Shale membrane filtration is the process that controls the groundwater geochemistry of part of the Saginaw Formation aquifer in south-central Michigan. This process purports that certain rock types such as shales act as semi-permeable membranes which can selectively retard the movement of dissolved ions in a water migrating through the membrane. Based on the recharge information and surficial bedrock lithology, two study areas were chosen in south-central Michigan to test the occurrence of shale membrane filtration in the Saginaw Formation. Tritium analysis of selected wells, in one area, supports the presence of local 'point recharge' through sands and gravels to sandstone at the surface of the Saginaw Formation. The other area, based on tritium analysis, does not show the presence of local point recharge. Ion ratios from bedrock waters in the two study areas were found to increase or decrease relative to each other as would be predicted by shale membrane filtration theory, laboratory experiments, and field studies. Water-rock interactions and mixing with other chemically different waters do not correctly explain the observed ion rations, or cannot explain all the ratios as does shale membrane filtration. Shale membrane filtration best explains the observed geochemistry of Saginaw Formations's waters from the study area where conditions are favorable for the occurence of membrane filtration.
RECORD ID: 8302483
F&G CODE: 02f; 02k
Publication
Long, D.T., and Larson, G.J., Field Evidence for Shale Membrane Filtration of
Groundwater, South-Central Michigan: Available from the National Technical
Information Service, Springfield; VA 22161 as PB83-190488, Price codes: A04 in
paper copy, A01 in microfiche. Institute of Water Research Completion Report,
Michigan State Univ., East Lansing, March 1983. 51 p, 6 Fig, 6 Tab, 45 Ref, 1
Append. OWRT A-108-MICH(1), 14-34-0001-1124.
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