maintenance Guide

Old Castle – Dual Vortex Separator – Circular




The DVS is a hydrodynamic separator that removes Total Suspended Solids (TSS), gross solids, trash and debris as well as petroleum hydrocarbons from stormwater runoff. The DVS enhances pollutant removal by directing incoming flow to two vortex tubes that operate in parallel. The configuration of the vortex tubes and the extended flow path maximize residual time to increase the settling of solids. Sediment is collected in an isolated storage area while floating trash, debris and petroleum hydrocarbons are retained behind internal baffles.
The DVS unit can be used to help meet TMDL requirements for removal of solids, trash, debris and petroleum hydrocarbons. The unit can also be a critical component of a comprehensive LID strategy to help increase the service life of infiltration, detention and retention systems as well as other stormwater treatment BMPs
Operation and Maintenance:
Routine maintenance includes removal of accumulated pollutants through the vortex tubes with a vacuum truck. Frequency of maintenance depends on the conditions of the site and the performance of the system.

Old Castle – Dual Vortex Separator – Square

The DVS is a hydrodynamic separator that removes Total Suspended Solids (TSS), gross solids, trash and debris as well as petroleum hydrocarbons from stormwater runoff. The DVS enhances pollutant removal by directing incoming flow to two vortex tubes that operate in parallel. The configuration of the vortex tubes and the extended flow path maximize residual time to increase the settling of solids. Sediment is collected in an isolated storage area while floating trash, debris and petroleum hydrocarbons are retained behind internal baffles.
Operation and Maintenance:
Routine maintenance includes removal of accumulated pollutants through the vortex tubes with a vacuum truck. Frequency of maintenance depends on the conditions of the site and the performance of the system.

Hydro International – Downstream Defender


Capture and retain sediment, oils and floatables from stormwater runoff over a wide range of flows in a small footprint.

Downstream Defender® is an advanced hydrodynamic vortex separator that provides impressive and reliable removals of sediments, oil and floatables from stormwater runoff.

The Downstream Defender® offers long maintenance intervals and consolidates pollutant removal to a single point in the drainage system.

Downstream Defender Operation and Maintenance Manual

The video below demonstrates the Downstream Defender’s ability to remove sediment at a high flow rate.

Hydro International – First Defense


Capture and retain stormwater sediment, trash and floatables in a unit that saves site space and adapts to smaller or logistically difficult site locations.
First Defense® is a versatile stormwater separator that works with single and multiple inlet pipes and inlet grates. It is easily maintained from the surface by standard vacuum tanker.

First Defense Operation and Maintenance Manual

The video below describes the process utilized to remove pollutants by the First Defense system.

Rinker – In-Line Stormceptor

The Inline Stormceptor is the standard design for most stormwater treatment applications. The patented design allows the Inline unit to maintain continuous positive treatment of stormwater for the removal of pollutants such as total suspended solids (TSS), free oils and nutrients year round, regardless of the flow rate

Operation and Maintenance:
Inspect and maintain the In-line Stormceptor® from the surface, without entry into the unit. Ideally, perform maintenance once the stored volume reaches 15 percent of the total volume in the lower chamber, or immediately in the event of a spill.
Maintenance intervals vary depending on the application. We recommend quarterly inspections during the first year of installation to accurately establish the maintenance schedule.

Rinker – Inlet Stormceptor

The Inlet Stormceptor® is designed to accept Stormwater from either on top through a grated cover, from the side in a storm line or both. The Inlet Stormceptor design operates in the same manner as the inline unit, providing continuous positive treatment, and ensuring that captured material is not re-suspended.

Operation and Maintenance:
Inspect and maintain the In-line Stormceptor® from the surface, without entry into the unit. Ideally, perform maintenance once the stored volume reaches 15 percent of the total volume in the lower chamber, or immediately in the event of a spill.
Maintenance intervals vary depending on the application. We recommend quarterly inspections during the first year of installation to accurately establish the maintenance schedule.

Rinker – Submerged Stormceptor

The Submerged Stormceptor can accommodate a partially or fully submerged pipe application. Submergence is common in areas close to lakes, rivers, coastal areas and areas with high groundwater tables. The insert in these applications has a custom weir height and second drop pipe set at the existing water elevation. Both the weir height and the height of the second drop pipe are site specific depending on the level of submergence. The second drop pipe elevation corresponds to the actual submergence elevation while the weir is built to be 9” higher than the submergence elevation.

Operation and Maintenance:
Inspect and maintain the Submerged Stormceptor® from the surface, without entry into the unit. Perform maintenance once stored volume reaches 15 percent of the Stormceptor® capacity, or immediately in the event of a spill.
Maintenance intervals vary depending on the application. Quarterly inspections should be during the first year of installation, so you can accurately establish a maintenance schedule
Remove oil and sediment through the 24 inch diameter outlet riser pipe. Or you may remove floatables and hydrocarbons through the 6 inch oil inspection port.

BaySaver Technologies – BaySeparator

Proven structural BMP’s designed to efficiently and effectively treat stormwater by separating debris and trapping pollutants before they enter the waterways. All BaySeparators, can be fabricated into multiple sizing combinations to fit a variety of applications and custom installations.

BaySeparator Inspection and Maintenance

The link below is an interactive demo that shows the process that the BaySeperator utilizes to remove pollutants for various flow rates.

BaySeparator Demo