Project Name: Ford Motor Company Factory (Barac et al 1999)
Location: Genk, Belgium
Scientists: Tanja Barac (a); Nele Weyens (a); Licy Oeyen (a); Safiyh Taghavi (b); Daniel van der Lelie (b); Dirk Dubin (c); Marco Spliet (d); Jaco Vangronsveld (a)
(a) Environmental Biology, Hasselt University, Diepenbeek, Belgium
(b) Biology Department, Brookhaven National Laboratory, Upton, NY, USA
(c) Ford Motor Company, Genk, Belgium
(d) Ingenieurbetrieb Dr.-Ing. W. PützBrühl, Germany
Date installed: 1999
Number of trees/ species installed: 275 Populus trichocarpa x deltoides cv. “Hoogvorst” and “Hazendans”
Amendments: Soil mixed with compost and backfilled into boreholes
Contaminant: Hydrocarbons: BTEX, TPH
Target Media & Depth: Groundwater at 4-5 meter (13-16.5 foot) depth
Underground storage tanks at a Ford Factory in Genk Belgium were found to be leaking solvent and fuel into the ground since the 1980’s. Contamination resulted in 4-5 meter (13-16.5 foot) deep groundwater laden with BTEX, fuel oil as well as nickel and zinc. The leaking tanks were removed and above ground replacements were constructed. A conventional pump and treat system was installed at the core of the plume and ran 23 hours a day. However, the plume was still migrating. A phytoremediation scheme was installed to halt further migration of the contamination plume by providing hydraulic containment.
The phytoremediation installation began in April 1999 and consisted of 275 hybrid Poplar trees (Populus trichocarpa x deltoides cv. “Hoogvorst” and “Hazendans”). Poplars were chosen based on their high evapotranspiration capacity to target the migrating groundwater and the individual cultivars were selected based on their resistance to fungal disease. The Poplars were planted in a 2 hectare (5 acre) zone (75 x 270 meters or 246 x 846 feet), perpendicular to the flow of the contaminated groundwater. 4 meter (13 foot) tall cuttings were placed in 80 centimeter (32 inch) deep boreholes. Soil in the boreholes was amended with compost to supply cuttings with sufficient nutrients, and backfilled. The cuttings were planted 7 meters (23 feet) on center in 9 rows of 30 trees.
By May 2000, 13 months after planting, roots from the cuttings had not reached the groundwater and the contaminant plume. However, after 42 months, in October 2002, the BTEX plume had been “cut off” by the planting installation, where as previously it had extended beyond the factory area and under a nearby highway. In June 2003, 55 months after planting, the plume concentration declined between 50 – 90% in the planting zone. Measurements taken in 2003, after five growing seasons, indicated that the plume had been entirely eliminated from the planted area.
Additional Lessons Learned:
- Because the remediation strategy was successful, preventative phytoremediation buffer plantings of poplar and willows were later planted around above-ground storage tanks and around parking lots on the factory campus, to treat any potential future releases.
- This study also included an examination of endophytic bacteria (living in the plant roots, stems and leaves) and rhizosphere bacteria (living in root zone) in the phytoremediation treatment zone. The presence of the BTEX (Benzene, Toluene, Ethylbenzene, Xylene) plume increased the number of bacteria capable of degrading toluene around the Poplar planting. Laboratory cultures indicated that the bacteria were using toluene as their sole carbon source. Tests outside the treatment zone found fewer numbers of these bacteria. Testing in 2006, after the plume had been completely degraded, found no toluene degrading bacteria inside or outside the treatment zone, indicating that once toluene had been lost as a carbon source, its capacity to be degraded was lost as well. Testing also showed horizontal gene transfer, indicating that DNA coding for toluene degrading abilities was being shared within the microbial population and could be built up and increased over time.