In situ source characterisation of dense non-aqueous phase liquids (DNAPLs) in a fractured rock environment

The remediation of sites contaminated by dense non-aqueous phase liquids (DNAPLs) continues to present a significant environmental challenge globally. Contributing to this challenge is the difficulty in locating source zones due to local heterogeneities in the sub-surface. Heterogeneities are significant in fracture rock environments, such as those found in South Africa, which together with the fluid properties determine the fate and transport of DNAPLs. This research is based on evaluating the effectiveness of combining traditional and novel source zone characterisation methodologies in order to delineate chlorinated hydrocarbon DNAPLs in a fractured rock environment. The research documents and evaluates the characterisation process followed in the application of various methodologies to an Investigation Site in South Africa. A site-specific conceptual site model is presented indicating the delineation of the multiple chlorinated hydrocarbon DNAPL source zones at the site. Additionally, a DNAPL source characterisation approach is proposed for application in fractured rock environments. This approach allows for the convergence of traditional approaches (such as drilling within a fixed grid) with more novel approaches (such as high resolution sampling and analysis). The pioneering use of ribbon NAPL samplers (FLUTeTM activated carbon technology membranes) in South Africa is documented in this research. In situ source zone characterisation using this technology in a fractured rock environment is shown to be successful in determining depth discrete fracture transmissivities and residual DNAPL zones that would have gone unobserved through methods such as direct observation and testing rock cores with hydrophobic dyes. The efficiency of this technology renders it ideal for future continued use in South Africa.