Installation Date:
10/1999

Contaminants:
Polycyclic aromatic hydrocarbons (PAHs), Phenols, Benzene-toluene-ethylbenzene-xylene (BTEX), Total petroleum hydrocarbons, Trichloroethene, cis-1,2-Dichloroethene

Reactive Media:
Activated Carbon

Cost:
$750,000

Construction:
Adsorptive Reactors with Hydraulic Barrier

Point of Contact:
Peter Niederbacher
Engineering Consultant for Technical Geology
Tel: 43-2243-22844
Fax: 43-2243-22843
Email: niederbacher@
geol.at
Weidlinger Strasse 14/3
A 3400 Klosterneuburg
, Austria Austria

A full-scale permeable reactive barrier (PRB) system was installed at the site of a former tar plant and linoleum production plant in Brunn am Gebirge, Austria in 1999. The system of adsorptive reactors combined with a hydraulic barrier was designed to adapt to the landscaping and architecture of a business park, fit into the local environment, be operational within a restricted time frame, and cost far less than excavation and disposal. Polynuclear aromatic hydrocarbons (PAH), phenoles, benzene, toluene, ethylbenzene, xylene (BTEX), hydrocarbons (HC), tricholoroethylene (TCE), and cis-dichloroethylene (cDCE) are the contaminants of concern at the site. Investigation indicated contamination of the unsaturated and saturated zone with maximum concentrations of 8.6 mg/L for PAH, 0.34 mg/L for phenoles, 29 µg/L for benzene, 50 µg/L for toluene, 6.6 mg/L for HC, 0.8 µg/L for TCE, and 27 µg/L for cDCE. The total area involved is greater than 376,600 ft².

The site is located near the western edge of the southern Vienna Basin, a pull apart Alpine structure filled with tertiary sediments. The general profile shows 0-7 ft of anthropogenic deposits on top and alluvial sediments (sandy silty gravel) 10-20 ft thick. These sediments are underlain by shales of the mid Pannonian age with intercalations of coarser layers in which artesic water occurs. The top of the tertiary sediments shows a relief, roof-like dip from east to west, a north-south oriented erosional depression, and a rising shoulder toward the east where the confining layer reaches the surface. The ground-water table is 7-13 ft below ground surface (bgs). The base of the aquifer is 10-20 ft bgs. Tests indicated permeabilities ranging from 9.8 × 10^-3 to 3.3 × 10^-5 ft/s. The natural ground-water flow is west to east with a bend to the southeast, following the erosional depression. This causes a migration of contaminants outside of the property's boundary.

In order to accommodate a ground-water pond planned at 5 ft below the actual ground-water level and avoid polluting the pond, a site-adapted solution was developed. It called for the installations of four adsorptive reactors filled with a total of 23 tons of activated carbon combined with a hydraulic barrier 2-5 ft thick. The west to east directed 720 ft long jet grouting barrier cuts into the shoulder of tertiary shales at its eastern edge. This forms an L-shaped barrier which keeps contaminated ground water separated form the catchment area and the artificial pond. The adsorptive reactor units are located close to the barrier. Four wells 9 ft in diameter and 26-30 ft deep were drilled to install the filter units. The base of the wells are several meters into the confining layer. The filter units are made of cylindrical glass fiber fortified synthetic material with filter windows at the aquifer level. The activated carbon is 350-420 ft³ in each filter. The contaminated water enters the reactor through filter windows, passes the reactor column and is collected at the bottom of the filter cylinder. The outlet of each reactor crosses the barrier and is led to the monitoring and collection shaft. At that point, the level of draw down is controlled by changing the outlet level to the discharge system. Design costs were $100,000. Installation, including construction and materials, ran $650,000.

The system has been effective in causing a significant draw down north of the catchment area, forcing the ground water to enter the adsorptive reactors. The ground-water flow was induced to reverse direction by 1800 on the way to the filter units. The levels of contamination continue to vary depending on the highs and lows of the ground water and probably as a result of the general draw down of the ground-water level. A uniform trend cannot be observed at this time. However, it is expected that the level of contamination will decline as a result of natural attenuation. Water samples are taken at both the intakes and discharges of the reactors and at the monitoring wells quarterly. The water level is controlled by sensors and wireless transmissions and control measurements are taken manually. An additional investigation of the long term behavior of the system is performed as part of the PEREBAR Project of the European Community.

Lessons Learned

Protecting the system from O₂ entering into the ground water helps avoid aerobic microbiological activity. Careful selection of materials for those parts which come into contact with the ground water and reactor material is essential.

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