Contaminated site Langes Feld

Survey

A total of 1,460m of exploratory boreholes were drilled and 31 pumping tests conducted to determine the thickness of the seal wall. Shafts totalling 1,600m were also created. In addition to this exploratory drilling, chemical analyses and landfill gas tests were conducted as part of the risk assessment.

Securing the existing waste

The area was used as a landfill for decades, with waste deposited in an uncontrolled manner. Anything that was no longer needed was disposed of here, from demolition waste and domestic refuse to materials that would now require separate, specialist treatment. Some of the materials deposited here found their way into the groundwater, or were in the groundwater fluctuation range, which presented an acute risk to the groundwater. It was imperative to remediate the site and secure the waste. This project applied the Vienna chamber system, which offers multiple advantages:

• The chamber system makes it possible to check each individual chamber to ensure it functions properly. This involves raising or lowering the water level in each chamber by several metres above or below the groundwater level over a given period of time. This makes it possible to identify and rectify potential defects.
• Long-term monitoring of the system also makes it possible to observe changes in the permeability of the chamber walls upon construction and in the future. This way, specialists can make informed predictions about its durability.

Seal walls

Two methods were used to construct seal walls in order to minimise water leaching from the enclosed area.

Membrane wall installation

In this method, a heavy steel beam is rammed into the ground using a vibratory hammer. As the piles are extracted, a sealing wall mixture made of bentonite, water, rock flour and cement is injected under pressure into the resulting cavities. This process occurs almost seamlessly, which creates a jointless wall. At the Langes Feld site, we were able to create membrane walls on an industrial scale to depths of up to 33m.

Diaphragm wall installation

These diaphragm walls were installed in two separate cycles using the two-phase technique. In the first phase, the soil is excavated while a pure bentonite slurry is used to stabilise the diaphragm walls.

In the second phase, the support fluid is replaced with the actual diaphragm wall material. The drained bentonite is used to create the separation layer.

It is important to ensure that no leachate escapes from the enclosed area into the surrounding groundwater horizon and deeper-lying aquifers. The dewatering system therefore constantly maintains a potential difference of 50cm between the outside and the inside and between the bottom and the top. The groundwater drawdown required within the landfill site and in the seal wall chambers is achieved using a computer-assisted, fully automatic dewatering system.

Dewatering also takes place between the parallel seal walls. Setting the chamber water levels to 20cm above the landfill water level offers additional protection against leachate. Changes in the quantities to be pumped out are an early indication of defects in the sealing walls, allowing these to be quickly repaired without any leachate escaping.

Technical data

Seal wall area approx. 225,000m², including 186,000m² of membrane wall to a depth of 33m and 39,000m² of diaphragm wall to a depth of 56m. Enclosure length approx. 4,200m, incl. single-walled membrane wall on Markomannenweg. 42 seal wall chambers constructed using the Vienna chamber system with a length of approx. 90m and a width of 5m. 104 chamber level gauges.

Enclosure construction period

Part 1: 06/07/1992 - 01/12/1993

Part 2: 01/08/1996 - 01/05/1997

Once the contaminated site was secured, the area was used as a landfill.

Timeline of remediating an environmental problem child.

In 1990, Altlastensanierung und Abraumdeponie Langes Feld GmbH was founded to remediate Contaminated Site W15: Langes Feld. From 1992, the company remediated the surveyed contaminated site and created a landfill in the area. The seal wall chamber system was completed in 1997. In 2017, the Environment Agency Austria (Umweltbundesamt – UBA) designated the contaminated site as secured.

You can find further information on the UBA homepage at:

https://altlasten.gv.at/atlas/verzeichnis/Wien/Wien-W15.html