Meghan Hodges
Water pollution is a widespread problem that jeopardizes human health. Aquifers, which are underground stores of water, are particularly vulnerable to contamination. Groundwater pollution occurs when harmful substances such as chemicals, waste, and other pollutants make their way into an aquifer, rendering it unsafe for human use. Differences in contaminant concentrations among aquifers can be attributed to variations in geology, hydrology, and human activities. High-volume pumping and irrigation have increased the vulnerability of drinking water supplies to contamination from nitrate, pesticides, and other chemicals. Additionally, irrigation and artificial recharge can cause different types of water to mix, leading to the release of naturally occurring contaminants from aquifer rocks and sediments. The vulnerability of aquifers to pollution is a critical issue, as nearly 40% of Americans rely on groundwater for drinking water.
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What You'll Learn
Pollution from land and water use above ground
Groundwater pollution is a critical issue that jeopardizes human health and the environment. Aquifers, which are underground storehouses of water, are particularly vulnerable to contamination from human activities and natural processes. The parts of aquifers that get the most polluted vary depending on several factors, including geology, hydrology, and human land and water use practices.
Aquifers with direct connections to the land surface or surface water, known as unconfined aquifers, are more susceptible to pollution from land and water use above ground. These aquifers can be rapidly recharged by infiltration or directly from surface water. One example is the Central Valley aquifer system in California, which is vulnerable to contamination due to its permeable and unconfined nature.
Excessive well drilling, for instance, can lead to aquifer pollution and salinization. Improperly constructed or abandoned wells can become pathways for industrial waste, oil, and other contaminants to enter the groundwater. Septic systems and sewers that are not properly maintained are significant threats to water supplies, exposing groundwater to bacteria, viruses, and chemicals.
Agricultural activities, such as intensive farming and the use of pesticides and fertilizers, also contribute to aquifer pollution. High-volume pumping and irrigation practices can alter groundwater flow and increase the vulnerability of drinking water supplies to contamination from nitrate and other chemicals. Additionally, irrigation and artificial recharge practices can cause different types of waters to mix, leading to the unexpected release of naturally occurring contaminants from aquifer rocks and sediments.
Another source of aquifer pollution from land and water use is the discharge of treated and untreated wastewater. Conventional sewage treatment plants only partially remove micropollutants like hormones, pharmaceuticals, and other residues, which can then reach aquifers through infiltration or discharge into local surface water bodies. Similarly, the application of wastewater to land can contaminate aquifers if it is not properly treated and applied in areas where groundwater is shallower than three meters.
The vulnerability of aquifers to pollution from land and water use above ground underscores the importance of effective aquifer management and land-use planning. Implementing protection measures, such as land-use restrictions and groundwater protection zones, is crucial to safeguard these vital water resources from contamination.
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Septic systems and sewers
Septic systems are used by many homeowners for the treatment of wastewater, which then filters into the soil. However, if the system is not properly designed, installed, or maintained, it can contaminate nearby water bodies. Failing septic systems can discharge untreated wastewater, which contains pathogens (e.g. E. coli), nutrients, and other harmful substances directly into the groundwater or surface waters. This can lead to serious health hazards, especially for children and pets.
The impact of failing septic systems is particularly significant when they are in close proximity to each other and to water bodies in environmentally sensitive areas. Proper maintenance and upgrades to septic systems are crucial to preventing contamination of nearby water sources. Homeowners can take various steps to mitigate the impact of their septic systems, although some of these upgrades can be expensive.
In urban areas, sewer networks are critical for protecting the water environment and ensuring public health and safety. However, when sewer pipes deteriorate or leaks occur, wastewater can contaminate aquifers. Unconfined aquifers, where only the lower limit is an impermeable layer, are more vulnerable to pollution than confined aquifers due to their high permeability. Leaky sewers can introduce microbial pollution, as well as chemicals and personal care products (PCPs) into the groundwater.
The vulnerability of aquifers to contamination also varies depending on local geology, hydrology, and human activities. High-volume pumping and irrigation can alter groundwater flow and increase the risk of contamination from nitrate, pesticides, and other chemicals. Additionally, irrigation and artificial recharge can cause different types of waters to mix, leading to the unexpected release of natural contaminants from aquifer rocks and sediments.
Groundwater contamination is a serious issue, as it can render aquifers unusable for extended periods and is challenging and costly to remediate. Preventing and mitigating pollution of aquifers is crucial to ensure the availability of safe drinking water, as groundwater is a vital source of drinking water for millions of people.
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Industrial waste and oil
Mining operations, for instance, often involve dewatering, where groundwater inflows are pumped out to access mines. This practice can lower the water table and potentially contaminate nearby aquifers. Acid mine drainage, caused by water coming into contact with sulfide-rich materials, is another concern. It can persist long after mining has ceased and contains toxic metals that can enter the groundwater system.
Oil and gas extraction activities, such as hydraulic fracturing, require large amounts of water and can contaminate aquifers. The use of chemicals and the high water intensity of these processes pose significant risks to groundwater quality.
In addition to extraction industries, other industrial activities contribute to aquifer pollution. Industrial waste disposal sites, particularly those located near sand and gravel aquifers, pose a high risk of widespread contamination. Leaks and spills of petroleum products and industrial liquids can directly pollute groundwater sources.
Furthermore, industrial wastewater discharges can contain metals, solvents, and toxic sludge, which can infiltrate and contaminate aquifers. The improper disposal of hazardous materials and chemicals by industries can also lead to groundwater pollution.
The slow movement of groundwater makes it challenging to detect and address pollution promptly. Once an aquifer is contaminated, it may remain unusable for extended periods, and the contamination can spread to nearby water bodies. Preventing industrial waste and oil pollution in aquifers is crucial due to the challenges and costs associated with remediation.
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Pesticides and fertilisers
Pesticides are chemicals designed to kill pests, including insects (insecticides), weeds (herbicides), and fungi (fungicides). They are often applied to soil as granules or drenches to control pests and help plants grow. However, their overuse and misuse can lead to water contamination and harm the environment and human health.
Pesticides can enter water bodies through point sources, which originate from fixed sites such as chemical runoff during improper storage, loading, or disposal, as well as the misapplication of pesticides to water bodies. Point sources of pesticides include pesticide manufacturing plants, mixing-and-loading facilities, spills, wastewater recharge facilities, waste disposal sites, and sewage treatment plants. Nonpoint sources, on the other hand, are diffuse and widely dispersed, such as pesticide application on agricultural fields or residential landscapes, where they can seep into the groundwater below.
The solubility of pesticides plays a crucial role in their ability to contaminate water. Water-soluble pesticides are more likely to leach into the groundwater, while those that degrade quickly or bind strongly to soil particles are more likely to be retained in the upper soil layers until they break down into non-toxic by-products. The time lag between pesticide application and their arrival at a water source, such as a well, is important to consider when managing groundwater quality. This time lag is shorter with increasing aquifer permeability and decreasing depth to water.
Pesticides have been detected more frequently in surface waters than in groundwater, with some pesticides found above critical thresholds, posing potential harm to the environment and human health. In Europe, for example, the Water Framework Directive (WFD) sets environmental quality standards for pesticides in surface water, and the Groundwater Directive sets a precautionary quality standard of 0.1 µg/L for pesticides in groundwater.
Fertilisers, when overused or misused, can also contribute to water contamination. They can enter waterways and degrade water quality, leading to potential health risks, especially for young children. Like pesticides, fertilisers can filter through the soil and contaminate groundwater used for drinking.
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Pharmaceuticals
A study of 20 public wells in a sand and gravel aquifer found that 15 wells contained at least one organic wastewater compound (OWC), with antibiotics and perfluorosurfactants being the most frequently detected chemicals. The concentrations of these pharmaceuticals were correlated with the extent of unsewered development in the surrounding area, indicating that septic systems are a primary source of OWCs in groundwater.
Another study by the US Geological Survey detected PFAS ("forever chemicals") in 20% of private wells and 60% of public wells sampled across 16 eastern states. PFAS contamination has also been found in drinking water wells in the Ohio Valley and New England regions, with levels in a West Virginia well reaching 1,500 parts per trillion (ppt), significantly exceeding health advisory limits.
The vulnerability of aquifers to pharmaceutical pollution varies, with unconfined sand and gravel aquifers being particularly susceptible due to their vulnerability to contamination from septic systems and wastewater treatment plant effluent. However, it is important to note that the debate around aquifer vulnerability is ongoing, with hydrogeologists discussing whether vulnerability should be assessed generally or specific to each pollutant.
The presence of pharmaceuticals in aquifers has become an increasing concern due to the massive increase in their consumption worldwide. Conventional treatment plants often struggle to remove these emerging contaminants, leading to ongoing research into new techniques such as mycoremediation and bioremediation systems.
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Frequently asked questions
Aquifers can be polluted by a variety of factors, including leaking sewers, pesticides and fertilisers, waste from landfills, industrial waste, and septic systems.
Unconfined aquifers, such as the Central Valley aquifer system in California, are especially vulnerable to contamination. Shallow groundwater is also more susceptible to pollution, as it can be moved deeper into drinking water supplies by irrigation and pumping.
Groundwater can move great distances through unseen aquifers, spreading contamination far from the original source.
To avoid aquifer pollution, governments often implement regulations to control the storage and use of hazardous materials and pesticides. Individuals and businesses must also cooperate to keep groundwater sources clean.
