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Contaminant Fate and Transport Model <br /> AT123D <br /> ' The background, assumptions, and input parameters required to simulate <br /> contaminant transport using AT123D are presented in the following text The input <br /> parameters specific to the Stockton Service Center are also presented. Following this <br /> ' discussion is the model output in graphical and code formats The graphical output <br /> consists of charts that plot the concentrations of individual chemicals versus time at the <br /> ' receptor point. The code format is the Fortran output that lists the input parameters <br /> and the individual chemical concentrations at 5-year increments over the simulation <br /> tperiod <br /> Background <br /> AT123D is a generalized analytical, transient, one-, two-, and three-dimensional <br /> code for estimating the transport of wastes in a groundwater porous system The model <br /> was developed by G T Yeh at Oak Ridge National Laboratory in 1981 and is included in <br /> the United States Protection Agency's Graphical Exposure Modeling System AT123D <br /> solves the differential mass balance equation that describes contaminant fate and transfer <br /> in the saturated zone and accounts for advective and dispersive effects AT123D <br /> includes three-dimensional dispersion, one-dimensional uniform advection, linear, <br /> ' reversible equilibrium adsorption, and lumped first-order decay The model allows input <br /> of the source as a point, line, area, or volume oriented in different ways along the x, y, <br /> and z directions AT123D also allows specification of the mass loading as a constant <br /> mass release rate for the entire simulation, as a constant mass release rate for a specified <br /> period of time, and as an instantaneous release <br /> Assumptions <br /> ' The assumptions underlying the AT123D model include the following <br /> • The saturated zone is homogenous, isotropic, and of uniform geometry <br /> ' • The water table is steady without any fluctuations <br /> 0 The flow direction is uniform, one-dimensional, and steady state <br /> ' a Contaminant decay follows a lumped first order decay rate <br /> • Contaminant adsorption follows linear adsorption <br /> 0 Concentrations in the liquid and solid phase of the aquifer are in equilibrium at <br /> all times <br /> ' 96R7 East Bay Municipal Utility District <br /> 40429700 fcr Final Closure Report <br />