Soil Aquifer Treatment as a Tool for Sustainable Groundwater Use in Hanoi/Vietnam

doi:10.4236/jep.2011.27100

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Journal of Environmental Protection, 2011, 2, 882-887

doi:10.4236/jep.2011.27100 Published Online September2011 (http://www.SciRP.org/journal/jep)

Soil Aquifer Treatment as a Tool for Sustainable

Groundwater Use in Hanoi/Vietnam

Axel René Fischer1, Catalin Stefan1, Kay Silabetzschky1, Peter Werner1, Bui Hoc2

1Institute of Waste Management and Contaminated Site Treatment, Technische Universität Dresden, Pirna, Germany; 2Vietnam As-

sociation of Hydrogeology, Hanoi, Vietnam.

Email: [email protected]

Received June 3rd, 2011; revised July 29th, 2011; accepted August 31th, 2011.

ABSTRACT

Due to the subtropical climate the average annual precipitation in Vietnam is high. Nevertheless it is observed that

groundwater levels in the capital Hanoi have decreased dramatically. As a consequence more and more settlemen ts of

buildings have been registered since the beginning of the new millennium. Reason for this tremendous impact is the

increasing demand of areas and the extensive surface sealing in the course of the industrial development. This paper

describes the “state of th e art” and the develo pmen t of sustainab le so lution s to maintain and even in crease th e declined

groundwater levels in Hanoi.

Keywords: Groundwat er Wi t hdrawal, Groundwater Recharge, Land Subsidence, Settlements

1. Introduction

Water resources in Vietnam are difficult to manage due

to the high levels of precipitations. During the last

decade groundwater was used intensively for different

purposes due to the growing demands of a fast devel-

oping nation. After the reunion of North and South

Vietnam in 1975, the country expanded more and more

to a leader under the crop and vegetable exporting na-

tions. In the course of this development groundwater

extraction became an important factor e.g. for the irri-

gation of coffee plants. For example Dak Lak province

is estimated to produce 405,000 t coffee per year for

the world market [1].

Due to the development of the infrastructure in fast

growing cities settlements of buildings by groundwater

drawdown are a worldwide and also well known phe-

nomenon [2,3]. At first view this should be excludable

in Vietnam because heavy rainfalls occur at least in the

summer time. However, an important degree for the

“water stress” of a country is not the overall rainfall but

rather the ratio of withdrawal to renewable water re-

sources. Although only weak water stress is generally

present in the South Eastern Asian region (ca. 4.8%),

the ratio in Vietnam (about 17% - 18%) is comparable

to Europe [4]. Additionally, the majority of rain fall is

supplied mainly during the rainy season. Therefore,

groundwater levels are fluctuating over the year to a

high extent. The enormous grow of industry in the

capital of Vietnam has influenced its water balance.

Hanoi’s population is estimated to reach five million

inhabitants by 2015 [5]. Groundwater levels in Hanoi

have decreased during the last years resulting in mani-

fold detriments e.g. settlements of buildings [6] and

elevated arsenic levels by vertical drawdown of water

from other groundwater stories [7].

In the course of this development efforts are made to

find sustainable solutions for the megacity Hanoi [8].

Hanoi will quickly develop in the next years which

offers also a chance to find a strategy with sustainable

solutions for a well balanced water economy which

could be also applied to similar cases.

2. State of the Art

2.1 Water Demand and Following Problems

The capital Hanoi is located in northern part of Vietnam.

There are five rivers and more than 100 lakes and ponds

within the city. Red river (northwest and south) and

Duong river (northeast) are the main streams of Hanoi

which serve also as receiving waters (Figure 1).

Beside some small “septic tanks” which have been in-

stalled for the wastewater of private houses Hanoi has no

sewerage system i.e. nearly all industrial and private

wastewaters are directly infiltrated into a recipient e.g.

the Red River. Groundwater levels are changing from

Soil Aquifer Treatment as a Tool for Sustainable Groundwater Use in Hanoi/Vietnam883

Figure 1. Map of Northern Vietnam.

month to month to a high extent due to the heavy rain-

falls.

Most of the rainwater occurs in hot season but more

than the half of this amount is lost by immediate evapo-

ration.

The wastewater is transported through a joint drainage

and sewage system to the water bodies throughout the

city [9]. Figure 2 shows the groundwater levels for wells

in some districts of Hanoi in 1993, 2005 and the sup-

posed levels in 2020, respectively [10,11]. A decrease of

the groundwater levels of up to 17 m in 15 years can be

observed. The intensity of the loss is not uniformly and

depends on the intensity of the groundwater usage in the

related areas.

Overall groundwater usage in Hanoi has increased

during the last years. In an approximately 5 km wide

zone along the Red River, the Holocene and Pleistocene

aquifers are mainly recharged from the river, with the

more distant Pleistocene aquifer predominantly re-

charged by vertical percolation from the Holocene aqui-

fer [12]. Near the beginning of Duong River the subsur-

face is composed of unconsolidated sediments of Pleis-

tocene and Holocene age as described in Table 1. It is

known that some soil layers consist of high permeable

sand fractions which can even connect the different aq-

uifers [13]. The analysis of vertical soil profiles in the

above region reveals a high un-homogeneity of subsur-

face layers caused by the long term development of the

area and by the steady actions of the two rivers (sedi-

ments deposition, changes of flow paths etc). A high

amount of arsenic is mobilized every year from the Hol-

ocene sand and discharged into the Red River [14].

The rapid urbanization caused an impervious pave-

ment of areas. It is known that soil and especially coarse

clay swells to a high extent if it imbibes high amounts of

Figure 2. Groundwater levels in some districts of Hanoi in

1993 (top), 2005 (middle), and 2020 (bottom) (prognosis

based on data from 1993 and 2005).

water [15]. Therefore, withdrawal of water in conjunc-

tion with coverage of possible influents led to a tremen-

dous impact of the geohydrology of Hanoi which has

influenced the static conditions of the soil. Figure 3

shows the surface settlements for 10 different districts in

Hanoi from 2003 to the end of 2006 [16].

Based on monthly monitoring data on groundwater

Soil Aquifer Treatment as a Tool for Sustainable Groundwater Use in Hanoi/Vietnam

884

Table 1. Hydrogeological stratigraphy of Hanoi between Red River and Duong River (near fork of both rivers, [11]).

Layer from top Layers Depth (m)

1 Unconfined Holocene aquifer 2-12 (mean: 6.8)

2 Pleistocen-Holocene 1-23 (mean: 10.2)

3 Semi-confined upper Pleistocene aquifer 2-28.3 (mean: 14.9)

4 Pleistocen impermeable layer 0-19 (mean: 6.4)

5 Confined mid-lower Pleistocene aquifer 21.5-47 (mean: 32)

6 Complex water stored Neogene system

Figure 3. Surface settlements in 10 districts of Hanoi (HCA,

2007).

level and land subsidence, the qualitative assessment of

land subsidence in Hanoi area has shown that:

- The land subsidence has been occurring at all moni-

toring stations

- Average land subsidence rate was nearly constant

over the whole year

- The biggest yearly subsidence rate has been observed

in Thanh Cong (46 mm/year)

Due to these facts a further intensive use of ground-

water is only advisable under the precondition that sus-

tainable methods for groundwater recharge would be

established.

2.2. Geological Conditions and Water Balance in

Hanoi

Hanoi metropolitan area relies mainly on groundwater

for its water supply. Due to the local geogenic conditions

some groundwater stories contain arsenic. The concen-

trations can differ even in a small region [17]. The people

are protected from the hazardous influence of this toxic

compound by the usage of groundwater levels which do

not contain remarkable amounts.

The detailed analysis of vertical soil profiles has

shown a high un-homogeneity of subsurface layers

caused by the long term development of the area and by

the steady actions of the two main rivers (sediments

deposition, changes of flow paths etc).

The existing intermediary impermeable layers situated

in between groundwater aquifers have a sporadic and

inconsistent character and appear in forms of lenses and

very thin layers. A calculation of groundwater replen-

ishment shows that only 5% of the annual precipitation

reaches the aquifer (Figure 4). Main loss is the evapora-

tion fraction (932 mm/a: 58.4%). The rapid urbanization

of Hanoi coupled with impervious pavements of devel-

oping areas and combined with extensive groundwater

withdrawal as sole source for drinking water led to

drawdown and land subsidence. Additionally, weak-

nesses within the internal administration and the lacking

awareness of the future problems prevented to date the

implementation of adequate methods and technologies.

3. Tools for Groundwater Recharge

Artificial groundwater recharge is worldwide a common

measure to secure an increase of groundwater levels. It is

often combined with natural attenuation measurements

i.e. a soil passage of wastewater effluents [18-20]. The

elected techniques depend from the origin of the used

water and comply mainly with the climatic conditions i.e.

the average precipitation. Cheap treatment of wastewater

Figure 4. Water balance in Hanoi (Hoc, 2009).

Soil Aquifer Treatment as a Tool for Sustainable Groundwater Use in Hanoi/Vietnam885

by infiltration into the vadose zone with groundwater

reclamation as a positive secondary effect is usually

made in arid regions like Israel [21]. Fresh water (rain)

for groundwater enrichment is preferred in wet regions

like India [22]. Rainwater harvesting can be managed by

many methods e.g. by using cisterns or settling tanks.

These measurements can be combined with cleaning

systems e.g. constructed wetlands. An important question

is in each case the kind of infiltration of the treated or

untreated water. Table 2 shows advantages and disad-

vantages of several infiltration scenarios. A sustainable

technique has to ensure that fecal coliforms are not de-

tectable or below certain limits. However, very small

values (< 1) of fecal coliform concentrations are only

possible after a lateral movement of about 100 m through

the aquifer [24] (Table 3).

The optimum solution would be a technique which

handles water from different sources e.g. from rain and

wastewater. At present all solutions are only theoreti-

cally feasible and a transformation into real changes

seems to be unlikely. The reason for that is not only the

expenditure. Due to the heavy rainfalls in Vietnam the

resource “water” is unappreciated and the strategy against

growing water demands is still the exploitation of the

groundwater. A rethinking of the people is necessary

and it must be achieved upon a political way. Only in the

long term it is feasible that the taxation system could be

renewed and taxation revenue could support the con-

struction and maintenance of sewage and drainage infra-

structure [9].

4. Conclusions

The capital Hanoi has falling groundwater levels and

subsequent damages like land subsidence. The lack of

water is enforced by the fact that surface sealings prevent

the heavy rainfalls during summer time from reaching

the groundwater. The frequent floods during the rainy

season are also amplified by that. First efforts have been

made to find sustainable solutions which take into ac-

count the fast growing need of areas. It is essential that

quality of reclaimed wastewater has to fulfill certain

health standards. Experiences from other wastewater

reclamation systems show that quality of the reclaimed

water is not the problem at all. However, all these efforts

are made without enough revenue for a complete renova-

tion of the wastewater systems. A solution of the prob-

lem could be a certain tax which should be allocated to

sewage, drainage and wastewater treatment in Hanoi.

However, this is a question where the answer lies in the

social and governmental levels.

Table 2. Comparison of selected recharge scenarios.

Criteria Recharge ponds Shaft wells Infiltrations wells

Hydrogeological condi-

tions

−

possible only in shallow

impermeable layers

+ +

suitable in some districts

+ +

recharge of confined and

unconfined aquifers

Land use

−

large parcels needed

mostly in green areas

less area than recharge

ponds

+ +

less land use

also inhabited zones

Costs + +

using existing ponds

can be dug manually

−

high drilling costs

Infiltration water quality

+ +

clogging prevention by sand

layers

aquifer clogging to be

avoided

−

higher quality of infiltration

water

Table 3. Cleaning efficiency of soil aquifer treatment (adapted from [24, 25]).

Parameter Typical input

values [mg/l]

Typical output

values [mg/l]

biological oxygen

demand (BOD) 250 ≤ 30

total suspended

solids (TSS)

total organic

carbon (TOC)

> 10

< 1

< 5

total nitrogen (TN) 60 < 10

total phosphorous (TP) 8 < 1

fecal coliforms (FC) > 10,000

[n/100 ml]

< 1 - 22

[n/100 ml]

Soil Aquifer Treatment as a Tool for Sustainable Groundwater Use in Hanoi/Vietnam

886

5. Acknowledgements

This paper was conducted as a part of the excellence ini-

tiative “International Water Alliance Saxony (IWAS)”,

Ref. No. 02WM1028. Additional support came from the

Bundesministerium für Bildung und Forschung (BMBF,

Germany; project no. 02WA1148 “Evaluation and en-

hancing ground water effluent recharge technology”).

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