PREWORKS FOR A FUTURE IWRM - MONITORING OF WATER RESOURCES IN NAM ĐỊNH PROVINCE

LÊ THỊ LÀI¹, J. KASBOHM², NGUYỄN ĐỨC RỠI¹,
ĐOÀN VĂN CANH³, ĐỖ VĂN BÌNH³

¹Institute of Geological Sciences; ²Greifswald University & geoENcon Ltd.;
³Hà Nội University of Mining and Geology

Abstract: In the time period from 2002-2004 and 2006-2008, more than 1000 measurements of water quality were carried out on the following parameters: COD, BOD, NH₄, NO₂, NO₃, TDS and selected heavy metals.

The results clearly revealed that the groundwater of the Holocene aquifer in most investigated locations is highly contaminated by iron, with a high content of salinity. Also, water from the Pleistocene aquifer shows a higher concentration of ammonia; the water is free from NH₄ only in a small area along the coastal line from Nghia Hung to Hai Hau. The salinity in water of the Pleistocene aquifer is also a serious problem, especially in the northeastern part of the province. The degree of water level in the coastal area is observed. This downward trend may reflect an unsustainable extraction regime of the groundwater.

A monitoring plan for groundwater level and salinity trends is recommended in addition to the existing national observation wells.

The surface water resource, such as water from Red River, Day River and Ninh Co River and from lakes and ponds in the Nam Định City is impaired mostly by TDS, COD, BOD₅, and pathogens (coliforms) compared to TCVN 5842- 1995 A. A river water quality monitoring plan for characterizing the water quality using diatoms is recommended as a biological method.

I. INTRODUCTION

The IWRM-MoST-Nam Định project is a part of the Research Project IWRM-Vietnam. It is a collaboration between the Greifswald University, the Frauenhofer Research Institute (FhG UMSICHT), and the companies MOSKITO-GIS GmbH and Iaks GmbH, Germany and the Institute of Geological Sciences, VAST, Việt Nam. The project is funded by the German Federal Ministry of Education and Research (BMBF) and MoST, Việt Nam, for a period of from 2006 to 2009.

Nam Định Province has high potential in water resources with a dense river and stream network, an annual average rainfall of 1,700 to 1,800 mm, and also a groundwater reserve with an estimated exploitation potential of 203,453 m³/day. But, these water resources are more and more impaired due to the rapid growth of population, the progress of urbanization and the uncontrolled waste water discharge into the nature.

Pre-investigations to get basic data for designing a water quality monitoring program are the frameworks of the IWRM-Nam Định-MoST Project.

In order to identify the elements, which may impair the water sources, surface water as well as groundwater, in the time period of 2002-2004 and 2006-2008, more than 1000 water samples were analyzed chemically and biologically. Additional data about water levels are collected from national monitoring wells.

This paper presents the results of the water quality assessment. Based on this data, a concept for water quality monitoring program for Nam Định Province is recommended.

II. OVERVIEW OF WATER RESOURCE IN NAM ĐỊNH PROVINCE

1. Surface water

As Nam Định is situated in the Red River delta, the natural drainage system is well-developed and dominated by the Red River along with its tributaries as Đào, Ninh Cơ and Đáy rivers. The river network inside Nam Định province consists of ca. 530 km, with a stream density of 0.33 km/km². Additionally, there are ca. 7,120 ha of lakes and ponds and the Xuân Thủy wetlands bio-reserve, a member of the Ramsar International Convention on Wetlands with a natural area of ca. 7,100 ha [1]. Therefore, the province contains a high potential in surface water. In Table 1, the maximum and minimum average of river water discharge at different locations in Nam Định province are presented in order to give an overview about the surface water potential in this region.

Table 1. Average water discharge from the Red and Đào Rivers

River and observed location	August( Qmax m^3/s)	February(Qmin m^3/s)
Red River (observed at Phú Hào)	3,800	450
Đào River (observed at Nam Định)	2,010	260

2. Groundwater

The Red River Delta is one of 6 important hydrogeological regions in Việt Nam. In this region, groundwater mostly exists in loose sediments. There are five available aquifers in this area [1-3], but only two of them play an economic role as groundwater sources: the Holocene aquifer in the Hải Hưng Formation (Q₂ hh) and the Pleistocene aquifer in the Hà Nội Formation (Q₁^2-3 hn). The main hydrogeological feature of the region is briefly summarized according to data published in [2, 3] and shown in the Table 2.

Table 2. Hydrogeological character of water-bearing formations in the Nam Định area

Age	Formation	Thickness (m)	Lithology	Water table	Discharge (l/s)	Water type
Holocene	Thái Bình (Q2 tb)	2-28	Sand, silty clay, clay containing fauna and plant remains	0.5-3	0.05-1.45	Na-Mg-HCO3-Cl
	Hải Hưng (Q2 hh)	1.3-27.5	Fine sand, silty sand, silty clay, interbedded with sand lenses	0.5-3.4	0.5- 5	Na-HCO3-Cl
Pleistocene	Hà Nội (Q1^2-3 hn)	10-50	Quartz sand, grit and pebbles containing polymictic pebbles	0-2.5	> 5	Na-HCO3-Cl
Pliocene	Vĩnh Bảo (N2 vb)	35-85	Fine and medium sandstone containing pebbles, siltstone and clay shale	0.6-1.2	< 12	HCO3
Triassic	Đồng Giao (T2a đg)	100	Gray and dark gray massive and thick-bedded limestone	0.2	5.78	Na-Ca-HCO3-Cl

The most significant of the hydrogeological situation in this area is the existence of fresh-water lens within the Pleistocene aquifer located in the coastal region. This lens occupies the whole area of Hải Hậu, Nghĩa Hưng Districts, the southern part of Nam Trực, Trực Ninh and some parts of Xuân Trường, Giao Thủy Districts. The water of this lens is of very good quality and is a precious resource for drinking water supply.

III. WATER QUALITY AND RISKS OF WATER QUALITY

1. Surface water quality

Surface water is an essential element in the social life and different economic sectors of Nam Định province. It is used for irrigation, municipal water supplies, and other uses. More than 90 percent of the drinking water supply works in Nam Định have the source from surface water.

Compared the results of 300 surface water sample analyses and the Vietnamese Standard for surface water as supply source for drinking water (TCVN 5842-1995 A), we have identified that water from Red, Đáy and Ninh Cơ Rivers is impaired mostly by TDS, COD, BOD₅, and pathogens (coliform). In Figures 1, 2 and 3, the water quality of the Red, Đào and Đáy Rivers are presented concerning the parameters TDS, COD, BOD₅. In the figure 4 the coliforms in the water of some lakes of Nam Định City are shown. Total coliform and fecal coliform are the indicators used to determine sanitary quality of water sources.

Figure 1. Water quality of the Red River (data in mg/l).

Figure 2. Water quality of the Đào River (data in mg/l).

Figure 3. Water quality of the Đáy River (data in mg/l).

2. Groundwater quality

The Holocene aquifer (qh) is in contact with the surface without a confining layer. So it has a direct relationship with the surface and stays under interaction with human activities. Therefore the water in this aquifer may be affected through different pathways from the surface. Results from our investigation from 2002-2008 (Tab.3) show that the groundwater of the Holocene aquifer in Nam Định is widely contaminated by COD and BOD₅, iron and ammonia, while the nitrite content is not a dangerous pollutant [2, 3]. However, the fact that a number of analyzed samples show a nitrite concentration exceeding WHO’s guideline is a valid reason for finding a solution in the near future, in order to avoid the implicit dangers for human use [2]. Also the high salinity in this shallow groundwater source is a serious problem for a safe water supply for domestic use.

The top 6 pollutants (COD, BOD₅, NO₂, NO₃, NH₄ and Fe) are responsible for over 30% (COD) 45% (BOD₅), 60% (NH₄) and 75% (Fe) of analyzed water samples.

Up to now, an effective waste water treatment system exists neither in craft settlements nor in the industrial zones. Untreated waste water flows directly into the nature. In addition, because of a very high population density in the craft settlements, many ponds were filled up with waste to make place for production. These are some of the main pathways for pollution in this shallow groundwater source.

Table 3. Average content of some environmental parameters in water of Holocene and Pleistocene aquifers in Nam Định Province

Value	Parameter (mg/l)
	BOD5	COD	pH	NO2	NO3	NH4	Fe
Holocene aquifer
Max	24.0	78.6	8.03	13.5	12.4	176.4	26.3
Min	2.6	5.1	6.55	0.01	<0.1	0.01	0.02
Mean	9.0	26.5	7.11	1.4	1.2	51.3	6.18
Pleistocene aquifer
Max	114.0	174.0	8.0	12.8	9.5	75.7	-
Min	0.6	2.4	6.55	0.01	0.01	0.01	-
Mean	9.3	24.6	7.0	1.14	0.75	8.65	-
VN-Standards TCVN 1995*	<4	10	6.5-8.0	0.1	10.0		5.0
WHO**				0.1	10.0		0.30

* Vietnamese guideline for groundwater

** World Health Organization Guideline for drinking water

The Pleistocene aquifer, covered by a confining layer (qh vp), is only in contact with the surface and upper aquifers via “hydrogeological windows”, e.g., regions near the Red River. In both rainy and dry seasons, the Red River is the regular natural supplemental water source. The risk of pollution spreading through this pathway is therefore very high. However, the increase of ammonium concentration in the Pleistocene aquifer at areas near the Red River can not be interpreted by this mechanism, because on one hand, the ammonium concentration in Red River is very low (<1 mg/l), while on the other hand, there is a clear proportional relation between the salinity and ammonium concentration in Pleistocene aquifer.

The pollution infiltration at a confined aquifer in areas with thick confining cover is small, since the water compression level in this aquifer is always higher than in the upper ones. The intensive water exploitation, however, has a strong effect on the water level decrease, which may creates the vertical gradient speeding up of the convection for pollution infiltration. In our four studied seasons, at some points, the western area of Nghĩa Hưng District has the ammonium concentration increasing significantly with time. This area is also the place where the groundwater in the Pleistocene aquifer was the most intensively exploited in the last ten years. This inappropriate water exploitation can be targeted as the reason for the ammonium pollution in groundwater in this aquifer [3].

Considering the sedimentary cross section in the east-west direction from Vụ Bản through Nghĩa Hưng to Hải Hậu [3], the sedimentary thickness of confining cover near Vụ Bản is very thin with the value of only 10 to 25 m, while near Hải Hậu it increases from 30 to 80 m. This is clearly the reason for the organic compound and ammonium pollutions in Holocene and Pleistocene aquifers in the northeastern and northern parts of the province.

At the moment, the Pleistocene aquifer along the seashore of Hải Hậu and Nghĩa Hưng districts is still in good quality: free of ammonium and other nitrogenous compounds. It serves as the water supply for over 90 percent of residents in the coastal region. Most of the residents in this area get the drinking water from individual private water wells (called as UNICEF wells).

However, in terms of biochemical oxygen and chemical oxygen demand, the water in this area has already been in the early stage of pollution.

IV. IWRM-MONITORING PLAN

The goal of an IWRM-monitoring plan in Nam Định is aiming to provide scientifical data and informations on the important chemical, physical and pertinent biological characteristics of water, from the major rivers and major aquifer systems of the province.

The objective of such plan is to identify and document the conditions of Nam Định water resources, to document potentially problematic areas and to identify the water quality as well as the water level changes over the time.

1. Surface water quality monitoring by using diatom as bio-indicator

Because of its sensible reaction on the environmental change, diatoms are used for the characterization of the biological surface water quality in Europe since beginning of 20^th Century, to estimate the trophic state, saproby system as well as other characteristic parameters like temperature, oxygen content or pH value of lentic or flowing water bodies. In frame of the IWRM-Nam Định Project, an investigation of surface water quality in some water course of the Nam Định province was carried out in the 2006-2007 years by using diatoms with the goal of transferring a simple biological method from Europe to Vietnam, for the evaluation of the surface water quality. The method and results are described in details in [4]. It shows that the evaluation of surface water quality based on the distribution and concentration of different diatom taxons is especially suitable for flowing water bodies in Nam Định.

As an example, saproby indices of diatoms from the water samples of Dao River were estimated. The calculation shows the water of Dao River is characterized by sabroby levels of β-mesosaprobic and α-β-mesosaprobic. According to [5], the water quality of the Đào River is in the categories II and II-III. This is comparable with the water quality evaluation according to the chemical parameters.

Therefore diatoms are recommended for the surface water quality monitoring, especially for the river water bodies in Nam Định. The identification of saproby and trophy indices provide a rapid and comprehensible evaluation of the water body, especially concerning its nutrient situation.

2. Salinity monitoring

Our groundwater quality studies from 2002 to 2004 and from 2006 to 2008 show that the problem of high concentration of iron, ammonia, and salinity in groundwater in both the Holocene and Pleistocene aquifer olocene is a serious issue for Nam Định.

Our goal in developing a groundwater quality monitoring program is to answer the question: what are the seasonal and long-term trends in groundwater quality especially the variation of the salinity? How is the boundary of fresh water and brackish water shifted? How could mirrored in future any water management activities in frame of IWRM-processes in the groundwater resources? Is a recharge of groundwater by methods of rain harvest or using of in future treated waste water also a possible option to improve the groundwater resources and its quality?

As in the Nam Định area, the monitoring system has to be designed for both aquifers, Holocene and Pleistocene ones. However, extra attention should be paid to the Pleistocene aquifer because this is the main one where most of the water is being exploited.

A national monitoring wells system always exists in Nam Định to observe the long-term change in groundwater level. But the wells are very sparely distributed; many of them have been degraded, damaged or ineffective. In the future, these problems have to be solved in order to guarantee comprehensive monitoring and accurate data collection. A well system needs to be completed, which is based on the following foundations and principles:

1. Arranging the monitoring wells perpendicularly to the fresh and brackish water boundary. This boundary is determined on the basis of geophysical data (measured by resistance method or sampling to analyze water quality). These monitoring wells are arranged perpendicularly to the brackish/fresh water boundary. The wells are arranged in straight lines.

2. For the observation of groundwater dynamics, the dynamics of surface water (river water) must also be taken into consideration, therefore a station for monitoring the Red River water at Ngô Đồng is recommended.

Following works have to be implemented in the coming time:

1. The degraded wells from the national observation well system (with broken concrete bases, unclear information table, vandalized geodesic marks, stolen protective lids and tubes on borehole ...) need to be repaired and maintained.

2. Adding 7 monitoring wells to the area of Ý Yên, Hải Hậu, Nam Ninh, Xuân Trường, and Giao Thủy. Among these: 1 in Ý Yên, 3 in Hải Hậu, 1 in Nam Trực, 1 in Xuân Trường, and 1 in Giao Thủy, to observe the water salinity and the movement of the brackish/fresh water boundary.

3. Geophysical resistance measurement of the wells must be carried out twice a year, in May and in November.

4. Sampling and analyzing water samples from observation wells twice a year, in May and in November.

5. Well data documentation and analysis.

V. CONCLUSION

The problem on the trends of groundwater quality, especially the variation of the salinity and the movement of fresh/brackish water boundary, is a large task for Nam Định. The national well system needs to be upgraded. In addition, 7 other observation wells have to be newly set up, in order to be efficient and effective in generating data that serve its needs in management decision. This program should also include surface water.

Acknowledgements: The authors would like to thank the Federal Ministry for Education and Research ( BMBF) and the Ministry of Science and Technology of Việt Nam for the financial and logistical support (41/2007-NDT).We would like to express our special thanks to the authorities and colleagues of DOST and DONRE of Nam Định and Yên Xá People Committee.

REFERENCES

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2. Đoàn Văn Cánh, Lê Thị Lài, Hoàng Văn Hưng, Nguyễn Đức Rỡi, Nguyễn Văn Nghĩa, 2005: Groundwater resources of Nam Định province. J. of Geology, B/25 : 31-43. Hà Nội.

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