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site in Ambler, Pennsylvania where a pipe line leak had introduced an estimated 380,000 liters of high octane gasoline into the underlying aquifer ' Approximately two-thirds of the gasoline was recovered using conventional pump/treat systems, however,the time estimated for complete restoration using these systems was more than 100 years A nutrient amendment scheme was implemented at the site The nutnents added were oxygen, ammonium sulfate,disodium phosphate,and monosodium phosphate During the period of nutrient addition,the concentration of gasoline in the ground water did not decline, however,ten months later gasoline could not be detected in the ground water(Raymond et at, 1975) There are many methods of introducing oxygen into contaminated aquifers Brown et al (1985) used air sparging at a gasoline contamination site Wilson and Ward (1987) have suggested other methods, such as sod venting or air flooding The problem that one faces is that these methods can only provide ' dissolved oxygen concentrations of 8 to 12 mgA depending on the temperature of the ground water Hydrogen peroxide, pure oxygen and ozone have been proposed as more efficient methods of supplying oxygen into contaminated aquifers Concentrations of 40 to 50 mg/1 can be achieved with pure oxygen, but pure oxygen is somewhat expensive, may bubble out of solution before the microorganisms can use it,and ' is extremely flammable (Brown etal, 1984) Hydrogen peroxide is another possible source of oxygen, however, it is used as a stenlant at ' concentrations of 3 percent and levels as low as 200 ppm can be toxic to microorganisms (Thomas et at,1987) In a column study in which oxygen concentration was vaned from 8 to 200 ppm using air, pure oxygen, or a hydrogen peroxide solution,microbial growth and gasoline degradation were greater in columns amended with hydrogen peroxide which provided the highest concentration of available oxygen (Brown et al, 1984) A more thorough review of field studies using hydrogen peroxide can be found in Thomas et al (1987) Ozone can also be used as a source of oxygen, but very little research has been done on it 1 1 3 Biodegradation Modeling Modeling biodegradation and biorestoration processes involves 1)description of the kinetics of ' biotransformation in the subsurface,2)description of transport processes of the contaminant and available nutrients, and 3) an appropriate procedure for predicting the effect of biorestoration A few investigators have begun work on describing some of these processes ' Kosson et at (1985) use a simple one-dimensional finite difference solution to simulate the movement of hazardous industrial wastewater through an acclimated soil column The model adequatly matches experimental data from the later portion of the column where an acclimated microbial population has developed Angelakis and Rolston (1985) present a mathematical model for simulating the movement of insoluble and soluble organic carbon through the unsaturated sod profile The results of the simulation compare favourably with experimental data from a series of column tests performed using primary wastewater effluent Baehr and Corapcioglu (1985) present a one-dimensional model for simulating gasoline transport by air,water, and free hydrocarbon phases No experimental data are presented to test the model Molz et al (1986) present a numerical model for simulating substrate and oxygen transport and use ' by attached microorganisms The microbial population is assumed to be immobile and present in microcolonies of an average radius and thickness Transport into the microcolonies of oxygen and substrate is limited by diffusion through a stagnant layer adjacent to the microcolony Laboratory testing of ' the model is planned Borden and Bedient(1986) present a numerical model of oxygen-limited biodegradation of Hydrocarbons in the saturated zone Their model is discussed in detail in the following section as it provides the basis for the development of BIOPLUME II Borders et al (1986) have applied the model to simulate oxygen-limited biodegradation of creosote wastes at a Superfund site The model gave an ' 1-2