In-borehole measurements of chemical parameters in a wellfield affected by iron fouling

摘要

Variations in temperature, electrical conductivity, pH, pe and dissolved oxygen with depth were collected for boreholes affected by iron biofouling in the Calitzdorp wellfield, South Africa. From the data, zones of inflow and chemical reaction could be identified in the standing water column. Trends in pH and pe in the upper part of the boreholes correlate well with expected conditions for the equilibrium between dissolved ferrous iron and amorphous ferric oxyhydroxide precipitates. The depth of the oxidation zone suggests that it is virtually impossible to control iron fouling by managing water table drawdown in this wellfield. In-borehole measurements have proved useful for improving our understanding of the iron fouling phenomenon.