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The ability of supersaturated water injection (SWI) to recover non-aqueous phase liquids (NAPLs) was studied at the field scale as part of an ongoing program to evaluate its applicability to groundwater remediation. SWI uses Gas inFusionTM technology to efficiently dissolve gases into liquids at elevated pressures. SWI has been shown to both volatilize and mobilize residual NAPL ganglia (Li, 2004). During SWI pressurized water containing high concentrations of CO2 is injected into the subsurface below the zone of contamination. Once the injected water is in the aquifer the pressure drops substantially and the concentration of CO2 is no longer in equilibrium with the water and as a result CO2 bubbles nucleate. These bubbles then migrate upwards through the contaminated zone towards the water table. As they move they come into contact with residual NAPL ganglia and they either volatilize this NAPL, resulting in a bubble comprised of CO2 and gaseous NAPL, or mobilize this NAPL, resulting in a film of NAPL surrounding the bubble. In either case the bubbles continue to rise until they reach the water table at which point they are removed by a dual phase extraction system. In this work, a known amount of NAPL was emplaced below the water table at residual concentrations to represent a residual source of weathered gasoline. The source was created in a hydraulically isolated cell in an unconfined sand aquifer at CFB Borden, Ontario. After the source was emplaced SWI was used to remove as much of the contaminant mass as possible in 22.25 days of operation over three months. The goal of this project was to determine if SWI was capable of removing residual NAPL at a field site. It was successful in removing volatile NAPL but not non-volatile NAPL. 64% of the volatile compounds were removed but contaminant mass was still being removed when the system was shut down so with continued operation more mass would have been removed. There is no way of knowing how much more would have been removed had the project continued. These results indicate that continued development of the technology is warranted.

This thesis describes the hydrochemistry of three sub-catchments of the Uda Walawe basin, Sri Lanka. The basin is underlain by crystalline hard rocks and parts of the sub-catchments have been developed under an irrigation scheme. Groundwater is used for agricultural and drinking water purposes, but is vulnerable to poor water quality, particularly from high fluoride (F) concentrations and microbiological contamination. Dental fluorosis is endemic in the basin where F concentrations reach 9 mg/L. The Uda Walawe basin is marked by two major geological zones, the Highland Series and the Eastern Vijayan Complex. Highland Series rocks are subjected to a greater fracture network density and have higher yields and transmissivities compared to the Eastern Vijayan Complex. Groundwater is found in the alluvial soils, weathered regoliths and in the fractured layers of the crystalline rocks. Shallow wells are recharged by water leakage from irrigation canals and provide significant amounts of groundwater. Groundwater movement is southwards and discharges to the River Walawe and the southern coast of Sri Lanka. A detailed hydrochemical survey of dug wells and tube wells completed as part of this thesis showed that a Ca-Mg-HCO3 water type is present in shallow and deep groundwaters and a Na- Cl type in a few shallow wells in southern coastal districts. Prevalence of HC03" with high pCO2 indicates H2CO3 as the main acid for silicate weathering and release of major cations (Ca2+, Mg 2+ and Na) and F. Biotite and hornblende are the commonly occurring F bearing silicate minerals in the study area, as seen in other parts of the world. The occurrence of accessory minerals such as carbonates, apatites and fluorite are very limited and are not considered an important source releasing F to groundwater. Groundwater in the discharge areas of the study area is saturated with respect to these accessory minerals indicating controls of mixing of different waters and an increase in dissolved constituents, but not providing a control on F concentrations. Of secondary importance, F concentrations are higher in areas where there is limited recharge that may result in a longer residence time that promotes greater rock-water interactions. F concentrations show a positive correlation with weathered depths in shallow and deep wells. High evaporation in the downstream catchment areas concentrates fluoride ions in the shallow waters but, in the upstream areas, F concentrations are additionally controlled by dilution effects. Nitrate (up to 136 mg/L) and phosphate (up to 116 mg/L) are contributed from fertiliser or sewage sources but only occur in high concentrations in a few shallow well localities in those areas with low recharge and less dilution, and where favourable oxidising conditions exist. Nitrate is generally reduced in paddy fields and the risk of contamination in this situation is limited. Arsenic occurs in high concentrations (up to 0.36 mg/L) in a few shallow well localities, also in areas with low recharge. Sulphide oxidation is likely to favour arsenic release in the study area. Total coliforms and E. coli. levels are high in the surface waters and shallow groundwaters. The presence of E. coll. bacteria in the groundwaters suggests the predominance of point sources of contamination. In general, areas under irrigation in both geological regions show low and medium groundwater This thesis describes the hydrochemistry of three sub-catchments of the Uda Walawe basin, Sri Lanka. The basin is underlain by crystalline hard rocks and parts of the sub-catchments have been developed under an irrigation scheme. Groundwater is used for agricultural and drinking water purposes, but is vulnerable to poor water quality, particularly from high fluoride (F) concentrations and microbiological contamination. Dental fluorosis is endemic in the basin where F concentrations reach 9 mg/L. The Uda Walawe basin is marked by two major geological zones, the Highland Series and the Eastern Vijayan Complex. Highland Series rocks are subjected to a greater fracture network density and have higher yields and transmissivities compared to the Eastern Vijayan Complex. Groundwater is found in the alluvial soils, weathered regoliths and in the fractured layers of the crystalline rocks. Shallow wells are recharged by water leakage from irrigation canals and provide significant amounts of groundwater. Groundwater movement is southwards and discharges to the River Walawe and the southern coast of Sri Lanka. A detailed hydrochemical survey of dug wells and tube wells completed as part of this thesis showed that a Ca-Mg-HCO3 water type is present in shallow and deep groundwaters and a Na- Cl type in a few shallow wells in southern coastal districts. Prevalence of HC03" with high pCO2 indicates H2CO3 as the main acid for silicate weathering and release of major cations (Ca2+, Mg 2+ and Na) and F. Biotite and hornblende are the commonly occurring F bearing silicate minerals in the study area, as seen in other parts of the world.