Plume concentration using MT3DMS grid approach in GMS v3.1

[Surajit]

Dear members of the forum,

I designed a 2-D transport problem of a confined aquifer with constant head boundaries at the North and South of the model domain and with no flow boundaries at the East and West of the model domain using MT3DMS grid approach in GMS v3.1. I also assigned one injection well at the upstream with a particular rate (100 cubic metre per day) and three pumping wells at the downstream with different rates. After the flow simulation, I assigned a plume concentration value of 100 ppm, but I got the concentration values of individual cells with values much lower than 100 ppm after different transport steps. Near the vicinity of the injection well some values like 18 ppm, 16 ppm, etc. concentration vales were found out after the transport simulation. Is the result correct or should it be near to 100 ppm near the vicinity of the injection well? Please suggest.

Thanking you,

Yours faithfully,

Surajit Deb Barma

[Sean Czarniecki]

Surajit,

It's my opinion that you haven't really provided enough details for someone to give you an answer. Depending on the flow and transport parameters, as well as length of transport steps, it certainly could get to those levels....unless you made it a constant concentration.

[Alan Lemon]

It sounds like you assigned the 100 ppm concentration to the well boundary condition from the MODFLOW model. So you save 100 ppm entering the model at a rate of 100 cubic metre per day but you have to remember that there is already "clean" water in the model cell. So your 100 ppm will be diluted with the volume of water that is in the cell. Also as time moves forward in your model, the water entering the model will be clean also and further dilute your concentration.