In situ measurement by chemoprobe of groundwater from in situ sanitation of versatic acid spill

A new cone-mounted device-the chemoprobe-is presented for the in situ measurement of ground-water quality. The measured parameters of groundwater quality are pH, redox potential and electric conductivity. Redox potentials measured shown an inverse relationship with pH but are hard to interpret in terms of redox couples present in groundwater. These parameters are master variables of chemical equilibria as used in transport models like CHEA for inorganic substances. A field trial is presented at an in situ sanitation project, where a solution of sodium hydroxide is infiltrated to dissolve a floating layer of versatic acid (mainly decanoic acid solution). The chemoprobe was applied to measure the extent of infiltration into an upper aquifer and contamination of a lower aquifer. At two depths within the upper aquifer high values of pH and electrical conductivity were present, separated by a region with background values for pH but not for electrical conductivity. In the lower aquifer, no signs of contamination by versatic acid or sodium hydroxide were found. Results from CHEA modelling help explain the results obtained by the use of the chemoprobe.