Discussion on Salinization Pollution Control of Groundwater Resources in Yingkou City

(Geology and Environment Department of the Fifth Geological Brigade of Liaoning Province, Dashiqiao, Liaoning Province, 1 15 100)

Aiming at the problem of groundwater pollution in Yingkou city, this paper analyzes the pollution status of groundwater fresh water resources in Yingkou city from three aspects: pollution factors, pollution ways and pollution degree, and puts forward some methods to improve groundwater environment and control pollution, such as well irrigation, salt discharge and desalination, and puts forward the working steps of pollution control.

Keywords: Salinization of Fresh Water in Yingkou City

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Yingkou City belongs to the coastal plain, bordering Liaodong Bay in the west, Liaohe Plain in the northwest and hilly terrain in the southeast. The terrain is flat and slightly inclined to the sea, with a slope of < 2. The altitude is1.6 ~ 8.6m. ..

Geographical coordinates: east longitude:122 37' 30 "-122 49' 23", north latitude: 40 38' 23 "-40 44' 57".

The urban area is about 104km2. For details, see Scope Map of Investigation Work Area for Prevention and Control of Groundwater Salinization in Yingkou City.

According to the monitoring results of groundwater in Yingkou Geological Environment Monitoring Station for many years in recent years, the underground fresh water resources in Yingkou City are seriously polluted. The underground fresh water resources above -320 m above sea level have been invaded by the upper salt water, and the problem of fresh water salinization pollution has become more and more prominent, especially in the last two or three years, which has developed to the point of affecting residents' daily water use. If it is not treated in time in the near future, it will form a wider range of water salinization, which will eventually lead to the pollution of groundwater and fresh water resources in Yingkou City. It directly affects the economic development and people's health in Yingkou.

Hydrogeological background of 1

On the basis of fully accepting tertiary deposits, huge Quaternary loose deposits have been continuously deposited in this area. Since the Middle Pleistocene, it has experienced three times of seawater immersion, which makes the Quaternary loose deposits in this area have various genetic types and form overlapping complex geological structures. With the intrusion and infiltration of seawater, a double-structure aquifer with salt water in the upper part and fresh water in the lower part has been formed in this area.

2 Analysis of the pollution status of underground fresh water resources

The determination of the change trend of chloride ion content in groundwater shows that chloride ion is increasing at a rate of 40 ~ 60 mg/L per year. The interface between salt and fresh water migrates from west to east in the horizontal direction, and with the increase of water intake depth, salt water will penetrate downward in the vertical direction.

2. 1 pollution factor

The basic factors that cause salt water mixed with fresh water layer to pollute water quality are irregular and unplanned deep well construction and backward well completion technology, as well as the damage of water stop position of old wells or well pipe. According to the survey, there are more than 20 old wells in Yingkou City that make the water salty, mostly distributed in the western urban area.

2.2 pollution routes

Salt water seeps from abandoned wells into fresh water aquifers, leading to direct pollution. The way of pollution is that when water is taken near the well with salty water quality, the water intake horizon is the same, so that salt water can quickly replenish fresh water through the waste well, causing pollution. Take No.42 well of Xicheng Guangda bleaching and dyeing factory as an example. The chloride ion content in the water was 50 ~ 60 mg/L at the initial stage of sinking. Because the water quality of No.45 well (about 200m away from No.42 well) in East Thermal Insulation Material Factory has become salty, the chloride ion content in the groundwater of No.42 well199965438+February reached 780 mg/L. This caused the well to stop using four years ago. 4/The distance between Well Kloc-0/and Well 42 150m, 1997 ~ 1999, and the chloride ion content keeps rising, reaching 150mg/l in February. The salinization of one well leads to the salinization pollution of other adjacent wells, which has been connected in the western region. With the passage of time, the interface between salt and fresh water will decrease in the horizontal and vertical directions. In the end, the underground fresh water resources in Yingkou City were all polluted.

2.3 Pollution degree

Monitoring stations were set up in the monitoring area from 1980, and more than 200 water quality monitoring samples were collected in different seasons (dry season and wet season), including more than 90 hydrochemical analysis items, 35 analysis items, 20 simple analysis items and 24 analysis items, totaling more than 6,000 hydrochemical analysis items.

From the hydrochemical analysis results of the same monitoring point at different times, it can be seen that all the components of groundwater meet the national standard "Groundwater Quality Standard" (GB/T 14848-93) without salt water, the water quality becomes salty, and the chloride ion content increases at a rate of 40-50 times a year. Other toxic and harmful substances have also increased, especially NO2-,which exceeds the drinking water standard by 500 times in some areas. Arsenic changed from undetected to over background content, and the hydrochemical type changed from HCO 3-Na type to Cl-Na type. Well water with water level above -320 m has been completely polluted, with chloride ion content as high as 1000mg/l and some as high as 6700mg/l, which has formed a saline water pollution zone. This is the most serious geological disaster in the development and utilization of high-quality groundwater sources in Yingkou city.

3 Discussion on Pollution Control

According to the factors, pollution ways and development trend of groundwater fresh water pollution in Yingkou city, combined with the actual hydrogeological conditions in this area, the author thinks that it is feasible to improve groundwater environment and control pollution by pumping water from well points, discharging salt and desalting seawater. This method is simple, applicable and low-cost, and the total cost of treating a well does not exceed 1 10,000 yuan, especially for wells with intact borehole wall and broken water stop.

The steps are as follows:

(1) Water pollution survey

Using 1∶25000 hydrogeologic mapping, the distribution positions of all production wells and abandoned wells in the area were found out, and the water quality constants and microfacies were analyzed. Understand the pollution degree and determine the pollution range.

(2) Find out the interface between salt water and fresh water in the salty well.

By means of hydrogeology, hydrogeology and geophysical exploration, the interface between salt and fresh water can be determined, or the top layer of fresh water, namely clay or mudstone, can be found as the location for further treatment.

(3) Determine the well depth

Measure the actual depth of the salt well. If the depth is greater than the water-resisting layer of the fresh water roof, fill the lower end of the water-stopping part with sand, plug it, and then stop the water. If it is less than, that is, the sediment in the well is higher than the water stop layer, then dredging should be carried out first to expose the water stop part, so as to lay a good foundation for the next work.

(4) Perforation

Treatment of abandoned wells under different conditions by hydrogeological drilling and perforating guns. Perforation gun is used to perforate the water-resisting layer (water-stopping part) of fresh water roof as the grouting channel, and the holes formed by perforation should be evenly distributed around the borehole wall pipe, so that the injected cement slurry can be evenly distributed outside the well pipe.

(5) Grouting

Grouting with high-pressure pump and drill pipe as grouting conduit, the grouting position (perforation position) is calculated, and the upper and lower plugs are closed, so that the cement slurry can be integrated with the surrounding clay layer along the outer space of the well pipe as much as possible. To close the channel between salty and fresh water, the cement should be above 500 #, and an accelerator can be added to accelerate the setting.

(6) Do a good job in pumping and draining water, discharging salt and brackish water, and improve the groundwater environment.

Periodically pumping water for sampling and testing to reach the chloride ion content standard before salinization.

(7) check

Next to the treated well (10~20m ~ 20m), re-drill a well. The water stop and water intake level of the new well is the same as that of the treated salinization well. After completion, pump water, sample and determine chloride ion content. As the pumping time goes on, the chloride ion content is continuously sampled and determined, and the relationship between chloride ion content and pumping time is observed. If the chloride ion content is high first and then low, it will eventually approach the chloride ion content before salinization in the original well. This means that the processing is successful.

4 Disposal of abandoned wells

Re-laying pipelines or drilling abandoned oil wells. If the well that is no longer used is determined, the water stop position should be strictly closed, backfilled and sealed to avoid man-made pollution on the surface.

5 conclusion

The survival of human beings and the development of social economy depend on the support of good natural environment and geological environment system. Through science and technology, human beings can improve or transform the natural environment and make it more conducive to the development of human society. On the contrary, if human activities, especially production and construction, do not follow the objective laws of nature, they can also destroy the natural environment and cause great damage to social economy and human production. Salinization pollution of underground fresh water resources in Yingkou city is the result of serious deterioration of ecological environment due to lack of environmental awareness.

It is the best way to curb the current pollution and continue the pollution in the future to formulate the groundwater development and protection plan and put forward effective countermeasures to control the groundwater salinity pollution.