Would you drink this water?
This water is obviously dirty, but some of the worst contaminants that can be in water are invisible. Those contaminants, especially when they are in groundwater, are extremely difficult to remove.
Preventing groundwater contamination is much easier and cheaper than cleaning it. To clean groundwater, the water, as well as the rock and soil through which it travels, must be cleansed. Thoroughly cleaning an aquifer would require cleansing each pore within the soil or rock unit. For this reason, cleaning polluted groundwater is very costly, takes years, and is sometimes not technically feasible. If the toxic materials can be removed from the aquifer, disposing of them is another challenge.
Stages of Groundwater Cleaning
Elimination of the Pollution Source
If the source is an underground tank, the tank will be pumped dry and then dug out from the ground. If the source is a factory that is releasing toxic chemicals that are ending up in the groundwater, the factory may be required to stop the discharge.
Monitoring the Extent of the Pollutant
Hydrologists must determine how far, in what direction, and how rapidly the plume is moving. They must determine the concentration of the contaminant to determine how much it is being diluted. The scientists will use existing wells and may drill test wells to check for concentrations and monitor the movement of the plume.
Test wells are drilled to monitor groundwater pollution.
Modeling the Contaminant Plume
Using the well data, the hydrologist uses a computer program with information on the permeability of the aquifer and the direction and rate of groundwater flow, then models the plume to predict the dispersal of the contaminant through the aquifer. Drilling test wells to monitor pollution is expensive.
First, an underground barrier is constructed to isolate the contaminated groundwater from the rest of the aquifer. Next, the contaminated groundwater may be treated in place.
Bioremediation is relatively inexpensive. Bioengineered microorganisms are injected into the contaminant plume and allowed to consume the pollutant. Air may be pumped into the polluted region to encourage the growth and reproduction of the microbes. With chemical remediation, a chemical is pumped into the aquifer so the contaminant is destroyed. Acids or bases can neutralize contaminants or cause pollutants to precipitate from the water.
The most difficult and expensive option is for reclamation teams to pump the water to the surface, cleanse it using chemical or biological methods, then re-inject it into the aquifer. The contaminated portions of the aquifer must be dug up and the pollutant destroyed by incinerating or chemically processing the soil, which is then returned to the ground. This technique is often prohibitively expensive and is done only in extreme cases.
- There are four stages needed to clean groundwater: remove the pollutant source, monitor the pollutant, model the contaminant plume, and perform remediation.
- By testing the water in many wells for a contaminant, scientists can model the contaminant plume in an aquifer.
- Cleaning groundwater in an aquifer usually requires bioremediation, the use of microorganisms that are bioengineered to consume a pollutant, or chemical remediation, which causes neutralizing chemical reactions.
Use this resource to answer the questions that follow.
1. What was the Hanford site used for?
2. What river needs to be protected?
3. How much contamination was released into the soil?
4. How much has the contamination decreased?
5. What is the goal at Hanford?
6. What is being done to clean up the water?
7. How much of the groundwater has been treated?
1. Why does cleaning groundwater in an aquifer also require cleaning the soil or rock that the water travels through?
2. Describe how bioremediation works. Why is this a good way to clean an aquifer without removing the water?
3. How do scientists monitor and model a contaminant plume?