QUANTIFYING ALKALINE PROCESS FLUIDS IN SOILS AND GROUNDWATER FROM LEAKS AND SPILLS

Thomas, G. and Gerritse, R.

Presence of alkaline process fluids in soils and groundwater from leaks and spills is commonly associated with elevated alkalinity, pH and related parameters in pore water, extracted from soils, and in groundwater. Alkalinity and pH, however, can be affected by soil-chemical processes such as oxidation of reduced Fe, elevated CO2 pressures, and, in soils with appreciable amounts of clay, ion-exchange and clay-alkalinity reactions. In such situations, ranges of Na/Br ratios in pore water or groundwater aff ected by alkaline process fluids are characteristic of a refinery’s alkaline process fluids, where bromide is mobilized in the Bayer process from organic matter in bauxite.

The concentration of Na in soil pore water and groundwater is affected mostly by alkaline process fluids but also by ion exchange at clay surfaces and alkaline soil reactions plus the pore water extraction process. Although the concentration of Br is not affected by ion exchange or soil reactions, it can be affected by ‘salt-sieving’ through surface charges in clays in combination with size exclusion of Br ions relative to Cl ions. These processes can result in apparent increases of Cl/Br ratios in groundwater and in pore water, when extracted from clayey soils. This paper discusses the problems commonly encountered in quantifying effects of alkaline process fluids in soils and groundwater and which require a thorough and careful comparison of resulting changes in pH, alkalinity and both Na/Cl and Cl/Br ratios.