Adrian R. Lawrence

Groundwater in urban development : assessing management needs and formulating policy strategies

People have clustered at the waters edge throughout civilization for the most fundamental of reasons: without water there is no life. Every major city in the world has a body of water or aquifer nearby, since rivers and lakes predetermined where people would gather and dwell, groundwater constitutes about 98 percent of the fresh water on our planet (excepting that captured in the polar ice caps). This makes it fundamentally important to human life and to all economic activity. Groundwater resources in and around the urban centers of the developing world are exceptionally important as a source of relatively low-cost and generally high-quality municipal and domestic water supply. At the same time, the subsurface has come to serve as the receptor for much urban and industrial wastewater and for solid waste disposal. There are increasingly widespread indications of degradation in the quality and quantity of groundwater, serious or incipient, caused by excessive exploitation and/or inadequate pollution control. The scale and degree of degradation varies significantly with the susceptibility of local aquifers to exploitation-related deterioration and their vulnerability to pollution. Management strategies need to recognize and to address the complex linkages that exist between groundwater supplies, urban land use, and effluent disposal. Groundwater tables have become the focus of keen interest in recent years, as the supplies of water underlying urban areas have dwindled and deteriorated, threatening the millions of people who live above. When conditions are right, aquifers refill regularly from infiltrating rainfall and runoff, although sometimes with a substantial time lag. But those favorable conditions are severely altered when the ground above is overbuilt.

A method for determining volatile organic solvents in chalk pore waters (Southern and Eastern England) and its relevance to the evaluation of groundwater contamination

Abstract Conventional methods of sampling groundwater in Chalk aquifers sample the mobile water in the fissures only and not the non-mobile water held in the microporous matrix. However, the microporous matrix can play an important role in modifying groundwater quality by attenuating contaminant migration through diffusion exchange and, in the long term, by acting as a reservoir for contaminant retention. A method for extracting and analysing chalk pore waters for chlorinated solvents has been developed. Chalk pore water-depth profiles at the site of a spillage of tetrachloroethene demonstrated that the immiscible phase of the solvent had migrated to depths of 50 m, producing solvent concentrations in the matrix pore waters of up to 40,000 μg L −1 . In addition, the pore water-depth profile indicated that the immiscible phase had ponded upon a less permeable horizon within the Chalk aquifer at shallow depths.

Pesticides in groundwater: some preliminary results from recent research in temperate and tropical environments

Abstract The paper summarizes the preliminary results of field investigations of pesticide behaviour in the UK, Barbados and Sri Lanka. Field observations of groundwater pesticide concentrations in these studies range up to 100 µgl−1, but are more commonly less than 5 µgl−1. The risk of pesticide concentrations in pumped water reaching 10 or 100 times guideline values from normal agricultural use at recommended application rates is probably small. Simple laboratory determinations of degradation rates support earlier studies and general considerations of subsurface environmental conditions in suggesting that pesticides are likely to be more persistent in groundwater than in soils. Simple modelling of the saturated zone movement of pesticides towards wells indicates that concentrations in pump discharge are highly sensitive to aquifer porosity, pesticide half-life and extent of cultivated area. The greatest risk to groundwater from normal usage of pesticides in agriculture will occur where persistent compounds are applied over aquifers which are shallow, permeable and thin, and overlain by permeable soils.