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Tributary stream infiltration as a source of herbicides in an alluvial aquifer

January 1, 1999

Where Walnut Creek flows across the South Skunk River alluvial aquifer, it provides a potential source of herbicides and herbicide metabolites. This straightened reach of the creek loses water and dissolved contaminants to the alluvial aquifer through a layer of fine‐grained flood plain deposits. Estimates of potential flux of chemicals were based on measurements taken during baseflow in April 1994 before herbicides were applied to the watershed and in June 1994 after chemical application and when stream discharge included runoff and tile‐drainage water. Hydraulic head measurements between the creek and flood plain deposits and between the creek and aquifer confirmed the potential for downward groundwater flow during both sampling periods. Hydraulic conductivity estimates from slug tests were used to calculate an average linear groundwater velocity of 0.5 m d−1 in the fine‐grained flood plain deposits. At this velocity, contaminants could be advectively transported to the aquifer within 6 d. The potential for atrazine (2‐chloro‐4‐ethylamino‐6‐isopropylamino‐s‐triazine) flux to the aquifer from the creek was estimated to be between 60 and 3000 µg d−1 m−2. This rate is one to three orders of magnitude greater than the estimated flux via leaching beneath a typical field. If the process of vertical stream leakage occurs in many hydrologic settings, it may constitute a substantial source of herbicides to shallow alluvial aquifers in many areas of the Midwest.

Publication Year 1999
Title Tributary stream infiltration as a source of herbicides in an alluvial aquifer
DOI 10.2134/jeq1999.00472425002800010007x
Authors Michael R. Burkart, William W. Simpkins, Paul J. Squillace, Martin Helmke
Publication Type Article
Publication Subtype Journal Article
Series Title Journal of Environmental Quality
Index ID 70021962
Record Source USGS Publications Warehouse
USGS Organization Iowa Water Science Center