Dr. Andrew O'Reilly

Areas of Expertise

Subsurface hydrology, Groundwater modeling, Contaminant transport, Green Infrastructure, Artificial recharge.

Recent Projects

Hybrid Spectral-Decomposition Artificial Neural Network Models for Simulating the Forcing-Response Behavior of Hydrologic Systems

Over the last several decades, machine learning has become increasingly popular for modeling hydrologic systems. While first-principles models are essential components of advancing our understanding of hydrologic phenomena, such models may be difficult to run on large, multidecadal datasets and often fall short in replicating observations. Machine learning is well suited for modeling of system forcing-response behavior using large datasets. We are using spectral decomposition of climatic and anthropogenic forcing time-series to develop hybrid wavelet analysis (WA) or moving window average (MWA) artificial neural network (ANN) models. The WA-ANN and MWA-ANN techniques are explored by modeling historical hydrologic response time-series (e.g. lake water level and groundwater level) in order to provide understanding of potential causes of the observed fluctuations. Discrete wavelet transform (DWT) is used to decompose the input time-series data into various levels of approximate and details wavelet coefficients, whereas MWA acts as a low-pass signal-filtering technique for removing high-frequency signals from the input data. Selection of the appropriate decomposition level for DWT and window size for MWA helps in understanding the important time scales of forcing time-series, such as rainfall, that influence water levels.

Examining the Use of Vadose-Zone Recharge Wells in the Mississippi River Valley Alluvial Aquifer as a Viable Artificial Recharge Method

Increasing concerns regarding depletion of groundwater resources in the Delta region of Mississippi has 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, which is common for alluvial aquifers. Vadose-zone recharge wells are a simple alternative because they are not limited by the layer of fine soils at the surface. Instead, the wells are drilled through the capping layer and screened in the unsaturated (vadose) zone of the aquifer. 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. 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 alluvial aquifer in Delta, results are expected to be relevant to other areas. This research is being performed in collaboration with the Dr. J.R. Rigby, U.S. Department of Agriculture, National Sedimentation Laboratory.

Fate and Transport of Cyanotoxin Anatoxin-a in Alfisols and Vertisols in Granada County, Mississippi

Cyanotoxins are produced by many species of cyanobacteria (blue-green algae) in lakes, wetlands, and marine environments across the globe and have been known to cause severe liver damage, nerve damage, and often death in many organisms that live in or depend on these habitats. Although several studies have focused on the production, fate, and transport of these toxins in surface waters, significantly fewer studies have been conducted on their occurrence and fate in soils. Furthermore, many studies that describe subsurface mobility of the toxins only do so with respect to grain-size distribution and microbe abundance in homogeneous sediments, but fail to describe adsorption and degradation processes with respect to specific soil orders and individual stratigraphic soil horizons. Studies that have addressed cyanotoxin fate in soil have focused on microcystin and, to a lesser degree, cylindrospermopsin; little research is available on anatoxin-a. The purpose of this study is to (1) develop anatoxin-a isotherms for a range of soil types in Granada County; and (2) assess the potential fate and transport of anatoxin-a based on soil species, basic soil properties (grain size, pH, organic carbon content, cation exchange capacity), and microbial activity.

Oxbow Lake-Wetland Systems as a Source of Recharge to the Mississippi River Valley alluvial aquifer

Mechanisms controlling groundwater recharge from oxbow lake-wetland systems in the Delta region of Mississippi are poorly understood, and the potential for these systems to provide recharge to the Mississippi River Valley alluvial aquifer (MRVAA) is unknown. Recharge from oxbow lakes and forested perimeter wetlands, which are numerous in the Delta, has traditionally been assumed insignificant due to the prevalence of fine-grained bottom sediments. However, more recent research at Sky Lake, an oxbow lake in the Delta near Belzoni, Mississippi, suggests the presence of preferential flow paths in the wetland bottom sediments that potentially convey significant recharge to the MRVAA. We are collecting continuous water levels (lake, wetland, and groundwater) and subsurface temperatures at Sky Lake. These data will be used to estimate vertical recharge fluxes in the fine-grained wetland sediments and to assess the potential for recharge to the underlying MRVAA.

Characterization of Vadose-Zone Properties and Strategy for Enhancing Groundwater Recharge in the Mississippi Delta

Current and planned water conservation and irrigation best management practices are projected to not fully alleviate the long-term depletion of groundwater stored in the Mississippi River Valley alluvial aquifer. Therefore, a better understanding of groundwater recharge processes is needed. However, the mechanisms that control groundwater recharge in the fine-grained, cohesive soils of the Mississippi Delta are not fully defined, in part due to a lack of quantitative data on physical and hydraulic properties of the vadose zone. Undisturbed soil cores and disturbed grab samples were collected at various depths in two hand-augered boreholes in the vicinity of Sky Lake near Belzoni, Mississippi. Field and laboratory measurements are being used to determine the type of soil and its saturated hydraulic conductivity to better understand its infiltration ability and determine if artificial recharge using vadose-zone wells is viable.

Quantification of Natural and Anthropogenic Effects in Groundwater and Lake-Level Data in Central Florida Using Data Mining

Complex interactions between the surface and subsurface environments in a karst terrain are difficult to simulate with physics-based models. Alternatively, substantial historical hydrologic data are available for central Florida, which are well suited for empirical modeling. The primary objectives of the study were to (1) identify and quantify both natural and anthropogenic effects in historical groundwater-level, spring flow, and lake-level data by using artificial neural networks (ANNs) and other data-mining techniques, and (2) develop a decision support system (DSS) composed of multiple site-specific ANN models to predict groundwater levels, spring flows, and lake levels in central Florida that may be used to evaluate scenarios of interest to the area's water managers.

Nitrogen Transport and Transformation beneath Stormwater Infiltration Basins in Karst Areas, Marion County, Florida

Elevated concentrations of nutrients, particularly nitrate, in groundwater and springs in Florida are a growing resource management concern. Stormwater infiltrations basins, which are a common stormwater management practice in the well-drained karst terrain areas of Florida, are a potentially important source of nutrients to the groundwater system because stormwater exits the basin by only evaporation or infiltration. The primary objectives of the study were to (1) identify and evaluate the natural processes (physical, chemical, and biological) that control the nitrogen cycle in soil and groundwater beneath stormwater infiltration basins, and (2) design, implement, and monitor a new stormwater infiltration best management practice for nutrient (nitrogen and phosphorus) reduction.

Transport of the Cyanotoxins Microcystin-LR and Cylindrospermopsin in Groundwater beneath Stormwater Ponds

Cyanobacteria may proliferate in stormwater ponds, and cyanotoxins produced by these organisms represent potential public health concerns. The objective of the study was to investigate the potential for transport of microcystin-LR and cylindrospermopsin (toxins produced by cyanobacteria, also called blue-green algae) in groundwater by using two vertical, down-flow columns packed with sand to simulate typical stormwater pond sediment in Florida.


Journal Articles:

O’Reilly, A.M., Holt, R.M., Davidson, G.R., Patton, A.C., and Rigby, J.R., 2020, A dynamic water-balance/nonlinear-reservoir model of a perched phreatic aquifer–river system with hydrogeologic threshold effects: Water Resources Research. In Press. doi:10.1029/2019WR025382.

Gifford, J.N., Platt, B.F., Yarbrough, L.D., O’Reilly, A.M., and Al Harthy, M.H.M., 2020, Integrating petrography, x-ray fluorescence, and U-Pb detrital zircon geochronology to interpret provenance of the Mississippian Hartselle Sandstone, U.S.A: Journal of Geology. In Press.

Gratzer, M.C., Davidson, G.R., O’Reilly, A.M., and Rigby, J.R., 2020, Groundwater recharge from an oxbow lake-wetland system in the Lower Mississippi River Valley: Hydrological Processes 34: 1359–1370. doi:10.1002/hyp.13680.

Abera, L.E., Surbeck, C.Q., and O’Reilly, A.M., 2018, Simulated performance of in-place pervious concrete under varying storms, surface areas, and infiltration rates: Journal of Sustainable Water in the Built Environment 4(2): 04018003. doi:10.1061/JSWBAY.0000852.

O'Reilly, A.M., Wanielista, M.P., Chang, N.B., Xuan, Zhemin, and Harris, W.G., 2012. Nutrient removal using biosorption activated media: Preliminary biogeochemical assessment of an innovative stormwater infiltration basin: Science of the Total Environment 432: 227–242. doi:10.1016/j.scitotenv.2012.05.083.

O'Reilly, A.M., Chang, N.B., and Wanielista, M.P., 2012. Cyclic biogeochemical processes and nitrogen fate beneath a subtropical stormwater infiltration basin: Journal of Contaminant Hydrology 133: 53–75. doi:10.1016/j.jconhyd.2012.03.005.

O'Reilly, A.M., Wanielista, M.P., Chang, N.B., Harris, W.G., and Xuan, Zhemin, 2012. Soil property control of biogeochemical processes beneath two subtropical stormwater infiltration basins: Journal of Environmental Quality 41(2): 564–581. doi:10.2134/jeq2011.0204

Shoemaker, W.B., Huddleston, S., Boudreau, C.L., and O’Reilly, A.M., 2008. Sensitivity of wetland saturated hydraulic heads and water budgets to evapotranspiration: Wetlands 28(4): 1040–1047. doi:10.1672/08-105.1

Technical Reports:

Bellino, J.C., Kuniansky, E.L., O’Reilly, A.M., and Dixon, J.F., 2018, Hydrogeologic setting, conceptual groundwater flow system, and hydrologic conditions 1995–2010 in Florida and parts of Georgia, Alabama, and South Carolina: U.S. Geological Survey Scientific Investigations Report 2018–5030, 103 p.

O'Reilly, A.M., Roehl, E.A., Jr ., Conrads, P.A., Daamen, R.C., and Petkewich, M.D., 2014. Simulation of the effects of rainfall and groundwater use on historical lake water levels, groundwater levels, and spring flows in central Florida: U.S. Geological Survey Scientific Investigations Report 2014–5032, 153 p.

Sepúlveda, Nicasio, Tiedeman, C.R., O'Reilly, A.M., Davis, J.B., and Burger, P., 2012. Groundwater flow and water budget in the surficial and Floridan aquifer systems in east-central Florida: U.S. Geological Survey Scientific Investigations Report 2012-5161, 214 p.

O'Reilly, A.M., 2007. Effects of the temporal variability of evapotranspiration on hydrologic simulation in central Florida. U.S. Geological Survey Scientific Investigations Report 2007-5100, 36 p.

O'Reilly, A.M., 2004. A method for simulating transient ground-water recharge in deep water-table settings in central Florida by using a simple water-balance/transfer-function model. U.S. Geological Survey Scientific Investigations Report 2004-5195, 49 p.

Shoemaker, W.B., O'Reilly, A.M., Sepúlveda, Nicasio, Williams, S.A., Motz, L.H., and Sun, Qing, 2004. Comparison of estimated areas contributing recharge to selected springs in north-central Florida by using multiple ground-water flow models. U.S. Geological Survey Open-File Report 03-448, 31 p.

O'Reilly, A.M., Spechler, R.M., and McGurk, B.E., 2002. Hydrogeologic and water-quality characteristics of the Lower Floridan aquifer in east-central Florida. U.S. Geological Survey Water-Resources Investigations Report 02-4193, 60 p.

Knowles, Leel, O'Reilly, A.M., and Adamski, J.C., 2002. Hydrogeology and simulated effects of ground-water withdrawals from the Floridan aquifer system in Lake County and in the Ocala National Forest and vicinity, north-central Florida. U.S. Geological Survey Water-Resources Investigations Report 02-4207, 140 p.

O'Reilly, A.M., 1998. Hydrogeology and simulation of the effects of reclaimed-water application in west Orange and southeast Lake Counties, Florida. U.S. Geological Survey Water-Resources Investigations Report 97-4199, 91 p.