Research on the reactive transport of arsenic
At the site Lampertheim-Neuschloss in Hessen the operation of a chemical factory during the last century led to the contamination of the subsurface. On behalf of the HIM ASG, the working group Hydrogeochemistry and Hydrogeology unbiased reevaluated the groundwater contamination with arsenic within the scope of an applied research project. Aim of the investigations was to break down the amount of arsenic bound in depots with new extraction methods, to balance this amount and to evaluate the threat for the ground water with special regard for the waterworks Bürstadt, downstream of the contaminated site.
During October 2009 and June 2011, the branch Rhein-Main of the engineering firm CDM Consult and commissioned specialist companies with scientific support by the University of Heidelberg performed the following inquiries. Groundwater and Sediment samples were taken at the site. The samples were prepared and analyzed at the laboratory of the University of Heidelberg.
- Samples were taken twice at the existing groundwater observation wells.
- Undisturbed percussion drillings and Direct-Push-explorations to take sediment samples and to establish measuring points.
As the working group of Prof. Dr. Isenbeck-Schröter has been working and publishing about projects on the mobility of arsenic in the past, the University of Heidelberg was consulted regarding this question. Besides common analytical methods, specialized procedures were developed and deployed to measure arsenic species. These methods of extraction were aimed to be optimized within this project in Lampertheim.
Chemical binding forms of arsenic are unstable under atmospheric conditions. Therefore, a special treatment was developed and used to preserve milieu conditions in the sediment samples. Accordingly, the samples were prepared in an anoxic environment. Different extraction methods used on the sediment samples were modified and refined.
Key element of the research project was to investigate the mobility of arsenic under various milieu conditions. Thus, eight column experiments were designed, in which artificially mixed test waters were flowing through sediments from the site. Thorough studies of arsenic mobility and the responsible reactions with changing water composition extended the state of scientific knowledge about these reactions.
Mathematical interpolations (application package SURFER) and numerical modeling (PHREEQC and MODFLOW) were used to interpret the results and to predict future developments. Furthermore, through additional programming a newly acquired software was adapted in order to model the transport of arsenic in consideration of the proceeding reactions. This area offers extensive possibilities of development and immersion for the working group, as the used model programs are also useful for other research projects.
This research project provided the opportunity for major parts of a dissertation, two diploma thesis and four bachelor theses. The aim is to publish the results in at least three international, peer-reviewed scientific journals.
Present insights and evaluations show for the study site, that recent state of the art remediation measures or surveillance of groundwater contamination would have to continue indefinitely to fully protect the waterworks downstream of the contamination. Scientific findings of laboratory experiments indicate the possibility do develop an alternative remediation method based on active mobilization of the adsorbed arsenic from the sediment. This method could reduce the duration of remediation measures and thus reduce the arising expenses considerably. It is intended to offer the county of Hessen (represented by the regional council of Darmstadt) a follow-up project for the site Lampertheim. This new remediation approach should be developed within this project through additional laboratory tests and a pilot project at the research site.
Maier M. (2014): Insitu-Mobilisierung von Arsen im Grundwasser durch Phosphat: Prozessstudie und Entwicklung einer neuartigen Sanierungsmethode an einem Altstandort in Hessen, Deutschland / Südwestdeutscher Verlag für Hochschulschriften, ISBN-13: 978-3-8381-5015-4
