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The South District Wastewater Treatment Plant in South Miami-Dade is largely a circle of holes on more than 450 acres. At each hole all one can see is a massive pipe that bores straight into the ground. Under pressure, every day, about 80,000 gallons of lightly treated sewage are sent shooting down thirteen of the seventeen pipes. On each concrete pad, near the pipe, is a separate well the county uses to monitor whether the aquifer is contaminated. It is this state-enforced inspection that uncovered signs of the problem back in 1994. Today, on the eve of a possible drought in South Florida, a majority of the monitoring wells at the South Miami-Dade plant show signs of chemicals that indicate sewage in the Floridian aquifer -- the county's reserve source of drinking water.
Ironically enough, deep well injection began in 1972, with passage of the Federal Clean Water Act. The law mandated new stringent water-quality standards for local bodies of water. Until then small treatment plants handled sewage for the ever-growing subdivisions. After light treatment the plants dumped the sewage into the canals, which proved disastrous for South Florida's sensitive tourist gems, Biscayne Bay and the Everglades.
The EPA knew local governments would never be able to comply with the new water-quality standards without federal support. The Clean Water Act included a construction grants program, but to get the money, the county had to decide on a plan that would be the cheapest environmentally acceptable wastewater disposal method. It came up with two options: Send it out to sea or inject it into the earth through wells.
The idea of shooting pressurized wastewater thousands of feet underground had gained currency among certain geologists and consulting firms. They based their idea on South Florida's unique geology. Starting roughly 2500 feet beneath the surface of Southeast Florida is an area commonly known as the “boulder zone.” This layer is open and cavernous. Directly above it is a slab of dolomite about fifteen feet thick that is relatively nonporous.
Above the dolomite is the upper Floridian aquifer, at about 2000 feet. It's composed of different kinds of limestone. Stretching about 1500 feet, it's much more porous than the dolomite. While the water found here is too salty to drink, it is still classified as drinkable because it's easily cleaned and meets the EPA standards for low salt content. Above the upper Floridian is another confining layer, which is made of tight sand and clay. Nobody knows the size of this layer or whether it's full of fractures. Finally, above that is one of South Florida's most precious resources, the Biscayne aquifer, from which the county currently draws its drinking water.
The geologists and consultants proposed to inject the sewage into the boulder zone, beneath the lowest confining layer that stretches at least to Palm Beach, although nobody really knows how far for sure. Water in the boulder zone is too salty to qualify as drinkable. The national consulting firm CH2M Hill theorized that it would take the sewage hundreds of years to travel out of the boulder zone. In fact CH2M Hill estimated it would be 7000 years before it made it out to sea. The firm did acknowledge it might migrate to the upper Floridian aquifer and estimated it would take 343 years to penetrate the first confining layer. When the sewage surfaced deep in the ocean or in the aquifer, time would have purified it, so the explanation went.
Their theories depended largely on guesswork. The consultants formed conclusions without the aid of much geological research, and no one has ever seen the boulder zone. Yet government regulatory agencies signed off on their hypothesis.
Injecting the sewage also complied with the EPA's mandate for a cheap solution. The county could place a couple of wells on as little as one acre of land. Each well would cost less than a million dollars to build.
The EPA decided to approve deep well injection as the preferred option. But agency officials failed to recognize how fast the population would grow and how much sewage would end up injected as a result of their decision. “When we were really talking about underground injection, we weren't looking at a hundred million gallons a day,” remembers Richard Harvey, director of the EPA's South Florida Water Management Division. Harvey worked for the state environmental agency at the time. He says the EPA and the state assumed by the year 2000 there would only be a few million people in Southeast Florida, creating at most 20 million gallons of wastewater daily.
In any event the cheap way to dispose of waste encouraged unfettered development. Today, instead of the EPA's initial calculations, about five million people are responsible for about 279 million gallons per day of injected sewage.
Besides underestimating how much waste would be shot underground, government officials made two other faulty assumptions: that Miami-Dade County would drill the wells properly and that the confining layer would truly cap the wastewater. They were wrong on both counts.
Donald McNeill knows it's hard to make geology interesting to non-aficionados. So when the research scientist (although he works for the University of Miami, his investigation of deep wells is independent of the school) wants an audience to understand what separates their sewage from their drinking water, he brings out props. First he passes around a heavy stone pulled from the earth in Broward County. This is a fragment of the confining dolomite layer just above the boulder zone. The piece is heavy, with a beige to brown color. He places it on a table and pours water over it. The water pools but does not permeate the stone. Then he passes out a lighter grayish rock, a sample of the kind that sits above the dolomite. When he tries the water trick, the liquid seeps through the stone.