| dc.description.abstract | Until the seventies storage of toxic pollutants in The Netherlands was (and in some countries still) done carelessly. The chemicals were often dumped in landfills which were designed for domestic waste. This carelessness has led to many soil contaminations which form ecological and human risks for the direct environment. Nowadays, governments and companies are therefore obliged to remediate such historic contaminations. Remediation of chemical landfills is often done with unsustainable techniques such as, wastemining (excavation, sorting and relocating or incinerating) or complete isolation.
In this study the feasibility and efficiency of a draining trench for the remediation or stabilization of a groundwater contamination, in this case from a chemical landfill, is studied. Essential for this study is the value which organic material (peat or green compost) could add to this remediation concept, named the adsorption drain. This technique could form a sustainable and cost effective solution for locations were other techniques prove to be too expensive.
For this research, hydraulic conductivity (column) and adsorption (batch) experiments have been done on five types of peat and green compost. Peat type 05 and green compost were selected for further research, because these materials seemed to have the highest potential for application in the adsorption drain (trench). Additional adsorption experiments (batch and column) were conducted on the materials. Benzene was selected as contaminant, because benzene is a critical pollutant in groundwater plumes (also in the landfill leachate of Zeeland). Benzene is therefore a determining pollutant for the success of the adsorption drain.
From the results of the column and batch experiments a retardation factor between 3.84 and 4.9 is found for peat 05. This corresponds to a Kd value between 22.9 and 31.1 l/kg for adsorption of benzene to peat 05. The retardation factor and Kd value of green compost showed a larger variation, because benzene seemed be more adsorbed during the column experiments. A retardation factor between 2.84 and 4.4 is found for green compost, which corresponds with a Kd value between 3.49 and 6.45 l/kg.
A MODFLOW groundwater model was used for a sensitivity analysis concerning the working of the adsorption drain. The interception depth of the trench and the residence time of groundwater in the trench are the most important properties for the remediating effect. The goal of the model was to demonstrate the influence of different hydrological parameters on these properties. It is shown that mainly the drain bed resistance and the drain discharge influence the residence time. The natural groundwater flux is the most important factor regarding the interception depth for a specific drainage discharge.
The roll of biodegradation in the adsorption drain is only appointed and estimated in this study. Future research should show if organic material, used as in the adsorption drain, could stimulate biodegradation in the adsorption material and in the surface water.
In general it could be concluded that the feasibility and efficiency of a remediation with an adsorption drain (trench) depends mainly on the local hydrological- and contaminant situation. Shallow pollutants in slowly flowing groundwater are desirable when such a system is applied. This implies that the drainage of the trench can be low which increases the lifespan of the organic material that is used as adsorption medium. Besides that, benzene retardation for the studied materials appeared lower than expected. This is probably caused by the low specific surface and low organic carbon content of green compost and the relatively low density of peat. Relative little organic carbon per volume peat is available, due to the low density. The adsorption capacity and therefore the lifespan of organic material as adsorption medium will however be larger for contaminants with a higher partitioning coefficient than benzene. | |
