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� �.. _. _ �,.,.r ;s_ ,—q;� ,yam - -ass>t£ n •-�r.Va q, WATER S HAZARDOUS WASTE L4BORATOR`+ CERTIFIED by CALIFORNIA DEPT of HEALTH SERVICES CHANCES IN FUEL COMPOSITION UPON RELEASE TO THE ENVIRONMENT ' relative proportions of fuel components discharged tO the environment will b., changed due to volatilization, differential solubility in water, differences in biodegradation rates and relative affinities for soil components. Volatile components such as propones, butanes, pentanes and hexanes will have a stronger tendency to be lost from surface spills because they hove a higher vapor pressure than other full components. Lighter fuel components as shown in TABLE I have a greater solubility in water than do heavier components. Accordingly, these will be preferentially stripped away as rainwater moves through hydrocarbons spilled in the vadose zone an its way to become groundwater. Thus the vadose zone will be depleted in lighter fractions f-eiotivs to the original fuel while the groundwater will be enriched. Similarly, unsoturoted and cyclic components are more soluble than their straight chain and saturated i counterparts. For example, the 6olubility of butene is more than three times larger than that of butane while the solubility of batt hexene and cyclohexane are more than four times larger than that of hexune. Aromatics exhibit even larger increases in solubility relative to the corresponding aliphatics. For exomple, benzene is more than 100 times as soluble as hexor,e. Thus gasoline fractions remaining in the vodose zona lase their light ends and aromatics and begin to resemble diesel #2. Diesel A'2 fractions dissolving in groundwater become enriched in light ends and aromotics and therefore begin to resemble gasoline. In order to properly identify fuel types in the environment it is necessary to take these factors into account. The issue of changes in fuel composition upon release to the environment is further complicated by the differences in affinity which fuel components trove - 'ar soils. In general, organic-rich soils and finer soils will retard the -.....ovement of fuel components more strongly than organic-poor and coarser sails. Retardation of dissolved fuel components by fine soils is not to be confused with the tendency of free product to gother in coarse soil lenses which is a function of free volume rather than the tendency of the product to adhere to the soil. Since the nffinities of fuel components for soil and aoil organics are often the reverse of their so:ubilities, the selective differentiation of these components according to solubility is further accentuated by their relative retardation by the soils into vinich they have been released. Biodegradation rates are also strongly influenced .by molecular structure. In general, straight-chain saturated hydracarbons are degraded more readily than aromatics which, in turn, are degraded more readily than alicyclics and highly branched aliphatic hydrocarbons. Since much of Lhis biodegradation takes place In the vadose zone, contaminated soils are often enriched in alicyclics and hirjhly hronchEd aliphatic: relative to the hydroaarbon. product which was the ;ounce of the spill. Alkylaromatics such as toluene can be biochemically degraded either by attack on the ring to produce 3-methylcotechol or by succesoive oxidation of the side chain to produce benzyl alcohol, benzaldehyde, benzoic acid and then catechol. p-Xylene undergoes a similar steowise biodegradation to produce 4-methylbenzyl alcohol, 4-methyibenzaidehyde, p-toluic ocid and 4•methylcotechol. Aerobic biodegradation con often be enhanced when sampling exposes oxygen-poor groundwaters to the atmosphere. It is therefore very important to properly preserve groundwater samples containing hydrocarbons. Page CENTRAL COAST ANALYTICAL SERVICES Son Luis Obispo, California (805) 543-2553 E C. .-IMP18M.RN"M ONE