Contaminated groundwater is being extracted and treated above ground. The site owners want to consider enhanced biological degradation as alternative for the long term extraction by groundwater extraction. The motive for reconsideration is the need to replace the water treatment plant and the fact that more effective remediation methods have been developed over the last decade. Two substrates will be tested for their effectiveness at the site for the degradation of CVOC.
The aim of the pilot is to assess whether the groundwater conditions can be optimized for complete anaerobic degradation of CVOC by means of injection of a shock load of substrate. The second aim is to select one of two substrates. With the results of this pilot field study it should be possible to decide if the current practice of groundwater extraction can be stopped and be replaced by enhanced biological degradation.
The site is located in an industrial area, 250 meters south of a river. It has a surface area of approximately 1.1 hectares and is being used by a laundry facility. Soil type is moderately fine to moderately coarse sand above a clay layer at approximately 10 meters below surface. Injection took place in the relative homogeneous sand layer.
Groundwater is contaminated with DCE, TCE, DCE and VC. Under natural conditions, the biological degradation seems to be stagnating at VC; VC is not being degraded to ethene and ethane.
Figure: the remediation site idicated by the red line; picture based on Google Maps image.
Two substrates have been injected: one that dissolves easily (nutrolase) and has a short life time and one oil product (Soya bean oil) that will improve conditions over a longer period. Before and after (9x) injection, monitoring of groundwater has been carried out by analyses of the following parameters that provide information about the migration and effectiveness of the substrates:O2, Eh, EC en pH, bromide, DOC, nitrate, nitrite, sulfate, nutrients, Dehalococcoidesand CVOC, ethene en ethane. At day 119 and day 331 after injection, all parameters have been analyzed or measured in the field, during the other monitoring moments a less extensive set of parameters has been used.
Results show that injection of nutrolase is an effective substrate which provides a good alternative remediation approach.
Base don the result of the pilot study, it is recommended to stop the infinite extaction of groundwater and above ground treatment. Injection of nutrolase enhances the groundwater conditions for anaerobic degradation of the contaminants. Future monitoring during the remediation should not only focus on the contaminants but also on degradation parameters, such as has been applied in this field pilot study. In this way, progress of the remediation project can be monitored.