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Effects of Initial Solute Distribution on Contaminant Availability, Desorption Modeling, and Subsurface Remediation

^a Hydro Geo Chem, Inc., Tucson, AZ 85705
^b Dep. of Geography and Environmental Engineering, Johns Hopkins Univ., 3400 Charles St., Baltimore, MD 21218

View larger version (20K): [in this window] [in a new window]   Fig. 1. Schematic representations of the batch (top) and flow (bottom) systems.

View larger version (20K): [in this window] [in a new window]   Fig. 2. Relative solute concentration profiles for the equilibrium (EQ), gradient in (Grad-In), and gradient out (Grad-Out) scenarios. Each scenario has the same initial mass.

View larger version (16K): [in this window] [in a new window]   Fig. 3. Average relative sorbed concentrations for the equilibrium (EQ), gradient in (Grad-In), and gradient out (Grad-Out) scenarios with the multiple first-order rate desorption model fits to each scenario. The plot is shown on a linear scale (left ordinate scale) for 0 to 2500 d and on a semi-log scale (right ordinate scale) for 2500 to 5000 d.

View larger version (21K): [in this window] [in a new window]   Fig. 4. Effluent concentrations and mass remaining with pore volumes pumped for the equilibrium (EQ), gradient in (Grad-In), and gradient out (Grad-Out) scenarios in the steady pumping simulations.

View larger version (20K): [in this window] [in a new window]   Fig. 5. Intraparticle concentration profiles for the equilibrium (EQ), gradient in (Grad-In), and gradient out (Grad-Out) scenarios for three different pumped pore volumes (PV) in the steady pumping simulations.

View larger version (26K): [in this window] [in a new window]   Fig. 6. Relative mass remaining (M/Mo) with pore volumes pumped (top) and with time (bottom) for the simulations with the variable (vble) pumping rates and the steady (stdy) pumping rates. The plots are truncated at M/Mo = 0.3, which is the fraction of remaining mass that was arbitrarily selected as sufficient to meet cleanup criteria without pumping. Variable pumping was initially set at the maximum rate but was then allowed to drop as needed to keep effluent concentrations at a maximum allowable value of C/C0 = 0.3. The pore volumes pumped and time scales are not easily related because pumping is not at a steady rate.

View larger version (20K): [in this window] [in a new window]   Fig. 7. Relative pumping rate, q/qmax, as a function of number of pore volumes pumped (top) and time (bottom) for the simulations with the variable pumping rate. qmax is the steady pumping rate used to generate the data in Fig. 6a and 6b. Variable pumping was initially set at the maximum rate but was then allowed to drop as needed to keep effluent concentrations at a maximum allowable value of C/C0 = 0.3. The pore volumes pumped and time scales are not easily related because pumping is not at a steady rate.