MANAGING NITRATE PROBLEMS FOR DOMESTIC WELLS IN IRRIGATED ALLUVIAL AQUIFERS

Many irrigated areas in the United States and abroad overlie unconfined aquifers. The soils are coarse texmred with low water-holding capacity, and irrigation water is frequently necessary for crop growth. Many of these areas experience elevated nitrate levels in water from shallow domestic wells. It is often observed that the nitrate plumes are stratified with depth with the highest concentration just near the surface. The irrigation wells are generally screened toward the bottom part of the aquifer where the material is coarse and the available drawdown is greater. Pumpage is typically cyclic but can be somewhat continuous during drought conditions. It is often believed that the floating nitrate plume is recycled by the irrigation wells. Simulations were carried out to show that slight deepening of domestic wells in both stratified and more homogeneous aquifers could eliminate nitrate problems for many domestic wells even in close proximity of irrigation wells.