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Field study of dispersion in a heterogeneous aquifer: 4. Investigation of adsorption and sampling bias
Author(s) -
Boggs J. Mark,
Adams E. Eric
Publication year - 1992
Publication title -
water resources research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.863
H-Index - 217
eISSN - 1944-7973
pISSN - 0043-1397
DOI - 10.1029/92wr01759
Subject(s) - tracer , aquifer , groundwater , adsorption , bromide , soil water , hydrology (agriculture) , sampling (signal processing) , soil science , chemistry , environmental chemistry , environmental science , mineralogy , geology , inorganic chemistry , physics , geotechnical engineering , organic chemistry , filter (signal processing) , computer science , nuclear physics , computer vision
The declining mass balance trend observed for bromide and three fluorobenzoate tracers during a natural gradient experiment at a site near Columbus, Mississippi, prompted investigations related to the reactivity of the tracers and the representativeness of the tracer samples obtained from multilevel samplers. A laboratory soil column study indicated that adsorption of bromide during the field experiment was of the order of 20% and that up to 10% of the three fluorobenzoates was adsorbed. The presence of iron oxides and kaolinite in the alluvial aquifer combined with the low ground water p H of 4.8 produced geochemical conditions conducive to adsorption of the anionic tracers. Multilevel samplers (MLS) used in the field experiment were evaluated by comparing bromide concentrations from the MLS with water samples extracted from adjacent soil cores. Vertically averaged bromide concentrations for the MLS were 21% lower than those for the cores. A matrix diffusion process in conjunction with a natural tendency for preferential sampling from permeable regions in the heterogeneous alluvial sediments is proposed as an explanation for the apparent bias in the MLS sample concentrations. This process is shown to be qualitatively consistent with the tracer mass balance observed during the natural gradient experiment.