Catchment-scale (>40 km2) contamination of the Chalk aquifer of Hertfordshire by bromate, emanating from a disused industrial site north of St Albans, represents the largest occurrence of point-source groundwater contamination in the UK. The influences of ‘double porosity’ diffusive exchange and rapid transport along solution-enhanced conduits complicate predictive modelling of contaminant transport to threatened public supply wells. Tracer testing indicates that solution-enhanced flow routes exist beyond the surface distribution of dissolution features in Hertfordshire, more extensively than previously thought. A quantitative conceptual understanding of this flow system has been incorporated into a spatially distributed equivalent porous media representation in MODFLOW and MT3D-MS. The calibrated model reproduces essential features of the aquifer system, including heads and flows, seasonal responses, and the timing and spatial distribution of observed tracer breakthroughs in the solution-enhanced aquifer, but does not fully capture the magnitude and form of tracer and bromate advance. Due to the influence of local solution enhancement and matrix effects, detailed breakthroughs at receptors cannot be resolved at the coarse grid scale. However, the model is able to simulate general trends.
Bromate (BrO(3)(-)) is a disinfection by-product formed during ozonation of potable water supplies containing bromide (Br(-)). Bromate has been classed by the World Health Organisation as a 'possible human carcinogen', leading to implementation of 10-25 microg L(-1)(as BrO(3)(-)) drinking water limits in legislative areas including the United States and European Union. Techniques have been developed for bromate analysis at and below regulatory limits, with Ion Chromatography (IC) coupled with conductivity detection (IC-CD), post-column reaction and ultra-violet (UV) detection (IC-PCR), or inductively coupled plasma-mass spectrometry detection (IC-ICPMS) in widespread use. The recent discovery of bromate groundwater contamination in a UK aquifer has led to a requirement for analysis of bromate in a groundwater matrix, for environmental monitoring and development of remediation strategies. The possibility of bromate-contaminated water discharge into sewage treatment processes, whether accidental or as a pump-and-treat strategy, also required bromate analysis of wastewater sources. This paper summarises techniques currently available for trace bromate analysis in potable water systems and details studies to identify a methodology for routine analysis of groundwater and wastewater samples. Strategies compared were high performance liquid chromatography (HPLC) with direct UV or PCR/UV detection, IC-CD, IC-PCR, and a simple spectrophotometric technique. IC-CD was the most cost-effective solution for simultaneous analysis of bromate and bromide within groundwater samples, having a 5 microg L(-1) detection limit of both anions with limited interference from closely-eluting species. Wastewater samples were successfully analysed for bromate only using HPLC with PCR/UV detection, with detection limits below 20 microg L(-1)(as BrO(3)(-)) and low interference. HPLC with direct UV detection was unsuitable for bromate analysis within the concentration range 50-5000 microg L(-1) which was required for this project, but column choice was shown to be a major factor in determining limits of detection. Spectrophotometry could not reproducibly determine bromate concentration, although the technique showed promise as a quick field method for high-level groundwater bromate analysis.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.