Fractured rock formations represent a valuable source of groundwater and can be highly susceptible to contamination by dense, non-aqueous phase liquids (DNAPLs). The goal of this research is to evaluate the effectiveness of three accepted remediation technologies for addressing DNAPL contamination in fractured rock environments. The technologies under investigation in this study are chemical oxidation, bioremediation, and surfactant flushing. Numerical simulations were employed to examine the performance of each of these technologies at the field scale. The numerical model DNAPL3D-RX, a finite difference multiphase flow-dissolution-aqueous transport code that incorporates RT3D for multiple species reactions, was modified to simulate fractured rock environments. A gridding routine was developed to allow the model to accurately capture DNAPL migration in fractures and aqueous phase diffusion gradients in the matrix while retaining overall model efficiency. Reaction kinetics code subroutines were developed for each technology so as to ensure the key processes were accounted for in the simulations. The three remedial approaches were systematically evaluated via simulations in two-dimensional domains characterized by heterogeneous orthogonal fracture networks parameterized to be representative of sandstone, granite, and shale. Each simulation included a DNAPL release at the water table, redistribution to pools and residual, followed by 20 years of ‘ageing’ under ambient gradient conditions. Suites of simulations for each technology examined a variety of operational issues including the influence of DNAPL type and remedial fluid injection protocol. Performance metrics included changes in mass flux exiting, mass destruction in the matrix versus the fractures, and percentage of injected remedial fluid interacting with the target contaminant. The effectiveness of the three remediation technologies covered a wide range; the mass of contaminants destroyed were found to range from 15% to 99.5% of the initial mass present. Effectiveness of each technology was found to depend on a variety of critical factors particular to each approach. For example, in-situ chemical oxidation was found to be limited by the organic material present in the matrix of the rocks, while the efficiency of enhanced bioremediation was found to be related to factors such as the location of indigenous bacteria present in the domain and rate of bioremediation. In the chemical oxidation study, the efficiency of oxidant consumption was observed to be poor across the suite of scenarios, with greater than 90% of the injected permanganate consumed by natural oxidant demand. This study further revealed that the same factors that contributed to forward diffusion of contaminants prior to treatment are critical to this remediation method as they can determine the extent of contaminant destruction during the injection period. Bioremediation in fractured rock was demonstrated to produce relatively good results under robust first-order decay rates and active microorganisms throughout the fractures and matrix. It was demonstrated that under ideal conditions, of the total initial mass present, up to 3/4 could be reduced to ethene, indicating bioremediation may be a promising treatment approach due to the effective penetration of electron donor into the matrix during the treatment period and the ongoing treatment that occurs after injection ceases. However, when indigenous bacteria was assumed to exist only within the fractured walls of sandstone, it was found that under the same conditions, the rate of dechlorination was 200 times less than the Base Case. Since the majority of the mass resided in the matrix, lack of bioremediation in the matrix significantly reduced the effectiveness of treatment. Surfactant treatment with Tween-80 was proven to be a relatively effective technique in enhanced solubilisation of DNAPL from the fractures within the domain. However, by comparing the aqueous and sorbed mass at the start and end of the Treatment stage, it is revealed that surfactant treatment is not efficient in removing these masses that reside within the matrix. Furthermore, DNAPLs identified in dead end vertical fractures were found to remain in the domain by the end of the simulations across all scenarios studied; indicating that the injected surfactant experiences difficulty in accessing DNAPLs entrapped in dead end fractures. Altogether, the results underscore the challenge of restoring fractured rock aquifers due to the field scale limitations on sufficient contact between remedial fluids and in situ contaminants in all but the most ideal circumstances.

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The method of using stimulated reductive dechlorination when remediating sites contaminated with chlorinated solvents is not unusual, but not many studies have been done on the overall process outside of a controlled environment. In order to investigate the process, principal component analysis (PCA) and partial least square (PLS) regression was used to identify the most important parameters for the degradation of the chlorinated solvents. The most important parameter for all chlorinated compounds turned out to be oxygen, with levels of degradation products increasing with decreasing levels of dissolved oxygen. Dissolved oxygen was deemed the most important variable to measure during a control program on the site. The degradation dynamics of the process were investigated to examine the behaviour of the chlorinated solvents and their degradation products. The degradation products of the main contaminant TCE were found in all observation points, which indicates an ongoing reductive dechlorination all over the site. A large amount of the mother product, TCE, was found in two observation points, which were believed to be situated close to the sources of the TCE contamination. Over the observation period of 2,5 years the levels of TCE in the source areas decreased significantly to below the remediation goal. However, the levels of TCE increased in another observation point further downstream, with concentrations still increasing at the end of this study. The levels in this point were lower than those measured initially in the source area, but still much higher than the accepted values. Possible reasons for this appearance of TCE could be an isolated sheet of contaminants being pushed into the observation point from a nearby location or transport of the contaminants from the source area in units of higher conductivity such as sand lenses or fractures in the clayey soil. / Att använda stimulerad reduktiv deklorering som metod för att sanera fastigheter förorenade med klorerade lösningsmedel är inte ovanligt, men få studier har undersökt det övergripande saneringsförloppet utanför de kontrollerade förhållanden i en labbmiljö. För att undersöka nedbrytningsprocessen användes principalkomponentsanalys (PCA) och partial least square (PLS) regression i syfte att identifiera de parametrar som hade störst påverkan på nedbrytningen av de klorerade föroreningarna. Den enskilt viktigaste parametern visade sig vara halten löst syre i grundvattnet, då halterna av nedbrytningsprodukter ökade med minskande syrehalt. Därför ses syre som den viktigaste parametern för att följa förloppet och är den parameter som bör mätas i kontrollprogram över nedbrytningsprocessen.   Nedbrytningsdynamiken analyserades under en observationsperiod på 2,5 år för att studera hur de klorerade föroreningarna betedde sig under nedbrytningsförloppet. Nedbrytningsprodukter hittades i provtagningspunkter över hela fastigheten vilket visar på en pågående reduktiv deklorering. En stor mängd av moderprodukten TCE hittades i två punkter som bedömdes vara källor till TCE-spridningen. Under observationsperioden sjönk halterna av TCE i dessa två punkter till under gränsen för åtgärdsmålet, dock ökade koncentrationen av TCE i en annan provpunkt längre nedströms källområdet. Halterna i provpunkten var inte lika höga som de initiala halterna i källområdet, men de var långt högre än det fastställda åtgärdsmålen och ökade fortfarande när undersökningen avslutades. Möjliga förklaringar till varför halterna ökade i denna provpunkt är att ett sjok av TCE från omkringliggande sediment har transporterats till provpunkten, eller att en föroreningstransport har skett från källområdet via områden med högre konduktivitet i till exempel sandlinser eller sprickor.