NAWaBo: Natural Degradation of Groundwater Contaminants in Sediments

What is the best approach to deal with contamination at the interface between soil and water?

Whether a soil contamination needs to be cleaned up depends on the risks it poses to the environment. A specific example of this is the situation where pollution in the groundwater discharges into the surface water. The question is whether this poses a risk for the quality of the surface water? Bioclear earth helps clients not only with the technical substantiation (what exactly happens to the contamination and how to control the situation), but also with the policy/legal consideration of this situation.

Nature is smarter than you think

A really good thing is, that when a pollutant rises to the surface water it must first pass through the sediment. This usually consists of a sludge layer, a natural reactor vessel containing a collection of natural processes that do not always occur in the soil or surface water itself. These (biological filtering) processes ensure that seepage of groundwater contamination does not always have to cause problems in the surface water. In fact, when the natural processes in a sludge layer work well and break down the pollution, it is better not to disturb this biological system with active measures. If we take too much action, we will in fact be hindering nature’s hard work.

Bioclear earth has a lot of experience in researching and validating natural degradation and sequestration processes in sediments. The validation and application of these processes as (part of the) solution for soil pollution we call NAWaBo: Natural degradation in sediments (Dutch: Natuurlijke Afbraak in WaterBodems). For each location and type of contamination, we design a customized research approach. The research consists of taking samples of groundwater, surface water and the sludge layer, performing various chemical and microbiological analyses on the samples and performing calculations. We show whether the right micro-organisms are present in the sludge to break down the targeted contamination and demonstrate whether degradation actually occurs.


Assessment Natural Discharge into Surface Water

The discharge of soil pollution into surface water is also referred to in the Dutch language as NLO (Natuurlijke lozing op Oppervlaktewater): natural discharge into surface water. The assessment framework for this is not unambiguous, because both the Soil Protection Act and the Water Act and different interpretations of these laws play a role. Because you are dealing with the interface between soil and water, there are always several parties involved in the assessment. That is why, in addition to the technical substantiation Bioclear earth has been thinking along with municipalities and water boards concerning the policy foundation of this solution from the first application of NAWaBo in 2010. Our starting point is that a solution is only good if it is technically, politically and legally correct. If the latter is not self-evident at a location, we bring the parties involved together and guide them to a joint assessment of the best approach or assessment of the situation.

Case study: NAWaBo as Best Available Technology

In 2020, the Dutch Ministry of Infrastructure and Water Management drew up an updated 'NLO Manual' for the assessment of 'discharges' of groundwater pollution into surface water. We were asked to assess a soil remediation project that had been in progress since the 1980s on the basis of the draft version of this manual. In recent years, the active measures at this location had been phased out. The residual contamination and in particular the seepage into a waterway and the natural degradation in the sediment were monitored.

For the purpose of the assessment on the basis of the NLO manual, we have detailed and costed three remediation variants: excavation of the residual contamination, restarting the geohydrological control of the plume and applying NAWaBo. The latter option, which is already in progress today, proved to be the most cost-effective and, moreover, fully complies with the required immission tests. These tests are used to determine whether a discharge has an unacceptable effect on the receiving surface water. In terms of discharge permits, NAWaBo can therefore be considered the Best Available Technology at this location.

In our experience, in most cases a good technical foundation of the effect of NAWaBo is sufficient to substantiate that (additional) remediation of a groundwater contamination is not necessary. In case it is necessary, we can also help you with the design, supervision and monitoring of the required measures, for instance stimulating the natural decomposition of the contamination in soil and sediment.

Are you dealing with a groundwater contamination incident that discharges into surface water? Would you like to know what the effect is on the surface water and whether NAWaBo is sufficient to control the contamination? Please contact Adri Nipshagen or Cirsten Zwaagstra.

Adri Nipshagen
Senior consultant soil
Cirsten Zwaagstra
Consultant soil & water