Managed aquifer recharge using a borrow pit in connection with the Mississippi River Valley alluvial aquifer in northeastern Arkansas

Authors: LESLIE, DEBORAH - Arkansas Technical University; Reba, Michele; CZARNECKI, JOHN - University Of Arkansas

Submitted to: Journal of Soil and Water Conservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/14/2022
Publication Date: 12/1/2022
Citation: Leslie, D.L., Reba, M.L., Czarnecki, J.B. 2022. Managed aquifer recharge using a borrow pit in connection with the Mississippi River Valley alluvial aquifer in northeastern Arkansas. Journal of Soil and Water Conservation. 78(1):44-57. https://doi.org/10.2489/jswc.2023.00021.
DOI: https://doi.org/10.2489/jswc.2023.00021

Interpretive Summary: Groundwater overdraft from the Mississippi River Valley alluvial aquifer has resulted in several cones of depression in eastern Arkansas, largely due to groundwater use for irrigation. While surface water diversions are planned for one of these areas to relieve some groundwater pumping, there are currently no such planned diversions to address groundwater declines in northeast Arkansas. This study was undertaken to investigate whether infiltration basins could be used to enhance local groundwater recharge. Results showed that the removal of surface soil, higher in clay content, provided a quicker pathway for surface water to infiltrate the unsaturated zone. This subsurface zone of unsaturated sand above the water table, which has expanded due to declining groundwater levels, provided a natural filter as well as a potential underground storage area. These findings support infiltration basins as a method to increase aquifer recharge within northeast Arkansas, which could be one way to promote groundwater sustainability within a primarily agricultural area dependent on reliable irrigation.

Technical Abstract: A managed aquifer recharge experiment was conducted to determine whether infiltration basins could be used to mitigate groundwater decline in critical groundwater areas of northeast Arkansas. In 2015, the Arkansas Department of Transportation (ARDOT) contracted sand excavation of fallow land owned by a collaborating producer. This excavation pit would serve as a test case to measure the rate of infiltration into the Mississippi River Valley alluvial aquifer using nearby surface water as the recharge source. Prior to excavation, soil core analyses revealed soil properties within the confining clay layer of red-brown clay and silty clay soils (0-3.7 m deep) with sand below (ARDOT, personal communication). Once excavation was completed to a depth of about 6 m, the uppermost-unsaturated section of the alluvial aquifer, consisting of well-sorted medium grain size sand, was exposed and free of the confining clay layer. The excavation pit floor was about 27 m above the existing water table, and it was hypothesized that this exposed unsaturated aquifer section would infiltrate water at a faster rate than an area topped with the confining clay layer. Prior to water input, the excavation pit was surveyed to collect location and elevation data to determine size. Sediment samples were collected from the pit floor and sidewall pre- and post-experiment to characterize particle size, textural class, and organic matter. Submersible pressure transducers were installed within the bottom of the pit and in a nearby irrigation well to monitor water level changes. Meteorological data were collected on-site to measure the components of the water budget. Water level declines and infiltration within the pit were evident throughout the experiment. An initial infiltration rate of 192 mm day-1 was measured that decreased until March, with rates of 0-136 mm day-1 that varied until June. A lack of monitoring equipment through the unsaturated zone to the saturated zone in close proximity prevented direct observation of water movement downward. Removal of the confining layer through the construction of the pit exposed sand, and provided a pathway for surface water to infiltrate the unsaturated zone. The unsaturated sand of the alluvial aquifer provided a natural filter as well as potential subsurface storage area. The use of infiltration basins as a managed aquifer recharge strategy could provide some arrest of groundwater decline problems locally. However unless widely adopted, the approach would not address the region-wide challenges of groundwater decline in eastern Arkansas.