In recent days, the underground sewage has spread from the Internet to many local governments. It is irrelevant whether the evidence of the company's underground sewage discharge is true or not. It is an indisputable fact that China's groundwater pollution is serious. On this issue, a reporter from the "Environment and Life" magazine interviewed Wang Hao, a Chinese hydrology and water resource expert and academician of the Chinese Academy of Engineering.

Sixty percent of groundwater in my country is seriously polluted

"Environment and Life": You are an authoritative expert on groundwater. Can you tell us about the current situation of groundwater in our country?

Wang Hao: More than 1.5 billion people in the world mainly rely on groundwater as drinking water. my country's groundwater resources account for 1/3 of the country's total water resources, maintaining 70% of the country's population for drinking, 40% of farmland irrigation and 38% of industrial production.

Due to the discharge of industrial wastewater and domestic sewage, the use of ultra-quantitative fertilizers and pesticides, the leaching of garbage dumps and the leakage of underground oil tanks, groundwater is suffering more and more serious pollution. An expert from the China Geological Survey once pointed out that 90% of China's groundwater is polluted to varying degrees and 64% is seriously polluted.

In the shallow groundwater in the plain area of ​​1.97 million square kilometers evaluated by the National Water Resources Survey, the Taihu, Liaohe, Haihe, and Huaihe river basins have the most serious groundwater pollution.

Chemical fertilizers and pesticides cause the "three nitrogen" (ie ammonia nitrogen, nitrate, nitrite) to exceed the standard in groundwater. In all provinces and cities in the Yangtze River Delta region, excessive nitrate nitrogen in groundwater was found.

Organic pollution still exists in groundwater pollution. Relevant domestic authorities have conducted investigations and evaluations on groundwater pollution. Trace organic matter has been generally detected. Carcinogenic, teratogenic, and mutagenic "three-causing" substances have been detected to varying degrees. These substances are not easily exposed to water. Microorganisms degrade, but are easily absorbed by organisms, and return to the human table through the food chain. More than 100 kinds of pollutants have been detected in groundwater in Beijing, Tianjin, Hebei and other places, many of which are "three cause" substances.

In recent years, due to a large amount of over-extraction of groundwater, a large area of ​​groundwater funnel has been formed underground, thus aggravating the backflow of ground sewage to groundwater. The official report shows that the underground water in North China has been over-exploited by 120 billion cubic meters, which is equivalent to the amount of 200 Baiyangdian lakes. The continuous decline of the groundwater level has created a huge groundwater fall funnel area in the North China Plain. Sewage discharge in these areas will not only pollute the shallow groundwater, but as the shallow sewage continues to flow to the deeper layers, the deep groundwater is also easily polluted.

In short, China's groundwater pollution has evolved from point to surface, from east to west, from urban to rural, and from local to regional.

Agriculture, industry, humans are victims

"Environment and Life": What harm will such groundwater pollution cause?

Wang Hao: First of all, it directly affects the water quality of drinking water sources. Contaminated groundwater has too high hardness. As a source of drinking water, it is not only bitter and difficult to drink, but also causes gastrointestinal dysfunction, such as vomiting, diarrhea, and flatulence. When the local sewage is polluted, it often causes changes in the content of three nitrogen in the water. Too high levels of three nitrogen in the water will cause harm to the human body (especially infants) and cause acute nitrate poisoning. Under certain conditions in the human body, trinitrogen can also be converted into carcinogens, nitrosamines, leading to cancer and even death. In addition, if the groundwater source is severely polluted by organic or even heavy metals, the "three causes" substances produced in the water body will cause greater harm to human health. In recent years, the emergence of "cancer villages" in Taihu, Chaohu and other places has aroused widespread concern about the relationship between water pollution, an environmental factor, and cancer incidence.

Secondly, in the field of food safety research, the impact of irrigation water pollution on the quality of agricultural products is also one of the hot topics.

Furthermore, in my country, especially in the northern regions, groundwater accounts for a large proportion of industrial production water, and groundwater pollution will seriously affect industrial production. Increasing the hardness of groundwater will cause scaling in the boiler and pipeline walls, which not only wastes fuel, but also directly affects the life of the boiler and even causes an explosion; as far as the textile printing and dyeing industry is concerned, washing products with high hardness water slurry will not only consume a lot of lotion, but also And it will produce inferior products or waste products; in addition, high hardness groundwater will also cause harm to many industries such as chemical industry, pharmaceuticals, wine making, power generation, and papermaking. This forces some industries to soften and purify hard water, thereby increasing production costs.

Finally, after pollutants are discharged into rivers and lakes, in addition to causing harm to natural fish and aquatic organisms in the water body, excessive nitrates will also make rivers and lakes acidic and corrosive, affecting the normal growth of aquatic organisms, and even Can lead to the extinction of certain aquatic life.

Improper treatment of sewage and waste liquid in my country

"Environment and Life": What role does underground sewage play in the status quo of groundwater pollution in my country?

Wang Hao: Government departments have issued corresponding policies for corporate sewage and sewage treatment standards to minimize the negative impact of industrial development on the environment.

However, some unscrupulous enterprises have blatantly discharged industrial sewage and waste liquid containing highly toxic carcinogens that are difficult to degrade (for example, undegradable heavy metals such as arsenic and mercury, or polycyclic aromatic hydrocarbons, etc.) into the ground. In addition to digging seepage pits and secretly draining seepage wells, in order to avoid investigation and punishment, some polluting enterprises also use high-pressure pumps to directly inject large amounts of sewage into the ground. Some enterprises in the south even discharge sewage into underground caves.

For example, the cadmium pollution incident in Guangxi in February 2012 was caused by two companies emitting cadmium pollutants through caves.

It is not uncommon to see sewage through seepage pits and seepage wells. This method of sewage discharge provides low-cost and easy-to-operate conditions for surface water infiltration. Such sewage often penetrates into the underground aquifer through the well-permeable sand, gravel and rock and other layers of the underground water layer, thereby causing groundwater pollution.

A common method of underground sewage discharge in my country is the use of shallow wells, that is, the untreated sewage is secretly discharged into the groundwater through a 300-500m deep well, and this location is usually where the groundwater is available for drinking. Due to the improper treatment of sewage and waste liquid and the immaturity of sewage disposal technology in China, underground sewage has undoubtedly become the chief culprit of groundwater pollution in my country.