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R-Tank® Stormwater Modules

Underground Modular Stormwater Storage

R-Tank® Stormwater Modules provide both an efficient and versatile underground stormwater storage system. They assist with stormwater detention, infiltration, and rainwater harvesting applications. Furthermore, with 95% void space, this system reduces the underground stormwater storage footprint. As a result, it resolves utility conflicts and frees up space for future expansion. Due to the patented design of the system, it is one of the most efficient systems on the market. Comparatively, it is a cost-effective alternative to stormwater basins and other underground systems.

Utilize R-Tank Modules in creative applications – from linear green infrastructure, under permeable pavers and soil media for enhanced storage, or combined with pump equipment for harvest and re-use

Five different module configurations (LD, HD, SD, UD & XD) provide module options from 2” to over 7’ tall. In addition, R-Tank® Stormwater Modules deliver support for HS-20 and HS-25 traffic loads, with cover depths ranging from 6 inches to over 16 feet.

A critical component of any R-Tank design is the geotextile fabrics used to wrap the tanks. The fabrics used can change the application. For instance, depending on the fabric used, R-Tanks can discharge the stormwater runoff into a drainage system, release the stormwater back into the ground, or contain the water for future use.

Key features of R-Tank® Stormwater Modules:

  • High-capacity (95% void space) and high-strength
  • Offers HS-20 and HS-25 support for traffic loads with cover depths from 6″ to over 16′
  • Modular design allows for easy installation in most footprints
  • Increased infiltration and ex-filtration
  • Easy-to-transport
  • Lightweight and quick to install
  • Permanent and maintainable storage volume
  • Can be pre-assembled or easily assembled on-site

View complete CAD details.

Hydrocad® Stormwater Modeling System

R-Tank systems can be easily modeled with the HydroCAD® Stormwater Modeling System. This offers a simplified analysis of the system’s behavior in a drainage and stormwater management system. HydroCAD includes custom rating curves for these devices, which can be used with the “special outlet” capability to easily define the device’s stage-discharge characteristics.


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What is the void ratio of R-Tank?

Most R-Tank modules are 95% void, including the LD, HD, SD, and UD lines. However, the XD modules contain more plastic, making them 90% void. Refer to the back page of the R-Tank Brochure for more information.

What is the life expectancy of R-Tank?

R-Tank modules are made from polypropylene, one of the most inert materials available. They are resistant to rot and corrosion along with most chemicals commonly found in soils. There are a number of factors that affect the life of an installed R-Tank system, perhaps the most significant of which is creep – the tendency of plastic to deform over time. The 180-day creep testing performed on R-Tank modules done using the test methodology described in CIRIA C609 demonstrated that R-Tank modules should provide a service life of at least 40 years. If you’d like the full tech note on creep, please contact your local ACF Representative.

How long has R-Tank been on the market?

Underground polypropylene modular stormwater systems have been in use around the world since the early 1990’s. In the United States, the technology was introduced in the early 2000’s. The R-Tank System was first used internationally in 2009, and it was first sold in the United States in 2011.

What is the recycled content?

R-Tank is made from 100% post-industrial polypropylene. Refer to the back page of the R-Tank Brochure for more information.

Since the sides of the R-Tank are open, how does backfill stay out of the R-Tank?

R-Tank is wrapped with a geosynthetic material prior to backfill. This material can be a variety of different materials that align with the goals of the project.

What geotextiles do you recommend to wrap the R-Tank System?

There are four different types of materials that can be used to wrap an R-Tank system:

  1. Nonwoven Geotextile is the standard material used for most projects
  2. Woven monofilament is used for most infiltration applications
  3. Geomembranes (Polyethylene and PVC are most common) can be used to retain runoff in the system for harvesting applications, as well as preventing infiltration where there are concerns about karst or groundwater contamination
  4. Microgrids can be used with stone backfills in bioretention and other similar applications

Can R-Tank support AASHTO HS20 and HS25 traffic loads?

All modules except the Light Duty (LD) modules can be designed to support HS20 and HS25 traffic loads. Each of the different modules (HD, SD, UD, and XD) has a different cover requirement to support different load classes. For more details, review the Tech Note on loading capabilities.

What cover is needed to support traffic loading?

An independent engineering firm reviewed 3rd party testing on each of the R-Tank modules and developed loading models used to recommend minimum cover requirements for various loading classifications. These models are available to designers and include the following minimum cover depths to support AASHTO HS20 loading:

  • Heavy Duty (HD) – 20″
  • Super Duty (SD) – 18″
  • Ultra Duty (UD) – 12″ (with stone backfill) or 14″ (with sand backfill)
  • Extreme Duty (XD) – 6″

To see the HS20 loading mode and access additional information about loading, review the Tech Note on Loading Capabilities.

Can I use R-Tank be used beneath a parking garage or building to meet the storage requirements?

R-Tank has been successfully used beneath a number of parking garages and buildings. However, this is a highly technical application, and we suggest you work with our support team by e-mailing or contacting your local ACF Representative.

How do you maintain the system?

There are three different types of maintenance that can be performed, depending on what features were included in the system design:

  1. Most systems include pre-treatment structures located within the drainage system upstream of the R-Tank. These are designed to prevent contamination of the R-Tank, and they should be maintained regularly.
  2. Systems designed and built after 2018 may include a Treatment Row that can be accessed through an adjacent drainage structure. Treatment rows are designed to trap sediment and debris that bypasses the pre-treatment structures, and they are maintained with standard jet/vac equipment.
  3. Most systems include Maintenance Ports throughout the footprint of the system. These can be used to backflush the system by injecting water through the ports to resuspend sediments which can then be removed with standard vac equipment.

More information is available in the Maintenance Tech Note on our website.

What equipment is necessary to clean the R-Tank System?

R-Tank systems are cleaned with standard jet/vac equipment. There are no special or proprietary components needed for the process. To review these guidelines and access step-by-step instructions on maintaining an R-Tank system, download the Operation, Inspection, and Maintenance Guide from the ACF website.

Is a specialty or certified contractor needed to maintain the system, or can town/county crews perform the maintenance?

While there are contractors familiar with the process available to assist R-Tank System owners, many public works and/or municipal maintenance crews have the equipment and experience necessary to maintain an R-Tank system. For step-by-step instructions on maintaining an R-Tank system, download the Operation, Inspection, and Maintenance Guide from the ACF website.

How much does it cost to clean the R-Tank System?

Costs will vary widely based on the project location, design, and size of the specific system. To get the most accurate pricing from a maintenance contractor, it is helpful to provide them with details of the system from the original project plans. Contact your local ACF Representative if you need assistance identifying a maintenance contractor.

How often must the system be cleaned?

Systems should be inspected at least annually and cleaned when sediment accumulation has reached specific levels based on the configuration of the specific system. Access these guidelines in the Operation, Inspection and Maintenance Guide. Experience has shown that the most cost effective plan is to concentrate maintenance efforts on the pre-treatment systems, which will minimize the need to maintain the full R-Tank system.

What’s the best way to pre-treat runoff?

ACF recommends a two-step approach to pre-treatment:

  1. Use Trash Guard Plus units distributed throughout the upstream drainage network to prevent heavy sediment and debris from entering the R-Tank
  2. Use a Treatment Row inside the R-Tank to trap and segregate materials that make it past the Trash Guard Plus

For more information on pre-treatment, review the R-Tank Maintenance Tech Note.

Do the modules come assembled?

R-Tank modules can be delivered in one of three ways that best fit the customer’s preference:

  1. Unassembled, to be assembled on site by the customer, with ACF providing the training on proper assembly (assembly videos also available)
  2. Unassembled with ACF providing assembly service on-site
  3. Fully assembled

How do you connect storm pipes to R-Tank?

Most pipes are butted to the side of the R-Tank and sealed with a geotextile boot. Pipes connecting into the Treatment Row should be 12″ SDR35 PVC and should be inserted 3-6″ into the opening. CAD details are available through your local ACF Representative.

Is it acceptable to use duct-tape for pipe boot connections instead of steel clamps?

R-Tank modules are supplied with pipe boot kits (one for each pipe connection) that include two stainless steel clamps. Duct tape can be used to temporarily connect the boot flap to the geotextile enveloping the R-Tank, but the clamps must be used to seal the neck of the boot around the pipe. CAD details are available through your local ACF Representative.

Do you have to use stone to backfill around the R-Tank?

There are several backfill options for R-Tank. While AASHTO #57 stone is very common (and often used as supplemental storage capacity), there are sand options that will meet the backfill material specification. See section 2.03 of the R-Tank Specification for more details.

Why does the perimeter stone around the R-Tank need to 2 ft wide?

Providing 24″ of clearance around the perimeter of the system provides adequate access for compaction of backfill materials using vibratory equipment such as a trench roller or plate compactor. There are some unique applications that do not require a 24″ perimeter for backfill. Contact your local ACF Representative with details on your project if you are considering alternatives to the standard guidelines.

Why do self-compacting backfill materials require vibratory compaction?

Vibratory compaction of backfill materials is critical to the stability of the system. In addition to aiding in consolidation of the backfill materials (which helps mitigate the potential for differential settlement), the vibratory action of the equipment helps eliminate micro-gaps between modules, making the system of individual modules much stronger in the process. See the R-Tank Installation Guide for more information.

How quickly can I get material?

Required lead times for projects will vary based on the size of the project and the type of modules being used. Our goal is to provide materials as quickly as you need them, but proper planning is critical to meet your timeline. Contact your local ACF Representative for more information.

Can I use R-Tank to get pollutant removal credit?

In many locations, using the R-Tank as an infiltration system can generate pollutant removal credit. Additionally, in some states the R-Tank Treatment Row can be used to get credit for pollutant reduction. Contact your local ACF Representative for clarification on options specific to your project location.

I have karst/contaminated soils, how does R-Tank prevent infiltration?

When needed, the R-Tank system can be wrapped in an impermeable geomembrane to prevent stored water from infiltrating into the surrounding soils. In these applications, 100% of the stored water will exit through an outlet pipe.

Can R-Tank be used on sites with high ground water tables?

R-Tank has been used on hundreds of sites with high water tables. With highly efficient storage capacity (95%) and a variety of available module heights (including the XD at only 2″ tall and the SD at 9.5″ tall) most systems can be designed to avoid conflict with the water table. However, R-Tank has also been used where it interfaces with the water table. Some of these systems have been designed to allow ground water to enter the modules and exit the system through the drainage network, while others have been designed to prevent groundwater intrusion, which requires additional engineering to manage the buoyant forces of the groundwater. Contact your local ACF Representative for design assistance in scenarios where ground water is likely to affect the R-Tank installation.

When designing R-Tank Systems that will be affected by seasonally high ground water tables, does the R-Tank resist uplift, or should it be braced against flotation?

Some R-Tank systems have been designed to use cover materials to balance the uplift forces of groundwater. These designs require additional attention, which can be provided by your local ACF Representative.

Can R-Tank be used in leach fields?

R-Tank has been used in many different types of leach fields. Made from polypropylene, it is resistant to many chemicals and can be an ideal system for industrial leach fields. When allowed by local regulations, R-Tank is an excellent choice for residential septic leach fields, as well.

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