Florida’s aquifers — a perfect design

Religion aside, when I look at the perfection of an aquifer system, I believe in intelligent design. Aquifer systems can provide water purification and storage on a massive scale, potentially able to provide entire states with clear, fresh drinking water.

Let’s look at the structure and function of two types of aquifers found in Florida, the surficial aquifer and the artesian aquifer.

The shallowest wells are drilled into the surficial unconfined sand and gravel aquifers. These wells are common for individual residences, and irrigation purposes. In general, a sand and gravel aquifer is made up of layers of loose, unconsolidated sediment. These sediments are highly permeable, which means water flows through them easily. They have potentially high flow rates, and large areas for water storage. As water travels from the surface into the ground, the water is purified through a combination of physical, biological, and chemical processes.

Physical processes that purify surface water include mechanical straining, which is basic filtration. The dense layers of gravel, in addition to layers of finer sand, create a matrix of microscopic gaps. This physical screening traps silt, clay, debris and suspended solids, as the water seeps through the layers. 

Biological processes in a sand and gravel aquifer create a living ecosystem, teeming with microorganisms like beneficial bacteria and protozoa. These organisms consume pathogens, organic impurities, and to some extent hydrocarbons such as motor oil. This living layer is a predatory ecosystem that neutralizes pathogens and breaks down dissolved organic waste. 

Chemical processes adsorb tiny suspended contaminants, including bacteria, heavy metals, and organic molecules, as they chemically bond to the rough surfaces of sand grains. Particles are trapped by the sand as they bond to its surface.

Sand and gravel aquifers are easier and less expensive to access because of their shallow depth. They are readily recharged with surface water and have a relatively rapid conversion of surface water to drinking water. Unfortunately, because they are unconfined, these aquifers are vulnerable to surface activities that can contaminate the aquifer beyond its ability to adequately purify the water. Residents who rely on surficial aquifers must also rely on their neighbors and communities to protect the land surface from pollution, so their individual water supplies are safe. 

Artesian aquifers are found much deeper and do an even better job of purifying and storing water. They operate on a longer time scale, with some artesian water being as old as 27,000 years, and are large geologic structures formed over millions of years. Artesian aquifers are made of carbonates, which are ancient marine deposits including limestone and dolomite.

The limestone and dolomite rocks are physical filters for water purification, similar to sand and gravel aquifers. In addition, processes such as pH neutralization, heavy metal precipitation, and chemisorption occur. The pH of limestone is alkaline; as slightly acidic water flows through the rock, a reaction occurs that causes beneficial calcium and carbonate ions to be released. These ions neutralize the acidity in the water and protect pipes from corrosion. Because of the elevated alkalinity of the aquifer, dissolved heavy metals become insoluble and precipitate (become solids) out of the water. Like the sand and gravel aquifer, the limestone has many rough surfaces that trap and bind impurities and pollutants through the process of chemisorption.

Limestone aquifers have many small porous spaces within the rock itself which hold water, in addition to huge cavities within larger geologic structures like caves and underground springs. 

Artesian aquifers are confined, meaning they are capped by an impermeable clay layer, which traps the water underground under pressure. Artesian water can come to the surface when either a well is drilled through the cap rock or the aquifer meets the surface of the land, creating artesian springs. These springs create extensive river ecosystems and provide enjoyable recreation in Florida.

The state of Florida has the greatest overall saturated volume of water in the nation and one of the most productive groundwater systems in the world. This is a treasure worth protecting. Florida is blessed with thousands of artesian springs all over the state. If you have never swum in a crystal clear, 70-degree artesian spring, drop everything and go!