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

This paper presents findings from the back-analysis of a pump-and-treat ope ration for a site polluted with trichloroethylene (TCE). The groundwater ex traction system had been installed to remove the historic spillage from a h ousing estate in the southern Dutch City of Tilburg. The spillage originate d from a textile factory formerly located at the site. Over a period of sev en years, continuous pumping of groundwater had failed to reduce significan tly the annual extraction of TCE. As a result, the City of Tilburg was face d with ongoing remediation costs combined with concern over the full extent of pollution at the site and the long-term commitment for groundwater pump ing. Between 1989 and 1996, the pump-and-treat system extracted approximate ly 4400 kg of TCE, with 570 kg of TCE being extracted in aqueous solution a lone in 1996. Stagnation of the pump-and-treat operation led the municipal authorities of Tilburg to commission a feasibility project that would inter pret the seven years of groundwater monitoring data and provide a better un derstanding of the nature and extent of pollution beneath the housing estat e. A three-dimensional groundwater model was developed for the site using t he two finite difference programmes MODFLOW and MODPATH. The model linked c hanges in the direction of the groundwater flow caused by variations in pum ping rates with fluctuations in the aqueous concentration of TCE recorded f rom monitoring wells. This enabled the remediation strategy to be refocused by either limiting the extraction of groundwater to the main source of pol lution or to enhance the recovery of the pollutant using steam injection.