Stormwater Ponds 101

Stormwater Ponds 101

Well-maintained stormwater ponds can become attractive amenities that also improve water quality. Photo credit: Carrie Stevenson, UF IFAS Extension

Prior to joining UF IFAS Extension, I spent three years as a compliance and enforcement field inspector with the local Florida Department of Environmental Protection (FDEP) office. It was a crash course in drinking water regulation, wetlands ecology, stormwater engineering, and human psychology. For about half of that time, I worked in the stormwater section with an engineer, certifying the proper construction and specifications of stormwater treatment ponds built for residential and commercial developments. During a construction boom in 2000-2003, my coworkers and I traversed back roads from Perdido Key to Freeport, trying to catch every new project and make sure it was done right. If they weren’t, it also fell to the 3 of us to make sure mistakes were corrected.

Since 1982, Florida Statutes have required that rainfall landing on newly constructed impervious surfaces (rooftops, streets, parking lots, etc.) must be treated before turning into runoff that leaves the property and ends up in local water bodies. The pollutants in stormwater runoff—heavy metals, fertilizer, pesticides, trash, bacteria, and sediment—are the biggest sources of water quality problems for the state, more so even than industrial and agricultural sources.

The most common stormwater ponds have sandy bottoms, grassed berms, and piped inlets with riprap to slow the influx of water. Photo credit, Michelle Diller

Therefore, new developments are required to treat that runoff. This may be accomplished by several means, including regional stormwater ponds. However, the most common are still curbs and gutters, which drain to an often-rectangular hole in the ground with a chain-link fence around it. Ideally, water pools into these dry ponds while raining, reducing flood risk and holding water long enough to allow it to soak into the soil. Most of the ponds in northwest Florida have sandy bottoms that percolate easily. Maintenance is required, however, and when heavier soils, trash, or muck accumulate they must be cleaned out to function properly. Depending on the geology of any given location, the ponds may need sand filters or “chimneys” added to allow water to soak into the native soil.

Admiral Mason Park, adjacent to the Veterans’ Memorial Park along Pensacola Bay, is an example of a regional City stormwater treatment facility that also serves as a park. Photo credit: Visit Pensacola

If an area is naturally low-lying, close to the water table, or has highly organic, water-holding soils, it may be necessary to construct a “wet” stormwater pond. In these, water stands to a level below an overflow device, and can become a water feature for the development. Many residential developers will sell lots around a stormwater pond as “waterfront property” and a well-maintained one really can be a nice amenity. However, at their core, these are stormwater treatment mechanisms. A wet pond functions differently than a dry one and is dependent on healthy stands of shoreline vegetation to take up extra nutrients, metabolize them, and render them into harmless compounds. Many of these ponds have fountains to aerate the water and keep them from becoming stagnant. The City of Pensacola and Escambia County have several great examples of these types of ponds that serve as regional stormwater detention and community amenities. These were constructed in lower-lying areas to handle chronic problems with stormwater in areas that were built up and paved many decades before stormwater rules came into effect. Many other innovative and newer stormwater treatments exist as well, including bioretention, rainwater harvesting, green roofs, and pervious pavement.

 

Septic System Do’s and Dont’s After a Flood


Special care needs to be taken with your septic system after flooding. Image: B. White NASA. Public Domain

During and after floods or heavy rains, the soil in your septic system drainfield can become waterlogged. For your septic system to treat wastewater, water needs to drain freely in the drainfield. Special care needs to be taken with your septic system under flood conditions.

A conventional septic system is made up of a septic tank (a watertight container buried in the gound) and a drainfield. Image: Soil and Water Science Lab UF/IFAS GREC.

A conventional septic system is made up of a septic tank and a drainfield or leach field. Wastewater flows from the septic tank into the drainfield, which is typically made up of a distribution box (to ensure the wastewater is distributed evenly) and a series of trenches or a single bed with perforated PVC pipes. Wastewater seeps from these pipes into the surrounding soil. Most wastewater treatment occurs in the drainfield soil. When working properly, many contaminants, like harmful bacteria, are removed through die-off, filtering and interaction with soil surfaces.

What should you do if flooding occurs?

The U.S. Environmental Protection Agency (EPA) offers these guidelines:

  1. Relieve pressure on the septic system by using it less or not at all until floodwaters recede and the soil has drained. Under flooded conditions, wastewater can’t drain in the drainfield and can back up in your septic system and household drains. Clean up floodwater in the house without dumping it into the sinks or toilet. This adds additional water that an already saturated drainfield won’t be able to process. Remember that in most homes all water sent down the pipes goes into the septic system.
  2. Avoid digging around the septic tank and drainfield while the soil is waterlogged. Don’t drive vehicles or equipment over the drainfield. Saturated soil is very susceptible to compaction. By working on your septic system while the soil is still wet, you can compact the soil in your drainfield, and water won’t be able to drain properly. This reduces the drainfield’s ability to treat wastewater and leads to system failure.
  3. Don’t open or pump the septic tank if the soil is waterlogged. Silt and mud can get into the tank if it is opened and can end up in the drainfield, reducing its drainage capability. Pumping under these conditions can cause a tank to float or ‘pop out’ of the ground, and can damage inlet and outlet pipes.
  4. If you suspect your system has been damaged, have the tank inspected and serviced by a professional. How can you tell if your system is damaged? Signs include: settling, wastewater backs up into household drains, the soil in the drainfield remains soggy and never fully drains, a foul odor persists around the tank and drainfield.
  5. Keep rainwater drainage systems away from the septic drainfield. As a preventive measure, make sure that water from roof gutters doesn’t drain towards or into your septic drainfield. This adds an additional source of water that the drainfield has to process.
  6. Have your private well water tested if your septic system or well were flooded or damaged in any way. Your well water may not be safe to drink or use for household purposes (making ice, cooking, brushing teeth or bathing). You need to have it tested by the Health Department or other certified laboratory for total coliform bacteria and coli to ensure it is safe to use.

For more information on septic system maintenance after flooding, go to:

More information on having your well water tested can be found at:

More Information on conventional and advanced treatment septic systems can be found on the UF/IFAS Septic System website

After Flooding, Test Your Well Water

After Flooding, Test Your Well Water

If your private well was damaged or flooded due to hurricane or other heavy storm activity, your well water may not be safe to drink. Well water should not be used for drinking, cooking purposes, making ice, brushing teeth or bathing until it is tested by a certified laboratory for total coliform bacteria and E. coli.

Residents should use bottled, boiled or treated water until their well water has been tested and deemed safe.

  • Boiling: To make water safe for drinking, cooking or washing, bring it to a rolling boil for at least one minute to kill organisms and then allow it to cool.
  • Disinfecting with bleach: If boiling isn’t possible, add 1/8 of a teaspoon or about 8 drops of fresh unscented household bleach (4 to 6% active ingredient) per gallon of water. Stir well and let stand for 30 minutes. If the water is cloudy after 30 minutes, repeat the procedure once.
  • Keep treated or boiled water in a closed container to prevent contamination

Use bottled water for mixing infant formula.

Where can you have your well water tested?

Contact your county health department for information on how to have your well water tested. Image: F. Alvarado Arce

Most county health departments accept water samples for testing. Contact your local department for information about what to have your water tested for (they may recommend more than just bacteria), and how to collect and submit the sample.

Contact information for Florida Health Departments can be found here: County Health Departments – Location Finder

You can also submit samples to a certified commercial lab near you. Contact information for commercial laboratories that are certified by the Florida Department of Health are found here: Laboratories certified by FDOH

This site includes county health department labs, commercial labs as well as university labs. You can search by county.

What should you do if your well water sample tests positive for bacteria?

The Florida Department of Health recommends well disinfection if water samples test positive for total coliform bacteria or for both total coliform and E. coli, a type of fecal coliform bacteria.

You can hire a local licensed well operator to disinfect your well, or if you feel comfortable, you can shock chlorinate the well yourself.

You can find information on how to shock chlorinate your well at:

After well disinfection, you need to have your well water re-tested to make sure it is safe to use. If it tests positive again for total coliform bacteria or both total coliform and E. coli call a licensed well operator to have the well inspected to get to the root of the problem.

Well pump and electrical system care

If the pump and/or electrical system have been underwater and are not designed to be used underwater, do not turn on the pump. There is a potential for electrical shock or damage to the well or pump. Stay away from the well pump while flooded to avoid electric shock.

Once the floodwaters have receded and the pump and electrical system have dried, a qualified electrician, well operator/driller or pump installer should check the wiring system and other well components.

Remember: You should have your well water tested at any time when:

  • A flood occurred and your well was affected
  • The color, taste or odor of your well water changes or if you suspect that someone became sick after drinking your well water.
  • A new well is drilled or if you have had maintenance done on your existing well
  • There has been any type of chemical spill (pesticides, fuel, etc.) into or near your well

The Florida Department of Health maintains an excellent website with many resources for private well users: FDOH Private Well Testing and other Reosurces which includes information on potential contaminants and how to maintain your well to ensure the quality of your well water.

The Connection Between Nitrogen and Water Quality

The Connection Between Nitrogen and Water Quality

Recently there was a report of high fecal bacteria in a portion of Perdido Bay.  I received a few concerned emails about the possible source.  Follow up sampling from several agencies in both Florida and Alabama confirmed the bacteria was there, the levels were below both federal and state guidelines (so no advisory issued), and a small algal bloom was also found.  It was thought the cause was excessive nutrients and lack of rain.

 

We hear this a lot.

Excessive nutrients and poor water quality.

What is the connection?

Many people understand the connection, others understand some of it, others still do not understand it.  UF IFAS has a program called LAKEWATCH where citizen science volunteers monitor nutrients in some of lakes and estuaries within the state.  Here in Escambia County, we have six such volunteers.  Some of the six bodies of water have been monitored for many years, others are just starting now, but the data we have shows some interesting issues – many have problems with nitrogen.  Let’s look closer.

The nitrogen cycle.
Image: University of Florida IFAS

We have all heard of nitrogen.  Many will remember from school that it makes up 78% of the air we breathe.  In the atmosphere nitrogen is present as a gas (N­2).  It is very common element found in living creatures – as a matter of fact, we need it.  Nitrogen is used to build amnio acids – which builds proteins – which is needed to produce tissue, bone, blood, and more.  it is one of the elements found in our DNA and can be used to produce energy.  However, it cannot do these in the atmospheric gas form (N2) – it needs to be “converted” or “fixed”.

 

One method of conversion is the weather.  Nitrogen gas are two molecules of nitrogen held together by strong chemical bonds (N2).  However, lightning provides enough energy to separate N2 and oxidize it with oxygen in the atmosphere forming nitrogen dioxide (NO2).  This NO2 combines with water in the atmosphere to form nitric acid (HNO3).  Which can form nitrates (NO3) with the release of the hydrogen and nitrate (NO3) is usable by plants as a fertilizer… a needed nutrient.

 

But much of the usable nitrates do not come from the atmospheric “fixing” of nitrogen via lightning.  It comes from biological “fixing” from microbes.  Atmospheric nitrogen can be “fixed” into ammonia (NH3) by bacteria.  Another group of bacteria can convert ammonia into nitrite (NO2), and a third group can convert it from nitrite to the usable form we know as nitrate (NO3).  Ammonia can also be found in the environment as a waste product of life.  As we use nitrogen within bodies it can be converted into ammonia – which can be toxic to us.  Our bodies remove this ammonia via urine, and many times we can smell this when we go to the restroom.  Nitrogen fixing bacteria can convert this ammonia to nitrites as well and complete the nitrogen cycle.

 

Once nitrogen has been fixed to the usable nitrate it can be taken up by plants and used within.  Animals obtain their needed nitrogen by eating the plants or eating the animals that ate the plants.  In both cases, nitrogen is used for protein synthesis in our bodies and unused nitrogen is released into the environment to continue the cycle.

 

So, what is the connection to water quality?

You might think that excessive nitrogen (nutrients) in the water would be a good thing.  Released ammonia, though toxic, could be “fixed” into nitrite and eventually nitrate and recycled back into life.  And you would right.  Excessive amounts of ammonia though, may not be converted quick enough and a toxic state could occur.  We see this in aquaculture ponds and home aquaria a lot.

Members of the herring family are ones who are most often found during a fish kill triggered by hypoxia.
Photo: Madeline

But what about excessive nitrates? Shouldn’t that be good for the plants?

The concept makes sense, but what we see with increase plant growth in aquatic systems is problematic.  Excessive plant growth can cause several problems.

1)      Too much plant growth at the surface (algae, leafy vegetated material) can block sunlight to the other plants living on the bottom of the waterway.  This can cause die off of those plants and a mucky bottom – but there is more.

2)      Excessive plant growth at the surface and the middle of the water column can slow water flow.  Reduced water flow can negatively impact feeding and reproductive methods for some members of the community, cause stagnation, and decrease dissolved oxygen – but there is more.

3)      Plants produce oxygen, which is a good thing, so more plants are better right?  Well, they do produce oxygen when the sun is up.  When it sets, they begin to respirate just as the animals do.  Here excessive plants can remove large amounts of dissolved oxygen (DO) in the water column at night.  If the DO levels reach 3.0 µg/L many aquatic organisms begin to stress. We say the water is hypoxic (oxygen starving).  When a system becomes hypoxic the animals will (a) come to the surface gasping, (b) some even approach the beach (the famous crab jubilee of Mobile Bay), (c) leave the water body for more open water, (d) die (a fish kill).  This is in fact what we call a dead zone. Not always is everything dead, in many cases there is not much alive left – they have moved elsewhere so we say the bottom is “dead”. Here is something else… as the dead fish and (eventually) dead plants settle to the bottom they are decomposed by bacteria.  This decomposition process requires dissolved oxygen – you guessed it – the DO drops even further enhancing the problem.  In some cases, the DO may drop to 0.0 µg/L.  We say the water is now anoxic (NO oxygen).  I have only seen this twice.  Once in Mobile Bay, and once in Bayou Texar.  But I am sure it happens more often.  The local environment can enhance (or even cause) this problem as well.  Warm water holds less oxygen and much of the oxygen dissolved in water comes from the atmosphere – by way of wave action.  So, on hot summer days when the wind is not moving much, and excessive nutrients (nitrogen) is entering the water, you have the perfect storm for a DO problem and possible fish kill.

4)      Oh, and there is one other issue… some of the algae that produces these blooms release toxins into the water as a defense.  These are known as harmful algal blooms (HABs).  Red tide is one of the more famous ones, but blue-green blooms are becoming more familiar.  So now you have a possible hypoxic situation with additional toxins in the water that can trigger large fish kills.  Some of these HABs situations have killed marine mammals and sea turtles as well.

Though this process can occur naturally (and does) excessive nutrients certainly enhance them, and in some cases, initiate them.  So, too much nitrogen in the system can be bad.

 

So, what does the LAKEWATCH data tell us about the Pensacola Bay system?

Well, first, we have not had volunteers on all bodies of water for the same amount of time.  We currently have volunteers monitoring (1) northern Pensacola Bay, (2) Bayou Texar, (3) Bayou Chico, (4) Bayou Grande, (5) Big Lagoon, and (6) lower Perdido Bay.  Pensacola Bay has JUST started, and Big Lagoon has not even started yet (COVID-19 issues) – so we only have data from the other four.  Bayou Texar has the longest sample period at 13 years.

Lakewatch is a citizen science volunteer supported by the University of Florida IFAS

Second, this program does not sample for just nitrogen, but another key nutrient as well – phosphorus.  When you look at a bag of fertilizer you will see a series of numbers looking like:  30-28-14.  This would be nitrogen, phosphorus, and potassium.  People adding fertilizer to their lawns should know which nutrient they need the most and can by a fertilizer with a numerical concentration that is best for their lawn.  You can have your soil tested at the county extension office.  But the point here is that there is more than nitrogen to look at and, as we have learned, more than one form of nitrogen out there.  So, what we do at LAKEWATCH is monitor for total nitrogen (TN) and total phosphorus (TP).

 

Another parameter monitored is total chlorophyll a (TC).  The idea is… if there are excessive amounts of nutrients in the water there will be excessive amounts of algae.  You could collect a sample of water and count the number of algal cells in the water – but another way is to measure the amount of chlorophyll in the water as a proxy for the amount of algae.  Chlorophyll, of course, is the compound within plants that allows photosynthesis to happen.  There is a chemical process used to release the chlorophyll within the cells and you can then use an instrument to measure the amount of chlorophyll in the water.

 

LAKEWATCH volunteers also monitor water clarity.  It is true that clarity can be impacted by sediments in the water as much as an algal bloom, but anything that contributes to less sunlight reaching the bottom can be problematic for some bodies of water.  This is done by lowering a disk into the water and measuring the depth at which it “disappears”.

 

For those not familiar with the term salinity, it is the measure of the amount of dissolved solids in the water – what most people say, “how salty is it?”.  For reference, the Gulf of Mexico is usually around

35‰, most open estuaries are between 20-30‰.

 

Below is a table of the LAKEWATCH data we have as of the spring 2020.

 

Year of Sampling Body of Water Total Phosphorus (µg/L) Total Nitrogen (µg/L) Total Chlorophyll (µg/L) Water Clarity (feet) Salinity (‰)
2014 – 2018 Bayou Chico 20-30 350 – 600 10 – 30 2.6 – 4.2 7.0 – 8.2
2012 – 2017 Bayou Grande 16 – 19 320 – 340 5 -6 4.0 – 5.2 17 – 18
2007 – 2018 Bayou Texar 17 – 18 600 – 800 6 – 8 3.4 – 3.8 8 – 10
2014 – 2018 Lower Perdido 15 -16 350 – 360 5 -6 5.3 – 6.1 13 -14
STATE AVG. (includes lakes) 25.0 309 3.7    

 

There are a couple of things that stand out right away

(keep in mind some water bodies have not been monitored very long by LAKEWATCH).

 

1)      Phosphorus is not as big a problem in our part of the state.  In the peninsula part of Florida there is a lot of phosphorus in the sediments and much of it is mined.  You can see this in the average value for the state.  Actually, because of this, many of the central and south Florida lakes are naturally high in phosphorus and this is not considered “polluted”.  All that said, there are higher levels of phosphorus in Bayou Chico.  Which is interesting.  More on solutions in a moment.

2)      We have a lot of nitrogen in our waters.  Bayou Texar in particular is much higher than the state average.  More on this in a moment.

3)      We have a little more chlorophyll than the state average, but not alarming.

4)      Bayou Grande and lower Perdido are clearer than Bayou’s Texar and Chico.

5)      All these bodies of water are less than 20‰.  More on this as well.

 

So, comments…

 

1)      We already discussed the phosphorus issue (or non-issue), but what about Bayou Chico?  Phosphorus is NOT introduced to the system from the atmosphere as nitrogen is – rather, it comes from the sediments.  High levels of TP would suggest high levels of sediments in the water column (the water clarity data supports this) – which suggest high levels of run-off.  The watershed for Bayou Chico is highly urbanized and run-off has historically been a problem.

2)      Nitrogen can come from many sources, but when numbers get high – many will hypothesize they are most likely from lawn run-off (fertilizers), or sewage (septic leakage, sanitary sewage overflows, animal waste).  There are certainly other possibilities, but this is where most resource managers and agencies begin.

3)      Elevated chlorophyll indicates elevated primary production.  This is not unusual for an estuary.  They are known for their high productivity.  Bayou Chico seems have more algae than the others.  Most probably due to the increase levels of nutrients entering the watershed.

4)      Bayou Grande and lower Perdido Bay have better water clarity than Bayou’s Chico and Texar.  Though all four bodies of water have significant coastal and watershed development, Bayou’s Chico and Texar and completely developed as well as their “feeder creeks”.  Again, indication of a run-off problem.

5)      All four bodies of water have several sources of freshwater input as well as stormwater run-off that has contributed to the lower salinities found here.  It is possible that the salinities here were less than 20‰ prior to heavy development.

Possible Solutions….

There is a common theme with each of these – stormwater run-off.  Rain that historically fell on the land and percolated into the ground water, now flows off impervious surfaces (streets, driveways, parking lots, even buildings) into drainage pipes and discharges into the waterways.  This stormwater carries with it much more than just fertilizers and animal waste, it carries pesticides, oil, grease, solid waste, leaf litter, and much more.

 

How do you reduce stormwater?

Well, there is not much you can do with impervious surfaces now, but the community should consider alternative materials and plans for future development – what we call “Green Infrastructure.  Green roofs, pervious streets and parking lots, there are a lot of methods that have been developed to help reduce this problem.

 

Another consideration is Florida Friendly Landscaping.  This is landscaping with native plants that require little (or no) water and fertilizer.  It also includes plants that can slow run-off and capture nutrients before they reach the waterways and methods of trapping run-off onto your property.

 

If you happen to live along a waterway, you might consider landscaping your property by restoring some of the natural vegetation along the shoreline – what we call a living shoreline.  Studies have shown that these coastal plants can remove a significant amount of nitrogen from the run-off of your property as well as reduce coastal erosion and enhance fisheries by providing habitat.

Closed due to bacteria.
Photo: Rick O’Connor

What about sewage issues?

Unfortunately, most septic systems were not designed to remove nitrogen – so leaks occur and will continue.  The only options you have there are (a) maintain your septic by pumping once every five years, (b) consider taping into a nearby sewage line.

Sewers systems are not without their problems.  Sanitary sewage overflows do occur and can increase nitrogen in waterways.  These are usually caused by cracks in old lines (which need to be replaced), are because we flush things down drains that eventually “clog the arties” and cause overflows.  Things such as “flushable wipes”, which are flushable – they go down the drains – but they do not breakdown as toilet paper does and clog lines.  Cooking grease and oil, and even milk have been known to clog systems.

 

Our LAKEWATCH volunteers will continue to sample three stations in each of their bodies of water.  We are looking for a volunteer to monitor Escambia Bay.  If interested contact me.

 

If you are interested learning more about green infrastructure, Florida Friendly Landscaping, or living shorelines lines contact your county extension office (850-475-5230 for Escambia County).  If interested in issues concerning sanitary sewage overflows or septic issues, contact your county extension office, or (if in Escambia or Santa Rosa counties) visit ECUAs FOG website (Fats, Oils, and Grease) https://ecua.fl.gov/live-green/fats-oils-grease.

 

Urbanization and MS4s in Stormwater

Urbanization and MS4s in Stormwater

Urbanization—the process of conversion from forests, grasslands, or agricultural fields to predominantly residential, commercial, and industrial settings—can cause profound changes to the pathways that rainfall takes to become streamflow. This landscape conversion leads to less water infiltrating into soil and more water running directly into streams and other nearby water bodies (such as lakes, wetlands, and bayous). Urban water runoff carries pollutants that have accumulated on the landscape and in soil since the previous rainfall. If the concentrations of pollutants in streams are large enough, they can cause problems for the organisms that live in streams as well as those in the bays and bayous those streams flow into (often called receiving waters).

Stormwater conveyance in Santa Rosa nd Escambia counties.
Photo: Matt Deitch

Local governments play a key role in mitigating the impacts of urbanization on aquatic ecosystems. In northwest Florida, County government is often responsible for limiting pollutant inputs from the network of surface and underground stormwater conveyances known as “municipal separate storm sewer systems” (abbreviated as MS4s). The United States EPA requires urban areas to be regulated as sources of pollutant discharge through their National Pollutant Discharge Elimination System (abbreviated NPDES); departments within Escambia County and Santa Rosa County government coordinate the administration of these permits with the US EPA.  

The requirements of these MS4 water quality permits vary depending on the population of the area. Permits for medium and large cities or counties having populations greater than 100,000 are categorized as “Phase I” MS4s, while areas with smaller populations are categorized as being “Phase II” MS4s. These two categories have many similar requirements, but also have a few important differences. Permits for both types of MS4s require local agencies to develop methods for community outreach on stormwater pollution issues, controlling runoff from construction sites, and requiring stormwater management in new developments. In addition to the requirements listed above, Phase I MS4s require the implementation of a water quality monitoring program and a plan to reduce pollutants from developed areas.

Stormwater conveyance in Santa Rosa and Escambia counties.
Photo: Matt Deitch

In Spring 2020, the southern portion of Santa Rosa County transitioned from a Phase II MS4 region to Phase I. This means that Santa Rosa County will begin implementation of a surface water monitoring program to evaluate pollutant concentrations in stormwater conveyances (including creeks); and develop plans for reducing pollutants from their MS4s entering the Pensacola Bay System. This program will make important contributions to understanding the effects of urban development on our local streams and estuaries, and improve water quality in the Pensacola Bay System.

 

This is a great opportunity to remind us of the importance of disposing our personal protective equipment including face masks, plastic gloves, and other single-use items we use to protect ourselves from the coronavirus in the trash after use. Leaving it on the curb or in parking lots means that it can wash into stormwater ponds or creeks and bayous, which can cause problems for the animals that live there.

Stormwater conveyance in Escambia and Santa Rosa counties.
Photo: Matt Deitch

The Incredible Floridan Aquifer

The Incredible Floridan Aquifer

Pitt Spring in the Florida Panhandle is one of more than 1,000 freshwater springs in the state. Springs serve as ‘windows’ to groundwater quality, since the water that flows from them comes largely from the Upper Floridan Aquifer. Photo: A. Albertin

As Florida residents, we are so fortunate to have the Floridan Aquifer lying below us, one of the most productive aquifer systems in the world. The aquifer underlies an area of about 100,000 square miles that includes all of Florida and extends into parts of Alabama, Georgia and South Carolina, as well as parts of the Atlantic Ocean and the Gulf of Mexico (Figure 1). The Floridan Aquifer consists of the Upper and Lower Floridan Aquifer.

Figure 1. Map of the extent of the Floridan Aquifer. Areas in gray show where the aquifer is buried deep below the land surface, while areas in light brown indicate where the aquifer is at land surface. Many springs in Florida are found in these light brown areas. Source: USGS Publication HA 730-G.

Aquifers are immense underground zones of permeable rocks, rock fractures and unconsolidated (or loose) material, like sand, silt and clay that hold water and allow water to move through them. Both fresh and saltwater fill the pores, fissures and conduits of the Floridan Aquifer. Saltwater, which is more dense than freshwater, is found in all areas of the deeper aquifer below the freshwater.

The thickness of the Floridan Aquifer varies widely. It ranges from 250 ft. thick in parts of Georgia, to about 3,000 ft. thick in South Florida. Water from the Upper Floridan Aquifer is potable in most parts of the state and is a major source of groundwater for more than 11 million residents. However, in areas such as the far western panhandle and South Florida, where the Floridan Aquifer is very deep, the water is too salty to be potable. Instead, water from aquifers that lie above the Floridan is used for water supply.

There are actually several major aquifer systems in Florida that lie on top of the Floridan Aquifer and are important sources of groundwater to local areas (Figure 2):

  • The Sand and Gravel Aquifer in the far western panhandle is the main source of water for Santa Rosa and Escambia Counties. It is made up of of sand and gravel interbedded with layers of silt and clay.
  • The Biscayne Aquifer supplies water to Dade and Broward Counties and southern Palm Beach County. A pipeline also transports water from this aquifer to the Florida Keys. The aquifer is made of permeable limestone and less permeable sand and sandstone.
  • The Surficial Aquifer System (marked in green in the map in Figure 2) is the major source of drinking water in St. Johns, Flagler and Indian River counties, as well as Titusville and Palm Bay. It is typically shallow (less than 50 ft. thick) and is often referred to as a ‘water table’ aquifer, but in Indian River and St. Lucie Counties, it can be up to 400 ft. thick.
  • Not included in Figure 2 is a fourth aquifer, the Intermediate Aquifer System in southwest Florida. It lies at a depth between the Surficial Aquifer System and the Floridan Aquifer. It is found south and east of Tampa, in Hillsborough and Polk counties and extends south through Collier County. It is the main source of water supply for Sarasota, Charlotte and Lee counties, where the underlying Floridan Aquifer is too salty to be potable.

    Figure 2. A map of four major aquifer systems in the state of Florida at land surface. The Floridan Aquifer (in blue) underlies the entire state, but in areas north and east of Tampa it is found at the surface. The Surficial (green), Sand and Gravel (red), and Biscayne Aquifer (purple/pink) lie on top of the Floridan Aquifer. A confining unit (area in brown) consists of impermeable materials like thick layers of fine clay that prevent water from easily moving through it. Source: FDEP.

All of the aquifer systems in Florida are recharged by rainfall.  In general, freshwater from deeper portions of the aquifer tends to have better water quality than surficial systems, since it is less susceptible to pollution from land surfaces. But, in areas where groundwater is excessively pumped or wells are drilled too deeply, saltwater intrusion occurs. This is where the underlying, denser saltwater replaces the pumped freshwater. Florida’s highly populated coastal areas are particularly susceptible to saltwater intrusion, and this is one of the main reasons that water conservation is a major priority in Florida.

More information about the Floridan Aquifer System and overlying aquifers can be found at the Florida Department of Environmental Protection (https://fldep.dep.state.fl.us/swapp/Aquifer.asp#P4) and in the UF EDIS Publication ‘Florida’s Water Reosurces’ by T. Borisova and T. Wade (https://edis.ifas.ufl.edu/fe757).