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Groundwater Contamination and Environmental Authorisation 

The role of groundwater is becoming more important in meeting global water supply needs. Already, 70% of the South African Development Community (SADC) relies on groundwater for their basic needs. Groundwater resources need to be protected from contamination; an increasingly challenging task when considering the rampant population growth rate. Communities, individuals, regulators and industry need to be mindful and diligent in the type of activity undertaken and look toward reducing the impacts imposed on aquifers. Urbanisation, waste disposal, mining, agriculture and other industries all pose a risk to groundwater resources if not properly planned, executed and monitored.  Before any activity is carried out, site sensitivity and contamination assessments should be undertaken to determine whether the activity may pose a risk to the surrounding environment.  

Contamination vs Pollution 

Contamination of groundwater happens when any foreign substance enters the groundwater resource. Groundwater contamination is mainly a consequence of human activities, with a direct link to the unsuitable placement of land-based activities. It is only considered pollution when the contamination occurs at harmful, elevated levels. However, what is not harmful to us may be harmful to the fauna and flora occurring in groundwater dependent ecosystems. The source of contamination is called the hazard. Contamination can occur either as point sources like leaky pipelines, or non-point (diffuse) sources like agricultural runoff or aerosol deposition. It can also be a once-off event like an oil spill, or continuous, like leachate from a landfill occurring over decades.  

What is the Source-Pathway-Receptor Approach? 

Risk is defined as the likelihood of a hazard or contaminant entering the groundwater system, compounded by the level of adverse impacts it may have. The essential part to any risk assessment is understanding the source-pathway-receptor trifactor and how it applies to local groundwater conditions. Once a contaminant enters the environment, it travels along certain pathways through various elements of the environment en route to exposure. The receptor is the living organism – plant, animal, or insect – which suffers the adverse effect of the contaminant directly through consumption or ingestion of contaminated waters, or indirectly through the degradation of groundwater-dependent habitats and ecosystems.  

The fate of a contaminant depends on its own physical and chemical properties, as well as that of the pathway. Some contaminants, such as E.coli, are relatively non-persistent in groundwater and they will die off naturally. Others, like mercury and other heavy metals, may take a long time to degrade naturally and can remain in a groundwater system for decades. 

Properties along the pathway can offer natural solutions and remedies to contaminants, such as attenuation, sequestration, decomposition, and biodegradation. This is often a useful defence against groundwater contamination. Some of the elements of the pathway that will help to mitigate or reduce contamination risk include: 

  • Terrain – the surface cover, slope and land use will influence the amount of runoff, infiltration and evapotranspiration that occurs. For example, concrete surfaces induce runoff and reduce infiltration, while vegetated surfaces increase infiltration. Certain vegetation types at surface may also aid in natural attenuation of contaminants before reaching the groundwater.  
  • Water flux (recharge) – the amount of water occurring on the surface controls the contaminant load which may enter the subsurface through recharge.  
  • Vadose (unsaturated) zone – the thickness and hydraulic conductivity (the rate at which water moves) of the vadose zone controls the amount of time available for contaminants to undergo natural degradation, attenuation and/or sequestration through natural processes, like plant uptake, or sorption, near the surface before reaching the groundwater.  
  • Phreatic (saturated) zone – the hydraulic conductivity of the aquifer controls residence time of the contaminant, i.e., how long it will take to travel from source to receptor. Higher residence times allow for more natural attenuation, sequestration, and decomposition of contaminants. Groundwater in the aquifer can also dilute or react with contaminants, and confining layers, such as clay, offer further protection if present.  
  • Groundwater flow direction – Contamination plumes will move in the direction of local or regional groundwater flow. If flow direction is away from the receptor, then risk is reduced.  
  • Geology – the geological composition of the aquifer material will play a role. Certain lithologies like clay offer a physiochemical “buffering capacity” to contaminants, while other lithologies, such as sand, offer little resistance to contamination but can aid in dispersion and dilution.  

We cannot rely on these factors alone to safeguard our groundwater because they only mitigate or reduce risk. We must also prevent risk by putting structural controls in place. These are man-made measures, facilities, or devices that are designed to manage pollution, such as berms and gabions to control flow, or water filters. 

article 5
An illustration of the source-pathway-receptor approach used in groundwater contamination. Sources of contamination can be natural or anthropogenic, they move along pathways through the aquifer, and are received by the groundwater users or consumers. It is important to identify and understand the potential sources, pathways and receptors before carrying out any anthropogenic activity so that pollution of precious water resources can be prevented. 

Why contamination Risk Assessments? 

Since groundwater contamination is mainly a consequence of human activities through land-based activities, Environmental Authorisation is needed before carrying out any human development or activity. We must ensure that we protect ourselves by protecting the environment that we live in. This principle is governed by the National Environmental Management Act (NEMA), No. 107 of 1998.  

Authorisation is gained by carrying out several specialist studies that indicate the impacts of the activity on the environment. The level of investigation and assessment required is site specific because certain areas have certain sensitivities to certain activities. For example, sites in the Cradle of Humankind will have archaeological sensitivities and will require a particular specialist study. Or sites such as the Steenbras Wellfield in the Cape Floristic Region (a UNESCO World Heritage Site) require specialist ecological and botanical studies to protect the endangered flora of the region.  

A look at the Department of Forestry, Fisheries and the Environment’s National Screening Tool 

The Department of Forestry, Fisheries and the Environment has provided the National Screening Tool to help identify and inform on which site specific specialist studies are required across a variety of themes. The tool is free to use and relatively comprehensive, covering themes such as agriculture, animal and aquatic biodiversity, archaeological and cultural heritage, palaeontology, plant species and terrestrial biodiversity, and even themes of civil aviation and defence.  

Although sufficiently geared to identify sensitives of surface water bodies, the screening tool fails to include sensitivities to groundwater systems. The onus is on us, the public and the specialists, to identify when sensitivities to groundwater exists. Rooted in the source-pathway-receptor approach, groundwater contamination risk assessments must be carried out for all activities which generate waste or discharge water to the environment. Typically, a tiered approach is taken for these specialist studies.  

  1. An initial investigation and qualitative desktop study to determine the source-pathway-receptor routes since there may be several. 
  1. Informed by the desktop study, more quantitative site investigations are carried out for site characterisation. 
  1. Further quantitative site investigations, assessment of environmental pathways and evolving contaminant concentrations, with analytical or numerical modelling provides a general risk assessment with comparison to existing international, national or local guidelines and standards.  
  1. A quantitative risk assessment of the evolving contaminant concentrations and how it will be exposed to the receptors and the impacts they will have. This may include recommendations for mitigation, rehabilitation, and treatment methods.  

Higher tiers are carried out if the previous tier indicates that further investigation is required. This general tiered approach is cost effective and time efficient while accounting for both human health and environmental risks. 

Why are contamination assessments important?  

Groundwater contamination assessments, along with other specialist studies that are highlighted through the National Screening Tool, are important to, firstly, protect the environment, and secondly, comply with NEMA. Umvoto can carry out these surface water and groundwater related specialist studies. Through collective efforts, understanding of the contaminant sources and their physiochemical properties, identifying pathways through the environment and who or what the receptors are, and by implementing structural controls, we can help ensure that water quality standards are maintained in a beneficial way for both human and environmental sustainability.  

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