Piraveena Thavendren

Groundwater faces significant challenges, including depletion due to overuse, pollution from various sources, and the impacts of climate change. Over-extraction for irrigation and other uses leads to lower water tables, saltwater intrusion, and even land subsidence. Pollution from agricultural runoff, industrial waste, and improper waste disposal further degrades groundwater quality. Climate change exacerbates these challenges by altering precipitation patterns and increasing evaporation, reducing recharge rates and increasing demand.

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Human activities have a significant impact on groundwater resources, affecting both their quantity and quality. The primary factors influencing groundwater include:

Over-extraction: Excessive withdrawal of groundwater for agricultural, industrial, and domestic use can lead to a reduction in the water table and aquifer depletion. This is particularly evident in areas where groundwater extraction exceeds the rate of natural replenishment, resulting in long-term sustainability concerns, such as land subsidence and reduced water availability.

Agricultural Runoff: Agricultural practices often involve the use of fertilisers, pesticides, herbicides, and animal manure, which can leach into the soil and infiltrate groundwater. This contamination process introduces nitrates, phosphates, heavy metals, and pathogens into the groundwater, leading to eutrophication and compromised water quality. High nitrate concentrations, for instance, can cause methemoglobinemia in infants and may lead to long-term health risks.

Industrial Pollution: Industrial activities, including manufacturing, mining, and chemical processing, can contribute significantly to groundwater contamination. Improper disposal of hazardous waste, leakage of solvents, and the release of heavy metals such as lead, mercury, and arsenic can percolate through the soil and contaminate aquifers, posing severe risks to public health and the environment.

Urbanisation and Land Use Changes: The conversion of natural land cover to urbanised areas, such as cities and roads, reduces the permeability of the ground surface. This reduces natural groundwater recharge, as rainwater is unable to infiltrate the soil efficiently and instead becomes surface runoff. Additionally, urban areas often have infrastructure like sewage systems and septic tanks that can leak pollutants into the groundwater.

Landfills and Waste Disposal: Unlined or poorly managed landfills, septic systems, and waste disposal sites can act as sources of groundwater contamination. Leachate, which is a liquid formed from the decomposition of waste materials, can carry harmful chemicals such as volatile organic compounds (VOCs), heavy metals, and organic pollutants into the surrounding groundwater.

Mining Activities: Mining, particularly the extraction of coal, metals, and minerals, can lead to groundwater contamination through the release of toxic substances such as arsenic, cyanide, and sulfuric acid. Acid mine drainage, for instance, can significantly reduce groundwater pH and mobilise heavy metals, making the water toxic to both humans and aquatic life.

Climate Change: Variations in precipitation patterns due to climate change can alter groundwater recharge rates. More intense rainfall can increase surface runoff, preventing infiltration, while prolonged droughts reduce the amount of water replenishing aquifers, causing further depletion of groundwater resources.

Deforestation: The removal of vegetation reduces the soil's ability to absorb and retain water, thereby decreasing groundwater recharge. The lack of plant cover also increases surface runoff and erosion, resulting in a loss of soil structure and a reduction in the land's capacity to retain water.

Avind and Rajdeep have outlined the chief problems pretty accurately. I'd like to mention a salient consequence of aquifer depletion and dropping groundwater tables (which usually occurs due to long-term unsustainable pumping rates)--(1) more energy is required to pump up groundwater as the water table elevation declines, and (2) the aquifer may be irreversibly damaged due to subsidence/compaction, which may decrease the storage capacity and permeability of the aquifer matrix, resulting in a deeper cone of depression for the same pumping rate, and further requiring more energy to pump up a unit volume of groundwater. Of course, if the groundwater level drops enough, it may drop below the bottom of many wells tapping the aquifer, rendering these wells useless for water supply (this has been and continues to happen for many wells in many aquifer systems thruout the world).