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UPDATE 30 11-11-94 <br /> from clay silts to sand will also interrupt the lateral <br /> movement of liquid product <br /> A portion of the product will also be bonded by surface <br /> tension to the soil grains or absorption onto soil carbon <br /> and will not move laterally or vertically. These residue <br /> hydrocarbons can only be transported in the dissolved or <br /> vapor phase <br /> We believe that that the hydrocarbons remaining at the site <br /> are these residue hydrocarbons <br /> 2 Dissolved Hydrocarbons, Leachate <br /> In the dissolved phase, the hydrocarbons are dissolved in <br /> water and move in the water The movement of the ground <br /> water in soil is similar to that of the liquid product <br /> described above The amount of hydrocarbon transported by <br /> the ground water is dependent on the solubility of the <br /> product and the amount of product present in the liquid and <br /> vapor phases The low solubility of hydrocarbons remaining <br /> in the soil at this site, and the low rainfall 1 1 feet per <br /> year decrease the importance of this mode of transport for <br /> the residue hydrocarbons at this site <br /> 3 Vapor Phase <br /> As shown in the Vleach model the dominant transport <br /> mechanism at this site is vapor diffusion. The dominant <br /> forces in this phase are vapor pressure and diffusion rate . <br /> The diffusion rate in soil is governed by the amount of non <br /> saturated porosity available and how torturous the movement <br /> paths are Normally the nonsaturated porosity is less and <br /> the movement paths are more torturous in fine grained <br /> sediments, slowing vapor movement in these sediments <br /> As briefly discussed above , site specific lithologic barriers and <br /> attenuation mechanisms affecting the migration of gasoline range <br /> hydrocarbons include formation (s) lithology type, depositional <br /> environment, effective porosity, moisture content, organic carbon <br /> content , bedding planes, facies changes and vertical conduits <br /> (natural ie , fractures, faults, solution cavities, lava tubes, <br /> etc or man made, i e wells, excavations, tunnels, utility <br /> trenches etc ) <br /> Other factors effecting natural attenuation of gasoline range <br /> hydrocarbons include biodegradation, adsorbtion and <br /> volatilization <br /> The following is a discussion of the above mentioned lithologic <br /> barriers and attenuation effects for the migration of gasoline <br /> range hydrocarbons <br /> Former Regal Station 604 does not contain any vertical conduit, <br /> page8 <br />