Does GEPS® Work When the Water Table Is High?

Jul 29
4 min read

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It's one of the first questions clients ask us. Their site sits low, the ground stays damp, and water seems to be waiting just beneath the surface. So the concern makes sense: if the soil is already wet, how can a passive system meant to move water through that soil possibly help?

It's a fair question, and it usually rests on a picture of the water table that isn't quite accurate. Once you have the real picture, the answer becomes a lot clearer. Both our field studies and installations in high water table areas around the world point the same way: GEPS® works in these conditions.

What actually is the 'water table'?

Most people imagine the water table as an underground lake, some hidden pool you'd hit if you dug deep enough. That image is where a lot of the worry comes from, and it's misleading in nearly every setting we work in.

In reality, the water table is simply the depth below which the soil is fully saturated. Above that line, soil is a mix of solid particles, water, and air in the tiny gaps between grains. Below it, those same gaps are almost completely filled with water. There's no open cavern down there. It's still soil, just wet soil, with water occupying almost every pore instead of sharing that space with air.

A "high water table" only means this saturation line sits close to the surface. On our Belle Isle site in Detroit, for example, it ranged from about half a foot to six feet below ground depending on the season and recent rainfall. That's about as high and as variable as it gets, and it's exactly the kind of site clients worry about.

Why the misconception matters

If you believe there's a pool of water underground, GEPS® sounds like it shouldn't function. You picture the system trying to push water into a space that's already full, or draining surface water straight down into that pool and making things worse.

But GEPS® was never designed to dump water into an empty void. It works with the soil itself, and saturated soil is still soil that water moves through. The saturation line isn't a wall. It's just a point where the balance of water and air shifts.

Why GEPS® still performs in wet ground

GEPS® improves how water moves through the soil matrix, helping it travel more freely and spread out rather than pooling at the surface. The units sit roughly two feet down, with a cap that keeps surface water from channeling straight to the groundwater. That distinction matters, because it means the system isn't a drain punched into the earth. It changes the way the surrounding soil accepts and transmits water.

We put this to the test under deliberately harsh conditions at a Detroit site, the Coleman A. Young International airport. There, an infiltration basin was kept flooded with seven to eight inches of standing water for months, creating fully saturated soil around the units. This was designed as an extreme scenario to test the effectiveness of GEPS®.

Even in that saturated state, the units continued to redistribute moisture into the surrounding soil. Just as importantly, the tracer testing showed that water did not simply free-fall through the units as if they were open pipes. Infiltration happened through the soil, at a measured and controlled rate. In other words, GEPS enhanced the soil's natural ability to take on water even when that soil was already full, and it did so without behaving like an uncontrolled shortcut to the groundwater.

What Belle Isle proved over the long term

The study conducted at Detroit's Belle Isle is some of our clearest long-term evidence.

Over roughly two years of independent, third-party monitoring on a site with a water table as shallow as half a foot, stormwater runoff into the storm sewer dropped by about 80% once the system had acclimated.

Two things stand out for anyone worried about high water tables. The groundwater level was not pushed up, or mounded, by the installation. Monitoring wells at the treated site tracked right alongside the untreated control site throughout. And water quality held steady, with no meaningful difference between the two areas. The system reduced surface flooding and runoff without raising the water table or degrading what was already there.

The takeaway for high water table sites

A high water table describes wet soil near the surface, not a reservoir the system has to fight against. GEPS improves how that soil moves and accepts water, which is useful precisely when the ground is already saturated and struggling to drain.

The evidence backs this up, from a controlled saturated-soil test to years of monitoring on one of the shallowest water tables we've worked with, alongside installations in similar conditions worldwide. If your site sits low and stays wet, that isn't a reason GEPS won't work. In many cases, it's the reason it helps.