Geochemical modeling of the Madison aquifer in parts of Montana, Wyoming, and South Dakota

Journal Article · Sat Sep 01 04:00:00 EDT 1990 · Water Resources Research; (United States)

DOI:https://doi.org/10.1029/WR026i009p01981· OSTI ID:6263346

Plummer, L N; Hanshaw, B B ^[1]; Busby, J F ^[2]; Lee, R W ^[3]

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1. Geological Survey, Reston, VA (USA)
2. Geological Survey, Austin, TX (USA)
3. Geological Survey, Nashville, TN (USA)

Stable isotope data for dissolved carbonate, sulfate, and sulfide are combined with water composition data to construct geochemical reaciton models along eight flow paths in the Madison aquifer in parts of Wyoming, Montana, and South Dakota. All reaction models reproduce the observed chemical and carbon and sulfur isotopic composition of the final waters and are partially validated by predicting the observed carbon and sulfur isotopic compositions of colomite and anhydrite from the Madison Limestone. The geochemical reaction models indicate that the dominant groundwater reactionin the Madison aquifer is dedolomitization (calcite precipitation and dolomite dissolution driven by anhydrite dissolution). Sulfate reduction, (Ca{sup 2+} + Mg{sup 2+})/Na{sup +} cation exchange, and halite dissolution are locally important, particularly in central Montana. The groundwater system is treated as closed to CO{sub 2} gas from external sources such as the soil zone or cross-formational leakage but open to CO{sub 2} from oxidation of organic matter coupled with sulfate reduction and other redox processes occurring within the aquifer. The computed mineral mass transfers and modeled sulfur isotopic composition of Madison anhydrites are mapped throughout the study area. Carbon 14 groundwater ages, adjusted for the modeled carbon mass transfer, range from modern to about 23,000 years B.P. and indicate flow velocities of 7-87 ft/yr (2.1-26.5 m/yr). Most horizontal hydraulic conductivities calculated from Darcy's Law using the average {sup 14}C flow velocities are within a factor of 5 of those based on digital simulation. The calculated mineral mass transfer and adjusted {sup 14}C groundwater ages permit determination of apparent rates of reaction in the aquifer.

• OSTI ID: 6263346
• Journal Information: Water Resources Research; (United States), Journal Name: Water Resources Research; (United States) Vol. 26:9; ISSN 0043-1397; ISSN WRERA
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
540311 -- Environment
Aquatic-- Basic Studies-- Radiometric Techniques-- (1990-)
540320* -- Environment
Aquatic-- Chemicals Monitoring & Transport-- (1990-)
AQUIFERS
CARBON 14 COMPOUNDS
CARBON COMPOUNDS
CARBONATES
CHALCOGENIDES
CHEMICAL REACTIONS
CHEMISTRY
CONTAMINATION
DEVELOPED COUNTRIES
DISSOLUTION
ECOLOGICAL CONCENTRATION
FEDERAL REGION VIII
GEOCHEMISTRY
GROUND WATER
HYDRAULIC CONDUCTIVITY
HYDROGEN COMPOUNDS
ION EXCHANGE
ISOTOPE APPLICATIONS
ISOTOPE DILUTION
LABELLED COMPOUNDS
MASS TRANSFER
MATHEMATICAL MODELS
MONITORING
MONTANA
NORTH AMERICA
OXYGEN COMPOUNDS
POLLUTION
REDOX REACTIONS
SOUTH DAKOTA
SULFATES
SULFIDES
SULFUR COMPOUNDS
TRACER TECHNIQUES
USA
VELOCITY
WATER
WATER CHEMISTRY
WATER POLLUTION
WYOMING