Problem Set #3 – Part 3 - Remediation Numerical error caused by high Peclet number TVD Solution

There is a source of error in Part 3 of PS#3 owing to approximate representation of the removal of the source.

PS#3: Part 3. Remediation simulation t = 1 year (last time step in first stress period Concentration distribution around the constant concentration source cell

t = 1.020141 yr; 1st time step in the 2nd stress period Note: Some mass is flowing into the constant concentration cell and is removed from the model.

t = 1 yr Before removal of the source

t = 1.020141 yr After removal of the source During remediation the model removes contaminant via --the pumping well --flow out the lower boundary -- through the constant concentration cell In the field, mass is removed only through the well & the lower boundary

t = 3 years In the model, around 1.3% of the total mass removed is erroneously removed through the constant concentration cell.

A better way to represent the removal of the source would be to change the constant concentration cell to an active cell at the end of the 1st stress period. This would require re-starting the simulation with new initial concentrations. That is, we would need two GWV simulations.

2 runs; constant conc. cell is active during 2nd stress period Constant concentration cell has zero concentration during 2nd stress period.