Water Soluble Phase Oxygenates in Gasoline From Five New Jersey Service Stations

摘要

Mixing experiments were conducted using gasoline samples collected at five different central New Jersey gasoline service stations in February 2000 to identify water soluble phase oxygenates along with benzene, toluene, ethylbenzene, xylenes (BTEX), naphthalene and isopropylbenzene. Gasoline from one station was sampled twice over a two year period to compare changes in fuel composition. Tests were conducted in a 2000-ml separatory funnel at a water to fuel ratio of 4:1 using 87 and 89 octane gasoline. Mixing duration was 16 hours with 3 gentle stirring events. The oxygenates searched for in the water phase were MTBE, TBA, Ethanol, Methanol, DIPE, TAME, ETBE and TBF. Analysis was conducted by a NJDEP certified lab using EPA Method 8260B (GC/MS). Ethanol and methanol were analyzed using EPA Method 8015 (GC/FID). All of the gasoline samples showed TBA occurring in the water soluble phase at approximately 83% of the concentration of MTBE. MTBE concentrations averaged 1,638,000 ug/1 while TBA averaged 1,356,000 ug/1 (after 16 hours). All samples contained methanol ranging from 26,000 to 51,000 ug/1. One sample showed ethanol at 17,300 ug/1 and another sample contained TAME at 153,000 ug/1. DIPE, ETBE and TBF were not detected. Total BTEX concentrations in the water-soluble phase were about 0.75% of total oxygenate concentrations. For one of the mixing experiments, water samples were collected at 16, 48 and 96 hours to evaluate the effect of mixing time on concentration and time to reach equilibrium. BTX, MTBE and TBA concentrations more than doubled between 16 and 96 hours, however the relative concentration of total BTX remained constant at 0.87% of total oxygenate concentration at 16, 48 and 96 hours. The wide occurrence of TBA, at similar concentrations to MTBE, indicates that caution needs to be exercised in drawing any conclusions about potential biological decay under field conditions using TBA as an indicator. A comparison of the mixing experiments to previous mixing experiments of Kramer and Hayes (1987) and API (1991) is provided. Field data showing the behavior of MTBE and TBA in source area wells at gasoline retail outlets in New Jersey is provided. The mixing experiment explains the presence of TBA and MTBE at similar concentrations in groundwater at gasoline retail sites and confirms that TBA is present in gasoline and is a significant contributor to the total oxygenate content of the water-soluble phase. TAME and Methanol were detected in most samples, but at significantly lower concentrations than MTBE and TBA.