Water security is one of the most critical worldwide concerns in the face of an increasing human population, agricultural expansion and climate change.
Groundwater is the world’s greatest distributed store of fresh water, critical to ecosystem sustainability and human resilience to climatic fluctuation and change.
Groundwater resource management is especially important because aquifers supply 50% of the world’s drinking water and 43% of irrigation.
Groundwater contamination happens when man-made items such as gasoline, oil, road salts and chemicals enter the groundwater and render it unsuitable for human consumption.
Surface materials from the land can migrate through the soil and end up in groundwater.
Pesticides and fertilizers, for example, can find their way into groundwater supplies over time.
Road salt, hazardous compounds from mines and spent motor oil may also contaminate groundwater.
Furthermore, untreated septic waste and dangerous chemicals from underground storage tanks and leaking landfills have the potential to contaminate groundwater.
What is groundwater remediation?
Groundwater remediation involves the removal of pollutants from contaminated groundwater.
Although most groundwater is pure, it can become contaminated as a result of excessive fertilizer or pesticide application, spills from industrial activities, runoff, or leakage from landfills.
Groundwater contamination endangers human health, which is why groundwater remediation is required to solve these concerns.
Types of groundwater remediation
Groundwater remediation is divided into two kinds based on treatment location:
In-situ remediation
In situ remediation entails treating groundwater rather than removing it from the aquifer.
Using in-situ treatment methods, contaminants can be eliminated, immobilized, or removed.
Permeable reactive barriers and in situ chemical oxidation and reduction are two examples.
It is characterized by:
– It is a basic procedure that consists just of impregnating subterranean soil with nutrients that activate microorganisms.
– It is a less expensive procedure than excavation and removal.
– It is a procedure that may be used even on soil directly beneath buildings or on active industry sites where excavation is difficult.
– It is a low-impact approach that eliminates the need to remove and transport contaminated soil.
Ex-situ(off situ) remediation
Ex-situ remediation entails extracting contaminated water and transporting it off-site.
This procedure has the advantage of preventing more damage to the existing place, but it prolongs the process and is more expensive.
Ex-situ cleaning is generally favored when subsurface contamination levels are higher than those that can be cleaned in situ.
Aside from their high cost, these approaches are extremely efficient, easy to manage, quicker and can treat a wide range of soil pollutants.
Land farming, pile, windrow, soil washing, composting, bioreactor, ion exchange, adsorption/absorption, pyrolysis and ultrasound technology are examples of ex-situ processes.
These approaches may be used to successfully treat fuel hydrocarbons, halogenated and non-halogenated organic chemicals and different insecticides.
Methods of groundwater remediation
There are several strategies for remediating a site or restoring soil and groundwater to acceptable conditions.
Several groundwater remediation methods may be used to clean up groundwater.
Groundwater remediation technologies are categorized into physical, chemical and biological technologies.
Physical technologies
The most basic type of groundwater remediation uses air to filter water (air sparging).
Physical technologies include the following:
Pumps and treat
It is a common process for cleaning up contaminated groundwater that contains dissolved substances such as industrial solvents, metals and fuel oil.
Groundwater is recovered and sent to an above-ground treatment system, where impurities are removed.
Containment plumes are also contained using pump and treat systems.
Pumping directs tainted water toward the wells, preventing the plume from spreading.
This pumping keeps toxins out of drinking water wells, wetlands, streams and other natural resources.
Its applications:
This approach may be tailored to remove any pollutant or combination of contaminants.
Common pollutants include:
– Volatile Organic substances or semi-volatile.
– Heavy metals such as lead, chromium and so on.
– Pesticides
– pH
Air sparing
It is an in situ remedial approach that involves the direct injection of fresh air/hot air into the subsurface saturated zone.
When bubbles rise in the groundwater and are transported up into the unsaturated zone, contaminants are removed from the groundwater through physical contact with the air.
Its applications:
It has been observed that air sparging can help to reduce concentrations of:
– Volatile organic compounds can be found in petroleum products such as gasoline and diesel.
– Components from BTEX.
– Chlorinated solvents such as PCE, TCE, DCE and so on.
Containment
Containment is a method of preventing groundwater plumes from moving.
This is achieved by employing a vertically planned, subsurface impermeable barrier.
Vertical engineered barriers (VEBs) are underground walls that restrict the flow of groundwater.
Polluted groundwater flow may be diverted away from drinking water wells, wetlands and streams using VEBs.
They may also be used to confine and isolate polluted soil and groundwater, preventing them from contaminating pure groundwater.
VEBs vary from permeable reactive barriers in that they neither clean nor allow groundwater to travel through them.
Slurry walls and sheet pile walls are two common forms of verbs.
To avoid groundwater plumes from spreading, contaminant solutions may also rely on the pump and treat method.
Chemical technologies
This approach may take longer to implement and may be more expensive, but it may be the only choice for some pollutants.
Chemical remediation can achieve clean groundwater through carbon absorption, ion exchange, chemical precipitation and oxidation.
These are the most often utilized groundwater remediation procedures and each has advantages and disadvantages.
The objective is the same for all of them: to eliminate impurities while leaving clean, drinkable drinking water behind.
Chemical precipitation
Chemical precipitation is a traditional technology that involves adding chemical precipitants, coagulants and flocculants to a pumped groundwater stream in a stirred reaction vessel to increase particle size through aggregation, either batch-wise or with a steady flow and then separating the precipitated solids from the cleaned water.
Its applications:
– Remove groundwater hardness, heavy metals, fats, oils and greases (FOG), suspended particles and certain organics It may also be used to remove inorganics such as phosphorus, fluoride, ferrocyanide and others.
– Mining-related water
– Material volume, whether large or little
– Technology used alone or in collaboration with others
– Many pollutants of concern
Ion exchange
Ion exchange for groundwater remediation is almost typically accomplished by forcing water downward under pressure through a fixed bed of resins, granular medium, or spherical beads, where ions, cations and anions in the resins are exchanged for cations and anions in the polluted water.
Zeolites and synthetic resins are the most often employed ion exchange media for cleanup.
Some resins may be regenerated for re-use once their capacity has been depleted, whereas others are intended for single use.
Its applications:
– Ion exchange can clean water of dissolved metals (chromium), radionuclides and other inorganic pollutants.
– Non-metallic chemicals such as perchlorate, nitrate and ammonia can also be removed using this method.
Carbon absorption
Liquid phase carbon adsorption is a full-scale method that involves pumping groundwater through one or more containers containing activated carbon, to which dissolved organic pollutants are adsorbed.
When the concentration of pollutants in the bed’s effluent surpasses a particular threshold, the carbon can be regenerated either on-site or at an off-site facility.
Its applications:
– Hydrocarbons, SVOCs and explosives are the target contaminant classes for carbon adsorption.
– Liquid phase carbon adsorption is effective in removing pollutants at low concentrations (less than 10 mg/L) from water at almost any flow rate, as well as contaminants at high concentrations from water at low flow rates.
– It is especially useful for cleaning water discharges from other remedial technologies to achieve regulatory compliance.
– It can be installed quickly and has excellent contamination removal efficiency.
Biological technologies
To clean polluted water, this approach employs organic debris, microbes and plants. Bio-augmentation, bioventing, and bio-sparging are three methods of using biological material to break down certain chemicals and compounds found in industrial waste in groundwater.
Biological approaches are advantageous since the polluted water may not even need to be removed to be treated.
Overall, groundwater remediation is a vital aspect of environmental preservation and we are delighted to help by offering a variety of treatment methods for contaminated areas.
New challenge
You’ve probably heard about PFAS (per- and polyfluoroalkyl substances), a category of thousands of chemical compounds that have been found almost anywhere anyone has cared to investigate, including much of the United States drinking water.
PFAS exposure has been linked to many serious health issues, including cancer.
Identifying and remediating the sources of PFAS-impacted groundwater is therefore crucial to preserving safe drinking water.
Groundwater extraction and filtration is the most often used treatment method for removing PFAS risks.
Interceptor wells are used in this strategy to pump groundwater to the surface and filter out PFAS using granular activated carbon or ion-exchange resins.
Landfill disposal of PFAS waste may be considered as relocating the problem, with the potential for re-release into the environment depending on how carefully the facility manages leachate.
In situ (i.e., in-place) filtration with colloidal activated carbon is a more recently developed treatment method for eliminating PFAS from groundwater (CAC).
Permeable reactive barriers (PRBs) put between a PFAS source area and a potential receptor are commonly used in situ CAC treatments.
By eliminating PFAS from groundwater, possible exposure is avoided, as is the risk to human health and the environment.
In this regard, the in-situ CAC approach, like its ex-situ equivalent, P&T, filters PFAS out of groundwater.
Aside from PFAS, the in-situ CAC treatment method has effectively treated other organic pollutants in groundwater and safeguarded drinking water sources at hundreds of sites across the world.
References
[1] IEC, The Most Common Methods of Groundwater Remediation, (online), available at https://www.iec-nj.com/common-methods-groundwater-remediation/
[2] REGENESIS REMEDIATION SOLUTIONS, August 10, 2017, how groundwater is remediation
(Online), available at https://regenesis.com/en/how-is-groundwater-remediated/
[3] EPA, How Superfund Addresses Groundwater Contamination, (online)available at https://www.epa.gov/superfund/how-superfund-addresses-groundwater-contamination
[4] Rachael Burton, September 21, 2021, HANDEX, A Comprehensive Guide to Groundwater Remediation, online, available at https://www.hcr-llc.com/blog/a-comprehensive-guide-to-groundwater-remediation
[5] Anjali Sharma, Prof. Dr. N. S. Varandani, April 23, 2013, UERT,(online) available at https://www.ijert.org/ground-water-remediation-technologies
[6] The Challenge of Remediating PFAS in Groundwater,(online) available at: https://www.wqpmag.com/editorial-topical/pfas/article/10959848/the-challenge-of-remediating-pfas-in-groundwater
