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well fields on the western end of the island and an effort to salvage storm 

 water and recharge it into the aquifer through infiltration fields. The 

 present horizontal rate of advance of the saline wedge in southwestern 

 Nassau County varies from 3 m to 60 m per year depending on local pumping 

 rates and recharge by variations in rainfall. Fig. 8.8 presents a cross 

 section through southwestern Nassau County. 



8.4.2 Miami. FL 



The initial cause of salinity intrusion in this area was a series of 

 surface drainage canals . These canals both lowered the fresh water table 

 as they were designed to do and also allowed salt water to penetrate up 

 these canals, thereby contaminating the groundwater from the surface. 

 Fig. 8.9 portrays the increase in intrusion from 1904 to 1959. Increased 

 salinity required several well fields to be abandoned in the Miami -Fort 

 Lauderdale area. 



Remedial measures have included construction of saltwater barriers in 

 the drainage canals and the establishment of water management areas which 

 serve to pond fresh water for aquifer recharge. 



8.4.3 Los Angeles. CA 



Saltwater intrusion was noticed in the early 1930s as a result of 

 water usage for agricultural, domestic and industrial purposes. A water 

 injection barrier project has been implemented along a 11 km portion of the 

 shoreline. A total of 94 injection wells cause a pressure "ridge" in the 

 confined aquifers, thereby establishing a seaward gradient which prevents 

 seawater encroachment. The piezometric head of the barrier is maintained 

 at 1 to 3 m above sea level, requiring approximately 1,500 m^/day of 

 injected water. Figure 8.10 presents a cross section perpendicular to the 

 shoreline which demonstrates the increase in the pressure ridge from 1963 

 to 1967. 



8.4.4 The Potomac -Raritan-Mago thy Aquifer System 



Lennon et al. (1987) have reported on a numerical model study to 

 evaluate the effectiveness of creating a hydraulic barrier to salinity 

 inflow for the Potomac -Raritan-Magothy (PRM) aquifer system. The optimum 



