Gasoline remediation

Remediation of groundwater impacted by dense phase chlorinated solvents is more difficult than spills of chemicals such as gasoline or diesel fuel. Gasoline and diesel fuel are less dense than water and tend to float near the surface of the watertable. 

The demand for aviation gasoline during World War II was so great that isobutanc from alkylation feedstock was insufficient. This deficiency was remedied by isomerization of abundant normal butane into isobutane using the isomerization catalyst aluminum chloride on alumina promoted by hydrogen chloride gas. 

Gas control is required, because the vapor phase of gasoline components in an unsaturated zone can pose a significant health and safety threat. The gas control and safety concern are discussed in another chapter. Some of the remedial technologies presented in subsequent sections of this chapter can also act as gas control measures. 

The remedial technologies83-85,90-93 described in previous sections for gasoline release are applicable, for the most part, for remediation of DNAPLs. For example, the pumping or trench method for free products, vacuum extraction, biodegradation, pumping and treatment, soil flushing, and soil excavation and treatment are suitable for cleanup of various phases of DNAPLs. Again, because of... 

Wilson, J.T., Fate and transport of MTBE and other gasoline components, in MTBE Remediation Handbook, Moyer, E.E. and Kostecki, P.T., Eds, Amherst Scientific Publishers, Amherst, MA, 2003. 

Remediation commenced with the interception of the recoverable gasoline. One 4-in.-diameter vapor extraction well and three 2-in. vapor monitor wells were installed. Each well was constructed with 4 ft of well screen placed and filter packed across the unsaturated portion of the shale. The annulus of the wells was sealed to the surface with bentonite and cement grout according to local standards. The monitor wells were located in a triangular pattern around the vapor extraction well at distances of 5.3, 10.6, and 25.4 ft. 

The SVE case history discussed is included as a typical situation, similar to many projects encountered in the field that diverge from the ideal case. The site is located adjacent to a vehicle maintenance building in southern California. A 3000-gal and a 5000-gal UST were used to store unleaded gasoline, and a 550-gal UST was used to store petroleum-based paint thinner (Figure 10.15). To add to the situation, different phases of the project were completed by different consultants, and, due to administrative issues, almost 4 years passed between removal of the USTs and completion of the remediation activities. 

When all necessary nutrient supply systems are in balance and functioning properly, aerobic biological remediation can be relatively rapid. Gasoline components have been observed to have a half-life of days to months under well-controlled field conditions. Chemicals such as tetrachloroethylene that are best degraded under anaerobic conditions require significantly more time. Published half-lives for similar chlorinated solvents under field conditions are on the order of 300-day half-lives. Several computer programs are available that calculate the probable life expectancy of remedial projects. For best results, these programs require input of real field data. 

The site is a carwash facility located in the city of Escondido, in southern California. A sequence of investigative and remedial activities has been performed since 1987 that established the presence, nature, and extent of subsurface hydrocarbons derived from former USTs. Since conducting these activities, the former USTs have been removed and the hydrocarbon-affected soil surrounding the USTs has been excavated. Additionally, all potentially recoverable LNAPL (i.e., gasoline) has been removed, leaving only residual hydrocarbon saturation (i.e., smear zone) in place at the water table. Subsequent pump-and-treat activities have reduced dissolved BTEX concentrations to asymptotic levels (Figure 13.9). 

Groundwater samples taken from monitoring wells at gasoline stations undergoing remediation in Florida contained both kerosene and fuel oil at unspecified concentrations (Thomas and Delfino 1991a). 

At another site, the cost of remediation of gasoline- and fuel-oil-contaminated soil was estimated to be 100 to 120 per ton however, if the unit was used at more than one site, net treatment costs could be as low as 20 to 30 per ton (D12140U, p. 34). 

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