Improved site characterisation of contaminated land using pump-and-treat data

This paper presents findings from the back-analysis of a pump-and-treat operation for a site polluted with tri-chloroethylene (TCE). The groundwater extraction system had been installed to remove the historic spillage from a housing estate in the southern Dutch City of Tilburg. The spillage originated from a textile factory formerly located at the site. Over a period of seven years, continuous pumping of groundwater had failed to reduce significantly the annual extraction of TCE. As a result, the City of Tilburg was faced with ongoing remediation costs combined with concern over the full extent of pollution at the site and the long-term commitment for groundwater pumping. Between 1989 and 1996, the pump-and-treat system extracted approximately 4400 kg of TCE, with 570 kg of TCE being extracted in aqueous solution alone in 1996. Stagnation of the pump-and-treat operation led the municipal authorities of Tilburg to commission a feasibility project that would interpret the seven years of groundwater monitoring data and provide a better understanding of the nature and extent of pollution beneath the housing estate. A three-dimensional groundwater model was developed for the site using the two finite difference programmes MODFLOW and MODPATH. The model linked changes in the direction of the groundwater flow caused by variations in pumping rates with fluctuations in the aqueous concentration of TCE recorded from monitoring wells. This enabled the remediation strategy to be refocused by either limiting the extraction of groundwater to the main source of pollution or to enhance the recovery of the pollutant using steam injection