What Is a Groundwater Study?
Groundwater refers to the water that exists in the rock voids below the ground, and narrowly refers to the water in a saturated aquifer below the groundwater surface. In the national standard "Terms of Hydrogeology" (GB / T 14157-93), groundwater refers to various forms of gravity water buried below the surface.
- Chinese name
- groundwater
- Foreign name
- Ground water
- Storage place
- Stratum void below aeration zone
- Scope of affiliation
- Water resources
- Features
- Stable water quantity and good water quality
- Definition
- Water buried and moving in rocky voids in soil layers
- Groundwater refers to the water that exists in the rock voids below the ground, and narrowly refers to the water in a saturated aquifer below the groundwater surface. In the national standard "Terms of Hydrogeology" (GB / T 14157-93), groundwater refers to various forms of gravity water buried below the surface.
- Foreign scholars believe that there are three definitions of groundwater: one refers to all water buried in groundwater that is significantly different from surface water, especially the part of water in the saturated zone in the aquifer; Saturate and replenish the water of springs and wells; the third is water stored in underground rock cavities and in the voids that make up the crust. [1]
- Groundwater is an important part of water resources. Because of the stable water quantity and good water quality, it is one of the important water sources for agricultural irrigation, industry and mining, and cities. However, under certain conditions, changes in groundwater can also cause adverse natural phenomena such as swampification, salinization, landslides, and ground subsidence.
Groundwater body types
Groundwater distribution
- Main objectives of groundwater pollution prevention
- Plain-basin groundwater. Groundwater is mainly found in loose sediments and low-consolidated rock formations. Generally, it has abundant water and has important mining value. It is distributed in the mountains of China's major plains, mountain basins, large river valley plains, and inland basins. The former plains and deserts mainly include the Huanghuaihai Plain, Sanjiang Plain, Songliao Plain, Jianghan Plain, Tarim Basin, Junggar Basin, Sichuan Basin, and Hexi Corridor, Hetao Plain, Guanzhong Basin, Yangtze River Delta, Pearl River Delta, and Yellow River Delta, Leizhou Peninsula, etc. The groundwater distribution area in China's plain basin is 273.89 square kilometers, accounting for 28.86% of the total area of the national evaluation area; the amount of groundwater recoverable resources is 168.609 billion cubic meters per year, accounting for 47.79% of the total groundwater recoverable resources in China.
- The Huanghuaihai Plain is the largest groundwater enrichment area in China. The area of the evaluation area is 24.13 square kilometers, accounting for 2.64% of the total area of the national evaluation area. The amount of groundwater recoverable resources is 37.337 billion cubic meters per year, accounting for 10.58% of the total national groundwater recoverable resources. The scope includes southern Beijing and Tianjin. Most of the areas are in the east of Hebei Province, northeast of Henan Province, northwest of Shandong Province, northern Anhui Province and northern Jiangsu Province. The Sanjiang-Songliao Plain is the second largest groundwater enrichment area in China. The area of the evaluation area is 34.2 square kilometers, accounting for 3.74% of the total area of the national evaluation area. The amount of groundwater recoverable resources is 30.64 billion cubic meters per year, accounting for 8.68% of the total national groundwater recoverable resources. The scope includes most of Heilongjiang Province, Western Jilin Province, western Liaoning Province, and the northeastern region of Inner Mongolia Autonomous Region.
- Groundwater in the loess area. Groundwater in the loess region is a type of plain-basin groundwater, which is a major feature of China. It is mainly distributed in northern Shaanxi Province, southern Ningxia Hui Autonomous Region, western Shanxi Province, and southeastern Gansu Province, that is, east of Riyue Mountain and Luliang. The Loess Plateau area west of the mountain, south of the Great Wall, and north of the Qinling Mountains. The groundwater in the loess area mainly exists in the loess area. In some larger areas, the groundwater is abundant and has water supply value. The area of the evaluation area is 171,800 square kilometers, accounting for 1.81% of the total area of the national evaluation area; the amount of groundwater recoverable resources is 9.744 billion cubic meters per year, accounting for 3.0% of the total groundwater recoverable resources in the country.
- Land subsidence map of Xi'an
- The northern karst area mainly includes the Beijing-Tianjin-Liao karst area, the Jin-He-yu karst area, and the Jixuhuai karst area. It is distributed with Beijing, Shanxi, Hebei, Henan, Shandong, Jiangsu, Anhui, Liaoning, Tianjin and other provinces (cities, districts). ) In some areas. The karst groundwater in the north has the characteristics of concentrated distribution, and often forms large and extra large water sources, becoming an important source of water for cities and large industrial and mining enterprises. The karst area in the south is mainly distributed in the karst rocky mountain area in the southwest, including most of Yunnan, Guizhou, and Guangxi, and parts of Guangdong, Hunan, and Hubei provinces. The karst groundwater in the south mainly exists in the underground underground river system, and the groundwater is abundant. However, the groundwater surface water is frequently transformed, and the karst groundwater is difficult to be well developed and used. It often forms "a heavy rain floods the ground, and there is no rain everywhere." Special drought situation.
- Groundwater in bedrock mountain area. It is widely distributed in other mountainous and hilly areas other than karst areas. Groundwater is present in the cracks of rocks such as magmatic rocks, metamorphic rocks, clastic rocks and volcanic lava. It is one of the most widely distributed groundwater types in China. The groundwater in the bedrock mountain area is rich in water only in some areas such as the structural fracture zone, and most of the areas are poor. Generally, it is not suitable for centralized mining, but it has an important effect on the water consumption of people and livestock in mountainous and hilly areas and plateau areas. The distribution area of groundwater in mountainous areas is about 5,749,800 square kilometers, accounting for 60.60% of the total area of the national evaluation area; the amount of groundwater recoverable resources is 97.167 billion cubic meters per year, accounting for 27.54% of the total groundwater recoverable resources in the country. 2. The natural formation capacity of groundwater is reflected by the amount of groundwater recharge resources (supply modulus) per unit area. The amount of groundwater natural replenishment resources refers to the amount of renewable groundwater in the groundwater system that participates in the modern water cycle under natural conditions. It mainly depends on three aspects: first, the source of water supply, such as rainfall size, temporal and spatial distribution of rainfall, and conditions of rivers and lakes; and second, infiltration conditions at the surface, for example, sandy soil is better than clay soil, and limestone The area has better infiltration conditions than the granite area; the third is the underground water storage capacity, including porosity, fissure, and groundwater burial depth of the aquifer. Affected by factors such as natural conditions, geological structure, and water storage capacity, regional differences in groundwater production capacity in China are large.
Groundwater mineralization
- Groundwater is divided into four categories according to the degree of mineralization: (1) fresh water, with a mineralization of less than 1 g / L; (2) brackish water, with a mineralization of 1-3 g / L; (3) brackish water, mineralization The degree of salinity is 3-5 g / l; (4) The salinity is more than 5 g / l.
- Freshwater distribution area. Distributed in vast areas of our country. The area of underground freshwater distribution area is about 8.1065 million square kilometers, accounting for 85.39% of the total area of the country; the amount of underground freshwater recoverable resources is 352.778 billion cubic meters per year, accounting for 94.67% of the total groundwater recoverable resources in the country.
- Brackish water distribution area. It is mainly distributed in Hebei, Shandong, Jiangsu, Ningxia Hui Autonomous Region, Xinjiang Uygur Autonomous Region, Inner Mongolia Autonomous Region, Gansu, Shanxi, Shaanxi and Jilin Provinces. The area of the underground brackish water distribution area is about 529,200 square kilometers, accounting for 5.68% of the total area of the country; the recoverable resources of underground brackish water are 14.402 billion cubic meters per year, accounting for 3.87% of the total groundwater mineable resources in the country. .
- Brackish water and salty water distribution areas are mainly distributed in many areas of Xinjiang Uygur Autonomous Region, Ningxia Hui Autonomous Region, Inner Mongolia Autonomous Region, Qinghai Province, and parts of Gansu Province; Tianjin, Hebei Province, Shandong Province, Liaoning Province, Shanghai, Some coastal areas of Jiangsu Province and Guangdong Province. The area of the underground brackish water and salty water distribution area is about 847,300 square kilometers, accounting for 8.93% of the total area of the country; the amount of recoverable resources is 5.446 billion cubic meters per year, which accounts for 1.46% of the total groundwater recoverable resources in the country.
Groundwater nutrition
- The human body contains more than 40 elements, of which 9 elements such as iron, fluorine, zinc, copper, chromium, manganese, iodine, molybdenum, and cobalt are necessary for the human body. They are very important to the normal metabolism of life, and they are indispensable and indispensable. many. Many endemic diseases are caused by people drinking substandard water for a long time, such as high fluoride water causing fluorosis, low iodine water causing large neck disease, and high arsenic water causing skin
- (Picture) Groundwater
- The "groundwater environment background map of China" was compiled based on groundwater environment background data from all over the country, reflecting the regional distribution of low-iodine water, high-fluorine water, high-arsenic water, and high-iron water.
- Low iodine water. It is mainly distributed in mountainous and hilly areas, including most areas of the Yunnan-Guizhou Plateau, Nanling Mountainous Region, Zhejiang-Fujian Mountainous Region, and Hengduan Mountain, Qinba Mountain, Taihang Mountain, Yanshan Mountain, Qilian Mountain, Kunlun Mountain, etc. The distribution area of low-iodine water is about 1.7 million square kilometers, accounting for 17.8% of the country's land area.
- High fluorine water. It is mainly distributed in the Changbai Mountains, the eastern Liaoning Mountains, the central Songliao Plain, the central Huanghuaihai Plain, the central basin of Shanxi Province, the Inner Mongolia Plateau, and the frontier areas of the alluvial sloped plain in the northwest inland basin. In addition, in the hilly hot spring distribution areas of southeast China, the fluorine content in groundwater is relatively high, generally greater than 5 mg / liter, and up to 35 mg / liter. The fluorine content of hot springs in southern Tibet is also relatively high. The distribution area of high-fluorine water is about 1.6 million square kilometers, accounting for 16.7% of the land area.
- High arsenic water. It is mainly distributed in the Weigan River Basin in the Tarim Basin in Xinjiang and the Kuitun River in the Junggar Basin. The distribution area of low-iodine water is about 10,000 square kilometers, accounting for 0.1% of the land area.
- High molten iron. It is mainly distributed in the Qinghai-Tibet Plateau, Sanjiang Plain, Xialiaohe Plain, and Jianghan Plain. The distribution area of high-speed molten iron is about 700,000 square kilometers, accounting for 7.3% of the land area. Groundwater pollution exists to varying degrees in large and medium-sized cities in China. Among them, groundwater pollution in nearly half of urban areas is increasing, and it has evolved from point pollution to strip and surface pollution. The groundwater drainage areas in the central areas of some large cities and the suburbs have the most serious groundwater pollution, and the shallow groundwater in some cities can no longer be directly consumed. Groundwater pollution is characterized by the fact that northern cities are heavier than southern cities, and are mainly distributed in the North China Plain, Songliao Plain, Jianghan Plain, and the Yangtze River Delta.
Groundwater burial conditions
- Groundwater is a huge family. It is estimated that the total amount of groundwater in the world is as high as 150 million cubic kilometers, accounting for almost one-tenth of the earth's total water, more than the entire Atlantic Ocean. According to different underground burial conditions, groundwater can be divided into three categories: upper stagnant water, diving and confined water.
- Upper water stagnation: It is a water storage body formed by shallow water cracks or sedimentary layers caused by the infiltration of atmospheric precipitation due to local water blocking.
- Diving is the groundwater buried in the first stable aquifer below the surface. Most of the groundwater that is usually seen is diving. A spring forms when groundwater flows out of the ground. Diving exists above the first stable aquifer below the surface and has the gravity of a free surface. It is mainly replenished by precipitation and surface water infiltration.
- Confined water (artesian water) is groundwater buried deep between the two aquifers. Confined water fills the water in the aquifer between the upper and lower aquifers. It withstands pressure, and when the overlying impervious layer is cut through, water can rise or spray from the borehole. According to the type of water-containing voids, groundwater is divided into pore water, fissure water and karst water. This kind of groundwater often has a large water pressure, especially when the upper and lower water barriers are inclined, the water body in the barrier must bear greater water pressure. When a well or borehole passes through the upper roof, the strong pressure will cause the water body to gush out, forming artesian water.
- I. Principles of groundwater classification
- One is to classify according to a certain characteristic of groundwater; the other is to consider several characteristics of groundwater for classification.
- Classification of groundwater
- 1. According to different origins, groundwater can be divided into infiltration water, condensate water, primary water and buried water.
- Karst water
- Condensate: The groundwater formed by the condensation of water vapor is called condensate. When the temperature of the ground is lower than the temperature of the air, the water vapor in the air will enter the gaps between the soil and the rocks, and condensate on the surface of the particles and rocks to form groundwater.
- Primary water: It is neither formed by infiltration of precipitation nor condensation of water vapor, but formed by condensation of gas separated from magma. This water is the result of magma and becomes primary water.
- Buried water: Groundwater formed at the same time as the sediment or seawater penetrates into the pores of the original sediment becomes buried water.
- Aerated water: refers to the water in the aerated zone above the diving surface. There are absorbing water, film water, capillary water, gaseous water and temporary gravity water. The seasonally existing water above the local aquifer in the aerated zone is called upper stagnation. Entrains water in underground rock and soil voids. Water-bearing rock and soil is divided into two zones, and the upper part is an aerated zone, that is, an unsaturated zone. Here, in addition to water, there is also gas. The lower part is a saturated zone, that is, a saturated zone. The voids in the saturated soil are filled with water. Groundwater in the narrow sense refers to water in a saturated zone.
- 2. According to the degree of mineralization, it can be divided into fresh water, brackish water, salt water, brine and brine.
- See the following table for details:
- Groundwater classification table
- Groundwater type total salinity (g / l)
- Freshwater <1
- Brackish water 1 3
- Salt water 3 10
- Brine 10 to 50
- Brine> 50
- 3. Classified according to aquifer properties, it can be divided into pore water, fissure water, and karst water.
- Pore water: Water in the pores of loose rocks. Pore water is groundwater stored in the pores of loose Quaternary sediments and a few poorly cemented sediments of the Tertiary system. The sedimentary environment during the period of sediment formation has a great influence on the characteristics of the sediment, making its spatial geometry, material composition, particle size, and degree of sorting all have different characteristics. Pore water exists in groundwater in rock and soil pores, such as groundwater in loose sand, gravel, and sandstone layers. Fissure water is water that exists in the cracks between hard rocks and some clay layers. Karst water, also called karst water, refers to groundwater that exists in the crevices of soluble rocks (such as limestone, dolomite, etc.).
- Fissure water: Gravitational water that exists in the cracks of hard, semi-rigid bedrock. The burial and distribution of fissure water has heterogeneity and a certain direction; the aquifer's shape is diverse; it is obviously controlled by the factors of geological structure; the hydrodynamic conditions are more complicated.
- Karst water: Water that exists in karst voids. Water is rich and unevenly distributed, and there are relatively uniform sections among the heterogeneous; multiple aqueous media coexist in the aquifer system, both a water network with a uniform water level and a relatively isolated pipeline flow; a directional drainage area The movement of water and the mutual drainage between the water channel and the water storage network; the dynamics of water quality and water volume are controlled by the degree of karst development. In the strongly developed area, the dynamic changes are large and the response to atmospheric precipitation or surface water recharge is fast; Karst water is not only the water that exists in karst pores, crevices, and karst caves, but also the driving force for transforming its entrapped environment, and constantly promotes the evolution of water-containing spaces.
- 4. According to different burial conditions, it can be divided into upper water stagnation, diving and pressure water.
- Upper water stagnation: Gravity water buried above the surface and partially impermeable in the aerated zone. Generally, it is not widely distributed, showing seasonal changes. The rainy season appears and the dry season disappears. Its dynamic changes are closely related to changes in climate and hydrological factors.
- Diving: Gravity water buried below the surface, above the first stable aquifer, with a free surface. Diving is widely distributed in nature, and is generally buried in the pores of quaternary loose sediments and in cracks and karst caves of weathered crusts of hard bedrock.
- Confined water: Gravity water buried and filled in an aquifer between two stable aquifers. The confined water is subject to hydrostatic pressure; the supply area is not consistent with the distribution area; the dynamic change is not significant; the confined water does not have a free surface like diving, so its movement mode is not free flow under the action of gravity, but under hydrostatic pressure Under the action of water, exercise in the form of water alternating.
Groundwater waters division
Groundwater recharge
- The nation's groundwater natural recharge resource evaluation area is 91,497 thousand square kilometers. The total amount of groundwater natural recharge resources is 923.472 billion cubic meters per year, and the average recharge module is 109,900 cubic meters per square kilometer per year. The recharge amount of groundwater resources in China has decreased from the southeast coastal area to the northwest inland area. Hainan, Guangdong and other provinces have the largest amount of groundwater recharge resources, at 500,000 cubic meters per square kilometer. Above Xinjiang, Inner Mongolia Autonomous Region has the smallest, less than 50,000 cubic meters per square kilometer per year. The Distribution Map of Groundwater Recharge Resources in China is based on hydrogeological units and based on the natural recharge resources of groundwater per unit area. Five levels are used to reflect the richness of groundwater recharge.
- Groundwater replenishment areas. Groundwater recharge per unit area is greater than 500,000 m3 / km2, mainly distributed in Hainan, Guangdong, Hubei and parts of Guangxi Zhuang Autonomous Region, Heilongjiang, Jilin, Sichuan, Taiwan, Shaanxi, Ningxia Hui Autonomous Region also has sporadic distribution. The area of groundwater resource-rich areas is about 186,600 square kilometers, accounting for 1.96% of the total area of the country.
- Groundwater replenishment areas. The amount of groundwater recharge per unit area is 200,000-500,000 cubic meters per square kilometer per year, distributed in most areas of Hainan Province, Guangxi Zhuang Autonomous Region, Guangdong Province, Fujian Province, Guizhou Province and Shanghai, Jiangsu Province, Chongqing City, Shandong Province, Liaoning Province, Beijing, Hunan Province, Tibet Autonomous Region and Xinjiang Uygur Autonomous Region are also distributed. The area with richer groundwater resource replenishment covers an area of about 1.376 million square kilometers, accounting for 14.51% of the total area of the country.
- Groundwater recharge medium area. The amount of groundwater recharge per unit area is 100,000-200,000 cubic meters per square kilometer per year. It is mainly distributed in the Huanghuaihai Plain area in the northern region, Yunnan, Guizhou, Sichuan, Jiangxi, and Hunan provinces in the south. Karst rocky mountain areas, plain river valleys in the northwest, northeast, and southwest are also distributed. The area of groundwater resource-rich areas is about 1.783 million square kilometers, accounting for 18.79% of the country's total area.
- Groundwater recharge is poorer. The amount of groundwater recharge per unit area is less than 50,000-100,000 cubic meters per square kilometer per year. It is distributed from the eastern coastal areas to the western inland areas, mainly concentrated in the central region, and covers almost all provinces in the country, including the northeast. The hilly areas of the three provinces (shandong, shanxi, hebei, henan, anhui, jiangxi, sichuan, chongqing) and other provinces (cities) are scattered sporadically. Groundwater resources replenishment-rich areas cover an area of 2.363 million square kilometers, accounting for 24.87% of the country's total area.
- Groundwater replenishment in poor areas. The amount of groundwater recharge resources per unit area is less than 50,000 cubic meters per square kilometer per year. It is distributed in most parts of northwest China, western northeast China, northern north China, and parts of southwestern China. It is mainly distributed in Xinjiang Uygur Autonomous Region, Inner Mongolia Autonomous Region, Ningxia. Most areas of the Hui Autonomous Region, Shaanxi Province, and Gansu Province are also distributed in Qinghai Province, Shanxi Province, Hebei Province, and Tibet Autonomous Region. The area of groundwater resources replenishment is about 3.783 million square kilometers, accounting for 39.87% of the country's total area.
- Three nationwide underground freshwater recoverable resources amount to 352.779 billion cubic meters per year. The actual state of extraction (1999) is 105.833 billion cubic meters per year. The remaining amount of underground freshwater is 246.945 billion cubic meters per year. Looking at the country as a whole, there is still more underground freshwater, accounting for 70% of the recoverable resources. However, the distribution of underground freshwater residues is extremely uneven. The remaining amount in the northern region is 74.477 billion cubic meters per year and the remaining amount in the southern region is 172.469 billion cubic meters per year, accounting for 30.2% and 69.8% of the national groundwater freshwater residual respectively. 48.5% and 86.8% of the local groundwater recoverable resources.
Groundwater extraction
- The "Map of China's Groundwater Resources Exploitation Potential" is compiled based on the statistical results of prefecture-level administrative units across the country, and is divided into six potential levels, which basically reflects the overall law of China's groundwater resource exploitation potential. Groundwater overexploitation in many areas in Beijing, Tianjin, Hebei, Henan, Shandong, Shanxi, Shaanxi, Gansu, and Xinjiang; groundwater exploitation potential in the vast areas of the northern part of the "Three North" region is small; Northeast Plain, Tarim Basin, Sichuan Basin, Jianghan Plain , Bayankala Mountains, and parts of the south, the potential for groundwater exploitation is medium; the potential for groundwater exploitation in the Yangtze River Basin, Huaihe River Basin, and Pearl River Basin is greater or greater.
- groundwater
- Basic balance area. The groundwater exploitation potential is 0-1 million cubic meters per square kilometer per year, and the mining cannot be expanded blindly. The northern region should reserve this part of water for ecological use. It is mainly distributed in North China, Northwest China, and the Northeast of Northeast China, including most parts of Inner Mongolia Autonomous Region and Tibet Autonomous Region, Jiuquan in Gansu Province, and parts of Xinjiang Uygur Autonomous Region, as well as In some areas. The area of groundwater extraction-compensation balance covers an area of 2,736,400 square kilometers, accounting for 28.8% of the country's total area.
- Areas with less mining potential. In areas with groundwater exploitation potential of 10,000 to 50,000 cubic meters per square kilometer per year, groundwater can be appropriately developed and utilized. It is mainly distributed in most areas of Qinghai, Xinjiang, Chongqing, and Fujian, Songnen and Songliao plains in Heilongjiang, Jilin, and Liaoning, and parts of Yunnan, Guizhou, and Hunan. The area with less groundwater exploitation potential covers an area of 4,298,500 square kilometers, accounting for 45.3% of the total area of the country.
- Medium potential area. In areas with groundwater mining potential of 50,000-100,000 cubic meters per square kilometer per year, the intensity of groundwater mining can be appropriately increased and the use of surface water can be reduced. It is mainly distributed in the Yangtze River Basin and southern China, including Sichuan, Guizhou, Hunan, Hubei, Anhui, Guangdong, Guangxi, and other regions in Guangxi Zhuang Autonomous Region. The northern region is only distributed in the Sanjiang Plain and other local areas. The area of groundwater exploitation potential is 1,058,800 square kilometers, accounting for 10.6% of the total area of the country.
- Areas with greater mining potential. In areas with groundwater exploitation potential of 100,000-200,000 cubic meters per square kilometer per year, the development and utilization of groundwater should be encouraged to take full advantage of the characteristics of excellent groundwater quality, dynamic stability, and years of regulation. It is mainly distributed along the Yangtze River, the Huaihe River, and southern China, including most parts of Jiangsu, Anhui, Guangdong, and Hainan Provinces. There are also sporadic distributions in Guizhou Province, Hunan Province, and Hubei Province. The groundwater exploitation area has a large area of 470,700 square kilometers, accounting for 5.0% of the total area of the country.
- Large potential area. Areas with groundwater exploitation potential greater than 200,000 cubic meters per square kilometer per year are mainly distributed in a small part of Guangxi Zhuang Autonomous Region, Guangdong Province, and Hainan Province. Although these areas have great potential for groundwater exploitation, due to abundant precipitation and abundant surface water, socioeconomic dependence on groundwater is not high, and the actual value of groundwater exploitation potential is not great. The area of groundwater exploitation potential is 4.82 square kilometers, accounting for 0.5% of the total area of the country. Remarks:
- 1. The distribution of groundwater resources and their mining potentials mainly depends on the recharge conditions and mining conditions of different levels of hydrogeological units. According to the administrative unit's analysis of groundwater mining potentials, the results will inevitably be inconsistent with local facts.
- 2. Groundwater is an in-situ resource. In an area, overexploitation and resource surplus often coexist. The regional average results sometimes mask the objective reality of local surplus and local overexploitation in some areas. I hope that when using this map, To avoid misunderstanding.
Groundwater pollution
- Based on the National Groundwater Quality Standard (GB / T 14848-93), the "Groundwater Pollution Status Map of China" compares the current status of groundwater quality under the influence of human activities with the "background value" of groundwater quality under natural conditions to determine that groundwater pollution exceeds the standard The components are compiled according to the principle of single-factor evaluation and multi-factor comprehensive evaluation, reflecting the two aspects of urban groundwater pollution and pollution components. The degree of groundwater pollution is divided into three categories: severe pollution, medium pollution and light pollution.The reflected groundwater pollution components include nitrate nitrogen, nitrite nitrogen, ammonia nitrogen, lead, arsenic, mercury, chromium, cyanide, volatile phenol, Petroleum and permanganate indexes.
- Groundwater pollution in heavy industries and oilfield development zones in the Northeast is severe. Groundwater pollution in Northeast China has different characteristics in different regions. The main pollutants in the Songnen Plain are nitrite nitrogen, ammonia nitrogen, petroleum, etc .; nitrate nitrogen, ammonia nitrogen, volatile phenol, and petroleum pollution in the lower Liaohe Plain are common. The pollution degree of groundwater in different large and medium cities is different. Among them, the pollution of groundwater in Harbin, Changchun, Jiamusi, Dalian is more serious.
- Groundwater pollution in North China is generally increasing. Human economic activity is strong in North China, and groundwater pollution is relatively common from urban to rural areas. The main pollution components are nitrate nitrogen, cyanide, iron, manganese, and petroleum. In addition, the total hardness and salinity of groundwater in the area exceeded the standard, and the total hardness of most cities and regions exceeded the standard. Among them, Beijing, Taiyuan, Hohhot and other cities were more polluted.
- Groundwater in Northwest China is relatively less affected by human activities and is less polluted. Groundwater pollution in the Northwest is generally lighter. The main pollution component of the inland basin area is nitrate nitrogen; the main pollutants in the middle reaches of the Yellow River and the Loess Plateau are nitrate nitrogen, nitrite nitrogen, chromium, lead, etc., which are distributed in points and lines in cities and industrial mines. The surrounding areas of the enterprise, among them, Lanzhou, Xi'an and other cities are more polluted.
- groundwater
- The general rule of groundwater quality distribution in China is that the quality of groundwater in the south is better than the quality of groundwater in the north, the quality of groundwater in the eastern plains is better than that of the western inland basins, the quality of groundwater in mountainous areas is better than that of plains, and the quality of groundwater in the piedmont and intermountain plains is better than in coastal areas. The quality of groundwater in the ancient channel belt is better than that in the inter-region, and the quality of deep groundwater is often better than shallow groundwater.
- The quality of groundwater in Northeast China is uneven and local pollution. The quality of groundwater in Northeast China changes from good to bad from mountain to plain. The quality of groundwater in bedrock is better than that of loose rock, and the quality of confined groundwater is better than diving. Most of the groundwater in this area is for domestic and industrial and agricultural water supply. The quality of groundwater in the middle of Songliao Basin is not good and should not be used directly. Heavy industry and oil field development have caused groundwater pollution in some cities and regions.
- The pollution of groundwater quality in North China is obviously widespread. North China is one of the areas with the strongest human activities. The groundwater environment is greatly affected by human interference. Groundwater in this area mainly occurs in the Huanghuaihai Plain and its surrounding mountainous areas. The distribution of shallow groundwater quality has obvious zoning rules. From mountainous areas, plains to coastal areas, the quality of groundwater changes from good to bad, and groundwater pollution in urban areas is widespread. Groundwater is available for direct drinking in most areas.
- The quality of groundwater in Northwest China is generally poor and the pollution is light. The quality of groundwater in the northwest region is naturally poor, and it changes from mountainous areas to the basin, from the edge of the basin to the middle of the basin. The quality of the groundwater changes from good to bad, and it is characterized by a ring-shaped distribution. 18% of the total area of the district. In the Northwest, the impact of human activities on groundwater is mainly manifested by changes in the ecological environment caused by mining, and the degree of groundwater pollution is generally light.
- groundwater
- With the rapid development of social economy and the continuous improvement of groundwater development technology, China's groundwater development is developing to "deep" and "wide", the mining layer is continuously deepening, and the mining scope is continuously expanding. Of the 660 cities in the country, there are more than 400 cities that mine groundwater; the effective groundwater irrigation area is 748 million mu, accounting for 40% of the country's total cultivated land area; in the past, areas where groundwater was never mined in the southeast coast in the past, a lot of groundwater was mined; In other areas, due to shallow groundwater pollution, a large amount of groundwater mining has turned to deep groundwater. The development and utilization of groundwater, on the one hand, provides water source support for social and economic development, and on the other hand, unreasonable and excessive exploitation of groundwater, has induced many environmental geological problems. Especially in northern cities and regions where groundwater is the main source of water supply, predatory mining is serious, and environmental geological problems caused by it are prominent.
- The "Map of China's Groundwater Environmental Geology" is compiled based on the national groundwater environmental survey and monitoring data. The main environmental geological problems reflected are regional groundwater fall funnels, ground subsidence, ground subsidence, ground fissures, seawater intrusion and soil salinization. Distributed in areas where groundwater is concentrated and over-exploited.
Groundwater recharge
- Groundwater mainly includes precipitation infiltration, irrigation water infiltration, surface water infiltration recharge, over-current recharge and artificial recharge. Under certain conditions, there is also lateral replenishment. Groundwater drainage includes springs, diving evaporation, drainage to surface water bodies, crossflow drainage and artificial drainage. Springs are the main way of natural drainage of groundwater.
Main functions of groundwater
- Groundwater has a close relationship with humans.
- groundwater
- As an important body of water on the earth, groundwater has a close relationship with human society. The storage of groundwater is like forming a huge reservoir underground. With its stable water supply conditions and good water quality, it has become an important source of water for agricultural irrigation, industrial and mining enterprises, and urban domestic water. It has become an important and important water resource for human society, especially It is in arid and semi-arid areas where surface water is scarce. Groundwater often becomes the main source of local water supply.
- According to incomplete statistics, more than 75% of Israel s water in the 1970s depended on groundwater supply, and many cities in Germany also rely on groundwater. France s groundwater extraction volume accounts for about 1/3 of the country s total water consumption; like the United States, In countries with abundant surface water resources, such as Japan, groundwater accounts for about 20% of the country's total water consumption. Groundwater extraction and utilization in China accounts for about 10-15% of the country's total water consumption. Among them, northern provinces and autonomous regions have large groundwater exploitation and utilization due to insufficient surface water resources. According to statistics, in 1979, the utilization rate of shallow groundwater in the plain area of the Yellow River Basin reached 48.6%, and that of the Haihe and Luanhe River basins was as high as 87.4%; in 1988, the actual pumping capacity of more than 2.7 million machine wells nationwide was 52.92 billion cubic meters. The capacity is over 80 billion cubic meters.
- On the other side of the problem, due to excessive mining and unreasonable use of groundwater, the groundwater level is often severely lowered, forming a large area of groundwater descent funnel. In urban areas where groundwater is concentrated, it may also cause ground subsidence. In addition, the large infiltration of industrial wastewater and domestic sewage often pollutes groundwater sources seriously and endangers groundwater resources. Therefore, it is of great significance to systematically study the formation and type of groundwater, the movement of groundwater, and the mutual recharge relationship with surface water and atmospheric water.
Groundwater composition structure
- The spatial dimensionality of the groundwater flow system is one of the main differences between groundwater and surface water. The vertical hierarchical structure of groundwater is a concrete representation of the three-dimensional nature of groundwater space. Basic model of vertical hierarchical structure of groundwater under typical hydrogeological conditions. From the surface to the impermeable bedrock at a certain depth, it can be divided into two parts: aeration zone and saturated water zone. The aerated zone can be further divided into three sub-zones: soil water zone, intermediate transition zone and capillary water zone; the saturated water zone can be divided into two sub-zones: diving zone and confined water zone. From the perspective of the water storage form, the corresponding aerated zone is the presence of bound water (including hygroscopic water and membrane water) and the capillary water; the saturated water zone corresponds to gravity water (including diving and pressure water). The above is the basic model of groundwater hierarchy. Under the specific hydrogeological conditions, the actual hierarchical structure of groundwater in different regions is not consistent. Some levels may develop fully, while others are not developed. For example, in a severely dry desert area, the aerated zone is very thick, and the saturated aquifer is buried deep in the ground, or even basically does not exist. On the contrary, in wet and humid areas, especially in low-lying and flood-prone areas with poor groundwater drainage, the aerated zone The zone is often thin, and even the surface of the underground diving surface is exposed, so the groundwater hierarchy is not obvious. As for the existence of pressure-bearing water belts, specific water storage structures and pressure-bearing conditions are required. And this structure and pressure conditions are not available everywhere, so the distribution of pressure water is greatly restricted. However, the above-mentioned regional differences in groundwater hierarchy do not deny the overall regularity of the vertical structure of groundwater. This hierarchical structure is of great significance for people to understand and grasp the nature of groundwater, and has become the basic basis for classification of groundwater according to burial conditions.
- The hierarchical structure of groundwater in the vertical direction also shows that there are also obvious differences in the forces received by groundwater at different levels, forming different mechanical properties. For example, the hygroscopic water and film water in the aerated zone are bound to the surface of the rock and soil particles by the molecular suction. Generally, the smaller the geotechnical particles, the larger the specific surface area of the particles, the greater the molecular adsorption force, and the more the moisture absorption and film water content. Among them, hygroscopic water is also called strong binding water. The molecular attraction between water molecules and the surface of rock and soil particles can reach thousands or even tens of thousands of atmospheres. Therefore, it is not affected by gravity, cannot move freely, has a density greater than 1, and does not dissolve salts. It is non-conductive and cannot be absorbed by plant roots.
- Film water is also called weakly bound water. They are affected by molecular forces, but the adsorption force between film water and rock and soil particles is much weaker than moisture absorption water. As the film becomes thicker, the effect of molecular force continues to weaken. Until the transition to free water. Therefore, the properties of thin film water are also between free water and hygroscopic water. It can dissolve salts, but its solubility is low. The film water can also be moved from the surface of the particles with a thick film to the surface of the particles with a thin layer of water until the film thicknesses of the two are equal. And its outer layer of water can be absorbed by plant roots. When the external force is greater than the shear strength of the combined water itself (referring to the ultimate ability to resist shear stress damage), the film water can not only move, but also transmit hydrostatic pressure.
- Capillary water When the voids in the rock and soil are less than 1 millimeter, the voids communicate with each other, like capillary tubes. When these small voids store liquid water, capillary water is formed. If the capillary water rises from the groundwater surface, it is called capillary rise water; if it has nothing to do with the groundwater surface, the capillary water formed by the infiltration of water from the ground is called suspended capillary water. Capillary water is affected by gravity and negative hydrostatic pressure, and its water content is continuous, and it can connect the saturated water zone with the aerated zone. Capillary water can transmit hydrostatic pressure and can be absorbed by plant roots.
- Gravity water When the voids in the aquifer are filled with water, groundwater will seep and move in the rock and soil pores under the action of gravity, forming osmotic gravity water. The groundwater in a saturated water zone moves from high to low under the action of gravity and transmits hydrostatic pressure.
- To sum up, groundwater in the vertical direction not only forms different hierarchical structures such as combined water, capillary water, gravity water, etc., but also the forces on each level are different, forming a vertical mechanical structure.
Groundwater movement mode
- Most groundwater movements are laminar. In a wide gap, if the water flow speed is high, it is easy to show turbulent motion.
- Groundwater system potential. The so-called "potential" refers to the work required to move unit mass of water from a potential zero point to another point. It is an indicator of groundwater energy. According to Richards' measurement, it is found that the potential energy () decreases with distance (L), and it is proved that the potential energy gradient (-d / dL) is the driving force of groundwater movement in rock and soil. Groundwater always moves from the part with higher potential energy to the direction with lower potential energy.
- The action potential of the groundwater system can be divided into gravity potentials, hydrostatic pressure potentials, osmotic pressure potentials, and adsorption potentials according to its force source properties. The combination of these potentials is called total water potential.
- 1. Gravity potential (g) refers to the energy required to move a unit of mass of water from a reference surface with zero gravity potential to a given position in the gravity field, and is defined as g = Z, where Z is the groundwater position height. In specific calculations, the height of the groundwater level is generally used as the reference standard, and the gravity potential at that position is regarded as zero. The gravity potential above the groundwater level is positive, and the gravity potential below the groundwater surface is negative.
- 2. Hydrostatic potential (p) The hydrostatic pressure generated by the continuous water layer on the water below it. The resulting potential is called hydrostatic potential. Since hydrostatic potential is defined relative to atmospheric pressure, Under equilibrium, the hydrostatic pressure at the free surface of the groundwater is zero, and the water below the groundwater surface is above atmospheric pressure, carrying the hydrostatic pressure. The pressure increases with the depth of the water. The expression is the positive hydrostatic potential. On the contrary, the groundwater in the unsaturated zone above the groundwater surface is under the atmospheric pressure. Due to the existence of closed gas in the unsaturated zone and the adsorption of water by the adsorption force and capillary force, the energy level of the groundwater is reduced, and a negative pressure effect is produced, which is called negative hydrostatic pressure, also known as Fundamental potential.
- 3. Osmotic potential (0), also known as solute potential, is caused by soluble substances that attract and align the water molecules around them due to hydration when they are dissolved in water to form ions. The ability of water molecules to move freely. This potential energy generated by the solute is called the solute potential, and its potential value is exactly equal to the osmotic pressure of the solution, but the two directions of action are exactly the opposite. Obviously, the osmotic pressure is negative.
- 4. Adsorption potential (a) Rock and soil as a water-absorbing medium, so it can absorb and retain water, mainly due to the effect of adsorption force. After water is adsorbed by the rock and soil medium, its ability to move freely is correspondingly weakened. If it is not affected by the medium As the free water potential is zero, the potential value of the water absorbed by the medium must be negative. This potential value generated by the medium adsorption is called the adsorption potential. Or dielectric potential.
- 5. Total water potential The total water potential is the combination of the above potentials, that is, = g + p + 0 + a, but the groundwater in different water zones has different potentials.
Basic characteristics of groundwater
Groundwater flow system
- Although groundwater is buried underground and difficult to observe with the naked eye, it has a catchment area like rivers and lakes on the surface. The groundwater flow in the same catchment area constitutes a relatively independent groundwater flow system.
- Basic characteristics of groundwater flow systems
- Under certain hydrogeological conditions, all the water flows collected in a drainage area form a relatively independent groundwater flow system, also known as groundwater flow system. Groundwater in the same water flow system often has the same source of replenishment, and there is a close hydraulic connection between them to form a relatively unified whole. Groundwater belonging to different groundwater flow systems points to different drainage areas, and there is no There are only very weak hydraulic connections. In addition, compared with surface water systems, groundwater flow systems have the following characteristics:
- groundwater
- 3. The coexistence of descent and ascent in the direction of flow Under the action of gravity, the surface river flow always flows from high to low; however, the direction of groundwater flow shows a decline in the supply area, but it often shows an rise in the drainage area. Some even form fountains.
- In addition to the above characteristics, the area covered by the groundwater flow system is generally relatively small, and it cannot be combined into a large watershed system with an area of hundreds of thousands or even millions of square kilometers as the surface rivers. According to Toth's research, in a small area, due to the control of local composite terrain, a multi-level groundwater flow system, different levels of water flow systems, and their supply and drainage areas can be alternately distributed on the ground.
Groundwater catchment area
- The groundwater area is the catchment area of the groundwater flow system. It is also significantly different from surface water basins. The flow of surface water is mainly controlled by terrain, and its watershed range is bounded by terrain watersheds, which are mainly in the form of planes.
- Groundwater funnel map of North China Plain
- Generally, each groundwater area has a corresponding recharge zone and drainage zone on the surface. The surface of the recharge zone is often dry and deficient due to the continuous infiltration of surface water into the ground. In the discharge zone, the groundwater flow has increased. The amount of water on the ground is relatively moist. If groundwater is discharged as a spring in the drainage area, this groundwater area can be called a spring area.
Groundwater storage space
- Groundwater is buried in the gap between underground rock and soil and can flow. Therefore, its distribution, movement, and water properties are deeply affected by the characteristics of the rock and soil and the spatial characteristics of the storage space. Compared with surface water systems, groundwater systems appear more complex and diverse, and exhibit the characteristics of three-dimensional structure.
- Aqueous media, aquifers and aquifers
- Rocks and soils in nature are porous media and exist between their solid skeletons
- Related books
- For those rock masses that contain water but have little or no water permeability, they are called water barriers, such as dense igneous rocks, metamorphic rocks, and fine porosity shale and clay layers. Floor. In fact, there is no clear boundary between aquifers and aquifers. Their divisions are relative and can be transformed into each other under certain conditions. Such as a clay layer full of bound water, under normal conditions, it cannot penetrate and feed water and become a good water barrier; but under the action of a large head, the clay layer can be transformed by the water barrier due to the movement of part of the bound water. Aquifer.
- Porosity and Hydrology of Aqueous Media
- 1. Porosity of the aqueous medium The vacancy of the aqueous medium is one of the prerequisites for the existence of groundwater. The number, size, uniformity and connectivity of the voids directly determine the burial, distribution and movement characteristics of groundwater. In general, the voids between loose sediment particles are called pores. The voids caused by rupture of hard rocks are called fissures, and the voids in soluble rocks are called dissolved gaps (including huge caves, caves, etc.).
- 1) Porosity (n), also known as porosity, is an important indicator of the characteristics of an aqueous medium. It is expressed by the ratio of the pore volume (Vn) to the rock and soil volume (V), including n = Vn / V × 100%. The size of the porosity depends on the size of the rock and soil particles, the arrangement of the particles, the degree of separation, and the shape and cementation of the particles.
- Groundwater research model
- 2) Fracture rate (KT) The fracture rate is the ratio of fracture volume (VT) to rock volume (V) including fractures: KT = VT / V × 100%. Compared with pores, the distribution of cracks has obvious heterogeneity. Therefore, even in the same kind of rock, the crack rate KT of some parts may reach tens of percent, and the KT value of some parts may be less than 1%.
- 3) The karst rate (KK) is expressed by the karst rate, that is, the ratio of the volume of the karst gap (Vk) to the rock volume (V) including the karst gap: K k = Vk / V × 100%. Compared with fissures, karst gaps are more ever-changing in shape and size. Small karst holes are only a few millimeters in diameter, large karst caves can reach hundreds of meters, and some form underground underground rivers that extend for several kilometers. Therefore, the karst rate is extremely uneven in space.
- To sum up, although the definitions of fracture rate (KT), karst rate (Kk) and porosity (n) are similar, they all explain the proportion of void space in rock and soil. However, the practical significance is quite different, among which the porosity has a good representative and can be applied to a wide range; while the fracture rate is limited by the unevenness of the fracture distribution, the application range is greatly limited; for the karst rate (Kk ), Even the average value cannot fully reflect the actual situation, so it is more limited.
- 2.Hydraulic properties of rock and soil voids in water-containing media, although they provide space for groundwater, but whether water can enter and leave these spaces freely, and the ability of rock and soil to retain water, is related to the conditions under which water activity is controlled on the surface of rock and soil The nature has a lot to do with it. These rock properties related to water storage capacity and movement are called the hydrological properties of the water-containing medium, including the water and rock holding capacity, water holding capacity, water supply capacity, water storage capacity, water permeability, and capillary properties.
- 1) Water holding capacity refers to the ability of rock and soil voids to hold a certain amount of water under normal pressure, which is measured by water holding capacity. Water capacity (Wn) is defined as the ratio of the maximum volume Vn of rock and soil to water and the total volume V of rock and soil, that is, Wn = Vn / V × 100%. It can be known from the definition that the value of the water holding capacity Wn depends on the amount of rock and soil voids and the degree of water filling in the voids. If all the voids are filled with water, the water holding capacity is numerically equal to the porosity; Clay, its volume will increase after being filled with water, so the water holding capacity can be greater than the porosity.
- 2) Water-retaining water-saturated rock and soil are capable of maintaining a certain amount of water by molecular force and capillary force after drainage under the action of gravity. Water holding capacity is expressed in terms of water holding capacity. Water holding capacity Wr is defined as the ratio of the volume of water Vr and the total volume of rock and soil V retained by the saturated rock and soil after gravity drainage. That is, Wr = Vr / V × 100%, and its value depends on the adsorption capacity of water molecules on the surface of rock and soil particles. In loose sediments, the finer the particles and the smaller the void diameter, the larger the specific surface area in the same volume and the larger Wr.
- 3) Water supply refers to the ability of saturated rock and soil to discharge water freely under the action of gravity, and its value is expressed by the water supply degree (). Water supply is defined as the ratio of the volume Vg of free water and the total volume V of rock and soil under the action of gravity under the action of gravity, that is, = Vg / V × 100%.
- From the above three definitions, it can be known that the sum of the water and water holding capacity of the rock and soil is equal to the water holding capacity (or porosity), that is, Wn = Wr + or n = Wr + . Where n is the porosity.
- 4) Water permeability refers to the ability of rock and soil to allow water to pass under certain conditions. The water permeability is generally expressed by the value of the permeability coefficient K. Its value is firstly related to the diameter and connectivity of rock and soil voids, and secondly to the number of voids. For example, the porosity of clay is very large, but the pore diameter is small. When water moves in these micropores, not only is it difficult to pass due to the large friction between water and the pore wall, but also a layer of bound water film is formed due to the adsorption of clay particle surfaces This water film occupies almost the entire pores, making it more difficult for water to pass through. Although there is no strict boundary between the permeable layer and the impervious layer, rocks and soils with a permeability coefficient K value of less than 0.001 m / day are often included in the impervious layer. Rock and soil greater than or equal to this value belong to the pervious layer.
- 5) Water storage The water and water holding capacity of the rock and soil mentioned above are suitable for diving without deep burial (thick water), but for deep confined aquifers, they often exist. Obvious error. The main reason is that the amount of water released under high pressure conditions is related to the elastic release performance of the confined aqueous medium and the elastic expansion of the confined water itself. Usually buried
- Vertical distribution structure
- Water storage structure
- The so-called water storage structure refers to a geological structure capable of enriching and storing groundwater, which is composed of a permeable rock layer and a water-proof layer. A water storage structure must have the following three basic conditions. First, there must be a water storage space composed of permeable rock formations or rock bodies. Second, there must be a water-proof boundary formed by the opposite water-resistant rock formations or rock bodies. Third, it has permeable boundary, supply water source and excretion way. Different water storage structures have a great impact on the burial of aquifers, the amount of groundwater recharge and water quality. Especially in hard rock formation distribution areas, we must first find out the impoundment structure before we can find the ideal groundwater source. Such water storage structures mainly include: monoclinic water storage structures, anticline water storage structures, syncline water storage structures, fractured water storage structures, karst water storage structures, and the like. In river valleys and piedmont plains where loose sediments are widely distributed, some people have divided them into piedmont alluvial water storage structures, valley alluvial water storage structures, and lake basin sediments based on the types of sediments, their spatial distribution, and water source conditions. Water storage structure.
Groundwater contains components
- The most widely distributed groundwater is
- Groundwater system potential
Groundwater quality monitoring
- In June 2013, the Ministry of Environmental Protection announced the 2012 Environmental Bulletin.
- 57.3% "poor" national groundwater quality monitoring
- PM2.5 related indicators decline
- The communique said that China's total pollutant emissions have all declined. The four pollutants mandated by the Ministry of Environmental Protection to reduce emissions, chemical oxygen demand and ammonia nitrogen related to wastewater, have all decreased compared to 2010, and sulfur dioxide and nitrogen oxides related to exhaust gas have also decreased compared to the previous year.
- In 2011, the total amount of nitrogen oxides, which is closely related to PM2.5, increased that year. The Ministry of Environmental Protection had explained that this was related to the fact that the indicator had just increased and had not yet reached the emission reduction node. In 2010, the nation's nitrogen oxide emissions also began to decline across the board.
- However, the reduction of discharged waste gas does not represent an improvement in environmental quality. According to the Gazette, in 2012, 325 prefecture-level cities and above nationwide, if measured by the new air quality standards, the proportion of cities that met the standards was only 40.9%, and the compliance rate of 113 key environmental protection cities was only 23.9%.
- Contaminated rural drinking water sources
- Regarding the water environment, the Ministry of Environmental Protection stated that "the quality is not optimistic." Pilot monitoring of rural environmental quality in 798 villages across the country showed that rural drinking water sources and surface water were polluted to varying degrees.
- In addition, the Ministry of Environmental Protection believes that environmental problems in rural areas are becoming increasingly apparent, with prominent pressures on industrial and mining pollution, local pollution intensification, and severe pollution in livestock and poultry farming.
- In 2012, the Ministry of Environmental Protection approved 240 environmental impact assessments for construction projects, involving a total investment of nearly 1.4 trillion yuan, of which 79 were infrastructure and livelihood projects, accounting for about half of the total investment, and 24 projects were returned to the EIA. No approval or deferral approval is involved, involving a total investment of more than 100 billion yuan.
- The theme of China on World Environment Day 2013 is "Working with Breathing", with a focus on prevention and control of air pollution with PM2.5 as the focus.
- Water Environment
- Of the 4,929 groundwater monitoring points in 198 cities, the ratio of monitoring points of excellent-good-good water quality was 42.7%, and the ratio of monitoring points of poor-very poor water quality was 57.3%. The water environment problem in rural areas is even more serious. The water quality compliance rate of drinking water sources in pilot villages is only 77.2%, and the water quality compliance rate of groundwater sources is only 70.3%. The compliance rate of surface water is only 64.7%.
- Prevention plan
- In May 2019, the five national departments issued an implementation plan for pollution prevention [2] .
Groundwater quality level
- Class I water quality: The water quality is good. Groundwater need only be sterilized, and surface water can be provided to domestic drinkers after simple purification (such as filtration) and disinfection.
- Type II water quality: Water quality is slightly polluted. After conventional purification treatment (such as flocculation, sedimentation, filtration, disinfection, etc.), its water quality can be used by domestic drinkers.
- Three types of water quality: suitable for secondary protection areas of centralized drinking water sources, general fish protection areas and swimming areas.
- Four types of water quality: suitable for general industrial protection areas and entertainment water areas where the human body is not in direct contact.
- Five types of water quality: suitable for agricultural water areas and general landscape requirements. Water bodies that exceed the five water quality standards are basically no longer functional
Groundwater influencing factors
- Overexploitation
- Some areas (such as the North China Plain in China, etc.
- groundwater
- Over the past 30 years, the amount of groundwater extraction in China has increased at a rate of 2.5 billion cubic meters per year, which effectively guarantees the needs of economic and social development. However, over-exploitation of groundwater in the northern and eastern coastal areas has become increasingly serious. According to preliminary statistics, more than 100 large-scale groundwater dropping funnels have been formed nationwide, covering an area of 150,000 square kilometers and over-exploitation areas covering 620,000 square kilometers. Nearly 60 cities have been severely over-exploited, causing many springs to be cut off and some water sources depleted. Groundwater overmining areas are mainly distributed in the North China Plain (Huanghuaihai Plain), the six major basins in Shanxi, the Guanzhong Plain, the Songnen Plain, the Xialiaohe Plain, and parts of the northwest inland basin (Shiyang River, Turpan Basin, etc.), the Yangtze River Delta , Southeast coastal plains and other areas. The North China Plain is the most serious. The overexploitation of groundwater in the Hebei Plain and Beijing Plain area has reached 50 billion cubic meters and 6 billion cubic meters, respectively; due to severe land subsidence, Tianjin can no longer continue to overexploit groundwater. The long-term continuous over-exploitation has caused the deep groundwater level in the North China Plain to continue to decline, and the storage resources have been continuously reduced. At present, the groundwater level in an area of nearly 70,000 square kilometers is below the sea level. At more than 80 meters above sea level, groundwater storage resources are nearly depleted.
- Ground subsidence
- Nearly 70 cities across the country have induced ground subsidence due to the unreasonable exploitation of groundwater. The subsidence range is 64,000 square kilometers. The largest settlements in the settlement center exceed 2m. Shanghai, Tianjin, Taiyuan, Xi'an, Suzhou, Wuxi, Changzhou and other cities, Tianjin The settlement of Tanggu reached 3.1m. Ground subsidence in Xi'an, Datong, Suzhou, Wuxi, Changzhou and other cities is accompanied by ground fissures, posing a serious threat to urban infrastructure. Ground fissures also occurred in Hebei, Shandong, Yunnan, Guangdong, and Hainan.
- Karst collapse
- Large-scale centralized mining of groundwater and mine drainage caused frequent ground subsidence, showing a trend of concentration to towns and mines, with an increasing scale and increasing losses. According to incomplete statistics, more than 1,400 karst collapses have occurred in 23 provinces (autonomous regions and municipalities directly under the central government), with a total of more than 40,000 collapse pits, posing a serious threat to national economic construction and people's lives and property. For example, on August 4, 2003, the karst collapse of Yangchun City, Guangdong, caused the collapse of 6 residential houses, two casualties, and more than 400 people in more than 80 households. On April 6, 2000, the karst collapse of Hongshan District in Wuhan caused the collapse of 4 residential houses, 150 More than 900 people were affected by the disaster. In the 1980s, the Tai'an karst collapse in Shandong caused the Beijing-Shanghai Railway to be temporarily interrupted and slowed down for a long time. The Guizhou-Kunming Railway experienced a train subversion event due to karst collapse. The ground collapsed. Ground collapse caused by overexploitation of karst groundwater is mainly distributed in provinces (regions) such as Guangxi, Guangdong, Guizhou, Hunan, Hubei, and Jiangxi, and also in provinces (regions) such as Fujian, Hebei, Shandong, Jiangsu, Zhejiang, Anhui, and Yunnan . Kunming, Guiyang, Liupanshui, Guilin, Tai'an, Qinhuangdao and other cities have the most typical karst collapses, and some mines in Hunan and Guangdong have the largest number of collapses caused by pit drainage. There were more than 3,000 karst collapses across the country, with an area of more than 300 square kilometers.
- Seawater intrusion
- In the Bohai Rim region, some coastal cities in the Yangtze River Delta, and the southern coastal areas, seawater intrusion to varying degrees caused by excessive exploitation of groundwater has shown a trend of development from point intrusion to surface intrusion. The intrusion of seawater caused different degrees of salinization of groundwater, which caused local people's drinking water difficulties, salinization of the land, and most farmland reduced yields by 20% -40%, severely reaching 50% -60%, and very severely reaching 80%. Even extinct. The south bank of Laizhou Bay in Shandong is one of the areas with the most serious seawater invasion in China, causing more than 8,000 agricultural machinery wells to be scrapped, 400,000 people having difficulty drinking water, 600,000 mu of arable land losing production capacity, a cumulative reduction of 3 to 4.5 billion kilograms of grain output, and direct economic losses of 40 100 million yuan.
- Soil salinization
- The problem of salinization of naturally occurring native soils is mainly distributed in the Songnen Plain and Northwest China, as well as in the Huanghuaihai area. The main provinces are Heilongjiang, Jilin, Inner Mongolia, Ningxia, Gansu, Xinjiang, Hebei, Henan, and Shandong. Long-term climate drought, continuous increase in agricultural irrigation and industrial water use, has caused the groundwater level to generally decline, the salt in the topsoil is leached to the ground, the degree of soil salinity is reduced, the area of salinization is reduced, and the soil salt in China is reduced The affected area is only 31.4% of the distribution area in the early 1980s. The problem of secondary soil salinization caused by human activities is mainly distributed in agricultural areas where surface water irrigation is heavily used in the middle reaches of the Yellow River and northwest inland basins in China. In addition, high arsenic water, high fluoride water, and low iodine water are distributed in parts of China. About 100 million people nationwide are drinking substandard groundwater, causing people in these areas to suffer from arsenic poisoning (skin cancer) and toenail. Disease, endemic fluorosis, Keshan disease and other endemic diseases.
- Water pollution
- The results of the new round of groundwater resource evaluation show that China's groundwater quality is generally good. According to the distribution area statistics, 63% are available for direct drinking, 17% are suitable for drinking after proper treatment, 12% are not suitable for direct drinking but can be used by agriculture and some industrial sectors, and less than 8% of groundwater has a mineralization degree greater than 5 G / L of saline water and a small amount of seriously polluted groundwater are not suitable for direct use or may require deep treatment before they can be used.
- However, the unreasonable or substandard discharge of urban and industrial "three wastes" has increased rapidly, and the large-scale use of pesticides and fertilizers in agricultural and pastoral areas has led to the increasingly serious pollution of groundwater in China. Expansion trend.
- Under the influence of various pollution sources, shallow groundwater pollution in China is serious and the pollution speed is fast. In 2011, in the monitoring of groundwater quality in 200 cities across the country, the "poor-very poor" water quality ratio was 55%, and it was worse than that of 15.2% in 2010.
- According to a ten-year survey by the Ministry of Land and Resources, 60% of the 1.97 million square kilometers of plain area has shallow groundwater that is no longer drinkable. The situation of groundwater is urgent. According to the plan formulated by the Ministry of Environmental Protection and other departments, by 2020, comprehensive monitoring of typical groundwater pollution sources will be implemented.
- From 2000 to 2002, the Ministry of Land and Resources conducted a nationwide evaluation of groundwater resources. According to the "Groundwater Quality Standards", 37% were already inedible water.
- In 2011, groundwater quality monitoring was carried out in a total of 200 cities across the country, of which the percentage of "poor-extreme" water quality monitoring points was 55%. Compared with 2010, the water quality at 15.2% of the monitoring points is worsening.
- According to the National Groundwater Resources Evaluation of the Ministry of Land and Resources from 2000 to 2002, the monitoring results of 195 cities across the country show that 97% of urban groundwater is polluted to varying degrees, and 40% of urban pollution is aggravated; 16 of the 17 capital cities in the north are polluted The trend has intensified, and three of the 14 provincial capital cities in the south have intensified their pollution trends. [3]
Groundwater plant state
- In arid regions, many plants depend on groundwater for their lives. Such is the case of Populus dlersifolia , which grows on the banks of rivers in desert areas. Take Ejina Banner, the westernmost part of Inner Mongolia as an example. The annual precipitation there is less than 40 mm, and the evaporation is more than 3000 mm. However, due to the shallow groundwater level on the river bank, Populus euphratica can survive. At present, Populus euphratica has died in a large area due to a large decrease in incoming water.
- In areas with very dry climates, some plants have deep root systems that can reach the groundwater surface or the edge of the capillary tube, so they can directly use groundwater. Such plants are called submerged plants. For example, the camel thorns ( Alhagi pseudathagi ) growing in desert areas have a height of only about 20 cm above ground and a depth of more than ten meters below ground. [4]