The importance of understanding groundwater flow history in assessing present-day groundwater contamination patterns: a case study

Abstract

Abstract Locating and delineating suspected or known groundwater contamination is often a difficult and costly task. Prior to drilling the first borehole or taking the first sample it is standard practice to undertake a desk study. This is likely to involve investigating the history, geology and hydrogeology of the site. Often, only present-day groundwater flow patterns are used to assess the current situation and plan a site investigation. This paper uses a recent experience to illustrate the importance of understanding the history of groundwater flow in planning a successful and cost-effective groundwater investigation. The site of an old coal carbonization (coking) plant in the UK East Midlands was selected as a field site to undertake research into coal tar related contamination in sandstone aquifers. From the evidence of previous studies, contamination was known to exist in the aquifer, although its exact location and extent was unknown. A comprehensive desk study, extensive surface geophysics and a solute transport modelling exercise were undertaken prior to doing any drilling. Based on the results of this work a number of monitoring wells were installed and samples taken. Results from these initial wells confirmed the original hypothesis. As more wells were completed it became evident that our understanding was not entirely correct and that the evolution and distribution of the contamination was more complex than the initial investigations indicated. Ongoing investigations have revealed a complex groundwater flow and contaminant history. This paper intends to illustrate how limited information can be made to fit and ‘prove’ expectations, whereas in reality an entirely different situation may exist.