Date of Award
1-1-2019
Document Type
Thesis
Degree Name
M.S. in Biological Science
First Advisor
Andrew O'Reilly
Second Advisor
Robert Holt
School
University of Mississippi
Relational Format
dissertation/thesis
Abstract
Increasing concerns regarding depletion of groundwater 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. From field tests data the calculated transmissivity ranged from 5800 to 7800 m2/day. The calculated hydraulic conductivity ranged from 150 to 220 m/day. The calculated storativity of the aquifer ranged from 0.19 to 0.22. Field tests indicated that there is inverse correlation between barometric pressure and water level in the monitoring wells indicating a barometric efficiency of approximately 60%. Despite 50 hours of injection test there were small water table rises from well recharge. Water table rises decreased with increasing distance from the vadose-zone wells ranging from 1 to 4 cm. Small water-table rises likely are due to the high hydraulic conductivity of the aquifer vertical heterogeneity screen location of the monitor wells or some combination of these factors. Eight soil samples were collected from the site and for some samples their saturated hydraulic conductivities (Ksat) and wetting/draining curves were determined using falling head permeability test METER Hyprop and hanging water-column method. An axisymmetric model was developed using VS2DTI software. The simulations were run with a range of Kand porosity (n) values. The results of the simulations show that head changes at the nearest monitor well will occur faster and be smaller with a greater ratio of Ksat/n and vice versa. In addition 3D numerical variably-saturated model was developed using HYDRUS-3D software. This model simulated the injection of water from four vadose-zone wells in an alluvial aquifer. Simulated pressure head differences in five observation nodes that are located 0.17 m below the water table shothat the observation node that is below the vadose-zone well had the largest water level increase and the observation node that is furthest from the vadose-zone well had the smallest water level increase ranging from 0.6 to 2 cm. Different water-table responses between the final field test and model simulations are likely due to the differences in the amount of water injected into the system and the positions of the monitor wells. A total of 272 m3/day of water was injected during the field test whereas only 88 m3/day of water was injected during the HYDRUS simulation and the field monitor wells were screened deeper than the depths of the observation nodes in HYDRUS. This research provides 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.
Recommended Citation
Kwak, Kyungwon, "Field testing and simulation of vadose-zone recharge wells in the Mississippi river valley alluvial aquifer as an artificial recharge method" (2019). Electronic Theses and Dissertations. 1961.
https://egrove.olemiss.edu/etd/1961