Did you know that more than half of the U.S. population depends on groundwater for drinking water? This includes people served by public water systems, as well as those who get their drinking water from a private source, such as a well.
When groundwater and soil become contaminated, it poses health risks not only for people who might rely on the groundwater as a source of drinking water. It can also be hazardous to wildlife, livestock and even pets. Contaminated drinking water can also affect plants, including crops intended for consumption by people and livestock.
While there are numerous causes of soil and groundwater contamination, several widespread activities are responsible for the majority of contaminated soil and groundwater:
- Local waste disposal
- Land development
- Industrial dumping
- Heating oil tanks
If a Phase 2 environmental site assessment (ESA) reveals the presence of hazardous materials or contamination, then additional investigation, as well as soil and groundwater remediation, may be necessary to resolve the issue. A geophysical survey can help locate buried tanks and other sources of contamination.
Groundwater Remediation Methods
Various methods are available for cleaning up contaminated groundwater. Which method is used depends on the type of contamination.
There are two basic types of physical groundwater remediation: air sparging, and a method known as “pump and treat.”
- Air sparging is used to treat groundwater contaminated by volatile organic compounds, or VOCs. This involves drilling an injection well into the contaminated water table and then injecting pressurized air through the well. The pressurized air causes the hydrocarbons in the VOC to dissolve into vapor. The vapor percolates up through the water and is channeled into an extraction system to remove the contaminants. The clean air is then released into the atmosphere.
- A pump and treat system is used when dissolved chemicals, such as industrial solvents, metals and fuel oil, have contaminated the groundwater. In this case, the groundwater is pumped from one or more wells up into an above-ground treatment system to remove the contaminant(s). This type of system can also be used to prevent contaminated water from spreading.
Environmental factors, cost and the type of pollutant can influence which type of biological remediation is deemed most appropriate.
- With bioaugmentation, naturally occurring, adapted microorganisms (bacteria and fungi) are added to treatment systems to aid in the biological degradation of contaminants such as ammonia.
- Bioventing involves drilling one or more injection wells into the contaminated area and then pumping air through the well(s) into an unsaturated zone. The air provides oxygen to enhance the growth of existing microorganisms that can aerobically degrade compounds that are contaminating the groundwater. Nutrients and heat can be added to the bioventing process to speed it up.
- Biosparging is used to remove contaminants such as mineral oil or aromatic compounds like benzene. Aerobic bacteria are added to the contaminated groundwater to break down the pollutants. For deeper, anaerobic layers of groundwater, injection filters are used to furnish oxygen to the bacteria.
Similar to biological remediation methods, the choice of chemical remediation processes depends on various factors such as cost and the type of contaminant present.
- Carbon capture is a method of groundwater remediation in which activated carbon is injected into the contaminated area. The carbon captures and sequesters carbon dioxide and is then transported to a deep underground storage reservoir.
- Ion exchange is often used to remediate groundwater contaminated by toxic metals. With this method, the ionic contaminant is removed from the groundwater by exchanging it with another ionic substance. The process is similar to that used for water “softening.”
- With chemical precipitation, counter-ions are used to reduce the solubility of ionic contaminants, changing them into solid particles that can be more easily removed.
- Chemical oxidation involves injecting or mechanically mixing oxidants into the area to be treated. Electrons from the oxidizing reagent are transferred to the contaminant, converting it to a less hazardous, stable or inert compound.
Soil Remediation Methods
Some of the same methods used in groundwater remediation can be used for soil remediation, also referred to as “soil washing.” And just like groundwater remediation, the method selected to remove pollutants from the soil depends on the particular situation that needs to be addressed.
With this type of decontamination, the soil is subjected to high temperatures to evaporate the contaminants. Typically, a conveyor belt is used to feed the soil into an oven chamber, where it is baked. The materials that are extracted are captured, cooled and disposed of, and the soil is tested to ensure that it can be safely recycled.
With encapsulation, rather than filtering the contaminant(s) from the soil, the contaminated soil is mixed with a substance such as lime, cement or concrete to prevent the contaminants from spreading to surrounding soil or groundwater.
The process is similar to that used to treat groundwater contamination. Large volumes of pressurized air are injected into the contaminated soil to remove VOCs. This method of treating soil contamination is commonly used when carbon filtering systems cannot be used.
As with bioremediation for groundwater contamination, this process involves the introduction of adapted aerobic and anaerobic bacteria into contaminated soil. The bacteria consume the contaminants, breaking them down into nonhazardous components.
Your Portland, OR groundwater and soil remediation expert
If you have a situation that may require soil or groundwater remediation, call Alpha Environmental. We can assess the soil and groundwater in question and implement any remediation processes that may be needed.
We’ll help you explore the options available to resolve your unique set of circumstances and help you decide which is the best choice.