New Focus on the soil remediation of a former gas plant site at Oude Tonge

Before 1969, the year that Goeree Overflakkee was connected to the natural gas network, most municipalities on the island used gas extracted from coal. In 1912 a gas plant was opened at Oude Tonge in order to produce this coal gas. At that time, its main use was as a source for light and it was therefore called “light gas”. Today, the gas plant no longer exists, but the soil of the 1.2-hectares site still bears traces of the past. As a result of the production, the groundwater and the soil are contaminated with substances like thiocyanate, BTEX and PAHs.

In 2015 a partial remediation was carried out to reduce human and ecological risks. Unfortunately, the risk of slow dissemination of the contamination is not yet controlled sufficiently. Therefore, the Dienst Centraal Milieubeheer Rijnmond (DCMR) has commissioned Bioclear earth to study the possibilities of remediating the subsoil on this former industrial site.

The size and mix of contaminants, in addition to the fact that the soil consists of various types of soil (peat, clay and sand) make the remediation of the area a complex challenge. In addition, the site is located close to a flood defence. Taken together, these conditions require an approach that includes removal of the contaminant load and, possibly, multiple (in situ) remediation techniques. In order to achieve this goal, we have considered the most optimal use of biological, chemical and civil technology. Because we are dealing with a complex situation, each of the techniques comes with important failure risks.

A decision matrix assists in making the right choices

In order to provide the Province with a clear picture of the possibilities for remediating the area, we identified four different remediation scenarios. For each scenario, we have made the costs for remediating the subsoil and groundwater transparent. Bioclear earth has also identified the failure risks for each approach and defined a fallback plan. In addition, a number of scenarios for the topsoil have been weighed independently of the subsoil, with the future function of the site being the decisive factor. This resulted in a decision matrix for our clients. For each choice it’s clear what the consequences are, both for the various future development possibilities, the duration of the remediation, and for the costs.

Bioclear earth has identified all the necessary ingredients to make a well-informed decision and formulated a concrete recommendation.

Would you like to know more about the remediation of complex soil contamination? Please contact Jacob Buist.

Jacob Buist
Senio consultant soil & water and energy