(Anhui Geological Environment Monitoring Station, Bengbu 233000)

Huaibei Plain in Anhui Province is located in the north of the province, and the maximum settlement of Fuyang City in the west of the plain is 150 1mm, and the land subsidence of water-collecting type is further expanded. It is speculated that a large area of land subsidence occurred in the western plain. Endemic diseases of drinking water with high fluorine content are widely distributed in Huaibei Plain, and endemic fluorosis areas account for 40% of the total area of the whole region. Among them, there are mild sick villages 17942, accounting for 79.3% of the total number of sick villages; There are 4529 moderately ill villages, accounting for 20.0%; Seriously ill villages 148, accounting for 0.65% of the total number of sick villages. The total population of epidemic townships is13.444 million, accounting for 66% of the total population of Huaibei Plain. Regional groundwater level continues to decline, and groundwater quality continues to deteriorate. Through the discussion of the above main water environment problems, some suggestions are put forward for the future work direction in plain areas.

Keywords: land subsidence; Endemic fluorosis; Water quality; Water level; Work direction; suggestion

Huaibei Plain is located in the north of Huaihe River in northern Anhui Province, bordering Jiangsu in the east, Huaihe River in the south, Henan in the west and Shandong in the north. The geographical coordinates are11450' ~115' and 32 25' ~ 34 40' north latitude, and the range generally includes Fuyang, Bozhou, Jieshou, Taihe, Linquan and Jietou.

Anhui province has less water resources per capita and per mu [1]. Per capita 122 1.46m3, with an average area of 923.73m3, which is only close to the national average 1: 2. The regional distribution of water resources varies greatly, which is incompatible with the distribution of population and cultivated land. Huaibei is an important agricultural and energy base in China, with a population of 42% and cultivated land of 46%. However, water resources only account for 16% of the whole province, and the per capita water resources (476.29m3) and the per mu water resources (654.84m3) are the lowest in the whole province, resulting in an extremely short water resources situation. However, the high exploitation of groundwater has a profound impact on the circulation conditions of groundwater. The centralized development and utilization of groundwater has completely changed the groundwater flow field in Huaibei area, and the groundwater environmental problems caused by it need to be solved urgently.

Geological environment background of 1

1. 1 meteorology and hydrology

Huaibei Plain belongs to warm temperate zone and semi-humid monsoon climate zone, with four distinct seasons. The annual average temperature is 14℃ ~ 15℃. From north to south, the average annual precipitation is generally 700 ~ 900 mm, accounting for about 60% ~ 70% of the annual precipitation from June to September every year. The average annual evaporation is 1300 ~ 1000 mm.

Huaibei Plain belongs to Huaihe River Basin, which is the southern boundary of this area and flows through the plain for about 340km. The average flow of Huaihe River for many years is more than 800 m3/s, the maximum is nearly 2300m3/s, and the minimum is only 100 m3/s (Bengbu Station). The main tributaries of Huaibei Plain are Guhe, He Run, Heying, Xifei, He Peng, Guohe, Beifei and Tuohe. Because of the gentle river bed slope, numerous tributaries and concentrated precipitation along the coast, floods are prone to occur.

1.2 Terrain

Huaibei Plain belongs to the southern part of North China Plain, bordering on eastern Henan Plain and northern Jiangsu Plain in the west, north and east respectively, and bordering on Jianghuai wavy plain in the south. It includes three parts: the flood plain of the old Yellow River in the north, the low hills in the northeast, and the plain between the valleys and rivers in the south. Except for the low hills scattered in the northeast like "islands", the rest of the terrain is flat and open, gently sloping from northwest to southeast, with a slope of 1: 8000. The plain is composed of abundant Quaternary sediments, showing a typical accumulation landscape. Since the Holocene, the Yellow River has frequently burst and changed its course, and a large amount of sediment, about 20m thick, has accumulated in the flood areas of Henan, Shandong and Anhui, and gradually thinned from north to south, superimposed on the denuded plain in the late Pleistocene, which increased the inclination of the ground in Huaibei, forming a special landscape of the Yellow River flooding today.

1.3 Formation lithology and structure

The strata in this area belong to Xuhuai Stratigraphic Division of Shanxi-Hebei-Shandong-Henan Stratigraphic Zone in North China Stratigraphic Zone. Late Proterozoic to Paleozoic strata are mainly carbonate rocks, and Mesozoic strata are mainly red clastic rocks. The Cenozoic Tertiary strata are mainly semi-consolidated sand of river bed facies and cohesive soil of river and lake facies, and the thickness can generally reach hundreds of meters. Quaternary strata are mainly alluvial, alluvial sand and cohesive soil, with a thickness of tens to hundreds of meters, covering the whole area widely.

The tectonic units in this area belong to the southern margin of the Sino-Korean paraplatform. The structural systems are mainly east-west fault zone, NEE Neocathaysia structural zone and Xu Su arc structural zone. Before Cenozoic, the basement structure was complex, with the Yang Guo-Mengcheng-Fengtai line as the boundary, the western faulted basin and the eastern folded uplift, forming a loose accumulation pattern with a thickness of several hundred meters in the west and several tens of meters in the east.

1.4 Hydrogeology

Loose rock pore water is widely developed in this area. According to the burial conditions, hydraulic characteristics of groundwater and its relationship with atmospheric precipitation and surface water, it is divided into shallow pore water and deep pore water from top to bottom. Shallow pore water occurs in Holocene and Upper Pleistocene strata with a depth of 50m, which is closely related to atmospheric precipitation and surface water. Generally, it is diving, and there is a little pressure locally. The buried depth of water level is 1 ~ 3m, and the water-rich degree varies. The ancient river channel can reach 30 ~ 50m3/h, generally 10 ~ 30m3/h ... It is mainly the main water source for agricultural irrigation and rural people and animals, and the water abundance of the aquifer is controlled by the sand layer in the ancient river channel zone. Its water quantity can meet the needs of agricultural irrigation and rural human and animal water use, and the hydrochemical types are HCO 3-Na (Mg), HCO 3-Ca Na (Ca Mg) and so on. The total dissolved solids are about 0.5～65438±0.5g/l/L.

Deep pore water exists in the unconsolidated layer below 50m. With the increase of depth, its connection with atmospheric precipitation gradually weakens or even basically closes. There is no direct hydraulic connection with surface water. Deep pore water is mainly the water source for urban residents' life and industry. It belongs to confined water, and the water inflow of a single well is large, generally above 500m3/d. The groundwater level in the region is generally 2 ~ 4m, and the dynamic water level in the urban centralized water supply area can reach 80m. Hydrochemical types include HCO tricalcium sodium (calcium and magnesium), HCO trisodium, HCO trisodium chloride, HCO trisodium sulfate and so on. The total dissolved solid is 0.7 ~ 2.0g/L. ..

The water-bearing strata in clastic pores and fractures are mainly composed of Permian-Lower Triassic clastic rocks. Its water-rich property is poor.

Carbonate fracture karst water-bearing rock group is mainly composed of Middle Cambrian-Middle and Lower Ordovician. Its karst is developed, groundwater is under pressure, and the buried depth of static water level in the covered area is shallow, generally 3 ~ 5 m, which is rich in water. The water inflow of ordinary single hole is greater than 50m3/h.

2 groundwater environmental problems

In Huaibei Plain, Anhui Province, due to the unreasonable exploitation of groundwater and mine drainage, the environmental quality of groundwater is declining year by year, which is mainly manifested in the continuous decline of regional groundwater level, the continuous expansion of land subsidence caused by water resources exploitation, the prevalence of endemic diseases with high fluorine content, and the worsening trend of groundwater quality.

2. 1 The groundwater level in the region continues to decline [2]

The exploitation degree of shallow pore water in Huaibei Plain is not high, and the water level dynamics are still mainly controlled by precipitation and evaporation. Urban area is affected by mining, and the change of water level is most closely related to precipitation. The average water level is 13.70 ~ 4 1.00 m, and the buried depth is 0.88 ~ 7. 14 m, which is quite different between north and south. The average water level is 365,438+0.88 ~ 465,438+0.00 m, and the buried depth is 2.67 ~ 7.65,438+04 m; The average water level in the west of Fuyang is 24.44 ~ 34.8 1m, and the buried depth is 1.58 ~ 3.72m: the average water level in Suling Temple in the northeast is 15.32 ~ 25.95 m, and the buried depth is1.23 ~ 2.26 m; The average water level along the Huaihe River in the south is 13.70 ~ 24.82 meters, and the buried depth is 0.84 ~ 4.23 meters ... The general trend of water level is still high in the northwest and low in the southeast, and groundwater flows from northwest to southeast, which is basically consistent with the flow direction of surface water.

The dynamics of deep pore water level is mainly affected by the degree of mining. Before 1970s, the deep pore water was basically not exploited, and the buried depth of water level was small. The whole western region is a gravity flow area, and the water level is 0. 1 1 ~ 4.27 m higher than the surface. Groundwater generally flows from northwest to southeast, and the hydraulic gradient is1:15000 ~1:10000. In 1970s and 1980s, with the urbanization, deep pore water gradually became the water source of urban water supply, with the exploitation increasing year by year and the water level decreasing year by year. By the end of 1980s, the phenomenon of gravity flow basically disappeared, and the exploitation of deep pore water in cities and towns began to take shape. After 1990s, the amount of groundwater exploitation further increased, and deep wells were dug deeper and deeper. In the areas where wells are concentrated in the western region, the groundwater level further drops and spreads rapidly, and the groundwater funnels in Fuyang City, jieshou city City, Bozhou City, Guoyang County and Mengcheng County meet one after another, forming a regional descending funnel (Figure 1). The water level in Fuyang City, jieshou city City and Guoyang County is 50-80m deep.

Figure 1 groundwater isoline map in the west of Huaibei plain

2.2 Water mining ground subsidence continues to expand [3]

Water-collecting land subsidence refers to the land subsidence caused by the use of deep porous groundwater for urban water supply, which makes the cohesive soil layer compacted and releases water. There are two places to carry out special research on land subsidence in Huaibei Plain: Fuyang City [4], with a large amount of subsidence. The other is Suzhou, where the land subsidence is weak.

The land subsidence of Huaibei Plain in Anhui Province first occurred in Fuyang City, which is located in the west of Huaibei Plain, with a flat and open terrain and a ground elevation of 26 ~ 33m. Land subsidence in this city began in 1970s, and the range of land subsidence was about 122km2 in the early 1980s and 4 10km2 in the 1990s (Figure 2). In 1980s and 1990s, the subsidence rates of the ground subsidence center were 78.9 mm/year and 59.3 mm/year, respectively. In 2002, the maximum settlement of the center was about 150 1 mm [3]. See table 1 for changes in the center of ground subsidence funnel.

Table 1 Change Table of Reference Elevation of Funnel Center

Note: The figure shows the descending value of the difference between the leveling point elevation of the current year and the original leveling point elevation (unit: mm).

With the development of the deep pore water falling funnel in Fuyang city to the north, the land subsidence will also expand to the north, and its land subsidence will be further aggravated. The western part of Huaibei Plain in Anhui Province is located in Fuyang-Bozhou fault basin, where thick Neogene and Quaternary sediments were deposited. The stratigraphic structures of Fuyang, Jieshou, Bozhou and Yang Guo are basically the same, and the deep pore water exploitation has reached a scale, and the groundwater level is 50-80m deep. Due to the lack of land subsidence measurement in other areas, land subsidence occurred in the last three areas after engineering analogy estimation. With the development of urbanization, the scope and depth of land subsidence will continue to expand, which is an indisputable fact.

Fig. 2 Trend diagram of land subsidence expansion

1992, Anhui Geological Environment Monitoring Station carried out the second-class leveling of land subsidence in Suzhou City, which showed that land subsidence had occurred in the city, with the maximum subsidence in the center of 44 mm [5].

2.3 groundwater quality deterioration trend intensified [2]

According to the monitoring data of groundwater quality in dry season of Anhui Geological Environment Monitoring Station over the years, the groundwater in Huaibei Plain is generally colorless, tasteless, odorless and transparent, mostly bicarbonate neutral water, and the total dissolved solids are less than1000 mg/L/L. Due to the influence of primary environment, the contents of iron and manganese in groundwater generally exceed the standard. The F- content in groundwater in Hejian area is greater than 1.0mg/L, with the highest value of 6.79 mg/L; In some areas along the Huaihe River floodplain, the content of as in groundwater is relatively high, the highest is 0.251mg/L. Due to human activities, the content of "three nitrogen" in groundwater along the polluted river and around the suburbs generally increases, and the deterioration trend of groundwater quality intensifies.

2.3. 1 shallow pore water

Class II and III water is distributed in a large area, and Class IV water appears in some areas. Grade IV water is mainly distributed around Dangshan, Jieshou, Fuyang, Suzhou, Bengbu and other cities and along the Huaihe River in the east. Due to the dense population and serious pollution, the main components exceeding the standard in groundwater are COD, total hardness and total dissolved solids.

From south to north, the hydrochemical types of groundwater gradually changed from simple HCO3-Ca (mg) to complex HCO3-Na (ca mg) and HCO3-SO4-Ca (na mg), and the total dissolved solids gradually increased from less than 500mg/L to equal to or greater than 1000mg/L, with a pH of about 7.0.

Compared with 1996 in 2000, the total dissolved solids increased by 20% and 4% annually. The total hardness increased 10.9% and 2.2% annually. The detection rate of "three nitrogen" is generally on the rise.

Deep pore water

Class III water is distributed in a large area, and Class II and IV water appears in some areas. Grade ⅳ water is mainly distributed in Dangshan and Bengbu areas, which is caused by pollution. Class II water is distributed in Jieshou-Fuyang area. The change trend of "three nitrogen" is similar to that of shallow water, but the detection rate and content are lower than that of shallow pore water.

2.3.3 Karst fissure water

It is mainly distributed in the hilly area in the northeast of the plain, and it is mostly Class I water with good water quality. Located in Huaibei City, a densely populated area, the total dissolved solids and total hardness of groundwater are on the rise due to artificial mining (see Figure 3).

Fig. 3 Trend diagram of total solids and total hardness dissolved by fractured karst water.

2.4 endemic diseases with high fluoride are widely distributed [6]

Huaibei plain in Anhui province is a drinking water type high fluorine area. According to the investigation and statistics of the health department and Anhui geological environment monitoring station, endemic fluorosis areas account for 40% of the total area of the region. There are 892 epidemic towns, and the total number of sick villages is 226 19. Among them, there are mild sick villages 17942, accounting for 79.3% of the total number of sick villages; There are 4529 moderately ill villages, accounting for 20.0%; Seriously ill villages 148, accounting for 0.65% of the total number of sick villages. The total population of epidemic townships is13.444 million, accounting for 66% of the total population of Huaibei Plain. Endemic fluorosis areas are basically distributed in a strip from northwest to southeast, and sick villages are mainly distributed in flat and low-lying places such as Hejian depression, fan front, Houhe depression and Hejian flat land. The distribution of endemic fluorosis areas is completely consistent with that of high fluorine groundwater.

Severe illness area. It is distributed in Xinxing and Panlou areas in northern Yang Guo, with an area of about112.5km2. The fluorine content in drinking water in this area is above 4.0mg/L, with the highest of 6.79mg/L. The average prevalence rate of dental fluorosis is 94%, and there are more patients with skeletal fluorosis.

Moderate ward. It is mainly distributed in Yang Guo Qingtuan, Lixin Jiang Ji, Lixin Wang Ren, Suxian Taoyuan, Sixian Caomiao, Xiaoxian West and Dangshan North, with a total area of 1650km2. The prevalence rate of dental fluorosis is about 90%, and the fluorine content in drinking water is 2.0 ~ 4.18mg/L.

The total area of light endemic areas in this area is about 1.4× 104km2, which is mainly distributed in the Hejian area, but also in the fan depression and fan front area where the Yellow River breaches.

In addition, although the F- content of groundwater in Huaibei coal mine area is below 0.5mg/L, the prevalence rate of dental fluorosis reaches 30%, and there are many patients with skeletal fluorosis, which belongs to mild and moderate endemic fluorosis area, which may be related to fluorine pollution.

3 Suggestions for the future work direction

There are many groundwater environmental problems in Huaibei Plain, Anhui Province, and a lot of work needs to be done. According to the needs of the current national economic development and the reality of Anhui Province, the focus of work in recent years can be started from the following aspects.

3. 1 Construction of Land Subsidence Investigation and Monitoring Network

Although land subsidence is a slowly changing geological disaster, after years of development, it has directly or indirectly caused certain harm to the urban construction and economic development of Fuyang City, mainly as follows:

Destroy water conservancy facilities, lower flood control standards, and aggravate flood disasters. He Ying Fuyang city control gate is also the main road of urban traffic. Due to the influence of uneven settlement, the bottom plate of the sluice cracked in many places, the pier was dislocated and the hinge seat was tilted. As a result, the opening and closing of the gate is ineffective, and the cracks in the door body widen year by year. Seriously threaten the operation safety of sluice. The flood discharge capacity decreased from 3,500m3/s when 1959 was completed to 2,500m3/s ... The dam heights of Heying Dam and Quanhe Dam in the subsidence area decreased with the ground subsidence, which failed to meet the original design flood control standard of once every 20 years. The ground elevation of other subsidence areas is also lower than the river flood level of 1 ~ 2m, and the land subsidence intensifies its flood disaster.

Destruction of municipal and water supply and drainage facilities. The ground subsidence caused some deep pore water exploitation wells to be tilted and dislocated, the well pipe was relatively lifted, and the well platform was cracked and deformed.

The failure of ground leveling points destroyed the urban survey control network and restricted the sustainable development of local economy.

In view of the fact that land subsidence has spread to the whole western region and there are signs of land subsidence in the central region, it is necessary to carry out land subsidence investigation in the whole region, establish a land subsidence monitoring network, and incorporate it into the land subsidence monitoring network in North China as a part of it.

3.2 Study on demonstration well engineering of safe water supply in high fluorine endemic areas

Rural and urban residents in moderate and severe disease areas in Huaibei Plain are seriously ill and need clean water urgently. According to the known data, there are low fluorine groundwater suitable for exploitation in endemic fluorosis areas, and the suitable well depth is generally less than 200m, and the water quantity can meet the drinking water demand of local people and animals. The cost of well drilling is low, economical and practical, and easy to implement.

Combined with the planning of small towns, the demonstration well project of low fluorine groundwater was implemented in suitable towns in severe and moderate endemic areas to solve the problem of safe water supply in high fluorine endemic areas, so as to prevent the further development of endemic fluorosis by drinking low fluorine groundwater and improve the quality of life of farmers.

3.3 Focus on groundwater quality investigation, and put forward prevention and control schemes.

Anhui Geological Environment Monitoring Station has set up more than 300 groundwater monitoring holes in Huaibei Plain to monitor all kinds of aquifers, and formed a regional monitoring network, collecting a certain number of fully analyzed water samples every year to carry out regional water quality change research. However, due to the serious shortage of working funds, the depth of water quality change research is far from meeting the needs of social and economic development. Therefore, groundwater quality investigation should be carried out in key urban areas and pollution-free agricultural farming areas, and targeted and operable prevention measures should be put forward according to the different ways, ranges and depths of groundwater variation in different functional areas. You can choose Bengbu City, Fuyang City, Huaibei City, Dangshan County and other cities and counties to carry out work in advance.

3.4 Adjust the water production structure to control the further decline of groundwater level.

Huaibei Plain is rich in shallow pore water resources. Re-understand and study the structure and performance of groundwater aquifer system, adjust the structure of groundwater source, expand the exploitation of shallow pore water, reduce the exploitation of deep pore water, explore a reasonable joint exploitation scheme of deep and shallow pore water, and reduce the decline of groundwater level. Fuyang city can be selected as a pilot in the early stage: controlling the exploitation of deep pore water, selecting rich water areas in the periphery of the city, establishing shallow pore water supply plants respectively, adjusting the urban water supply structure, and controlling the further decline of groundwater level.

refer to

Peng, Chen Wei, et al. Evaluation of groundwater resources in Anhui Province. Anhui geological environment monitoring station. 2002

[2] Chen Wei, Xiao Qinghua and Shi Rongxin. Five-year report on geological environment monitoring in Anhui Province. Anhui geological environment monitoring station. 2002

Yang, Lei Zhuping, Wang Zaojian etc. Construction scheme of land subsidence monitoring network in Fuyang city. Anhui geological environment monitoring station. 2004

[4] Li, Guan Yu, Xue Konghuan, etc. Comprehensive detailed investigation report on hydrogeology, engineering geology and environmental geology in Fuyang city. Anhui Geological Environment Monitoring Station. 199 1

Yang, Sun Jian politician, Wei Jidong, etc. Comprehensive detailed investigation report on hydrogeology, engineering geology and environmental geology in Suzhou and its adjacent areas. Anhui Geological Environment Monitoring Station. 1993

, Wang, Jiang, etc. Investigation on geological environment of endemic fluorosis in Huaibei area of Anhui Province and research report on its prevention and control direction. Anhui geological environment monitoring station.45438+0993

Study on Groundwater Environment in Huaibei Plain of Anhui Province

Yang

(Anhui Geological Environment Comprehensive Monitoring Station, Anhui u 233000)

Abstract: Huaibei Plain is located in the north of Anhui Province. In the west of the plain, there has always been the largest ground subsidence in Fuyang City, and the subsidence center is 150 1 mm. With the further expansion of pumping capacity, land subsidence has declined, so large-scale land subsidence will occur in the western plain. Drinking-water fluorosis is all over Huaibei Plain, and fluorosis areas account for 40% of the whole region. There are 4529 villages with mild illness 17942, 4529 villages with moderate illness and 48 villages with severe illness 148, accounting for 79.35%, 20.0% and 0 respectively. 65% of the total number of sick villages. The sick population 13444000, accounting for 66% of the total population of Huaibei Plain. With the continuous decline of groundwater level in this area, the amount of groundwater is getting less and less. In view of the above-mentioned main water environment problems, some suggestions are put forward for the future work direction in plain areas.

Keywords: land subsidence; Fluorosis; Water level; Water quantity; Work direction; suggestion