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Hillsborough County Water Quality. Hillsborough County (Tampa, Florida).
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With the cost of everything rising so rapidly, it’s hard to put water in the right context. We, in Florida, often take our water resources for granted. We appreciate our time at the beach, fishing our fabulous lakes, boating and floating. But we generally don’t make a direct connection between our recreational water and our drinking water. But it’s there.
Notice the picture on the right shows grass where water once was . . . 1970s 1990s
Where does Hillsborough County Water Come From? • For the last century, the primary source of Hillsborough County's high quality water has been an underground limestone formation called the Floridan aquifer. • The Floridan aquifer is one of the highest producing aquifers in the world.
What the Floridan aquifer looks like: Although it is large, the Floridan Aquifer isn't immune to harm. Fertilizers, pesticides and treated sewage water (that is allowed to be pumped into the aquifer) are some threats. Originally this project was going to investigate these issues until . . . . .
I noticed: SALT in the aquifers! • When levels of freshwater in the ground are lowered, due to droughts or water withdrawals, saltwater can move into the freshwater portions of aquifer. This is called saltwater intrusion. • Salt Water Intrusion is a problem because when freshwater becomes salty, it can’t be used for drinking without expensive treatment. This problem is mainly seen in coastal areas such as Hillsborough County.
What is a WATER TABLE? • The water table is the level of water in the ground. During times of low rainfall, the water table drops. This is true since the aquifer is dependent on rainfall to replace or recharge what is pumped out. • In Florida, we're lucky. We have the Gulf to our west, the Atlantic to our east and a number of winding rivers, lakes and springs in between. Living near so much water makes it easy for Floridians to forget that the supply of freshwater is not unlimited.
Population growth • The Tampa Bay region is growing. In the past five years, the region has added numerous housing developments and schools, new shopping and dining opportunities, and more roads and highways. All of these activities require more water.
More problems… • To meet the growing demand, St. Petersburg and Pinellas counties simply increased the amount of water they pumped from Hillsborough county. • But the residents living in Hillsborough county began to notice major changes to their landscape. Wetlands that had existed for years were vanishing. Lake levels were dropping and sinkholes were developing. The beautiful landscape that contributed to the quality of life in the region was changing and people didn’t like it.
Politics-- • In the 1990s, devastating impacts to the environment led to heated debate over regional water policy. Residents, politicians and environmentalists questioned the wisdom of the water withdrawals that caused wetlands, lakes and ponds to disappear—some permanently. (Remember the picture of Big Fish lake?) • Eventually (1998), a regional agreement to pump less groundwater and develop new sources of water was made. The hope was that by reducing the withdrawals, the environment would recover.
DESALINATION: the future? • Co-located near the TECO Big Bend power plant in Apollo Beach, the Tampa Bay Seawater Desalination plant is still the largest of its kind in the country. • Partially funded through the Partnership Agreement, Tampa Bay Water, and SWFWMD this plant started out as the most affordable desal water in the world. • Using reverse osmosis, the plant is designed to produce 25 million gallons a day (mgd) of affordable, desalinated water each day. It was designed to expand to produce 35 mgd, if necessary.
How Does it work? • The technology most frequently referred to when talking about membrane desalination is reverse osmosis. In reverse osmosis, feedwater (which can be either sea or brackish water) is pumped at high pressure, generally around 1,000 psi, through semi-permeable membranes that have pores roughly 0.0001 micrometer, or a tenth of a nanometer. These membranes allow the tiny water molecules to pass through, while the much larger mineral salts are trapped and held by the membrane. The feedwater first passes through a pretreatment system, typically a variety of filters, to remove particles, such as bits of seaweed and other organic matter, which would clog the membranes.
Desal plant: The need for a steady source of energy and a coastal location makes proper siting a critical component to the success of a seawater desalination plant."The most cost-effective location for a seawater desalination plant is right on the coast, next to a power plant," said Hal Furman, executive director of the U.S. Desalination Coalition. http://www.youtube.com/watch?v=Y7w58dGm3lQ
Pressure Vessels • Pressure vessels at Tampa Bay Water (above) hold the reverse osmosis membranes.
Then . . . • The end result is clean, drinkable water that typically will undergo post-treatment before being stored or delivered. • What's left over is a brine that's roughly twice as salty as the original feedwater. This brine, known as concentrate, is typically discharged back into the ocean, in the case of seawater, or buried in a deepwater well, in the case of brackish water. Other options for inland concentrate disposal include the use of evaporation pools and landfills.
Brine • Tampa Bay Water said that environmental models of the effects of concentrate disposal done in his area concluded that the effects of pumping the brine back into Tampa Bay were minimal and acceptable. Tampa Bay Water has monitored the salinity of the bay, and the local biological system in the vicinity of the discharge has not changed significantly.
Problems? • Pretreatment has been a problem at his facility since before it came nominally online in October 2003. "The more robust your pretreatment system, the longer your membranes last," he said. "But we have high organic loading in our feedwater and fluctuating water quality, which our dual sand pretreatment process isn't handling adequately." The end result is that the cartridge filters upstream of the sand filters, which are designed to act as a safety net that captures anything that passes through the pretreatment, are removing the suspended particles that the pretreatment system should be catching. And, those cartridge filters are lasting only about two weeks, instead of the three to four months they should last, according to Herd.
Bad for Environment? • Both reverse osmosis and distillation processes use harmful chemicals, produce waste and pollute their local environment. Cleaning agents such as chlorine, alkaline solutions, chemical disinfectants and crystal growth inhibitors are used to maintain their systems from build up.
Good for environment? • Desalination plants are able to recover pure salt from their waste brine, which is then usable as raw material for chlorine, caustic soda, and hydrochloric acid. • According to Tampa Bay Water, less chemicals are used to treat desal water than aquifer water.
http://www.youtube.com/watch?v=D6NifZwRfSw • Either way… by working to reduce our dependency on groundwater, Hillsborough County is taking an important step toward protecting the environment for the future. As other counties and communities around the state and nation struggle to meet increasing demand for water, Hillsborough County is confident of its ability to provide a dependable and affordable supply to its residents. • Hillsborough County is making strides to preserve the quality of the environment for the future.
Future desal plans? • Although the Tampa Bay project was the first of its kind, several large desalination projects are moving through testing and permitting in California and Texas.
