Dear All

I am trying to model the transport of car tire particles in saturated porous media. I am running a column experiment with a homogeneous sand bed of 26 cm supported by two gravel layers of 0.25 cm at the top and bottom of the column (only the sand bed is of interest). My influent fluid is artificial rainwater mixed with DOC, and my tire particles are introduced as a 3 mm uniform layer of the tire-sand-induced mixture at the top of my column, followed by a small layer of sand and a final gravel layer at the very top. I am using zinc concentrations as a proxy to do the mass balance computations, i.e., for the 400 mg of tire particles introduced at the top of the column, I want to know what part of that mass leaves my column outlet and what mass is retained. So, effluent samples are collected at the outlet, analysed for zinc concentration, and then these need to be converted into mass of tire rubber at the outlet. However, I need to fit my experimental data into HYDRUS using the inverse solution approach and understand the transport mechanisms of these particles inside my column. I ran a conservative tracer experiment and used HYDRUS to estimate some initial parameters like dispersivity and assess the packing of the column. 1. Do I use this same value of dispersivity in my subsequent modelling? Or this value is only applicable to my conservative tracer? 2. Which non-equilibrium solute transport model should I use? 3. What would be my upper and lower solute boundary conditions for my system? (this was easy for the tracer but a bit difficult to figure out for the tire particles.) 4. How do I eventually model the transport of these particles in my column since I am introducing them at the top of my column? I look forward to your help