Journal of Geology, Series B, 29/2007, p. 59‐68 

GROUNDWATER INVESTIGATION: APPROACH TOOL FOR
THE INTEGRATION WATER RESOURCE MANAGEMENT
IN NAM ĐỊNH PROVINCE
LÊ THỊ LÀI
Institute of Geological Sciences, VAST, Hà Nội

Abstract: In the Nam Định Province only two available aquifers play the
economic role as groundwater sources: the Holocene aquifer in the Hải Hưng
Formation (Q2 hh) and the Pleistocene aquifer in the Hà Nội Formation (Q12-3 hn).
The depth of Holocene water level is about 3-4 m from surface. The unconfined
Holocene aquifer has a maximum specific capacity of 4.5 l/s [7, 9]. The depth of
the confined Pleistocene aquifer is increasing in direction toward the sea from 30
to 35 m in the North until 80-90 m in Hải Hậu District, in some places even to
100 m. The potential exploitation reserve of Pleistocene fresh water lenses in
coastal areas is estimated as 203,453 m³/day [4, 7]. Forecasting exploitation
reserves of well field distributed along the Ninh Cơ River is 145,000 m³/day and
72,000 m³/day within Nghĩa Hưng District distributed along the Đáy and Ninh Cơ
Rivers.
Especially, in Vụ Bản, Mỹ Lộc and Ý Yên Districts, the Holocene aquifer
contains mostly brackish water. Groundwater of the Holocene aquifer
in Nam Định Province is widely contaminated by COD and BOD, iron and
ammonia. Generally, the Holocene aquifer has only a small potential for water
supply. The northeastern part of Pleistocene aquifer is characterized mainly by
exceeded NH4-values.
In Nam Định, Vụ Bản and Giao Thuỷ Districts have not any available natural
groundwater reserves for a safe water supply in Holocene and Pleistocene
aquifers. These districts have to use surface water as the only source for their
water supply.
The groundwater level change is a serious problem in Nam Định, and a

sustainable water resource exploitation is highly recommended.
 
I. INTRODUCTION

Nam Định has a total area of 1,6413 km2 and 225 communes, with 74 handi craft
settlements and 3 ongoing industry zones, both in Nam Định City and in the rural area. As a
result of the last 15 years of strongly development of industrial and aquaculture production,
the economical situation in the province has been significant changed. Even the main income
in the province is from agriculture, but the industry plays at present important role in the
society and economy. The population is of 1,935,000 inhabitants (2005); with an actual
population growth rate of 0.9 % a population of 2,040,000 is expected for the year 2010.
The relief of the province´s teritory is flat and even at 0.2 - 3 m above the sea-level with
only some areas in the northwestern part reaching 7-100 m above sea-level. The periodical
wet tropical climate of Nam Định Province is characterized by a total annual rainfall of 1,400
- 1,750 mm and mean monthly temperatures of 18 - 29°C. As the province is situated in the
Red River (Sông Hồng) delta the naturally drainage system is well developed and dominated
by the Red River and its tributaries as Đào, Ninh Cơ and Đáy Rivers.


The sewerage is one of most serious problems, because it in fact does not exist. The waste
water is drained by canals and ditches to the on-site preflooder.
For the future development of Nam Định Province the technology and know-how demand
is focused on water resource management and planning, water supply, water distribution,
sewerage, and environmental monitoring [6].
Based on the results of former ground water investigation works in the Red River Delta
and especially in Nam Định, such as: Đoàn Văn Cánh, Bùi Học [2], Lê Thị Lài & Đoàn Văn
Cánh [7] etc. a summary of main important features of groundwater in this area is given as
support tool for a further integrated water resource management in the province. Additionally,
some results on ground water quality investigation especially in Pleistocene aquifer as framework for the development of water quality monitoring system will be reported briefly.
II. GROUNDWATER RESOURCES IN NAM ĐỊNH PROVINCE

1. Main groundwater aquifers

The Red River Delta, building up the Red River and Thái Bình River System, which
extends from Việt Trì City to the East Sea, is one of 6 important hydrogeological regions in
Việt Nam [11, 12]. It covers an area of 17,000 km2, that is a part of the Hà Nội neotectonic
depression. The tectonic movement of the Red River deep-seated fault system is one of the
most dominant geological process in the area. The basin is filled up mainly with deltaic
sediments of the Red River System and marine transgressional sediments of from coarse- to
fine-grained materials, such as pebble, gravel, sand and silty, clay, silty clay. The relief is
declined from northwest to southeast. That means also the groundwater flow direction too.
The elevation varied between 2-10 m. The Nam Định area is situated in the most Southeastern
part of this basin and has a elevation of about 2 m.
Groundwater in this hydrogeological area exists mostly in loose sediments. There are five
available aquifers in the study area [4], but only two of them play an economical role as
groundwater sources: the Holocene aquifer in the Hải Hưng Formation (Q2 hh) and the
Pleistocene aquifer in the Hà Nội Formation (Q12-3 hn). The main hydrogeological feature of
the region is briefly summarized according to data published in [4, 7, 9] and shown in the
Table 1.
The Holocene aquifer is widespread in the province, the upper part ocures in the Thái
Bình Formation (Q2 tb), and the lower part in the Hải Hưng Formation (Q2 hh). The lithography is

characteristic by sand, silty clay, clay containing fauna and plant remains and fine sand, silty sand,
silty clay, interbedded with sand lenses. The depth of water level is about 3-4 m from surface. The
Holocene aquifer is unconfined one with a maximum specific capacity of 4.5 l/s [7, 9].

The Pleistocene aquifer is distributed all over the province, but is not exposed on the
surface. The lithological composition of the aquifer consists mainly of quartz, sand, gravel
and pebbles with a little amount of polymictic pebbles. The aquifer covers directly Neogene
sediments in the major area of province; only in some localities in the west it covers limestone
and Proterozoic metamorphic rocks. According to the drilling profile, the depth of the aquifer

is relatively stable. Following a cross-section with a northwest-southeast direction, one can
see that in the northwestern part (it means the southern part of Vụ Bản District) the depth is
smallest (30-35 m), to the middle part of Hải Hậu District the aquifer deepens to 80-90 m, in
some places even to 100 m (Fig. 1). The thickness of the aquifer increases in approaching the
sea, too. In the northwestern part belonging to the south of Ý Yên and Vụ Bản Districts, the
thickness of the aquifer is only 10-15 m. Towards, the sea it gradually increases, locally
reaching 30-40 m. The average thickness of the aquifer is 45 m.


Table 1. Hydrogeological character of water-bearing formations in the Nam Định area

Age

Formation

Holocene

Thái Bình
(Q2 tb)

Hải Hưng
(Q2 hh)

Pleistocene

Hà Nội
2-3
(Q1 hn)

Pliocene


Vĩnh Bảo
(N2 vb)

Triassic

Đồng
Giao
(T2a dg)

Thickness Lithological composition Water Discharge
(m)
(l/s)
table
2-28

Sand, silty clay, clay
containing fauna and
plant remains

Water
type
NaMgHCO3Cl

0.5-3

0.05-1.45

0.53.4


0.5- 5

NaHCO3Cl

10-50

Quartz sand, grit and
pebbles
containing
polymictic pebbles

0-2.5

>5

NaHCO3Cl

35-85

Fine
and
medium
sandstone
contains
pebbles, siltstone and
clay shale

0.61.2

< 12


HCO3

100

Gray and dark gray
massive and thickbedded limestone

0.2

5.78

Na-CaHCO3Cl

1.3-27.5

Fine sand, silty sand,
silty clay, interbedded
with sand lenses

The Pleistocene aquifer is a confined one; its piezometric level raises 40 m to 60 m and the
static level is about 0.0-2.5 m from the ground surface. Formerly, in the rainy season, water of
the wells in coastal areas reaching this aquifer overflows onto the surface [4,7,9].

2. Groundwater potential and water level change

The most significant of the hydrogeological situation in this area is the existence of freshwater lenses within the Pleistocene aquifer located in the coastal region. These lenses occupy
the whole area of Hải Hậu and Nghĩa Hưng Districts, the southern part of Nam Trực, Trực
Ninh and some parts of Xuân Trường, Giao Thủy Districts. The water of these lenses is of
very good quality and a precious resource for exploitation [4, 7]. Using Visual Modflow 2.8.2

the exploitation potential reserves of these fresh groundwater lenses in the coastal area has
been evaluated The potential exploitation reserves is estimated as 203,453 m3/day. They are
formed from static elastic reserve of 177,770 m3/day (87.37%), with the leakage of 25,683
m3/day (12.63 %) [4, 7].
Furthermore, a possibility of large scale exploitation by concentrated well-fields has also
been forecasted. Results of forecasting can be applied to establish concentrated groundwater
exploitation master plan for Nam Định City, coastal resort water supply and fresh-water
export. Forecasting exploitation reserves of well field including 69 wells distributed along
the Ninh Cơ River is 145.000 m3/day. Forecasting exploitation reserves of well field including
40 wells within Nghĩa Hưng District distributed along the Đáy River and Ninh Cơ Rivers
is72,000 m3/day. Sources forming the exploitation reserves include mainly static elastic
reserves occupying 80-90% of total production of the well field [4, 7].
 


Figure 1. A NW-SE cross section passing the national monitoring
netwok wells from Vụ Bản to Hải Hậu
The Holocene aquifer as mentioned has a specific capacity from very small to 4.5 l/s and
hence a medium water potential is expected for this. In some area of the province, where the
water quality is as good as the Việt Nam standard VN-TCVN-1995 for drinking water, is may
satisfy for water supply in small scale suburban region and districts centres or for small dug
wells in rural area, but in many region in the province, especially in Vụ Bản, Mỹ Lộc and Ý
Yên Districts, the Holocene aquifer contains mostly brackish water, so that the use of this
water resource for fresh water supply is very limited.
The monitoring data from national monitoring well system in the Red River Delta in the
last 14 years from the Division of Hydrogeology and Engineering, North Việt Nam show,
that in the region, where ground water is exploited intensively, such as Hà Nội, Nam Định and
Hải Phòng, the water level is changed significantly. At the national monitoring well 109a, for
example, in Hải Hậu, Nam Định, the average water level from Pleistocene aquifer decreased
from ca. -1.0 m (1996) to ca. -8.0 m (2006). It is estimated for July 2007 of ca 8.92 m under

the surface respectively, and this will be expected for July 2007 of ca. 9.10 m under the
surface. That means 0.28 m deeper (Fig. 2).

III. GROUNDWATER CHEMISTRY AND POLLUTION

Long-term stational monitoring data from the National Monitoring Well Network and
results of chemical analysis of groundwater from different ground water investigation projects
implemented by the Hà Nội University of Mining and Geology and Institute of Geological
Sciences show, that the chemical composition of this groundwater changes insignificantly by
dry season and rainy season.
The chemical type of brackish groundwater in rainy season is as follow:


Figure 2. Water level change from 1994 - 2006 estimated at the national monitoring
well No.109 a, Hải Hậu, Nam Định (data from the Division of Hydrogeology and
Engineering, North Việt Nam)

M1.08
In dry season:

M1.23
The chemical type of fresh groundwater from lenses in rainy season:

M0.39
In dry season:

M0.38
Results from former investigation show that the groundwater of the Holocene aquifer in
Nam Định is widely contaminated by COD and BOD, iron and ammonia, while the nitrite
content is not a dangerous contamination. However, the fact that a number of analyzed

samples showing a nitrite concentration exceeding the WHO’s guideline is a real reason for
finding a solution in the near future in order to avoid the implicit dangers for the human use of
this “unsafe” water [7]. Also the high iron and ammonia content in this shallow groundwater
source is a serious problem for a safe water supply for domestic use.
Some estimated environmental parameters from Holocene and Pleistocene aquifer resulted
from former investigations is given in the Tab. 2.
It is possible to see that the NH4+-concentration in water of Pleistocene aquifer ranges from
0.01 to 75.7 mg/l with average of 8.65 mg/l. It is recognized, that water samples originate
from Northeastern part of the province has a higher NH4+concentration (Fig. 3). From 147
analyzed samples 28.57 % have a NH4+-concentration, lower than the VN-standard, the other


Table 2. Average content of some environmental parameters of Holocene
and Pleistocene aquifer 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

0.1

10.0

0.30


WHO**

* Viet namese guideline for groundwater
** World Health Organisation Guideline for drinking water

70% of samples have a NH4+concentration, exceeding the VN-Standards. Most of polluted
areas are in Giao Thuỷ, Nam Trực and Mỹ Lộc Districts.
The nitrate concentration of groundwater in Pleistocene aquifer is quite low. Among 147
studied samples, there are only a low percentage of samples, which have a nitrate
concentration exceeding the VN-Standard.
The nitrite concentration of water from Pleistocene aquifer is estimated from 0.01- 13.5
mg/l. The variety ranges from 0.05-12.8 mg/l in the rainy season and 0.01-13.5 mg/l in the dry
season. According to VN- standards (TCVN- 1995) about 40% of the studied samples have a
NO2-values exceeding the VN- standards and the WHO- Guideline for drinking water. These
samples with high NO2-values are mostly from Thịnh Long, Yên Định, Hải Anh, Hải Đường,
Hải Giang Communes of Hải Hậu District; Giao Long Commune of Giao Thuỷ District; Trực
Hưng, Trực Đạo Communes of Trực Ninh District; Nghĩa Tân, Rạng Đông, Nghĩa Sơn, Nghĩa
Hùng Communes of Nghĩa Hưng District and Mỹ Hưng Commune in Mỹ Lộc District.
It is shown that groundwater from Holocene and Pleistocene aquifers in Nam Định
contains almost high value of NH4 and organic compound. This value is in water from
Holocene aquifer however much higher than this one in water from Pleistocene aquifer.
The Holocene aquifer (qh) is in contact with the surface without confining layer. It has a
direct relationship with the surface and stays under interaction with human activities.
Therefore the water in this aquifer is strongly effected through different pathways.
Up to now, exists neither in craft settlements nor in the industrial zones an effective wastewater treatment system. Untreated wastewater flows directly in to the nature. Additionally,
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 pollution’s pathways for
the groundwater.



Figure 3. Distribution of NH4-values in Pleistocene aquifer of Nam Định Province
The Pleistocene aquifer, covered by confining layer (qhvp), is only in contact with the
surface and upper aquifers via “hydrogeological windows”, e.g., region near 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 Pleistocene aquifer at areas near the Red River can
not be interpreted by this mechanism. Since, on one hand, the ammonium concentration inRed
River is very low (<1 mg/l), and on the other hand, there is a clear proportional relation between the salinity and ammonium concentration in Pleistocene aquifer.
The pollution infiltration at confined aquifer in areas having 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 strongly effects on the water level decrease, which may
creates the vertical gradient speeding up the convection for pollution infiltration. In the four
studied seasons, at some points in the western area of Nghĩa Hưng District, the ammonium
concentration increases significantly with the time. This area is also the place where the
groundwater in Pleistocene aquifer was the most intensively exploited in the last five years.
This inappropriate water exploitation can be target as the reason for the ammonium pollution
in groundwater in this aquifer.
Considering the sedimentary cross section in the east-west direction from Vụ Bản through
Nghĩa Hưng to Hải Hậu (see Fig. 1), the sedimentary thickness of confining cover near Vụ
Bản is very thin with the value of only from 10 to 25 m, while near Hải Hậu that increases
from 30 to 80 m. This consideration 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.
The Pleistocene aquifer along the seashore of Hải Hậu and Nghĩa Hưng Districts, at the
moment, is still in good condition (Fig. 3-5): free of ammonium and other nitrogenous compounds though ammonium concentration increasing with the time has been detected in Nghĩa
Hưng yet. It is in fact a natural potentiality for regional economic development and inhabitant


Figure 4. Distribution of salinity in Pleistocene aquifer of Nam Định Province


Figure 5. Distribution of Fe-values in Pleistocene aquifer of Nam Định Province
living. In term of biochemial oxygen and chemical oxygen demand, this area however has
already been in the early stage of pollution.


IV. CONCLUSIONS

The groundwater potential in Nam Định is really satisfied for water supply for all purpose.
However, because of its quality, the use of water from Holocene aquifer is very limited. But,
it is very important not to outright reject this shallow groundwater concerning its high iron
and nitrogen content as a fresh-water resource. It is possible that this kind of water resources
could be used effectively by a number of potential industries.
Further more, to have a fully understanding for the problem of water quality in the
province is very important and it needs to develop a cohesive strategy about ‘safe’ water
supply in regional and local basins.
The water level change is a serious problem in Nam Định, and a sustainable water
resources exploitation is highly recommended.
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