Proceedings of the 2019 Mississippi Water Resources Conference

Year: 2019 Authors: Tran G., Johnson D.

The U.S. Army Corps of Engineers (USACE) is assisting the Agricultural Research Service (ARS) in the design and construction of a pilot groundwater injection project in Leflore County, MS. The project will have a single withdrawal well and two injection wells. One aspect of the assistance the Corps consists of obtaining all applicable permits for the wells from MS Department of Environmental Quality (MDEQ). Because the well will require periodic back flushing to remove biofouling of the gravel pack surrounding the well, a National Pollutant Discharge Elimination System (NPDES) permit is required. The permitting process identified iron as a potential contaminant of concern. Groundwater samples obtained from sites close to the injection site had dissolved iron concentrations which exceeded the chronic aquatic life criteria (CALC) for iron (1.0 mg/l). The USACE has designed a water treatment plant to remove the iron, but use of such a plant may affect the viability of a large scale implementation of injection project to restore the declining alluvial aquifer. As the Mississippi Delta has more than 20,000 existing irrigation wells, which discharge excess irrigation water in the Delta's lakes and streams, the USACE conducted a study to determine if there are any indications of existing iron contamination of surface waters. The USACE obtained all available ground and surface water data from the United States Geological Survey National Water Information System (USGS NWIS) database. The average concentration of iron in groundwater is 600 ppb, and is more than 50 times greater than the average surface water concentration. Occasional surface water samples did exceed the ALC, but these instances were extremely infrequent.