Lowered groundwater level

For ISSZT, a physical barrier, such as a slurry wall or vertical membrane barrier, is installed around the area of contamination to a depth that will be slightly below the future lowered groundwater level to limit the escape of air from the area. Existing clay or silt may serve as a cap for the system, otherwise a man-made cap is installed. Wells are installed into the soil to inject the low-pressure compressed air beneath the cap. As the air pressure increases, the groundwater is lowered. The injected air is prevented from escaping by the cap at the top, the barrier along the sides, and the water table at the bottom. 

Nitrite (or compounds at the same or lower oxidation level) is produced microbiologically from nitrate, and may then react with the substrate to produce stable end products. The production of nitrite is the sole metabolic function of the bacteria and, in view of concern over the presence of nitrate in groundwater, the following possible environmental significance of these or analogous reactions should not be overlooked ... 

Figure 61. Lowering of the groundwater level. By pumping in air at top of the borehole...

With an airproof lid on top of the borehole and an air valve it would be possible to pump air into the casing. This way the groundwater level will be lowered, to preferably a bit above the lower edge on the casing as shown in Figure 61. 

The salt content of groundwater, surface water, and soils is a major factor in determining their benefit to the community, the economy, and the environment. In many areas around the globe, increasing demand for water has created tremendous pressures on water resources, which resulted in lowering water levels and increasing salinization. 

Use. Drained areas under cultivation and irrigation in the Klamath district produce good yields of alsike clover, rye, barley, and grasses initially, but yields decline when evaporation lowers the groundwater level and salts accumulate. 

After this area was pumped dry it was discovered that the groundwater levels in the old land around the perimeter of the newly created polder were much lower. This resulted in a drying out of the old land. They concluded that a peripheral lake between the polder and the old land would have kept this from occurring. 

Another groundwater contaminant that can be removed by reduction reactions is perchlorate. Ammonium perchlorate is a solid rocket fuel, and wastes from its manufacturing have contaminated some irrigation and drinking water sources, among them the lower Colorado River in the American Southwest. Elevated perchlorate levels have been linked to human health effects, and because perchlorate has been found in vegetable crops such as lettuce, there is concern that this contamination could have serious consequences. 

---