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

Abstract

English: 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.

Afrikaans: Die remediëring van terreine wat besoedel is met digte vloeistowwe in ’n nieakwatiese fase (DNAPL’s), bied steeds wêreldwyd ’n wesentlike omgewingsuitdaging. Die problematiese bepaling van bronsones weens die lokale heterogeniteite ondergronds dra verder by tot hierdie uitdaging. Heterogeniteite is betekenisvol in breukrotsomgewings soos wat in Suid-Afrika aangetref word, wat tesame met die vloeistofeienskappe, die lot en vervoer van DNAPL’s bepaal. Hierdie navorsing is gegrond op die evaluering van die doeltreffendheid van tradisionele en ongewone bronsone-karakteriseringsmetodologieë in kombinasie om chloorkoolwaterstof-DNAPL’s in ’n breukrotsomgewing te delinieer. Die navorsing dokumenteer die karakteriseringsproses wat in die toepassing van verskeie metodologieë met betrekking tot ’n Ondersoekterrein in Suid-Afrika gevolg is. ’n Terreinspesifieke konseptuele terreinmodel word aangebied wat die deliniasie van die veelvuldige chloorwaterstof-DNAPL-bronsones op die terrein toon. Daarbenewens word ’n DNAPL-bronkarakteriseringsbenadering voorgestel wat in breukrotsomgewings toegepas kan word. Hierdie benadering maak daarvoor voorsiening dat tradisionele benaderings (soos om in ’n vaste rooster te boor) en ongewone benaderings (soos hoëresolusie-monsterneming en analisering) samelopend gevolg kan word. Die baanbrekerswerk in die gebruik van NAPL-lintmonsters (FLUTeTM-geaktiveerde koolstoftegnologiemembrane) in Suid-Afrika word in hierdie navorsing gedokumenteer. Waar hierdie tegnologie in ’n breukrotsomgewing vir in situ bronsone-karakterisering gebruik is, was dit suksesvol in die bepaling van dieptediskrete breuktransmissiwiteite en residuele DNAPL-sones wat nie deur metodes soos direkte observasie en die toets van rotskerne met hidrofobiese kleurstowwe waargeneem sou word nie. Die doeltreffendheid van hierdie tegnologie maak dit ideaal vir voortgesette toekomstige gebruik in Suid-Afrika. 209