South Bay: long-term monitoring of piezometers at South Bay Mine site / a report prepared for M. Kalin

Abstract

Groundwater flow can constitute one of the major flow paths along which contaminants are transported away from a particular surface site. The surface site can, generally speaking, be relatively easily managed with the appropriate containment structures, flow and chemistry monitoring, etc. Accidental spills and escapes are generally immediately noticed and remedial measures are, in most instances, relatively easily implemented. However, the liquid component of any waste stored at surface, unless very specific engineered measures are taken, is in contact with the underlying sediments. This scenario is the rule rather than the exception. Liquids with their contained contaminant load will infiltrate the underlying sediments. The degree and rate of infiltration is a multicomponent function of the underlying sediments, the waste and the hydrogeological setting. Once the contaminants are incorporated in the groundwater, the hydrogeological environment will determine the rate and the direction of flow away from the surface containment area. Furthermore, it should be realized, that liquids, which infiltrate sediments and are incorporated in the groundwater flow system, will, with time, be discharged to the surface environment again. In order to obtain a reasonable framework of the subsurface environment, test drilling is done to define the stratigraphy and piezometers are installed to obtain information on the hydraulic head and permeability distribution. In addition, water samples are taken to define the chemistry of the groundwater and to monitor the movement of the contaminants. Groundwater flow is an essential component of the water budget and its chemistry in any given area. Groundwater flow differs from surface water flow by its inherent time delay. In other words, contaminant transport in surface water is, relatively speaking, immediate, while in the subsurface it is, generally speaking, very slow. This means, that although there is active groundwater contamination below a waste site, it can take many years before it re-occurs at surface some distance away from the site. This further means, that the monitoring requirements for the subsurface are unequivocally long-term