The Gear Box: Rising Sea Levels Mean Trouble for Coastal Septic Systems

If your septic service company operates in any location with a high water table, you know it can and often does mean trouble. But if your service area includes coastal communities, then flooding, land loss, wetland change, damage to infrastructure, and saltwater intrusion are all a part of your everyday life or eventually will be.

As you’re aware, coastal communities tend to have their own on-site wastewater treatment systems. Ordinarily, we simply refer to these as septic systems. But in coastal areas, the issue is a little more serious due to the precarious situation these systems tend to exist within.

In North Carolina, for example, approximately one million homes rely on septic systems that are either on a coastline, within a watershed, or drain directly into the sea.

For these systems to work effectively and remain reliable for serviceable periods of time, they require unsaturated soil which is used to filter the wastewater. These soil filtering systems are designed in such a way as to direct the flow of wastewater away from the homes that use them.

However, when rising groundwater makes these soil filtering systems unstable, the result can be a catastrophic failure. The result is unpleasant, and sometimes unsafe for residents. If the problem is bad enough, it can make homes uninhabitable until it is remedied.

As professor Michael O’Driscoll of East Carolina University explains, “Septic systems in North Carolina need at least one and a half feet of unsaturated soils beneath the system.”

Professor O’Driscoll is the coauthor of a geological study that was presented to the Geological Society of America in 2022. There, he and his partners explained how these septic systems are vulnerable, and that many of them no longer work the way they were designed to.

How Coastal Septic Systems Work

Ordinarily, the drainage field of these systems is isolated from the ground and seawater by both distance and elevation. The drainfield is set back from the tide, protected by setback and separation distance. It is also elevated above the groundwater and above the expected rise-water level from below.

But in recent years, groundwater levels have been rising above the vertical buffer zone beneath the drainfield. This disrupts the structural integrity of the drainfield, causing it to drain in unpredictable ways. Sometimes it can continue to drain in the correct direction, toward the sea. But oftentimes it will begin to drain in different directions at different times of the year, sometimes draining in the direction of the sewage pipe and septic tank, back up toward the home where it came from.

If the pressure is strong enough, it can revisit the occupants of the home. In the worst instances, this return can be both strong and persistent. In these cases, that one-and-a-half feet called for by O’Driscoll is obliterated.

How Coastal Septic Service Providers are Dealing With Rising Groundwater

Groundwater data for North Carolina dates back to the early 1980s. The data shows that groundwater has risen, reducing the buffer zone made up of unsaturated soil beneath the drainage fields and oftentimes eliminating it completely.

The way some septic systems experts are dealing with the problem is by installing an artificial buffer that raises the drainage field and protects it from rising groundwater. This artificial buffer includes a field of sand to surround the septic system.

For now, this approach is working. But it is expected to fail eventually as sea levels continue to rise. When they do, they will disrupt these raised buffers of sand, and destabilize the drainage field just as before.

O’Driscoll warns that a more permanent solution will be necessary.

In areas where the rising water problem is worst, shared systems and enhanced health initiatives have been put in place.

A More Permanent Solution

We spoke with local septic systems experts and craftsmen in our area, and their opinion is unanimous. Septic service providers will need new technology, new permits, and new standards in order to deliver the same level of service to their customers.

There are two alternatives to this. The first is the complete dependence of all homeowners on government-built, designed, and serviced systems. The other is failure.

In the final analysis, independent septic service providers like you will end up picking up the slack. The question is, will our coastal communities have to endure an epidemic of septic failure before such an industry-changing event happens?


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