Conditions of the surface water and ground water resources in the rural area of the Mekong Delta, Vietnam

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The objective of this paper is the appraisal of the hydrological, hydrogeological, as well as the chemical and microbiological conditions of the surface water and ground water resources of the two study sites. In order to allocate the two study sites into a regional context an intense research on the conditions of the surrounding area was also matter of the survey

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Nội dung Text: Conditions of the surface water and ground water resources in the rural area of the Mekong Delta, Vietnam

Conditions of the surface water and ground water resources in the rural area of the Mekong Delta, Vietnam – exemplary investigations at the study sites An Binh and Hoa An Thomas Nuber1, Harro Stolpe1, Le Anh Tuan2, Vu Van Nam2 1 Environmental Engineering and Ecology, Ruhr-University Bochum, Germany, Univer- sitätsstr. 150, 44780 Bochum, Germany 2 College of Technology, University of Can Tho, Can Tho City, Vietnam 1. Introduction As a consequence of a fast-growing economy the Mekong Delta region is facing severe envi- ronmental problems related to industrial and agricultural activities. These environmental problems include soil reclamation (LE QUANG MINH ET AL., 1997), deforestation (MILLER ET AL., 1999) and water quality problems due to pollution of the water resources by pesticides, herbicides and fertilizers (LE QUY AN, 2000). Besides those anthropogenic impacts on the water resources also climatic and geogenic factors play an important role: severe floodings occur during the end of the rainy season (NGUYEN VIET PHO, 2000), surface water bodies are polluted by acid sulphate soils (LE QUANG MINH, 1996), saltwater intrudes into the surface and ground water bodies from the sea (SIWRMP, 1995; NGUYEN HONG TOAN, 2000). Also ground water is often polluted by high chloride or iron concentrations (DO TIEN HUNG ET AL., 2000). In this context a survey was carried out for the rural areas of the Mekong Delta. The goal of the survey was the appraisal of the water resources in terms of quality and availability in or- der to develop a concept for the rural drinking water supply. In the focus of this survey were two exemplary study sites in the rural area of the Mekong Delta. The objective of this paper is the appraisal of the hydrological, hydrogeological, as well as the chemical and microbiological conditions of the surface water and ground water resources of the two study sites. In order to allocate the two study sites into a regional context an in- tense research on the conditions of the surrounding area was also matter of the survey. 2. Description of the study sites 2.1. General description The investigations were done at the two study sites An Binh and Hoa An. The study site An 1
Binh is located in the suburban area of Can Tho City, whereas the study site Hoa An is approx. 40 km southeast of Can Tho City located in the Province Hau Giang (see figure 1). Both study sites are characterized by an agricultural land use with farms, mainly cropping rice and fruits. Some of the farms maintain small animal husbandries and fishponds. Surface water, rain water and ground water are used for the drinking and the domestic water supply. Many farms and households have small scale tube wells to withdraw ground water. In some cases the waste water is treated with small biogas plants before discharged into the canals. Usually the domestic waste water and waste water from the animal husbandries are dis- charged into the rivers, canals or ponds (see figure 2). Besides the general similarities of the two study sites there are also major differences. In addition to socio-economic differences (e.g. higher living standard in An Binh (see WIENEKE, 2005)) one of the most important differences are the soil-conditions. Here, the study site An Binh is characterized by alluvial clay soils, whereas the study site Hoa An is burdened by acid sulphate soils. This leads to different cropping systems and also to an acidification of the surface water bodies in Hoa An. 2.2. Hydrological conditions The entire Mekong Delta is characterized by a large network of rivers and canals of 10.000 km in length. Those canals are mainly used for irrigation and for transportation of goods and people. The canal system is connected to the open sea. In An Binh the canals are influenced by the tidal regime of the South Chinese Sea. Here, the tidal amplitude is approx. 1.5 m. The study site Hoa An is located in an area where an inter- action of the tidal regimes of the South Chinese Sea and of the Gulf of Thailand eliminate each other. Here, the tidal amplitude is less than 10 cm. Because of its lower elevation se- vere flooding occurs in Hoa An by the end of the rainy season for approx. two or three months. 2.3. Hydrogeological conditions A detailed description of the hydrogeological conditions of the Mekong Delta can be found in HUNG ET AL. (2000). According to HUNG ET AL. (2000) there are five major geological units in the Mekong Delta: Holocene, upper-middle Pleistocene, lower Pleistocene, Pliocene and upper Miocene (see table 1), whereas the ground water use from the upper-middle Pleisto- cene aquifer is prevailing. According to geological profiles of the study site An Binh and Hoa An (see figure 3) the thick- ness of the covering Holocene layer in An Binh is approx. 65 m and in Hoa An about 60 m. 2
At both study sites the Holocene layer is formed as an aquiclude, although with a water satu- rated layer in the first 5 to 10 m below surface. Underneath that Holocene layer is the upper middle Pleistocene aquifer which consists of middle to coarse sand. 3. Methods For the appraisal of the surface water and ground water resources water sampling and analyses regarding the chemical and microbiological conditions were carried out. The inves- tigations were carried out by the end of the rainy season 2003. The parameters and analyti- cal methods are listed in table 2. The results of the analyses were tested on their plausibility performing an ion-balance according to (DVWK, 1992). Also, data on surface water and ground water quality, climatic data and data on ground water levels was collected and evaluated for the surrounding area. Here, a GIS was set-up, various evaluation-methods were used including the illustration with Piper-diagrams (PIPER, 1944) and the ground water classification method according to (FURTAK & LANGGUTH, 1967). The ground water resources of Can Tho City and Hau Giang province were also classified regarding the concentration of the predominant water species. Here, the classification distin- guishes three different ground water types following the Vietnamese standards for ground water TCVN 5944 –1995 (see table 3). The results of the analyses of the surface water sam- ples were compared to the Vietnamese standards for the use of surface water for drinking water purposes TCVN 5942 –1995 (A). Additionally slug & bail – tests for the determination of the hydraulic conductivity of the aqui- fers (Benstöm et al., 2005) and quality tests of the hand pumps were done (Nuber et al., 2005). 4. Results and Discussion 4.1. Ground Water For Can Tho City and Hau Giang province the spatial distribution of the different ground wa- ter types (see table 3) is illustrated in figure 4. The study site An Binh is located in an area where the ground water quality is characterized by a moderate hardness, a moderate chloride content (around the taste limit of 200 mg/l) and a ferrous iron concentration around 2 mg/l. According to the classification method described in chapter 3, it can be rated as ground water type II. Unlike in An Binh, the ground water quality in the area of Hoa An is characterized by a high chloride concentration, a high hardness and a high ferrous iron concentration. According to 3
The classification method described in chapter 3 it can be rated as ground water type III. Those observations can be confirmed by the water analyses taken at the study sites An Binh and Hoa An during the survey (see table 4). In figure 5 the ion-composition of the ground water samples taken at both study sites are illustrated in a Piper-diagram. According to the classification method by FURTAK & LANGGUTH (1967) the ground water in An Binh can be rated as a alkaline-earth water with higher alka- line content with a predominantly hydrogen carbonatic content whereas in Hoa An there is alkaline ground water with a predominantly chloridic content. 4.2. Surface Water As already described in chapter 2.2 the quality of the surface water is generally influenced by the discharge of domestic and industrial waste water, agricultural entries and a high amount of suspended solids as well as fuel residues. In comparison to the ground water situation there are local differences regarding the water quality within Can Tho city and Hau Giang province. But additionally and probably more important there are seasonal differences as well. The surface water at the study sites An Binh and Hoa An are influenced by leachate water from the irrigation ditches of the rice fields. At both study sites the values for the pH, BOD, NH4 and phosphate are conform to the requirements of the Vietnamese standards for the use of surface water as drinking water TCVN 5942-1995 (see table 5). Only the values for COD and the microbiological indicator values E.coli and total coliformes do not meet the re- quirements. At the study site Hoa An the surface water quality is also influenced by the acid sulphate soils (see chapter 2.1) which is the reason for the low pH-values. At both study sites the main problems of the surface water bodies are the high amount of suspended solids and hygieni- cally pollutants. 5. Conclusions and Outlook Regarding the ground water and the surface water quality the two study sites Hoa An and An Binh are typical for the conditions of the rural area of the Mekong Delta. At present, there are substantial local differences within Can Tho city and Hau Giang province in terms of quality and quantity of the available water resources. Thus, the improvement of the rural drinking water supply requires investigations regarding the specific local conditions. For instance, two totally different concepts are necessary for the improvement of the water supply situation at the two exemplary study sites An Binh and Hoa An. 4
In An Binh the usage of surface water should be minimized despite of its suitability for drink- ing water purposes. Here, it can be expected that the surface water quality is going to be worsened because of its close location to Can Tho city. In the future the industrial and agri- cultural influence will grow. Thus, the use of ground water should be emphasized by the con- struction of small centralized ground water treatment plants in which the treatment is adapted and optimized to the ground water quality. In Hoa An the use of ground water for drinking water purposes should be minimized because of the high chloride, high hardness and iron-concentrations. Here, the treatment of the ground water requires a softening and desalinization which could be realized by reverse os- moses or ion-exchange. But those methods are technologically to complex and therefore to expensive for an implementation on a regional scale. In spite of the moderate surface water quality the use of surface water should be considered. Here, the combination of technologi- cally simple but effective methods is possible. One possible treatment scheme could be a flocculation with a rapid filter to eliminate the high amount of suspended solids in combina- tion with a slow sand filter for the decay of organic matter and disinfection. At both study sites and also for the entire Mekong Delta the use of alternative water re- sources (e.g. rain water) should be considered. In this context artificial ground water re- charge or the pure storage of rain water in aquifers over the dry season could be a supple- mentary water resource. Especially in areas where the situation of the water resources is very strained those methods could be applied. But the water resources management and the water supply in the Mekong Delta will remain a challenge in the future. Because of the high population- and economical growth rates it can be expected that the water demand will increase rapidly. Additionally, the impact of waste water on the surface waters will increase. 5
6. Literature Benstöm, F.; Nuber, T.; Stolpe, H.,2005: Determination of Hydraulic Conductivity with Slug and Bail Tests in Small Diameter Wells in the South of Vietnam, in Department of Geol- ogy and Minerals of Vietnam (eds..): Journal of Geology, Series B, No. 25, Hanoi, pp. 58-63. Do Tien Hung; Nguyen Hong Bang; Pham Van Giang, 2000: Availability and Quality of Groundwater Resources, Ministry of Industry, Department of Geology and Minerals Divi- sion of Hydrogeology and Engineering Geology for the South of Vietnam (DHES), Ho Chi Minh City Furtak, H; Langguth, H.R., 1967: Zur hydrochemischen Kennzeichnung von Grundwässern und Grundwassertypen mittels Kennzahlen, Mem. IAH-Congress, Hannover DVWK, 1992: Entnahme und Untersuchungsumfang von Grundwasserproben – DVWK- Merkblatt 128, Parey-Verlag, Hamburg Lam Minh Triet and Nguyen Thanh Hung, 2001: Problems of Drinking Water Supply and En- vironment in Flood-prone Areas in the Mekong Delta, Journal of Environmental Protec- tion. Ministry of Science, Technology and Environment. Hanoi, No. 4-2001 Le Anh Tuan, 2003: Research Proposal – SANSED Project, Work Group Hydrogeology and Water Resources Management, SANSED Workshop, 24th – 29th March 2003, Can Tho University, Can Tho City, Vietnam Le Quy An, 2000 : Bio-diversification and Problemes in Biological Resources Protection, Journal of Environmental Protection, Vol. 8, 6-10 Le Quang Minh, 1996 : Integrated Soil and Water Management in Acid Sulfate Soils – Bal- ancing Agricultural Production and Environmental Requirements in the Mekong Delta, Vietnam, PhD-Thesis at the University of Wageningen, Netherlands Le Quang Minh, Tuong, T.P., Mensvoort M.E.F., Bouma, J., 1997: Contamination of surface water as affected by land use in acid sulphate soils in the Mekong River Delta, Vietnam, Journal Water Management and Ecosystems, Vol. 61, 19-27 Miller, F.,Nguyen Viet Thinh and Dio Thi Minh Duc, 1999: Resources Management in the Vietnamese Mekong Basin. Asian Research Centre on Social, Political and Economic Change, Murdoch University, Western Australia Nguyen Hong Toan, 2000:Vietnam National Mekong Committee and Cooperation for Sus- tainable Development of the Lower Mekong Basin. In: Tran Cao Thanh (ed.) Vietnam and Mekong Subregion Development Cooperation. The Gioi Publisher, Hanoi 6
Nguyen Viet Pho, 2000: Management and Sustainable Development of the Mekong Delta, Journal of Environmental Protection, Vol. 11, 8-11 Nuber, T. and Stolpe, H., 2004: Drinking water Resources in the Mekong Delta - Field Inves- tigations and GIS Visualization, Proceedings of the International Symposium on Geoin- formatics for Spatial Infrastructure Development in Earth and Allied Sciences, 16.09 - 18.09 2004, Hanoi, Vietnam Nuber, T.; Stolpe, H.; Vu Van Nam; Tran Van Ty, 2005: Quality Tests of Hand Pump Wells in the Mekong Delta, in Department of Geology and Minerals of Vietnam (eds.): Journal of Geology, Series B, No. 25, Hanoi, pp. 63-69. Piper, A.M., 1944:A graphic procedure in the geochemical interpretation of water analyses – Trans. Am. Geophys. Union, 25; Washington D.C.,pp 914-928 SIWRMP, 1995: Major Issues in Water Resources Development in the Mekong Delta, Report of the Sub-Institute of Water Resources Management and Planning, Ho Chi Minh City Wieneke, F., 2005: Acceptance Anaylsis of New technologies for Sustainable Water Man- agement and Sanitation – A Case Study of Operating Farm Households in the Mekong, Delta, Vietnam, Disseration, Faculty of Agr., University of Bonn, Bonn Germany World Bank, DANIDA and MONRE, 2003: Vietnam Environment Monitor 2003 – Water, Ha- noi 7
figure 1: provinces, provincial capitals and location of the study sites within the Mekong Delta 8
figure 2: setting of rural areas in the rural area of the Mekong Delta (modified after LE ANH TUAN, 2003) 9
figure 3: geological logs in An Binh (left) and Hoa An (right) 10
figure 4: ground water types of Can Tho City and Hau Giang province 11
80 80 60 60 40 40 Legend: 20 20 An Binh Hoa An Mg SO4+NO3 80 80 60 60 40 40 20 20 80 60 40 20 20 40 60 80 Ca Na+K HCO3 Cl figure 5: piper diagrams for the ground water samples in An Binh and Hoa An in mmol(eq%)/l 12
table 1: geological units of the Mekong Delta (modified after HUNG ET AL., 2000) thickness description symbol lithology stratigraphy (m) 1st aquifer QIV U,T,S 55 – 80 Holocene /aquiclude upper-middle 2nd aquifer QII-III fS-mS, G 15 – 40 Pleistocene aquiclude - U,T 10 – 20 - lower 3rd aquifer QI gS, mS, fS 10 – 60 Pleistocene aquiclude - U, T 10 – 20 - 4th aquifer NII S, G 25 – 120 Pliocene aquiclude - U, T 50 – 120 - 5th aquifer NI S, G 0 – 100 Miocene 13
table 2: Methods Parameters Method ph, temperature, oxygen, On-Site, DIN 38 404 C, WTW-Probes electric conductivity, redox chloride, alkalinity, arsenic On-Site, Titration-method, Merckoquandt, calcium, magnesium, ferrous Iron, manga- On-Site, Reflectometric-method, Reflectoquandt, nese, phosphate, nitrate BOD Off-Site, Dilution-method COD Off-Site, Dichromate-method E.coli, total coliform Off-Site, MPN-method (ISO 9308-2) heavy metals Off-Site, AAS 14
table 3: ground water classification ferrous chloride hardness sulphate ground water types iron [mg/l] [mg/l CaO] [mg/l] [mg/l] Type I < 200 < 80 1–2 2 2 >200 Type III > 600 > 180 >2 < 200 o. > 200 Limit according to 600 180 1 200 TCVN 5944 – 1995 15
table 4: results of the ground water samples (selected parameters) Limits according to Parameter Unit An Binh Hoa An TCVN 5944-1995 pH - 6,5 – 7 6,5 – 6,6 6,5 – 8,5 EC µS/cm 1.000 – 1.300 3.800 – 4.100 no limit specified chloride mg/l 150 – 250 880 – 1.200 600 hardness mg/l 80 – 130 560 – 630 180 ferrous iron mg/l 1,6 – 2,5 6,2 – 7,1 1 16
table 5: results of the surface water samples (selected parameters) Limits according to Parameter Unit An Binh Hoa An TCVN 5942-1995 pH - 6,6 – 6,8 6,0 – 6,6 6 – 8,5 EC [µS/cm] 148 – 220 179 – 250 no limit specified BOD mg/l 1,5 – 2 1,5 – 2