Distribution of mercury in soils at a decommissioned gas plant

Abstract

The range and distribution of mercury in soils at a decommissioned gas plant near Turner Valley, Alberta were investigated in order to facilitate risk assessment and the remediation and development of the site into a tourism area. Although high levels of Hg were thought to be present in some areas on the site, it was unclear whether the source of the Hg was industrial processes or from river deposition of HgS impurities after erosion of upstream sulfide deposits. Background Hg concentrations in undisturbed soils and surficial bedrock near the gas plant were also unknown. Mercury concentrations in surface soil material on the gas plant site were found to range up to 230 mg Hg kg−1 soil, with the highest concentrations found next to process building doorways. Investigation of Hg distribution with soil depth showed that levels were generally highest at the surface, dropping rapidly with depth to near background levels of 0.07 mg Hg kg−1 soil or lower. The highest Hg concentrations were associated with the clay fraction, which contained up to 2300 mg Hg kg−1 soil. The results are consistent with an anthropogenic source from spillage of elemental Hg contained in manometers and pressure monitoring devices used in plant buildings. Mercury concentrations at depth and in uncontaminated surface soils were similar to those reported by Dudas and Pawluk (1976) for surface soils formed in glacial and fluvial deposits elsewhere in Alberta. Key words: Mercury, contamination, soils, Turner Valley