Use of tritium and stable water isotopes to assess contaminant transport at a burial site in Middelburg, Mpumalanga

Abstract

When different water resource components coexist in nature, they usually have an impact on each other. Studies of how they impact each other in terms of water quantities, flow dynamics, quality and contamination are therefore necessary to ensure an appropriate water and environmental management is conducted. A study in Middleburg comprised a literature review and field investigations at and around a cemetery, as part of a Water Research Commission project on impacts on the water resource from large-scale burials. A literature review conducted has enabled familiarisation with similar studies that have been conducted around the subject. Reliable methodologies have therefore been adopted from the published literature and applied on the current research. A seasonal wetland is located downgradient of the cemetery, between the cemetery and a stream that flows past the cemetery. In order to assess possible flow pathways of near-surface and groundwater from the cemetery to the stream, monthly monitoring of surface and groundwater quality and level fluctuations was carried out on the stream, as well as existing and newly installed boreholes at the cemetery. Water samples collected were analysed for inorganic constituents, tritium, and stable water isotopes. The tritium and stable water isotope results – revealed the comparative influence of rainfall and shallow groundwater contributions to streamflow, while groundwater provides base-flows as the stream levels recede. The depth to groundwater reduced with increasing rainfall, indicating direct recharge. The difference in concentrations of some inorganic parameters in the stream compared to the groundwater at the cemetery revealed the effect of natural attenuation in the vadose zone due to reduced conditions and the wetland acting as a filter to improve the water quality of the shallow interflow on reaching the stream. Since isotope data indicated to be a useful tool in studying water resource interactions, the methodology should form part of site investigations for cemetery development or on existing cemeteries to study the current impact and/or predict future impacts that the cemetery may have on the water resources. The methodology best applies in areas with multiple water resources, where there may be an interconnection between them. The isotope studies can also be used to estimate recharge and thus contaminant transport rate of the cemetery leachate.