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KPSI Level & Pressure Transducers: Application NotesSaltwater Intrusion Succumbs to the Pressure of Advanced Monitoring TechniquesAs seen in Waterworld, June 2008 |
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Freshwater has become an increasingly important resource throughout many areas of the world due to factors including drastic climate changes as well as population growth. The largest available source of freshwater lies underground in aquifers and it is critical to sustain this supply by observing and addressing those forces acting negatively upon this resource with the use of advanced monitoring techniques. Freshwater aquifers are susceptible to the impacts of saltwater intrusion along the coasts of large bodies of water. The phenomenon of saltwater intrusion occurs when the saltwater, with a denser composition, intrudes into the freshwater portions of the aquifer. This process occurs when the freshwater level or head declines from either climatic or man-made (i.e., pumpage) stresses, having a negative impact on the natural balance between fresh and saltwater. To effectively manage coastal groundwater resources, it is critical to have a quantitative understanding of the occurrence of the freshwater/saltwater interface as well as those factors that influence the process of saltwater intrusion. Specifically in Southwest Florida, saltwater intrusion has been an ongoing issue among the southern west-central Florida ground-water basin (SWCFGWB), which serves as a public water source for domestic, utilities, recreational, industrial and agricultural applications.
Originating in 1974, the Southwest Florida Water Management District (SWFWMD) undertook a comprehensive assessment of the risk saltwater intrusion posed to the Upper Floridian aquifer water supply. The main goals of this extensive program were to explore and test existing conditions as well as to construct dedicated monitor wells for future monitoring of water levels and water quality. As analysis techniques become more sophisticated through computer modeling, there is an even greater demand for advanced monitoring. Today, using some of the latest technologically advanced level and pressure measurement instrumentation, the SWFWMD is expanding and improving this hydrogeological exploration program with the use of dedicated monitoring wells, The SWFWMD has constructed coastal monitor well transects consisting of two to three monitor well sites that serve as monitoring and testing sites. This coastal monitoring program provides the opportunity to observe the movement of saltwater either landward or seaward. The data collected from these sites is used in the various water resource studies conducted to better manage the sensitive coastal aquifers of the SWCFGWB. The first phase of this investigation includes discrete zone testing within a borehole with the use of a packer assembly. Water levels above the packer within the annulus are monitored to ensure the packer was properly sealed to the formation. Any water level fluctuation within the annulus would be very small, requiring precise water level measurements. To achieve exact measurements, the SWFWMD called upon Pressure System’s KPSI™ Series 335 Submersible Level Transducer for its high level of accuracy in environmental test applications. This small-bore transducer is ideal for monitoring this annulus and many other water level monitoring applications requiring high precision static accuracy. The SWFWMD also chose the Series 335 because it offers a super high precision static accuracy of +0.05% FSO, is 100% computer tested and calibrated, and is fully temperature compensated and data logger compatible. In addition, this transducer features high performance internal signal conditioning and is available with standard voltage and current loop outputs.
This program of slug tests is repeated 50 to 100 feet as the borehole is advanced to depths of up to 3,000 feet below the land’s surface. In order to monitor the rapidly changing water levels during these tests, the SWFWMD again turned to Pressure System’s transducer for its high-speed data acquisition. The SWFWMD uses a different Pressure System KPSI™ transducer, the Series 735 Submersible Pressure Transducer, along with a ¼-inch nominal pipe thread, to measure air pressure within the pneumatic slug testing head to record the slug magnitude of the test. The submersible pressure transducer was used to accurately measure the water level displacements that occurred within the test interval. Constructed in a small, rugged package, this pressure transducer is ideal for accurately recording pressure measurements within a close proximity, which is exactly what the SWFWMD needed. The SWFWMD also relies on this transducer for its ability to read pressure ranges from 0-2 psig through 0-100 psig as well as its advanced on-board electronics that provide outputs of 4-20 mA. Provided in a small rugged package constructed of corrosion-resistant 316 stainless steel, the Series 735 offers precise level measurement in hostile environments. Approximately 30 years of exploration combined with highly developed monitoring technologies implemented by environmental professionals have helped the SWFWMD to collect accurate and reliable data for groundwater resource studies involving saltwater intrusion related issues. These advancements in monitoring techniques, in turn, have enabled the SWFWMD to be one step closer to achieving its mission of ensuring continued availability of this natural resource. REFERENCES: |
return to KPSI Level and Pressure Transducer Application Notes
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In the early 1900s, the Upper Floridian aquifer in the SWCFGWB discharged approximately 530,000 cubic meters per day of freshwater from the aquifer into the coastline. The decline of groundwater levels within the aquifer has resulted in saltwater intrusion. With goals to minimize or even reverse the impact of saltwater intrusion, water managers must monitor the aquifers closely. 
During the packer test, the SWFWMD conducts a program of four or more slug tests consisting of a near-instantaneous stress or a slug being added (or removed) from the well. With a very permeable formation, these low magnitude slug tests result in a rapid water level response. 
