A modelling approach to determine the origin of urban ground water.

A simple modelling approach was developed to link patterns of urban land-use with ground water flow and chemistry in three dimensions and was applied to characterize the origin of recharge in the aquifer beneath the old industrial city of Nottingham, UK. The approach involved dividing land uses into types, and times into periods, and assigning the recharge from each an individual tracer-solute with a unit concentration. The computer code MT3DMS was used to track the multiple tracer-solutes in transient, three-dimensional simulations of the important urban aquifer. A depth-specific hydrochemical dataset collected in parallel supported the model predictions. At depth under the industrial area studied, a large component of ground water originated of older agricultural origin, with relatively low nitrate concentrations. Shallower ground water originated mainly from residential and industrial areas, with higher nitrate concentrations probably arising from leaking sewers and contaminated land. The results highlighted the spectrum of ground water from different origins that amalgamate even at short well screens in a non-pumped borehole and remind us that the non-point-source pollution of ground water from anthropogenic activities will involve more years of slow degradation of quality.

Microbial contamination of two urban sandstone aquifers in the UK.

Development of urban groundwater has historically been constrained by concerns about its quality. Rising urban water tables and overabstraction from rural aquifers in the UK have led to a renewed interest in urban groundwater, particularly the possibility of finding water of acceptable quality at depth. This study assessed the microbial quality of groundwater collected from depth-specific intervals over a 15-month period within the Permo-Triassic Sherwood Sandstone aquifers underlying the cities of Nottingham and Birmingham. Sewage-derived bacteria (thermotolerant coliforms, faecal streptococci and sulphite-reducing clostridia) and viruses (enteroviruses, Norwalk-like viruses, coliphage) were regularly detected to depths of 60 m in the unconfined sandstone and to a depth of 91 m in the confined sandstone. Microbial concentrations varied temporally and spatially but increased frequency of contamination with depth coincided with geological heterogeneities such as fissures and mudstone bands. Significantly, detection of Norwalk-like viruses and Coxsackievirus B4 in groundwater corresponded with seasonal variations in virus discharge to the sewer system. The observation of low levels of sewage-derived microbial contaminants at depth in the Triassic Sandstone aquifer is explained by the movement of infinitesimal proportions of bulk (macroscopic) groundwater flow along preferential pathways (e.g., fissures, bedding planes). The existence of very high microbial populations at source (raw sewage) and their extremely low detection limits at the receptor (multilevel piezometer) enable these statistically extreme (microscopic) flows to be traced. Rapid penetration of microbial contaminants into sandstone aquifers, not previously reported, highlights the vulnerability of sandstone aquifers to microbial contamination.