Gao Hongqiang¹, Bi Fuke¹, Liu Zhigang², Chen Zongyu³, Luo Guozhong¹, Liu Lijun¹

1.Hebei Institute of Geological Survey，Shijiazhuang  050081;

2.Hebei Bureau of Geology and Mineral Investigation，Shijiazhuang  050081;

3. Institute of Hydrogeology and Environmental Geology，CAGS，Shijiazhuang  050061

Abstract: Hebei Plain is a one of the water scarce region in China. Overexploitation of deep fresh groundwater has induced some geo-environmental problems, such as land subsidence. However, there are plenty ofbrackish and saline groundwaters within the shallow aquifers. Thus, exploitation and rational utilization of these saline groundwaters are vital to improve the ecosystem and to meet the ever increasing demand for water. At present, there are three utilization modes of saline groundwater in Hebei plain, which include direct use, indirect use and desalination use. The total production rate of saline groundwater in 2003 was about 4.035×10⁹ｍ^３. Exploitation and rational utilization of saline groundwater in this plain is of substantial practical importance, since pumping saline groundwater can decline the water table to an optimal depth and help replenish aquifers, such as reducing water evaporation loss for increasing amount of water resources; vacating the space of the shallow aquifers for increasing storage capacity of aquifer and preventing waterlogging ordrought; improving groundwater salinity and controlling the process of soil salination; alleviating the threat for the resource of fresh water. This paper was focused on discussion of the prospect of saline groundwater utilization for agricultural irrigation, industrial uses, domestic uses and ecological water use etc. And then, some suggestions and measures were given for exploitation and rational utilization of saline groundwaters.

Key words: Hebei Plain, saline groundwater, utilization mode, prospect, measures

Water resources play an important role in the sustainable social and economic development. China is one of the countries of water scarcity and the Hebei plain is the most water scarce region in China. Fresh water shortage in Hebei has become to be one of the important factors to restrict economic development. Especially in the region where are plenty of brackish or saline groundwaters. Water shortage with quantity and quality in this region has resulted in overexploitation of groundwater resources, producing a large water depression cone with an area of 40,000 km² around Cangzhou City. The depths to the potentiometric surface in the central parts of the cone has declined to 101 m (-94.53 m above the sea level) in 2005. Overexploitation of groundwater resources has also caused serious environmental problems, such as land subsidence, ground fissure, saline and sea water intrusion.

For alleviating the water crisis and improving the ecological environment in Hebei Plain, especially in the saline water region, Exploitation and rational utilization of saline groundwater are the valid measure to solve the above water and environmental problems

1 The Characteristics of Saline Groundwater Distribution in Hebei Plain

Greoundwaters with different TDS are distributed in whole Hebei plain. The area of fresh groundwater (TDS< 1g/l) is about 30206.5km², occupied 41.3% of the total area. The area of brackish groundwater (TDS: 1–3 g/L) is about 33729.2Km², accounted for 46.1% of the total area. The area of semi-saline groundwater (TDS: 3 – 5 g/L) is about 4511.9km², accounted for 6.2% of the total area. The area of saline groundwater (TDS> 5g/L) is about 4681.4km², occupied 6.4% of the total area (Table 1).

The TDS for saline groundwaters ranges from 1 g/l to 10 g/l in the Hebei plain. Saline groundwater with TDS more then 10g/l is mainly distributed in the littoral plain, the eastern region along Fengnan-Laoting-Qinhuangdao, and the southern regionalongLangfang-Gu’an-Bazhou-Suning-Xinji-Renxian-Handan (Figure 1).

Table 1 The area of saline groundwaters in the Hebei Plain

Fig.1 Distribution of saline groundwater in Hebei plain

The boundary of fresh and saline groundwater is approximately at front of distal fan (Figure 2) in the piedmont. The fresh groundwater is distributed in the piedmont in west part. And the saline groundwater is distributed in central and littoral plain in east part. The ship of saline water is approximately a cuneal water body that its thickness increases from west to east. The aquifer below this saline aquifer contains fresh water. Generally, the depth of upper boundary of saline aquifers ranges from 0m to 70m, and is 10～30m in the palaeochannel. The depth of lower boundary of saline aquifer is 10～30m in transition zone between fresh water and saline water region, 40～120m in central plain, 120～240m in Zhanghe River and Weihe River area, more than 200m in littoral such as Huanghua, Haixing and Laoting, greater than 500m at Liguizhuang in Cangzhou.

In summary, the characteristics of saline groundwater distribution are as follow:

（1）large distributed area. The area of saline groundwater is 42922.5km²，about 58.7% of total area of Hebei plain.

（2）large water storage capacity. It is estimated that the storage capacity of saline groundwater is about 2111×10⁸m³ in Hebei plain

（3）shallow depth of water table. The depth of water table is 10～30m in transition zone between fresh water and saline water region, 2～7m in central and littoral plain.

（4）occurrence in different geologic formation. Both Holocene and Pleistocene formation may contain saline water.

（5）the upper boundary of saline aquifer is controlled by landform and the lower boundary is controlled by basal structure.

2 Exploitation and Utilization of Saline Groundwater

2.1 Present yield of saline groundwater

The brackish and saline groundwater has not been exploited in a lager scale in Hebei plain yet. The yield of groundwater with TDS more than 2g/l was less than 3×10⁸m³ in 1980s, and 9.98×10⁸m³ in 2000. In the past three years, the yield of saline groundwater was increasing with economic growth. The yield was about 40.3482×10⁸m³ in 2003, in which the yield for groundwater with TDS of 1-2 g/l, 2-3 g/l, 3-5 g/l and more than 5 g/l was about 24.5506×10⁸m³ (60.8% of total yield), 12.6916×10⁸m³ (31.5% of total yield), 2.0639×10⁸m³(5.1% of total yield), and 1.0421×10⁸m³ (2.6% of total yield), respectively (Table 2).

Table 2 Yield of saline groundwater in 2003

More than 90% exploiting saline groundwater was used for irrigation. Industrial uses with 1.8×10⁴ｍ^３/day has been pumped in Cangzhou city for fertilizer production since the 2000 year.

2.2 Types of utilization

2.2.1 Direct use

At present, the brackish water was directly used for irrigation. Hebei is one of the earliest provinces of exploiting saline groundwater in China. There are 13 integrated experimental zones which have been established since 1970s. Most data were obtained from the Zhangzhuang and Wumaying experimental zones. These provide good practice for the further utilization of saline groundwater.

In the littoral area, saline groundwater was mainly used for aquiculture, such as crab and prawn. In addition, saline groundwater (TDS 3.2 -9.5 g/l) was successfully used to grow mushroom in Huanghua.

2.2.2 Indirect use

Indirect uses of saline groundwater involve in rotational irrigation and proportion irrigation of fresh and saline water. Rotational irrigation is a scheme for alternating use of fresh and saline groundwater based on the water quality, crop types and salt tolerance in different growth stage. Proportion irrigation of fresh and saline water is a scheme of proportional mixing fresh and saline water for irrigation. The fraction of fresh and saline water is determined by the following equation:

where： M－TDS of mixing water (g/L）；

M₁－TDS of saline water（g/L）；

M₂－TDS of s fresh water（g/L）；

V₁－volume of saline water（m³）

V₂－volume of fresh water（m³）。

There are many areas using proportion irrigation for agriculture in Hebei province. The Zhonggaocun village in Hengshui, with population of 486, is one of the areas for using proportion irrigation. There are 4 groups of double-well for irrigation of 942667 m² farm land. The fresh water (TDS: about 0.7g/l) well, about 220-250 m depth, has pumping rate of 1200m³/day. And the saline groundwater (TDS: 3-4g/l) well, about50m depth, has pumping rate of 432 m³/day. The TDS of mixing water is 1.5g/l with the mixing proportion of fresh and saline water1:2.77.

2.2.3 Desalination use

（1）Industrial use

A project for desalination of saline groundwater was finished and put into action in Cangzhou Chemical Corporation. Total 30 production wells with depth of 120-250m and water TDS of 12.6g/l, are drilled in an area of 75.5km². This project provides 1.8×10⁴m³/day fresh water (TDS: 0.213g/l) for the Corporation by using reverse osmosis desalination system.  

（2）Domestic uses

Desalted saline groundwater has been used for country water supply in Cangzhou. At present, there are hundreds of villages using desalted water.

The desalination method for Domestic uses is electro-dialysis. The saline water with TDS of 3-5g/l was desalted to TDS less than 1g/l. One equipment can provide 2-5 m³/h fresh water. An investment of 100,000¥RMB will provide drinking water for 1000～2000 person. The cost for this desalination is about 3 ¥RMB/m³. Wangdaben, a village in Huanghua, has a population about 1376. A desalted saline groundwater system with investment of 135, 000 ¥RMB was built at this village in September 2002. The saline groundwater with TDS 4.5g/l was desalted to fresh water with TDS 0.07 g/l by this system. it is estimated that this system provides 2 m³/hour fresh water for drinking and is cost of 3.20 ¥RMB/m³.

3 Importance of Exploitation and Utilization of Saline Groundwater

3.1  Increasing water resources

Saline groundwater is mainly distributed in the east part of Hebei plain where is the most water scarce region. In the past decades, overexploitation of fresh groundwater for meeting the increasing water demand had result in serious environmental problems. In view of shallow depth of saline water table, exploitation of these waters may decline the water table and therefore avoid the water loss by evaporation and increase water resources by reduction of fresh wate abstraction.

3.2  Enhancing water storage capacity

The shallow saline groundwater body occupied the space of the shallow aquifers and restricted the precipitation infiltration. Exploitation of shallow saline groundwater may decline the water table to an optimal depth and enhance water storage capacity of aquifer which lies 3-5 m below ground surface. In addition, this can prevent waterlogging or drought.

3.3  Improving eco-environment

Before 1980s, small amount of saline groundwater was exploited and used for irrigation. As the water table was very shallow, drought，flooding，Salinization and alkalization were occurred frequently. Thus, exploitation and utilization of saline groundwater is vital to mitigate these natural disasters.

After 1980s, more saline groundwater was exploited to meet the increasing demand for water. As a result, water table was declined and water loss by evaporation was reduced. Meanwhile, the Salinization was mitigated and the agricultural production was increased. In addition, the decline of water table disturbed natural flow regimes of saline groundwater. This is helpful for water infiltration, aquifer replenishment and increasing available resource.

3.4  Mitigating saline intrusion of fresh water aquifer

Owing to overexploitation of fresh groundwater from the deep confined aquifer, a hydraulic head difference occurred between saline water aquifer and fresh water aquifers. This induced the saline water leakage into the fresh water aquifer and caused salt contamination of fresh water. At the interface of saline and fresh water, the upper saline water intruded into lower confined aquifer. If it was possible to decline water table by exploitation of saline water, the hydraulic head difference between the two aquifers would be reduced. And then the risk of saline intrusion would be minimized.

4 Prospect on Exploitation and Utilization of Saline Groundwater

4.1 Potential of exploitation and utilization of saline groundwater

Since small amount of saline groundwater is exploited in the eastern plain, especially in littoral area, the saline groundwater is in the natural state. The water table is very shallow (2-7m below ground surface) and this causes more water loss by evaporation. Generally, there has a great potential of exploiting saline groundwater for reducing evaporation and increasing water resources.  This is also important to improve eco-environment of this plain.

Based on the data of water table in Dec. 2003, the areas for the depths of water table less than 2m, 2-4m, 4-7m and 7-10m were about 635km², 6744 km², 12567 km² and 12519 km², respectively. If the water table is declined to 10m below ground surface, the available resource of saline water is about 78.7×10⁸m³. For preventing sea water intrusion, a protected zone should be built along the 487m coastline. In this case, the available resource of saline water is about 54×10⁸m³ (Table 3). Up to 2010, the pumping rate of saline water is estimated to be increased by 71×10⁸m³/a。

Table 3 Available resources for the depths of water table less than 10m

The average groundwater loss by evaporation in Hebei plain is 9.78×10⁸m³. If water table is declined to 10m below surface, this water loss would be available. In the case of protected zone, the available resource captured from evaporation will be about 3.33×10⁸m³. Up to 2010, the increased available resource will be about 11×10⁸m³/a.

4.2 Utilization for different purposes

（1）Irrigation

There are three types for irrigation by using saline groundwater, direct irrigation, rotational irrigation and proportion irrigation. Unlike irrigation by fresh water, saline water irrigation needs control the salinity for different crops because of salt tolerance. The salinity control requires the soil salt accumulation is less than salt tolerance. Rotational irrigation and proportion irrigation are the better way for controlling salinity.

（2）Industry

For the industry of low water quality requirement, such as chemical plant, power plant, textile mill, foundry and cement plant, the shallow saline groundwater may be used directly. For the large enterprises in littoral, deep saline groundwater (well depth > 120m) could be used after desalination. Exploitation of deep saline groundwater, however, is expensive and may result in some environmental problems. For example, the water level declined fast due to exploitation in the water source of Cangzhou Chemical Corporation. This should be monitor and study further.

（3）Drinking water for village

Desalination of saline water for drinking has been widely used in rural areas of Hebei plain because of low cost and high efficiency, Especially in Cangzhou area. This solves not only the problem of drinking water, but also improves the eco-environment. As a new industry, desalination of saline water is bringing good economic and social benefits to Cangzhou. Based on the extending scheme of desalination of saline water from the Cangzhou water authority, the problems of drinking water for 659 villages with population of 675,000 will be solved by using desalination method.

（4）Domestic uses for city

Dual water supply is a better way for city water supply system. In recent years, the dual water supply has been successfully tested in Cangzhou city by the water authority. Because the saline groundwater was not exploited a few years ago, precipitation could not infiltrate into aquifers and water table rise in spring season resulted in road frost boiling. In Oct.2002, a saline reclaimed water system was built in Cangzhou. After one year testing, the average monthly domestic water use for one person was 4.07m³ in which tap water was about 1.7m³ (42%) and saline water was 2.37m³ (58％). Direct uses of saline groundwater cost lower than reclaimed water from waste water treatment. The area for saline groundwater in Hebei plain occupies about 58.7% of the total area. For solving the problems of water shortage and supporting the sustainable development, the experience of Cangzhou should be extended to some cities, such as Hengshui and Langfang.

5 Suggestions and measures on exploitation and utilization of saline groundwaters

5.1 Hydrogeological investigation on saline groundwater

Before exploitation of saline groundwater, some information about aquifer property and water quality must be known. Thus, it is necessary to carry out hydrogeological investigation. In addition, some problems, such as land subsidence and sea water intrusion may occur due to water table decline after exploitation. It is also important to evaluate the environmental impact of groundwater development.

5.2 Consideration of local conditions, rational exploitation

Exploitation of saline groundwater should combine the concentrated and dispersed wells and focus on the shallow aquifer with well depth of 10-50m. Although the brackish water has been widely used forirrigation, the waters with TDS greater than 3g/l are not exploited for irrigation. For using these waters, proportion irrigation of fresh and saline water should be encouraged.

In addition, deep fresh groundwater in Tertiary aquifer is used by reinjection for oil production in Rinqiu and Jidong. It is necessary to study the reinjection of saline groundwater.

5.3 Promoting industrialization of desalination of saline water

Desalination of saline water is a new industrialization. Hebei Plain is a one of the water scarce region. However, there are plenty of brackish or saline groundwaters within the shallow aquifers. This provides a prerequisite and basis for desalination industrialization. The saline water desalting system with production of 18000m³/d fresh water in Cangzhou Chemical Corporation has demonstration effect on the utilization of saline water. We should hold of development opportunity to tap new sources of economic growth and desalination industrialization by establishing the preferential policy, enhancing investment, importing advanced equipment and professionals for grandness of production scale.

5.4 Integrated water resources management and protection of geo-environment

In view of the status of water resources in Hebei province, on the principle of making overall plans and taking all factors into consideration, comprehensive development and rational utilization  of water resources, combined use of surface water and groundwater, a long-term plan for exploiting saline groundwater should be made to prevent drought, waterlogging, salinity and saline. Groundwater monitoring is the basis of groundwater resource assessment and development. A saline groundwater monitoring network should be established as soon as possible in Hebei plain.

A 10km wide protected zone should be built along the coastline. In this zone, exploitation of saline groundwater must be forbidden for preventing land subsidence and sea water intrusion. For the high salinity tail water from desalination, a concentrated treatment method should be adopted in order to avoid secondary salt contamination

5.5 Improving management work of government

In order to improve the technology for exploitation and utilization of saline groundwater, government should enhance the efficiency of resource utilization, encourage enterprises to use saline groundwater and provide financial support for the villages which use desalination of saline water as drinking water. At the same time, we must launch an extensive public awareness campaign on importance and prospect of using saline groundwater.

References

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