New Jerusalem Drainage District (NJDD) operates a subsurface drainage water removal system to maintain the productivity of 12,000 acres of agricultural land in the vicinity of Tracy, California. The removed drainage water has historically been discharged to the San Joaquin River. Such discharges must meet water quality objectives that are becoming increasingly more restrictive. NJDD sought assistance in evaluating alternate strategies for managing the water in case the discharge could not meet water discharge objectives or standards. This report presents the findings of an investigation that evaluatedthe water quality condition of the drainage water and alternative management strategies. The strategies are based on water quality and the need to maintain crop yields and soil health in the area of the NJDD drainage system or any other location where the drainage water may be utilized or discharged.
The investigation revealed that the drainage water has some limitations for the most salt- and ionsensitive crops but that a significant amount of the water could be reused carefully or, alternately when the salinity of the river is low, continued to be discharged. One additional finding was that nitrates increased dramatically in the drainage sampled more recently (2012). The nitrate levels could impede direct discharge to the river. The current mix of crops does not have very many acres considered highly sensitive to salt or the ions reviewed in this study. Reuse will not cause alteration of the soil since the drainage water is high in calcium and magnesium.
The management alternatives range from continued discharge to the river to recycling and reuse but also include dedicated reuse areas under control of the District or with special agreements of landowners needing supplemental water supplies. The dedicated reuse area alternative also includes the option to concentrate the drainage water to the extent there is no discharge using the system known as integrated on-farm drainage management (IFDM).
The principal difference between the current discharge to the river and the future management alternatives is that management of the water under any of the new alternatives will need to be “active” rather than the current passive system that turns on and off with float-actuated pumps that discharge the drainage to the river. The result is the District will need to be both more technically and managerially involved in subsurface drainage water management.