Proceedings of the 2019 Mississippi Water Resources Conference

Year: 2019 Authors: Kwak K., O'Reilly A.M., Rigby J.R.

Increasing concerns regarding depletion of groundwater in the Mississippi River Valley alluvial aquifer in the Delta region of Mississippi have led to a need to augment natural recharge. Infiltration basins are often one of the simplest means of artificially recharging aquifers. However, the Delta has a layer of clay and silt at the surface, so it is a better idea to use vadose-zone recharge wells that are not limited by the surficial layer of fine soils. The purpose of this study is to use full-scale field testing to assess the feasibility of using vadose-zone wells for artificial recharge of the Mississippi River Valley alluvial aquifer by using a combination of field, laboratory, and computer simulation techniques.
An initial field test indicated each of two vadose-zone wells could intake 100 to 170 m³/day by gravity flow. Eight soil samples were collected from the site and their saturated hydraulic conductivities (K_sat) and wetting/draining curves will be determined using falling head permeability test, METER Hyprop, and hanging water-column method. An axisymmetric model was developed using VS2DTI software from the USGS. The simulations were run with a range of K_sat and porosity (n) values. The results of the simulations show that head changes at the nearest monitor well are likely to be smaller with a greater ratio of K_sat/n and vice versa. A final full-scale field test will be performed by simultaneously running multiple (up to four) vadose-zone wells. A three-dimensional variably saturated flow model will be developed to analyze the final test. This research will provide understanding of the hydraulic properties controlling vadose-zone wells and operation of the artificial recharge system. As most alluvial aquifers have similar geological settings as the Delta, results are expected to be relevant to other areas.