If you’ve ever been part of a construction project in a city, you know the drill —  every square foot of land matters. Between zoning restrictions, parking minimums, and tight budgets, trying to make everything fit can feel like a real-life game of Tetris. And when you throw stormwater management into the mix, things get even trickier.

Surface ponds take up a ton of room. That’s land you can’t use for parking, buildings, green space, or anything else productive. However, regulations still require proper on-site stormwater management.  So what’s the fix when there just isn’t space for a big open basin?

That’s where underground stormwater systems come in.

We’re not talking about a few buried pipes and hoping for the best.  We’re talking about modular plastic block systems that can be built to fit nearly any space — under parking lots, roads, parks, or wherever space is limited.  These systems give you the storage you need without sacrificing the land you need for everything else.

And here’s the cool part:  they’re becoming more popular because they actually work, even on tough sites.  Let’s talk about how they work, where they shine, and a real-world example that shows why more developers are turning to them.

So What Exactly Are Modular Stormwater Systems?

Picture a bunch of strong plastic blocks that lock together like Lego. These blocks form an underground tank that stores stormwater runoff when it rains. Once the water is stored, it can either slowly soak into the ground or be released at a controlled rate. The entire setup is wrapped in a geo-textile fabric or an impermeable liner, depending on whether the goal is infiltration (ie: soak into ground) or detention (ie: store & slowly release).

The best part?  These systems are made with about 96% empty space. That means they can hold a lot of water in a small footprint  -  taking up a small fraction of the overall space.

BARR Plastics is a notable supplier of the market leading, GRAF EcoBloc, below ground, modular block Stormwater Management system. It’s one of the most efficient and versatile systems on the market and can be stacked in layers to increase capacity without needing more surface area.  That makes it a great choice when every inch counts.

Why Go Underground?

Let’s say you’re working on a small commercial site. You’ve got just enough space for a building, the required parking, and a bit of landscaping. The last thing you want is a detention pond eating up 15% of your land.
By going underground, you free up that surface space. The parking lot stays a parking lot. The green space stays green. And you still meet stormwater requirements. It’s a win-win.

These systems are also strong.  When properly installed, they can handle the weight of cars, trucks, and even heavy equipment. That means they’re not just tucked away in quiet corners—they can go right under high-traffic areas.

Fast to Install, Easy to Handle

Another plus?  They go in fast. The blocks are lightweight — weighing approx. 11 kgs — so a small team can put them together by hand without needing big machinery or cranes. On many jobs, the tank can be assembled in just a day or several days depending on size.

That saves time, keeps the jobsite simple, and helps keep projects on schedule.

Let’s Look at a Real-Life Example

There’s a great case study from Surrey, BC, where a developer was building a multi-use site on just 1.2 acres.  Between the building footprint and parking requirements, there wasn’t much room left.  The city had strict runoff rules, and there was no way they could fit a surface pond into the layout.

So, the Developer went with a modular underground system using GRAF EcoBloc Smart blocks,  supplied by BARR Plastics.  The tank had to hold 85 cubic meters of stormwater, and it needed to sit over 5 meters deep due to site grading and parking design.
Sounds like a challenge, right?  But the installation was smooth. The whole tank was assembled in just three days, and the full project wrapped up in about two weeks.
The finished system sits under a paved area and handles all the runoff.  It checks all the boxes for local regulations, supports the weight of traffic above and left the entire surface area available for parking and landscaping. That’s a smart solution if we’ve ever seen one.

Where These Systems Work Best

The beauty of modular stormwater systems is how flexible they are.  Here are just a few places where they shine:

Urban Developments: When space is tight, going underground just makes sense. These systems tuck under courtyards, alleys, parking pads, and more.  You get the drainage you need without eating into highly valuable, usable space.
Commercial Projects:  Think shopping centers, office parks, or big box stores. Surface ponds eat up valuable land.  Putting stormwater storage under the parking lot helps maximize every square foot.

Residential Subdivisions:  Instead of scattering small basins across backyards, some developers install a single underground system under a park or road. That means more usable space for homeowners and simpler maintenance and increased safety.

Industrial Sites: These sites generate a lot of runoff and often need deep systems that can handle heavy loads. Modular systems (especially when designed and reinforced like Ecobloc) can meet those needs while keeping the surface available for equipment, storage or parking.

How Do They Compare to Other Options?

You’ve got a few choices when it comes to underground storage: modular block systems, concrete vaults, and plastic tunnel-like chambers.

Concrete Vaults are solid and durable. They’re great for really heavy-duty jobs or when you need to access the inside of the structure. But they take up more room to install and require very heavy and costly equipment to place. That means longer install times and higher upfront costs.

Plastic Chambers are another option. They’re simple to install and cost-effective for larger open areas.  But they require 40 - 60% more stone bedding and a much larger footprint to reach the same storage volume as the Ecobloc modular block system. That can be a deal-breaker on tighter sites or regions where aggregate is more expensive to acquire, ship to site and place on-site  -  making systems like Ecobloc a much more eco-friendly and cost effective choice.

Modular Systems, like the GRAF EcoBloc from BARR Plastics, hit a sweet spot. They offer high storage volume in a small space, go in quickly, and can be shaped to fit unusual layouts. They’re strong, flexible, and ideal when space is tight and time is limited.

Long-Term Durability and Maintenance

These systems are built to last. The plastic materials don’t rust or corrode, and many are rated to perform for 50 years or more.  As long as they’re installed properly—with good backfill, geotextile wrapping, and protection from sediment—they’ll do their job for decades.

That said, maintenance matters. Because the inside isn’t easily accessible, most systems include inspection ports and are paired with sediment traps or filters upstream. That keeps debris out and helps prevent clogging. With the right setup and solid technical guidance from a supplier like BARR Plastics, maintenance is pretty low-key.

More Than Just Storage: Supporting Sustainability Goals

If your project aims for green building standards like LEED, going underground with modular systems can help. Some setups are designed for infiltration, which lets water soak back into the ground and recharge aquifers - this returns rainwater back to earth directly where it lands - which is ideal and as nature intended. Others can be combined with pumps for rainwater reuse—like irrigation or flushing toilets.
Plus, many of these systems are made from recycled materials and require far less aggregate than traditional stone-based systems. That means a smaller environmental footprint overall.

So Why BARR Plastics?

BARR has been closely involved in the stormwater management systems industry game for well over a decade and has been in business for 57 years overall and we know how to work with tight spaces, complex regulations, and fast-paced construction schedules.  Our team helps engineers and builders across Canada find solutions that actually work—no fluff, just solid support and reliable products.

With options like the GRAF EcoBloc, we can help you put together a system that fits your site design, your timeline, and your budget.  Whether you’re designing for infiltration, detention, or rainwater reuse, we’ve got the tools, the Team and know-how to make it happen.

Wrapping It Up

Stormwater management doesn’t have to take up half your site. With the right underground system, you can meet the rules, keep your surface space, and stay on track with your build.

Modular stormwater systems are proving themselves every day on real projects. They’re fast, flexible, and space-saving—exactly what most developers need right now.
If you’re working on a site that needs stormwater storage but doesn’t have the room for a pond or vault, it might be time to think underground modular block system  -  ie: Ecobloc.

Need a smarter way to manage stormwater? Explore proven solutions that protect your site and make every square foot count — get the full details here.