Murdock, Nebraska, Groundwater Flow and Transport Modeling in Support of Long-Term Monitoring

Fall 2002 Assignments: • Update all models to MODFLOW-2000 • Re-calibrate original Murdock steady-state groundwater flow model to November 25, 1998 observed water levels (Phase 1 hydrology) • Determine time when climatological/hydrolic regime changed in eastern Nebraska. Groundwater levels observed in 2002 are significantly lower than all values observed previously (1997-1999). Palmer Hydrologic Drought Index. • Determine appropriate groundwater level data for calibration of new (Phase 2) groundwater flow model representing current hydrologic regime (avg. of 2002 observations) • Re-evaluate/recalculate initial CCl4 concentrations for MT3D-99 solute transport model calibration – 1996/97 concentration data. Too much CCl4 mass in eastern portions of original transport model • Re-calibrate Murdock MT3D-99 solute transport model to November 1999 observed concentrations using revised initial 1996/97 concentrations • Include historical average concentrations at S2 as a constant concentration in transport model • With re-calibrated solute transport model simulate CCl4 dissolved phase transport from December 12, 1996 to December 31, 1999 with Phase 1 goundwater flow model • Simulate CCl4 solute transport from January 1, 2000 to December 12, 2012 with Phase 2 groundwater flow model and CCl4 initial conditions set at December 31, 1999 simulated values (i.e., Phase 1 model ending concentrations) • Plot simulated CCl4 concentration time series for all trigger action wells, and non-trigger action wells monitored during 2002 for all layers inclusive in each well screened interval • Set the trigger action level to the maximum simulated screen interval concentration for each trigger action wel