The contamination risk that landfill leachate poses to groundwater can be effectively managed through diligent monitoring practices and timeous intervention. This is becoming increasingly important as the country relies more on precious groundwater resources to supply a growing population resulting in expanding urban areas, which may encroach on landfills, according to SRK Consulting South Africa (SA).
“However, all too often, groundwater monitoring is mainly done just to comply with legislation as opposed to being used to effectively manage the groundwater resource,” said Richard O’Brien, principal environmental geochemist and partner at SRK Consulting SA. “It is essential that groundwater monitoring is conducted scientifically and diligently – and that the data is technically analysed so that any required action can be taken.”
SRK monitors groundwater around landfill sites on behalf of several municipalities and waste-management organisations. This is to provide municipal managers and operators with insight into contamination risks emerging from potential leachate plumes arising from these facilities.
O’Brien emphasised that it is essential for sampling to be performed consistently and accurately to ensure the collection of comparable data of a known quality; the results are then interpreted by experts to detect changes in groundwater chemistry, which could indicate signs of groundwater contamination.
Accurate groundwater sampling
However, collecting accurate samples that represent groundwater as it occurs in an aquifer is not a simple process as it is dependent upon well-maintained monitoring infrastructure. This is not always the case on a typical South African landfill site where monitoring well headboxes are often damaged allowing dust and debris ingress into the monitoring well.
As part of one of the company’s monitoring contracts, SRK Consulting SA is also maintaining monitoring infrastructure to ensure integrity of results. For instance, the accumulation of silt in a well can negatively impact the sample chemistry and restrict sampling depth. The functionality of a monitoring point can be restored as required and well in advance of sampling by removing the silt.
“Use of internationally applicable groundwater sampling methodologies is critical for the collection of representative groundwater samples. Groundwater samples taken from ‘standing water’ which has contact with the atmosphere will undergo chemical changes such as oxidation. As such, they will not deliver an analytical result that accurately reflects the aquifer chemistry,” said O’Brien.
Consistent and comparable results
Another important consideration when monitoring groundwater is sampling depth in relation to the water table.
“When installing the monitoring pump, we ensure that it is positioned in the target zone so that results are consistent and comparable over time. We monitor electrical conductivity, indicating the level of dissolved salts in the water, and measure indicators like pH, redox potential, dissolved oxygen, temperature and drawdown,” he said.
The company executes detection monitoring protocols by diligently collecting samples, testing them at accredited laboratories, and interpreting the results. In this way, municipalities and waste-management organisations can determine if they comply with the parameters laid out in regulatory licenses for landfills, and if operations are impacting groundwater quality and increasing risk.
“This monitoring data also provides insight regarding the evolution of the landfill leachate they generate,” he added. “In this way, we can draw conclusions about the interaction between leachate and groundwater chemistry.”
Broad expertise deployed
An effective monitoring programme requires broad expertise, including sampling technicians and scientists who are, in turn, led by a professional geohydrologist, environmental geologist, or geochemist.
Outside of the landfill context, O’Brien encourages the private sector to also implement sound groundwater monitoring practices – in the interests of compliance and risk mitigation to timeously identify sustainable solutions, if necessary.
“By encouraging a broader water stewardship approach, we motivate clients to glean as much insight as possible from the monitoring process – and then to interrogate the data more closely to generate valuable strategic and operational guidance,” he said.
“There is tremendous value in groundwater data, in terms of understanding and minimising the impact of every industrial operation; and this impact, of course, is the key indicator that all companies should be working to reduce.”
