The migration of hydrocarbon constituents from a containment tank.

摘要

On February 27, 1996 a single bare steel 4,000 gallon gasoline underground storage tank (UST) was removed from the New Jersey Department of Transportation (NJDOT) Maintenance Facility at Hackettstown, Morris County, New Jersey. This UST was used for the storage of unleaded gasoline. Since there is no record on the date of the installation of this tank, and based eyewitness account, there is a suspicion that this tank also stored leaded gasoline. This tank did not have cathodic protection nor any other protection for spills and overfills. At the time of the removal of the tank, holes were observed in its walls. Following New Jersey Department of Environmental Protection (NJDEP) directives a series of monitoring wells were installed to accurately determine the extent of contamination. The creosote used on light poles was also taken into account as a source of potential hydrocarbon source.; Monitoring wells in the immediate area of the former UST had considerable amounts of pure product (gasoline and petroleum components). Further studies determined that the extent of the free fuel plume may have reached 1,400 feet downgradient west from the source. However, there was a significant discrepancy between the data provided by the model and the data collected from monitoring wells. Contaminants were found only at approximately 800 feet from the source. The contaminants studied were benzene, chloromethane, toluene and methyl tertiary butyl ether (MTBE). A tri-dimensional computer model was used for these studies (MODFLOW). This program takes into account such factors as the permeability, gradient, total porosity, effective porosity, fractures and all the characteristics of the soil, dispersivity, half life of the contaminants, decay and retardation parameters of the contaminants, velocity and dispersion of the groundwater, precipitation, seepage and surface runoff. In addition, capillary action and biodegradation were also taken into account.; The site is located within two geological physiographic units: the Piedmont and the Highlands. The UST was located in a recharge zone approximately at 710 feet above mean sea level. The movement of groundwater in the vicinity of the UST is more vertically/downward than lateral. The soil is a mixture of weathered gneiss and glacial till. Bedrock was found in the range of 6.5 to 35 feet below the surface. The bedrock showed fractures spacing from approximately 0.25 to 6 inches.; Groundwater was sampled according to the New Jersey Department of Environmental Protection (NJDEP) directives. The samples were analyzed using trap Gass Chromatography/Mass Spectrometry (GC/MS).; MTBE is the only contaminant presented in this thesis that has been detected downgradient of the groundwater treatment system. However, its low concentration (a maximum of 0.67 ppm is indicative of no health hazard at the study site).