Changes in groundwater quality averaging 0.13 millimhos electrical conductivity and 35 ppm chloride increase are documented between 1940 and 1972. The decrement in the water quality of the surficial aquifer is attributed to the interaction of four major mechanisms. Brine leakage from underlying artesian aquifers, natural recharge of the surficial aquifer by saline waters, recharge of the aquifer by concentrated agricultural waters, and lateral groundwater movement through saline lacustrine beds appear to be the major salt sources. A chemical thermodynamic computer model of recharge water quality, and the construction of iso-chemical maps from analyzed water samples show artesian aquifer leakage to be the significant contribution of salts to the system.