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' this area (i.e., North Miami Beach, Highland Beach, and Boca Raton in Southeast Florida) have had to move or expand their well fields further ' inland away from the saltwater wedge. The obvious method of preventing this saltwater contamination is to maintain the water table around the wells high enough above sea level to prevent the saltwater wedge from moving inland and reaching the wells. ' 3.2.2 IRRIGATION PRACTICES ' Large withdrawals of water from the Floridan Aquifer were used to irrigate agricultural crops within Indian River County. Due to the higher salinity ' of this irrigation water, salts began to concentrate within the soil of the agricultural fields which then percolated with rainwater down into the ' surficial shallow aquifer. Subsequently, the chloride concentrations within the surficial aquifer became higher. Other sources of contamination caused by waters of the Floridan Aquifer are deep wells which are leaky and ' those wells that are left either poorly or inappropriately abandoned. ' 3.2.3 ONSITE WASTE DISPOSAL ' Degradation of the groundwater quality can be caused by onsite waste treatment systems such as septic tanks. There are numerous cases on record ' of well supplies becoming polluted due to septic tank discharges (see Section 3.4). The septic tank effluent is of poor quality by today's wastewater treatment standards as can be seen in Table 3-1. It can cause ' detrimental increases in nitrogen, chloride, sodium, other ions, total dissolved solids, and the microbiological level of the local ' groundwater. ' Several features inherent to the operation of septic tank systems make them prone to contaminating the groundwater without any visual indication. For ' example, if the tanks are undersized or not emptied whereby sludge and scum accumulation reduces the tank's treatment volume, a poorer quality effluent results. If high groundwater conditions (within 3 to 4 feet of drain field ' IRC.VB4 6/4/87