Since May 1968, an industrial organic waste has been injected at rates of 100-200 gal/minute into Upper Cretaceous sand and gravel aquifers near Wilmington, North Carolina. The industrial waste, an aqueous solution of acetic acid, formic acid, and various isomers of phthalic acids and their methyl esters, has been injected through 2 wells into 2 aquifers containing saline water, at depths of 850-1,000 ft (260-305 m) below land surface. The movement and transformations of the waste have been monitored in this study since February 1971, by a network of 14 observation wells which surround the injection wells at varied distances and depths.

Samples obtained from 4 observation wells which penetrate the disposal aquifers near the injection well indicate very little degradation of the waste near the point of injection. The composition of recently injected waste was essentially identical to the waste before injection

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except for increased concentrations of silica, aluminum, and certain trace elements indicating slow dissolution of alumino-silicate minerals by the organic acids in the waste. Native aquifer water was mostly displaced by the injected waste, and carbonate minerals within the Upper Cretaceous sands and gravels were dissolved and decomposed by the organic acid waste constituents.

Since June 1972, trace quantities of waste were detected in an observation well 1,500 ft (457 m) north of the original injection wells, and a weekly sampling program was instituted to monitor the geochemical transformations during passage of the waste front. After the appearance of methane gas, the dissolved organic carbon concentration of the waste varied inversely with methane gas evolution, indicating reductive conversion of the waste to methane. Increased concentrations of ferrous iron, hydrogen sulfide gas, and sulfide precipitates were additional indicators of geochemical and microbiologic reductive processes.

The waste front was found to be broad and diffuse to the extent that the waste would disappear during certain periods of sampling. Measurements made up to February 1973 indicated that the waste concentration was not sufficiently high to affect pH, alkalinity, specific conductance, and most of the standard inorganic water-quality parameters.

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