Achievements

STRATEGIES FOR GROUNDWATER RESOURCE AND ITS ENVIRONMENT PROBLEMS IN BEIJING

Updated :10,23,2012

Ye Chao¹, Shao Jingli², Xie Zhenhua¹, Chen Zhihong¹, Wang Xinjuan^1,2

1 Beijing Institute of Hydrogeological & Geological Engineering, Beijing, 100037;

2 China University of Geosciences, Beijing, 100083

Abstract: The characteristics of groundwater resource and its environment under the condition of long-time exploitation are focused on in this paper, and the strategies for reasonable development of groundwater are brought forward. Above all, groundwater evaluation is made based on analysis of water balance. The average groundwater recharge is 35.98´10⁸m³/a and the safe yield is 26.33´10⁸m³/a for multi-year. During the latest 30 years, the groundwater exploitation quantity is about 26-28´10⁸m³/a, which is at the state of over-exploitation and has resulted in the geological environmental problems, such as sustaining groundwater drawdown, land subsidence, water quality deterioration and so on. Now the area of groundwater depression-cone is over 1000km², and the area with more than 200mm’s accumulative land subsidence is up to 350km². Aiming at the current situation of water resource shortage in Beijing and based on analysis of water supply and demand, strategies for groundwater reasonable development and assurance of municipal water supply security before and after water from South-North Water Diversion coming into Beijing are presented, such as supplying groundwater according to its quality, groundwater-surface water conjunctive use and emergent well field’s exploitation and recharge and so on.

Key words: groundwater resource, safe yield, geological environment, emergent well field, groundwater recharge

1 Introduction

Beijing is the capital of P.R. China and locates in the north of Huabei Plain, with a total area of 16410.54km², of which there are mountain area 9882.54km² and plain area 6528km². It belongs to the typical warm temperate zone with a semi-humid and continental monsoon climate. The average precipitation for multi-year is 609.9mm (figure 1). Its water system belongs to Haihe river basin, and is mainly made up of YongdingRiver, Chaobai River, Daqing River, Beiyun River and Jiyun River, which flow from northwest to southeast on the whole. Groundwater plays an important role in water supply of Beijing, and occupies about 2/3 of the total water supply quantity. With the extending of city scale and development of economy, demands of water resource keep increasing. Continuous over-exploitation during the latest 40 years has caused the serious deficit of groundwater in the plain area of Beijing, and resulted in some geological environmental problems at the same time, such as land subsidence and groundwater quality deterioration. Although the South-North Water Diversion Engineering can resolve the water shortage problems at a certain extent, but as the main source of water supply, groundwater still has a vital effect on assurance of water supply security in Beijing. So it is necessary to know the current situation of groundwater resource and its environment problems in Beijing, then present the strategies for groundwater reasonable exploitation and utilization before and after the South-North Water Diversion Engineering implemented.

Figure 1 precipitation and the accumulative storing variable of groundwater in Beijing

Beijing is the region that started hydrogeological work very early and has high study degree in this field in our country. In 1944, in order to build the well field in the northeast suburb, Japanese North China Development Company investigated groundwater in urban area of Beijing and the area around it, and submitted the report of Groundwater in Beijing and Its Surrounding Area ^[1]. A lot of hydrogeological work has been done after 1949. In the 1950s, the regional hydrogeological survey was focused on, and the municipal water supply prospect was also developed at the same time. For example, Group 901 of the Geology Ministry started the hydrogeological and geological engineering investigation in the suburbs of Beijing in 1955 ^[2], and Beijing Institute of Hydrogeological and Geological Engineering did the municipal water supply prospect at the scale of 1: 50,000 in 1958, and brought forward the Groundwater Safe Yield in the suburbs for the first time^[3]. In the 1960s and 1970s, the municipal and field water supply prospect was focused on, and the groundwater safe yield in the investigated area was evaluated^[4-6]. Investigations and experiments of groundwater artificial recharge were also primarily studied^[7-9]. In the 1980s and 1990s, with the increasing of water

demand in Beijing and the occurrence of a series of environment problems due to serious over-exploitation, besides water supply prospect, quite a lot of work has been done, like assessment of groundwater resource in Beijing^[10-11], studies and investigations of groundwater recharge^[12-14], environmental hydrogeological investigation^[15], as well as monitoring and study on land subsidence ^[16-17]. Coming into the 21^st century, Beijingencountered 7 dry years continuously which is infrequent, and the government began to pay much attention to the capital’s groundwater environment. So the work such as argumentation and water supply engineering of emergent well fields^[18-19], groundwater-surface water conjunctive use and investigation of organic pollution to groundwater^[20], and the groundwater environmental impact assessment after the South-North Water Diversion Engineering implemented^[21] has been started. Moreover, since 1956, Beijing has gradually built and perfected groundwater monitoring work^[22], and established the experimental station of groundwater balance in Liaogongzhuang^[23]. Since 1966 Beijing has done the large-scale surveying and mapping work on land subsidence for 3 times, and set up the Land Subsidence Monitoring Center in 2004. The above work has basically made clear the hydrogeological conditions and characteristics of groundwater distribution. It not only has provided the primary guarantee for sustainable development of social economy in Beijing, but also presents reliable basis for further reasonable development of groundwater as well as management and improvement of its environment.

2 Groundwater-forming Condition

Bedrock mountain area distributes in the northwest of Beijing, in which Carbonate outcrops cover an area of 2900km². Karstic fissure water exists in the Ordovician and Cambrian limestones and in the Middle-Upper Proterozoic dolomites, which are mainly distributed in seven regions such as Changgou-Zhoukoudian in Fangshan, Lujiatan-Yuquanshan in West Mountain and the 20-mile Long Mountain in Shunyi etc. It is mainly recharged by precipitation and infiltration of surface water, and flows to the lower places along the landform. Some of it discharges into rivers. Some flows to the deeper area and becomes the recharge source of buried Karstic aquifers. And part of it discharges into the Quaternary pore water. Bedrock mountain area except Carbonate outcrops mainly contains bedrock fissure water. Such area has little groundwater recharge and poor water-bearing.

The plain area of Beijing (except Yanqing Basin) is mainly made up of the alluvial-pluvial fans formed by Yongding River, Wenyu River, Chaobai River, Jiyun River and Juma River. Its Quaternary pore water mostly exists in the sand and gravel aquifers formed by river’s alluvial and pluvial effects. It is the monolayer phreatic aquifer in the upper part of the alluvial-pluvial fan, with the litholory of monolayer sand and gravel. The aquifer has good water-bearing conditions, and its water discharge of specific well is generally more than 5000m³/d. In the middle and upper parts of all the alluvial-pluvial fans and the area around the groundwater overflow zone, the aquifers gradually become multi-layer structures, and they are the intensive exploitation regions. Especially in the middle and upper parts of the alluvial-pluvial fans (UMPAF) in Yongding River andChaobai River, the aquifers are coarse-grained and thick. They have huge storing space for groundwater and good conditions for recharge. So the specific well rate usually can reach 3000-5000m³/d. In the alluvial-pluvial plain area of urban and southeastern Beijing, the aquifers with multi-layer structure are mainly consisted of medium-coarse sand, fine sand and silty sand. The lower confined aquifers are the main exploitation layers. And the specific well rate is usually 500-1500m³/d.

Groundwater in the plain area is mainly recharged by precipitation, infiltration of river and irrigation and lateral inflow from mountainous area, in which precipitation is the primary recharge source. Under natural conditions, groundwater is mainly consumed by evaporation and discharge to river. But due to large exploitation at present, the artificial pumping has become the main discharge way of groundwater.

The flow direction of the Quaternary pore water in the plain area changes with the landform. It flows from mountain to plain and from northwest to southeast. With the long-time intensive exploitation of groundwater, the regional depression-cones have occurred in the area with large exploitation quantity, and groundwater flow field also has changed a lot.

3 Groundwater Exploitation and Utilization

Beijing has a long history of water resource exploitation and utilization. According to the statistics ^[1], in the year of Guangxu 11 in Qing Dynasty (1855), there were 1245 artificial wells in and around Beijing. To 1949, there were 123 pumping wells. But the annual exploitation quantity of groundwater by pumping wells was only 803´10⁴m³. With the growing of population and development of economy after liberation, the exploitation quantity of groundwater increased quickly and greatly. It achieved the maximum quantity with the amount of about 28´10⁸m³/a till 1980s. After then, by the measures of water saving and industry structure’s adjustment and so on, the groundwater exploitation quantity maintains 26-27´10⁸m³/a despite of continuous extending of city scale (figure 2).

Figure 2 Changes of groundwater exploitation quantity in Beijing in past years

Groundwater exploitation is mainly in the plain area of Beijing. In 2000, for example, the total exploitation in the whole city was 27.08´10⁸m³/a and the amount in the plain area was 25.51 ´10⁸m³/a, in which the exploitation quantity in Yanqing Basin was 0.70´10⁸m³/a. Analyzing from water consuming structure^[24], the current groundwater exploitation quantity for agriculture is about 16´10⁸m³/a, which occupies 61.8% of the total amount. And the exploitation quantities for industry and living take 15.47% and 22.6% respectively. It is known from statistics in terms of exploitation patterns that, the pumping rate of the eight centralized well fields in Beijing is 3.21´10⁸m³/a (figure 3), and the exploitation of the self-provided wells in the suburbs of Beijing is 2.67´10⁸m³/a. From the exploitation layer point of view, most centralized well fields locate at UMPAF in Yongding River and Chaobai River, and pump the phreatic and shallow confined water. The Eighth Water Plant near Chaobai River, which has large pumping rate, exploits 1.64 ´10⁸m³ groundwater annually, and the annual exploitation quantity of the Third Water Plant located at UMPAF in Yongding River is 0.88´10⁸m³. Their sum take about 55% of the total pumping rate of all the centralized well fields. As a whole, water in the shallow layers is mainly exploited (including the phreatic and shallow confined water, generally referring to the aquifers within the depth of 150m), and the exploitation quantity of deep layers beyond the depth of 150m is relatively less. The deep wells are mostly distributed in the alluvial plain area of southeastern Beijing.

4 Groundwater Resource Evaluation

4.1 Recharge Resource

Groundwater resource in Beijing has been evaluated for several times since 1960s. The latest one divided the area into the plain area and the mountainous area, and employed water balance and dynamic balance to estimate the recharge rsource^[20]. The annual mean (1980-2000) of groundwater recharge in Beijing is 35.98 ´10⁸m³/a, among which 27.68 ´10⁸m³/a is in the plain area, 15.17 ´10⁸m³/a in the mountainous area and the overlap is 6.85 ´10⁸m³/a. Table 1 shows the annual mean of individual source of groundwater recharge in Beijing. It can be seen that the recharge from the precipitation infiltration as the most important source is 27.2´10⁸m³/a, taking 75.6% in the total amount. The plain area receives the lateral recharge of 6.85 ´10⁸m³/a from the mountainous area, which takes 24.75% among the total recharge in the plain area, and this part of recharge also comes from precipitation infiltration in the mountainous area.

Table 1 Annual mean of individual source of groundwater recharge in Beijing unit: 10⁸m³/a

Recharge Source	Plain Area	Mountainous Area	Sum
Precipitation Infiltration	13.26	15.17	28.43
Lateral Recharge	6.85	-6.85	0.00
River Leakage	3.10		3.10
Channel Leakage	0.91		0.91
Irrigation Infiltration	3.49		3.49
Artificial Recharge	0.07		0.07
Sum	27.68	8.32	35.98

4.2 Safe yield

Groundwater safe yield refers to those guaranteed resources whose perspective exploration will not bring negative impacts on the ecological system and will not make water quality degrade or cause undesirable geological phenomena (such as land subsidence and sewage intrusion) under the current conditions of economy and technology^[25]. Combined with the demands of local water supply, estimation of the regional groundwater safe yield relates closely to the designed and programmed exploitation scenarios, and varies with conditions. Based on the considerations of the current exploitation patterns and conditions, establishment of emergent well fields, preventing geological and ecological problems related to groundwater and guaranteeing urban planning and municipal water supply security, dynamic balance method is used to estimate the groundwater safe yield in the plain and mountainous areas respectively ^[20]. The total amount in Beijing is 26.33´10⁸m³/a, among which 24.55´10⁸m³/a is in the plain area and 1.78´10⁸m³/a is in the mountainous area. Table 2 presents the safe yield and the current exploitation index (2000) of each administrative district in the plain area of Beijing, respectively. The exploitable modulus averaged in the whole area is 37.6 ´10⁴m³/a·km². The most aqueous areas respectively distribute in the Mi-Huai-Shun Plain area and the western suburbs which are in UMPAF of Chaobai River and Yongding River, respectively. The groundwater safe yield in the former is 6.05´10⁸m³/a and 5.80´10⁸m³/a in the latter. The exploitation degree is relatively large and the current exploitation modulus in some area has reached 130 ´10⁴m³/a·km².

Generally, the plain area of Beijing (except Yanqing Basin) is over-exploited for groundwater. Results of multi-year annual balancing show that groundwater storage in the plain area has decreased by nearly 70´10⁸m³ since the 1960s (Figure1). From the 1980s on the annual consumption of groundwater storage is nearly 2´10⁸m³ per year. The serious over-exploitation regions distribute in the western suburbs, Daxing, Tongzhou and part of the Mi-Huai-Shun Plain area. The serious over-exploitation area is already 3,312 km², the over-exploitation area is 1,743 km², and the non-over-exploitation area is 1,473 km² (figure 3).

Moreover, in the plain area of Tongzhou, Daxing, Pinggu, Changping and western suburbs, there are exploitable buried Karstic aquifers with areas of about 1,730 km². Some investigation and research have indicated that the current puming rate of Karstic water is about 2´10⁸m³/a and its safe yield is about 4 ´10⁸m³/a. The Karstic water may act as the important strategy reserve for Beijing. Although some related investigation and research have been carried on for Karstic water^[26], the hydrogeological conditions are so complex that its exploitation conditions and safe yield need to be further studied.

Table 2 Statistics of Groundwater Safe Yield and Its Current Exploitation Index in the Plain Area of Beijing

Administrative district	Safe yield (10⁸m³/a)	Exploitable modulus (10⁴m³/a·km²)	Current exploitation modulus (10⁴m³/a·km²)	Current exploitation index
Suburbs	6.05	61	5～130	1.11
Tongzhou	2.10	24	15～50	1.17
Daxing	2.60	26	28～50	1.09
Changping	2.20	27	15～50	1.01
Fangshan	2.90	44	15～100	1.15
Mi-Huai-Shun Plain area	5.80	42	10～130	1.0
Pinggu	2.00	59	15～100	0.62
Yanqing	0.90	18	5～25	0.76
Sum/Average	24.55	37.6	39.08	1.03

5 Groundwater Environmental Problems

5.1 Regional continuous groundwater drawdown

The long-time over-exploitation has resulted in continuous groundwater drawdown in Beijing Plain. The large-scale depression-cone is found in the northeastern suburbs where exploitation is concentrated (figure 4). In the 1970s and 1980s, with the increasing of groundwater exploitation, a depression-cone covering about 400km² area was formed in the eastern suburbs. In the middle of 1990s, with the continuous groundwater drawdown, the range of the depression-cone has extended from the eastern suburbs to Changping, Shunyi and Tongzhou year by year. Its area reached up to 740km² in 1996. 1998 later, the depression-cone extended further due to the reducing of recharge and increasing of exploitation caused by continuous drought. And it has covered an area of nearly 1000km² in 2001.

5.2 Land subsidence

The history of land subsidence measurement in Beijing can date back to 1935, when it only occurred in areas of Xidan and Dongdan. In 1955~1966, the center of land subsidence occurred in the regions from industrial area of textile at East Balizhuang to industrial area of electronics at Jiuxianqiao, with the amount of 58mm in the former and 30mm in the latter. During 1966~1983, two centers of land subsidence were gradually formed in the industrial area in the eastern suburbs, among which there was 277mm accumulative subsidence in Laiguangying Center in the north during 1956~1983, and 532mm in Balizhuang-Dajiaoting Center in the south. By 1987, the land subsidence area extended to 800km², among which the area with more than 100mm accumulative subsidence extended to 260 km², and the area with more than 200mm accumulative subsidence extended to 96 km².

Figure 3 Subareas of Groundwater Exploitation Degree in the Plain Area of Beijing

After 1987, the area of land subsidence in Beijing increased rapidly. A number of new subsidence centers emerged in Shahe-Dongsanqi of Changping,

Pinggezhuang of Shunyi and Panggezhuang-Yufa of Daxing while the old areas continued sinking. Its area has reached 1,800 km², and the area with more than 200mm accumulative subsidence has extended to 350 km²(figure 4). It has resulted in breaking of walls of factories and buildings, sinking of foundations, destroying of underground pipelines, inaccurate leveling points and decreasing of seismic capacity of buildings in the land subsidence areas.

Figure 4 clearly demonstrates the consistency between distributions of land subsidence and groundwater depression-cone. The rate and range of land subsidence correlate linearly to the groundwater drawdown at the same location^[20], which fully indicates the land subsidence in Beijing is mainly caused by long-time extensive over-exploitation of groundwater in the confined aquifers.

5.3 Quality deterioration and pollution of groundwater

Recent investigation^[20] indicates the overall quality of groundwater in Beijing is good, but because of destruction and change of human activities to the geological environment as well as pollution of contaminants in environment to groundwater, it has resulted in quality deterioration and pollution of groundwater in some parts of the area. The major deterioration and pollution indexes are the Total Hardness, Total Dissolved Solids (TDS), Nitrate Nitrogen and so on. The Total Hardness of groundwater keeps going up in the latest 30 years. Currently the areas exceeding the standard of Total Hardness in the plain area of Beijing mainly distribute in the urban area, the suburbs, Fangshan and Daxing. Areas exceeding the standard of TDS are mainly in the center of the city and Fengtai, also scattered in Liangxiang of Fangshan and Lixian of Daxing. The old City is the main area exceeding the standard of Nitrate Nitrogen.

6 Strategies for Groundwater Sustainable Utilization

6.1 Water resource supply and demand

According to the investigation results of water consumption in Beijing in 2000^[24], the total water demand of Beijing in 2010 will be 42.62-48.56 ´10⁸m³/a. The total surface water used in Beijing in the latest years is 13.40 ´10⁸m³/a. Even calculated by the lower scheme, 29.22 ´10⁸m³/a groundwater still must be exploited to meet Beijing’s water demand before water from the South-North Water Diversion coming into Beijing, which has greatly exceeded its safe yield. The situation of water shortage must occur before the South-North Water Diversion Engineering can supply water to Beijing in 2010. So Supply water in Beijing absolutely depend on the local groundwater resource, and must take some methods and techniques such as using the huge groundwater storage and supplying water according to different quality to lighten the water shortage situation. Besides, after the South-North Water Diversion can supply water, there is some water surplus during a certain period. So groundwater can be moderately stopped pumping and recharged gradually under the above conditions, which are worth to study.

6.2 Reasonable allocation

As the above-mentioned, groundwater quality of Beijing is good as a whole, but the quality of water in the shallow layers in the suburbs and its southeastern area is poor. Because industrial, agricultural and domestic water have different requirements for quality, supplying water according to different quality can be considered. The utilization efficiency and safe yield of groundwater can be improved by its reasonable allocation. Excellent groundwater that meets the drinking water standard can be mainly supplied for people’s living. Groundwater dissatisfying the drinking water standard can be supplied for industry and agriculture, environment and municipal mixed consumption. For example, in the central (within Third Ring Road) and south area of Beijing where groundwater is of poor quality and polluted seriously, it is mainly used for industrial and agricultural production and municipal mixed consumption. In the southeastern suburbs and Tongzhou, due to agricultural sewage irrigation and infiltration of contaminants receiving rivers, the quality of phreatic water and water in the first confined aquifer (generally with the depth of 0~60m) is relatively poor and can’t meet the drinking water standard, so it can be used for industry and agriculture. The quality of water in the second confined aquifer and aquifers below it can meet the drinking water standard, so it can be mainly used as domestic water.

Figure 4 Distribution of groundwater depression-cones and land subsidence in Beijing plain area

6.3 Establishments of emergent well fields

Since 1999, Beijing continuously encounters drought for 7 years, which makes the available quantity of surface water reduce rapidly. North China where Beijing locates also belongs to the water shortage area, and it is only probable to divert quite little regulative water from its river systems, which enhances the situation of water shortage in Beijing. Utilizing adequately the huge groundwater storage and its strong regulative capacity to establish emergent well fields is one of the effective ways to lighten the pressure of water supply. Beijing Institute of Hydrogeological and Geological Engineering presents four emergent well fields (figure 3) and their exploitation patterns (table 3), which can increase water supply quantity of 83 ´10⁴m³/d for Beijing.

Now the Lianghe emergent well field in Huairou and Wangduzhuang emergent well field in Pinggu have been officially connected with the water supply net system and supplied water for Beijing, which plays a key role for lightening the pressure of water supply in the latest years. The observed water table data of emergent well fields in operation show that, their exploitation has caused continuous groundwater drawdown in part of area, which indicates that the exploitation comes mainly from groundwater storage. After the South-North Water Diversion Engineering is implemented, it can make the water level and storage come up again by stopping pumping of these well fields. As the reserved water source, emergent well fields can greatly improve the assurance of municipal water supply, and are helpful to groundwater-surface water conjuncttive use, which will improve the efficiency of water resource utilization.

Table 3 Surveys of emergent well fields

Number	Well field	Exploitation layer	Exploitation capacity（10⁴m³/d）	Note
Ⅰ	Lianghe emergent well field in Huairou	The Quaternary pore water	33	Construction of 21 pairs of wells has been completed. Deep and shallow wells are used together and have been officially connected with the water supply net system.
Ⅱ	Pinggu emergent well field	The Quaternary pore water and Karstic water	30	Wangduzhuang Emergent Well Field has officially supply water with the amount of 18×10⁴m³/d. Zhongqiao Emergent Well Field is in construction.
Ⅲ	Xishan Karstic well field	Ordovician Karstic water	10	Using adequately the existing wells in the Third Water Works to distribute new wells and in construction now.
Ⅳ	Fangshan Karstic emergent well field	Wumishan Karstic water	10	In construction with ten wells completed.

6.4 Groundwater-Surface water conjunctive use

Dominated by southeast monsoon climate, the precipitation and surface runoff in Beijing distribute unevenly in a year, and vary greatly from year to year. Continuous dry years and continuous wet years appear sometimes, which result in alternant occurrences of drought and waterlog, and badly threaten municipal water supply security. It’s advisable to take full advantage of the huge groundwater storage and capacity. In dry years groundwater can be moderately over exploited, and in wet years it can be recharged through groundwater-surface water conjunctive use. This can increase the groundwater safe yield, improve the assurance of municipal water supply, and relieve the geological and environmental problems caused by continuous groundwater drawdown.

The UMPAFs in Yongding River and in Chaobai River are the areas with best groundwater-bearing and maximum exploitation intensity in Beijing. Over-exploitation for many years has released huge space for groundwater recharge. With Yongding River and its upriver Guanting Reservoir as well as Chaobai River and Miyun Reservoir upriver as recharge sources respectively, and taking riverways and large-area sand and rock pits as recharge fields, the two UMPAFs are the best suitable places for artificial recharge to groundwater. According to calculations^[21], the groundwater capacity of UMPAF in Yongding River is 6.24 ´10⁸m³, and the area of its reservoir is 333km²; the capacity of UMPAF in Chaobai River is 6.00´10⁸m³ and the area of its reservoir is 391km².

In addition, there are many middle and small reservoirs in Beijing. They discharge certain amount of water in the flood seasons every year due to poor regulative capacity. This part of water can be fully used to recharge groundwater through riverways, channels, sand pits and large open wells. The completed work shows good results of recharge ^[12-14,

^27-28].

6.5 Groundwater reasonable development after the south-north water diversion engineering supply water

There will be some water surplus after the South-North Water Diversion Engineering supplies water to Beijing. Under this condition groundwater exploitation should be reasonably reduced or partly stopped, and at the same time it should be recharged by the natural and artificial ways, to make seriously over-exploited groundwater replenished gradually. The main principles are: (1) In the areas of serious over-exploitation, the pumping must be greatly limited. Close part of industrial self-provided wells in the suburbs and reduce exploitation of water works in the urban area. Change the agricultural structure in the Mi-Huai-Shun area of the UMPAF in Chaobai River, such as returning farmland to forest and grass. Reduce agricultural exploitation, conserve groundwater and improve ecological environment. Guarantee industrial and domestic water in urban areas and the satellite towns. (2) In the areas of serious land subsidence, groundwater exploitation in the deep layers should be reduced greatly to control the land subsidence, such as in the eastern suburbs and Yufa of Daxing. (3) In the areas where the ecological environment related to groundwater need to be recovered, groundwater exploitation should be reasonably reduced, such as in riverways and the areas around it, and natural and artificial wetlands.（4）In the areas where groundwater quality is relatively poor, it should be used for other purposes instead of as drinking water.

Some work, such as groundwater reasonable exploitation and its environmental assessment after the South-North Water Diversion supplies water, has been done^[21], but there are still many problems worth further research, like the determination of optimal amount and area of stopped exploitation; the range and area of water level re-rising after stopping exploitation and its impact on environment (wetlands recovery, building floating resistance and soaking, waste soaking in informal landfill fields ^[29], etc).

7 Conclusions

Groundwater resource in Beijing is rich, especially in UMPAFs in Yingding River and Chabai River in the plain area. The average groundwater recharge for multi-year is 35.98×10⁸m³/a in the whole area, among which 27.66 ´10⁸m³/a is in the plain area. The annual mean safe yield is 26.33 ´10⁸m³/a, with 24.55 ´10⁸m³/a in the plain area.

In the recent 20 years, the total exploited groundwater is 26-28 ´10⁸m³/a in the plain area of Beijing.

Because of long-time over-exploitation, the groundwater storage has been reduced by 70×10⁸m³, and the depression-cone covering nearly 1000km²has formed, which resulted in land subsidence with more than200mm accumulative amount reaching 350km². Moreover, the quality of groundwater in the shallow layers is poor in the urban area and Daxing. The major exceeding indexes are the Total Hardness, TDS and Nitrate Nitrogen.

Before the South-North Water Diversion can supply water, the situation of water shortage must occur in Beijing. The construction of 4 emergent well fields can increase 83×10⁴m³/d water for Beijing, which greatly lightens the pressure of water supply.

The utilization efficiency and safe yield of groundwater can be improved by supplying water according to different quality and groundwater-surface water conjunctive use. The groundwater reservoirs in the UMPAFs respectively in Yongding River and Chabai River are the best suitable places for recharge due to their huge capacity, enough water source and good infiltration ways.

After the South-North Water Diversion supplies water, groundwater level and storage can come up again and its environment can be improved through reasonably reducing exploitation or stopping it. As the reserved water source for Beijing, the completed emergent well fields have improved the assurance of municipal water supply.

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[26] Feasibility Report on Karstic Groundwater Resource and Its Exploitation and Utilization in Beijing, Beijing Geology and Mineral Resources Prospecting and Developing Bureau, Institute of Geology and GeophysicsChinese Academy of Sciences, 2001.

[27] Feasibility Report on the Engineering of Retaining Flood for Recharge in West Suburb of Beijing, Beijing Planning and Design institute of water resources, 1999.

[28] Experimental Report of Groundwater Artificial Injection with Large-diameter Wells in the Area of Capital Steel Company, Beijing Institute of Hydrogeological & Geological Engineering, 1981.

[29] Investigation and Assessment of Landfill Field’s Current Situation and Its Influence to Groundwater in West Suburb of Beijing, Beijing Institute of Hydrogeological & Geological Engineering, 1999.

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