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This time is referred to as the 'adaptallon period' and Is generally represented by a 'lag' or inactive period As the process of synthesizing inducible enzymes Is academically demanding for the microbes, adaptation Is most likely to occur under conditions where the cOmaminwg Is the only source of carbon. Under conditions where other sources of carbon (such as carbohydrate) are present, organisms will preferentially utilize the food source which requires the least amount of energy. In this case, the carbohydrate may be degraded preferentially, since inducible enzymes may not be required of Its catabolism (i.e. constitutive enzymes are used, requiring less energy to synthesize). The chemical and physical enNronmaC can Influence tiro rat t which a population mows. Temperature, pH, and the concentration of nutrients, oxygen, heavy metals, and water can all dramatically affect give growth and blodegradativn capabilities of microbial populations. To illustrate, microorganisms have asserted enzymes and cell membranes that function best at the temperatures they normally encounter. For some bacterial species this specific temperature may be as high as 45 damage Celsius or as low es 10 damage Celsius. The temperature at which populion retlucetlgro s at Its maximum men Is called the optimum growth temperature. Spec y en the temperature is above Or below the Coleman, thus resulting in a decrease in the population (and M1mdegradagve capabilities) of the organisms. The responses 10 Oxygen among bacteria are remarkably variable as well and me Important fa ors In the blodelum allon OrOrganic compounds, with respect to Catabolic rates and generated r product(s). For example, IM1e catalytic breakdownoe Of hydrocarbons by axnzyme In the presence of oxygen (aeoblc) results In the wirmate production w Carbon dioxide and water. Under anaerobic conditions (no oxygen), however, memane is the major terminal end product. It is necessary, then, to determine the types of breakdown products that may be generated es a result Of Iha respiratory anchor metabolic requirements of tire biodegrading Organisms. These factors vary from site to site and subsequently the degradation which occurs biologically will vary from site to site. Another factor responsible far the 'weathedng, or 'aging' of gasoline Is vapor delusion. This is Me mechanism by which the more volallve fractions OI gasoline escape through the available pore spaces within soils to the atmosphere. This process is depends"[ upon atmospheric conditions (i.e. temperature, humidity, etc.), sell permeability, soil porosity, absorption soil particle _ padicular compound solubility and the compound specific vapor pressure ulldin po tit. The more volafive constituents of gasoline; benzene, toluene, (M holders, (N) hexane antl IF) pentane are the Initial compounds to diffuse Or loc atllize to the atmosphere. The whet primary [attar affecting gasoline in the environment Is soil IeacMng/llushing. This process Involves the particular soluble compound(s) within gasoline being Rushed or reached from the soils wateras which is Introduced at The site's source (either naturally or argicially) migrates downward through the affected soils. While most constituents of gasoline are nor extremely soluble. parlone of the available benzene, alhylumbeg a, toluene and xylem are soluble. These factors cited gasoline compounds within soils to varying degrees and vary from site to site. However, these factors affect the gasoline In such a uniform degree that standardizes tables listing the roeeposiled of new versus weathered gasoline are utilities throughout the engineering field. This point Is emphasized in the enclosed MBy�June 1990 article enlhled 'Ouardiaive Analysis For The Cleanup Of Hydrocarbon-Contaminated Soils By In SiteSoil Venting' by P.C. JOhndon, M.W. KKemblowseo J.kl andJ.D. Colthad. Contained in this origin are tables which list the Composition w re gasoline line ble 1 d the composition of what IM1e article offers to as weathered gasoline (Table 3). These tables contain the specific components and their associates mass and mole fractions. Labwaorles, by comparing this freshening of the Individual components w gasoline can Calamine whether or net the gasoline is weathered.