MANAGING AND PROTECTING GROUNDWATER QUALITY IN RAPIDLY GROWING URBAN AREAS

Keeping cities healthy and sustainable represents a major challenge for the 21st century. In the US, recently published data suggest that impermeable surfaces - roads, parking lots, roofs etc. - are expanding rapidly and will soon be equal in size to the state of Ohio. Worldwide, 3 billion people live in urban areas and this number will likely double within 50 years. Fortunately, the science of urban groundwater has progressed significantly during the past 40 years with major improvements in our understanding of the urban water balance, shallow subsurface flow and contaminant pathways. Good progress has also been made in the areas of contaminant source characterization, recharge management and methods for the containment and disposal of urban waste. The task ahead is to maintain this momentum while ensuring advances in the science are adequately incorporated into the urban planning process. Cities that rely on groundwater as a source of drinking water are well aware of the potential threats posed by urbanisation. Key problems include contaminated wells and springs due to a multitude of pollutant sources, and rising groundwater levels due to leaking water distribution networks. Unfortunately, the message is fast becoming clear that maintenance of healthy, vibrant cities requires us to manage and protect urban groundwater whether or not it represents a drinking water resource! This is a major departure from traditional thinking and has important implications for every city on the planet! Toronto, Canada is a classical example of a city dependent on surface water that chooses to ignore looming groundwater problems. Groundwater beneath the city is seriously contaminated due to decades of road salt use. Yet, despite evidence that groundwater levels are rising locally and that groundwater-receiving wetlands, springs and rivers are being degraded, the city has no groundwater monitoring program, let alone a program for groundwater management and protection. That said, the popular vulnerability index approach to groundwater protection holds little practical value in most urban groundwater situations. Thus, a primary goal of ongoing research is to develop quantitative techniques for groundwater protection that give due consideration to contaminant loadings, groundwater fluxes and pre-existing groundwater quality.