Evidence of recent and post-glacial recharge in a thick, Late Wisconsin and Pre-Illinoian sequence in central Iowa
- PRC Environmental Management, Inc., Denver, CO (United States) Iowa State Univ., Ames, IA (United States)
- Iowa State Univ., Ames, IA (United States). Dept. of Geological and Atmospheric Sciences
Pre-Illinoian till, Wisconsin loess, and late Wisconsin till of the Des Moines Lobe overlie the bedrock aquifer in central Iowa. Determination of the velocity and age of groundwater in late Wisconsin and Pre-Illinoian units is necessary to determine if till units protect aquifers from contamination. Hydraulic gradients are downward with the average values of 0.01 and 1.26 in late Wisconsin and Pre-Illinoian till, respectively. Based on a Darcy's Law calculation, the vertical average of linear velocities of the groundwater are about 9 cm/yr and 0.3 cm/yr in late Wisconsin and Pre-Illinoian till, respectively. Ages of the groundwater should be less than 300 and about 13,600 years old in the base of late Wisconsin till and in Pre-Illinoian gravel layer, respectively. Environmental isotope data corroborate these velocity estimates H-3 data indicates that the water above 6 meters in late Wisconsin till is less than 20 years old. delta O-18 in groundwater in late Wisconsin till ranges from [minus]8.0 [per thousand] to [minus]6.5 [per thousand], which is within the range of modern meteoric water in Iowa, suggesting ground water was recharged under conditions similar to the modern climate condition in Iowa. Slightly more negative delta O-18 values in the groundwater in Pre-Illinoian till suggest that the groundwater there was recharged under a slightly cooler climate but not cold enough to correspond to the maximum glacial conditions of the late Wisconsin glaciation in Iowa. The mass balance method was used to correct the methane effect on C-14-DIC data in late Wisconsin till and loess, and C-14 ages were calculated using PHREEQE-CSOTOP model. The calculated ages were consistent with those obtained by other methods: groundwater in late Wisconsin till is less than 300 years old, and in Pre-Illinoian gravel layer is about 13,400 to 15,500 years old.
- OSTI ID:
- 5587320
- Report Number(s):
- CONF-921058--
- Journal Information:
- Geological Society of America, Abstracts with Programs; (United States), Journal Name: Geological Society of America, Abstracts with Programs; (United States) Vol. 24:7; ISSN GAAPBC; ISSN 0016-7592
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
540210 -- Environment
Terrestrial-- Basic Studies-- (1990-)
58 GEOSCIENCES
580000* -- Geosciences
AGE ESTIMATION
AQUIFERS
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
CARBON 14
CARBON ISOTOPES
DEVELOPED COUNTRIES
EVEN-EVEN NUCLEI
FLOW RATE
GROUND WATER
HYDRAULIC CONDUCTIVITY
HYDROGEN COMPOUNDS
HYDROGEN ISOTOPES
HYDROLOGY
IOWA
ISOTOPE RATIO
ISOTOPES
LIGHT NUCLEI
MATTER
NORTH AMERICA
NUCLEI
ODD-EVEN NUCLEI
ORGANIC MATTER
OXYGEN 18
OXYGEN COMPOUNDS
OXYGEN ISOTOPES
RADIOISOTOPES
RECHARGE
STABLE ISOTOPES
TRITIUM
USA
WATER
YEARS LIVING RADIOISOTOPES