Rhoonse Grienden is a nature reserve that consists of washland with osier-beds, located in a unique outer-dike tidal fresh water area. From the sixties both domestic and industrial waste, including waste from the petrochemical industry, has been dumped in this area directly along the outside of the river dike. At the end of the sixties this dumpsite was covered with a layer of debris and sediment, and the area was rehabilitated into a nature and recreational area. Until today this design has remained unchanged. In the vicinity of the dumpsite a landscape park may be developed in the future.
Study
Commissioned by the province of Zeeland, ACV started with the preparation towards remediation in 2008. After a supplementary study, which included tests into degradation potential and diffusion behaviour, ACV opted for the ‘natural approach’. This is an approach where the former dumpsite is remediated in the most natural way possible.
ACV set to work on several issues related to the dumpsite:
- An updating study into the ground and groundwater contamination situation in, below and around the dumpsite
- A study into possible effects of the dumpsite on the adjacent Zegenpolder and Rhoonse Grienden
- Bringing in possible solutions for these effects.
The results of the study showed that the dumpsite is severely contaminated with aromatics, oleaginous substances, phenol and cresol. The contamination turns out to be spreading in the groundwater to the adjacent polder ditch.
Remediation vision
Based on the updating study ACV assessed four possible solutions: total excavation, the principle of isolation, management and control (Dutch: IBC-principle) and two natural remediation measures. After assessing the variants on technical feasibility, safety of the dike, sustainability, environmental effects, risks and costs, a natural management of the spread into the Zegenpolder was opted for by means of taking (design) measures. Mid 2010 it will be investigated, in consultation with the parties involved, which (design) measures are the most feasible and affordable. The starting point is: 'the more solid and dynamic the water system, the larger the purifying capacity'.
Relation to environment
In view of the many parties involved and the history, two major aspects in this project were environmental communication and environmental management. This is also related to the future plans for the Rhoonse Grienden. In addition to the dumpsite remediation, the development and design of a 600-hectare landscape park will play a major role. ACV’s role within the environmental management has resulted in acquiring a basis for further development of the proposed vision.