Pit water

Mine water (also bay water) is the amount of water that accumulates in the mine and is sponsored by the drainage -days. The accumulated at the lignite mine water is called Sümpfungswasser.

Formation

Although all the water that enters the mine, ultimately originating from atmospheric precipitation, the miner distinguishes between produced water and groundwater. The daily water penetrates through openings days in the mine. Part of the rainfall percolates through the soil into deeper soil layers and accumulates above impermeable layers and groundwater at. Mine water is mostly groundwater, which is located in the pore and fracture space of the rocks and from there, seeping into the mine. It should be noted that this water will take a relatively long time to reach greater depths. In the catchment area of ​​the tunnel Burgfeyer Mechernicher Bleierzbergbaureviers were for groundwater age ( mean residence times ) of at least three years, but partly also determined more than 100 years.

Temperature and quantity of mine water

The temperature and amount of water daily is subject to seasonal fluctuations. Since the groundwater occurs at greater depths, its amount and temperature all year round are pretty consistent. The temperature of the mine water increases with depth according to the geothermal gradient. Mine water in 1000 meters depth has an average temperature of 30 ° Celsius.

The amount of the mine water in a mine depends on various factors. Firstly, the surface finish of the area plays an important role. In mountainous areas the rainfall water flows rapidly into the valley and can not easily penetrate into the mine. This is different for mines whose deepest soles are below the Taloberfläche. The weather conditions have an impact on the amount of mine water. In regions with low rainfall usually occurs less pit water than in regions with high rainfall. The permeability of the rock layers that occur at the Earth's surface has a corresponding effect on the amount of water from the pit, as well as the structure of the deeper strata on the distribution of groundwater. The amount of mine drainage water increases generally in greater depths. When coal mining is the average amount of water to be lifted from a depth of 700 meters about 2 m3 per ton of usable coal.

Composition

The mine water has, due to a number of mineral substances in the earth, usually has its own chemistry to. Especially when the oxidation of pyrite, pyrite, chalcopyrite and related sulfides leads to acid mine water (pH values ​​up to 3.6 are known), the mine water is highly mineralized. In addition to the dissolved minerals, the mine water can cause mold with also by rotting wood pit. The additional components of the water vary from mine to mine:

• In coal mines, the mine water contains 4-6 per cent saline and proportions of nickel sulfate, iron and manganese. Iron then falls in oxygen-rich water in the form of iron ( III) oxide hydrates ( " ocher " ), which form a characteristic red-brown precipitate. Depending on the rock layer, the mine water can be either Contains sulphate or chloride content. If these mine waters mixed together, it comes to precipitation of barium sulfate. This precipitate the radium contained in the waters is coprecipitated.

• The mine water from brown coal mines often contains levels of calcium, of iron, zinc, magnesium, sodium, ammonium and manganese. Similar compositions are also often in the mine water of silver mines.

• The mine water from uranium mines contain under certain conditions, traces of uranium and radium, this is particularly true in the flooded mine workings.

Penetration into the pit building

During driving in water-bearing strata, the water penetrates through fissures into the mine. From a water intrusion occurs when a mine is unexpectedly flooded with water. If operation is abandoned, one speaks of a " sunken " pit. In order for these pits can be used again for extraction of raw materials, they must be gesümpft before.

In underground mining of mineral resources to set the overburden. The top layers above the mining field are loosened and are formed column and crevices, can seep into the mine through the groundwater. When sinking shafts, water-bearing layers are penetrated. If the well casing is not executed at these points carefully waterproof, water penetrates into the bay. In older wells, leaks can occur due to damage to the Schachtausmauerung due to a bay near depletion. Another source of the occurrence of pit water are water bubbles that are approached in the degradation.

Problems caused by mine water

Particularly problematic was the penetration of water while sinking shafts. Again and again had Abteufarbeiten deferred, because the pump capacity was not sufficient to dissipate the considerable amounts of water. Striking example is the sinking shaft Rheinpreußen 1, which lasted over a period of 20 years from 1857 to 1877. The Abteufarbeiten had to be stopped repeatedly, as the then technically available pump the amount of water could not dissipate. First developed in the first decade of the 20th century freeze well method solved the problem of water penetration during shaft sinking.

Another problem of mine water are water bubbles that are approached in the degradation. By this sudden appearance of large amounts of water throughout soles can be flooded, and there is a significant risk to miners. The mining disaster Lassing in 1998 was caused by such a water intrusion.

Tunneling

In tunneling means the unwanted water mountain water, especially if water-bearing rift or fault zone is cut during excavation. In longer periods can also flooding through pore or groundwater take place, but this one is not at extremely small tributaries in each case to the mountain water.

Water comes from mountain clefts or triggered by the construction of fault in the underground water resources and normally requires certain technical measures for the disposal or isolation, be increased by the cost. During the construction of some alpine railway or tramway tunnel, the water spills can be several 100 liters per second, but can be obtained by geophysical and geological exploration of the mountain structure somewhat more predictable. The elevated temperature of this water can be used for power generation, the so-called tunnel thermics, used.

Use

While the mine water has been used previously in many ways ( salt production, raw material extraction by precipitation, hot water ), nowadays this is hardly common.

Heat utilization

For the use of the thermal energy of the mine water left open and flooded mines is well suited. The mine water is heated to well due to the relaxation of the mountains and are achieved depending on depth, temperatures between 20 and 30 ° C. However, required because of the only moderate temperatures for heat recovery of the mine water heat pumps. The use of the heat energy of the mine water has already been tested successfully in several projects, for example in Ehrenfriedersdorf, but also in Heerlen / NL. For the use of certain licensing-related aspects must be considered. To obtain the geothermal energy, there are essentially two methods: the doublet and the single probe system. With the system duplicates a larger amount of energy can be obtained continuously, the single probe system is more cost effective.

Domestic water use

The resulting in opencast lignite mines Sümpfungswasser, depending on the degree of soiling, often used as process water. For this purpose, it is, if necessary, been clarified, and then pumped to the industry. Since lignite power plants are generally located in the immediate vicinity of the open pit mines, a large part of the water is used as cooling water in power plant operation. However, the sulfate content of the water must not exceed 300 milligrams per liter. In addition, the Sümpfungswasser is used either directly or after appropriate filtering as drinking or process water for the mining operations. A significant portion of the water is used for water management compensation measures.

Drinking water use

If mine water has no special dirt, it can be converted to transport drinking water. This has already been carried out in the middle of the 20th century in several villages in the winning country. There, the mine water of the disused iron ore mine Pützhorn was filtered and used for drinking water use.

Environmental impact

Mine waters are derived unfiltered into the next receiving water after their elevation in the rule. Depending on the composition of the mine water can be disrupted the chemistry of the surface waters and it can sustainable disruption to the environment is expected. Strong alkaline mine waters are not as harmful to the environment such as acid mine drainage. If by acidisches mine water, the pH of the surface water lowered increases the solubility of iron, manganese and other heavy metals. The greater bioavailability of heavy metals there is an accumulation of heavy metals in algae and plants and also in the entire food chain. This may result in certain toxicity limits are exceeded, the death by suffocation of aquatic species. The problem can thereby be water eruptions from mine buildings. This can stand water courses or by penetrating surface water, in extreme events such as floods, occur. This can lead to massive sediment relocations from the mine workings. These events occur due to the large quantities of water for dilution of the pollutants, it may, in turn, selectively result in an increase of the concentrations of heavy metals.

Through the introduction of radium mine water occurs radium enrichments in the rivers. In the Old Rhine area radium enrichments were found, which are due to discharges of radium -containing mine waters. However, the activity levels were below the detection limit in many cases.

Other effects

When mines are abandoned, usually the water is pumped out of service. This means that over time the water level rises up to its natural level. This water can adversely affect the Verfüllsäule the discarded chutes. This can lead to the extent that the Verfüllsäule slipping and there is a Schachtverbruch. In addition, the rising mine water can lift the concrete plug the custody shafts. Terrain elements that are deeper than the water outlet points of the mine water can be flooded. In many mines, the mine water is very salty. If now this pit of water at the rise in the underground aquifers that are used as drinking water, the fresh water can be chemically affected by the chloride content of the existing mine water. The sharp rise of the mine water can cause elevations of the soil, thereby raising may cause damage to buildings. The rise of the mine water also causes a rise in the groundwater level, this may in the affected regions, lead to waterlogging of building foundations and basements, with appropriate moisture damage.