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Greg Nelson

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  1. I am using GMS version 6.0 and am familiar with using the Observation coverages for MODFLOW. I have read in the tutorials and help that the MT3DMS concentration observation package is available (TOBS). I am unable to figure out how to create a concentration observation coverage in the Map module or to use the TOBS package in GMS. When in the Grid module, under the MT3D menu, there is an item titled "Transport Observation Package". This opens a dialogue box. I check the "Compute concentrations at observation points" box and get the message, "No observation coverages defined." I thought by chance, if I created a "head" observation coverage, by default the concentration coverage would be created; this is not the case - I still get the same message. I am familiar with MT3DMS and with how to use the TOBS package. But I would prefer not having to go to all of that hard work in text editors outside of GMS. The GMS help menu says this option is available: "Transport Observation Package "The Transport Observation Package (TOBS) package is used to provide summaries of simulated concentrations at observation wells and mass fluxes at source sink objects. "Observation Wells "With previous versions of GMS, it was possible to associate observed concentrations (in addtion to heads) at observation wells. When a transport solution computed by MT3DMS was read into GMS, the simulated concentrations at the observation well were found by interpolating from the surrounding cell centers to the obesrvation well location. This interpolation was peformed internally to GMS at the instant the file was imported. With the new TOBS package, the interpolation and summation of the simulated concentrations is performed internally to MT3DMS.This provides a number of advantages, including the following: "The summation of the simulated concentrations is weighted by MT3DMS according to the size and location of the well screen, similar to how simulated heads are summed by MODFLOW. "The interval at which the simulated concentrations are reported can be at a different interval than that used to save the concentration data for contouring. The output interval for observation wells can be quite small without requiring a large amount of disk space. "When an MT3DMS solution is read into GMS, the simulated concentrations are automatically associated with the proper observation wells and the concentration residuals can be plotted. Furthermore, the global error norms (mean error, mean absolute error, root mean square error, etc.) are stored with the MT3DMS solution and can be viewed by right-clicking on the solution in the Project Explorer." How do I get this option to work in GMS? Greg
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