Tracertest to determine the groundwater flow regime between injection wells and CMT monitoring wells at the former dry cleaner Ferster
Under the building of a former dry cleaner a spatially limited contaminant source zone of chlorinated hydrocarbons was detected. Following the results of an intensive site investigation a source zone remediation using nano-iron was conducted in 2007. The aim was to reduce the source strength in order to cease the groundwater remediation that is operated since almost 10 years within the next years.
In order to evaluate the results of the nano-iron remedy VEGAS was asked to conduct a tracer test to investigate the hydraulic flow regime between the nano-iron infiltration wells and the downstream located CMT monitoring wells. The tracer test lasted from March 2009 until end of July 2009.
In the beginning the tracer infiltration wells and the infiltration level was selected using short time pumping tests and the method of borehole dilution. A fluorescent dye (uranine) was used. The vertical tracer declination profile was detected using optical fibres and fluorescence measurement devices (fluorometer). During the tracer test the uranine was infiltrated two times with different concentration along the selected level as a Dirac-pulse and a time offset of several weeks. To detect the tracer small scale fibre sensor tips were located in the filter screen sections of the CMT monitoring wells. The lengths of the fibre optical sensors ranged between 10 - 30 m. In order to detect the tracer in the nearby region of the CMT filter screens groundwater was continuously pumped using mini bladder pumps.
In general the investigations confirmed the groundwater flow direction according the hydraulic head distribution in the field. The hydraulic system was dominated by the operated groundwater capturing and remediation system. The seepage velocity ranged between 0.1 - 0.2 m/d which was significantly lower as predicted from the hydraulic, permeability related calculations. The tracer was detected in the groundwater capturing wells. A mass recovery rate of approximately 50% during 3 months of operation indicates a higher pumping rate to entirely capture the emissions of the source zone.
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AAV Altlastensanierungs- und Altlastenaufbereitungsverband NRW
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