Sand column experiments were conducted to investigate the efficacy of colloidal particles (microspheres) as hydrological tracers. Two main questions were investigated:

1. What is the relationship between breakthrough volume and column height for latex microspheres in a sand column?

2. Is the fraction of latex microspheres filtered out by sand a function of column length?

Small-scale sand column experiments were carried out under both saturated and unsaturated conditions. Carboxylated latex microspheres were used as test-tracers. The pore volume of water that flows out of the column before the microspheres breakthrough was linearly related to column height in all trials. The fraction of latex microspheres filtered out by the sand column was not a function of column height unless the water is salty. In one set of unsaturated experiments using 10 mM of NaCl solution, the fraction of microspheres retained in the sand column was linearly related to column height. As this was a only a proof-of-concept or preliminary trial of microspheres for use as hydrological tracers, much further testing is needed to determine other aspects of the behavior of microspheres in the soil and water environment.