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' Excavation of the source supplemented by Soil Vapor Extraction: <br /> As identified in the guidelines for soil vapor Extraction, USEPA Soil Vapor <br /> Extraction Effectiveness is limited by clayey sods with high organic content as ,Ap. <br /> exists at this site Boring logs identify a oxlmately pre ominant tight grained --� <br /> fines with clays and silts predominanoi-Rio-n-ilbe limited vadose zone at this site <br /> Groundwater at approximately --10' b rade surface would be mounded and <br />' possibly interfere with soil vapor extraction systems at cubic foot per minute <br /> capacity necessary to create an achievable zone of influence in the relatively <br /> impermeable sots column to -10' bgs <br />' if the variation of the Freundlich parameters with contact time is known, the <br /> retardation factor can be estimated from,x <br /> IAI <br /> A 4 YV 1I Lel <br />' We note that the retardation factor calculated in Etc ._[7] is concentration and time <br /> dependent <br />' Apparent adsorption-desorption nonsingulanty has been observed frequently and <br /> several suggestions to parameterize this from experimental observations have <br /> been made (Ma et al , 1993, Huang and Weber, 1998b;Yuan and Xing, 2001) In <br /> this study, the apparent nonsingulanty was characterized by the expression of <br />' nonsingulanty suggested by Ma et al (1993) for desorption isotherms measured by <br /> the successive dilution technique, <br /> � Y 1 t(it) <br />' The value of the dimensionless Henry's law constant for MTBE is 0 022 at 25 <br /> degrees Celsius (°C) (Robbins and others, 1993), a compound with a value of 0 05 <br /> or larger would be very volatile from water Consequently, MTBE tends to stay in <br />' the water phase, which explains why MTBE is somewhat difficult to remove from <br /> water by aeration In contrast, the dimensionless Henry's Law constant for <br /> benzene is 0 22 at 25°C (Howard and others, 1990), which indicates that it <br />' volatilizes from water and can be removed by aeration Environmental Behavior <br /> ancLEate_of_Methyi Cert-Butyl Ether (MTBE) <br /> Q <br /> aul J Squillace,James F Pankow, Nlc E Korte,and John S Zogorski <br /> QePartment of the Inlenar-U S Geological Survey <br /> nal Water Quality Assessment Program(NAWQA) <br /> Sheet FS-203-96(Revised 2198) <br /> 3 <br /> 1 <br />