Leaks, spills, accidents and seepage from human activities can contaminate soil, air, surface and groundwater, posing serious risk to human and ecological health and adding liability to your project or property. The team at Tioga is equipped to assess alternatives and find the remediation solution that best fits your schedule, budget and priorities. Keep reading this month’s Top 10 with Tioga to learn more about your options for remediation.
1. Natural attenuation.
Simply defined as “doing nothing,” this is by far the least expensive option though rarely utilized. However, some constituents do readily attenuate or degrade over time. Certain situations allow for “doing nothing” and letting nature take its course, provided no risks are present to human or ecological health.
2. Continued monitoring.
As previously mentioned, some contamination will naturally attenuate. In many cases, a plume of contamination will degrade into harmless materials over time, and the best course of action is to watch it happen. Continued monitoring by the collection of groundwater or vapor samples can ensure that natural attenuation is working while making sure that the contaminant plume is not mitigating off-site. Again, provided human or ecological health is not a risk, monitoring natural attenuation can be used as a remedial strategy.
In the case of groundwater plumes, injecting materials that speed up natural attenuation or change harmful contaminants into benign materials can be highly successful tools for remediation. With this strategy, an injectant or combination of injectants is physically inserted into the soil and groundwater. The natural flow of groundwater can carry these injectants throughout a plume of contamination. Some areas, including Memphis, are strict about what can and cannot be injected into the ground, especially when drinking water resources can be impacted. In addition, injection may require installation of new water wells and continued monitoring of the plume over time to determine the effectiveness of the remedial strategy. In many cases, multiple rounds of injections may be required before a plume is
4. Dig and haul.
This is one of the oldest and most effective methods for remediation. Many times, the source of groundwater and vapor contaminant plume has a soil source where the hazardous materials were originally spilled. This soil contamination can slowly leach into the groundwater, which can become a vapor plume. If a known soil source of contamination is present, removing that source by excavation is a quick way to make major headway with a remediation project. Without a soil source, a groundwater plume will naturally attenuate much faster in most cases. The issue with the dig and haul method is that it’s not actually remediating the contamination but simply taking it somewhere else. In most cases, this means moving it to a Class I landfill.
5. Cap and seal.
For certain types of contamination, removing the chance of human contact can count as remediation. While this is technically mitigation since no contamination clean up occurred, it can be successful in the protection of human and ecological health. Certain types of contamination in the soil can leach into the groundwater through natural processes such as precipitation. Successful installation of a cap that prevents the migration of contamination with the natural absorption and flow of groundwater through the soil can effectively lock a contaminant plume in place and mitigate the risk to human health. For other types of contamination, such as arsenic and lead that do not readily dissolve or migrate with water, the placement of a cap can remove the risk of direct contact by humans. Generally, this strategy requires the use of deed restrictions, which ensure that the cap be maintained because, in many cases, the contamination will either attenuate at a much slower pace or, at times, not at all.
6. Pump and treat.
Pump and treat is an aggressive and effective method to remediate a groundwater plume, but it’s also expensive. It requires the physical removal of groundwater by pumping out of recovery wells. The systems that control the pumping can be as small as a single pump or as large as a multi-story building, depending upon the size of the plume. After the water is removed, it is either treated on-site or transported to an off-site treatment facility. These pump and treat systems run 24 hours a day, seven days a week, causing the cost to quickly add up thanks to utility bills, maintenance or systems and fees for discharging treated groundwater into sewers or streams. This strategy is generally used for groundwater contamination that poses a serious risk to drinking water sources based on its invasive and costly characteristics. However, if done correctly, this method is extremely successful.
7. On-site remediation.
This strategy is generally only used for soil contamination by volatile organic constituents. When a volatile organic constituent soil source of contamination is present at a property, it is possible to remediate on-site with a simple strategy – dig it up and turn it. When the correct conditions allow it, contaminated soil can be excavated and stockpiled. This soil is then mechanically turned over time with a backhoe or excavator. By turning the soil, contamination trapped in the soil can volatize into the atmosphere. Eventually, the soil will be clean enough to be put back in the ground. Issues with this are obvious, unless you want a large hole where you excavated the contaminated soil sitting on your property for years until you bring in clean backfill. If that is the case, you still have a large pile of contaminated (and probably stinky) soil on your property that must be mechanically turned on a regular basis. While this remedial strategy isn't common, it can be the most cost-efficient method in some cases to remediate a soil plume.
8. Soil vapor extraction.
While this strategy is generally employed to mitigate the risk from vapor intrusion in a facility, it can be effective in remediation of soil and groundwater plumes of contamination. Vapor plumes beneath a building can intrude into the indoor air where people become exposed to contamination. Removing this risk often includes the installation of a sub-slab depressurization system, a type of soil vapor extraction. By constantly removing air from the soil, you remove plumes of vapor from below a building along with volatile contamination from the soil. As the air is removed, soil contamination will volatize rapidly and lower the concentrations in a soil source. Without a soil source replenishing a groundwater plume, groundwater contamination will be reduced. This remedial strategy is employed when a serious risk from vapor intrusion is present. While technically a remediation strategy because it reduces the concentrations of soil and groundwater contamination, the primary function of most of these systems is to prevent exposure to contaminated vapors.
This is an expensive remedial strategy that involves the use of heat to help break down hazardous materials. While it is normally used in the remediation of volatile organic constituents, it can have applications with other concerning constituents. Thermal remediation can have multiple applications, from the burial of heating coils that physically bake the soil to the injection of steam into a soil or groundwater plume to facilitate attenuation and remediation. This strategy, like pump and treat, requires constant monitoring and equipment upkeep, in addition to prolonged monitoring of the plume for contamination. This method is generally only used in a situation where contamination is significant.
There are multiple strategies where a risk of contamination can be removed without actually removing the contamination. This strategy, called mitigation, can take multiple forms. Installation of a vapor barrier underneath a slab during construction can remove a risk from vapor intrusion. Depending on the severity of the risk, these vapor barriers can range from sheets of plastic, not unlike a standard sub-slab moisture barrier, to asphaltic structures that are multiple feet thick. In addition, volatile resistant floor coatings can be installed on top of existing building slabs to mitigate relatively minor risks from vapor intrusion. The installation of deed restrictions at properties can successfully mitigate exposure to contamination. The placement of industrial use-only restrictions at a property is common when a case of contamination could pose a risk to sensitive receptors, such as children or the elderly in a residential scenario. However, it does not pose a risk to personnel at an industrial facility due to the significantly less exposure that would be experienced. The implementation of groundwater use restrictions, that prevent installation of a water well, can successfully mitigate the risk from exposure to a groundwater plume of contamination. In the case of certain types of surficial soil contamination, two feet of clean soil can be brought to a property and the ground elevation can be raised to a point where the surficial soil contamination does not pose a risk. While mitigation does not physically clean or remove contamination, it can be a cost-effective method for ensuring the health of personnel or residents at a property.