Detecting a salinity plume in an unconfined sandy aquifer and assessing secondary soil salinization using electromagnetic induction techniques, North Dakota, USA |
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Authors: | D G Hopkins J L Richardson |
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Institution: | (1) Department of Soil Science, 225 Walster Hall, North Dakota State University, Fargo, ND 58105, USA Fax: +1-701-231-7861 e-mail: hopkins@badlands.nodak.edu, US;(2) Department of Soil Science, 214 Walster Hall, North Dakota State University, Fargo, ND 58105, USA, US |
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Abstract: | Land-use changes on the Sheyenne Delta in southeastern North Dakota, USA, have prompted research on impacts to the unconfined
Sheyenne Delta aquifer (SDA). This study examines effects of the saline discharge of a flowing artesian well that taps the
Dakota aquifer (DAK) on SDA groundwater chemistry and soil salinity. Objectives were to map the saline plume in the SDA using
induction techniques, to assess chloride migration in the SDA, and to evaluate induction sensitivity to moderately saline
sands. Induction data, collected in a 2.9-ha grid, were compared to 31 soil profiles analyzed for gravimetric moisture, electrical
conductivity, and chloride. Soil salinization is widespread, but only 7% of the area meets the 4-dS/m threshold for saline
soils. SDA chloride distribution was determined on transects oriented with and perpendicular to the flow path determined from
induction readings. Chloride was detected in the aquifer 550 m from the source, indicating a transport rate of 21 m/yr. Complex
recharge and discharge patterns and hummocky relief contribute to a wide chloride plume at this site. A mass balance based
on soil-water content and chloride concentration shows that only 4% of the chloride from the DAK well remains in the grid
volume.
Received, January 1998 · Revised, January 1999 · Accepted, March 1999 |
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Keywords: | USA equipment/field techniques geophysical methods groundwater quality salinity plume |
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