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4 _ 7 <br /> 4VElSS <br /> ASSOCIATES <br /> Gordon Boggs / 14 June 1988 / Page 5 <br /> downgradient of the western end of the excavation, where the highest concentrations Of <br /> the boring logs included for <br /> hydrocarbons in soil have been detected. Since, as shown on <br /> your convenience as Attachment A, the existing wells are not screened into the <br /> unsaturated zone, an additional ground water monitoring well will be installed <br /> downgradient of the northern end of the excavation. This well, identified as proposed <br /> monitoring well MW-4 on Figure I of our correspondence dated 34 March 1988 and also <br /> � included here for your convenience, will be serecned in the upper few feet of saturated <br /> soil and into the unsaturated zone. <br /> 5) AI-TERNATIVE REMEDIATION OPTIONS <br /> Since high hydrocarbon concentrations in soil are apparently only in unsaturated <br /> soil immediately adjacent to the excavation, the following remediation options are <br /> feasible for the site: <br /> 1) Soil excavation and subsequent treatment of the excavated material. A variety <br /> of treatment options can be applied to reduce hydrocarbon concentrations in the <br /> removed soil. This is our preferred remedial option. Details of this <br /> recommended option are presented in Attachment B. <br /> 2) In-situ biodegradation of hydrocarbons by stimulation of naturally occurring <br /> microorganisms_ <br /> 3) In-situ volatilization by vacuum and forced air venting. <br /> 4) Passive remediation involving no action. <br /> A brief description and feasibility assessment of each of these options is presented below. <br /> l) Ex v gin Treatr_rtj <br /> This remedial option involves the excavation of hydrocarbon-impacted unsaturated <br /> soil and subsequent above-ground treatment of the soil to reduce hydrocarbon <br /> concentrations to acceptable levels. Feasible treatment options for the soil once it is <br /> removed include: - <br />