Chemical and isotopic indicators of groundwater evolution in the basal sands of a buried bedrock valley in the Midwestern United States; implications for recharge, rock-water interactions, and mixing

Buried bedrock valley aquifers can be found throughout Canada and the northern United States where glacial deposits have filled in previously exposed bedrock valleys. The Mahomet bedrock valley is an east-west-trending buried valley in central Illinois containing basal Pleistocene sands and gravels... Full description

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doi: 10.1130/B26574.1
Authors:Hackley, K.C.; Panno, S.V.; Anderson, T.F.
Volume Title:Geological Society of America Bulletin
Source:Geological Society of America Bulletin, 122(7-8), p.1047-1066. Publisher: Geological Society of America (GSA), Boulder, CO, United States. ISSN: 0016-7606
Publication Date:2010
Note:In English. With GSA Data Repository Item 2009286. 92 refs.; illus., incl. sects., geol. sketch map
Subjects:Aquifers; Bedrock; Buried valleys; C-14; Carbon; Cenozoic; Clastic sediments; D/H; Deuterium; Experimental studies; Geochemistry; Ground water; Hydrochemistry; Hydrogen; Isotope ratios; Isotopes; Mixing; O-18/O-16; Oxygen; Paleohydrology; Pleistocene; Quaternary; Radioactive isotopes; Recharge; S-34/S-32; Sand; Sediments; Shallow aquifers; Stable isotopes; Sulfur; Tritium; Water-rock interaction; Illinois; Midwest; United States; Central Illinois; Mahomet Aquifer; Sankoty Mahomet Aquifer
Coordinates:N400000 N410000 W0873000 W0900000
Record ID:2010050185
Copyright Information:GeoRef, Copyright 2020 American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States, Reference includes data supplied by the Geological Society of America
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100 1 |a Hackley, K.C.  |u University of Illinois, Institute of Natural Resource Sustainability, Champaign, IL 
245 1 0 |a Chemical and isotopic indicators of groundwater evolution in the basal sands of a buried bedrock valley in the Midwestern United States; implications for recharge, rock-water interactions, and mixing 
300 |a p. 1047-1066 
500 |a In English. With GSA Data Repository Item 2009286. 92 refs. 
500 |a Key title: Geological Society of America Bulletin 
500 |a Source note: Geological Society of America Bulletin, 122(7-8), p.1047-1066. Publisher: Geological Society of America (GSA), Boulder, CO, United States. ISSN: 0016-7606 
500 |a Publication type: journal article 
504 |b 92 refs. 
506 1 |a Restricted access 
510 3 |a GeoRef, Copyright 2020 American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States, Reference includes data supplied by the Geological Society of America 
520 |a Buried bedrock valley aquifers can be found throughout Canada and the northern United States where glacial deposits have filled in previously exposed bedrock valleys. The Mahomet bedrock valley is an east-west-trending buried valley in central Illinois containing basal Pleistocene sands and gravels making up the Mahomet aquifer and the contemporaneous Sankoty Mahomet aquifer, which are the major sources of freshwater for east-central Illinois. The hydrochemical characteristics of the Mahomet and Sankoty Mahomet aquifers change significantly across the buried bedrock valley. To determine the geochemical processes controlling the chemistry of the water, possible groundwater mixing, and the regions of major recharge, over 80 samples from the Mahomet aquifer, the Sankoty Mahomet aquifer, and shallower aquifers were analyzed for their chemical and isotopic composition, including δ>18`O, δD, δ>13`C, δ>34`S, >14`C, and >3`H. Four geochemical regions were observed across the aquifers. The central and eastern region of the Mahomet aquifer had dilute chemistry and medium >14`C activities, suggesting relatively recent recharge from the surface. The northeastern Mahomet aquifer region had variable sulfate and δ>34`S values, medium chloride concentrations, and low >14`C activity, suggesting mixing with bedrock groundwater along with sulfate reduction. The western Mahomet aquifer region had the highest chloride, dissolved organic carbon, and methane concentrations and showed a continuous decrease in >14`C activity, suggesting seepage from bedrock units, strong reducing conditions, and isolation from surficial recharge. Characteristics of the Sankoty Mahomet aquifer indicated rapid freshwater recharge and mixing with western Mahomet aquifer water. The δD and δ>18`O values indicated little to no Pleistocene water in the Mahomet bedrock valley aquifer system, suggesting an age limit of ca. 11,000 yr B.P. for most of the groundwater. The tritium data indicated modern recharge in some shallower aquifers, but little to none in the Mahomet aquifer and Sankoty Mahomet aquifer, except near a river where stacked sands may have created a hydrologic window to the Mahomet aquifer. It appears that most of the Mahomet aquifer is well protected from surficial contamination. The approach used in this study enabled us to better understand and identify the processes that control the groundwater chemistry within the buried Pleistocene aquifer in central Illinois; processes that may be prevalent in other buried bedrock valley aquifers distributed throughout much of North America. 
650 7 |a Aquifers  |2 georeft 
650 7 |a Bedrock  |2 georeft 
650 7 |a Buried valleys  |2 georeft 
650 7 |a C-14  |2 georeft 
650 7 |a Carbon  |2 georeft 
650 7 |a Cenozoic  |2 georeft 
650 7 |a Clastic sediments  |2 georeft 
650 7 |a D/H  |2 georeft 
650 7 |a Deuterium  |2 georeft 
650 7 |a Experimental studies  |2 georeft 
650 7 |a Geochemistry  |2 georeft 
650 7 |a Ground water  |2 georeft 
650 7 |a Hydrochemistry  |2 georeft 
650 7 |a Hydrogen  |2 georeft 
650 7 |a Isotope ratios  |2 georeft 
650 7 |a Isotopes  |2 georeft 
650 7 |a Mixing  |2 georeft 
650 7 |a O-18/O-16  |2 georeft 
650 7 |a Oxygen  |2 georeft 
650 7 |a Paleohydrology  |2 georeft 
650 7 |a Pleistocene  |2 georeft 
650 7 |a Quaternary  |2 georeft 
650 7 |a Radioactive isotopes  |2 georeft 
650 7 |a Recharge  |2 georeft 
650 7 |a S-34/S-32  |2 georeft 
650 7 |a Sand  |2 georeft 
650 7 |a Sediments  |2 georeft 
650 7 |a Shallow aquifers  |2 georeft 
650 7 |a Stable isotopes  |2 georeft 
650 7 |a Sulfur  |2 georeft 
650 7 |a Tritium  |2 georeft 
650 7 |a Water-rock interaction  |2 georeft 
651 7 |a Illinois  |2 georeft 
651 7 |a Midwest  |2 georeft 
651 7 |a United States  |2 georeft 
653 |a Central Illinois 
653 |a Mahomet Aquifer 
653 |a Sankoty Mahomet Aquifer 
700 1 |a Panno, S.V. 
700 1 |a Anderson, T.F. 
773 0 |t Geological Society of America Bulletin  |d Boulder, CO : Geological Society of America (GSA), Jul. 2010  |x 0016-7606  |y BUGMAF  |n Geological Society of America Bulletin, 122(7-8), p.1047-1066. Publisher: Geological Society of America (GSA), Boulder, CO, United States. ISSN: 0016-7606  |g Vol. 122, no. 7-8  |h illus., incl. sects., geol. sketch map 
856 |u urn:doi: 10.1130/B26574.1