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percent) which range from C4 to C, Gasoline fuels contained a higher quantity of cyclic and branched alkanes due to their higher octane ratings The common constituents of aromatics include CO to C4 benzenes, and Co to C2 naphthalenes Aromatics are highly water soluble compared to other gasoline constituents Gasoline has a specific gravity of 0 75, an absolute viscosity of 0 45, an aqueous solubility of 156 mg/L, a saturated vapor concentration of 411 mg/L, and a distillation temperature range from 150- to 440-degrees F Nhddle Boiling Point Range Hydrocarbons Fuel oils are generally classified as middle distillate petroleum hydrocarbons While there is some variation is the composition of fuel oils, we will discuss their properties in general due to similarities in this range of products The most common constituents of fuel oils are linear alkanes (48- to 85- percent) which range from Cio to C24, and aromatics (16- to 38-percent) The n-alkanes are the major compound of fuel oils and are preferred due to their high BTU content The common constituents of aromatics include C3 to C5 benzenes, Co to Cs naphthalenes Co to Cs anthracenes, C„ to C-, phenanthrenes, Co to C2 tetralins, Co to C, biphenyls, and Co to C4 carbazoles Aromatics are generally undesirable constituents in fuel oils since they reduce the BTU rating and increase smoke No 2 Diesel has a specific gravity of 0 8 to 0 85, an absolute viscosity of 1 1- to 6 9-cP, and a distillation temperature range from approximately 200- to 640-degrees F Factors Controlling Petroleum Distribution The mayor factors to be considered in evaluating the subsurface distribution and transport of petroleum hydrocarbons include chemical partitioning characteristics with the parent fuel, soil mineral matter, organic matter, soil air, and soil water There are several approaches for estimating the concentrations of selected compounds in one phase when contacted with a known concentration in another phase, • under equilibrium conditions For the purposes of this CAP, RTD will use leaching factors calculated by EA Engineering, Science, and Technology in Total Petroleum H drocarbon Criteria Workin Group Project #3 Selection of Surrogate Fractions Based on Fate and Transport Considerations June 1995 Since only TPHd, and not TPHg or BTEX, has been detected in groundwater since impacted soils were removed, we will focus on the transport of diesel only For middle distillates such as diesel fuel, the most common constituents are the n-alkanes The calculated leaching factor for C 10 to C20 n-alkanes ranges from 0 00001- to 0 00000001-milligrams per liter per milligrams per kilograms (mg/L/mg/Kg) As a worst case, assuming a small pocket of remaining diesel impacts of 5,000-mg/Kg would leach out less than 0 05-mg/L of diesel dissolved in groundwater Given that the recent detections of diesel were associated with adsorption onto suspended solids and not dissolved in groundwater, it appears that the leachability factors are reasonable Since No 2 diesel is a complex mixture of more than 1,000 constituents, it is impractical to quantify each constituent The use of indicator compounds to evaluate potential exposure to complex petroleum mixtures (such as diesel fuels, gasoline, kerosene, het fuels, etc ) is recognized as a more practical approach Indicator compounds should represent those agents that are the greatest potential public health risks associated with the particular site The selected indicators should be the most toxic, in the highest concentration, the most mobile, and the most persistent (with regard to degradation properties) in the environment resulting in human exposure The toxicity, mobility, and persistence of individual compounds in diesel fuel oil may be different from these properties for those compounds acting alone The constituents making up the minor fraction of diesel fuel oil likely are responsible for the majority of the potential toxic effects of the petroleum mixture Two factors contribute to this potential 1) the minor constituents may be transported in subsurface soils and groundwater more rapidly than the major constituents, and, 2) the minor constituents may be more toxic than the mayor constituents The • United States Environmental Protection Agency (EPA) has selected benzene, toluene and total xylenes as indicator compounds due to their relatively high toxicity and water solubility Benzo(a)pyrene may - 4 -