MTBE and aromatic hydrocarbons in North Carolina stormwater runoff

A total of 249 stormwater samples were collected from 46 different sampling locations in North Carolina over an approximate 1-year period and analyzed to identify land use types where fuel oxygenates and aromatic hydrocarbons may be present in higher concentrations and at greater frequency. Samples were analyzed by gas chromatography–mass spectrometry in ion selective mode to achieve a quantitation limit of 0.05 μg/l. m-,p-Xylene and toluene were detected in over half of all samples analyzed, followed by MTBE; o-xylene; 1,3,5-trimethylbenzene; ethylbenzene; and 1,2,4-trimethylbenzene. Benzene, DIPE, TAME and 1,2,3-trimethylbenzene were detected in <10% of the samples analyzed. Median contaminant concentrations (when detected) varied from 0.07 μg/l for ethylbenzene to 0.11 μg/l for toluene. All of the locations with significantly higher contaminant concentrations were associated with direct runoff from a gas station or discharge of contaminated groundwater from a former leaking underground storage tank. For all of the aromatic hydrocarbons, the maximum observed contaminant concentrations were over an order of magnitude lower than current drinking water standards.