What Is Groundwater Discharge?

The general term for the physical properties and chemical composition of groundwater is an important characteristic and evaluation indicator of groundwater resources. China has formulated the "Groundwater Quality Standards" to standardize groundwater quality classification, groundwater quality monitoring, evaluation methods, and groundwater quality protection standards.

Groundwater quality

In order to protect and rationally develop groundwater resources, prevent and control groundwater pollution, protect people's health, and promote economic construction, the "

Groundwater quality evaluation is actually based on the

In 2016, the groundwater aquifer system was used as the unit, and the shallow groundwater mainly dominated by diving and the medium-deep groundwater mainly dominated by confined water. Groundwater quality monitoring was carried out in 6,124 monitoring points (including 1,000 national-level monitoring points). The evaluation results show that the monitoring points for water quality are excellent, good, better, worse and extreme, accounting for 10.1%, 25.4%, 4.4%, 45.4% and 14.7%, respectively. The main exceeding indicators are manganese, iron, total hardness, soluble total solids, "trinitrogen" (nitrite nitrogen, nitrate nitrogen and ammonia nitrogen), sulfate, fluoride, etc. Arsenic, lead, mercury, Heavy (class) metals such as hexavalent chromium and cadmium have exceeded the standard. Groundwater quality monitoring wells for water resources in river basins are mainly distributed in Songliao Plain, Huanghuaihai Plain, basins and plains in Shanxi and Northwest China, and key areas of Jianghan Plain. The monitoring objects are mainly shallow groundwater, which basically covers the degree of groundwater development and utilization. Large, heavily polluted areas. The comprehensive evaluation results of groundwater quality at 2104 stations showed that the overall water quality evaluation results were poor. The proportion of stations with good water quality is 2.9%, the proportion of good stations is 21.2%, there is no better station, the proportion of poor stations is 56.2%, and the proportion of extremely poor stations is 19.8%. The main pollution indicators, except for total hardness, soluble total solids, manganese, iron, and fluoride, may be due to high hydrogeochemical background values. "Trinitrogen" pollution is more serious, and some areas have heavy metal and toxic organic pollution. ^[4]

Groundwater pollution sources are very wide, among which surface water, precipitation, industrial "three wastes", domestic sewage, and domestic waste discharge are the main causes of groundwater resource pollution. In rural areas, the heavy use of pesticides and fertilizers has aggravated the deterioration of the groundwater environment. To sum up, it mainly includes the following aspects:

1. Pollution of groundwater resources by industry. While industrial production uses groundwater, it also directly or indirectly causes the deterioration of groundwater quality with the large amount of exhaust gas, waste water and waste residue it emits. The groundwater pollution caused by industrial production has the characteristics of large area and strong power. The harm of industrial production to groundwater is mainly reflected in the following three ways: First, industrial waste gas, a large number of toxic gases must be excluded in the production process of many factories, such as sulfur dioxide, nitrogen oxides and various acid waste gases emitted by the acid production industry; steel Metallurgical enterprises and non-ferrous smelting enterprises mainly emit sulfur dioxide, hydrogen chloride and metal compounds such as lead and manganese; the petroleum industry mainly emits hydrogen sulfide, carbon dioxide and sulfur dioxide. Pollutants also go deep into the ground with rain and snow, contaminating groundwater quality. The second is industrial wastewater. Untreated industrial wastewater is discharged into rivers (or other surface water bodies). First, it pollutes surface water and then pollutes groundwater. The pollution of industrial wastewater has the most direct and serious damage to groundwater quality.

2. Pollution of groundwater resources by agricultural production. China is a large crop producer, especially in the northern region. It uses a large amount of groundwater for agricultural production, and its impact on groundwater resources is increasing. The impact of agricultural production on groundwater resources is mainly divided into three aspects: First, the use of chemical fertilizers and pesticides. Chemical fertilizers often contain nitrogen, phosphorus, and potassium fertilizers. With the infiltration of irrigation water and precipitation into the ground, especially sewage irrigation, it will cause pollution to shallow groundwater. Pesticides contain a lot of harmful ingredients, such as dichlorvos, trichlorfon, 666, etc. Substances that are not easily volatile and decomposed remain in the soil, waters and organisms, and gradually condense in the animals and humans with the food chain, causing adverse consequences. The second is the discharge of domestic pollutants. It is mainly caused by manure pits, seepage wells, garbage dumps, etc., and directly infiltrates shallow groundwater through infiltration and leaching, which increases the total hardness of the groundwater and worsens the groundwater environment. The third is agricultural sewage irrigation. Because urban sewage often contains nitrogen, phosphorus, potassium, and organic carbides, the use of sewage for irrigation in agriculture can not only save fertilizer, but also improve soil fertility. Therefore, there are many ways to use sewage for irrigation in modern agriculture, but it is easy to use sewage for a long time. Pollution of groundwater and reduced crop yields.

3. Pollution of groundwater resources by mining activities. The destruction of groundwater resources by mining activities is mainly manifested by changes in burial conditions. The construction of surface water conservancy projects will change the surface water flow conditions, which will have a significant impact on the balance and burial status of groundwater. At the same time, the pH value of the pit water discharged from mining is usually very low. After the acidic water penetrates into the ground, some salts can enter the aquifer. The resulting salt effect promotes the dissolution of calcite and dolomite in the soil and causes calcium and magnesium ions. When dissolved into water, the total hardness of the groundwater increases.

4. Pollution of groundwater resources by domestic pollution. The pollution of groundwater resources in daily life, especially in urban life, is becoming increasingly apparent. During the rapid development of the city, the urban geological environment has been continuously transformed and disturbed by human activities, the original geological environment evolution trend has been destroyed, and the problem of urban geological environment deterioration has become increasingly prominent, especially the degradation of groundwater environment. Groundwater pollution from domestic pollution can be divided into two aspects: On the one hand, a large amount of domestic sewage is discharged. There are many sources of domestic sewage. Detergents, domestic waste, and excreta in daily life constitute the main sources of urban residents' domestic sewage; toxic chemicals, sewage, bacteria, and virus pollutants discharged by medical and health units and laboratories Waiting also threatens the quality of groundwater. On the other hand, urban transportation is becoming more and more developed, and large amounts of vehicle exhaust emissions, such as energy consumption and exhaust gas emissions, cause atmospheric pollution. These pollutants reach the ground after being washed away by rainwater, and the pollutant components that cannot be effectively degraded will infiltrate into the groundwater, resulting Groundwater pollution.

5. Natural reasons In some areas, due to the special natural environment and geological environment, the natural background of groundwater is bad, which contains toxic and harmful components that exceed the standard. According to the survey and statistics of China Geological Environment Monitoring Institute, high arsenic water, high fluorine water, and low iodine water are distributed in parts of China. About 100 million people across the country are drinking substandard groundwater, which has caused these areas to suffer from endemic diseases such as arsenic poisoning (skin cancer), scoriasis, fluorosis, and Keshan disease for a long time.

6. Pollution of terrestrial surface water and seawater Surface water and groundwater can be regarded as an ecological cycle system, so serious pollution of surface water bodies will inevitably worsen the deterioration of the groundwater environment. Surface water bodies that have been polluted, including rivers, lakes, and artificial reservoirs, will cause groundwater pollution if they are directly recharged. Similarly, in coastal areas, groundwater pollution caused by backwater inflow and saltwater intrusion due to overexploitation of groundwater may result. ^[5]