Show simple item record

dc.contributor.advisorSingha, Kamini
dc.contributor.advisorMcCray, John E.
dc.contributor.authorEngers, Aaron James
dc.date.accessioned2021-09-13T10:20:46Z
dc.date.accessioned2022-02-03T13:25:09Z
dc.date.available2021-09-13T10:20:46Z
dc.date.available2022-02-03T13:25:09Z
dc.date.issued2021
dc.identifierEngers_mines_0052N_12258.pdf
dc.identifierT 9216
dc.identifier.urihttps://hdl.handle.net/11124/176494
dc.descriptionIncludes bibliographical references.
dc.description2021 Summer.
dc.description.abstractHere we present a numerical modeling effort to estimate historical groundwater concentrations of perfluorooctanoate (PFOA), perfluorooctane sulfonate (PFOS), and perfluorohexane sulfonate (PFHxS) resulting from releases of aqueous film-forming foam (AFFF) near Colorado Springs, Colorado, U.S.A. AFFF was used during firefightier training at the Peterson Air Force Base upgradient of the towns of Security, Widefield, and Fountain, CO from 1970 to 2017. All three municipalities’ water supply systems relied heavily on groundwater during this time period. We developed one Modflow6 flow model and three MT3D-USGS transport models, one for each PFAS, to help evaluate human exposure to these compounds via drinking water. A Modflow6 model was calibrated using PEST. Locations and timing of potential source zones were established from Air Force documentation; the masses of contaminants introduced to the water table were estimated using inverse methods to match data collected during a 2018 sampling event of the municipal water wells. Concentrations estimated by our models provided reasonable approximations of historical exposures to PFOS, PFOA, and PFHxS in the Security-Widefield area, but not in Fountain. We conducted a Monte Carlo analysis to quantify uncertainty of the model results given available data. The average range between upper and lower 95\% confidence limits at our calibration targets was 174 ng/L, 108 ng/L, and 238 ng/L for PFOS, PFOA, and PFHxS, respectively. A mass balance between the PFASs assumed to be applied on the surface the calibrated mass loading to the water table indicated that 99.5\% of PFOS, 50\% of PFOA, and 88\% of PFHxS remained unaccounted for, which were assumed to be retained in the vadose zone near the source areas and along the transport pathway. The framework employed here may be suitable for a variety of poly- and perfluoroalkyl substance (PFAS) modeling problems where saturated-zone transport is the primary concern. However, a complete picture of PFAS fate and transport that accounts for all released mass is likely not feasible with traditional control-volume finite-difference simulators like Modflow6/MT3D-USGS; this will hopefully be better achieved when the analytical solutions and PFAS-specific simulators currently under development become more readily available.
dc.format.mediumborn digital
dc.format.mediummasters theses
dc.languageEnglish
dc.language.isoeng
dc.publisherColorado School of Mines. Arthur Lakes Library
dc.relation.ispartof2021 - Mines Theses & Dissertations
dc.rightsCopyright of the original work is retained by the author.
dc.subjectModeling
dc.subjectMonte Carlo
dc.subjectper- and polyfluoroalkyl substances (PFAS)
dc.subjectModflow
dc.subjectgroundwater
dc.subjectMT3D
dc.titleEstimating historical concentrations of per- and polyfluoroalkyl substances with groundwater flow and transport models and a Monte Carlo analysis
dc.typeText
dc.contributor.committeememberBenson, David A.
dc.contributor.committeememberHiggins, Christopher P.
dc.contributor.committeememberIllangasekare, T. H.
thesis.degree.nameMaster of Science (M.S.)
thesis.degree.levelMasters
thesis.degree.disciplineGeology and Geological Engineering
thesis.degree.grantorColorado School of Mines


Files in this item

Thumbnail
Name:
Engers_mines_0052N_12258.pdf
Size:
19.06Mb
Format:
PDF

This item appears in the following Collection(s)

Show simple item record