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UNDERGROUND STORMWATER SYSTEM DESIGN WITH MAINTENANCE IN MIND

While most people think that the word “maintenance” should be in the four-letter word category, it’s not surprising that it takes a bit more effort to spell out! Maintenance is a critical aspect in the lifespan of stormwater systems, including underground systems, but is often overlooked or viewed as an afterthought. Owners see maintenance as a burden, so keeping the process as simple as possible to clean collected materials out of these systems is both good design and an excellent client retention practice. While the requirements are very similar from one system to the next, it is important to pay attention to the huge differences in the maintenance PROCESSES and the time, money and effort required long-term. Selecting a system with a well-conceived maintenance program helps win jobs and keep clients coming back.

There are several maintenance concepts that can make or break a project. Here’s a short list of ideas to consider while designing your underground stormwater system:

PRE-TREATMENT

Pre-treatment systems are good investments. They keep heavy volumes of sediment, trash, and debris out of the system. Owners spend tens of thousands – sometime hundreds of thousands – of dollars on their underground detention systems, so it makes sense to protect it from contamination. When selecting a pre-treatment system, consider the types of pollutants coming from the contributing drainage area and match the pre-treatment system to the expected materials. We’ve found biodegradable materials to be the most difficult to manage, as they’re neutrally buoyant and bypass both sumps and skimmers. Screening systems like the Trash Guard Plus are our favorite devices, as they do a good job on all different types of pollutant loads. A few other options for pre-treating water include our permanent drop inlet devices or StormBasin.

CAPTURE SYSTEMS

Capture systems built into the underground system are a terrific back-up plan to catch materials that manage to bypass the chosen pre-treatment device. These are designed to take the first flush of runoff and retain the pollutants in a smaller portion of the system. Engineers need to carefully consider how to design the entry/bypass structure, as well as ensure there’s adequate access to remove accumulated materials.

BACKUP PLANS

Backup plans are important when you consider how often underground systems are completely forgotten about (out of sight, out of mind) and only rediscovered when they cause backups or flooding after having been overridden with collected material. How will the system be restored? How much of the system can be accessed for maintenance without causing damage or undermining the system? Having a good backup plan in place during the design phase can prevent having to completely demolish and rebuild a system, which is never easy on an active site.

underground stormwater system maintenance

ACCESS TO MAINTENANCE AREAS

Access to critical maintenance areas is an important consideration for future maintenance activities and associated costs. Can maintenance features be accessed directly from the paved surface, or are access roads and/or long hoses required? Do the processes involved in maintenance require confined space entry, or can they be accomplished from the surface? Considering the maintenance process in advance will play a big role in the long-term costs of the system.

GEOTEXTILES

There are many details that go into geotextile consideration – this could be an entire blog post on its own (stay tuned). When selecting a geotextile fabric, the type of material chosen should match its intended use. If the right fabric isn’t chosen, different parts of the system could plug up and cause a maintenance nightmare. For example, Nonwoven materials are great for regular detention systems, but may not be ideal for infiltration systems in clayey soils. Another example would be that if runoff is going to be harvested, a geomembrane will be needed to retain water within the system.

R-TANK MAINTENANCE PROCESS – AN ADVANTAGE

At ACF, R-Tank is our recommended system for underground stormwater management for various reasons, including the maintenance process and the system’s ability to be used with many different “accessories” like pretreatment devices. The process is well-documented and relatively simple.

From a pre-treatment standpoint, we recommend the system be designed using Trash Guard Plus to protect the modules. This device keeps debris in the catch basins where it can be easily accessed and removed. For capture, we recommend adding a Treatment Row designed to isolate sediment and debris that may be small enough to pass through Trash Guard Plus (or other pretreatment devices), retaining this material in one small (and easily accessible) area of the system. By trapping the sediment in an area designed to be accessible, it becomes simple and affordable to remove the debris. Finally for back-up, we include Maintenance Ports throughout the system in a belt-and-suspenders approach to allow for backflushing of 100% of the system if the unexpected occurs (or the whole system never gets maintained).

It is important to note that ALL of the processes involved in maintaining an R-Tank system can be completed from the surface, with no confined space entry requirements (systems are easy to access). This means that most contractors would be equipped to perform the process, creating a competitive bid process to perform maintenance and reducing the cost.

Recap:

Before you design your next underground stormwater system, ask yourself these questions:

  • Does the system I’m planning to use include all three levels (pre-treatment, capture, and back-up) of maintenance capabilities?
  • Can the entire system be maintained, or only specific portions? How can the system be restored if it is ignored for extended periods?
  • Is the system footprint so large that maintenance access points are located in areas that might be difficult to reach?
stormwater system maintenance