Impact of Reclaimed Water Irrigation on Groundwater in an Agricultural Area Jilai Liu
Tianming Huang, Jie Li
Hydrogeology and Engineering Geology Team of Beijing Beijing , China
[email protected]
Institute of Geology and Geophysics Chinese Academy of Sciences Beijing , China
[email protected],
[email protected]
Sufen Wang Beijing Hydrological Station Beijing , China
[email protected] threshold of water shortage (1000 m3) and ranked after one hundredth in the metropolis and capitals of the world.
Abstract—Utilization of reclaimed water instead of pumpage groundwater, is an effective approach to alleviate the crisis of groundwater resources depletion in water-scare areas when the quality of reclaimed water is satisfied for irrigation. A case study of Daxing, Beijing shows that the water quality of reclaimed water is suitable for irrigation. The groundwater depth in the reclaimed water irrigation area should be more than 6 m to prevent from reaching water table. Based on the result of numerical simulation, water table could maintain the minimal groundwater depth through the utilization of reclaimed water while decreasing 50% of groundwater pumpage from 2010 to 2020.
With the rapid development of society and economy, contradiction between water supply and demand has become more and more serious and has been the first bottleneck restraining the development of Beijing. Due to the lack of surface water, groundwater accounts for over 2/3 of water supply for the city and insures the sustained economic growth and water safety in Beijing. Since 1999, drought in Beijing has been over 10 years and the precipitation is only 75% of annual average precipitation. Mining groundwater is the only choice for meeting the city development. Some problems about water resources and environmental geology have been occurred like groundwater level decline, water quality deterioration, land subsidence and spring dried-up.
Keywords-reclaimed water; irrigation; water quality
I.
INTRODUCTION
In 2007, the total water supply is 3.48 billion m3 in Beijing, of which agriculture accounts for 37%. In 2010 reclaimed water has been 600 million m3. It is an effective measurement for alleviating the problem of water resources shortage in Beijing to use reclaimed water for irrigation. In this paper, the impact of reclaimed water utilization in an irrigation area in Beiyechang, south Beijing on groundwater has been investigated by water chemistry analysis and numerical simulation.
Utilization of reclaimed water is an effective approach to alleviate the problem of groundwater resources depletion [1]. In the early 1970s, wastewater treatment and reuse have been carried out on a large scale in the United States. The utilization of reclaimed water is also common in Russia, Israel, South Africa and Namibia [2]. In recent years, with the increase of population and the concern for water resources crises, the utilization of reclaimed water has gotten more and more attention all over the world [3-7]. According to statistics from Bixio et al. [8], nowadays there have been more than 3,300 projects related to reclaimed water utilization in the world for agricultural irrigation, industrial production and urban daily utilization, mainly in Japan, America, Australia and Europe.
II.
STUDY AREA
Beiyechang Irrigation Area (BIA) is located in the northeast of Daxing, south Beijing. The average annual temperature is 11.5 ć. The average annual precipitation (1956-2000) is 507 mm, which mainly occurs from June to September and accounts for more than 86% of the total precipitation. The average annual potential evaporation is 1021 mm (1980-2000).
During the last 50 years, the water resources quantity and distribution in the North China Plain have changed greatly. Less precipitation, higher temperature, human water-control and exploitation of groundwater are the main reasons for water resource depletion [9]. Beijing is located in north of the North China Plain with an average annual precipitation of 585 mm (from 1956 to 2000). Water resources per capita in Beijing is less than 300 m3, only 1/8 of the national average and 1/30 of the world average, which is far from the international accepted
Controlled by the Daxing uplift with south-north direction, the quaternary sediment shows obviously difference with a depth about 120 m in northwest Dongzhaozhuang area, 200300 m in the middle Zhaogezhuang area and 600 m in the southeast Houanding area. Generally speaking, from west to
The study is supported by Beijing Talents Project (2009D010002000002) and Beijing S&T Plan Public Project (D090409004009004).
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east the Quaternary thickness increases and the layers of aquifer increase while thickness of single aquifer, particle size and water yield decreases. From north to south the groundwater depth becomes shallower, which is about 30 m in the north and about 18 m in the south. Groundwater flows from northwest to southeast consistent to groundwater level. In recent years, groundwater level declines seriously in the BIA. Water pollution is the other issue induced by the agricultural pollution. In 2007, there is totally 20 million m3/a reclaimed water (55,000 m3/d), which draws from Huangcun sewage treatment plants in BIA. The treatment capacity of Huangcun sewage treatment plant was 110,000 m3/d in 2005 and 190,000 m3/d in 2010. In 2008, Xiaohongmen sewage treatment plant was put into operation and the treatment capacity was 600,000m3/d, half of which could be supplied to Daxing. The BIA could introduce reclaimed water from the two treatment plants. III.
water used for irrigation is 19.2 mg/L, less than the Kjeldahl nitrogen standard (30 mg/L). Major organic pollutant content and colibacillus content are satisfied for irrigation water quality standards. Hence the reclaimed water meets “Water Quality Standard for Farm Irrigation”. In addition, the unsaturated zone has significant removal effect on TN and TP in BIA. In the 5-m monitoring well, 83% TN is removed and in the 12-m well the removal ratio can be up to 97%. For TP, it is 95.5% and 98%, respectively. At the 12-m depth, the TP and TN content have been close to the background value of groundwater. The aquitard in the unsaturated zone over 6-8 m of depth could be prevented efficiently from groundwater pollution in the reclaimed water irrigation areas. IV.
SIMULATION OF RECLAIMED WATER IRRIGATION
A numerical model has been established to test several allocation scenarios of reclaimed water irrigation. The trend and extent of water table changes in different scenarios has been forecasted and the most reasonable one would bring forward for reclaimed water management.
THE FEASIBILITY ANALYSIS OF RECLAIMED WATER QUALITY FOR IRRIGATION
With the increase in amount of reclaimed water, the security of reclaimed water irrigation becomes a hot topic. The water quality standard for irrigation is the basis to check the security of reclaimed water irrigation. Based on the “National Water Quality Standard for Farm Irrigation” in China (GB5042-92), surface water and groundwater of Class IV and V all can be used for irrigation. The water quality of the reclaimed water from the Huangcun sewage treatment plant is restricted with the third class standard for discharge of Beijing.
A. Model Establishment The groundwater flow continuity equation and its definite condition were used to describe the anisotropic and isotropic 3D space structure and the nonsteady groundwater system. Such a definite solution problem was solved by groundwater modeling software FELOW to establish the groundwater numerical model of study area.
The total salt concentrations in the reclaimed water from the Huangcun sewage treatment plant ranges from 680 and 926 mg/L with an average of 803mg/L, lower than the water quality standards for farm irrigation. Therefore, the salt harm of reclaimed water irrigation is low. The sodium adsorption ratio (SAR) is 2.84-3.18 with an average of 3.01, which is in the range of irrigation water (0-10). It could be concluded that the reclaimed water irrigation is less likely to result in secondary salinisation. The concentration of COD5 and BOD is 39.9 mg/L and 19.7 mg/L respectively, which meets the standards for farm irrigation water but outrange the surface water standard III. The chloride content varies between 102 and 134 mg/L with an average of 118 mg/L, which also meets the standards for farm irrigation water and the surface water standard III. The LAS content is 0.54 mg/L, which meets the standards for farm irrigation water but outrange the surface water standard III. Heavy metal content of the reclaimed water is quite low, meeting the standards for farm irrigation water and the surface water standard III, and will not cause heavy metal pollution to soil and agricultural products. Results from Yang et al. [10] showed that the leachate concentration of As, Cd, Cu and Pb is lower than the Groundwater Quality Standards I , and suggested that reclaimed water irrigation would not result in those heavy metals pollution to shallow groundwater under reclaimed water leaching.
Initial condition was based on the monitoring data of shallow groundwater level in June 2004. The initial water level of unconfined and confined aquifer was obtained with interpolation and extrapolated method. Taking one month as time step, the simulation period was from June 2004 to June 2007. Through the repeated adjustment of parameters and groundwater budget, the groundwater system of study area was identified and verified to clarify the hydrogeological settingˈ model structure, parameters and groundwater budget items. At the end of the simulation period (June 2007) the calculated and measured water level of shallow aquifer fits well (Figure 1). The model could basically meet the accuracy requirement, satisfy the hydrogeological conditions and reflect the dynamic performance of groundwater system. So this model could used to predict the water level. B. Scenario Prediction The impact of reclaimed water irrigation on groundwater quality is related to the antifouling capability of unsaturated zone. The nitrogen and phosphorus pollution to groundwater could be prevented if the aquitard in the unsaturated zone is over 6-8 m. Henceˈthe groundwater depth of should be more than 6 m in the reclaimed water irrigation area. The four scenarios are assumed with groundwater pumpage for agriculture decreases by 25%, 50%, 75% and 100% and substituted by reclaimed water in the BIA. The trend of groundwater level to 2015 and 2025 is predicted. The average annual precipitation from 1990 to 1999 is employed as precipitation while ignoring the change of precipitation
The main form of nitrogen in the reclaimed water is NH4-N and organic N. The NH4-N accounts for 90% of the total inorganic N content, and the left is mainly NO3-N. There is only Kjeldahl nitrogen index in the “Nation Water Quality Standard for Farm Irrigation”. The total nitrogen in reclaimed
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recharge coefficient induced by water level change. Industrial and agricultural water consumption maintains the same in 2007. The initial water level bases on the monitoring data at the end of 2009. The results from the simulation show the scenario 2, i.e., reducing the groundwater pumpage by 50%, would make the water level rise and the groundwater depth commonly more than 8 m in the BIA after 5-year recovery. Sequentially after 10 years the water table would keep on rising and the groundwater depth still more than 6 m (Figure 2). Hence the scenario 2 is the most reasonable for the reclaimed water utilization in the area with the minimal groundwater depth in 2020.
V.
CONCLUSIONS
Agricultural water consumption usually accounts for a great proportion in agricultural areas. Instead of groundwater pumpage, utilization of reclaimed water is an effective approach to alleviate groundwater resources depletion. According to the study in the BIA, Daxing, Beijing, the water quality of reclaimed water is suitable for irrigation. The groundwater depth should be over 6 m in the reclaimed water irrigation area. Based on the numerical simulation results, when groundwater pumpage reduces by 50% while the reclaimed water used, the water table could maintain the minimal groundwater depth in 2020. REFERENCES J. T. He, Z. L. Shen ZL, “Trends of Reclaimed Water Infiltration Recharge,” Chinese J. Nature, vol 32, pp. 348-352, 2010. [2] J. Guo, Y. Z. Peng, “Research advances in removal and transformation of trace organic pollutants during wastewater treatment process,” Modern Chemical Industry, vol 37, issue S1, pp. 65-69, 2007. [3] B. Y. Ammary, “Waste water reuse in Jordan : present status and future plans,” Desalination, vol 211, pp. 164-176, 2007. [4] D. Bixio, C. Thoeye, J. De Koning, D. Joksimovic, D. Savic, T. Wintgens, T. Melin, “Waste water reuse in Europe,” Desalination, vol 187, pp. 89-101, 2006. [5] T. Asano, J. A. Cotruvo, “Groundwater recharge with reclaimed municipal waste water: health and regulatory considerations,” Water Research,vol 38, pp. 1941-1951, 2004. [6] A. N. Angelakis, M. H. F. Marecos Do Monte, L. Bontoux, and T. Asano, “The status of wastewater reuse practice in the Mediterranean basin: need for guidelines,” Water Research, vol 33, pp. 2201-2217, 1999. [7] C. G. Li, “Reference of America's Sewage Recycling,” Public Utilities, vol 23, issue 2, pp. 25-28, 2009. [8] D. Bixio, C. Thoeye, T. Wintgens, A. Ravazzini, V. Miska, M. Muston, H. Chikurel, A. Aharoni, D. Joksimovic and T. Melin, “Water reclamation and reuse: implementation and management issues,” Desalination, vol 218, pp. 13-23, 2008. [9] Z. Y. Chen, Y. Wang, J. Liu, W. Wei, “Groundwater changes of selected groundwater systems in northern china in recent fifty years,” Quaternary Sciences , vol 30, issue 1, 115-126, 2010. [10] J. Yang, Y. M. Zheng, T. B. Chen, Z. C. Huang, J. F. Luo, H. L. Liu, W. Y. Wu [11] “Leaching of heavy metals in soil column under irrigation reclaimed water :a simulation experiment,” Geographical Research, vol 25, issue 3, 499-456, 2006.
[1]
Figure 1 Observed and calculated water table in Qingyundian
Figure 2 Groundwater depth in 2020 following the scenario 2
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