AWWA WQTC58907

Deeper brackish ferrous and manganous water intrusion in freshwater aquifers is a frequent problem that can affect the quality of water resources. In San Lorenzo, a city of 30,000 inhabitants in Argentina, historical problems of water quality, provided by downtown wells, concerned water utilities from its origin in the 50s: high sulfates, chloride, sodium, ferric and manganese contents. Obstructions and occurrence of black water were common problems in the distribution system. Hydrogeological studies determined that brackish reduced aquifer underlies the freshwater aquifer used by the production wells. As a result of pumping, the hydraulic potential equilibrium of the aquifer was disturbed, causing saline, manganous and ferrous water intrusion to degrade the well water. A project was initiated consisting of restoring the hydraulics equilibrium of the aquifer by an extraction of brackish water by means of "a correction well" near the production well. This solution was firstly studied by modeling and, after a comparative analysis with other alternatives, implemented on site. The project has been ongoing since the beginning of 2000. At the source point and in the water network total dissolved solids (TDS) diminished from 2.5 to 1.2 g/L. Fe and Mn total contents passed from 0.9 and 0.7 mg/L respectively to <0.05 and <0.03 mg/L. A drastic reduction of taste and color customer claims and maintenance intervention over the network were registered in San Lorenzo city. Regarding investments, groundwater management was 8% less expensive than the classical treatment solution of reverse osmosis (RO). The operation cost was estimated to be more than 50% less expensive for this case in comparison to the RO solution. Includes 4 references, tables, figures.