Groundwater: characteristics and types. The main types of groundwater and their characteristics
When evaluating groundwater properties explore taste, smell, color, transparency, temperature and others physical properties groundwater, which characterize the so-called organoleptic properties water (determined by the senses). Organoleptic properties can deteriorate sharply when various impurities enter the water naturally or artificially (suspended mineral particles, organic matter, some chemical elements).
Temperature groundwater varies widely depending on the depth aquifers, features geological structure, climatic conditions etc. There are cold waters (temperature from 0 to 20 ° C), warm, or subthermal waters (20-37 ° C), thermal (37-100 ° C), overheated (over 100 ° C). Very cold groundwater circulates in the permafrost zone, in the highlands; superheated waters are characteristic of areas of young volcanic activity. At the water intake sites, the most common water temperature is 7-11 °C.
Chemically pure water colorless. Mechanical impurities (yellowish, emerald, etc.) give color to the water. The transparency of water depends on the color and presence of turbidity. The taste is associated with the composition of dissolved substances: salty - from sodium chloride, bitter - from magnesium sulfate, etc. The smell depends on the presence of gases of biochemical origin (hydrogen sulfide, etc.) or rotting organic substances.
Density of water is the mass of water per unit volume. It is maximum at a temperature of 4 °C. As the temperature rises to 250 °C, the density of water decreases to 0.799 g/cm 3 , and as the amount of salts dissolved in it increases, it rises to 1.4 g/cm 3 . Groundwater compressibility is characterized by compressibility factor, showing by what fraction of the initial volume of the liquid the volume decreases with an increase in pressure by 10 5 Pa. The compressibility coefficient of groundwater is 2.5 10 -5 ...5 10~5 Pa, i.e., water has elastic properties to some extent, which is important in the study of pressure groundwater.
Viscosity water characterizes the internal resistance of particles to its movement. As the temperature rises, the viscosity of groundwater decreases.
Electrical conductivity groundwater depends on the amount of salts dissolved in them and is expressed by resistivity values from 0.02 to 1.00 Ohm.
Radioactivity groundwater is caused by the presence in it of radioactive elements (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 underground waters always contain more or less salts, gases, and organic compounds in the dissolved state.
The gases dissolved in water (0 2 , CO 2 , CH 4 , H 2 S, etc.) give it a certain taste and properties. The amount and type of gases determines the 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 has bad taste and dangerous to human health.
Salt. In groundwater most widespread have chlorides, sulfates and carbonates. By general content dissolved salts, groundwater is divided into fresh (up to 1 g / l of dissolved salts), brackish (from 1 to 10 g / l), saline
(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).
IN natural conditions the general mineralization of underground waters is exceptionally diverse. There are underground waters with mineralization from 0.1 g/l (alpine springs) to 500-600 g/l (deep waters of the Angara-Lena artesian basin). General mineralization is one of the main indicators of groundwater quality.
In groundwater there are several dozen chemical elements of the periodic system of Mendeleev. Up to 90% of all salts dissolved in water are ions C1~, 80^, HCO3, Na +,
M§ 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 the assessment of the suitability of groundwater for various purposes. Water at pH = 6.5 ... 8.5 has the best drinking qualities.
The amount of dissolved salts should not exceed 1.0 g/l. It is not allowed to contain chemical elements harmful to human health (uranium, arsenic, etc.) and pathogenic bacteria. The latter can be neutralized to a certain extent by treating water with ultrasound, chlorination, ozonation and boiling. Organic impurities are determined by bacteriological analysis. Water for drinking purposes should be colorless, transparent, odorless, and taste good.
Rigidity And groundwater aggressiveness associated with the presence of salts. Hardness of water- this property is due to the content of calcium and magnesium ions, i.e., associated with carbonates, and is calculated by calculation from the total content of hydrocarbonate and carbonate ions in water. Hard water gives a lot of scale in steam boilers, does not lather well, etc. Currently, hardness is usually expressed in 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°). By 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°). best quality water has a hardness of not more than 7 mEq. Rigidity is permanent and temporary. Temporary stiffness associated with the presence of bicarbonates and can be eliminated by boiling. Permanent hardness, due to sulfuric acid and chloride salts, is not eliminated by boiling. The sum of temporary and permanent stiffness is called overall hardness.
Aggressiveness groundwater is expressed in the destructive effect of salts dissolved in water on Construction Materials in particular for 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 that assess the degree of aggressiveness of water in relation to concrete, except for chemical composition water, the coefficient of rock filtration is taken into account. The same water can be aggressive and non-aggressive. This is due to the difference in the speed of water movement - the higher it is, the more volumes of water will come into contact with the concrete surface and, therefore, the aggressiveness will be more significant.
In relation to concrete, the following types of groundwater aggressiveness are distinguished:
- general acid - estimated by the pH value, in the sands the water is considered aggressive if the pH
- sulfate - determined by the content of the ion; when the content of BO 2- in an amount of more than 200 mg / l, the water becomes aggressive;
- magnesian - is established by the content of the ion 1U ^ 2+;
- carbonate - associated with the impact on concrete of aggressive carbon dioxide, this type of aggressiveness is possible only in sandy rocks.
The aggressiveness of groundwater is determined by comparing the data of chemical analyzes of water with the requirements of the standards. After that, measures to combat it are determined. For this, special cements are used, waterproofing of the underground parts of buildings and structures is carried out, the level of groundwater is lowered by drainage, etc.
Aggressive action of groundwater on metals(corrosion of metals). Groundwater with salts and gases dissolved in it can be highly corrosive to iron and other metals. An example is oxidation (corrosion) metal surfaces with the formation of rust under the action of oxygen dissolved in water:
2nd+ 0 2 \u003d 2GeO 4GeO + 0 2 \u003d 2Re 2 0 3 Re 2 0 3 + ZN 2 0 \u003d 2Re (OH) 3
Groundwater has corrosive properties when it also contains aggressive carbon dioxide, mineral and organic acids, salts of heavy metals, hydrogen sulfide, chloride and some other salts. Soft water (with a total hardness of less than 3.0 meq) acts much more aggressively than hard water. May be subjected to the greatest corrosion metal constructions under the influence of strongly acidic (pH 9.0). Corrosion is promoted by an increase in the temperature of underground water, an increase in the speed of its movements, electric fields in soil layers.
The assessment of the corrosivity of waters in relation to some metals is carried out according to the current GOST. After that, according to SNiP, measures are chosen to prevent possible corrosion.
Groundwater classification. Exists whole line classifications, but there are two main ones. Groundwater is 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 household and drinking water, technical, industrial, mineral, thermal. The second includes: perched waters, ground and interlayer waters, as well as waters of cracks, karst, permafrost. For engineering-geological purposes, it is advisable to classify groundwater according to a hydraulic basis - non-pressure and pressure.
Household and drinking water. Groundwater is widely used for domestic and drinking purposes. Fresh groundwater -best source drinking water supply, so their use for other purposes, as a rule, is not allowed.
The source of household and drinking water supply is groundwater 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 or more).
IN last years brackish and saline underground waters are also being used for household and drinking water supply after their artificial desalination.
Technical water are waters that are used in various industries industry and Agriculture. Trebova-
atmospheric
connections to underground industrial waters reflect the specifics of a particular type of production.
industrial water contain useful elements (bromine, iodine, etc.) in the solution in an amount that has an industrial raw value. Usually they lie in a zone of very slow water exchange, their mineralization is high (from 20 to 600 g / l), the composition is sodium chloride, the temperature often reaches 60-80 ° C.
The exploitation of industrial waters for the purpose of extracting iodine and bromine is profitable only if the water depth is not more than 3 km, the water level in the well is not lower than 200 m, the amount of water extracted per day is not less than 200 m 3 .
mineral called groundwater, which have a high content of biologically active microcomponents, gases, radioactive elements, etc. They come to the surface of the earth with sources or are opened by boreholes.
Thermal groundwater have a temperature of more than 37 ° C. They occur everywhere at depths ranging from several tens and hundreds of meters (in mountainous folded areas) 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, the Caucasus). The reserves of these waters in the earth's crust are very large and they are actively used for heating cities and energy purposes, for example, in Kamchatka (Pauzhetskaya geothermal station). There are several areas of active geyser activity on Earth: Kamchatka, Iceland, the North-East of the USA, New Zealand.
Not all groundwater is groundwater. The difference between groundwater and other types of groundwater lies in the conditions of their occurrence in the rock mass.
The name "groundwater" speaks for itself - it is water that is underground, that is, in the earth's crust, in its upper part, and it can be there in any of its aggregate states - in the form of liquid, ice or gas.
Main classes of groundwater
Groundwater is different. list the main types of groundwater.
soil water
Soil water is contained in the soil by filling the gaps between its particles, or pore space. Soil water can be free (gravitational) and obey only the force of gravity, and bound, that is, held by the forces of molecular attraction.
ground water
Groundwater and its subspecies, called perched water, is the aquifer closest to the surface of the earth, lying on the first aquiclude. (An aquiclude, or a water-resistant layer of soil, is a soil layer that practically does not allow water to pass through. Filtration through an aquiclude is either very low, or the layer is completely impervious - for example, rocky soils). Ground water is extremely unstable in many factors, and it is ground water that affects the conditions of construction, dictates the choice of foundation and technology in the design of structures. The further exploitation of man-made structures is also under the relentless influence of the changing behavior of groundwater.
interstratal water
Interstratal water - located below groundwater, under the first aquiclude. This water is limited by two water-resistant layers and can be between them under significant pressure, filling the aquifer completely. It differs from groundwater in greater constancy of its level, and of course, greater purity, and the purity of interlayer water may be the result of not only filtration.
artesian water
Artesian water - just like interstratal water, is enclosed between layers of aquicludes and is under pressure there, that is, it belongs to pressure water. The depth of occurrence of artesian waters is from about a hundred to a thousand meters. Various geological underground structures, troughs, depressions, etc., are conducive to the formation of underground lakes - artesian basins. When such a basin is opened during the drilling of pits or wells, artesian water under pressure rises above its aquifer and can produce a very powerful fountain.
Mineral water
Mineral water is of interest to the builder, probably only in one case, if its source is on the site, although not all of this water is useful for humans. Mineral water is water containing solutions of salts, biologically active substances and trace elements. The composition of mineral water, its physics and chemistry is very complex, it is a system of colloids and bound and unbound gases, and substances in this system can be both undissociated, in the form of molecules, and in the form of ions.
ground water
Groundwater is the first permanent aquifer from the soil surface, located on the first aquiclude. Therefore, the surface of this layer is free, with rare exceptions. Sometimes there are areas of dense rocks above groundwater flows - a waterproof roof.
Groundwater occurs close to the surface, and therefore is very dependent on the weather on the surface of the earth - on the amount of precipitation, movement surface water, the level of reservoirs, all these factors affect the supply of groundwater. The peculiarity and difference of groundwater from other types is that it is free-flowing. Verkhovodka, or accumulations of water in the upper water-saturated soil layer above aquicludes from clays and loams with low filtration, is a type of groundwater that appears temporarily, seasonally.
Groundwater and the variability of its composition, behavior and thickness of the horizon are influenced by both natural factors and human activities. The groundwater horizon is unstable, it depends on the properties of rocks and their water content, the proximity of reservoirs and rivers, the climate of the area - temperature and humidity associated with evaporation, etc.
But a serious and increasingly dangerous effect on groundwater is human activity– land reclamation and hydrotechnical construction, underground works for the extraction of minerals, oil and gas. No less effective in the context of danger was agricultural technology using mineral fertilizers, pesticides and pesticides, and of course, industrial effluents.
Ground water is very accessible, and if a well is dug or a well is drilled, then in most cases it is ground water that is obtained. And its properties can turn out to be very negative, since this water depends on the purity of the soil and serves as its indicator. All contamination from sewer leaks, landfills, pesticides from fields, oil products and other results of human activity enter the groundwater.
Ground water and problems for builders
Frost heaving of soils is directly and directly dependent on the presence of groundwater. The damage from the forces of frost heaving can be enormous. When freezing, clay and loamy soils receive nutrition, including from the lower aquifer, and as a result of this suction, whole layers of ice can form.
The pressure on the underground parts of structures can reach enormous values - 200 MPa, or 3.2 tons / cm2 is far from the limit. Seasonal soil movements of tens of centimeters are not uncommon. Possible consequences the effects of frost heaving forces, if they were not foreseen or taken into account insufficiently, can be: pushing foundations out of the ground, flooding basements, destruction pavement, flooding and erosion of trenches and pits, and many other negative things.
In addition to the physical impact, groundwater can also destroy foundations chemically, it all depends on the degree of their aggressiveness. When designing, this aggressiveness is studied, both geological and hydrological surveys are carried out.
Impact of groundwater on concrete
The aggressiveness of groundwater to concrete is distinguished by type, we will consider them below.
According to total acid
At a hydrogen number of pH less than 4, the aggressiveness to concrete is considered the greatest, at a pH value of more than 6.5 - the smallest. But the low aggressiveness of water does not at all eliminate the need to protect concrete with a waterproofing device. In addition, there is a strong dependence of the influence of water aggression on the types of concrete and its binder, including the brand of cement.
Leaching, magnesia and carbon dioxide waters
Everyone destroys concrete in one way or another or contributes to the process of destruction.
sulfate water
Sulphate waters are among the most aggressive to concrete. Sulfate ions penetrate concrete and react with calcium compounds. The resulting crystalline hydrates cause swelling and destruction of concrete.
Methods for minimizing risks from groundwater
But even in cases where there is information about the non-aggressiveness of groundwater to concrete in a given area, the abolition of the waterproofing of the underground parts of the building is fraught with a good decrease in the service life concrete structures. Too great an impact on nature, including groundwater and the degree of its aggression, technogenic factors. The possibility of close construction is one of the causes of soil movements and, as a result, changes in the behavior of groundwater. And chemistry and its "accumulation", in turn, is directly dependent on the proximity of agricultural land.
Accounting for the level of groundwater, as well as seasonal changes in this level, is archival for private construction. High ground water is a limitation in choice. If not all, then a huge share of the economy of an individual builder depends on it. Without taking into account the behavior and height of groundwater, it is impossible to choose the type of foundation for the house, make decisions about the possibility of building a basement and basement, arrange cellars and a sewer septic tank. Paths, playgrounds and all site improvement, including landscaping, also require serious consideration of the impact of groundwater at the design stage. The matter is complicated by the fact that its behavior is closely related to the structure and types of soils on the site. Water and soils must be studied and considered as a whole.
Verkhovodka, as a type of groundwater, can create huge problems, and not always seasonal. If you have sandy soils, and the house is built on a high bank of the river, then you may not notice seasonal high water, the water will leave quickly. But if there is a lake or a river nearby, and the house stands on a low bank, then even if there is sand at the base of the site, you will be on the same level with the reservoir - like communicating vessels, and in this case the fight against perched water is unlikely to be successful, like any fight with nature.
In the case when the soil is not sand, reservoirs and rivers are far away, but the groundwater is very high, your option is to create an effective drainage system. What will be your drainage - ring, wall, reservoir, gravity or using pumping pumps, is decided individually, and many factors must be taken into account. To do this, you need to have information about the geology of the site.
In some cases, drainage will not help, for example, if you are in a lowland, and there is no reclamation canal nearby and there is nowhere to divert water. Also, it is not always that under the first water-bearing layer there is a non-pressure layer into which it is possible to divert the top water, the effect of drilling a well can be the opposite - you will receive a key or a fountain. In cases where the drainage device does not bring results, they resort to the device of artificial embankments. Raising the site to a level where groundwater will not reach you and your foundation is costly, but sometimes the only right decision. Each case is individual, and the owner makes decisions based on the hydrogeology of his site.
But in very many cases, the issue is solved precisely by drainage, and it is important to choose the right system for it and correctly organize the drainage system.
Find out the level of groundwater in your area and track its changes - the owners of individual sites deal with these issues on their own. In spring and autumn, GWL is usually higher than in winter and summer, this is due to intensive snowmelt, seasonality of precipitation, possibly with prolonged rains in autumn period. You can find out the level of groundwater by measuring it in a well, pit or well, from the water table to the surface of the soil. If you break through several wells in your area, along its boundaries, then it is easy to track seasonal changes GWL, and on the basis of the received data it is possible to make decisions on construction - from the choice of foundation and drainage systems, and ending with planning garden plantings, breakdown of the garden, landscaping, as well as the development of landscape design.
Through layers of sand, gravel, pebbles, cracked limestone. The layers composed of these rocks are called permeable.
But rainwater reaches the layer of clay and stops: after all, clay almost does not let water through. Layers of rocks that do not pass or very weakly pass water through themselves are called waterproof (waterproof). Granite, sandstone, shale can be attributed to water-resistant layers, but only if they do not have cracks.
Above the waterproof layer, groundwater accumulates, forming aquifer (horizon) - a layer of permeable rock that lies above the water-resistant layer and contains groundwater.
Springs (keys)
If the water-resistant layer has an inclination in one direction or another, then the water begins to flow along this layer in the direction of its inclination and usually comes to the surface somewhere in a river valley or in a ravine. The place of natural outlet of underground water to the surface is called source, key or spring(Fig. 84). The spring water is usually clean and cold.
There are especially many springs in ravines, along the banks of rivers, in cliffs, since water-resistant layers come to the surface there.
Mineral springs
In some areas the globe water comes to the surface of the earth, in which salts and gases are dissolved in a fairly large amount. This water is called mineral water. water mineral springs used to treat various diseases. Hospitals and resorts spring up around these springs. Resorts in the Caucasus (Borjomi, Kislovodsk, etc.) enjoy world-famous fame.
Hot Springs
- Wells.
Pictures (photos, drawings)
On this page, material on the topics:
Before making a choice offline source water supply for your suburban area It is worth studying the material on groundwater.
In this article, we will briefly talk about what groundwater is about their variety and depth.
What is groundwater?
The groundwater - represent pools of waters lying in layers earth's crust, in rocks in any of three states(liquid, gaseous or solid). Groundwater forms aquifers located between water-resistant layers of soil or rocks. Groundwater is divided into non-pressure and pressure, that is, self-flowing.
Classification of groundwater according to the conditions of occurrence
- ground water(overhead). Soil waters are located in the uppermost layer of the earth's crust at a shallow depth (0.2-1 m) and fill the gaps between soil particles. Soil water can move freely under the force of gravity, or be held by molecular forces. In the same category can be attributed verkhovodka - a layer of water occurring at a depth of up to 1.5 meters. Not suitable for drinking, the water level depends on natural precipitation. Verkhovodka can be a source for watering the garden.
- ground water. Groundwater refers to groundwater lying on the 1st water-resistant layer from the surface of the earth, which can be located at a depth of 1.5 meters or more. Ground water is drinkable, although it is easily polluted. Digging a well is usually carried out to the aquifer of groundwater. Groundwater levels fluctuate seasonally. In dry summers, the level can drop to critical, and in early spring or in the fall to rise as much as possible. The debit of the well water depends on the power of the aquifer of groundwater.
- Interstratal waters. This type of groundwater (aquifers) lies between layers of water-resistant layers and the water level in it is more constant than in groundwater. Accordingly, the water is purer, and the well is deeper. There are already pressure aquifers here.
- artesian waters. This aquifer lies at a depth of 100 meters or more between water-resistant rock layers. The name artesian waters comes from a province in France. Artesian water is the most suitable for drinking. It is not advisable to dig wells, so wells are drilled.
When ordering water well drilling, the price of the service is formed depending on the diameter of the casing string and the depth of the aquifer. The cost of drilling starts from 2100 per linear meter. It is believed that an artesian well has an unlimited debit. It is possible to drill a well for water supply of several country houses(water will be enough, and the price will be divided between customers) or a large cottage. - Mineral water . They belong to medicinal and drinking waters, contain mineral salts, useful chemical elements. Mineral waters are naturally gassed and therefore lie in mountain impervious layers under pressure. Used for medicinal purposes.
» new types of water. Visiting today - The groundwater. We will talk about what groundwater is, where it comes from and where it goes. Along the way, we will dispel a couple of common misconceptions about groundwater.
Groundwater is the collective name for various deposits of water underground. Underground water can be fresh, very fresh, brackish, salty, super-salty (for example, in cryopegs, which we touched upon in the article “Variety of water in the world“).
Common to all types of groundwater: they are located above the impermeable layer of soil. A waterproof soil layer is a soil that contains a large amount of clay (does not let water through) or a soil of solid rock with a minimum number of cracks.
If you go outside and spread a sheet of polyethylene on the ground, you get nothing more than a model of a waterproof soil layer. If water is poured onto polyethylene, it will collect in depressions and flow from higher places to lower ones. A model of groundwater distribution will be obtained. And if you make several holes in polyethylene different size, we get a model of the penetration of upper waters into the underlying horizons.
Similarly, groundwater reserves are formed where the impermeable layer creates depressions. Underground rivers are formed from higher depressions to lower ones. In places where the waterproof layer is interrupted, the upper waters descend to the lower level.
In the form of a figure, this can be represented as follows:
Now about where the groundwater comes from.
Main source: rain. Rain falls, soaks into the ground. Water penetrates through the loose upper loose layers of soil and accumulates in the depressions of the upper waterproof layer of the earth. This type of water is called "perch water". It strongly depends on the weather - if it rains often, there is water. If it rains less often, there is little or no water at all. It is also the most polluted layer of underground water, since filtration through the soil was minimal, and the water contains everything - oil products, fertilizers, pesticides, etc. and so on. The depth of occurrence of this type of water is mainly from 2 to 10 meters.
Further, in places of rupture of the upper waterproof layer, rainwater enters lower aquifers. Their number is different, the depth of occurrence is also very different. So, the upper limit starts from 30 meters and can reach 300 and deeper. By the way, for example, in Ukraine, individuals are prohibited from using water deeper than 300 meters, since this is strategic reserve countries.
An interesting pattern is that the deeper the aquifer is located, the less frequently there are places of connection with more upper layers. So, for example, in the Sahara Desert, groundwater is used that has fallen underground in Europe. Another pattern is that the deeper the water, the cleaner it is and the less it depends on precipitation.
It is often believed that groundwater is located in voids. It happens, but mostly groundwater is a mixture of sand, gravel, other minerals, and lots of water.
It was said where groundwater comes from, how it is moved, but it was not said where it goes. And they disappear either even deeper underground, or pour out to the surface in the form of springs, springs, geysers, springs and other similar phenomena. So, for example, the Dnieper originates from underground somewhere in Belarus. Near Cape Aya (Crimea, not far from Sevastopol), there is a source of fresh water flowing into the sea. I didn’t see it myself (he is kept secret :), but the diver said: you dive with a bottle, open it under water with the neck down, fresh water is drawn in there.
In addition to the natural types of groundwater outlets, there are also artificial ones. These are wells. And such an interesting phenomenon as artesian waters is associated with wells. For a long time, in France, in Artez, a well was drilled in search of water. And the water began to beat from the well in a fountain. That is, artesian waters are waters that rise from the ground without the help of pumps. There are few such cases, most often non-pressure wells come across.
So, like everything in nature, groundwater has a beginning, a change and an end - it gets underground with rain, travels underground from layer to layer and eventually pours out to the surface.
