SULFUR ISOTOPE VALUES OF DISSOLVED SULFATE IN GROUNDWATER AS A TRACER FOR BATTERY ACID CONTAMINATION

The application of sulfur isotope values of sulfate in groundwater provided the information necessary to evaluate the source, transport and fate of battery acid and associated contaminants at a contaminated site. The chemical and isotopic composition of groundwater beneath the site, a battery recycling facility in central Florida, varied more than expected for an area of comparable size. Sulfate (SO42-) values, for example, range from 1.2 to 11,500 mg/L and oxygen and hydrogen isotopes did not attenuate towards the weighted annual mean. Those samples that are high in sulfate generally had a low pH, which indicated battery acid (H2SO4) contamination as a potential source for the sulfate. The low pH and high reactivity of the sulfuric acid groundwater caused the formation of hydrogeological microenvironments due to preferential dissolution of carbonate minerals, which in turn caused enhanced recharge and groundwater flow in certain areas; thus, the extreme scatter in the data set. Because of the difficult hydrogeology it was not straightforward to delineate the point-sources of contamination and up to five potential scenarios were evaluated using a combination of sulfur, oxygen, and hydrogen isotopes in association with chemical tracers: (1) seawater intrusion, (2) upwelling of high-sulfate groundwater, (3) local dissolution of gypsum, (4) an up-gradient contaminant source to the northeast of the contaminated site and (5) battery acid contamination.