(a) Physical geography and socio-economic profile

The study area is located in Qiqihar City in the west of Songnen Plain, east of Nenjiang River, north of Fuyu County, east of Lin Dian and Dorbod Mongolian Autonomous County, and south of Tailai County. Geographical coordinates of the study area: east longitude123 53 ′ ~12415 ′, north latitude 4710 ′ ~ 47 24 ′, east-west length 720.9 km2, north-south width 26.32 km, with a total area of 722. The terrain is mainly plain, horseshoe-shaped, high in the southeast and low in the middle, and gradually decreases from north to south. Qiqihar has a continental monsoon climate in cold temperate zone, with a warm and arid agricultural climate in the south, a mild and semi-arid agricultural climate in the middle and a cool and semi-humid agricultural climate in the north. The annual average temperature is between 0.7 and 4.2℃, and the temperature difference between north and south is about 3.5℃. The annual precipitation is 400~550 mm, and the average frost-free period is122 ~151d. The soils in Qiqihar are mainly dark brown soil, black soil, chernozem, meadow soil, swamp soil, meadow alkaline earth and sandy soil. Most soils in Qiqihar are characterized by high heat, good permeability and light texture.

Qiqihar is one of the old industrial bases in Northeast China with heavy machinery and metallurgical industry as the main body, and the second largest city in Heilongjiang Province. It has a complete industrial system, including chemical industry, light industry, textile, building materials, food, electronics, medicine and so on. It is the center of politics, economy, science and technology, culture, education, commerce and trade and an important transportation hub in the western part of Heilongjiang Province. It governs 7 districts, 1 city, and the whole city governs 8 cities.

(2) Hydrogeological investigation

Qiqihar city is located in Nenjiang low plain, which spans three geomorphic units: alluvial inclined plain, alluvial valley plain and alluvial lake low plain. The hydrogeological conditions are complex, and the strata are composed of extremely thick Cretaceous and Neogene continental clastic sediments and loose deposits dominated by Quaternary gravel.

The Quaternary loose deposits in the study area are relatively thick, generally 160 ~ 190 m, and there are weakly permeable loam or clayey silt layers at 40 ~ 60 m, the thickness of which is generally less than 7 m. The aquifer is divided into upper phreatic water and lower confined water, and the hydraulic characteristics are obviously different. The upper phreatic layer is 24.3~43.0 m thick, and the water-bearing medium is mainly gravel, followed by medium coarse sand and medium fine sand, with several layers of loam and clayey silt lenses. The water level is 2 ~ 5 m deep, the water inflow of a single well is more than 2000 m3/d, the lower confined water aquifer is thick, the middle Pleistocene aquifer is generally 70 ~ 85 m thick, the water-bearing medium is gravelly medium coarse sand and gravel, and the lower Pleistocene aquifer is generally 20 ~ 50 m thick, and the water-bearing medium is gravelly medium coarse sand and medium fine sand. The buried depth of water level is 3 ~ 5 m, with abundant water. The water inflow of a single well in the north is more than 2000 m3/d, and the water inflow of a single well in the south and southeast is1200 ~ 2000m3/d. ..

The main recharge sources of diving are atmospheric precipitation infiltration recharge, river water infiltration recharge, lateral runoff recharge and irrigation water infiltration recharge, and the main discharge methods are artificial mining, evaporation and confined water overflow recharge. The main recharge sources of confined water are overflow recharge and lateral runoff recharge of upper phreatic water, and the main discharge methods are artificial mining and lateral runoff discharge.

Quaternary phreatic water and confined water in the area are neutral and low salinity bicarbonate fresh water. The pH value is generally between 6.6 and 8.36; TDS diving 230 ~ 800 mg/L, confined water140 ~ 380 mg/L; Total hardness: diving 120 ~ 500mg/L, confined water 90 ~170mg/l; The chemical types of water are basically the same, with calcium bicarbonate, HCO _ 3 calcium sodium and HCO _ 3 sodium calcium as the main components, followed by HCO _ 3 calcium-magnesium water. Because the diving has been seriously polluted, the hydrochemical types have become more complicated, and the polluted hydrochemical types characterized by a large number of nitrates and chlorides have formed in the central city-Damintun-Yushutun area. In addition, influenced by the primary environment, there is a muddy clay interlayer in the aquifer, and the organic matter in the muddy soil decomposes to form a reducing environment, which reduces medium and high-priced iron and manganese to low-priced iron and manganese. Therefore, the contents of iron and manganese in groundwater are generally high, but there is little annual change.

(3) Monitoring data of groundwater quality

The water quality monitoring data of this study mainly comes from the water quality analysis results of the long observation well 1998 ~ 2002 of groundwater dynamics set up by Qiqihar Geological Environment Monitoring Station. There are ***3 1 water quality monitoring points, including 4 diving wells 17 confined water wells 13-65437. The monitoring items mainly include pH, total hardness, ammonia nitrogen, nitrate, nitrite, arsenic and mercury. The groundwater quality evaluation and pollution early warning system in Qiqihar city has realized the basic management functions of adding, modifying, deleting and querying these monitoring data, as shown in figure 13-7.

Table13 ——14 Statistical Table of Groundwater Quality Monitoring Data in Qiqihar City

Table13 ——15 Statistical Table of Monitoring Data of Groundwater Quality in Qiqihar City

(4) Study the spatial information of the region.

Spatial information includes geographic base map, lithology distribution map, groundwater quality early warning parameter zoning map, water source and pollution source distribution map, and land use status map (see Figure 13-8 ~ Figure 13- 10).

Figure 13-7 Monitoring Data Management of Groundwater Quality in Qiqihar Area

Figure 13-8 Research Area Spatial Information Interface

Figure 13-9 Topographic Schematic Diagram of the Study Area

Original scale 1:50000

Figure 13- 10 Schematic diagram of lithologic distribution of vadose zone in the study area.

Original scale1:50000

Second, groundwater quality evaluation in Qiqihar City

The national standard method, fuzzy comprehensive evaluation method and BP neural network method are used to evaluate the annual diving and confined water respectively. The evaluation results include data grid, isoline and isoline map. As shown in figure 13- 1 1, the results of diving evaluation in 2002 were obtained by BP neural network evaluation method, and figure 13- 12 is the national standard comprehensive evaluation 1998 diving contour map.

Figure13 ——112002 diving BP neural network evaluation results.

Figure13 ——121998 Schematic diagram of comprehensive evaluation isoline of diving national standard.

The evaluation results show that the groundwater quality in Qiqihar has the following characteristics:

The components exceeding the standard in (1) area are ammonia nitrogen, nitrate, nitrite, arsenic, total hardness, chloride, sulfate, iron and manganese.

(2) Nitrogen pollution is serious. 14 of the diving monitoring points, the content of 10 is the highest, 2.35mg/L(2000 100), which is 8 times higher than the water quality standard; There are 7 cases of nitrate exceeding the standard, and the highest content is 444.12 mg/l (point 228, 2002), which is 4 times higher than the water quality standard; There is 12 nitrite exceeding the standard, and the highest content is1.680mg/L (No.2 point in 2002), which is 24.6 times higher than the water quality standard.

(3) The local total hardness exceeded the standard (15,27,228 points), and the highest content was1043.67 mg/L (228 points in 2002); In some places, arsenic exceeded the standard (2, 27 and 183 points), with the highest content of 0.079 mg/L (200 1 year at 27 points).

(4) The content of iron and manganese in groundwater in this area is generally high, which is mainly controlled by the primary environment. The aquifer in this area is mostly muddy clay interlayer, and the organic matter in muddy soil decomposes to form a reducing environment, which reduces high-priced iron and manganese in the medium into low-priced iron and manganese substances. Therefore, the content of iron and manganese in groundwater is generally high, but it has not changed much for many years.

3. Prediction of groundwater quality in Qiqihar City

Using the grey model GM( 1, 1) and the time series analysis model provided by the system, the water quality of all wells can be predicted at the same time, and the water quality of specific wells can also be predicted according to the conditions such as year, point number, water period and water layer. The grey model GM( 1, 1) is suitable for short-term and medium-term water quality prediction, as shown in figure 13- 13. Time series analysis is suitable for medium and long-term prediction of water quality. Before using time series analysis to make prediction, we should not only select the predicted points, water period and aquifer, but also set corresponding weights to make prediction. Theoretically, the setting range of weight is 0 ~ 1, but in application, the setting of weight depends on the objective and specific situation. If there is a big difference between the data of adjacent years, set a big weight; On the contrary, set a smaller weight. The general weight cannot exceed 0.3, as shown in figure13-14.

Fourthly, groundwater pollution risk assessment in Qiqihar area.

(i) Assessing the inherent vulnerability of aquifers

The data of seven evaluation factors of aquifer inherent vulnerability evaluation are processed and drawn into seven maps.

Figure 13 —— 13 Grey Forecast Results

Figure13 ——14 Time series analysis and prediction results

(1) aquifer buried depth d

The information of aquifer buried depth mainly comes from borehole data, and the spatial distribution map of aquifer buried depth is obtained by kriging interpolation, and then it is reclassified according to the evaluation standard table 13-2. The buried depth of phreatic aquifer in Qiqihar area is generally 2 ~ 5 m. See Figure13-15 for the classification of aquifer buried depth.

(2) net replenishment r

Net recharge = precipitation infiltration coefficient × average effective rainfall for many years (mm). The average effective rainfall in Qiqihar is 4 19.9 mm, and the infiltration coefficient is divided into five regions, which are 0.30, 0.05, 0.23, 0.65, 438+08 and 0.07 from west to east. After the calculation results are reclassified according to the evaluation criteria, the classification diagram of net replenishment is obtained, as shown in figure13-16.

Figure13 ——15 Schematic diagram of aquifer buried depth classification.

Figure13 ——16 Schematic diagram of net replenishment classification.

(3) aquifer medium type a

The lithology of aquifer in Qiqihar area is mainly gravel, fine sand mixed with gravel, fine sand, gravelly medium-coarse sand, gravelly medium-fine sand, gravelly coarse sand, medium sand, silty fine sand and gravelly medium sand, and their corresponding characteristic values are shown in table13-16. See Figure 13— 17 for the classification of aquifer media types.

Table13 ——16 Characteristic values of aquifer media types

(4) Soil medium type S

The main types of soil media in Qiqihar are sand, clay silt, loam, loess loam and miscellaneous fill. See table 13— 17 for the corresponding characteristic values. For the classification of aquifer media types, see Figure 13— 18.

Table13 ——17 Classification Standard of Soil Media Types

Figure13 ——17 Schematic diagram of aquifer medium type division.

Figure13 ——18 Schematic diagram of soil medium type division.

(5) Terrain slope test

Terrain slope is a slope map calculated by the elevation of elevation points through surface analysis in spatial analysis. See figure 13— 19 for the slope classification in Qiqihar area.

(6)J-type vadose zone medium

The media types of vadose zone in Qiqihar area are mainly sand, clayey silt, loess loam and loam. See table 13— 18 for the corresponding characteristic values. See figure 13-20 for the classification of media types in vadose zone.

Table13 ——18 Characteristic values of media types in vadose zone

Figure13 ——19 Schematic Diagram of Terrain Slope Classification

Figure 13—20 Schematic Diagram of Classification of Media Types in Aerated Zones

(7) Aquifer permeability coefficient c

The aquifer permeability coefficient is divided into four zones, and the grading standard is shown in Table 13-2, the corresponding relationship between the grade and the fragility conclusion is shown in Table 13- 19, and the grading is shown in Figure 13-2 1.

Table13 ——19 The correspondence between the level and the vulnerability conclusion.

According to the following formula, the classification map of each evaluation index is weighted and superimposed, and the inherent vulnerability zoning map of aquifer in Qiqihar area is obtained, as shown in figure 13-22.

Figure 13-2 1 Schematic Diagram of Aquifer Permeability Coefficient Classification

Figure 13—22 Schematic diagram of aquifer inherent vulnerability zoning in Qiqihar area

(2) Risk assessment of pollution source load

The risk assessment of pollution source load in Qiqihar city is based on the data in 2000. In 2000, the total pollutant discharge in this city was 33 044.39 t, including chemical oxygen demand 2 1 65438+59.46 t, suspended solids 65 438+0 576.86438+0 t, petroleum +26548. 166666676 cyanide/kloc-0.

The application of chemical fertilizers and pesticides in urban areas (1999) shows that the application amount of chemical fertilizers is 13 750 t, including 7563 t of nitrogen fertilizer, 2275 t of potassium fertilizer, 953 t of phosphate fertilizer, 2959 t of compound fertilizer and 295 t of pesticides.

Industrial solid waste and municipal waste: solid waste is mainly concentrated in Tiefeng District and Longsha District. There are *** 15 kinds of industrial solid wastes in the Ninth Five-Year Plan, 1335.58× 104t, among which fly ash, slag, smelting waste residue, hazardous waste and tailings are the main ones, accounting for 950.4 1× 104t. In 2000, all kinds of solid waste were as follows: hazardous waste 3.3206× 104t, smelting waste 9.30× 104t, fly ash 125.04× 104t, and slag 54.0438+0×/kloc-0.

Utilization of solid waste in 2000: hazardous waste 2.68× 104t, smelting waste 7.58× 104t, fly ash 74.83× 104t, slag 53.85× 104t and others 64.46× 65434.

By the end of the Ninth Five-Year Plan, the amount of hazardous waste had been reduced from 8.878× 104t in the initial period to 3.3206× 104t, the comprehensive utilization was 2.68× 104t, the utilization rate was 80.7 1%, and the disposal capacity was 0.6403. The generation of hazardous waste is mainly distributed in industries such as electromechanical and electronic equipment manufacturing in Fulaerji, Longsha and Nianzishan areas. The regional distribution is highly concentrated, and Fulaerji District accounts for 99.86% of the total hazardous waste.

In 2000, the output of domestic waste was 765,438+0× 65,438+004t, including 265,438+0.7× 65,438+004t for landfill treatment, 65,438+04.2× 65,438+004t for general treatment and 35.64t for simple treatment. See table 13-20 for the wastewater discharge in Qiqihar city.

Table 13—20 Waste Water Discharge in Qiqihar (unit: 104t)

Qiqihar North District 3 (Tiefeng District, Longsha District, jianhua district) * * has three domestic waste treatment plants in Hongxing, Liming and Xiangyang, and there is a garbage dump in Nanshan. Among them, Liming garbage disposal plant and Nanshan garbage dump cover an area of more than 30,000 square meters, and Hongxing garbage disposal plant covers an area of 40,000 square meters (3 ponds). Xiangyang waste treatment plant covers an area of 20,000 square meters. There are 6 sanitary landfill areas in the three garbage harmless treatment plants of Hongxing, Liming and Xiangyang, with a total construction area of 1.2 1.900 m2 and a volume of1.463m3.. Since May 12, 2000, three harmless treatment plants, Hongxing, Liming and Xiangyang, have been built and put into use one after another, with a daily treatment capacity of 800 t. Up to now, * * * has treated nearly 100× 104t of domestic garbage in the central city, and sucked and discharged landfill leachate104t. On June 5438+1 October1day, 2003, the centralized medical waste disposal project officially started construction. After it is completed and put into use, the medical waste in the central city will be treated harmlessly.

The oxidation pond in Qiqihar City was built at 1970, which is located in the southwest of old Jiang Tao 17.5 km. The west side of the oxidation pond is close to the left bank of Nenjiang River, and its tail is connected with Nenjiang River. The whole project consists of open channels, oxidation tanks, gates, pumping stations and other structures. The total length of the open channel is 6 km, and a pumping station is set at the junction of the channel and the pond head. The gate is 9.3 kilometers long from the head of the pond to the tail of the pond.

The oxidation pond starts from Huangnitan, Xinlitun in the north, and ends at Da Five Blessingg Ma, Ang Ang Xi District in the south. It is an old river with an area of 8 square kilometers, with an average water surface of about 5.6 square kilometers and a wet season of nearly 7 square kilometers. Undertake the self-care purification of urban mixed sewage with a population of 60× 104 in the urban area. The oxidation pond in Qiqihar accepts sewage 10× 104 m3 every day at the initial stage of construction, and 25× 104m3 every day after reconstruction. 1998 was damaged by floods in Nenjiang River. After 1999 dredging, the daily sewage receiving capacity reached 46× 104m3. Therefore, the main pollution sources in Qiqihar area are Hongxing, Liming and Xiangyang domestic waste treatment plants, workers' industrial solid waste dumps, oxidation ponds and sewage outlets. After the operation of the system, the load risk of pollution sources in Qiqihar area is shown in figure 13-23.

(3) Pollution hazard assessment

According to the current map of land use in Qiqihar City, groundwater in residential areas is regarded as drinking, groundwater in vegetable fields, paddy fields and farmland is regarded as non-drinking, and the rest areas are not used. See figure 13-24 for the pollution hazards in Qiqihar area obtained by the system.

(4) Pollution risk assessment

After evaluating the inherent fragility of aquifer, the load risk of pollution source and pollution hazard, the pollution risk map of Qiqihar area is obtained by comprehensive consideration and superposition. The specific evaluation method is shown in table 13- 10, and the evaluation result is shown in figure 13-25 through computer operation. Where "0" means low risk, "1" means medium risk and "2" means high pollution risk.

Figure 13—23 Schematic diagram of pollution source load risk in Qiqihar area

Figure 13—24 Schematic diagram of pollution hazards in Qiqihar area

Verb (abbreviation of verb) Early warning of groundwater pollution in Qiqihar City

The early warning of groundwater pollution comprehensively considers the present situation of groundwater quality, the changing trend of groundwater quality and the risk of groundwater pollution. * * * There are 45 possible states, and different states can be determined by computer analysis and calculation. The result of early warning is indicated by warning degree, and "0" means "no warning"; "1" to "4" are mild warning, moderate warning, severe warning and extreme warning, and the results show that the threat of groundwater pollution is becoming more and more serious.

(1) personal warning

Through the evaluation of groundwater quality, it is found that ammonia nitrogen, nitrate, nitrite, arsenic, total hardness, iron and manganese in groundwater in Qiqihar area exceed the standard seriously, in which iron and manganese are mainly controlled by the primary environment and have not changed much for many years. Therefore, the single factor early warning of water quality can be used for the early warning of ammonia nitrogen, nitrate and arsenic.

Taking arsenic as an example, firstly, the concentration value of the evaluation factor is extracted from the database, and then the water quality of the factor in the observation well is evaluated according to the national standard (GB/T 14848-93). The spatial distribution map of the factor in the study area is obtained by spatial interpolation, as the result of water quality status, as shown in figure 13-26. Then Daniel's Spearman rank correlation coefficient method is used to analyze the multi-year variation trend of the factor concentration in the observation well, and the distribution map of the variation trend is obtained after spatial interpolation, as shown in figure 13-27; Finally, the early warning result diagram is obtained by analyzing and calculating the current situation distribution diagram, change trend diagram and pollution risk diagram through the computer system, as shown in figure 13-28.

Figure 13—25 Schematic diagram of pollution risk in Qiqihar area

Figure 13—26 Schematic diagram of arsenic distribution in Qiqihar area

Figure 13—27 Schematic diagram of arsenic change trend in Qiqihar area

Figure 13—28 Schematic diagram of early warning results of arsenic pollution in Qiqihar area

The arsenic concentration in most areas of the study area did not exceed the standard, but the arsenic concentration in three observation wells in the southwest reached the five-class water standard, and the monitoring results for many years showed a trend of further deterioration. Therefore, this area belongs to a huge police area and the pollution is very serious. In addition, the arsenic concentration near the urban area meets the third-class water standard, and there is no obvious change trend over the years, but the pollution risk is high. This area belongs to the heavy police area and needs special attention.

The early warning results of ammonia nitrogen and nitrate pollution are shown in figure 13-29. Ammonia nitrogen pollution area is small, nitrate pollution is very serious, and the total hardness in some areas is a severe warning.

Figure 13—29 Schematic diagram of early warning results of ammonia nitrogen and nitrate pollution in Qiqihar area

(2) Comprehensive early warning

Figure 13-30 shows the current situation of groundwater quality in Qiqihar. As can be seen from the figure, the water quality of shallow groundwater in the east of the study area is Class III water, while the water quality of shallow groundwater in the west of the study area is Class IV water, which is no longer drinkable. By analyzing the change trend of comprehensive pollution index of each monitoring well, the water quality of No.27 monitoring well near Gudian Station has improved, and the water quality of No.4 monitoring well located in Chahano Village has deteriorated, while the water quality of other monitoring wells has not changed obviously, as shown in figure 13-3 1. Figure 13-32 shows the early warning map of groundwater pollution in Qiqihar area. Because the shallow groundwater in this area has been generally polluted, the concentration of nitrogen in groundwater has reached the fourth and fifth water standards, so the calculation results are greatly influenced by the current situation of groundwater, and the early warning is mainly serious and huge in the urban area and its vicinity. In the east of the city, the early warning is mainly mild and moderate.

Figure 13—30 Schematic diagram of groundwater quality in Qiqihar area

Figure13-31Schematic diagram of groundwater quality change trend distribution in Qiqihar area.

Figure 13—32 Schematic Diagram of Early Warning Results of Groundwater Pollution in Qiqihar Area

In fact, the groundwater pollution early warning system should be used in areas where groundwater is not polluted to prevent pollution. However, in the areas where groundwater in Qiqihar is generally polluted to varying degrees, the role and significance of using pollution early warning system are limited and cannot play an early warning role.

(3) Causes and prevention measures of groundwater pollution in Qiqihar City.

1. Causes of groundwater pollution

Quaternary phreatic water pollution in Qiqihar area is serious, and the main causes of pollution are as follows:

(1) Early warning areas of groundwater pollution are mostly near oxidation pond, Nenjiang River and Labor Lake. Groundwater monitoring data confirmed that Nenjiang River and Laodong Lake supplied groundwater all the year round, and polluted ponds, rivers and lakes directly infiltrated and polluted Quaternary diving.

(2) The buried depth of aquifer in the area is generally less than 4.5 m, and the lithology of vadose zone is mostly loam, clayey silt and fine sand. There are many industrial pits, wells and domestic sewage wells in this area. Every year, 1 1 720 t of industrial wastewater and domestic sewage seeps into the ground through the pits and wells, causing groundwater pollution.

(3) A large number of pesticides and chemical fertilizers have been used in vegetable fields and agricultural areas in the suburbs for a long time. According to statistics, chemical fertilizer 1753 1t and pesticide 178t are used every year, and irrigation water or rainwater of these fertilizers and pesticides seeps into groundwater.

(4) The stacking and landfill of solid wastes such as industrial waste residue and domestic garbage are important point sources of groundwater. According to statistics, this area discharges industrial waste residue 186× 104t and domestic garbage 63 t every year. These waste residues and garbage have not been treated harmlessly, and most of them have no seepage control measures. Under the leaching action of atmospheric precipitation, a large amount of leachate containing various pollutants can be produced, which directly penetrates into the aquifer through the vadose zone, which is an important way to cause groundwater pollution in Quaternary.

2. Prevention and control measures of groundwater pollution

(1) It is strictly forbidden to discharge industrial wastewater beyond the standard, and the anti-seepage standards of oxidation ponds and sewage drainage channels should be improved to prevent sewage from infiltrating into the ground.

(2) To speed up the construction of urban drainage facilities, improve the drainage system, and gradually abolish urban sewage seepage pits and simple toilets, and it is strictly forbidden to discharge industrial wastewater in the form of seepage pits (wells).

(3) Accelerate the construction of municipal waste treatment plants, advocate scientific farming, rationally fertilize (increase the number of fertilizations and reduce the amount of fertilizations each time), and properly irrigate.

(4) Doing a good job in urban greening can not only beautify the environment and adjust the climate, but also absorb ammonia nitrogen in the soil and reduce the pollution of groundwater.