Iodine dispersion and effects on groundwater chemistry following a release to a peat bog, Manitoba, Canada

Abstract

The migration and behaviour of I was investigated in a sphagnum bog on the Precambrian Shield in eastern Manitoba, Canada. A 6 M solution of KI was released at the base of the bog to stimulate a pulse discharge of contaminated groundwater from a fracture in the granitic rock. A network of piezometer tubes was used to monitor the dispersion of the I and the groundwater chemistry over 1 year. Cores of peat were also taken for analysis to supplement the groundwater data and to investigate the sorption of I. The introduced I dispersed 2 m horizontally and 1 m vertically within a month. After this, the system stabilized and further migration was insignificant. The pattern of I dispersion indicated that the bog hydrology was very complex with flow directions changing substantially with depth. The groundwater concentrations of the major cations rose in response to the mass action effect of K displacing them from reaction sites in the peat. Humic materials in the groundwater decreased in size after the KI release and returned to their pre-release conformation one month later. The geometric mean soil distribution coefficient value, K d , for I in the bog was 1.36l/kg, but it was strongly related to pore water concentration. Thus, a single K d value was insufficient for describing the system. Clearly, good groundwater chemistry, sorption and hydrological data are necessary for meaningful modelling of contaminant transport in bogs.