1. Application in agriculture and soil management
1. Groundwater pollution caused by agricultural activities
The current problem of groundwater pollution caused by pesticides has caused People are becoming more and more worried. Some people believe that pesticide pollution will become one of the major pollution problems today. Pesticides that pollute the environment include herbicides, insecticides, and fungicides. In addition, groundwater is also vulnerable to pollution sources such as manure piles, farm sewage, waste, disinfectant water and silage feed liquids in agricultural production. The number of pesticides banned by international water management agencies is increasing. For example, DDV is banned, aldrin, dieldrin and chlordane are discontinued, and iodobenzonitrile and bromoxynil are restricted. Pesticides and nitrates pose serious threats to groundwater quality and are more difficult to eliminate than surface sewage pollution.
2. Groundwater pollution and treatment by seawater
When the freshwater level drops, seawater will infiltrate, causing an increase in groundwater saltwater and a decrease in freshwater. This phenomenon is common in the southeastern coastal areas of my country. Salt water immersion can reduce the quantity and quality of agricultural products, and can also harm the survival of existing freshwater animals and plants. When the concentration of salt water is high, it can cause physiological effects on humans. Produce symptoms of hypertension.
Due to excessive development of groundwater along my country's coast, seawater intrusion is a common phenomenon. There are large areas of salt water around the Bohai Sea. The Chinese Academy of Sciences carried out ground electrical sounding work in Laizhou, Shandong Province to control seawater intrusion in Laizhou City. Figure 5-2-1 is an equivalent section diagram of apparent resistivity, which shows seawater intrusion channels (low resistance) and freshwater ancient river channels (high resistance). The measurement results compiled a resistivity map and curve type distribution map, and divided the seawater serious intrusion area (ρs=2~17Ω·m), the mild intrusion area (ρs=17~30Ω·m) and the non-intrusion area (ρs=30 ~100Ω·m). Curve types QQ and KQ are severely invaded areas, H type is lightly invaded area, and K type and A type are uninvaded areas. The degree of intrusion classified according to electrical sounding is shown in Table 5-2-1. In Table 5-2-1, area III is an easy-to-treat area, and area I is a difficult-to-treat area. Brine resources have been developed in some places. Due to the serious over-exploitation of groundwater in Laizhou City, two large groundwater funnels were generated in the offshore Wanghe and Zhuqiao River areas, with the water levels in the center of the funnels being -15 m and -10 m respectively. In recent years, the invaded area has expanded to 435 km2, and more than 6,000 wells have been abandoned, causing 500,000 acres of cultivated land to lose groundwater for irrigation, and 50,000 acres of cultivated land to undergo secondary salinization. Therefore, engineering measures to control seawater intrusion by blocking water and replenishing infiltration are proposed.
Figure 5-2-1 Equivalent section diagram of apparent resistivity
Table 5-2-1 Relationship between seawater intrusion degree and resistivity
3. Survey on Soil Salinization and Drought Control
The reclamation and irrigation of farmland have raised the groundwater level, leading to salinization. Soil salinity can be classified according to electrical conductivity, which can be determined by air or ground electrical methods, while the depth of the water table is generally determined by seismic refraction. Table 5-2-2 lists Australia’s soil salinity classification and its relationship with crop salt tolerance and root soil conductivity.
Table 5-2-2 Australia’s soil salinity classification and its relationship with crop salt tolerance and root soil conductivity
The severe droughts in recent years have brought serious consequences to India’s security situation. Drabang poses great difficulties. To control the drought, water and soil conservation and recharge measures are planned, which requires understanding the thickness of the soil, the thickness of the weathering crust and the relief of the bedrock. For this purpose, resistivity bathymetry was systematically carried out in typical rain-deficient areas of the state. Contour maps of soil thickness and bedrock depth were drawn based on the results of electrical sounding. In order to understand the changes in the thickness of the weathered layer and the presence or absence of water-filled fissures, geoelectrical sections were also made. Water and soil conservation measures will be adopted in the divided areas with thin soil, while areas with thick weathered layers and deep foundations will be used as artificial recharge locations.
4. Application in soil management
For soil pollution, we must first control and eliminate the source of pollution. Because soil has a certain purification ability; therefore, the migration and transformation of pollutants must be controlled so that they cannot enter the food chain.
(1) Control and eliminate soil pollution sources
1) Control and eliminate industrial “three wastes” emissions. Promote closed-loop, non-toxic processes to reduce or eliminate pollutants. Recycle and purify industrial "three wastes" and reduce the quantity and concentration of emissions to make them comply with standards.
2) Strengthen the monitoring and management of soil sewage irrigation areas.
Understand the composition, content and dynamics of pollutants, control the amount of sewage irrigation, and avoid soil pollution caused by abuse of sewage irrigation.
3) Control the use of chemical pesticides. Ban or restrict the use of highly toxic and high-residue pesticides, develop efficient, low-toxic, and low-residue pesticides, and develop biological pesticides. Use pesticides rationally, establish safe intervals, and establish allowable residues of pesticides.
4) Use chemical fertilizers rationally. In order to increase production, rational application of chemical fertilizers is necessary. However, excessive application will cause crop yield and quality reduction, and will also cause excessive nitrate content in crops, which will affect the health of people and livestock. It will also increase the content of heavy metal elements and cause soil pollution.
(2) Increase soil capacity and improve soil purification ability
Increasing soil organic matter content, sand mixing and improving sandy soil can increase and improve the type and quantity of soil colloids. Increase the adsorption capacity and amount of toxic substances in the soil, thereby reducing the activity of pollutants in the soil. Discovering, isolating and cultivating new microbial species to enhance biodegradation is also an extremely important step in improving soil purification capabilities.
(3) Application of geophysical prospecting methods in soil pollution source investigation
The waste residue and waste water discharged from industrial production and the waste gas emitted from fossil fuel combustion contain ferromagnetic substances. Therefore, measuring the magnetic susceptibility (к) and remanent magnetism M of materials, sediments and soils can trace the sources of lakes, oceans, and soil pollution. The M of soil has a positive correlation with the iron in pollutants and can be estimated from the M value. The iron content in lakes, oceans, and soil determines the degree of pollution of soil, water bodies, lakes, and shallow sea sediments. Figure 5-2-2 shows the magnetic measurement results of shallow sea silt pollution at the Athens Steel Plant in Greece. At a distance of 0.3 km from the steel plant, the magnetic susceptibility value of the surface layer is ten times that at a distance of 1 to 3 km. Guo Youzhao obtained similar results by conducting magnetic measurements on topsoil near a factory in Langfang, Hebei. On both sides of the Beijing-Tianjin railway, an increase in soil magnetism caused by domestic waste pollution was also detected.
Figure 5-2-2 Residual magnetism measurement results of marine sediments around the Athens Steel Plant in Greece
2. Application in environmental pollution assessment and monitoring
1. Groundwater pollution assessment and monitoring
Water contaminated by inorganic salts often reduces the resistivity due to an increase in ion concentration. Due to the obvious difference in resistivity between contaminated water and uncontaminated water, if it is not buried deep and has a certain volume, it can be detected through electrical methods. For example, in the Saukville coal ash accumulation site in Wisconsin, the United States, in order to understand the pollution of coal ash to groundwater, the government drilled 33 observation wells and conducted electrical detection near the wells. The measuring lines were perpendicular to the direction of groundwater flow. Electrical sounding is carried out simultaneously with water sampling, once a month. The cross-sectional map of the water pollution range produced based on the electrical sounding is much more detailed than the results obtained from only a few monitoring wells.
The University of Waterloo in Canada studied the contamination of ethylene (C2Cl4) used in clothing dry cleaning and metal cleaning. Every 1L of ethylene discharged can pollute 1000×104 liters of water. Steel plates were driven into the ground around the experimental site to cut off the hydraulic connections inside and outside the site. Ethylene was injected into the site through shallow holes. Neutron, density and induction logging were performed in the surrounding monitoring holes. The resistivity on the ground and in the wells were also measured regularly. , and conduct ground-penetrating radar profile measurements. The results showed that due to the chlorine in ethylene flotation neutrons, a negative peak appeared on the neutron log curve, and the high concentration of ethylene showed obvious reflection on the radar profile. According to the resistivity anomaly, it can also be seen that the change of ethylene over time of movement.
Petroleum pollution is the most common organic pollution. At an underground oil leak site in South Australia, the EM31 electromagnetic meter and geological radar were initially used to detect the oil leak location, but they were ineffective. Later, the electromagnetic wave profiling method was used to circle the pollution area, which was confirmed by drilling and trenching. During operation, the vertical transmitting coil and the horizontal receiving coil maintain a zero-coupling state and move along the survey line with equal coil spacing. Obvious low-value anomalies of the vertical component of the magnetic field appear within the pollution range.
2. Air pollution assessment and monitoring
Russian scientists have shown that the potential gradient is a sign of the degree of air pollution. Changes in near-surface atmospheric components caused by industrial traffic, such as changes in chemical components, increases in dust, solid and liquid smog, etc., have a great impact on the decomposition and migration of charges, reducing the atmospheric conductivity and causing potential gradients. The increase in the average value results in an increase in the vertical component of the electric field intensity E.
High levels of sulfur dioxide in the atmosphere lead to the formation of acid rain, and sulfur dioxide mainly comes from coal burning.
Sulfur content in coal can be analyzed on-site using X-ray fluorescence measurements. The measurement uses 55Fe as the X-ray source and the gas proportional scintillation tube as the detector. The energy resolution of the sulfur spectrum line is 11.8%, and the detection limit can reach 0.15%.
3. Evaluation and treatment of natural nuclear radiation
According to U.S. statistics, 82% of the nuclear radiation dose received by humans comes from natural sources, and 55% comes from radon. Radioactive gas radon easily adheres to dust particles and can cause lung cancer if inhaled by the human body. Radon gas hazards are widely distributed, and it would be time-consuming, laborious, and difficult to implement nationwide. We know that radon is the decay product of radium, and radium is formed by the decay of uranium. Therefore, it is important to classify areas with high uranium content (average content 2.5 to 10 times), such as granite, gneiss, rhyolite, Dacite, carbonaceous shale and other distribution areas. Therefore, the evaluation and treatment of natural nuclear radiation environmental pollution can be divided into three stages: wide area, community and indoor.
(1) Wide-area radiation environment monitoring
It is conducted by a unified national organization with the purpose of understanding the overall status and hazard level of the radiation environment in the entire country. It mainly uses aviation radioactive gamma energy spectrum measurements, radioactive geochemical measurements, regional geology and remote sensing data. Plane contour maps and cross-section diagrams of uranium, thorium, and potassium content measured by airborne radioactivity are actually the main basis for reflecting changes in ground radium content. In areas lacking aerial data, ground radioactivity measurements and geochemical measurements of uranium, radium, radon and other geochemical data can be used. Regional geology and remote sensing data can provide regional geological structural background such as rock distribution and fault zones.
For example, regional environmental radon assessment can carry out nationwide indoor radon sampling surveys, use unified measurement methods to calibrate detectors, and conduct unified laboratory analysis and data processing to study and understand radon. The degree of harm to the human environment.
(2) Monitoring and management of community and indoor radiation environment
In the high radiation area determined by the above method, use gamma radiation meter, activated carbon detector, and alpha track detection Monitor human living spaces (especially indoor radon) and water sources to determine sources of radiation pollution. According to statistics, about 8% to 25% of lung cancer deaths are related to the inhalation of radon radiation in the air. It is believed that the best indicator for evaluating the potential radon concentration in a residential location is the combination of soil radon and soil permeability.
The control of radiation environmental pollution should adopt corresponding methods for different pollution sources. Due to the radiation environmental pollution caused by the factory's waste residue and waste rocks, the site was cleaned up and deep pits were dug and buried in areas with stable geological structure and environment. For indoor radon pollution, if it comes from soil and rocks (accounting for 90% of the total radon entering the room, for example, 12% of houses in the United States exceed the limit of 4 pci/L), the sealing performance of the house panels needs to be improved, generally without gaps. Cement floors can shield most of the radon coming from underground. In areas with extremely high radon concentration in the soil, some special measures can be taken, such as mixing 25% activated carbon into the surface soil under the house foundation to form an adsorption layer that can reduce radon gas. The escape rate is more than 50%.
Radon from gas, coal and water mainly pollutes kitchens, toilets and bathrooms, so indoor ventilation should be strengthened. For pollution from building materials, a shielding layer should be laid on the wall or severely polluted building materials should be replaced. Contaminated drinking water sources should be discontinued and landfilled.
(3) Research on natural electromagnetic radiation
Research shows that magnetic storms, electric storms and radon storms that are harmful to human health may be a trinity. The concentration of radon in the atmosphere near the surface sometimes increases suddenly, which is called a radon storm. It is also accompanied by an electrical storm, that is, a sudden increase in the concentration of ions in the atmosphere, which can cause symptoms such as chest tightness, heart palpitations, migraines, insomnia, and anxiety. Some people believe that sunspots cause sudden changes in the geomagnetic field, causing magnetostriction of rock and soil, causing radon in its pores to be squeezed into the atmosphere. Experiments have shown that radon storms and electrical storms affect people's pituitary gland, adrenal system, cardiovascular and neurological symptoms.
Magnetic storms will interrupt high-frequency radio communications, cause the atmosphere to expand, increase the resistance of low-altitude satellites, distort their orbits, and cause satellite abnormalities. Currents induced by changes in the geomagnetic field can saturate or even burn out transformers in the power transmission system. This current can also cause corrosion of metal pipelines and interfere with electric railways.
(4) The impact of artificial vibration on the environment
Experiments have proven that people are most sensitive to vibrations of 2 to 10 Hz, and are most sensitive to vibrations of 0.5 to 2 Hz and 10 to 100 Hz. In short, it is not sensitive to vibrations of other frequencies.
Different parts of the human body have different response frequencies. When the vibration wave energy exceeds a certain value, people will feel discomfort, fatigue and reduced work efficiency.
The damage caused to buildings by artificial vibration has also attracted people's attention. In response to complaints from residents, real-time monitoring of ground surface vibrations has been started to measure the intensity, frequency and attenuation characteristics of ground vibrations. The United States uses the velocity of ground particles as a standard to measure the degree of damage to buildings.
Long-term vibration can also cause fatigue in soil and building structures. Russian research shows that the main factor affecting the changes in the properties of soil and building materials is not the amplitude, but the cumulative effect of long-term vibrations of different loads. For example, seismic measurements along the Moscow Metro show that the soil longitudinal wave velocity has dropped from 350 to 500 m/s to 180 to 200 m/s, and the elastic modulus is also decreasing.
(5) Monitoring of man-made radioactive pollution
The mining and mineral processing of uranium ore and other minerals associated with uranium will cause serious pollution. For example, in the 1950s, the United States maintained a concentration of 1.7 million tons of uranium ore at the Silo Concentrator, and later conducted aerial radioactivity measurements at the site, with an altitude of 46 m and a line distance of 76 m. The measurement results were expressed in terms of exposure rate and radium equivalent content. 14 abnormal areas caused by tailings, ores, slag, etc. were delineated.
Radioactive geophysical prospecting is also an important means of monitoring nuclear leakage accidents. After the Chernobyl nuclear accident, the former Soviet Union and surrounding countries conducted large-scale monitoring. For example, Sweden carried out aerial energy spectrum measurements at an altitude of 150 m and found significantly high values ??near Covle. The investigation then turned to southern Sweden to understand whether cows could be allowed to eat the new spring grass there. Finally, the entire Sweden was covered by aerial survey with a survey line distance of 50 km (the abnormal area was encrypted to 20 km), and it was found that the polluted area continued to expand towards the border between Sweden and Norway.
Fly ash is a large-scale and widespread source of pollution. According to statistics from the United Nations Atomic Radiation Commission, a thermal power plant that burns 10 tons of coal per day releases 1850 KBq of 238U radioactivity into the atmosphere. Measurements show that uranium is further enriched after coal is burned, and fly ash is more enriched than slag. Because fly ash is easily inhaled into the human body, the cancer mortality rate among residents around thermal power plants is 30 times higher than around nuclear power plants.