In-situ remediation of TCE contaminated groundwater
Design and Construction of a Horizontal zero valent iron (ZVI) based Permeable Reactive Barrier (PRB) System for the in-Situ-Treatment of Halogenated VOC in Groundwater at the Bernau Site near Berlin
| Country: Germany
| Start Date:
Project Type: Other
| Contract Number:
| Organisation Type:
Contaminated land-->Contaminants-->Chlorinated aliphatics
Contaminated land-->Contaminated land overview
| Project objectives:
PRB, TCE, c-DCE, in-situ, reductive dehalogenation, reductive dechlorination, iron, zero valent iron, LHKW remediation, horizontal reactor
In Germany, substantial experiences and technical improvements are expected from the performance of permeable reactive barriers (PRB) which count for high
efficiency in the passive treatment of VOC-contaminated groundwater. In order to estimate the longevity and efficiency of a granular reactive system consisting
of zero-valent iron (ZVI) under near-in-situ-conditions, a modular pilot plant was set up on the premises of a former dry cleaning facility of the former Soviet
Union army in the town of Bernau (30 km northeast of Berlin) in 2001. The specifically designed horizontal reactor system represents the first German plant
of its kind.
The pilot plant treats contaminated groundwater of two separate TCE plumes: Plume 1 in the upper aquifer reaches a depth of 8 meters below the ground surface
and extends horizontally for more than 500 m. Plume 2 in the lower aquifer reaches a depth of 40 m and extends horizontally for 350 m. TCE concentrations in the
central parts of both plumes range from 75 mg/L to 350 mg/L. Continued spreading of the plume is prevented by a sheet pile wall that encloses the source area.
The reactor is composed of 18 concrete modules, placed in a concrete trench six meters below the ground surface. VOC-contaminated is drawn from within the
sheet pile wall or wells nearby and flows through the modules. Within the modules the contaminants are dechlorinated on ZVI under anaerobic conditions. It
is possible to run the modules parallel or in a row to control the flow length and the treatment duration within the reactor, depending on the specific research
tasks or problems. The purified water is reinfiltrated upstream in the upper aquifer.
The long-term monitoring documented the continuous, very satisfying degradation of more than 99,5% TCE within the reactor. Even varying inlet concentrations
did not influence the degradation performance. Independent of the TCE degradation enduring c-DCE concentrations were detected.
The operation of the ZVI reactor with high flow rates in serial arrangement caused a heavy ferric corrosion in the beginning. In the course of reactor operation
the upper parts of the fill within the first modules were strongly passivated after 15.000 m³ of treated groundwater and 4.000 exchanged pore volumes. Due to
passivating an increasing loss of permeability was observed. Nevertheless the TCE-degradation was still outstanding.
The long-term monitoring results point out, that for the future reactor performance the reactor modules have to be operated:
- with low flow rates
- high TCE-loads.
- combined with subsequent purification on activated carbon to treat the enduring c-DCE concentrations
Beside extended maintenance ranges the optimised use of the complete ferric fill will yield a maximized reactivity.
In 2006 the reactor will be rebuilt and expanded in order to protect and remediate the TCE plume at the site in Bernau. The future reactor performance will allow
not even to monitor the long-term development of VOC-treated ZVI, but also to handle relevant research aspects of decontamination with ZVI in field scale
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Mr Peter Hein
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