Cindy Lorenzo’s house smells absolutely foul. There’s a noxious brown liquid bubbling up from her kitchen drain, and a sickening odor hits you as soon as you open the door to her Redland’s residence.

“It smells atrocious,” she complains.

Cindy’s septic tank is backed up. She’s had to call the plumbers today to have it pumped.

“This time of year, I see this kind of thing every day,” says Angel Rosario, owner of A Better Aim Septic, Inc.

He’ll be seeing even more of it in the future. That’s because climate change is set to cripple coastal septic systems. Ever more intense rain storms and rising seas are are going to raise groundwater levels in South Florida, flooding out systems like Cindy’s much more frequently.

The solution is expensive. According to a 2013 county study, bringing the 93,000 properties in Miami-Dade without sewer access into the system might cost $2.3 billion.

June is the rainy season in South Florida, and a few days before Cindy’s septic tank backed up, a month’s worth of precipitation fell in one week. Angel is halfway through the process of pumping out the overflowing septic tank when groundwater starts pouring in.

“When the water table rises, and you get saturation from the rain, the water has nowhere else to go but back (into the septic system),” he explains.

“That’s why you’re getting that heavy fecal smell,” explains Angel Rosario, owner of A Better Aim Septic, Inc.

A backed-up septic tank is pretty normal for the 1.3 million Floridians who treat their wastewater that way. But “areas where the ground elevation is low relative to sea level are going to be increasingly at risk to drain field failures,” warns Doug Yoder, deputy director of Miami-Dade’s Water and Sewer Department.

He suspects that low-lying neighborhoods close to the ocean may already be having trouble. Septic tanks in neighborhoods like Shorecrest or Surfside could be the first to need replacement.

Why septic tanks?

Septic tanks get installed in zones where it’s not practical or cost effective for local governments to put in a traditional sewer system. They function by collecting wastewater in impermeable tubs, and then just letting the liquid sit there for a while. Gravity does the work of separating out the solids (aka poop), and of pulling the liquid out into the septic drain field, where it slowly gets filtered through the soil.

For it to work, the bottom of the drain field needs to be at least a foot above the average height of the groundwater, explains Yoder.

A septic tank is just a water-tight tub where wastewater can chill for a while.

If there isn’t that foot of soil between the drain field and the groundwater, the system doesn’t filter right, and might even end up flooding, like Cindy’s did.

Because South Florida’s soil is so porous, rising sea levels and heavy rains can push groundwater level upwards. That means that low-lying Florida homes which treat their wastewater with septic tanks might be forced to spend beaucoup bucks switching systems long before the sea starts flooding their living rooms.

On average, it costs $40,000 to $50,000 to hook up an already built residence to the sewer system, explains Yoder. Developers usually roll the price of these connections into the total cost of a structure they are building, but homeowners may now be left holding the bill for new connections.

That’s partly because installing sewer systems after a property has been built usually involves things like ripping up roads and putting in new water and sewer mains.

Extension of service to commercial properties was estimated to be run around another $400 million, and neither of those numbers factor in the cost of the additional water treatment plants and pumping stations that would have to be built to handle all the new waste-water.

Wait a minute…

But before the county whips the checkbook out and calls the guys with the shovels, they have to determine whether or not people are actually going to stay in the homes they’re considering extending sewer service to.

“You don’t particularly want to invest what could be a very large amount of money to provide centralized sewer service if people are going to pick up and leave because because of frequent flooding conditions,” Yoder cautions.

Whether or not South Florida residents stick around is going to depend a lot on the viability of the regional drainage system, that series of canals and gates that keeps the area dry. Last year, we reported that the system needs a $7 billion investment to keep functioning, and soon, since it might lose 70 percent of its efficiency with just three inches of sea level rise.

Cindy also has a choice to make when it comes to the cost of fixing her septic tank. She can pay Angel, the plumber, $250 for just the pump out, or plunk down a cool $4,000 to get her drain field fixed.

“We’re moving away as soon as my daughter graduates high-school,” she explains, before handing Angel the smaller sum.