COMPARING STABLE ISOTOPE RATIOS IN CONTAMINATED WATER TO A POTENTIAL SOURCE

In Northwestern Arkansas, residents of Benton County have reported incidents of oily residue and gasoline odor in domestic water wells since 2006. Little is known about the source of the residue and odor in the wells, the Arkansas Department for Environmental Quality (ADEQ) has stated that it is naturally occurring. The purpose of this study is to compare the stable isotope ratios of carbon and oxygen in the affected water wells to samples taken from monitoring wells at a petroleum spill site. The contaminated water wells and the monitoring wells are both in the Boone Formation, a highly karstified Mississippian limestone with interbedded chert in the larger Springfield Plateau aquifer. The δ18O values of all samples from both sites are consistent with recharge values for Northwest Arkansas and are not indicative of microbial degradation of hydrocarbon. The δ13C of the non-aqueous layer in the contaminated water wells was determined to be consistent with the carbon isotope signature of crude oil.