ABSTRACT

Detailed distribution patterns of bomb tritium (³H), chloride (Cl^-), sulphate (SO^2-₄), oxygen-18 (¹⁸O), and deuterium (²H) are described for two unconfined shallow sand aquifers at Canadian Forces Base (CFB), Borden, Ontario, and Whiteshell Nuclear Research Establishment (WNRE), Pinawa, Manitoba, both in Canada. The study areas were highly instrumented with groundwater monitoring and sampling devices consisting of multilevel samplers and bundle piezometers. Groundwater samples were collected regularly and seasonally, and analysed for the isotopes (³H, ¹⁸O and ²H) and the dissolved geochemical constituents (Cl^- and SO^2-₄). The samples were collected at several depths within the aquifers and along various directions. The geochemical parameters were interpreted in relation to the groundwater movement. Bomb ³H showed two concentration patterns indicating two groundwater age-zones. An upper tritiated zone reflects young water recharged since the beginning of nuclear tests in 1953. The lower untritiated old water indicated water recharged before 1953. Thus, the recharge and discharge 0 areas were established, and groundwater velocity and hydraulic conductivity were calculated for the description of the groundwater flow. The chloride and sulphate patterns were used to delineate the areal extent of the leachate plume in the aquifer beneath an abandoned landfill at CFB Borden. The sulphate concentrations at WNRE aquifer indicated two possible sources of groundwater recharge. The ¹⁸O data for the Borden aquifer suggested that isotopic fractionation was occurring in the landfill so that ¹⁸O enrichment was observed within the leachate plume. The ¹⁸O and ²H data from WNRE aquifer showed that an evaporative effect on the recharged groundwater was evident, resulting in slight enrichment in ¹⁸O and ²H as reflected by the seasonal fluctuations on recharge.