Soil & Water Pollution: Forecasting Impact

By Annemieke Marsman 13 March, 2015

Dealing with large scale polluted areas is difficult. Dr Marsman shares how megasite modelling makes it easier

Dealing effectively with areas suffering from large scale soil and groundwater pollution appears to be difficult in practice. On the one hand, it is difficult to show the nature and extent of the pollution and the problem owners cannot be traced or held responsible. On the other hand, the public costs of remediation are extremely high and often outweigh the benefits.

“…in the long term, pollution will remain a risk factor for soil use and the quality of groundwater and surface water”

But in the long term, pollution will remain a risk factor for soil use and the quality of groundwater and surface water. Furthermore, legislation sets high quality demands for groundwater systems. At the same time, measures are implemented to guarantee groundwater quality.
For the research project WELCOME, which was financed by the EU, Deltares developed a risk and megasite approach to deal with large-scale pollution problems in a cost effective and sustainable manner.

Case study: the Rotterdam harbour 

The soil and groundwater of the Rotterdam harbour area has become polluted as a result of long term and large scale industrial activities. The pollution is extensive, complex and also has local cross border issues. Dealing with this pollution on a per case basis is not very cost effective. For this reason, Deltares chose a joint megasite approach, as management strategies can then be geared to one another and measures prioritized.

Dealing with extensive pollution on a per case basis is not as effective as a megasite approach

Commissioned by the Rotterdam Harbour Company, we have used our knowledge to develop a megasite approach strategy for the Rotterdam Harbour area, in cooperation with Royal Haskoning, Rotterdam Public Works Department, DCMR Environmental Service Rijnmond, The Ministry of Transport, Public Works and Water Management.

Megasite approach strategy

A more traditional approach shows the pathlines and receptors of separate sources of pollution.

Factoring in the natural resilience of soil & groundwater systems makes it is possible to identify critical pollutants

Our megasite approach goes about it differently, using receptors to gain insight into which sources form an actual threat and the corresponding timeframe. Many pollutants can be biodegraded in the soil and groundwater, given enough space and time. By taking into account the natural resilience of the soil and groundwater system, it is possible to determine which pollutants are critical and should be dealt with.

The megasite approach also makes it possible to combine spatial planning, such as redevelopment of industrial locations, water management and subsoil use with removal of large scale ground and groundwater pollution risks.
Three hypothetical interfaces have been set up for the Rotterdam harbour project to quantify the risk of distribution of pollution to groundwater and surface water. These interfaces are indicated as Planes of Compliance (PoC) and are defined as follows (see image):

• PoC1: interface between harbour area and surrounding surface water;
• PoC2: interface between Holocene (geological timescale from 11,700 calendar years ago and continues to the present¹) and Pleistocene (geological timescale which lasted from about 2,588,000 to 11,700 years ago²) aquifer; and
• PoC3: harbour area boundary.

The risk of exceedance of the legal intervention values for normative pollution can be determined for these PoC’s. Additionally, the effects of possible remediation measures, such as source removal, pump & treat and stimulated biodegradation can be determined.

Tools for transport modelling

Using common solute transport models, such as RT3D (a software for simulating three-dimensional, multi-species, reactive transport of chemical compounds/solutes in groundwater³), would require and enormous calculating capacity because of the size of the total Harbour area. Using these models is therefore not feasible.

Common transport models don’t allow for large scale modelling so Deltares developed their own reactive transport model

Deltares has thus developed a reactive transport model based on stream tube analysis. Regional distribution from individual pollution sources to deep groundwater and surface water can be determined based on flux calculations of this reactive transport model. The calculations take into account soil processes that possibly influence the distribution path of the pollution, such as biodegradation, adsorption on soil particles, density driven flow caused by a variation in salinity and preferential flow through sand poles.

Mitigating uncertainty of pollution sources, geohydrology and biodegradation

A characteristic of large-scale polluted areas is the extent of uncertainty concerning the pollution sources, geohydrology and biodegradation. When determining the risks it is very important to consider these uncertainties.

Large scale polluted areas come with uncertainties
The Monte-Carlo simulation reduces these

However, with the more traditional groundwater model approach this is only partially possible. We have therefore applied the Monte-Carlo simulation. A large number of scenarios is calculated, in which the values of uncertain or sensitive model parameters of every scenario are varied based on the corresponding probability distribution. The variation in the model outcome indicates how large the uncertainty of the model outcome is.
For the Monte-Carlo simulation we have varied the following uncertain and sensitive model parameters:

• Distribution of pollution in the source zones (source characterization, see following paragraph);
• The redox condition dependent biodegradation constant of each substance; and
• The characteristics and effects of sand poles (accelerated vertical distribution).

The distribution of pollution in the source zones and the existing redox conditions have been determined from field measures stemming from regular soil research in the harbour area. The distribution of probability of the biodegradation constant has been listed from literature studies and expert judgements.

Advantages of modelling pollution

The modelling tool clearly defines the risks of groundwater pollution on the receptors like deep groundwater and surface water. It also defines the effects of measures.

The modelling tool clearly defines the risks to ground & surface water and offers substantial cost reduction

Furthermore, for the remediation efforts, a substantial cost reduction is possible compared to the preventive approach of the Soil Protection Act. This is a Dutch act to prevent soil pollution and has a local approach instead of a megasite approach, i.e. Each company has to monitor and take remediation measures to prevent contamination from spreading outside the local area. The cost reduction with the megasite approach is possible by using natural decomposition and possibilities for remediation simultaneously. Only those sources likely to cause a not-acceptable pollution situation outside the area boundaries are remediated.
A specific monitoring programme is still needed to monitor the megasite approach. To conclude, the strategy described and the corresponding model is ideally suited to make a well-founded choice for an effective design of megasite groundwater management.

References

1 -https://en.wikipedia.org/wiki/Holocene

2 – https://en.wikipedia.org/wiki/Pleistocene

3 – https://bioprocess.pnnl.gov/

Further Reading

• Pollution Prevention: What’s The Plan? – The ‘Water Ten’, expected to be released during the National People’s Congress 2015 hasn’t been. So, what’s Beijing’s plan with pollution so clearly on everyone’s mind; though mainly air pollution with “Under the Dome”? CWR’s Dawn McGregor and Hongqiao Liu expand
• Taking The Waste Out Of Wastewater – Caps on water withdrawals & discharge plus gaps between supply & demand mean companies need to reuse water to ensure their water security. Award winning Dr. Matthew Silver and William Dean tells us how Cambrian technology can do this
• Water Source: Who Is Responsible? – Data shows water source quality improving but some experts question how accurate this can be without a specific standard? Moreover, pollutants, ineffective treatment & unclear ministry responsibilities pose threats. CWR’s Hongqiao Liu expands
• Rural Drinking Water Far From Solved – Experts say the Chinese government’s plan to ‘completely solve’ the problem of rural drinking water safety by the end of 2015 is a ‘mission impossible’. Find out why and more as CWR’s Hongqiao Liu expands
• The War on Water Pollution – Premier Li Keqiang has just declared war on pollution. Tan expands on the government’s stratagems & offensives and fundamental changes required to shore up the MEP’s arsenal in order to wage a successful war –
• China Lacks Experience to Clean Dirty Soil – Gao Shengda, from China Environmental Remediation Association, shares his views on soil pollution, the limitations of China’s soil standards and what China needs to do in order to clean its dirty soil
• Pollution: 5 Reasons to Remain Optimistic – Given the recent release of depressing groundwater & soil pollution statistics, Debra Tan gives us 5 reasons to stay optimistic – from changes in the law to water tariff hikes in Beijing