Source or Cause of Intrusion
Seawater in coastal aquifer
Upconing Oil field brine
Defective well casings Surface infiltration Saline water zones in freshwater aquifers
Modification of pumping pattern Artificial recharge Extraction barrier Injection barrier Subsurface barrier Modification of pumping pattern Saline scavenger wells Elimination of surface disposal Injection wells
Plugging of abandoned wells Plugging of faulty wells Elimination of source Relocation and redesign of wells
Source: D.K. Todd, 1980, Groundwater hydrology (John Wiley and Sons).
where d = depth to the initial interface below the bottom of the well. Salt water reaches the well, contaminating the supply, when the rise becomes critical at z = 0.3 to 0.5 d. Thus, the maximum discharge that keeps the rise below the critical limit is obtained when z = 0.5 d is substituted in Equation 9.10(9) as
In reality, brackish water occurs between fresh and salt water. Even with a low rate of pumping, some saline water inevitably reaches the pump. Increasing the distance d and decreasing the rate of pumping Q minimizes the up-coning effect.
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