PFOS groundwater transport from a former firefighter training site
Firefighter training sites are commonly long-term point sources of per- and polyfluoroalkyl substances (PFAS) to underlying aquifers, and can serve as case studies to illuminate transport at the field scale. In the 1970s, activities at a fire fighter training site in University Park, Pennsylvania introduced perfluorooctane sulfonate (PFOS) and volatile organic compounds (VOCs) to the underlying dolomite aquifer.
I am using 2D MODFLOW and MT3D models to history-match the contaminant data and determine the physical and chemical aquifer properties likely responsible for the observed plume shape. Although site‑specific Kd values should ideally be used to model field-scale PFOS transport, Koc values reported in the literature for generic cases may adequately describe PFOS transport in this shallow aquifer. Heterogeneity in aquifer total organic carbon content (% TOC) is most likely responsible for the observed shape of the plumes. This highlights an important consideration for modeling PFOS transport in aquifers that may have discrete layers of higher and lower TOC; models that use a homogenous site-average TOC instead of variable TOC zones can significantly underestimate PFOS transport distances and therefore misrepresent exposure risks.
Per and polyfluroalkyl (PFAS) sorption in soils below a spray field receiving wastewater treatment facility effluent
Vadose zones retain a large portion of introduced PFASs, but because PFASs have both hydrophobic and hydrophilic structures, the relative importance of different retention mechanisms (air-water interfaces, organic carbon, mineral surfaces) has not been fully determined. Soil cores from the Penn State Living Filter, a spray field receiving wastewater treatment facility effluent (a common source of PFAS to the environment), provides us with an opportunity to investigate
I plan to use multivariate statistics to evaluate relationships between soil properties (organic carbon content, mineralogy, clay content, grain size distributions) and concentrations of total and individual PFAS. The soil properties and PFAS concentrations will inform and validate numerical modeling of vadose zone flow and reactive transport, likely using STANMOD or Crunchflow. To help inform decision making at the Living Filter, I will model end-member effluent application scenarios to illuminate the historical PFAS mass balance and project potential scenarios for future PFAS retention and movement.
Nitrate transport and accumulation in Brazilian Oxisols
As deforestation and agricultural expansion continues within the Brazilian Amazon-Cerrado ecotone, changes to surface and subsurface water flow and chemistry may negatively impact both ecosystem and human health. Nitrate leaching is a concern under most agricultural lands, but due to high anion exchange capacities, the Oxisols prevalent in the region appear to be buffering stream and groundwater against nitrate pollution. Peak nitrate accumulations have been observed at depths > 4 m, but the mechanisms controlling the depth and longevity of these accumulations remain uncertain.
I am combining analytical and numerical models of unsaturated water movement with measurements of soil solution nitrate concentrations to estimate current nitrate leaching. Water flow models in HYDRUS-1D are informed and calibrated to TDR soil moisture data, and soil solutions have been collected from pan and tension lysimeters. By estimating current nitrate leaching rates and identifying the primary physical and chemical controls on the current nitrate distribution in the subsurface, I hope to provide insight into how nitrate leaching might change under future climate and land use conditions.
The sedimentology of storm-emplaced coastal boulder deposits in Ireland and Shetland
Undergraduate thesis that contributed to two articles: