Salt Water Intrusion
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What is Salt Water Intrusion? There are two major kinds of water in the environment, fresh water (the kind we drink) and salt water (the kind in the Ocean). Salt water is more dense than fresh water. You can remember that by thinking that Ocean water is fresh water with lots of particles of salt in it, and naturally weighs more. We pump our water for drinking out of the Biscayne Aquifer. If we take out more water than can get put back in naturally (by rain etc) then the level of the aquifer drops. The Biscayne Aquifer extends east to the Ocean. Pressure keeps the Ocean water in the Ocean, and the fresh water in the Biscayne Aquifer.
Also originally Hollywood was an area of poorly drained lowlands, with a couple of limestone ridges passing through the city in a north-south direction. Canals were constructed to drain these swampy areas, which they do, but they also allow sea water to intrude several miles inland, and also into the Biscayne Aquifer. This happens, because the canals lower the fresh water table, allowing the salt water to drain in. Hollywood's well fields for drinking water production are located within close proximity to the C-10 canal and are
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The Source Of Hollywood's Water Is
The Biscayne Aquifer
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| What's Under Hollywood?
| | A. Ground Level |
| B. Limestone |
C. Biscayne Aquifer
(10-200-feet below ground) |
| D. Marl (more limestone) |
E. Floridan Aquifer
(900-feet below ground) |
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less than one mile from a salt water front created by the intrusion of sea water inland. During high water table conditions, fresh water is moving towards the ocean in these canals, and helps to combat the intrusion. Unfortunately during drought or dry conditions salt water comes inland where it is able to soak into the aquifer through the canal floors carrying salt water into the Biscayne Aquifer.
While Hollywood receives, on average, about 60 inches of rainfall each year, greater demands for drinking water have been brought about by the expanding needs of South Florida's rapidly increasing population. This perpetuates the problem by creating a low area in the aquifer where the well pumps, again allowing salt water a greater chance to flow in. Since population growth began at the coast, and then grew inland, most of the drinking water production facilities in South Florida are in these more populated areas. Hollywood is no exception, with our plant located just over five miles from the Intracoastal Waterway.
Hollywood, along with all other utilities along the southeast coast of Florida rely on the Biscayne Aquifer for their water supplies. The Biscayne is a prolific surficial aquifer system containing fresh water that has relatively good quality along the coast. Recharge occurs primarily via rainfall, with some lateral movement from the Everglades and canal systems. When the level of the Biscayne Aquifer drops, the pressure separating the water is also reduced. Because the salt water is more dense it begins to "spill-over" (or Intrude) into the Biscayne Aquifer. The salt water mixes with the fresh water and if the content of salt becomes too high we can no longer use the water for drinking. Salt water intrusion has "creeped" westward from the Ocean and into the Biscayne Aquifer. Currently, the water in the Biscayne Aquifer west of 18th Avenue in Hollywood is still relatively free from salt water intrusion. Unfortunately, years of use from the Biscayne Aquifer without the understanding of the causes of salt water intrusion resulted in the water in the Biscayne Aquifer EAST of 15th Ave. to become too salty for even landscape irrigation.
The more water you use, the more water we need to pump from the Aquifer. The more fresh water we pump out without giving the Aquifer a chance to recharge, the faster the level drops and the further west the salt water intrudes. Conserve water for a very good reason. The following suggestions are provided to help you conserve water, thereby helping save our aquifers, AND YOUR MONEY! Conserve water because it is the right thing to do. Don't waste water just because someone else is footing the bill such as when you are staying at a hotel, or it's included in your rent. Try to do one thing each day that will result in a savings of water. Don't worry if the savings is minimal. Every drop counts. And every person can make a difference.
Actions that have been taken.
The South Florida Water Management District has imposed reductions in the raw water wellfield withdrawal allocations permitted by the. Additional reductions are anticipated as more water is diverted to the Everglades in the State's efforts to restore the ecosystem. The City of Hollywood is one of the utilities affected by both of these concerns. When the City applied for renewal of its water withdrawal (or consumptive use) permit, as issued by the South Florida Water Management District, the new groundwater supply allocation was reduced to 20.67 MGD from 28 MGD. The threat of saltwater intrusion caused this reduction. This problem required the City to review raw water supply options.
Holllywood augments its supply of Biscayne water by utilizing some wells drilled much deeper into the brackish Floridan Aquifer. In order to accommodate these new raw water sources, the City installed a reverse osmosis nano-filtration system necessary to remove the brackish materials from this water
Hollywood provides reclaimed water to a number of golf courses within the City. This provides a method to reuse some of the water treated by the Wastewater Plant, that otherwise would be lost to the ocean.
What is in the future?
In meeting the challenge of saltwater intrusion, the City has embarked upon an innovative project for injection of the reclaimed water along the coast as a salinity barrier. The intent of the City's salinity barrier project is to inject tertiary treated wastewater effluent into a portion of the Biscayne Aquifer that has been intruded with salt water, creating a barrier that will retard or reverse saltwater intrusion. Because the movement of the saltwater inland is slow, the City expects that the salinity barrier, will halt the landward saltwater movement, and with proper injection procedures, will push the intrusion line back toward the Atlantic Ocean by increasing the freshwater aquifer head.
No drinking water wellfields are down gradient from the proposed injection area! As a result, no withdrawal pressures are downstream of the injection well, meaning that no artificial head changes will be created in the areas of existing wellfields.
The results from a pilot well have been submitted for evaluation by regulatory agencies, and regulatory issues are expected to be the biggest obstacle to implementation of wide-scale barrier program.
