Meghan Hodges
Groundwater contamination is a critical issue that poses a threat to both human health and the environment. It is often caused by improperly constructed or maintained septic systems, chemical spills, and the improper disposal of hazardous materials. The slow movement of groundwater contamination makes it difficult and costly to reverse, with clean-up efforts requiring significant investments of time and money. To address this issue, various remediation techniques are employed, including pump and treat methods, in situ treatments, ex-situ remediation, and the use of vertical engineered barriers (VEBs) to contain and control the flow of contaminated groundwater. Additionally, natural processes such as monitored natural attenuation and filtration through activated carbon filters can also be utilized. While preventing pollution is significantly more cost-effective than remediation, cooperation between individuals, businesses, and governments is necessary to maintain clean and safe groundwater sources.
| Characteristics | Values |
|---|---|
| Methods | Pump and treat, ex-situ remediation, in situ treatment, air stripping, activated carbon filtration, bioremediation, phytoremediation, chemical oxidation, vertical engineered barriers (VEBs), Oxygen Release Compound (ORC), in situ sorption, biodegradation, in situ chemical oxidation (ISCO), enhanced aerobic or anaerobic biodegradation, bioaugmentation |
| Causes of groundwater pollution | Industrial solvents, metals, fuel oil, septic systems, sewers, landfills, underground storage tanks, chemical spills, pesticides |
| Effects of groundwater pollution | Unsafe drinking water, potential health problems, water sources dwindling or abandoned, harm to aquatic animal habitats |
| Prevention | Government regulations, environmental regulations, education and cooperation of individuals and businesses |
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What You'll Learn
In situ treatment
There are several methods of in situ groundwater remediation. One method involves injecting substances into the groundwater to degrade contaminants chemically or biologically, or to assist in their physical removal by recovery wells. This can be done through passive injection systems, which diffuse injectants into the subsurface. Examples of injectants include Oxygen Release Compound (ORC) socks, iSOC systems, and other gas infusion methods.
Another method is the use of permeable reactive barriers (PRBs), which can be located underground and are effective and affordable for remediating complex contaminated groundwater. PRBs have the advantages of low costs, high efficiency, and long service life.
Pilot tests are also used to evaluate the technical feasibility of a remediation strategy before developing a full-scale plan. These tests involve studying a small area, typically within 5% of the land surface above the known extent of groundwater contamination, to determine the best approach.
In situ remediation is particularly important for improving water quality and ensuring the safety of drinking water, especially in cases of mixed contamination, such as groundwater co-contaminated with heavy metals and petroleum hydrocarbons.
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Pump and treat
The process involves pumping groundwater from wells to an above-ground treatment system that removes the contaminants. This above-ground treatment of extracted groundwater often includes multiple technologies used in a treatment train. The treated water can then be discharged or beneficially reused, such as for irrigation, upon regulatory approval. Discharge options include releasing the water into a publicly-owned treatment works (POTW), a receiving surface water body (directly or through a storm drain system), or reinjecting it into the subsurface.
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Ex-situ remediation
Traditional methods of pumping and treating contaminated groundwater include well-siphoning and the disposal of pollutants through exemption processes such as carbon adsorption, air purification, oxidation/precipitation of substances, or natural reactors. However, these methods have high running costs and produce polluted waste.
Nanoremediation is an emerging technology that uses nanoparticles to treat polluted groundwater. It offers advantages such as lower costs, shorter cleanup times, and the ability to completely degrade some contaminants without removing the groundwater.
Overall, the choice between ex-situ and in-situ remediation depends on various factors such as soil properties, contaminants, and the specific remediation technique's advantages and limitations. Each project is unique, and the optimal remediation process must be determined on a case-by-case basis.
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Preventing groundwater pollution
Proper Construction and Maintenance of Septic Systems and Sewers
Improperly constructed or poorly maintained septic systems and sewers are a significant source of groundwater pollution. It is essential to ensure that these systems are correctly designed, installed, and regularly maintained to prevent the leakage of bacteria, viruses, and chemicals into groundwater sources.
Regulation of Hazardous Waste Disposal
Hazardous materials and chemicals improperly disposed of in landfills can contaminate groundwater through runoff from heavy precipitation. Strict regulations and proper waste management practices are necessary to prevent hazardous substances from reaching groundwater sources.
Secure Storage of Chemicals and Hazardous Materials
Millions of underground storage tanks containing chemicals and hazardous materials may leak over time, contaminating the surrounding soil and groundwater. It is crucial to enforce regulations that govern the secure storage of these substances, including regular inspections and proper maintenance of storage tanks.
Pesticide Regulation
Pesticides used in agriculture and other industries can be a source of groundwater pollution if not properly managed. Governments should implement regulations that control the use, storage, and disposal of pesticides to minimize their impact on groundwater quality.
Containment and Isolation of Contaminated Areas
In cases where contamination has already occurred, preventing the further spread of pollutants is essential. Vertical engineered barriers (VEBs) are walls built below ground to divert and contain contaminated groundwater flow, preventing it from reaching drinking water wells, wetlands, or streams. Pump and treat systems are also used to extract and treat contaminated groundwater, preventing the spread of pollutant plumes.
Natural Processes and Water Dilution
Natural processes, such as monitored natural attenuation, can be utilized to achieve remediation objectives over time. Additionally, water sources can act as natural diluters of contaminants, reducing their concentration to levels that may not be harmful. However, excessive pollution can exceed the dilution capacity of water bodies, emphasizing the importance of preventing pollution at its source.
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Containing contaminated plumes
The Arrow Street purge system, installed at Wurtsmith Air Force Base in Michigan, successfully addressed a plume of contamination, primarily consisting of trichloroethylene and dichloroethylene. This system lowered the concentration of these contaminants in the groundwater, preventing their escape from the base.
In situ remediation focuses on treating the contaminated groundwater on-site without removing it from the property. This approach includes various technologies, such as in situ sorption, in situ chemical oxidation (ISCO), and enhanced biodegradation. For example, Oxygen Release Compound (ORC) has been used to treat groundwater contaminants like benzene and vinyl chloride.
Ex-situ remediation involves excavating and removing the contaminated water from the site for off-site treatment. While this method can be more expensive and time-consuming, it ensures that no further damage is caused at the current location, especially in cases of high subsurface contaminant levels.
A study conducted in Arizona monitored the behaviour of a groundwater contaminant plume containing trichloroethene after implementing a source-containment operation. The plume resided in a multi-layer system of sand, gravel, and clay. Over time, the concentrations of trichloroethene in the groundwater pumped from the plume extraction wells significantly declined, indicating the effectiveness of the containment measures.
Additionally, a groundwater flow and mass transport model tested the use of shallow excavations filled with coarse, reactive media to remediate a hypothetical unconfined aquifer. The excavations, modelled as contaminant sinks, were placed downgradient of an initial contaminant plume. The dimensions of these trenches were adjusted to prevent the offsite migration of contaminants effectively.
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Frequently asked questions
There are several ways to clean up groundwater pollution, including:
- Pump and treat: Pumps are used to bring polluted water to the surface where it can be treated.
- Air stripping: Air is used to remove contaminants from water by pumping contaminated water through a large chamber where it is sprayed over packing material. A fan then blows air upwards, causing chemicals to evaporate out of the water.
- Activated carbon filtration: Carbon filters are used to remove contaminants from water.
- Bioremediation and phytoremediation: These processes break down contaminants in water.
Pump and treat is a common method for cleaning groundwater contaminated with dissolved chemicals, including industrial solvents, metals, and fuel oil. It is often used to contain contaminant plumes and prevent them from spreading further.
Pump and treat can be costly and time-consuming, as the water must be removed from the source and treated.
Ex-situ remediation involves excavating contaminated water and eliminating it off-site. This method ensures that no further damage is done to the current site.
