This pilot has been carried out in the period April 2007 – December 2008 by TNO BuiltEnvironment and Geosciences (since January 1st 2008 incorporated in Deltares) and a contractor (SITA), in cooperation with a major problem owner in the Netherlands.
Full report available in Dutch (see section Conclusion and Recommendations)
The aim of the HIP pilot is to optimize the chemical oxidation of CVOC.
The following research questions have been answered:
- How do the (geo)chemical composition and heterogeneity of the soil influence the Natural Oxidant Demand (NOD) and effectiveness of the application of Fenton’s and potassiumpermanganate?
- How to choose between Fenton’s reagens and potassium permanganate in order to improveeffectiveness of the ISCO remediation?
- Is it possible to optimize the remediation by separately treat the source and plume of thecontamination?
The location has been used as work station for trains, a cleaning area and storage of paint and oil. At this moment, the location is not being used. The soil and groundwater are contaminated with CVOC.
Until a depth of 15 meters below surface, the soil consists of a sand layer that is interrupted locally by a clay or peat layer. These poorly permeable layers are 0,1 to 1,4 meters thick. Regionally, a loam layer is present at 12 meters below surface. At the study area however, this layer has not been found. According to the regional profile, a poor-permeable clay layer is present at a depth of 135 meters below surface. The groundwater level is about 5 meters below surface.
The remediation is being carried out within the framework of site development. According to the contract of the contractor, the remediation technique is ISCO with Fenton’s reagens and potassium permanganate.
The HIP-pilot has been carried out in addition to the remediation. The study area for the HIP pilot consisted of a small area outside of the source area, within the contour of the soil contamination (according to previous soil research).
The soil and groundwater samples have been analyzed on CVOC. Total Reduction Capacity (TRC) has been determined by measurements of organic matter content and sulphate content. Matrix demand for potassium permanganate has been determined in the laboratory; chemical oxygen demand has been used as a indicator for the NOD for Fenton’s. Besides, groundwater samples were analyzed on carbon isotopes, general chemical parameters and redox parameters.
Natural Oxidant Demand: effect on remediation
Comparison of the matrix demand for the two oxidizing agents and TRC shows that during the CZV experiment 50% of TRC has been oxidized and 25% of TRC has been oxidized by use of permanganate. Due to the higher oxidizing capacity of Fenton’s, the NOD of the soil matrix during oxidation with Fenton’s reagens is twice as high as the NOD during oxidation with potassium permanganate. Besides, the results show differences between soil samples that were treated with the same oxidant. This indicates heterogeneity of NOD of the soil. NOD of clay layers is higher than NOD of sand layers. NOD of the groundwater is negligible compared to NOD of the soil sediment.
Within the study area of this pilot, no indications for the presence of free NAPL in the soil sediment was found. The contamination of the groundwater was less than expected. As a result of the low degree of contamination of the groundwater, the use of oxidant by the soil matrix is relative large compared to the use of oxidant by the contaminant. Because the groundwater will be displaced by the injected liquid, the reaction of the groundwater and the oxidant will only take place at the border of the injected volume.
Degradation of CVOC? Isotope fractionation analysis provide answers
Although sufficient amounts of oxidant (to overcome the demand of the contaminant and the NOD) have been injected during three of the four injection phases, no degradation of CVOC has been proven in the monitoring wells. Both increased and decreased CVOC concentrations have been observed. The lack of isotope fractionation indicates that decreased concentrations are not caused by the degradation of CVOC by Fenton’s reagens or potassium permanganate. The fluctuations of the CVOC concentrations are probably caused by changing groundwater flow directions. At one moment the monitoring well is located within the plume area while at another moment the contaminated groundwater is transported away from the monitoring wells. Laboratory experiments prove that injection of Fenton’s reagens or potassium permanganate cause oxidation of CVOC. The reason that no indications for degradation of CVOC were found in the groundwater in the monitoring wells is probably the insufficient volume of the injections to reach the monitoring wells (primary volume). More data about the groundwater flow direction and flow velocity can provide insight in the secondary radius of influence of the injection volume, caused by groundwater transport.
This HIP pilot provided insight in the reactivity of the soil and optimization of chemical oxidation of aCVOC contamination. Remains of the source can be remediated by ISCO through injection of oxidants. The plume is most effectively treated with a reactive zone (passive approach). If the groundwater is treated in an active way, we recommend several small injection volumes in order to improve the contact between contaminated groundwater and the oxidant that will be transported by the groundwater flow. Due to the instability of Fenton’s reagens compared to potassium permanganate, the latter is more suitable for this approach. It is important to gain insight in the groundwater flow direction and flow velocity. In case the flow direction or velocity is uncertain, regulated flow by pumping activity is recommended.