The aquifer of Volusia plus parts of Flagler and Putman Counties is designated by the federal Environmental Protection Agency (EPA) as a "Sole Source Aquifer". This is so defined because it is the source of essentially all of the potable water of the area covered. The limits are defined by the salt water of the ocean on the east, by saltwater underlying the St., Johns River on the west, and by a combination of poor water quality and low water movement on the south and north.
The aquifer is quite complex. There is a surficial aquifer composed largely of sand and shell with some clay. In places there is a layer of coquina rock, and in others the sand is cemented enough to be nearly impervious to water, so a local "perched" aquifer is formed. Over much of the area this aquifer component ends in a layer of clay, not completely continuous, forming a "semi-confining layer" which partly insulates the next lower component. At the Deland Ridge the bottom of the clay is near sea level, and at the east about 90 feet lower. The surficial formations can hold up to about 50% water, but the quality is rather poor, with considerable dissolved iron, often visible as a reddish stain where water from a lawn sprinkling well hits the side of a building or concrete pavement. Originally there was a special component of the surficial aquifer under the area coastal barrier island locally called "the peninsula", but this was small, and failed as pumping for lawns brought in salt water from either side.
The main aquifer is the top of a tilted block of limestone. This aquifer section is about 100 feet thick, and is called "The Upper Floridian". There is enough connection between these two layers to permit some vertical flow. The "potentiometric" is the level of water in an unpumped well penetrating into the aquifer formation. If the surficial potentiometric is the largest, the flow is downward, recharging the main aquifer. The opposite condition causes formation of small springs, seeps and wetlands, such as the cypress swamps in the center part of the county. The special condition of sinkholes, mostly in the Deland Ridge, causes very high recharge in this area. As a result the highest potentiometric is in the area occupied by Lakes Hires and Dias. Water quality is very good, almost no iron, salt or other dissolved solids. The water stored in limestone is much less than in sand, often less than one percent of the volume. This is the source of most of the drinking and irrigation water used.
This block extends under the ocean to the east. Originally, the potentiometric was higher than the surface of the land, so "artesian" water could flow from wells without pumping. The water level of wells close to the coast changes with the tide, showing a connection to the ocean. The location of the interface is not known, but is in the order of five miles. The fact that the aquifer extended under the ocean is the reason that the early wells so close to the ocean lasted, for a time.
A layer of dense dolomitic limestone partially blocks vertical flow to still lower sections, which are called "The Lower Floridan". Water quality is mostly low, or "hard" from dissolved solids. Except where there is some connection to the upper limestone, as at the Rima Ridge, there is little use of the lower layer.
Since fresh water is slightly less dense than salt water, it tends to form a floating "bubble". If the top of a bubble is elevated by one foot, the bottom is depressed to 42 feet lower. Since the original potentiometric was about 40 feet above sea level, the bottom of the fresh water was about 1600 feet below sea level.
When water is pumped from an aquifer, a reasonable analogy is the air in an auto tire. With no air pressure (as compared to the outside air) there is air in the tire. If air is pumped into the tire, the pressure and the amount of air both increase, with part of the increase being expansion of the tire. If there is a leak, the pressure on further pumping will eventually stay the same, the input just equaling the loss. For the aquifer, water is in the spaces between sand grains, or in small voids and occasional cracks in limestone. Naturally, for the aquifer, the leakage loss is in the springs, loss to the ocean, a little to adjacent areas, and some for evaporation and the needs of vegetation, the pair being called "transpiration".
The present situation of the main aquifer is that the combination of natural loss and human induced consumption from it exceeds the recharge from rainfall, which is the only source of replenishing water. This is shown by several tests:
- Starting about 1955, the average potentiometric level of the aquifer
started to decline. For a typical monitoring well the decline was about
3 inches a year. This has not changed greatly, so the decline to 1995 was
nearly 10 feet. Charts showing the decrease over the entire area are available.
No area has an increased potentiometric.
- The largest and lowest potentiometric in a year
also show a decline, but this is less marked, since both are sensitive
to rainfall. (For Volusia County the average is about 51 inches per year,
and the 1 in 100 year drought and wet years are 35 and 80 inches, respectively).
- For a more definitive measure of decline, the
rain in a month was compared to the change in monitoring well level in
that month, over a 5 year period. The resulting data shows scatter, largely
because the aquifer does not respond instantly to a heavy rain, and not
at all to a light one. Least square fit of the data shows that very nearly
56 inches of rain a year is needed to maintain aquifer level. To indicate
the effect of this as compared to the actual average, in three years out
of four, there is not enough rain to replenish the sum of natural plus
artificial withdrawal, and that the fourth year is not sufficient ot make
up the deficiency of the other three years. Data for a second five year
period, and for additional monitoring wells gives the almost exactly the
same results.
The aquifer is being over-pumped. The results of this include:
- Spring drying: See the record for Green and Gemini
springs. And the least squares projection for DeLeon Springs is that it
will become intermittent.
- Increase pollution of spring fed swimming areas,
due to lack of continuous flushing by pure aquifer water. Read the record.
- Drying of small springs and seeps. This is noticeable
in the Daytona Beach and New Smyrna Beach areas, where the seeps only appear
in periods of heavy rainfall.
- Drying of wetlands. This is evident in the central
area of Volusia County. And review the applications for wetland filling,
which often show the words "stressed wetland".
- Changes in vegetation due to reduction in transpiration
as the surficial aquifer level falls. Some species of trees are dying back.
And intrusive exotics are becoming more common. An end point can be the
appearance of prickly pear cactus, already found in some areas.
- Increased fire hazard: it does not seem to be
a coincidence that the large burnt over areas in the center of Volusia
and Flagler Counties are nearly at the same places as have appreciable
aquifer drawdown.
The District does not admit that this situation exists. Instead,
they claim that we are going to have a deficiency by 2020, and base all
of their plans on this assumption. Their proposed "corrective actions include:
- Further drawdown of aquifer levels in selected
locations, and further reduction in wetland areas
- Use of surface water, especially from the St.
Johns River
- Use of water purification, i.e., demineralization
or desalinization of poor and/or ocean water
- "Temporary" storage of water by injection into
the aquifer for later withdrawal, where temporary must be for an appreciable
part of a year.
In preparing these plans, the District is expecting present users to pay for the installations required and for the increased charges for water, this to allow continued growth. They have ignored the current wastage of rainwater by the 100 miles of drainage canals in Volusia County, and further have taken no effective steps to end or even reduce the use of aquifer water for non critical use.
For nearly 15 years, the Environmental Council has pressed the District to develop a true water budget model, showing the amount of water available, the needs to maintain natural processes, and the amount which can be used safely. They have refused to take this step.
The position of the Environmental Council is that the actions of the St. Johns Water Management District amount to the writing of checks without knowing what in in the the bank, and what the deposits and withdrawals are.