1.1.03 Permeable treatment walls – underground structures for successful remediation

Groundwater is an especially important and also vulnerable resource for our supply of drinking water. Often only the slightest amount of contamination is enough to render thousands of litres of water undrinkable. In order to dispense with the need to pump contaminated groundwater to the surface for cleaning, researchers in Germany and elsewhere have been intensively focussing on “in-situ” procedures for some years – technologies that can be applied directly in the aquifer. To drive forward new and further development of permeable treatment walls in Germany, the BMBF has been supporting the RUBIN research programme since 2000/2001.

Cleaning polluted groundwater is a complex task. Most remediation procedures involve an active pump-and-treat method, active meaning that the water is pumped to the surface and treated there in downstream plants. This is an extremely expensive process, and as the water is then frequently channelled into the sewer system this results in yet more cost.

Remediation within the aquifer

Recent years have seen intensive work on the development and testing of passive forms of in-situ remediation technology using permeable treatment walls. These are installed in the groundwater flow from the source of contamination to eliminate the pollutants in the aquiferIn the field of hydrogeology, an aquifer (from the Latin words aqua = water, and ferre = to bear or carry) is an underground layer carrying groundwater. Aquifers are also referred to as water-bearing strata. Different types of aquifer are distinguished depending on the individual rock type (and thus the rock’s porosity). itself. A unique new procedure is thus saving costs as there is no longer a need to pump or discharge the groundwater. Two types of technology have been primarily introduced to practical applications: the all-over permeable treatment wall and the funnel-and-gate system, whereby the groundwater is fed via guiding walls (funnel) to a permeable reaction zone (gate).

An all-over permeable wall involves a ditch reaching down to the layers where the groundwater flows being filled with reactive material. Elemental iron or activated carbonCollective name for a group of artificially produced, highly porous carbons with a sponge-like structure. This pure material is characterised by its large specific surface area (up to 300 m2/g). Activated carbon is manufactured from peat, wood, lignite, black coal or nutshells. The materials are first carbonised, during which tiny pores are created. Activated carbon adsorbs organic substances from water and the air and is thus able to clean contaminated water or polluted air. is primarily used for this purpose. The contaminated groundwater flows through the permeable barrier, and the reactive material operates like a filter to remove or break down the pollutants.

The technology involved in permeable treatment walls was primarily driven forward in North America. Germany had little practical experience with treatment walls.

RUBIN – the project

The BMBF-funded research programme entitled Use of permeable treatment walls for site remediation (RUBIN) saw industrial companies and research facilities working closely together in an interdisciplinary fashion at various locations across Germany. The main task was to conduct a detailed, far-reaching and co-ordinated investigation into the potential and limitations as well as the environmental impact and economic viability of permeable treatment walls at a large number of locations in Germany. One key goal of the research programme was to develop generalised criteria for the application of permeable treatment walls, such as

• Layout, design, construction and operation
• Performance and durability (degradation of pollution,
  as well as for mixed contamination/reactor systems
  and reactive reactor filling materials)
• Framework conditions and limitations for use
• Economy (procedural costs) and ecology (environmental impact).

Results for practical application

Projects were conducted at six sites to investigate durability, degradation levels, changes in material, material conversion processes, treatment wall systems, reactor filling materials and monitoring.

Another focus of the work saw employees from the University of Kiel set up and test quality management rules as part of the RUBIN project, with the aim of enabling reliable planning, execution and monitoring of standardised treatment walls in future. Experts from the University of Tübingen also compared the economic efficiency of the methods with conventional remediation procedures. These studies put those using this new technology in a position to carry out an in-depth cost comparison in future.

The quality management rules and economic efficiency observations are, along with the overall results of the programme, integral components of the handbook on the use of permeable treatment walls for site remediation, which presents the key results and findings of the project to interested parties. Created under the guidance of Ostfalia University, the co-ordination site of the RUBIN programme, this handbook is to serve primarily as a general orientation aid for users – e.g. authorities, those in charge of remediation, planners and environmental technology providers.

Scientists conducted further investigations to examine the results and findings at technical pilot facilities, with extensive planning, construction and trials involved. As a result, the technology was able to be rendered marketable and introduced to practical groundwater remediation within Germany. The BMBF funding therefore made it possible to develop a new, more cost-effective and more environmentally friendly method of removing pollution directly from the groundwater – one of the country’s most significant sources of drinking water – ready to put into practice and thus enhance Germany’s status within environmental technology.

Project website http://www.rubin-online.de/english/introduction/index.html

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1.1.04 In-situ treatment wall at Rheine

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1.1.02 Keeping tabs on pollutants