Evaluating long-term patterns of decreasing groundwater discharge through a lake-bottom permeable reactive barrier
Identifying and quantifying groundwater exchange is critical when considering contaminant fate and transport at the groundwater/surface-water interface. In this paper, areally distributed temperature and point seepage measurements are used to efficiently assess spatial and temporal groundwater discharge patterns through a glacial-kettle lakebed area containing a zero-valent iron permeable reactive barrier (PRB). Concern was that the PRB was becoming less permeable with time owing to biogeochemical processes within the PRB. Patterns of groundwater discharge over an 8-year period were examined using fiber-optic distributed temperature sensing (FO-DTS) and snapshot-in-time point measurements of temperature. The resulting thermal maps show complex and uneven distributions of temperatures across the lakebed and highlight zones of rapid seepage near the shoreline and along the outer boundaries of the PRB. Repeated thermal mapping indicates an increase in lakebed temperatures over time at periods of similar stage and surface-water temperature. Flux rates in six seepage meters permanently installed on the lakebed in the PRB area decreased on average by 0.021 md-1 (or about 4.5 percent) annually between 2004 and 2015. Modeling of diurnal temperature signals from shallow vertical profiles yielded mean flux values ranging from 0.39 to 1.15 md-1, with stronger fluxes generally related to colder lakebed temperatures. The combination of an increase in lakebed temperatures, declines in direct seepage, and observations of increased cementation of the lakebed surface provide in situ evidence that the permeability of the PRB is declining. The presence of temporally persistent rapid seepage zones is also discussed.
Citation Information
| Publication Year | 2018 |
|---|---|
| Title | Evaluating long-term patterns of decreasing groundwater discharge through a lake-bottom permeable reactive barrier |
| DOI | 10.1016/j.jenvman.2018.02.083 |
| Authors | Timothy D. McCobb, Martin A. Briggs, Denis R. LeBlanc, Frederick D. Day-Lewis, Carole D. Johnson |
| Publication Type | Article |
| Publication Subtype | Journal Article |
| Series Title | Journal of Environmental Management |
| Index ID | 70198851 |
| Record Source | USGS Publications Warehouse |
| USGS Organization | New England Water Science Center |
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Temperature and seepage data from a lake-bottom permeable reactive barrier, Ashumet Pond, Falmouth, MA, 2004-2015.
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- Data
Temperature and seepage data from a lake-bottom permeable reactive barrier, Ashumet Pond, Falmouth, MA, 2004-2015.
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Martin A. Briggs
Research HydrologistEmailDenis R LeBlanc (Former Employee)
Research HydrologistFrederick D. Day-Lewis (Former Employee)
Research Hydrologist, Hydrogeophysics Branch