Controls on contaminant migration at the Villa Farm Lagoons

Abstract

Summary The disposal of liquid wastes containing heavy metals and organic solvents into lagoons excavated to beneath the water table in a shallow, unconsolidated sand aquifer has resulted in local groundwater pollution. The development of the pollution plume appears to be controlled by the morphology of the aquifer, the distribution of permeability within it and the head distribution in the vicinity of the lagoons. On the basis of redox reactions three geochemical zones have been identified down hydraulic gradient in the transition from strongly reducing conditions near the lagoon and at the base of the aquifer to oxidizing conditions in natural groundwater. Heavy metals are attenuated within a short distance of the lagoons, probably as a result of precipitation as sulphides and carbonates, but organic wastes have been found in excess of 300 m from the site. With increasing distance from the lagoons changes in bacterial populations and the character of organic compounds present at the base of the aquifer suggest that organic transformations are occurring despite little change in the concentration of total organic carbon, although ultimately biodegradation to methane and carbon dioxide takes place. Studies are continuing in order to develop a three dimensional mathematical model integrating chemical reactions with groundwater flow.

Bacterial sulfate reduction and pyrite formation in a polluted sand aquifer

“…These confirm the overall picture described by Williams et al (1984) but show that since waste dumping has ceased there has been a general dilution of the plume, as the plume itself has spread (Williams et al, 1995). In particular, maximum chloride concentrations close to the lagoons fell from >4000 to 600 mg L" 1 .…”

“…A strong brown coloration is due to the presence of iron oxyhydroxides. Clays, mainly kaolinite and illite, can constitute up to 15% of the bulk mineralogy (Williams et al, 1984).…”

“…Replenishment of the aquifer in the area studied is controlled by infiltration from the lagoons, which have a 3 m hydraulic head above the water Williams et al (1984), with permission of the Geological Society Publishing House. hydraulic gradient and permeabilities obtained from constant head injection tests, are between 0.006 and 0.17 m day" 1 (Williams et al, 1984). Williams et al (1984) present a chemical model of the pollution plume in the Wolston Sand aquifer based on sampling from a suite of 45 boreholes.…”

“…hydraulic gradient and permeabilities obtained from constant head injection tests, are between 0.006 and 0.17 m day" 1 (Williams et al, 1984). Williams et al (1984) present a chemical model of the pollution plume in the Wolston Sand aquifer based on sampling from a suite of 45 boreholes. Natural groundwater, outside the pollution plume, is of a calcium sulfate type and has dissolved O 2 of 10% atmospheric saturation.…”

Emerging organic contaminants in groundwater: A review of sources, fate and occurrence

“…Christensen et al, 1992). This reducing environment has been shown to be important in controlling the transport and fate of some organic compounds with otherwise high attenuation potential (Williams et al, 1984;Holm et al, 1995). For sources of contamination from septic tanks it has also been suggested that a redox-mediated persistence of EOCs is important controlling factor (Carrara et al, 2007).…”