Topic: The main varieties of groundwater. Formation conditions. Geological activity of groundwater
2. The main types of groundwater.
1. Classification of groundwater.
Groundwater is very diverse in chemical composition, temperature, origin, purpose, etc. According to the total content of dissolved salts, they are divided into four groups: fresh, brackish, salty and brines. Fresh water contains less than 1 g / l of dissolved salts; brackish waters - from 1 to 10 g / l; salty - from 10 to 50 g / l; brines - more than 50 g / l.
According to the chemical composition of dissolved salts, groundwater is divided into hydrocarbonate, sulfate, chloride and complex composition (sulfate hydrocarbonate, chloride hydrocarbonate, etc.).
Waters with medicinal value are called mineral waters. Mineral waters come to the surface in the form of sources or are artificially brought to the surface using boreholes. According to the chemical composition, gas content and temperature, mineral waters are divided into carbon dioxide, hydrogen sulfide, radioactive and thermal.
Carbonic waters are widespread in the Caucasus, Pamirs, Transbaikalia, Kamchatka. The content of carbon dioxide in carbon dioxide waters ranges from 500 to 3500 mg / l and more. The gas is present in water in a dissolved form.
Hydrogen sulfide waters are also widespread and associated mainly with sedimentary rocks. The total content of hydrogen sulphide in water is usually small, but the therapeutic effect of hydrogen sulphide waters is so significant that an H2 content of more than 10 mg / l already gives them medicinal properties. In some cases, the content of hydrogen sulfide reaches 140-150 mg / l (for example, the well-known sources of Matsesta in the Caucasus).
Radioactive waters are divided into radon, containing radon, and radium, containing radium salts. The healing effect of radioactive waters is very high.
By temperature, thermal waters are divided into cold (below 20 ° C), warm (20-30 ° C), hot (37-42 ° C) and very hot (over 42 ° C). They are common in areas of young volcanism (in the Caucasus, Kamchatka, Central Asia).
2. The main types of groundwater
According to the conditions of occurrence, the following types of groundwater are distinguished:
· Soil;
· Top water;
· Ground;
· Interstratal;
· Karst;
· Cracked.
Soil water are located near the surface and fill the voids in the soil. The moisture in the soil layer is called soil water. They move under the influence of molecular, capillary and gravity forces.
In the aeration belt, there are 3 layers of soil water:
1.soil horizon with variable moisture content - root layer. It exchanges moisture between the atmosphere, soil and plants.
2. subsoil horizon, often "wet" does not reach here and it remains "dry".
capillary moisture horizon - capillary border.
Verkhovodka - temporary accumulation of groundwater in the near-surface layer of aquifers within the aeration zone, lying on a lenticular, wedging out aquiclude.
Verkhovodka - free-flow underground waters, occurring most close to the earth's surface and not having continuous distribution. They are formed due to the infiltration of atmospheric and surface waters trapped by impermeable or poorly permeable wedging out layers and lenses, as well as as a result of condensation of water vapor in rocks. They are characterized by a seasonality of existence: in dry seasons they often disappear, and during periods of rains and intense snow melting they reappear. They are subject to sharp fluctuations depending on hydrometeorological conditions (amount of precipitation, air humidity, temperature, etc.). Waters that temporarily appear in bog formations due to over-feeding of bogs also belong to upper water. Quite often, waterlogging occurs as a result of water leaks from the water supply system, sewerage, swimming pools and other water-carrying devices, which may result in waterlogging of the area, flooding of foundations and basements. In the area of distribution of permafrost rocks, the permafrost is classified as suprapermafrost waters. Verkhovka waters are usually fresh, slightly mineralized, but often contaminated with organic matter and contain increased amounts of iron and silicic acid. As a rule, Verkhovodka cannot serve as a good source of water supply. However, if necessary, measures are taken for artificial preservation: arrangement of ponds; branches from the rivers, providing constant power supply to the operated wells; planting of vegetation that retards snow melting; creation of waterproof lintels, etc. In desert areas, by means of grooves in clayey areas - takyrs, atmospheric water is diverted to the adjacent sands area, where a lens is created for the verkhovodka, which is a certain supply of fresh water.
Ground water lie in the form of a permanent aquifer on the first, more or less sustained, waterproof layer from the surface. Groundwater has a free surface called the mirror, or level, of groundwater.
Interstratal waters enclosed between water-resistant layers (layers). Interstratal waters under pressure are called confined or artesian. When the wells are opened, artesian waters rise above the top of the aquifer and, if the pressure level mark (piezometric surface) exceeds the mark of the Earth's surface at this point, then the water will pour out (gush). The conventional plane that determines the position of the pressure head in the aquifer (see Fig. 2) is called the piezometric level. The height of the rise of water above the waterproof roof is called the head.
Artesian waters lie in permeable sediments enclosed between watertight ones, completely fill the voids in the formation and are under pressure. The hydrocarbon established in the well is called piezometric, which is expressed in absolute marks. Self-flowing pressurized water has a local distribution and is better known among gardeners as "keys". The geological structures to which the artesian aquifers are confined are called artesian basins.
Rice. 1. Types of groundwater: 1 - soil; 2 - top water; 3 - ground; 4 ~ interstratal; 5 - waterproof horizon; 6 - permeable horizon
Rice. 2. Scheme of the structure of the artesian basin:
1 - impermeable rocks; 2 - permeable rocks with pressurized water; 4 - direction of groundwater flow; 5 - well.
Karst waters occur in karst cavities formed by dissolution and leaching of rocks.
Fissured water fill cracks in rocks and can be either pressure or non-pressure.
3. Conditions for the formation of groundwater
Groundwater is the first permanent aquifer from the earth's surface... About 80% of rural settlements use groundwater for water supply. Hot water has long been used for irrigation.
If the waters are fresh, then at a depth of 1–3 m they serve as a source of soil moisture. At a height of 1-1.2 m, they can cause waterlogging. If the groundwater is highly mineralized, then at a height of 2.5 - 3.0 m, they can cause secondary soil salinization. Finally, groundwater can make it difficult to dig construction pits, scorch built-up areas, aggressively affect the underground parts of structures, etc.
Groundwater forms different ways. Some of them are formed as a result of the seepage of atmospheric precipitation and surface water through the pores and cracks of rocks... Such waters are called infiltrative(the word "infiltration" means seepage).
However, the existence of groundwater cannot always be explained by the infiltration of atmospheric precipitation. For example, in areas of deserts and semi-deserts, very little precipitation falls, and they evaporate quickly. At the same time, even in desert areas, groundwater is present at some depth. The formation of such waters can only be explained condensation of water vapor in the soil... The elasticity of water vapor in the warm season in the atmosphere is greater than in soil and rocks; therefore, water vapor continuously flows from the atmosphere into the soil and forms groundwater there. In deserts, semi-deserts and dry steppes, water of condensation origin during hot times is the only source of moisture for vegetation.
Groundwater can form due to the disposal of the waters of ancient sea basins together with the accumulated sediments... The waters of these ancient seas and lakes could have survived in buried sediments and then seep into the surrounding rocks or emerge to the surface of the Earth. Such underground waters are called sedimentation waters .
Some of the groundwater origin may be associated with cooling molten magma... The release of water vapor from magma is confirmed by the formation of clouds and showers during volcanic eruptions. Underground waters of magmatic origin are called juvenile (from Latin "juvenalis" - virgin). According to oceanologist H. Wright, the vast expanses of water that exist at the present time, "grew drop by drop throughout the life of our planet due to water seeping from the bowels of the Earth."
The conditions of occurrence, distribution and formation of HS depend on the climate, relief, geological structure, the influence of rivers, soil and vegetation cover, and on economic factors.
a) The relationship between hot water and climate.
Precipitation and evaporation play an important role in the formation of mountain waters.
To analyze the change in this ratio, it is advisable to use the map of plant moisture supply. In relation to precipitation to evaporation, 3 zones (areas) are identified:
1.sufficient moisture
2.insufficient
3.slight moisturizing
In the first zone, the main areas of waterlogged lands are concentrated, requiring drainage (in some periods, moisture is required here). Areas of insufficient and insignificant moisture need artificial moisture.
In the three regions, the supply of HW by precipitation and their heat to the aeration zone are different.
In the area of sufficient humidification, the infiltration supply of groundwater at a depth of more than 0.5 - 0.7 m prevails over their thermal supply to the aeration zone. This pattern is observed in non-growing and growing seasons, with the exception of very dry years.
In the area of insufficient moisture, the ratio of precipitation infiltration with evaporation of HS at their shallow occurrence is different in the forest-steppe and steppe zones.
In forest-steppe, in loamy rocks in wet years, infiltration prevails over thermal HS into the aeration zone; in dry years, the ratio is reversed. In the steppe zone, in loamy rocks, during the non-growing season, infiltration nutrition prevails over the heat GW, and during the growing season, less consumption. In general, over the course of a year, infiltration recharge begins to prevail over the thermal recharge of groundwater.
In the area of insignificant moisture - in semi-deserts and deserts - infiltration in loamy rocks at a shallow bedding of GWL is incommensurably small compared to the flow rate into the aeration zone. In sandy rocks, infiltration begins to increase.
Thus, the supply of HS due to precipitation decreases, and the flow rate to the aeration zone increases with the transition from the region of sufficient to the region of insignificant moisture.
b) Connection of ground waters with rivers.
The forms of connection between groundwater and rivers are determined by the relief and geomorphological conditions.
The deeply incised river valleys serve as a sink for groundwater, draining the adjacent lands. On the contrary, with a small incision, typical of the lower reaches of rivers, the rivers feed groundwater.
Various cases of the ratio of surface water and groundwater are shown in the diagram.
Principal design scheme for the interaction of groundwater and surface waters under conditions of variability of surface runoff.
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a - low water; b - the ascending phase of the flood; c - the descending phase of the flood.
v) Relationship between groundwater and pressure water.
If there is no absolutely watertight layer between the groundwater and the underlying confined horizon, then the following forms of hydraulic connection are possible between them:
1) GWL is higher than the pressure water level, as a result of which the overflow of hot water into the pressure water is possible.
2) The levels are almost the same. With a decrease in the GWL, for example, by drains, the GW will be replenished by pressurized ones.
3) GWL periodically exceed the level of confined waters (during irrigation, precipitation), the rest of the time GW is fed by precipitation.
4) The groundwater level is constantly lower than the UNV, so the latter feed the groundwater.
Groundwater can be fed from artesian waters and through the so-called hydrogeological windows - areas where the continuity of the water-resistant layer is disturbed.
It is possible to feed hydrocarbons by pressure head through tectonic faults.
Hydrodynamic zones of GW, determined by the relief and geological structure, are closely related to the geostructural conditions of the territory. Areas of high drainage are characteristic of mountainous and foothill areas. Areas of low drainage are characteristic of troughs and depressions of platform plains.
The zoning of HS feeding is most clearly manifested in the zone of low drainage of the arid regions. It consists in a sequential increase in the mineralization of HS with distance from the source of the river, canal, etc. Therefore, in arid regions, water supply wells are usually placed along canals and rivers.
4. Conditions of formation and occurrence of artesian waters.
Artesian waters are formed at a certain geological structure - the alternation of permeable reservoirs with water-resistant ones. They are confined mainly to synclinal or monoclinal bed formations.
The area of development of one or more artesian layers is called an artesian basin. AB can occupy from several tens to hundreds of thousands of km 2.
The sources of pressure water supply are sediments, seepage waters of rivers, reservoirs, irrigation canals, etc. Pressure waters under certain conditions are replenished with groundwater.
Their consumption is possible by unloading them into river valleys, coming out to the surface in the form of springs, slowly seeping through the strata enclosing the pressure layer, with overflowing into groundwater. The selection of water supplies for water supply and irrigation also constitutes their expenditure items.
In artesian basins, areas of nutrition, pressure and discharge are distinguished.
Recharge area - the area where the artesian layer emerges on the surface of the earth, where it is fed. It is located at the highest elevations of the artesian basin relief in mountainous areas and watersheds, etc.
The pressure area is the main area of distribution of the artesian basin. Within its limits, groundwater has a pressure.
Discharge area - area of outlet of pressure water to the surface - open discharge (in the form of ascending springs or area of hidden discharge, for example, in river beds, etc.)
Wells that penetrate AB gush out, this is an example of artificial discharge of pressure water.
In formations containing gypsum, anhydrides, salts, artesian waters have increased mineralization.
Types and zoning of artesian waters
Artesian basins are usually typified by the geostructure of water-bearing and water-resistant rocks.
On this basis, two types of artesian basins are distinguished (according to N.I. Tolstikhin):
1.artesian platform basins, which are usually characterized by a very large area of development and the presence of several confined aquifers (these are the Moscow, Baltic, Dnieper-Donetsk, etc.)
2. artesian basins of folded areas confined to intensively dislocated sedimentary, igneous and metamorphic rocks. They differ in a smaller development area. Examples are the Fergana, Chui and other basins.
5. Geological activity of groundwater.
Groundwater carries out destructive and constructive work. The destructive activity of groundwater is manifested mainly in the dissolution of water-soluble rocks, which is facilitated by the content of dissolved salts and gases in the water. Among the geological processes caused by the WR activity, first of all, karst phenomena should be called.
Karst.
Karst is the process of dissolution of rocks by underground and seeping surface waters moving in them. As a result of karst, caves and voids of various shapes and sizes are formed in the rocks. Their length can reach many kilometers.
Of the karst systems, the Mammoth Cave (USA) has the greatest length, the total length of the passages of which is about 200 km.
Saline rocks, gypsum, anhydrides and carbonate rocks are subject to karst. Accordingly, karst is distinguished: salt, gypsum, carbonate. Karst development begins with expansion (under the influence of leaching) cracks. Karst determines specific landforms. Its main feature is the presence of karst funnels with a diameter of several to hundreds of meters and a depth of up to 20-30 m. Karst develops the more intensively, the more precipitation falls and the greater the speed of movement of underground streams.
Areas prone to karst are characterized by rapid absorption of precipitation.
Within the massifs of karst rocks, zones of downward movement of water and horizontal movement are distinguished in the direction of river valleys, the sea, etc.
In karst caves, drip formations of a predominant carbonate composition are observed - stalactites (growing down) and stalagmites (growing from below). Karst weakens rocks, reduces their quantity as a basis for GTS. Through karst voids, significant water leakage from reservoirs and canals is possible. And at the same time, groundwater trapped in karst rocks can be a valuable source for water supply and irrigation.
The destructive activity of groundwater includes suffusion (undermining) - this is the mechanical removal of small particles from loose rocks, which leads to the formation of voids. Such processes can be observed in loess and loess-like rocks. In addition to mechanical, chemical suffusion is distinguished, an example of which is karst.
The creative work of underground waters is manifested in the deposition of various compounds, cementing cracks in rocks.
Control questions:
1 Give the classification of groundwater.
2. Under what conditions is groundwater generated?
3. Under what conditions artesian groundwater is formed?
4. What is the manifestation of the geological activity of groundwater?
5. Name the main types of groundwater.
6. How does the vermicompost influence the construction?
When evaluating groundwater properties investigate the taste, smell, color, transparency, temperature and other physical properties of groundwater, which characterize the so-called organoleptic properties water (determined using the senses). Organoleptic properties can sharply deteriorate when various impurities (mineral suspended particles, organic substances, some chemical elements) enter the water naturally or artificially.
Temperature groundwater fluctuates widely depending on the depth of the aquifers, geological features, climatic conditions, etc. Distinguish between cold waters (temperatures from 0 to 20 ° C), warm, or subthermal waters (20-37 ° C ), thermal (37-10 ° C), overheated (over 100 ° C). Very cold groundwater circulates in the permafrost zone, in high mountain areas; superheated waters are typical for areas of young volcanic activity. In the areas of water intakes, the water temperature is usually 7-11 ° C.
Chemically pure water colorless. Mechanical impurities (yellowish, emerald, etc.) give the water color. The clarity of the water depends on the color and the presence of turbidity. The taste is associated with the composition of solutes: salty - from sodium chloride, bitter - from magnesium sulfate, etc. The smell depends on the presence of gases of biochemical origin (hydrogen sulfide, etc.) or decaying organic matter.
Density of water- the mass of water in a unit of its volume. It is maximum at a temperature of 4 ° C. With an increase in temperature to 250 ° C, the density of water decreases to 0.799 g / cm 3, and with an increase in the amount of salts dissolved in it, it rises to 1.4 g / cm 3. The compressibility of groundwater is characterized by compressibility factor, showing how much of the initial volume of liquid the volume decreases with an increase in pressure of 10 5 Pa. The coefficient of compressibility of groundwater is 2.5 10 -5 ... 5 10 ~ 5 Pa, that is, water to some extent has elastic properties, which is important in the study of pressurized groundwater.
Viscosity water characterizes the internal resistance of particles to its movement. With increasing temperature, the viscosity of groundwater decreases.
Electrical conductivity groundwater depends on the amount of salts dissolved in them and is expressed in resistivity values from 0.02 to 1.00 Ohm.
Radioactivity groundwater is caused by the presence of radioactive elements in it (uranium, strontium, cesium, radium, gaseous emanation of radium-radon, etc.). Even negligible concentrations - hundredths and thousandths (mg / l) of some radioactive elements - can be harmful to human health.
Chemical composition of groundwater. All groundwater always contains in a dissolved state more or less salts, gases, and organic compounds.
Gases dissolved in water (0 2, C0 2, CH 4, H 2 S, etc.) give it a certain taste and properties. The quantity and type of gases determines the degree of suitability of water for drinking and technical purposes. Groundwater near the surface of the earth is often contaminated with organic impurities (various pathogenic bacteria, organic compounds coming from sewer systems, etc.). Such water tastes unpleasant and is hazardous to human health.
Salt. Chlorides, sulfates and carbonates are the most widespread in groundwater. According to the total content of dissolved salts, groundwater is divided into fresh (up to 1 g / l of dissolved salts), brackish (from 1 to 10 g / l), salty
(10-50 g / l) and brines (more than 50 g / l). The amount and composition of salts is established by chemical analysis. The results obtained are expressed as the composition of cations and anions (in mg / l or meq / l).
Under natural conditions, the general mineralization of groundwater is extremely diverse. There are underground waters with mineralization from 0.1 g / l (high-mountain springs) to 500-600 g / l (deep-lying waters of the Angara-Lena artesian basin). General mineralization is one of the main indicators of groundwater quality.
Several tens of chemical elements of Mendeleev's periodic table are present in underground waters. Up to 90% of all salts dissolved in waters, ions C1 ~, 80 ^, HCO3, Ia +,
Mg 2+, Ca 2+, K +. Iron, nitrites, nitrates, hydrogen, bromine, iodine, fluorine, boron, radioactive and other elements are contained in water in smaller quantities. However, even in small quantities, they can have a significant impact on assessing the suitability of groundwater for various purposes. The best drinking qualities are possessed by waters at pH = 6.5 ... 8.5.
The amount of dissolved salts should not exceed 1.0 g / l. The content of chemical elements harmful to human health (uranium, arsenic, etc.) and pathogenic bacteria is not allowed. The latter, to a certain extent, can be neutralized by ultrasonic treatment of water, chlorination, ozonation and boiling. Organic impurities are identified by bacteriological analysis. Water for drinking purposes should be colorless, transparent, odorless, and pleasant to the taste.
Rigidity and aggressiveness of groundwater associated with the presence of salts. Hardness of water- This is a property due to the content of calcium and magnesium ions, that is, associated with carbonates, and is calculated by calculation by the total content of hydrocarbonate and carbonate ions in water. Hard water gives a lot of scale in steam boilers, does not wash well, etc. At present, hardness is usually expressed by the number of milligram equivalents of calcium and magnesium, 1 meq of hardness corresponds to the content of 20.04 mg of calcium ion in 1 liter of water, or 12, 6 mg magnesium ion. In other countries, hardness is measured in degrees (1 meq = 28 °). According to hardness, water is divided into soft(less than 3 mEq or 8.4 °),
medium hardness(3-6 mEq or 8.4 °), tough(6-9 mEq or 16.8-25.2 °) and very tough(more than 9 mEq or 25.2 °). The best quality is possessed by water with a hardness not exceeding 7 meq. Stiffness is permanent and temporary. Temporary stiffness associated with the presence of bicarbonates and can be removed by boiling. Constant stiffness, due to sulfuric acid and chloride salts, is not eliminated by boiling. The sum of temporary and permanent stiffness is called overall rigidity.
Aggressiveness groundwater is expressed in the destructive effect of salts dissolved in water on building materials, in particular, on Portland cement. Therefore, when building foundations and various underground structures, it is necessary to be able to assess the degree of aggressiveness of groundwater and determine measures to combat it. In the existing standards assessing the degree of aggressiveness of waters in relation to concrete, in addition to the chemical composition of water, the filtration coefficient of rocks is taken into account. The same water can be aggressive and non-aggressive. This is due to the difference in the speed of movement of water - the higher it is, the more volumes of water will come into contact with the concrete surface and, therefore, the more aggressive will be.
In relation to concrete, the following types of groundwater aggressiveness are distinguished:
- general acid - estimated by the pH value, in sands water is considered aggressive if the pH
- sulfate - determined by the ion content; when the content of BO 2- in an amount of more than 200 mg / l, the water becomes aggressive;
- magnesian - established by the content of the ion IV ^ 2+;
- carbonate - associated with the effect of aggressive carbon dioxide on concrete, this type of aggressiveness is possible only in sandy rocks.
The aggressiveness of groundwater is established by comparing the data of chemical analyzes of water with the requirements of standards. After that, measures to combat it are determined. For this, special cements are used, they waterproof the underground parts of buildings and structures, lower the groundwater level with a drainage device, etc.
Aggressive effect of groundwater on metals(metal corrosion). Groundwater with salts and gases dissolved in it can be intensely corrosive towards iron and other metals. An example is the oxidation (erosion) of metal surfaces with the formation of rust under the action of oxygen dissolved in water:
2? E+ 0 2 = 2GeO 4GeO + 0 2 = 2Pe 2 0 3 Fe 2 0 3 + 3N 2 0 = 2Pe (OH) 3
Groundwater has corrosive properties when it also contains aggressive carbon dioxide, mineral and organic acids, heavy metal salts, hydrogen sulfide, chloride and some other salts. Soft water (with a total hardness of less than 3.0 meq) is much more aggressive than hard water. Metal structures can undergo the greatest corrosion under the influence of strongly acidic ones (pH 9.0). Corrosion is promoted by an increase in the temperature of groundwater, an increase in its velocity by its movements, and electric fields in the soil strata.
The assessment of the corrosiveness of waters in relation to some metals is carried out in accordance with the current GOST. After that, according to SNiP, measures are chosen to prevent possible corrosion.
Groundwater classification. There are a number of classifications, but there are two main ones. Ground waters are subdivided according to the nature of their use and according to the conditions of occurrence in the earth's crust (Fig. 63). The former include potable water, technical, industrial, mineral, thermal. The latter include: upstream waters, ground and interstratal waters, as well as waters of cracks, karst, and permafrost. For engineering and geological purposes, it is advisable to classify groundwater according to hydraulic characteristics - gravity and pressure.
Household drinking water. Groundwater is widely used for household and drinking purposes. Fresh groundwater is the best source of drinking water supply, so its use for other purposes is generally not allowed.
The source of drinking water supply is the underground waters of the zone of intensive water exchange. The depth of occurrence of fresh groundwater from the surface of the earth usually does not exceed several tens of meters. However, there are areas where they occur at great depths (300-500 m and more).
In recent years, brackish and salty groundwaters after artificial desalination have also begun to be used for domestic drinking water supply.
Technical waters- these are waters that are used in various industries and agriculture. Trebova-
Atmospheric
to ground industrial waters reflect the specifics of a particular type of production.
Industrial water contain in the solution useful elements (bromine, iodine, etc.) in an amount of industrial raw material value. They usually occur in a zone of very slow water exchange, their salinity is high (from 20 to 600 g / l), their composition is sodium chloride, and the temperature often reaches 60-80 ° C.
The exploitation of industrial water for the extraction of iodine and bromine is profitable only when the water depth is no more than 3 km, the water level in the well is not lower than 200 m, and the amount of water extracted per day is not less than 200 m 3.
Mineral underground waters are called, which have a high content of biologically active microcomponents, gases, radioactive elements, etc. They come to the surface of the earth by sources or are exposed by boreholes.
Thermal underground waters have a temperature of more than 37 ° C. They occur everywhere at depths from several tens and hundreds of meters (in mountainous folded regions) to several kilometers (on platforms).
Through cracks, thermal waters often come to the surface of the earth, forming hot springs with temperatures up to 100 ° C (Kamchatka, Caucasus). The reserves of these waters in the earth's crust are very large and they are actively used for heating cities and for energy purposes, for example, in Kamchatka (Pauzhetka geothermal station). There are several regions of active geyser activity on Earth: Kamchatka, Iceland, the Northeast of the USA, New Zealand.
Groundwater - water located in the rock mass of the upper part of the earth's crust in a liquid, solid and gaseous state.
Classification
According to the conditions of occurrence, groundwater is divided into several types: soil, groundwater, interstratal, artesian, and mineral.
Soil water fill part of the gaps between soil particles; they can be free (gravitational), moving under the influence of gravity, or bound, held by molecular forces.
Ground water form an aquifer on the first water-resistant layer from the surface. Due to the shallow bedding from the surface, the groundwater level experiences significant fluctuations in the seasons: it either rises after precipitation or snow melts, then decreases in dry times. In harsh winters, groundwater can freeze through. These waters are more susceptible to pollution.
Interstratal waters- underlying aquifers, enclosed between two water-resistant layers. Unlike groundwater, the interstratal water level is more constant and changes less over time. Interstratal waters are cleaner than groundwater. Pressurized interstratal waters completely fill the aquifer and are under pressure. All waters enclosed in layers in concave tectonic structures have a head.
According to the conditions of movement in aquifers, groundwater is distinguished, circulating in loose (sandy, gravel and pebble) layers and in fractured rocks.
Depending on the occurrence, the nature of the voids of the water-bearing rocks, groundwater is divided into:
- porous - occur and circulate in Quaternary sediments: in sands, pebbles and other detrital rocks;
- fissure (vein) - in rocks (granites, sandstones);
- karst (fissure-karst) - in soluble rocks (limestone, dolomite, gypsum, etc.).
Groundwater reserves
Groundwater is part of the Earth's water resources; the total reserves of groundwater are over 60 million km³. Groundwater is considered a mineral resource. Unlike other types of minerals, groundwater reserves are renewable during operation.
Groundwater exploration
To determine the presence of underground water, exploration is carried out:
- geomorphological assessment of the area,
- temperature studies,
- radon method,
- support wells are drilled with coring,
- the core is studied and the relative geological age of the rocks, their thickness (thickness),
- experimental pumping is carried out, the characteristics of the aquifer are determined, an engineering-geological report is drawn up;
- for several reference wells, maps, sections are drawn up, a preliminary assessment of mineral reserves (in this case, water) is carried out;
Origin of groundwater
Groundwaters have different origins: some of them were formed as a result of the penetration of melt and rainwater to the first water-resistant horizon (that is, to a depth of 1.5-2.0 m, which form groundwater, that is, the so-called top water); others occupy deeper cavities in the ground.
Water is the most abundant substance on our planet that sustains life on it. It is found both in the lithosphere and in the hydrosphere. The biosphere of the Earth consists of ¾ water. An important role in the circulation of this substance is played by its underground species. Here it can be formed from mantle gases, during runoff, etc. In this article, we will consider the types of groundwater.
Concept
Underground waters are understood as the latter, located in the earth's crust, located in rocks below the surface of the Earth in various states of aggregation. They form part of the hydrosphere. According to V. I. Vernadsky, these waters can be located at a depth of up to 60 km. The estimated volume of groundwater located at a depth of 16 km is 400 million cubic km, that is, a third of the waters of the World Ocean. They are located on two floors. The lower one contains metamorphic and igneous rocks, so the amount of water here is limited. The bulk of the water is located in the upper floor, in which the sedimentary rocks are located.
Classification by the nature of exchange with surface waters
There are 3 zones in it: the upper one is free; middle and lower - delayed water exchange. The types of groundwater are different in composition in different zones. So, in the upper of them there are fresh waters used for technical, drinking and economic purposes. In the middle zone there are ancient waters of various mineral composition. In the lower part there are highly mineralized brines, from which various elements are extracted.
Mineralization classification
The following types of groundwater are distinguished by salinity: ultra-, fresh, having a relatively high salinity - only the latter group can reach a salinity level of 1.0 g / cu. dm; brackish, salty, high salinity, brines. In the latter, mineralization exceeds 35 mg / m3. dm.
Occurrence classification
The following types of groundwater are distinguished according to the conditions of occurrence: top water, ground, artesian and soil waters.
Verkhovodka is mainly formed on lenses and wedging out layers of low-permeability or water-resistant rocks in the aeration zone during infiltration of surface and atmospheric waters. Sometimes it is formed due to the illuvial horizon under the soil layer. The formation of these waters is associated with the processes of condensation of water vapors in addition to those listed above. In some climatic zones, they form fairly large reserves of high-quality water, but mainly thin aquifers are formed, which disappear during drought and are formed during periods of intense moisture. Basically, this type of groundwater is typical for loams. Its thickness reaches 0.4-5 m. The relief has a significant effect on the formation of the perch. On steep slopes, it exists for a short time or is absent altogether. On flat steppes with depressions in the form of saucers and flat watersheds, on the surface of river routes, a more stable top water is formed. It has no hydraulic connection with river waters, while being easily polluted by other waters. At the same time, it can feed groundwater, or it can be consumed for evaporation. The upper water can be fresh or slightly mineralized.
Groundwater is part of groundwater. They are located on the first aquifer from the surface, lie on the first aquifer, consistent in area. Basically, they are free-flow waters, they can have a small head in areas with a local waterproof overlap. The depth of occurrence, their chemical and physical properties are subject to periodic fluctuations. Distributed everywhere. They feed by infiltration of precipitation from the atmosphere, filtration from surface sources, condensation of water vapor and subsurface evaporation, additional nutrition from the lower aquifers.
Artesian water is a part of groundwater with a head, which occurs in aquifers between relatively water-resistant and water-resistant strata. They lie deeper than groundwater. In most cases, the areas of nutrition and creation of pressure do not coincide in them. Water appears in the well below the steady-state level. The properties of these waters are less susceptible to fluctuations and pollution compared to groundwater.
Soil waters are those that are confined to the soil water layer, take part in the supply of plants with this substance, and are associated with the atmosphere, aquifer and groundwater. They have a significant effect on the chemical composition of groundwater when they are deeply buried. If the latter are located shallowly, then the soil becomes waterlogged and waterlogging begins. Gravitational water does not form a separate horizon; it moves from top to bottom under the action of capillary forces or gravity forces in different directions.
Classification by formation
The main types of groundwater are infiltration, which are formed due to the percolation of atmospheric precipitation. In addition, they can form as a result of condensation of water vapor, which enters fractured and porous rocks along with air. In addition, relict (buried) waters are distinguished, which were in ancient basins, but were buried by thick layers of sedimentary rocks. Thermal waters, which were formed at the last stages of magmatic processes, are also a separate species. These waters form magmatogenic or juvenile species.
Classification of the movement of the objects under consideration
The following types of groundwater movement are distinguished (see figure).
Percolation and precipitation from the atmosphere occurs in the aeration zone. Moreover, this process is divided into free and normal infiltration. The first involves the implementation of movement from top to bottom under the influence of gravity and capillary forces through some tubules and capillary pores, while the porous space is not saturated with water, which contributes to the preservation of air movement. During normal infiltration, the above forces are combined with hydrostatic pressure gradients, which leads to the fact that the pores are completely filled with water.
In the saturation zone, hydrostatic pressure and gravity act, which contributes to the movement of free water along cracks and pores to the sides, a decrease in the pressure or slope of the surface of the horizon carrying water. This movement is called filtration. The highest speed of water movement is observed in underground karst caves and canals. The second place is taken by pebbles. Much slower movement is observed in the sands - the speed is 0.5-5 m / day.
Types of groundwater in the permafrost zone
These groundwaters are classified into suprapermafrost, interpermafrost and subpermafrost. The former are located in the thickness of permafrost on a confining layer, mainly at the foot of the slopes or at the bottom of river valleys. They, in turn, are divided into the seasonally freezing, top water, located in the active layer; on seasonally partially freezing, with the upper part in the active layer, on seasonally non-freezing, the occurrence of which is noted below the seasonally freezing layer. In some cases, a rupture of the active layer of various soils can occur, which leads to the release of some part of the suprapermafrost water to the surface, where it takes the form of ice.
Interpermafrost waters may be present in the liquid phase, but they are most widespread in the solid phase; as a rule, they are not subject to seasonal thawing / freezing processes. These waters in the liquid phase provide water exchange with above- and subpermafrost waters. They can come to the surface like springs. The permafrost waters are artesian. They can be from fresh to brine.
The types of groundwater in Russia are the same as discussed above.
Contamination of the objects under consideration
The following types of groundwater pollution are distinguished: chemical, which, in turn, is subdivided into organic and inorganic, thermal, radioactive and biological.
The chemical pollutants are mainly liquid and solid waste from industrial enterprises, as well as pesticides and fertilizers from agricultural producers. Heavy metals and other toxic elements affect groundwater to the greatest extent. They spread over aquifers over considerable distances. Radionuclide contamination behaves in a similar way.
Biological pollution is caused by pathogenic microflora. Sources of pollution are usually cattle yards, faulty sewerage, cesspools, etc. The spread of microflora is determined by the rate of filtration and survival of these organisms.
It is an increase in groundwater temperature arising from the operation of a water intake. It can occur in areas where waste water is discharged or when a water intake is located near a reservoir with more heated surface waters.
Use of subsoil
Extraction of groundwater as a type of subsoil use is regulated by the Federal Law “On Subsoil”. The extraction of these objects requires a license. It is issued in relation to groundwater for up to 25 years. The term of use begins to be calculated from the moment of state registration of the license.
Mining operations must be registered with Rosreestr. Then they draw up a project and submit it for state examination. Then they prepare a project for organizing an underground water intake sanokhrzone, estimate the reserves of these waters and transfer the calculations to the state expert examination, the Geoinformation Fund and the Rosgeolfond. Further, certificates of ownership of land are attached to the received documents, after which an application for a license is submitted.
Finally
What types of groundwater are there in Russia? The same as in the world. The area of our country is large enough, therefore, it contains permafrost, artesian, ground and soil waters. The classification of the objects under consideration is rather complicated, and in this article it is reflected incomplete, here its most basic points are shown.
All waters in the mass of rocks in a solid, liquid or gaseous state are called underground
On the continents, they form a continuous shell, which is not interrupted even in areas of dry steppes and deserts. Like surface waters, they are in constant motion and participate in the general water cycle in nature. The construction and operation of most surface structures and all underground ones are associated with the need to account for the movement of groundwater, their composition and condition. The physical and mechanical properties and state of many rocks depend on groundwater. They often flood construction pits, ditches, trenches and tunnels, and, coming to the surface, contribute to waterlogging of the territory. Groundwater can be an aggressive environment for rocks. They are the main reason for many physical and geological processes that occur in natural conditions, during the construction and operation of engineering structures.
Distinguish:
Drinking water- water, in terms of its quality in its natural state or after processing, meets regulatory requirements and is intended for drinking and domestic needs of a person, or for the production of food products. This type of water also includes natural mineral table waters, which include underground waters with a total salinity of not more than 1 g / dm 3, which do not require water treatment or do not change their natural composition after water treatment.
Technical groundwater - waters of various chemical composition (from fresh to brines), intended for use in production, technical and technological purposes, the quality requirements of which are established by state or industry standards, specifications or consumers.
Groundwater is also subdivided:
Groundwater is mainly formed as a result of seepage (infiltration) of atmospheric precipitation and surface water into the earth's crust. Water passes through permeable rocks to the water-resistant layer and accumulates on it, forming an underground basin or stream. This underground water is called infiltration... The amount of infiltration water depends on the climatic conditions of the area, relief, vegetation, composition of the upper strata rocks, their structure and texture, as well as the tectonic structure of the area. Infiltration groundwater is the most common.
Groundwater can also be formed by condensation of vaporous water constantly circulating in the pores of rocks. Condensing groundwater is formed only in summer and partly in spring and autumn, and in winter it is not formed at all. AF Lebedev explained the formation of significant reserves of underground water in the zones of deserts and semi-deserts, where the amount of atmospheric precipitation is negligible by the condensation of water vapor. Not only atmospheric water vapor can condense, but also water vapor released from magma chambers and other high-temperature zones of the earth's crust. Such groundwater is called juvenile .Juvenile groundwater is usually highly mineralized. In the course of geological development, buried water basins can be preserved in the thickness of the earth's crust. The water contained in the sedimentary strata of these basins is called relict.
The formation of groundwater is a complex process that begins with the accumulation of sediments and is closely related to the geological history of the region. Very often, groundwater of various origins mixes with each other, forming mixed by the origin of the water.
The upper part of the earth's crust, from the point of view of the distribution of groundwater, is usually divided into two zones: the aeration zone and the saturation zone. In the aeration zone, not always all pores of rocks are filled with water. All waters of the aeration zone are fed by atmospheric precipitation, intensively evaporated and absorbed by plants. The amount of water in this zone is determined by climatic conditions. In the saturation zone, regardless of climatic conditions, all the pores of the rocks are always filled with water. Above the saturation zone, there is a capillary humidification subzone. In this subzone, fine pores are filled with water, and large ones with air.
In the aeration zone, soil water and upper water are formed. Soil water lies directly at the surface of the earth. This is the only water that does not have a water seal under it and is represented mainly by bound and capillary water. Soil water is in a complex relationship with animals and plants. It is distinguished by sharp temperature fluctuations, the presence of microorganisms and humus. Builders encounter soil water only in swampy areas.
Verkhovodka formed in the aeration zone on waterproof lenses. Any temporary accumulation of water in the aeration zone is also called high water. Atmospheric precipitation, penetrating into this zone, can temporarily linger on low-permeability or compacted layers. Most often this occurs in the spring during the period of snow melting or during the period of heavy rains. During dry periods, the perch may disappear. The characteristic features of the upstream are the inconstancy of existence, limited distribution, low power and pressurelessness. Verkhovodka often creates difficulties for builders, since the presence or the possibility of its formation is not always established during engineering geological surveys. Formed upstream water can cause flooding of engineering structures, waterlogging of territories.
Ground is called the water that occurs on the first permanent waterproof layer from the earth's surface. Groundwater exists constantly. They have a free water surface called a mirror of groundwater, and waterproof bed. The projection of the groundwater table onto a vertical plane is called groundwater level (UGV). The distance from the aquiclude to the groundwater level is called the thickness of the aquifer. The groundwater level, and, consequently, the thickness of the aquifer are variable values and can change throughout the year depending on climatic conditions. Groundwater supply is mainly due to atmospheric and surface waters, but they can also be mixed, infiltration-condensation. The area of the earth's surface from which surface and atmospheric water enters the aquifer is called nutritional area groundwater. The area of groundwater recharge always coincides with the area of their distribution. Ground waters, due to the presence of a free water surface, are free-flowing, that is, the water level in the well is set at the same mark at which the water is encountered.
Depending on the conditions of groundwater occurrence, groundwater flows and basins are distinguished. Soil streams have an inclined mirror and are in continuous motion towards the slope of the aquiclude. Ground basins have a horizontal mirror and are much less common.
Groundwater, being in constant motion, has a close connection with surface watercourses and water bodies. In areas where precipitation prevails over evaporation, groundwater usually feeds rivers. In arid regions, very often water from rivers enters groundwater, replenishing underground streams. There may also be a mixed type of connection, when from one side the groundwater feeds the river, and from the other - the water from the river enters the ground flow. The nature of the connection may vary depending on climatic and some other conditions.
When designing and building engineering structures, it is necessary to take into account groundwater regime, that is, the change over time of indicators such as fluctuations in the level of groundwater, temperature and chemical composition. The level and temperature of groundwater are subject to the greatest changes. The reasons for these changes are very diverse and are often directly related to human construction activities. Climatic factors cause both seasonal and long-term changes in the level of groundwater. Floods on rivers, as well as reservoirs, ponds, irrigation systems, canals, drainage structures lead to a change in the groundwater regime.
The position of the groundwater table is depicted on maps using hydroisohypsum and hydroisobaths. Hydroisogypsum- lines connecting points with the same absolute elevations of the groundwater level. These lines are similar to the contours of the relief and, like them, reflect the relief of the groundwater table. The hydroisohypsum map is used to determine the direction of movement of groundwater and to determine the value of the hydraulic gradient. The direction of movement of groundwater is always perpendicular to the hydroisohypsum from higher to lower elevations. The directions along which groundwater moves with a steady motion that does not change in time are called streamlines. If the streamlines are parallel to each other, then such a flow is called flat. The stream can also be converging and diverging. The smaller the distance between the hydroisohypsum, the greater the hydraulic gradient of the soil flow. Hydroisobates- lines connecting points with the same groundwater depth.
Interstratal groundwater refers to aquifers that lie between two aquicludes. They can be non-pressurized and pressurized. Interstratal non-confined waters are rare. By the nature of the movement, they are similar to groundwater. Interstratal pressure waters are called artesian. The occurrence of artesian waters is very diverse, but the most common is synclinal. Artesian water always fills the entire aquifer from bottom to top and has no free water surface. The area of distribution of one or more levels of artesian aquifers is called artesian basin. The areas of artesian basins are huge and are measured in tens, hundreds, and sometimes thousands of square kilometers. In each artesian basin, areas of feeding, distribution and discharge are distinguished. The recharge area of artesian basins is usually located at large distances from the center of the basin and at higher elevations. It never coincides with the area of their distribution, which is sometimes called the area of pressure. Artesian waters experience hydrostatic pressure due to the difference in the marks of the supply area and the discharge area, according to the law of communicating vessels. The level at which artesian water is established in the well is called piezometric. Its position is determined piezometric line, or a pressure line, a conditional straight line that connects the supply area with the discharge area. If the piezometric line passes above the surface of the earth, then when the aquifer is opened with wells, gushing will occur, and the head is called positive. When the piezometric level is located below the surface of the earth, then the head is called negative, and water does not pour out of the well. Artesian waters are generally more saline and less associated with surface watercourses and bodies of water than groundwater.
Fissured waters underground waters confined to fractured igneous, metamorphic and sedimentary rocks are called. The nature of their movement is determined by the size and shape of the cracks. Fractured waters can be non-confined and confined. They are fickle and can change the nature of their movement. Erosion and dissolution of rocks lead to the expansion of cracks, and crystallization of salts and the accumulation of sediments - to their narrowing. Fracture water consumption can reach 500 m 3 / h. Fractured waters pose significant difficulties in the construction of underground structures.
Underground water in the city
In cities, the demand for water is great, but groundwater resources are limited. In many ways, the process of restoring water resources depends on the state of the urban environment itself, its ecology. This important factor is responsible not only for the volume of groundwater resources, but also for the level of their pollution.
In recent years, the study of groundwater in urban areas has been included in the section of hydrogeology.
Problems arising from the interaction of groundwater with the urban environment are groundwater pollution through sewage pipes, and lowering of the groundwater level by pumping systems, and the threat of groundwater flooding of underground spaces of the urban environment (for example, the subway).
Now the issue of preserving and protecting groundwater from pollution is especially acute. After all, the stability of the development of most cities largely depends on them, which brings the problem to a global level.
Starting from the tasks set and based on the latest achievements in the field of hydrogeology, scientists are developing new schemes for monitoring and monitoring the level of groundwater pollution, their activity within the underground space of the urban environment.
And yet, no matter what important role in the development of urban space its connection with groundwater plays, it is quite obvious that in this type of interaction the urban environment is assigned the lot of an external limiter, rather than an equal participant.
Many cities use underground water as drinking water. Everyone knows that water is a renewable resource, but at the same time it is strongly influenced by external factors. It is very important to monitor the level of groundwater and the degree of their pollution. This delicate balance is extremely important for the sustainable development of urban space. A negligent attitude towards water resources leads to very disastrous consequences. For example, in Mexico City, the constant decline in the water table has led to subsidence, and then to environmental problems.
Groundwater indicators in the Russian FederationThe resource potential of groundwater in Russia is 869.1 million m3 / day and is unevenly distributed throughout the territory, which is determined by the variety of geological and hydrogeological conditions and climatic features.
In the European territory of Russia, its value is 346.4 million m3 / day and varies from 74.1 million m3 / day in the Central to 117.7 million m3 / day in the North-Western Federal Districts; in the Asian territory of Russia - 522.7 million m3 / day and ranges from 159.2 million m3 / day in the Far East to 250.9 million m3 / day in the Siberian federal districts.
The modern role of groundwater in the drinking water supply of the population of the Russian Federation is characterized by the following indicators. The share of groundwater in the balance of household and drinking water supply (from surface and groundwater sources) is 45%.
More than 60% of cities and urban-type settlements satisfy their drinking water needs using groundwater, and about 20% of them have mixed sources of water supply.
In rural areas, groundwater in the drinking water supply accounts for 80–85% of the total water consumption.
The most difficult problem is the provision of drinking water to the population of large cities. About 35% of large cities have practically no underground sources of centralized water supply, and 37 cities have no proven reserves of groundwater at all.
The degree of use of groundwater in the household drinking water supply of the population is determined both by the regularities of the distribution of groundwater resources across the territory of Russia, and by the policy of supplying the population with drinking water through the priority use of surface waters, which has been pursued for many years.
Currently, there is a low level of use of explored groundwater deposits and their reserves. The average level of utilization of the total explored reserves is 18–20%, and within the exploited fields with proven reserves - 30–32%.
Over the past 5 years, the increase in the estimated operating reserves amounted to 6.8 million m3 / day.
From underground sources to meet the drinking needs of the population and water supply to industrial facilities, 28.2 million m 3 / day of water was taken. The total amount of extraction and extraction of groundwater amounted to 33.1 million m3 / day, without use, 5.9 million m3 / day was discharged (17.8% of the total amount of extraction and extraction of groundwater).
For household needs, 27.2 million m 3 / day were used, including: for household and drinking water supply 20.6 million m 3 / day (76%); industrial and technical water supply - 6.0 million m 3 / day (22%); irrigation of lands and watering of pastures - 0.5 million m 3 / day (2%).
As a result of the extraction and extraction of groundwater in some territories, large regional depression craters have formed, the areas of which reach significant sizes (up to 50 thousand km Petersburg).
In the city of Bryansk, the regional depression funnel, formed in the Upper Devonian aquifer, has a radius of more than 150 km and a lowering of the level of more than 80 m. Extensive depression funnels formed in the region of the cities of Kursk and Zheleznogorsk and at the Mikhailovsky iron ore quarry. The “Kursk” depression funnel in the Batkelloveysky aquifer has a radius of 90–115 km, the level decrease in the center is 64.5 m. At the Mikhailovsky open pit, the funnel has reached 60–90 km in radius, the level has decreased by 77.4 m since the beginning of the open pit drainage.
In the Moscow region, the intensive exploitation of underground waters of the Lower Carboniferous aquifer complex for 100 years has led to the formation of an extensive deep funnel, the area of which exceeds 20 thousand km 2, and the maximum decrease in the level is 110 m. the formation of a regional depression funnel with a total area of up to 20 thousand km 2 with a decrease in the level to 35 m.
On the territory of Russia, according to the state monitoring of the state of the subsoil of the Ministry of Natural Resources of Russia, 4,002 pollution sites have been identified, of which more than 80% are located in groundwater aquifers, which are usually not sources of drinking water supply for the population.
According to expert estimates, in the Russian Federation the share of polluted groundwater does not exceed 5–6% of the volume of their use for drinking water supply to the population.
The largest number of groundwater contamination sites are located on the territory of the following federal districts: Privolzhsky (30%), Siberian (23%); Central (16%) and South (15%). Of the total number of groundwater pollution sites:
§ 40% of pollution is associated with industrial enterprises;
§ 20% - with agricultural production;
§ by 9% - with housing and communal services,
§ 4% pollution occurs as a result of retraction of substandard natural waters in violation of the operating regime of water intakes;
§ 10% of groundwater pollution is “mixed” and is caused by the activity of industrial, municipal and agricultural facilities;
§ for 17% of sites, the source of groundwater pollution has not been identified.
The most tense ecological situation has developed in the areas of groundwater pollution with substances of I hazard class. These areas were identified in the areas of individual large industrial enterprises in the following cities and towns: Amursk (mercury), Achinsk (phosphorus), Baikalsk (mercury), Georgievsk (mercury), Essentuki (mercury), Yekaterinburg (phosphorus), Iskitim (beryllium), Novokuznetsk (phosphorus), Kazan (beryllium, mercury), Kislovodsk (phosphorus), Mineralnye Vody (mercury), Lermontov (mercury), Komsomolsk-on-Amur (beryllium), Magnitogorsk (tetraethyl lead), Novosibirsk (beryllium), Saya (mercury), Svobodny (mercury), Usolye-Sibirskoye (mercury), Khabarovsk (beryllium, mercury), Cherepovets (beryllium), etc.
The greatest environmental hazard is posed by contamination of groundwater, identified in individual wells at the intakes of drinking water supply.
