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Crude oil in a shallow sand and gravel aquifer-I. Hydrogeology and inorganic geochemistry

Applied Geochemistry

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, , ,

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Abstract

Changes in the distribution of inorganic solutes in a shallow ground water contaminated by crude oil document a series of geochemical reactions initiated by biodegradation of the oil. Upgradient of an oil body floating on the water table, oxidation of oil to carbonic acid dissolves carbonate minerals in the aquifer matrix. In this oxidized zone pH is depressed ???1 pH unit, and the concentrations of Ca, Mg and HCO3- increase to more than twice that of the native ground water. In the anoxic zone beneath the oil body concentrations of dissolved SiO2, Sr, K, Fe and Mn increase significantly. Here, Fe is mobilized by microbial reduction, pH is buffered by the carbonate system, and silicates weather via hydrolysis and organic-acid-enhanced dissolution. Farther down-gradient the ground water is reoxygenated and Fe precipitates from solution, possibly as iron hydroxide or iron carbonates, while SiO2 precipitates as amorphous silica. Other solutes, such as Mg, are transported more conservatively down-gradient where contaminated and native ground water mix. The observed changes in inorganic aqueous chemistry document changes in water-mineral interactions caused by the presence of an organic contaminant. These organic-initiated interactions are likely present in many contaminated aquifers and may be analogous to interactions occurring in other organic-rich natural waters. ?? 1993.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Crude oil in a shallow sand and gravel aquifer-I. Hydrogeology and inorganic geochemistry
Series title:
Applied Geochemistry
Volume
8
Issue:
6
Year Published:
1993
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Applied Geochemistry
First page:
529
Last page:
549
Number of Pages:
21