Laboratory study was carried out to investigate the effect of acidic and alkaline characteristics of groundwater medium on three tracers (rhodamine B, eosin and potassium dichromate) commonly used for groundwater investigations. This is with the view of improving the criterion used in the selection of tracers for groundwater investigations. The factors considered are: the maximum tracer concentration, Cmax, which could be observed during the experiment, the time, tm, at which this occur and the percentage of the tracer recovered during experiment. Others are the time, ti, of first detection of tracer and time, tf, of total disappearance of tracer from the investigation area. A lysimeter apparatus of circular cross section with diameter, D = 45 mm was constructed and uniformly filled with coarse sand and fine gravel (each at a time). Throughout the column, steady water discharge (2.5 ml/min) at a pH value between the ranges of 5 – 8 was maintained, to carry the tracer solution through the soil column. Effluent from the bottom of the lysimeter were subjected to spectrometric analysis to determine tracer concentration in it. The results of the tests suggest that rhodamine B is a suitable tracer for groundwater investigation in acidic medium but may not be suitable for alkaline medium. Values obtained for eosin showed the tracer to be good for investigation in both acidic and alkaline medium. The results obtained for potassium dichromate revealed that the tracer may be a good tracer in alkaline medium only. Keywords: Tracers, rhodamine B, eosin, lysimeter, groundwater investigation and potassium dichromate.

Keywords: Tracers, rhodamine B, eosin, lysimeter, groundwater investigation and potassium dichromate.