Residents living around old sand excavation pits saw lorry loads of discarded building site soil disappear in their formerly extremely deep and crystal clear bathing lake. Rusty bicycle wheels and floating polystyrene foam led to concerns. What else was getting into the water? A committee of experts in which ECN participated showed that the concerns were sometimes justified. “We presented a thorough and critical advisory report which was nevertheless generally well received,” says Rob Comans, of ECN Biomass, Coal & Environmental Research. “That was mainly thanks to the committee's efficient way of working. It definitely ought to be followed up.”

Locations where sand was excavated in the past for the construction industry have become lakes which are sometimes more than twenty metres deep and consequently extremely clear and clean. After all, hardly any life is possible in places not reached by sunlight. It is sometimes advisable to make a lake of this kind shallower. This may be for safety reasons, for example; the deep water is so cold that bathers can get cramp and the angle at which edges of the lake extend to the bottom is too steep. There may also be ecological reasons: to create opportunities for plants and animals and to integrate the lake in its surroundings.

Leaching processes
The Soil Quality Decree of 2008 states that in such cases lightly polluted building site soil, sludge and dredge spoil may be used to make the sand excavation pits shallower. The decree also includes statements on the degree of pollution permitted. However, are they sufficient? Surrounding residents, farmers and environmental organisations felt unsure. Questions the Lower House prompted Minister Cramer to establish an independent committee of experts in March 2009 which had to produce an advisory report within two months.
ECN researcher Rob Comans was asked to participate in the expert committee on sand excavation pits because of his expertise on leaching processes. “There's not much of a problem as long as the hazardous substances stay in the soil,” Comans says. “They only present a risk when they become detached from the soil and enter groundwater or surface water. So it's important to know the extent to which a particular substance leaches within a certain period under given conditions.”

Hearings
Comans is enthusiastic about the approach taken by the committee. “We met nine times within five weeks to coordinate our views of the problem from different angles. At the beginning we held a full day of hearings. All the stakeholders attended to express their concerns and wishes to us. We took them very seriously. We also went on a working visit to Mobagat Lake, near Barneveld, where there had been a lot of unrest in the preceding months. Both actions were informative for committee members but the visits also clearly demonstrated to the outside world that we were doing our job carefully.” It was probably partly because of the well-considered approach that the advisory report met with such a positive response when it was received in early June, not only by the minister but also by action groups, the press and the Lower House.
The committee recommends making a distinction between three situations.

Floodplains
The committee believes that the Soil Quality Decree provides sufficient protection for sand excavation pits in flood plains that are flooded by rivers in the winter. In such cases the soil is impacted by slightly polluted river sludge. Surrounding residents are familiar with this and the situation does not deteriorate when the Directorate General for Public Works and Water Management deposits the slightly polluted dredge spoil released by the widening rivers in neighbouring sand excavation pits.

Sand excavation pits
The committee believes that the standards set by the Soil Quality Decree should be made more stringent in the case of sand excavation pits within dyke areas. “Industrial soil may be perfectly suitable for raising the level of roads but the conditions in sand excavation pits are different. With our present knowledge we can't offer a satisfactory guarantee that industrial soil that meets current standards won't result in the level of leaching into groundwater exceeding the level we believe is acceptable,” says Comans. “Take arsenic,” he adds. “We know it's much more mobile in an area with a low oxygen content. Situations like that occur in deep sand excavation pits, where there's less oxygen in the water. So arsenic should only be present at the level of the natural background concentration in the soil being deposited.”

Vulnerable areas
The committee also delineated a category of vulnerable areas, such as those where drinking water is abstracted or where nature conservation depends heavily on the quality of the groundwater. There are no general rules about this and the licensing authority for the area will have to draw up a location-specific assessment. The committee offers guidelines for this.

Bridging function
Besides his job with ECN, Rob Comans is a part-time professor of Environmental Geochemistry at Wageningen University, and he enjoyed participating in the successful advisory project. “The professorship at Wageningen is mainly important because I help develop the latest knowledge about geochemistry and can acquire it myself too. At ECN I make sure that knowledge provides the quickest possible route to solutions for social problems. My role in the committee is a good example of that bridging function. On the one hand, you're concerned with general policy instruments and, on the other hand, with sand excavation pits in locations where very specific geochemical conditions apply. You have to dig deep to expose the fundamental processes and arrive at a solution that's still acceptable in terms of policy. That's precisely what I find interesting and what ECN is good at. And it's worked well here.”

Contact
Rob Comans
ECN Biomass, Coal & Environmental Research
Tel.: +31 (0)22 456 4218
E-mail: Rob Comans

Information
You can read or download the expert committee's extensive report (in Dutch only) here.

Text: Mariette Huisjes

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