Environmental protections, safeguards and monitoring ensure there are no adverse effects from the desalination plant.
During the Tampa Bay Seawater Desalination Plant's initial operations, extensive monitoring showed no changes in the salinity in Tampa Bay related to the plant's operations.
Studies conducted through the plant's first year of operations during 2003 showed the salinity outside the discharge point was the same whether or not the desalination plant was operating. Those same studies showed no measurable changes in salinity whether the plant was operating at 25 million gallons per day, a fraction of that, or completely off-line.
Construction and operations of the Tampa Bay Seawater Desalination Plant and pipeline required 18 separate permits. The permitting process was lengthy and extensive, particularly the Florida Department of Environmental Protection’s (DEP) permitting process. Over an 18-month period, DEP reviewed scientific research and public comments before permitting the facility.
The plant's permit applications were reviewed by other agencies, organizations and citizens concerned with protecting Tampa Bay, including the Agency on Bay Management, the Hillsborough County Water Team, the Audubon Society, the Tampa Baywatch and Tampa Estuary Program.
The plant has monitoring and alarm systems to track the salinity of the source water, desalinated drinking water and concentrated seawater discharged back into the bay. Measurements are taken in several areas before, within and after the plant.
Operators continuously monitor the blending ratio of the seawater being returned to Tampa Bay to ensure compliance with environmental permits.
The plant’s comprehensive alarm system will warn plant operators to check or adjust the system. The monitoring system will also automatically shut down certain affected areas of the facility if monitored levels exceed predermined parameters.
Tampa Bay Water conducts permit-required hydrobiological monitoring programs (HBMPs) for the Tampa Bay Seawater Desalination Plant as well as the Tampa Bypass Canal/Hillsborough River and the Alafia River. These comprehensive monitoring programs were developed to determine if initial predictions of environmental effects of these various water supplies are accurate and provide an early warning of potential changes.
The HBMPs monitor water quality, vegetation, benthic invertebrates, fish and other parameters in the Lower Hillsborough River, Alafia River, Palm River/Tampa Bypass Canal, McKay Bay and areas in Hillsborough Bay near Apollo Beach and the Big Bend power plant. The HBMPs are coordinated with other agency monitoring programs to maximize use of available data.
These monitoring programs use recent and historical data to develop a comprehensive baseline report against which post-operational data can be compared to identify any potential changes or trends.
Costing about $1.2 million annually, thousands of samples are collected, including continuous salinity measures every 15 minutes. The HBMP reports and related documents are provided to regulatory agencies and posted to Tampa Bay Water’s web site.
Several predictive modeling studies were conducted prior to the plant being constructed, including:
- Cumulative Impact Analysis for Master Water Plan projects (including desalination at 50 mgd)
- U.S Geological Survey of the Big Bend Power Station area
- Independent studies were conducted using a pilot plant:
- Mote Marine Laboratory
- Danish Hydraulic Institute
- University of South Florida (USF)
- Savannah Laboratory/STL Precision
- Marinco Laboratory
- Hillsborough County
Each study was approved by the Florida Department of Environmental Protection and conducted in accordance with DEP methods by a DEP-approved laboratory. Each study concluded that the desalination plant would produce high-quality drinking water without harm to the bay’s water quality or marine life.
Although the plant’s discharge is roughly twice as salty as Tampa Bay, it does not increase the bay’s salinity because it is diluted in up to 1.4 billion gallons of cooling water per day from Tampa Electric’s Big Bend Power Station before being discharged back into the bay. Salinity in the plant’s discharge is, on average, only 1.0 to 1.5 percent higher than Tampa Bay’s. This slight increase in salinity falls well within the natural, yearly salinity fluctuations of Tampa Bay, which vary from 16 to 32 parts per thousand, or by up to 100 percent, depending on the weather and the season.
Mote Marine Laboratory and the Danish Hydraulic Institute performed salinity studies using a pilot desalination plant, 1/1000th the size of the Tampa Bay Seawater Desalination facility. Scientists collected data during the 2000-2001 drought, where very little freshwater entered Tampa Bay. They combined this with a worst-case power plant operations scenario (only two of four of the power plant’s condensers working) and operational data from the pilot plant to determine potential long-term salinity changes in the bay. Based on Mote Marine Laboratory’s research, the Danish Hydraulic Institute reported that under these extreme conditions, a 2.5 percent increase in salinity is predicted in the area closest to the power plant and desalination plant and this would quickly dissipate.
The U.S. Geological Survey of the Big Bend Power Station area determined that salinity will not build up in Tampa Bay because it flushes often. “Water Transport in Lower Hillsborough Bay, Florida, 1995-1996,” found that each time the tide changes, more than 200 times as much water enters or leaves the bay as circulates through the power plant. The report also found that enough water flows in and out of the bay system near Big Bend to properly dilute and flush the plant’s discharges, further preventing any long-term salinity build-up.
Marinco Laboratory of Sarasota tested the toxicity levels of saline-sensitive animals such as mysid shrimp and Gulf silverside fish using concentrated seawater from the pilot desalination plant at a dilution ratio of 1:1 (one part seawater concentrate to one part “normal” seawater). Researchers found no long or short-term increase in mortality at the 1:1 dilution level, leading them to conclude the plant would not harm saline-sensitive marine life. Under normal operating conditions, the dilution for the seawater concentrate will be 70:1, and at least 18:1 or 36:1 even with two or three of Big Bend’s cooling units out of service.
Savannah Laboratory/STL Precision of Miramar, Florida, conducted tests to determine if undesirable chemicals already in Tampa Bay, which could harm water quality or marine life at higher levels, would be concentrated in the desalination process and discharged back into the bay. Researchers tested the discharge from the pilot plant for 200 compounds, none of which exceeded the Florida Department of Environmental Protection’s water quality standards for Tampa Bay.
The University of South Florida (USF), with Dr. Mark Luther as the principal investigator, studied the bay’s circulation to determine if desalination-related changes in salinity could change the currents in Tampa Bay. (Saltwater is heavier than freshwater so changes in salinity could affect the bay’s currents and the time it takes to flush the bay.)
Focusing on the farfield (areas away from the power plant and desalination facility), USF researchers found that desalination plant-related changes in the bay’s salinity were so slight, that even if all of Tampa Bay Water’s current water projects were to be implemented simultaneously, changes in circulation were not significant, and “There is no reason to suggest that the flushing time of the bay would be altered in a significant way.”
In other words, because the salinity of the bay normally varies widely – from 16 to 32 parts per thousand – depending on the weather and season, any change in its salinity linked to the desalination plant, even if all of Tampa Bay Water’s current Master Water Plan projects were implemented simultaneously, would fall well within this range of salinity and, therefore, have no effect on the currents, circulation or flushing of the bay.
Hillsborough County ’s own, independent study into the potential environmental impact of the desalination plant concluded that, “The marine ecology of the areas of major biological concern will not be affected by the desalination facility operations.”
