## Mass Dirac Delta Input?

A discussion forum for STANMOD users. STudio of ANalytical MODels is a software package for evaluating solute transport in porous media using analytical solutions of the convection-dispersion solute transport equation.

elgouzi.siham
Posts: 2
Joined: Tue Jul 03, 2012 11:43 am

### Mass Dirac Delta Input?

STANMOD:
CXTFIT ,
Type de Problem : inverse
deterministic eq. CDE
time and position dimensional (cm - min - mg/l)
Flux averaged concentration Cf ( L =5 cm)
No constraints for parameter estimation
Total estimation for total mass ( 20 Max)
Solute mass is know and kept constant
I apply 200 #61549;l of Bromide (tracer) C=0.2 M
But I do not know how calculating the Mass Dirac Delta Input?
Sum(C*dT) in display text output file is the same thing or no ?
And pore water velocity? I calculate the average of the experimental velocity (cm. min-1) this true or not?
Thanks

ntoride
Posts: 74
Joined: Fri May 21, 2004 12:50 pm
Location: Japan
I am not quite sure what is your problem. I will explain the delta and pulse inputs for the CXTFIT.

As shown in p. 7 of the CXTFIT manual, the delta input is given by
c_o(t) = (m_b / v) delta(t) Eq. (2.16b)
where m_b is the total amount of mass added to a unit area of the soil liquid phase. The m_b cab be related to a pulse input of c_o with a small duration time, t_o as
m_b/v = c_o*t_o
In other words, the amount of solute mass subject to a pulse input added to a unit area of the soil liquid phase is c_o*t_o*v. Hence the amount of mass per unit area of soil is m_b*theta for a delta input , and c_o*t_o*v*theta = c_o*t_o* water flux for a pulse input.

If any further questions, please do not hesitate to ask me.

Nobuo

elgouzi.siham
Posts: 2
Joined: Tue Jul 03, 2012 11:43 am
Dear Mr. Toride and everybody,

I am not sure what type of boundary condition I should use in the boundary value problem section. I work with saturated soil minicolumns (5 cm length and 2 cm i.d.) in order to asses the leaching of some pesticides. I apply a pulse of 0.1 mg of each pesticide and, after solvent evaporation, another pulse of 6.4 mg of Br- as a tracer. I use a Boyle-Mariotte container with different influent solutions under positive pressure head (water column length is 5 cm), so the influent flow decreases with experimental time. Finally, I collect the leachates at short periods of time so the total experimental time is around 24 h.

I would appreciate your help.

ntoride
Posts: 74
Joined: Fri May 21, 2004 12:50 pm
Location: Japan
I am sorry for my late reply. If the purpose of your experiment is to determine transport parameters such as the dispersion coefficient, it is necessary to establish a steady-state flow with constant water content in a homogeneous soil. The CXTFIT uses the CDE with constant theta and v. If flow rate is not constant, you need to use an average velocity for CXTFIT or use a numerical program such as HYDRUS to implement actual flow rates. However, it would be difficult to accurately determine transport parameters. Nobuo