The effect of industrial pollution on groundwater quality

Groundwater has one property that sets it apart from every other part of the environment: it responds late, and for a long time gives no signal at the surface. Contamination that entered the ground years ago may be crossing the property boundary right now — and nobody will notice without measurement.

How pollutants get in

• Infiltration from the surface — leaks, spills, poor storage of substances, run-off from manoeuvring and loading areas.
• Leaking underground installations — tanks, pipelines and separators whose condition is hard to assess without testing.
• Landfills and waste storage — leachate passing through permeable layers.
• Industrial wastewater — discharged contrary to permit or with a composition different from the one declared.

What we find most often

Samples of water and soil are analysed primarily for petroleum substances and heavy metals — mercury, lead, cadmium, zinc and arsenic. Added to these are chlorinated solvents, typical of metalworking plants and dry cleaners, and salinity, characteristic of mining and chemical industries.

Each group behaves differently in the ground. Petroleum substances, lighter than water, accumulate on the water table; chlorinated solvents, heavier, sink to the base of the aquifer. That distinction determines the depth at which a sample must be taken — which is why sampling points cannot be chosen at random.

Effects on the aquatic environment

Organic pollutants reduce dissolved oxygen, which directly affects the aquatic microflora responsible for natural self-purification. Heavy metals accumulate in organisms and bottom sediments, from which they can be released for years after emissions have stopped. Salinity changes the species composition of aquatic communities, including in surface waters fed by groundwater.

How it is detected

The basis is a network of piezometers placed with regard to the direction of groundwater flow, always with points upgradient and downgradient of the potential source. Samples are taken cyclically, to capture a trend rather than a single reading.

It is worth remembering that a local groundwater monitoring network is not mandatory equipment for every industrial facility — its scope follows from specific administrative decisions and can often be optimised. See environmental monitoring. Analyses are carried out with an accredited laboratory, because only such results carry evidential weight.