It is generally believed that natural is good, pure natural water is pure and impurity-free, good quality and drinkable. Is this really true? Is food derived from natural resources a safe and healthy green food? In fact, “pure natural†itself is meaningless, and everything that is not artificially synthesized can be called “ all natural".
Measuring the quality of things depends on a standard. The same is true for the quality of groundwater, and there are groundwater quality standards. China implemented the groundwater quality standard in 1993 and revised it in 2017. So, according to this standard, how is the quality of groundwater evaluated?
The “Groundwater Quality Standards†clearly state that “groundwater quality is a general term for the physical, chemical and biological properties of groundwaterâ€. There are 93 indicators for determining the quality of groundwater, including 39 “normal indicators†and 54 “unconventional indicatorsâ€. Routine indicators include sensory traits and general chemical indicators, microbial indicators, common toxicological indicators and radioactive indicators; unconventional indicators are extensions to conventional indicators, groundwater quality indicators based on regional and temporal differences or special circumstances, reflecting groundwater production The main quality issue.
Water composition
We all know that water consists of two hydrogen atoms and one oxygen atom. There is no other component in pure water. Water is a good solvent, starting from the moment the condensate falls in the clouds, it begins to dissolve the substances in contact with it. After infiltration into the earth's surface, the water flowing in the subterranean formation collides with and rubs against the surrounding rocks, and the minerals enter the groundwater, which we call "water rock action." The action of water and rock makes the groundwater rich in a variety of chemical elements, these chemical elements are called "native elements." Among them, the beneficial element is called "beneficial element [k1]," and the unfavorable one is called "harmful element". However, if the nutrient content is too high, it will be harmful to the human body. Some chemical elements dissolved in the groundwater natural groundwater flow process, some into the underground via industrial or agricultural activities, the latter is called "Pollutant", such as carbon tetrachloride, nitrates, hexavalent chromium . Water, a solvent, is a “living fossil†that faithfully records which substances it is exposed to during its flow. The groundwater we drink may have been transported for a long time and a long distance.
The quality of groundwater in China is divided into five categories. Among them, Class I, II and III groundwater chemical components are low in content and can be used as drinking water; Class IV water produces human health risks at a certain level; Class V water is not suitable as drinking water. Each type of water has a corresponding chemical content limit, such as a total dissolved solids type I water of less than or equal to 300 mg/L, a type II water of less than or equal to 500 mg/L, greater than 300 mg/L, and a type III water less than or equal to 1000 mg/L, greater than 500 mg/L; Class IV water is less than or equal to 2000 mg/L, greater than 1000 mg/L; Class V water is greater than 2000 mg/L.
Water quality standard classification
It can be seen from the above that the first three types of groundwater are for drinking water for domestic use and are harmless to the human body.
When assessing groundwater quality, all chemical components of a water sample are compared to groundwater quality standard limits. If each chemical component exceeds the Class III water limit, and the Class IV water is less than Class IV water, it is classified as Class IV water. Then, the results of the evaluation of each chemical component are combined, and the highest class is the category of the water sample.
A problem arises during the evaluation process, and “native elements†and “pollution quality†are involved in the evaluation. For example, the evaluation result is Class IV water. If the result is caused by “pollution qualityâ€, it indicates that the groundwater is contaminated; if it is due to the high “primary elementâ€, such as high fluorine water, etc., such type IV water Although the quality is poor, it is not polluted. Of course, regardless of whether the poor quality is caused by "native elements" or "pollution", such water is harmful to the human body.
High-fluorine groundwater and high- arsenic groundwater are distributed in many parts of the world. Similar problems exist in China, such as high levels of fluoride and arsenic in the groundwater of the eastern North China Plain. In order to solve the problem of drinking water in these areas, the Chinese government has implemented the South-to-North Water Diversion Project to ensure the safety of drinking water for residents in North China.
North Water Transfer Project
The Institute of Hydrogeology and Environmental Geology of the Chinese Academy of Geological Sciences collected a total of 6 063 groundwater samples in the North China Plain. The analysis and evaluation found that groundwater quality exceeds III (77.3%); shallow groundwater I-III accounts for 22%; %; V class accounted for 57%; deep groundwater I to III accounted for 26%; IV class accounted for 23%; V class accounted for 51%. Superclass â…¢ water contribution rate large shallow groundwater native indicators include manganese, total hardness, total dissolved solids, iodide, iron, arsenic and fluoride; deep groundwater is fluoride, iodide, manganese, Arsenic, etc.
Contribution rate of native single index to super-type shallow groundwater (a) and super-class III deep groundwater (b) in North China Plain
The data show that the quality of groundwater in North China is worrying, and the reason is largely caused by the excessive primary indicators. The protection and treatment of groundwater is necessary, but the reasons for the poor water quality are deducted under the big hat of “pollutionâ€.
Water is good for everything. Every drop of water may have been honed for decades, hundreds of years, wrapped in scouring and dissolved matter, and put into the next steam cycle to complete its historical mission. The poor quality of groundwater is not necessarily caused by pollutants produced by human activities. It is also an important reason for them to flow through natural hazardous areas. To protect water resources, we must not only save energy and reduce emissions, but also restrict human damage to the natural environment. We should also pay enough attention to environmental problems formed under natural conditions.
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