Evidence of Remediation-Induced Alteration of Subsurface Poly- and Perfluoroalkyl Substance (PFAS) Distribution at a Former Firefighter Training Area

Poly- and perfluoroalkyl substances (PFASs) are a class of fluorinated chemicals that are utilized in firefighting and have been reported in groundwater and soil at several firefighter training areas. In this study, soil and groundwater samples were collected from across a former firefighter training area to examine the extent to which remedial activities have altered the composition and spatial distribution of PFASs in the subsurface. Log K[subscript oc] values for perfluoroalkyl acids (PFAAs), estimated from analysis of paired samples of groundwater and aquifer solids, indicated that solid/water partitioning was not entirely consistent with predictions based on laboratory studies. Differential PFAA transport was not strongly evident in the subsurface, likely due to remediation-induced conditions. When compared to the surface soil spatial distributions, the relative concentrations of perfluorooctane sulfonate (PFOS) and PFAA precursors in groundwater strongly suggest that remedial activities altered the subsurface PFAS distribution, presumably through significant pumping of groundwater and transformation of precursors to PFAAs. Additional evidence for transformation of PFAA precursors during remediation included elevated ratios of perfluorohexane sulfonate (PFHxS) to PFOS in groundwater near oxygen sparging wells

Metal Release from Sandstones under Experimentally and Numerically Simulated CO₂ Leakage Conditions

Leakage of CO₂ from a deep storage formation into an overlying potable aquifer may adversely impact water quality and human health. Understanding CO₂-water-rock interactions is therefore an important step toward the safe implementation of geologic carbon sequestration. This study targeted the geochemical response of siliclastic rock, specifically three sandstones of the Mesaverde Group in northwestern Colorado. To test the hypothesis that carbonate minerals, even when present in very low levels, would be the primary source of metals released into a CO₂-impacted aquifer, two batch experiments were conducted. Samples were reacted for 27 days with water and CO₂ at partial pressures of 0.01 and 1 bar, representing natural background levels and levels expected in an aquifer impacted by a small leakage, respectively. Concentrations of major (e.g., Ca, Mg) and trace (e.g., As, Ba, Cd, Fe, Mn, Pb, Sr, U) elements increased rapidly after CO₂ was introduced into the system, but did not exceed primary Maximum Contaminant Levels set by the U.S. Environmental Protection Agency. Results of sequential extraction suggest that carbonate minerals, although volumetrically insignificant in the sandstone samples, are the dominant source of mobile metals. This interpretation is supported by a simple geochemical model, which could simulate observed changes in fluid composition through CO₂-induced calcite and dolomite dissolution

Evidence of Remediation-Induced Alteration of Subsurface Poly- and Perfluoroalkyl Substance Distribution at a Former Firefighter Training Area

Poly- and perfluoroalkyl substances (PFASs) are a class of fluorinated chemicals that are utilized in firefighting and have been reported in groundwater and soil at several firefighter training areas. In this study, soil and groundwater samples were collected from across a former firefighter training area to examine the extent to which remedial activities have altered the composition and spatial distribution of PFASs in the subsurface. Log <i>K</i>_oc values for perfluoroalkyl acids (PFAAs), estimated from analysis of paired samples of groundwater and aquifer solids, indicated that solid/water partitioning was not entirely consistent with predictions based on laboratory studies. Differential PFAA transport was not strongly evident in the subsurface, likely due to remediation-induced conditions. When compared to the surface soil spatial distributions, the relative concentrations of perfluorooctanesulfonate (PFOS) and PFAA precursors in groundwater strongly suggest that remedial activities altered the subsurface PFAS distribution, presumably through significant pumping of groundwater and transformation of precursors to PFAAs. Additional evidence for transformation of PFAA precursors during remediation included elevated ratios of perfluorohexanesulfonate (PFHxS) to PFOS in groundwater near oxygen sparging wells

Nitrogen Fate and Transport in a Conventional Onsite Wastewater Treatment System Installed in a Clay Soil: A Nitrogen Chain Model

Nitrogen cycling in clay-textured soils with onsite wastewater treatment systems is studied and modeled much less often than sand- and loam-textured soils because there is little data on onsite wastewater treatment system performance in these soils. An N chain model with water-content dependent first-order transformation rates for nitrification and denitrification was developed and calibrated using data from a conventional onsite wastewater treatment system installed in a clay-textured soil. The model predicted the N removal in the system. Estimates of N loss were specific to clay-textured soils and should be valuable to TMDL developers who need to predict load allocations for non-point sources in the Piedmont. Nitrogen cycling in clay-textured soils with onsite wastewater treatment systems (OWTS) is studied and modeled much less often than sand- and loam-textured soils because there is little data on OWTS performance in these soils. Information on the nitrogen loads from these systems is needed for quantification of total maximum daily loads (TMDLs). The objective of this study was to calibrate a 2D HYDRUS model using experimental soil pressure head and vadose zone nitrogen (N) and chloride (Cl) data from a conventional OWTS that was installed in a clay soil in the Piedmont region of Georgia. An N chain model with water-content dependent first-order transformation rates for nitrification and denitrification was developed. The overall predicted soil pressure heads and solute concentrations were similar to data collected from the field experiment. The calibrated model made it possible to estimate water and solute fluxes in the drainfield and N losses from the OWTS. The estimated annual N loss from leaching at the lower boundary of the experimental drainfield was 3.8 kg yr-1. Scaled up to an OWTS size typical for GA and a zoning density of 5 homes ha-1, the N load to groundwater would be 57.4 kg ha-1 yr-1, which is comparable to agricultural production losses to groundwater. The model predicted 52% of the N removal in the system was from denitrification, whereas plant uptake and change in N storage accounted for ≤5% of the N loss. These estimates were specific to clay-textured soils and should be valuable to TMDL developers who need to predict load allocations for nonpoint sources in the Piedmont. © Soil Science Society of America 5585 Guilford Rd., Madison, WI 53711 USA. All rights reserved