Gasoline Spill Site Research Articles

In Situ Decontamination of Soil

Abstract Methods for decontamination of soil in situ are receiving increased attention, as the requirement to clean these sites has become a national concern. The continual and costly liability is an important corporate incentive to clean contaminated soils. The development of an effective technology for in situ decontamination is a priority issue. Some in situ decontamination processes are similar to enhanced oil recovery schemes and use an integrated heating approach. One such method consists of heating by conduction and convection in conjunction with electrical heating. Advantages of electrical heating are that the energy can be focussed and the soil heated uniformly. The integrated heating approach has been extensively tested in the United States in a joint venture between Lawrence Livermore National Laboratories (LLNL) and the University of California at Berkeley. The most significant test was done at an abandoned Naval Air Base, now named the LLNL Gasoline Spill Site. It has been demonstrated that such an integrated approach can remove hydrocarbon contaminates from in situ at an accelerated rate. The objective of this paper is to present a mathematical model that solves the heat transfer problem for the integrated heating process. The model is also used to investigate the practicality of the process in terms of energy requirements and the time it takes to clean the soil. The mathematical model combines all of the principal heat transfer mechanisms of the process. These are electrical heating, convection, conduction and accumulation of energy. In addition, conductive heat losses from the sides and bottom of the heated volume and the substantial variation of electrical resistivity with temperature are included. Calculations made using the mathematical model developed in this paper are in good agreement with results obtained with the general-purpose reservoir simulator, TETRAD. Introduction Increasing the temperature of a contaminated soil helps in the removal of the hydrocarbons. The introduction of heat increases the solubility of the hydrocarbon with the water phase, increases equilibrium concentrations in the vapour phase and causes easier desorption from the clay mineral. These factors can accelerate the clean up process several times(1). Some proposed methods consider an integrated heating approach, consisting of heating by conduction and convection at the same time as heating electrically(2, 3). This approach has been successfully tested in the United States by Lawrence Livermore National Laboratories (LLNL) at the LLNL Gasoline Spill Site(2, 4). At this site, hydrocarbons have accumulated in situ and are in communication with the ground water system. Vertical injection/production wells completed with electrodes are strategically located to heat the soil. The heating of the soil is primarily by steam injection. The electrical heating is supplemental and is used to heat regions where the steam will not flow. The estimated cost to clean the contaminated soil(2), which has an area of about 2,000 m2 and is 15 m thick is of the order of $(CDN) 50/m3. The electrical heating component of the above process is limited because of the use of vertical electrodes spaced far apart. The current density at the electrode surface is large and decreases rapidly with distance.

Estimation of Rates of Aerobic Hydrocarbon Biodegradation by Simulation of Gas Transport in the Unsaturated Zone

The distribution of oxygen and carbon dioxide gases in the unsaturated zone provides a geochemical signature of aerobic hydrocarbon degradation at petroleum product spill sites. The fluxes of these gases are proportional to the rate of aerobic biodegradation and are quantified by calibrating a mathematical transport model to the oxygen and carbon dioxide gas concentration data. Reaction stoichiometry is assumed to convert the gas fluxes to a corresponding rate of hydrocarbon degradation. The method is applied at a gasoline spill site in Galloway Township, New Jersey, to determine the rate of aerobic degradation of hydrocarbons associated with passive and bioventing remediation field experiments. At the site, microbial degradation of hydrocarbons near the water table limits the migration of hydrocarbon solutes in groundwater and prevents hydrocarbon volatilization into the unsaturated zone. In the passive remediation experiment a site‐wide degradation rate estimate of 34,400 g yr−1 (11.7 gal. yr−1) of hydrocarbon was obtained by model calibration to carbon dioxide gas concentration data collected in December 1989. In the bioventing experiment, degradation rate estimates of 46.0 and 47.9 g m−2 yr−1(1.45 × 10−3 and 1.51 × 10−3 gal. ft.−2yr−1) of hydrocarbon were obtained by model calibration to oxygen and carbon dioxide gas concentration data, respectively. Method application was successful in quantifying the significance of a naturally occurring process that can effectively contribute to plume stabilization.

Use of a Reactive Gas Transport Model to Determine Rates of Hydrocarbon Biodegradation in Unsaturated Porous Media

A mathematical model is presented that simulates the transport and reaction of any number of gaseous phase constituents (e.g. CO2, O2, N2, and hydrocarbons) in unsaturated porous media. The model was developed as part of a method to determine rates of hydrocarbon biodegradation associated with natural cleansing at petroleum product spill sites. The one‐dimensional model can be applied to analyze data from column experiments or from field sites where gas transport in the unsaturated zone is approximately vertical. A coupled, non‐Fickian constitutive relation between fluxes and concentration gradients, together with the capability of incorporating heterogeneity with respect to model parameters, results in model applicability over a wide range of experimental and field conditions. When applied in a calibration mode, the model allows for the determination of constituent production/consumption rates as a function of the spatial coordinate. Alternatively, the model can be applied in a predictive mode to obtain the distribution of constituent concentrations and fluxes on the basis of assumed values of model parameters and a biodegradation hypothesis. Data requirements for the model are illustrated by analyzing data from a column experiment designed to determine the aerobic degradation rate of toluene in sediments collected from a gasoline spill site in Galloway Township, New Jersey.

Ground penetrating radar for the detection of liquid contaminants

The significance of ground penetrating radar (GPR) as a tool to detect near-surface contaminants is illustrated at a site in the Midwest representing petroleum product above the water table. Tests show that ground penetrating radar may provide a means of mapping hydrocarbons in the vadose zone. Results of controlled surveys in a sand test pit at The Ohio State University demonstrate conclusively that there is a clear GPR anomaly over containers of diesel fuel and containers containing the host sand material saturated with diesel fuel. Comparisons of GPR data measured at different times of the year (summer, fall, and winter) at a gasoline spill site in northern Indiana shows direct information on layers and lenses in the vadose zone that tend to accumulate water during times of high moisture and subsequently lose the moisture during dry periods. GPR data collected in the winter over partially frozen ground provided measurements that were more sensitive to the presence of the gasoline than measurements that were made during the summer and fall. The relative propagation transparency of the near-surface zone for GPR measurements from winter data over fozen ground allowed detection of the water table that could not be confidently identified from two of the other data sets. Four important points can be concluded from a comparison of the four data sets: (1) the quality and repeatability of GPR measurements over a clean sand depends on the amount of moisture located in the unsaturated zone above the water table; (2) reflections from sedimentary features can be distinguished from reflections from percolating groundwater; (3) GPR measurements made during the dry month of August are nearly devoid of reflections above the gasoline product, indicating that the water in the unsaturated region may have been displaced by liquid gasoline, or by gasoline vapors; and (4) most importantly, these tests illustrate the resolving power and sensitivity of ground penetrating radar.

LNAPL Retention in Sandy Soil

AbstractThe vertical distribution of free and residual aviation gasoline, a light nonaqueous phase liquid (LNAPL), through the capillary fringe of a uniform, medium sand is measured and used to calibrate an existing model. The total saturation profile is governed by a classical moisture retention characteristic, with the matric pressure head scaled by LNAPL/air surface tension in the presence of free LNAPL and water/air surface tension in the absence of free LNAPL. The residual LNAPL is described by an empirical equation reflecting hysteretical trapping due to a fluctuating water table. The existing theory is calibrated with new and published field data at an aviation gasoline spill site in Traverse City, Michigan.

Removing gasoline from soil and groundwater through air sparging

AbstractAlthough a soil vapor extraction system (SVES) had effectively remediated the vadose zone soils at a gasoline spill site in Pawtucket, Rhode Island, gasoline remained in the soils below the water table. The state Department of Environmental Management (DEM) closure criteria of 10,000 parts per billion (ppb) were still not met after five years. This article describes how an air sparging system was added to the effort for $57,000, and how after three weeks, closure criteria were achieved.

Bioventing to treat fuel spills from underground storage tanks

Bioventilation is a procedure to cleanse soil gas of volatile fuel hydrocarbons originating from storage tank leaks. The rate of vapor degradation is a controlling parameter in the design of a bioventing system. A laboratory microcosm procedure using sandy soil from an aviation gasoline spill site was used to measure relative kinetics of some fuel vapors.

Impact of Recharge Through Residual Oil Upon Sampling of Underlying Ground Water

AbstractAt an aviation gasoline spill site in Traverse City, Michigan, historical records indicate a positive correlation between significant rainfall events and increased concentrations of slightly soluble organic compounds in the monitoring wells of the site. To investigate the recharge effect on ground water quality due to infiltrating, water percolating past residual oil and into the saturated zone, an in situ infiltration experiment was performed at the site. Sampling cones were set at various depths below a circular test area, 13 feet (4 meters) in diameter. Rainfall was simulated by sprinkling the test area at a rate sufficiently low to prevent runoff. The sampling cones for soil‐gas and ground water quality were installed in the unsaturated and saturated zones to observe the effects of the recharge process. At the time of the test, the water table was below the residual oil layer. The responses of the soil‐gas and ground water quality were monitored during the recharge and drainage periods, which resulted from the sprinkling.Infiltrated water was determined to have transported organic constituents of the residual oil, specifically benzene, toluene, ethylbenzene, and ortho‐xylene (BTEX), into the ground water beneath the water table, elevating the aqueous concentrations of these constituents in the saturated zone. Soil‐gas concentrations of the organic compounds in the unsaturated zone increased with depth and time after the commencement of infiltration. Reaeration of the unconfined aquifer via the infiltrated water was observed. It is concluded that water quality measurements are directly coupled to recharge events for the sandy type of aquifer with an overlying oil phase, which was studied in this work. Ground water sampling strategies and data analysis need to reflect the effect of recharge from precipitation on shallow, unconfined aquifers where an oil phase may be present.

Biotransformation of monoaromatic and chlorinated hydrocarbons at an aviation gasoline spill site

Abstract A shallow water table aquifer under the U.S. Coast Guard Air Station at Traverse City, MI, has acclimated to the aerobic and anaerobic transformation of monoaromatic hydrocarbons (BTX) released from an aviation gasoline spill. The aquifer also exhibits reductive dechlorination of a chlorinated solvent spill adjacent to the aviation gasoline spill. The groundwater is buffered near neutrality. The aviation gasoline plume is methanogenic and the aquifer contains enough iron minerals to support significant iron solubilization. Field evidence of both aerobic and anaerobic biotransformation of monoaromatics was confirmed by laboratory studies of aquifer material obtained from the site. In the laboratory studies, the removal of the monoaromatics in the anaerobic material was rapid and compared favorably with removal in aerobic material. The kinetics of anaerobic removal of monoaromatics in the laboratory were similar to the kinetics at field scale in the aquifer. Biotransformation of the chlorinated solvents was not observed until late in the study, when daughter products from reductive dechlorination of the chlorinated solvents were identified by GC/MS.