Integrating Groundwater Observations with Models of Soil-Water Dynamics to Examine Recharge Patterns through Glacial Sediments in a Humid Continental Climate

Poster presented at American Geophysical Union meeting in 2015.Understanding the timing and magnitude of shallow groundwater recharge is critical for determining water balance and analyzing aquifer sensitivity for water resource planning. We analyzed data from six hydrometeorological monitoring stations using HYDRUS 1D to achieve physically based estimates of water-table recharge in various glaciated terrains in Indiana (USA). The models simulated runoff, root-water uptake, and flow through heterogeneous soil profiles to quantify water flux at the water table. Calibration by inverse modeling of data collected in 2013 yielded optimized hydraulic parameters that allowed accurate simulation of observed soil moisture (RMSE generally within 3%). The model validation period confirmed accurate simulation of soil moisture as well as correspondence between modeled recharge and observed water-table fluctuations. Additional modelling over a three-year study period indicated that diffuse water-table recharge in the region can be reasonably approximated as 35% of precipitation, but interannual and monthly variability can be significant depending on the glacial setting and pedological development. Soil parent material and horizon characteristics have a strong influence on average annual recharge primarily through their control on Ks, with clay-rich till parent materials producing values as low as 16% and coarse-grained outwash parent materials producing values as high as 58% of precipitation. The combined modelling and monitoring data reveal distinct seasonality of recharge, with most recharge occurring in the winter (seasonal mean of all sites was 66% of precipitation) and lesser but interannually stable amounts in the spring (44%), summer (13%), and autumn (16%). This ongoing research underscores the value of combining vadose zone characterization with hydrometeorological monitoring to more effectively represent how surface energy and moisture budgets influence the dynamics of surface water-groundwater interactions

Mapping the Variability of Groundwater Quality in an Abandoned Tailings Deposit using Electromagnetic Geophysical Techniques

Presentation was given at the 2010 National Meeting of the American Society of Mining and Reclamation, Pittsburgh, PA, June 5-11th 2010.A geophysical study was conducted at an abandoned coal mine site in southwestern Indiana in an effort to characterize the spatial variability of groundwater quality and to identify areas that contain high concentrations of total dissolved solids (TDS) and other indicators of acid mine drainage. The study utilized an EM34-3 terrain conductivity instrument to measure the apparent electrical conductivity of the underlying earth. Terrain conductivity is routinely attributed to the electrical conductivity of the underlying material, porosity, moisture content, and the dissolved electrolytes in pore fluid. To interpret the instrument response, terrain conductivity data were compared to field and laboratory chemistry of water samples collected from 27 monitoring wells. Terrain conductivity values ranged from 17-58 millisiemens/meter over the extent of the study area which included mine refuse, levee material, and natural soils. The contribution of pore water chemistry to the overall terrain conductivity was analyzed by measuring the specific conductance (SpC) of ground water samples which is a reflection of the concentration of TDS. The specific conductance ranged from 1380-5410µmhos/cm at 25° C; where the higher SpC values correspond to a higher concentration of TDS due to pyrite dissolution. A map of the terrain conductivity values indicated that high conductivity values were concentrated in specific areas which will need special attention in remediation plans. The mapping also indicated that the majority of the site contains groundwater with a low SpC and should be amenable to less intensive remediation. A map of the contamination plume based on terrain conductivity values was consistent with a groundwater flow model constructed for this site. A correlation was also observed between subsurface hydraulic conductivity and terrain conductivity measurements (R2=0.66) indicating an instrument response to soil permeability. This study indicates that shallow electrical geophysical exploration can be used to locate groundwater contamination plumes when subsurface hydraulic properties are taken into account

Hydrochemical Effects of Using Coal Combustion Byproducts as Structural Fill and Capping Material at an Abandoned Mine Lands Reclamation Site, Southwestern Indiana

Presentation was given at the 2010 National Meeting of the American Society of Mining and Reclamation, Pittsburgh, PA, June 5 – 11, 2010.The use of coal combustion by-products (CCBs) in mine reclamation has been advocated by some because of their low permeability and potential to generate alkalinity. However, others have argued that these benefits are outweighed by the potential for leaching of trace elements that can enter ground and surface waters. In 1996, an abandoned mine land (AML) site in southwestern Indiana was reclaimed using ponded ash as structural fill in highwall cuts, and fixated scrubber sludge (FSS) as capping material over pyritic refuse. Pre-reclamation and post-reclamation monitoring of surface water discharge from the site, groundwater elevations and chemistry, as well as soil moisture fluctuations in the unsaturated zone have provided a basis for evaluating the effects of CCBs on the hydrochemistry of the site and potential for off-site impacts. Limited recharge through the FSS is supported by barometric efficiency changes in the refuse aquifer, the presence of perched water measured in monitoring wells installed on the cap, and minimal fluctuations in soil moisture within and immediately below the cap. Reductions in oxygenated rainwater reaching the refuse are indicated by groundwater chemistry data, collected from the refuse aquifer between 1995 and 2007, which show an increase in pH along with decreasing trends in total acidity, specific conductivity (SpC), and arsenic. Concentrations of boron, a trace element commonly associated with CCBs, have declined to near pre-reclamation levels at most sites (~1 mg/L) after an increase immediately following reclamation. Although arsenic concentrations at 14 µg/L (EPA maximum contaminant level, or MCL, is 10 µg/L) along with boron (14 mg/L) remain slightly elevated in groundwater associated with ash-filled lakes, improvements in surface water quality leaving the site include significant reductions in total mineral acidity and total iron concentrations, while trace metal concentrations remain below EPA MCLs