Groundwater purification

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Groundwater purification (groundwater remediation) is the process used to treat polluted groundwater in such a way that the contaminants are either removed or turned into harmless substances. Depending on the type of contamination, there are different methods of remediation.

backgrounds

Groundwater is one of the most important food and production resources worldwide. Groundwater is water that fills the pores of layers of earth and rock in the subsurface. Globally, between 25% and 40% of drinking water is obtained from deep wells and shaft wells. In agriculture it is needed to irrigate cultivated areas and in industry it is used as process water and a means of production for everyday needs. Groundwater pollution has negative consequences for people and nature. Protecting and keeping the groundwater clean are of great importance. In Germany, the Water Management Act regulates the protection and use of water.

Causes of Contamination

Natural conditions and various human activities have generated large amounts of waste and by-products in the recent past. Originally there were no controls or regulations on the treatment of waste. Accordingly, waste was simply dumped in the countryside or, due to a lack of safety precautions, seeped into the ground at the point of origin and gradually contaminated the groundwater. Contamination of the groundwater, regardless of the substances, usually makes it unusable for further use.

Even today, the groundwater is repeatedly unintentionally contaminated. Causes include, for example, over-fertilization, incorrect use of pesticides, industrial accidents, uncontrolled municipal sewage and leachate from landfills. The use and fate of polluted groundwater in the environment has far-reaching negative consequences. To counter the problem, groundwater purification was developed.

Types of pollution

Pollution found in the groundwater is caused by a wide range of physical, organic and inorganic-chemical, bacterial and radioactive substances. Pollution and contamination can be eliminated or neutralized through the use of adapted techniques to such an extent that the groundwater then corresponds again to the required standard.

Technical cleaning processes

The selection of a technical process depends on the conditions for the continued use of groundwater or the limitation of the pollution of groundwater to the lowest possible level. Not all methods are equally well suited due to the local conditions.

Pump and Treat

Depending on the geology and type of soil, “pumping and treating” can be a good method to reduce high concentrations of pollution as quickly as possible or to limit its spread.

The polluted groundwater is pumped to the surface, treated and, in a purified state, added to a flowing water. However, due to the balance of binding and dissolving processes in the ground, it is difficult to achieve the desired low concentrations of pollutants in the remaining groundwater according to the applicable standards. Pump and Treat is not the first choice for remediation of contaminated sites. It is expensive and often tedious to treat the groundwater with this method.

The process is well suited to influencing the pressure conditions in the groundwater in such a way that further spread of the pollution is prevented.

Soil degassing

SVE (Soil Vapor Extraction), functional principle, side view with ventilation well

The prerequisite for using soil degassing (SVE, Soil Vapor Extraction) is an air-permeable cover layer (vadose zone) above the groundwater. This form of application takes place near the source of the contamination and prevents the spread of aerosol and gas contamination. A two-stage process is always used for soil degassing. The second stage is the above-ground treatment or neutralization of the extracted gaseous pollutants.

Ventilation with compressed gases

With this form of treatment, gases and vapors are expelled from the soil and groundwater through the introduction of compressed gases (air also in combination with other gases for direct treatment of the pollution in the subsoil) into the surface layer and the groundwater layer. The air sparging can also remove gaseous pollution and evaporable substances from the groundwater. They are also sucked out of the overlying layers of earth via suction wells with vacuum pumps and treated accordingly on the surface.

Ventilation with well

SVE (Soil Vapor Extraction), application principle, influence of ventilation

With a very porous type of soil (sand, gravel) in the vadose zone, simple ventilation wells can be used instead of compressed air. The introduced atmospheric oxygen can also have a positive effect on soil biology. The suction takes place again via suction wells using vacuum pumps.

Funnel and Gate

Funnel and Gate, principle, top view

The term literally means “funnel and gate”. This method has now proven to be the best and cheapest method for the remediation of groundwater pollution at the point of pollution. Here, groundwater flows with their impurities are blocked by a dense wall (funnel), collected in a funnel shape and fed to one or more gates (gates). The wall is built into the ground in such a way that the contaminated groundwater cannot flow around it. The systems and materials for water treatment are concentrated in the gates, suitable for the respective pollution. The systems are designed in such a way that the flow pressure of the groundwater is sufficient to pass the gates with the cleaning equipment without the use of pumps. The length of time the contaminated groundwater remains in the reaction and filter zones of the gates is determined by the length of the walls and the number of gates. If the "filter material" has to be changed over time, this is possible due to the concentrated arrangement in the gate.

The surface above the soiled area can be used almost entirely for construction purposes, because no machine houses or pumping stations are required. This fact and the low energy consumption make this process interesting.

Individual evidence

  1. ↑ Law on the organization of the water balance (WHG). Retrieved February 10, 2019 .
  2. ↑ SOIL VENTING / SOIL VAPOR EXTRACTION (overview, en). Retrieved February 10, 2019 .
  3. ^ The Center for Public Environmental Oversight (CPEO): "Air Sparging". Retrieved February 4, 2019 .
  4. ^ The Center for Public Environmental Oversight (CPEO): "Dual Phase Extraction". Retrieved February 4, 2019 .
  5. ↑ Volker Birke, Harald Burmeier, Diana Rosenau: Reactive walls for innovative remediation of contaminated sites. (PDF, 1,000 kB) 2000, accessed on February 10, 2019 .
  6. ↑ Wohnlich, Zosseder et al .: Calculation of a funnel and gate system for the passive renovation of a former gas works site. Retrieved February 10, 2019 .
  7. ↑ Sutherson, SS (1997). 'In situ' reactive walls. In: Sutherson, SS (ed.), Remediation Engineering: Design Concepts. CRC Press, ISBN 1-56670-137-6
  8. ↑ Weindl, Romboy, Koch: Long-term experience in operating a funnel-and-gate system. Terratec-BFM, September 2007, accessed on February 10, 2019 .