Development of a lithogeochemical map for prediction of water-quality patterns in Maryland and eastern Virginia

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Authors:Peper, John D.; McCartan, Lucy; Horton, J. Wright, Jr.; Bachman, L. Joseph; Brakebill, John W.; Bohlke, John Karl; Bricker, Owen P.
Author Affiliations:Primary:
U. S. Geological Survey, Reston, VA, United States
Volume Title:Geological Society of America, 1997 annual meeting
Source:Abstracts with Programs - Geological Society of America, 29(6), p.306-307; Geological Society of America, 1997 annual meeting, Salt Lake City, UT, Oct. 20-23, 1997. Publisher: Geological Society of America (GSA), Boulder, CO, United States. ISSN: 0016-7592
Publication Date:1997
Note:In English
Summary:A preliminary lithogeochemical map of Maryland and eastern Virginia has been produced to test the hypothesis that geologic controls on aquifer reactivity can be used effectively to predict the transport and discharge of reactive contaminants and where certain reactions are likely to occur. The map was produced digitally by classifying geologic units on the basis of specific mineralogical-chemical characteristics. Spatial correlations between lithogeochemical units and water-quality data are being evaluated to test and refine the lithogeochemical classification scheme. Some general correlations include: limestones and other calcareous rocks yield alkaline water; peat and carbonaceous or sulfidic shales and schists commonly yield reduced oxygen-poor water; and quartzose rocks and sediments have relatively little capacity to alter acidity or redox states of water. Specific lithogeochemical features can be related to ground-water chemistry locally in areas that have been studied in detail. For example, in Frederick Co., Md., limestones in the Frederick Valley have the highest acid-neutralizing capacity, followed by Catoctin metabasalt; intervening phyllite and quartzite are essentially non-reactive with acidic precipitation. At Coastal Plain sites in southern Virginia, fine-grained, organic-rich sediments cause oxygen and nitrate reduction soon after infiltration beneath agricultural land. At other sites in the Maryland Coastal Plain, unweathered glauconitic greensands reduce oxygen and agricultural nitrate that pass unaltered through overlying weathered (oxidized) greensand and quartz sand and gravel. The lithogeochemical units also have been compared to the distribution of surface-water base-flow nitrate yields, and to historical monitoring data on dissolved oxygen, nitrate, and iron in shallow wells. Results of these preliminary investigations indicate that lithogeochemical maps may be useful for regional extrapolation of local information about transport properties of reactive contaminants such as acid rain and agricultural nitrate in the Chesapeake Bay watershed.
Subjects:Acid rain; Agriculture; Aquifers; Atmospheric precipitation; Catoctin Formation; Classification; Controls; Discharge; Eh; Ground water; Hydrology; Infiltration; Monitoring; Nitrate ion; Nitrates; Patterns; Pollution; Precambrian; Prediction; Properties; Rain; Reactivity; Solutes; Transport; Water quality; Watersheds; Atlantic Coastal Plain; Chesapeake Bay; Frederick County Maryland; Maryland; United States; Virginia; Eastern Virginia; Frederick Valley
Record ID:1999003275
Copyright Information:GeoRef, Copyright 2018 American Geosciences Institute. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
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