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• <br /> 3000004w-- , conhnum tracer Supply at time 010 • ' <br /> t Co <br /> EXPLANATION <br /> Cu - Uniformity Coeff. 260 <br /> -- Extrapolated Curve D to 'Y U LO <br /> oc �+ � F r Ln <br /> � l � <br /> o <br /> 3000 E1rslonce--= p <br /> P (e) plepsrsed front o1 non-ralarard tolutr <br /> €' (b) Front of salute 111111 undtrgoag equERIUm panitW"b liquid and saikk L <br /> (e) Front of saline that underyoaa slower rate d tmnater to SONS M <br /> colt . , <br /> Figure 0-7. Advance of reactive and mawsactivs contaminants through a cdwnn. w <br /> Source Freeze and Cherry, 1979 (Copyright Prerrdas+iafi Inc P1137 U, <br /> 300 a `� Reprinted with permisslom.) ' <br /> a `V01* <br /> matographic effect over time. As a contaminant plume advances along <br /> now paths, the front is retarded as a pastier of the contarnittant mass <br /> sorbs to the solid phase(Figure 8-7). If the input of contaminant masa <br /> to the groundwater Is discontinued,and the groundwater concewations <br /> 30 '�`\ �� \\ drop (for example, as a groundwater pump and treat scheme pro- <br /> \ , gresses), contaminants may desorb from the sod back into the ground- <br /> ; water. Thus, it is doubtful that all of the contaminant can be perma- <br /> 1 \1\ \ 1 \\' ncntly Immobilized. even though the retardation of the concentration <br /> front may be strong However, a portion of the contaminants may be <br /> 3 *� <br /> irreversibly fixed relative to the time scale of interest(see Figure 8-8) <br /> Retardation is strongly affected by subsurface carbon content The <br /> effect on retardation differs, however.based on the phase of the carbon. <br /> Dissolved organic carbon (DOC) (e.g., highly soluble compounds such <br /> as MTBE and tertiary butyl alcohol and colloidal parttcies of humic and <br /> fulvic acids)may significantly lower retardation. Organic matter in the <br /> solid phase increases sorption and hence retardation. <br /> \ 1,` Garrett et al. (1986) report on how the presence of methyl tertiary <br /> butyl ether(MTBE)m gasoline spills affects the movement of the plume <br /> 0. and the detection of a release. MTBE has multiple effects related to <br /> . l 0.01 retardation and movement First, MTBE, which may comprise up to <br /> MEDIAN GRAIN DIAMETER (D ) IN mal <br /> 1 l%by volume of gasoline, is soluble its water l0 43,000 mg/L(Garrett � <br /> Vury 8-4 Fteis>rorts among hydrauiio oonducthrtty, unftrmitt► cooffiment, and et al , 1986), about 25 times more soluble than ' emmne. otherwise the ; <br /> median vwn dwmmw Source Robeon,1978 most soluble gasohne constituent at 1,780 mg/L. Generally, sorption of <br /> r organic compounds is inversely proportional to their solubility Thus, <br /> MTBE is likely to be minimally retarded,allowing it to travel faster than N <br /> l <br /> I <br />