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Ri0/71-51-1C <br /> 7 3 1 "No Action" or Passive Remediation <br /> Passive remediation involves no action for soil or groundwater This type of remediation <br /> relies upon several natural processes to destroy the compounds of interest These <br /> natural processes include biodegradation , volatization, photolysis, leaching and <br /> adsorption These processes as well as the feasibility of this method, are described in <br /> detail in this section <br /> Passive remediation relies on various natural processes which can assist or possibly <br /> accomplish site remediation if allowed to proceed without external interferences These <br /> processes depend on a variety of site-and chemical-specific parameters which are <br /> described briefly below <br /> o Biodegradation Soil is the natural habitat for large numbers of <br /> microorganisms many of which can convert petroleum products to carbon <br /> dioxide and water In situ micorbial species that utilize the petroleum <br /> product as a carbon source will tend to thrive in the area of the <br /> underground spill and multiply preferentially, thereby enhancing <br /> biodegradation <br /> o Adsorption Hydrocarbons in the subsurface may adhere to sod particles <br /> and resist further downward migration This is particularly true when the <br /> hydrocarbons are of relatively high molecular weight and low water <br />' solubility Adsorbed hydrocarbons will remain bound until acted upon by <br /> other natural mechanism such as leaching by infiltrating water <br />' o Volatilization Certain hydrocarbons will migrate to the subsurface or <br /> surface and vaporize to the atmosphere This is particularly true of <br /> constituents with a lower molecular weight and a high Henry's Law <br />' Constant <br /> o Contaminant composition The chemical composition of the contaminant <br /> is the single greatest influence on the operating mechanisms for passive <br /> remediation In situ microbial species favor lower molecular weight <br /> components and will utilize them preferentially through biodegradation of <br />' larger molecular weight components will occur over time <br /> o Depth to groundwater A shallow groundwater table will be more vulnerable <br />' to impact regardless of the contaminant involved Groundwater tables at <br /> greater depths allow natural adsorption and biodegradation mechanisms to <br /> 25 <br />