Meghan Hodges
Groundwater pollution is a pervasive and often irreversible issue, with over 80% of the world's population relying on groundwater for survival. Petroleum hydrocarbons (PHs) are a significant contributor to groundwater contamination, with leakages from fuel storage facilities, underground tanks, and pipelines being common sources. This pollution is a serious global issue due to the toxic, mutagenic, and carcinogenic nature of PHs, which can render water sources unsafe for human consumption and threaten public health. The physicochemical properties of PHs determine their movement and ecological toxicity in aquifers, with higher molecular weight fractions often being more toxic. Effective management and remediation strategies are essential to address this critical issue, protect water resources, and safeguard public health and the environment.
| Characteristics | Values |
|---|---|
| Petroleum Hydrocarbons (PHs) contamination of groundwater | A serious global issue |
| Causes of contamination | Unintentional spills, saltwater intrusion, improper management of landfills, injection wells, surface waste ponds, underground storage tanks, application of waste and pesticides on land, pipelines, septic tanks, disposal of radioactive waste, release of acidic drainage from mines, leaks from fuel storage facilities |
| Petroleum Hydrocarbons fractions | Volatile (C6 to C10), Semi-volatiles (C10–C16), Non-volatile (>C16 to C34), Lowest volatile and insoluble (>C35) |
| Impact of contamination | Toxicity, Carcinogenicity, Mutagenicity |
| Remediation approaches | Use of surfactants, Removal of contaminated soil, Controlling local hydrodynamic conditions, Groundwater remediation, Abandonment |
| Preventative measures | Stronger policies and legislation, Sustainable practices in the petroleum industry, Groundwater quality monitoring, Land zoning for groundwater protection, Correctly locating on-site sanitation systems |
| Groundwater sampling parameters | Temperature, pH, EC, TDS, Salinity, Total Petroleum Hydrocarbons (TPH) |
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What You'll Learn
Petroleum hydrocarbons (PHs) contamination
Petroleum Hydrocarbons (PHs) are the primary constituents of crude oil, gasoline, diesel, and a variety of solvents and penetrating oils. Crude oil consists of hydrocarbon molecules extracted from the ground and transformed in petroleum (oil) refineries into petroleum products. The proliferation of fuel stations in residential areas has increased the potential for leakages from underground fuel storage tanks, resulting in significant adverse effects. Underground fuel tanks represent a significant source of groundwater contamination due to their lifespan of 15–25 years, with an increased likelihood of leakage as they age. Even a small leakage rate of two drops per second can render nearly half a billion gallons of water unfit for drinking due to odour and taste issues.
Total Petroleum Hydrocarbons (TPH) is a term used to describe a broad family of several hundred chemical compounds that originate from crude oil. Most products that contain TPH will burn, and many have characteristic gasoline, kerosene, or oily odours. Because modern society uses so many petroleum-based products, contamination of the environment by them is potentially widespread.
Petroleum hydrocarbon (PH) contamination of groundwater is a serious global issue. The physicochemical properties of PHs determine their movement in aquifers from the source zone. PHs with higher molecular weight are usually toxic and seldom mobilise in subsurface plumes when compared to their low molecular weight counterparts. Due to the toxic, mutagenic, and carcinogenic nature of PHs, various remediation approaches are currently employed for their clean-up from the environment.
Soil pollution by PHs can be directly correlated to groundwater contamination since PH residuals in the soil persist for a long time, acting as a continuous source of PH contamination in groundwater. Aromatic hydrocarbons with one or more benzene rings as part of their structure are known or probable human carcinogens. Benzene is often the main groundwater contaminant of concern at petroleum release sites because of its higher toxicity and mobility compared to other petroleum hydrocarbons.
To address PH contamination, it is important to understand the fate of PH in the environment. Various remediation technologies have been developed to reduce PH concentrations in soil and groundwater. However, complete restoration of sites with petroleum contamination is challenging due to the immobile and migratory nature of certain chemical compounds. To promote the rehabilitation of contaminated groundwater, measures such as controlling local hydrodynamic conditions in the aquifer and setting grouting curtains in the down-gradient direction of pollutant migration can help mitigate pollutant movement and increase groundwater flow flux.
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Causes of groundwater pollution
Groundwater contamination is a serious global issue, with over 80% of the world's population relying on groundwater for survival and drinking water. The causes of groundwater pollution are varied and extensive in scope, with human activities posing significant threats to the environment. Here are some of the key causes of groundwater pollution:
Unintentional Spills and Leaks
Unintentional spills and leaks from fuel storage facilities and transportation are a major cause of groundwater pollution. This includes leaks from underground fuel storage tanks, pipelines, and septic tanks, as well as spills during the fueling process. Even a small leakage rate of two drops per second can render nearly half a billion gallons of water unfit for drinking.
Industrial and Chemical Waste
Industrial operations, factories, and power plants can release toxic chemicals and waste into the environment, which can eventually seep into groundwater sources. This includes chemicals used in hydraulic fracturing or "fracking," mining and quarrying waste, and the release of acidic drainage from mines. Additionally, stormwater runoff can carry automotive chemicals, road salts, and industrial waste into waterways, ultimately contaminating groundwater.
Agricultural Pollution
Agricultural practices can also contribute to groundwater pollution. The use of pesticides, fertilizers, fungicides, insecticides, herbicides, and animal waste can result in pollutants such as nitrates and bacteria seeping into underground water sources.
Petroleum Hydrocarbons
Petroleum hydrocarbons (PHs) are a significant cause of groundwater contamination. PHs can percolate through soil columns and reach groundwater aquifers, rendering them toxic. Leaks from fuel storage tanks and petroleum drilling practices can release PHs into the environment, posing serious health risks to nearby communities.
Military and Hazardous Waste
Military sites and hazardous waste disposal can release dangerous contaminants into groundwater supplies. Trichloroethylene (TCE) and per- and poly-fluoroalkyl substances (PFAS) are examples of contaminants found at military facilities that have drifted into groundwater. Radioactive waste, medical waste, and other hazardous materials can also contaminate groundwater if not properly disposed of.
Natural Sources
In addition to human activities, natural sources can also contribute to groundwater pollution. For example, precipitation and stormwater runoff can carry pollutants into groundwater. Additionally, geological factors such as saltwater intrusion can affect groundwater quality.
It is important to address these causes of groundwater pollution through prevention, control, and remediation measures to ensure the availability of clean and safe water for communities worldwide.
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Health risks of contaminated groundwater
Groundwater contamination is a serious environmental and social issue, threatening human health, environmental quality, and socioeconomic development. With over 80% of the world population relying on groundwater for survival, contamination of groundwater aquifers by petroleum hydrocarbons (PH) is a pressing concern. PH containing aromatic rings, such as polycyclic aromatic hydrocarbons (PAHs), are considered the primary cause of aquatic toxicity. The higher the concentration of PAHs, molecular weight, and boiling point, the more toxic the oil becomes.
The release of PH into the environment can occur through various anthropogenic factors, including leakages from fuel storage facilities, underground fuel tanks, and pipelines. Even minor leaks from underground tanks can render large volumes of water unfit for drinking due to odour and taste issues. Once PH contaminates the soil, it can persist for long periods, acting as a continuous source of groundwater contamination. The physicochemical properties of PH influence their ecological toxicity, with higher molecular weight PHs typically being more toxic, mutagenic, and carcinogenic.
The health risks associated with contaminated groundwater are significant. Microbial contamination, particularly from faeces, poses a grave threat to drinking water safety. Microbiologically contaminated water can transmit diseases such as diarrhoea, cholera, dysentery, typhoid, and polio, causing approximately 505,000 diarrhoeal deaths annually. Additionally, heavy metals, such as arsenic, cadmium, lead, and chromium, can leach into groundwater from various sources, including petroleum refineries and waste disposal. Consumption of water with high levels of heavy metals can lead to acute and chronic toxicity, liver, kidney, and intestinal damage, anaemia, and cancer.
Furthermore, groundwater nitrate contamination, predominantly from anthropogenic sources like fertilizers and wastewater, poses a risk to human health, especially for infants and children. Excessive nitrate concentrations in drinking water used for baby formulas can cause "blue baby syndrome," or infant methemoglobinemia. Other inorganic contaminants found in groundwater include anions and oxyanions (F-, SO42-, Cl-), and major cations (Ca2+, Mg2+). The presence of these contaminants can elevate total dissolved solids (TDS) in groundwater, which may have adverse health effects.
The natural presence of chemicals in groundwater, such as arsenic and fluoride, can also be a health concern. Additionally, chemicals like lead may leach into drinking water from water supply components, posing further risks. Climate change and inadequate management of wastewater contribute to the contamination of drinking water sources, endangering the health of hundreds of millions of people.
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Groundwater remediation methods
Groundwater remediation is the process of treating polluted groundwater to remove contaminants or convert them into harmless products. This is especially important as groundwater is often used for drinking water, agriculture, and industry. Petroleum hydrocarbon (PH) contamination of groundwater is a serious global issue, caused by factors such as leaks from fuel storage facilities, spills, saltwater intrusion, and the improper management of landfills.
One method of groundwater remediation is the pump-and-treat method, which involves pumping the polluted water to ground facilities to apply different treatment approaches. This can include air stripping, treatment towers, and granular activated carbon (GAC). Pressurized air bubbles are also used to treat contaminated groundwater, as well as dissolved chemicals, solvents, metals, and fuel oil.
Another approach is in situ remediation, which treats the groundwater without removing it from the aquifer. Biosparging, for example, uses indigenous microorganisms to biodegrade organic constituents in the saturated zone by injecting air (or oxygen) and nutrients. Bioventing is another in situ technique that enhances the activity of indigenous bacteria and stimulates the natural biodegradation of hydrocarbons by inducing air or oxygen flow into the unsaturated zone.
Permeable reactive barriers (PRBs) are also used in situ to intercept a contaminated plume. Reactive media, such as sand, is used to enhance hydraulic conductivity, allowing the plume of contaminants to pass through the PRB. Contaminants are then removed through physical, chemical, or biological processes.
Other methods of groundwater remediation include:
- Soil vapor extraction (SVE): Involves the injection of pressurized air to clean up the groundwater by changing the state of volatile hydrocarbons to a vapor state.
- Surfactants: Used to resolve tailing and rebound effects, with biosurfactants and mixed surfactants being the most effective.
- Prevention and control: Replacing single-wall storage tanks with double-walled tanks to eliminate the source of pollution, implementing anti-seepage measures, and controlling local hydrodynamic conditions to mitigate pollutant movement.
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Preventing petroleum leaks
Well Construction and Maintenance
Oil and gas wells should be constructed with multiple layers of steel casing and cement barriers to prevent leaks. This method is used to prevent the transfer of fluids between the well and the aquifer being drilled and to stop contamination from surrounding rock formations. The integrity of these steel casings and cement barriers is vital, as leaks can occur if they are damaged or poorly constructed.
Double-Walled Storage Tanks
In fuel stations, replacing single-wall storage tanks with double-walled tanks made from upgraded materials can help eliminate the source of pollution. This is because the secondary wall acts as a backup, containing any leaks from the primary wall, thus preventing the leakage of petroleum into the surrounding environment and groundwater.
Anti-Seepage Measures
Implementing strict anti-seepage measures in the storage tank area creates artificial barriers that block the migration path of pollutants. This prevents the spread of contamination and protects groundwater sources.
Groundwater Extraction and Treatment
Developing a groundwater extraction system can intercept and treat contaminated groundwater before it reaches residential areas. This system can remove the polluted water, treat it, and potentially make it suitable for human consumption again.
Regular Monitoring and Reporting
Establishing a continuous groundwater monitoring program helps track contamination concentrations and identify early warning signs. It is essential to develop a transparent reporting mechanism to inform residents, regulatory authorities, and the public about groundwater quality in real time.
Robust Policy Framework
Considering the vulnerability of groundwater to pollution, establishing a robust and consistent policy framework is imperative. This includes stronger policies, legislation, and sustainable practices in the petroleum industry to address water pollution and protect public health and the environment.
The prevention of petroleum leaks requires a combination of well-designed infrastructure, strict maintenance protocols, and proactive monitoring and containment strategies. By implementing these measures, we can safeguard groundwater sources and ensure the health and well-being of communities that depend on this precious resource.
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Frequently asked questions
Petroleum pollutants are contaminants that are characteristic of petroleum products, such as benzene, ethylbenzene, dichloroethane, and other organic contaminants.
Petroleum pollutants can enter groundwater aquifers through various ways, including leakages from underground fuel storage tanks, unintentional spills, saltwater intrusion, improper landfill management, injection wells, and pipelines, among other sources.
The movement and dispersion of petroleum pollutants in aquifers are influenced by factors such as soil characteristics, site geology, hydrogeology, and the nature of the contaminants. The physicochemical properties of the pollutants also play a role in their movement and ecological toxicity.
Petroleum pollutants in groundwater aquifers pose significant risks to human health and the environment. They can cause water-borne diseases, act as carcinogens, and impact aquatic ecosystems. With over 80% of the world population relying on groundwater, contamination by petroleum pollutants requires urgent attention and remediation.
To address petroleum pollution, management approaches include point-of-use water treatment, groundwater remediation techniques (such as using surfactants), and, as a last resort, abandonment of the contaminated source. To prevent pollution, measures such as upgrading storage tanks, implementing anti-seepage measures, and controlling local hydrodynamic conditions can be employed.
