(Henan Geological Survey Institute, Zhengzhou 450007)
Based on the results of environmental hydrogeological investigation and water quality analysis in 2003 and 2004, the water quality and pollution status of shallow groundwater in Sha Ying section of Huaihe River Basin were evaluated. The characteristics of non-point source pollution, zonal pollution, vertical pollution and pollution inside and outside the community of shallow groundwater are analyzed and studied.
Key words: shallow groundwater; Groundwater quality; Groundwater pollution; Pollution characteristics
1 preface
The study area is located in the middle and lower reaches of Sha Ying in the Huaihe River Basin (in the east of central Henan), which belongs to Xuchang City, Luohe City and Zhoukou City, with an area of about1.2000 km2, with an average population density of 900 people /km2, and the eastern part can reach1.2000 people /km2. The study area belongs to Huang-Huai alluvial plain, with flat terrain, high in northwest and low in southeast, ground elevation 100 ~ 36m, and ground slope of about 0.5‰. Shahe, Heying, Fenhe and Jia Luhe flow from northwest to southeast and leave the country in the southeast. Since the Quaternary, the crust has been in a state of continuous decline for a long time, and huge thick loose deposits have been deposited, with a thickness of about 300m or more. The surface lithology is mainly silt and silty clay.
Following the principle of "based on stratum stratification, based on hydrogeological elements and aiming at development and utilization", the underground aquifer system in the study area is divided into two aquifer groups: (1) shallow aquifer with a controlled depth of about 50m, mainly composed of Qh,
Stratigraphic composition; (2) The middle-deep aquifer, with a controlled depth of about 50 ~ 400 m, is mainly composed of strata.
2 shallow groundwater quality status
According to Technical Requirements for Environmental Geological Survey in Huaihe River Basin, 19 factors were selected, including: pH value, total hardness, total dissolved solids, sulfate, chloride, permanganate index, nitrate, nitrite, ammonia nitrogen, volatile phenol, iron, manganese, lead, arsenic, mercury, cadmium, chromium (hexavalent) and fluoride. According to Groundwater Quality Standard (GB/T 14848-93), the quality category of groundwater is determined.
Figure 1 shows the groundwater quality when the buried depth is less than 20m: Class III, IV and V water are mainly distributed, Class III water is only sporadically distributed, and Class V water has the largest distribution area. Class III waters are 44 1.8km2, accounting for 3.5 1%. Ⅳ Water: The distribution area is 3658.9km2, accounting for 29. 12%. The main factors exceeding the standard are total hardness, manganese, fluorine, iron and nitrite. Ⅴ class water area is 8465. 1km2, accounting for 67.37%. The main factors exceeding the standard are total hardness, nitrate, chloride, total dissolved solids, manganese, fluoride and sulfate.
The quality of groundwater at a depth of 20 ~ 50m is much better than that below 20m. Distribution area of Class II and III water 1238.0km2, accounting for 10.2 1%. The area of Class IV water is 7472.9km2, accounting for 59.47%. The main factors exceeding the standard are total hardness, fluoride and manganese. The distribution area of Class V water is 38 10.0km2, accounting for 30.32%. The main factors exceeding the standard are total hardness, fluoride, nitrate, chloride, sulfate and total dissolved solids.
Figure 1 Quality Evaluation Diagram of Shallow Groundwater (Buried Depth Less than 20m) (2003 ~ 2004)
3 water pollution status
3. 1 background value determination and evaluation method
In this groundwater pollution assessment, the methods to determine the background value of groundwater are as follows: Before 1980s, shallow groundwater was slightly polluted, and its background value can be calculated by using historical water quality data according to the mathematical statistics method [1]; For the factors without historical data, the corresponding background values shall be determined according to the upper limit of Class II water in Groundwater Quality Standard. The evaluation factors are basically consistent with the quality evaluation.
The evaluation method adopts Nemerow index method, and the pollution degree is classified and partitioned by Nemerow index PI. The formula for calculating Nemerow index is:
Compilation of geological survey results in East China: 1999~2005
Where: pi-comprehensive pollution index
Compilation of geological survey results in East China: 1999~2005
-the average value of the score i of each individual component; Imax-the maximum value of single component score I
According to the calculation result of PI value, the groundwater pollution level is divided according to the following table (table 1).
Table 1 Classification Table of Groundwater Pollution Grade
3.2 Groundwater Pollution Status
See Figure 2 for the current situation of groundwater pollution with a buried depth of less than 20m. The unpolluted area is dotted, with an area of 128.2km2, accounting for 1.02%. The lightly polluted area covers an area of 2656.4km2, accounting for 21.14%; The area of moderately polluted area is 4 132.9km2, accounting for 32.89%. The main pollution factors are chloride, nitrate, sulfate, total hardness, total dissolved solids and permanganate index. The heavily polluted area is 5648.4km2, accounting for 44.95%. The main pollution factors are chloride, dissolved total solids, nitrate, total hardness, sulfate and permanganate index.
Fig. 2 Assessment map of pollution status of shallow groundwater (buried depth less than 20m) (2003-2004)
The present situation of groundwater pollution with a depth of 20 ~ 50m is lighter than that with a depth of less than 20m, and the distribution of seriously polluted areas is similar, but the area is smaller. The unpolluted area is scattered, covering an area of 305.3km2, accounting for 2.43%. The lightly polluted area covers an area of 4076.4km2, accounting for 32.44%. Moderately polluted area covers an area of 5054.0km2, accounting for 40.22%; The heavily polluted area is 3 130.2km2, accounting for 24.965,438+0%. The main pollution factors are chloride, nitrate, total dissolved solids, sulfate and total hardness.
4 groundwater pollution characteristics
4. 1 regional pollution characteristics
According to the pollution evaluation map and other data, the pollution characteristics of shallow groundwater on the plane can be obtained.
(1) Unpolluted areas and lightly polluted areas are generally distributed in the upper reaches of cities, and no sewage pipes (ditches) pass through.
(2) Moderately polluted areas are generally located in areas with few sewage ditches and a certain distance from the city, and urban and industrial pollution is not serious. The main pollution is local domestic sewage, domestic garbage, pesticides and fertilizers.
(3) The heavily polluted area is generally located in the downstream sewage area of the city or the area where sewage is easily collected in the depression. The former, such as Zhoukou City, Luohe City and the downstream area of Xuchang City, has developed sewage ditches, and sewage pollutes groundwater through infiltration and irrigation. The latter, such as Nanwanggang area in Yanling, is low-lying, and the polluted river is easy to stagnate in this area through the diversion canal. In addition, sewage irrigation, local domestic pollution and agricultural pollution make the pollution worse.
4.2 Pollution characteristics of strip steel
The shallow groundwater near both sides of sewage river (ditch) is polluted, and the pollution width is related to the length of sewage discharge, the quality of sewage, the width and depth of river ditch, lithology and the relationship between recharge and discharge. Generally, the closer to the sewage river (ditch), the more serious the pollution is, and the width of the seriously polluted zone can generally reach 50 ~150 m.
As can be seen from Table 2, within 200m of the polluted river ditch, the water quality near the polluted river ditch is obviously worse than the groundwater far away from it; When the distance from the polluted ditch is more than 300m, the influence of the distance from the polluted ditch on the difference of groundwater quality is not obvious (see tables 2Qs054 and Qs055). The width of heavily polluted areas is generally150m.
Table 2 Comparison Table of Shallow Groundwater Quality at Different Distance from Sewage Ditch
4.3 Vertical pollution depth
The vertical pollution depth is controlled by factors such as stratum structure characteristics. According to the water quality comparison results of wells with different depths (close to each other) (Table 3), the water quality of wells with large depths is obviously better than that of wells with small depths, such as SW095 (7m deep) and SW094 (25m deep), and there are obvious differences in water quality, Nemerow index and main pollution factors.
Table 3 Comparison Table of Shallow Groundwater Quality at Different Depth Unit: mg/L
From the statistical results of groundwater quality categories with different well depths in the whole region (Table 4) and the statistical results of comprehensive pollution Nemerow index with different well depths in the whole region (Table 5), it can be seen that the buried depth is roughly 15 ~ 20m, which is obviously different from the quality categories and comprehensive pollution Nemerow index below it. As shown in Table 4, when the water content is above 15 ~ 20m, V water generally accounts for more than 70%, and the water content below 15 ~ 20m generally accounts for about 50%. For example, the average value of Nemerow index in Table 5, 15 ~ 20m is generally greater than 8, and below it is generally 3 ~ 6.
When the buried depth is more than 50m, its quality category and Nemerow index are obviously different from those of shallow groundwater. For example, only about 30% of the water belongs to category V, and the average Nemerow index is 2 ~ 5. There is a thick cohesive soil layer below 30 ~ 50m in the study area, which makes the connection between shallow water and middle-deep water weak. Therefore, the middle and deep water is basically not polluted by surface sewage and shallow groundwater, which can also be confirmed by the hydrochemical types and the contents of various factors in shallow and deep groundwater. For example, in Zhoukou-Shenqiu area, the shallow water is calcium-magnesium water with a total hardness of more than 500mg/L, and the deep water is sodium water with a total hardness of 60.
Based on the above analysis, the groundwater pollution depth in the study area can generally reach 30 ~ 40m, and the shallow groundwater with buried depth 15 ~ 20m is obviously higher, that is, with the increase of depth, the pollution degree decreases.
Table 4 Statistics of groundwater quality categories with different well depths
Table 5 Statistics of Mero Index of Groundwater with Different Well Depth
Remarks: Area S is located in the west, area N is located in the north, and area E is located in the middle and east.
4.4 Differences in water quality inside and outside residential areas
According to the statistical comparison of groundwater quality categories and Nemerow index in different wells inside and outside the village of 1 10, the following conclusions can be preliminarily drawn (Table 6).
Table 6 Comparison of water quality inside and outside the village
(1) When the well depth is less than 20m, the water quality outside the village is obviously better than that inside the village. The sample number of water quality category V in this village accounts for 87.69%, and water quality categories III and IV only account for 12.438+0%. The water quality outside the village accounts for 42.86% of Grade V, and 57. 14% of Grade III and IV. The average Nemerow index is 16.45 in the village and 3.32 outside the village.
(2) When the well depth is 20m, the water quality outside the village is still better than that in the village, but it is not as obvious as when the well depth is 20m. The water quality in the village accounts for 33.33% of Class V water, 66.67% of Class III and IV water, 20% of Class V water and 80% of Class III and IV water. The average Nemerow index is 3.84 in the village and 3.36 outside the village.
(3) There are obvious differences in groundwater quality at different depths, and the water quality of wells with small well depth is obviously better than that of wells with small well depth.
Based on the above analysis, the pollution of domestic garbage and domestic sewage in villages and towns is an important cause of shallow groundwater pollution.
5 conclusion
(1) The quality of shallow groundwater in Sha Ying section of Huaihe River Basin is worrying. The distribution area of ⅴ water accounts for 67.37% (buried depth less than 20m) and 30.32% (buried depth 20 ~ 50m) of the total area respectively.
(2) Generally speaking, the buried depth is about 15 ~ 20m, and the water quality below the boundary is obviously better than above the boundary.
(3) The deterioration of water quality in the study area is mainly caused by man-made pollution. The main pollution sources are urban wastewater, waste residue, rural domestic sewage, garbage pesticides, fertilizers and so on. The main pollution factors are total hardness, nitrate, chloride and total dissolved solids.
(4) According to Nemerow index, the pollution degree is evaluated and partitioned, and the plane distribution characteristics are as follows: the heavily polluted area is generally located in the downstream sewage discharge area of the city or in the area where topography and depressions are easy to collect sewage.
(5) The width of serious zonal pollution along polluted rivers (ditches) can generally reach about 150m. The vertical pollution depth can generally reach 30 ~ 40m.
(6) The difference of shallow groundwater quality inside and outside residential areas is very obvious, and the water quality in the village is obviously worse than that outside the village, which shows that the pollution of township life is an important factor of shallow groundwater pollution.
refer to
[1], left, etc. Investigation report on drinking water project in groundwater polluted area of shenqiu county. The First Institute of Geological Engineering, Henan Provincial Department of Geology and Mineral Resources, 1999.
Lu, Zhu, etc. Hydrogeological investigation report of farmland water supply in Xuchang area of northern Henan Province. Hydrogeology Team 3 of Henan Geological Bureau. 54438+0999
Joe, Qiu Jinbo, and so on. Hydrogeological investigation report on the causes and prevention of flood disaster in Quanhe River basin of Henan Province. Hydrogeology Team 3, Henan Bureau of Geology and Mineral Resources. 18860.8888888866 17
Li, Rong Lanfen, et al. Hydrogeological investigation report of farmland water supply in Zhoukou area. Hydrogeology Team 1, Henan Bureau of Geology and Mineral Resources. 198 1.
Hydrogeology team 1. 1:200,000 hydrogeological investigation report of Luohe River. Hydrogeology Team 1, Henan Bureau of Geology and Mineral Resources. 1980.
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Water Quality and Pollution Characteristics of Shallow Groundwater in Sha Ying Section of Huaihe River Basin
, left, Luo, Cheng Shengping, Xue
(Henan Geological Survey Institute, Zhengzhou 450007)
Abstract: The water quality and pollution status of shallow groundwater in Huaihe River Basin (Sha Ying section) were evaluated. According to the results of environmental, hydrological and geological investigation and water quality analysis in 2003 and 2004, the characteristics of non-point source pollution, zonal pollution, vertical pollution and internal and external pollution of shallow groundwater in residential areas were analyzed.
Key words: shallow groundwater; Groundwater quality; Groundwater pollution; Pollution characteristics