162 the sustainability risk of HCM

The aim of this study was to quantitatively estimate the risk of groundwater sali-nization in the Ho Chi Minh area due to saline water intrusion into the main coastal aquifer the Upper

Vol 19, No 3, p 547560, September 2015

DOI 10.1007/s12303-014-0052-4

ⓒ The Association of Korean Geoscience Societies and Springer 2015

The sustainability risk of Ho Chi Minh City, Vietnam, due to saltwater intrusion

ABSTRACT: Groundwater is important for domestic, industrial,

and agricultural uses in Ho Chi Minh City, Vietnam As the city has

developed in a coastal environment, the issue of the fresh water

supply must be solved for continuous development The aim of this

study was to quantitatively estimate the risk of groundwater

sali-nization in the Ho Chi Minh area due to saline water intrusion into

the main coastal aquifer (the Upper Pliocene aquifer) based on field

monitoring data, and to evaluate the sustainability of the city with

respect to groundwater resources From the national monitoring

data-base, water level data were obtained for the last 10 years (2000 to 2009),

and a total of 33 hydrogeochemical and isotope data sets were

obtained from the aquifer The sustainability of Ho Chi Minh City

with respect to the groundwater supply was quantitatively

evalu-ated at an aquifer scale using groundwater sustainability indicators

(GWSIs) suggested by the UNESCO/IAEA/IAH Working Group The

results indicated that groundwater in the southern region, part of

the western region, and the area along the Saigon riverside was of

poor quality, with very high total dissolved solids (>1,000 mg/L)

and high concentrations of Cl and Fe, exceeding the World Health

Organization’s drinking water guidelines The Br:Cl ratios and

the δ 2 H and δ 18 O values of the samples indicated that the

salini-zation of groundwater resulted mainly from mixing with seawater

over a long period During 2004–2009, the saline boundary moved

inland, with the farthest distance reaching ~3.2 km The long-term

abstraction of groundwater, which has been much greater than its

recharge capability, is probably causing the decline in water level

(in 39% of the aquifer area), the degradation of groundwater

qual-ity (in 62% of the area), and the continuously expanding saline water

intrusion (by 7.4% in 5 years) Thus, for the sustainable development

of Ho Chi Minh City, in addition to passive measures to regulate

over-pumping and pollution controls, active measures should be

considered to prevent further seawater intrusion and to increase

groundwater recharge through artificial recharge or better

man-agement of aquifer recharge (MAR)

Key words: saltwater intrusion, groundwater sustainability indicators

(GWSIs), Upper Pliocene aquifer, Ho Chi Minh City, aquifer recharge

1 INTRODUCTION

Currently, approximately 700 million people worldwide

live under conditions of water shortage, and by 2025, this

number is expected to increase to 3 billion (UNDP Human Development Report, 2006) Population increase results in increased demand on the water supply, and accordingly, water resource management to ensure national sustainable development has become an important subject of national policy around the world Moreover, half of the world's pop-ulation lives within 60 km of the sea, and three-quarters of all large cities are located in coastal areas (http://www.unep.org/ urban_environment/issues/coastal_zones.asp) In coastal environ-ments, where fresh water and saline water exist in a dynamic balance, increased exploitation of freshwater resources can disrupt the balance, causing saltwater intrusion into areas that previously contained freshwater Consequently, coastal areas under continuous development are facing sustainabil-ity risk due to the limited capacsustainabil-ity of the freshwater supply Because coastal areas are open to the ocean and the sur-face water is readily mixed with saline water, most coastal cities depend on groundwater for their freshwater supply Therefore, from the perspective of water resources, the sus-tainable development of coastal cities is dependent on the availability of fresh groundwater resources in the area, and thus, groundwater aquifers become the targets of water-resource development and management for protection and preserva-tion from contaminapreserva-tion and over-exploitapreserva-tion Groundwa-ter salinization by the intrusion of seawaGroundwa-ter, which results from the mass transport of saline waters into zones previ-ously occupied by fresh groundwater, degrades water quality

by raising the salinity of freshwater above acceptable levels for drinking or other purposes Numerous studies have exam-ined the risk of seawater intrusion (Werner and Simmons, 2009; Morgan et al., 2012; Park et al., 2012; Sophiya and Syed, 2013) and have suggested effective solutions such as pump-ing control (Mantoglou, 2003), use of injection wells (Allow, 2011), and reverse osmosis desalination (Vinson et al., 2011)

Ho Chi Minh City (previously known as Saigon) is located in the southeastern region of Vietnam and is the largest city in Vietnam, occupying an area of 2,095 km2, with more than 7.5 million inhabitants, and it functions as the country’s

Minh Thien Ngo

Jae Min Lee

Hyun A Lee

Nam Chil Woo*

} Department of Earth System Sciences, Yonsei University, Seoul 120-749, Republic of Korea Faculty of Geology, HCMC University of Science, Ho Chi Minh, Vietnam

Department of Earth System Sciences, Yonsei University, Seoul 120-749, Republic of Korea Korea Basic Science Institute, Seoul center, Seoul 136-075, Republic of Korea

Department of Earth System Sciences, Yonsei University, Seoul 120-749, Republic of Korea

*Corresponding author: ncwoo@yonsei.ac.kr

Fig 1 (a) A map of the study area (b) A schematic hydrogeological cross section: blue and brown layers indicate aquifers and aquitards,

respectively (Bui, 2010) The different shades indicate the rate of groundwater abundance Darker shades represent more abundant zones

of groundwater

economic center The city is bordered by neighboring

prov-inces and the Can Gio Sea in the south (Fig 1a), and its

topography is relatively higher (35 m above sea level) in the

north and lower in the south (0.5–1.5 m above sea level)

Two large rivers, the Saigon and the Dongnai, flow through

the Ho Chi Minh area from the northeast to the Can Gio Sea

in the south Both groundwater and river water have been

used in the city since the early 19th century (Ho Chi Minh City,

2010a) However, the existing water supply is insufficient

for the increased water demand, particularly during the dry

season, when rivers are seriously affected by seawater

intru-sion (Dan et al., 2007)

As for the groundwater resources in the area, several

studies have reported groundwater storages (Nguyen, 1991;

Tran, 1998), water level declines, water quality degradation,

and land subsidence (Nguyen 1998, 2008, 2009; Nguyen and

Tran, 2003; Dan et al., 2006, 2007) As it is located in a coastal

environment, Ho Chi Minh City also needs to solve issues of

freshwater supply for continuing development Therefore,

the aim of this study was to quantitatively estimate the risk

of groundwater salinization in the Ho Chi Minh area due to

saltwater intrusion into the main coastal aquifer based on

field monitoring data, and to evaluate the sustainability of

the city with respect to groundwater resources

2 STUDY AREA

The Ho Chi Minh City area has six regional aquifers

con-sisting of alluvial sediments (Nguyen and Tran, 2003) Each

aquifer is separated from the others by clay layers that act

as confining layers (Fig 1b; Bui, 2010) The confining

lay-ers vary widely in thickness, ranging from 1 m to more than

30 m in the study area, and are possibly absent in some local

areas The aquifers were named according to the formation

sequence, from the uppermost to the lowest, as follows: the

Upper Pleistocene aquifer (qp3), with an average thickness

of 23 m; the Upper‒Middle Pleistocene aquifer (qp2‒3), with

an average thickness of 27 m; the Lower Pleistocene aquifer

(qp1), with an average thickness of 27 m; the Upper Pliocene

aquifer (n22), with an average thickness of 38 m; the Lower

Pliocene aquifer (n21), with an average thickness of 34 m; and

the Miocene aquifer (n13) with an average thickness of 25 m

Currently, the Upper Pliocene aquifer (n22) is the main

source of groundwater supply because of its relatively large

thickness (38 m), high hydraulic conductivity (14 m/day),

and good water quality (Bui, 2010) Groundwater pumping

volume from this aquifer was estimated to be ~272,000 m3/

day, accounting for approximately 38% of the total pumping

volume for the city (717,000 m3/day) (Department of Natural

Resources and Environment of Ho Chi Minh City, 2009)

This study only focused on the groundwater in the main

aquifer (n22) due to the availability of long-term monitoring

data and its importance for water supply Our results provide

information essential for designing a management plan to

effectively protect and preserve the groundwater resource

3 MATERIALS AND METHODS

A total of 33 hydrogeochemical data sets from the aquifer (n22) were obtained from the National Monitoring Database for the Ho Chi Minh area, collected by the Division for Water Resources Planning and Investigation for the South of Viet-nam Measured parameters included pH, total dissolved sol-ids (TDS), Ca2+, Na+, K+, Mg2+, NH4+, Fe2+, Fe3+, HCO3‒, Cl‒,

SO42‒, and NO3‒ An additional sampling campaign was undertaken in April 2012 A total of 17 samples were taken for Br and Cl concentrations and analyzed using ion chro-matography (Model: Metrohm 883) at the hydrogeology laboratory of Yonsei University From 11 of the 17 samples, the stable isotopic ratios of hydrogen (δ2H) and oxygen (δ18O) were determined using a stable isotope ratio mass spectrometer (Prism II, VG Instruments) at the Korean Basic Science Institute The 11 selected samples were distributed throughout the research area from north to south, represent-ing both fresh and saline water All stable isotopic compo-sitions were reported in the standard notation in which δ = {(Rsample/Rstandard) – 1} × 1000 (‰), where Rsample and Rstandard represent the ratios of heavy to light isotopes in the sample and standard, respectively

Based on water-level data collected from 2000 to 2009, the long-term water level change was delineated using linear regression and the Mann-Kendall test The Mann-Kendall test, a rank nonparametric test developed by Mann (1945) and Kendall (1975), has been recognized as useful for detecting linear and non-linear trends (Hamed and Rao, 1998; Wu et al., 2008; Shadmani et al., 2012) In this test, the null hypoth-esis (H0) and the alternative hypotheses (H1) were the non-existence and non-existence of a trend in the time-series data, respectively (Shadmani et al., 2012) If the standardized test statistic ZM-K had a positive value, it indicated an increasing trend, whereas a negative value indicated a decreasing trend

in the time series When |ZM-K| > Z1‒α/2, H0 was rejected, and a significant trend was considered to exist in the time series Z1‒α/2 was the critical value of Z from the standard normal table at the 5% significance level

The sustainability of Ho Chi Minh City with respect to the groundwater supply was quantitatively evaluated using groundwater sustainability indicators (GWSIs) suggested by the United Nations Educational, Scientific and Cultural Orga-nization (UNESCO)/ International Atomic Energy Agency (IAEA)/International Association of Hydrogeologists (IAH) Working Group (Vrba and Lipponent, 2007) GWSIs are based

on measurable and observable data, and provide informa-tion about groundwater quantity and quality (contemporary states and trends) They focus on social (groundwater availabil-ity and use), economic (groundwater abstraction and pro-tection), and environmental (groundwater vulnerability and pollution) aspects of groundwater resources policy and

man-agement These indicators have recently been successfully

applied in different countries on various scales from the national

to the regional, and finally, to the aquifer scale (Girman, 2007;

Hirata et al., 2007; Pernia and Lamban, 2007; Lavapuro et al.,

2008; Lamban et al., 2011) Originally, the Working Group

proposed 10 indicators for estimating sustainability However,

in the present study, the following three indicators were adopted

based on the availability of the necessary data: (1) total

water abstraction/exploitable groundwater resources; (2)

ground-water depletion; and (3) groundground-water quality Additionally,

taking into consideration that this is a coastal aquifer system,

another indicator, (4) groundwater salinization, was developed and tested in this study

4 RESULTS AND DISCUSSION 4.1 Groundwater Quality

Table 1 presents a summary of the chemical compositions

of the 33 groundwater samples from the main aquifer (n22) The pH, TDS, Cl‒, and Fe concentrations exceeded the World Health Organization (WHO) guideline values for drinking water

Table 1 Statistical summary of the Upper-Pliocene aquifer (n22) data (N = 33) compared with the 2011 World Health Organization

(WHO) guidelines for drinking water

Fig 2 Piper diagram showing different water types and the saline boundary map of the main aquifer (n22) using the total dissolved solid (TDS) cutoff value of 1,000 mg/L

(WHO, 2011) in 33%, 33%, 42%, and 46% of the samples,

respectively, indicating a significant degradation of the

ground-water in the aquifer

Based on a TDS cutoff of 1,000 mg/L (Freeze and Cherry,

1979), groundwater in the study area could be divided into

two groups: fresh and saline (Fig 2) Groundwater in Region

I, the central and the northern areas, exhibited TDS

con-centrations of <1,000 mg/L, corresponding to fresh water,

whereas groundwater in Region II, the southern area, part

of the western area, and along the Saigon riverside, had

higher TDS concentrations corresponding to saline water The

water chemistry of the Region II samples was characterized

as the Na-Cl type in the Piper plot (Fig 2), implying the

influ-ence of saline water

Groundwater salinization can result from various

poten-tial sources of salinity including natural saline groundwater,

halite dissolution, seawater intrusion, agricultural effluents,

field brines, etc (Knuth et al., 1990; Richter and Kreitler,

1991; Karahanoglu, 1997; Xun et al., 2007; Ibrakhimov et

al., 2011; Shi et al., 2011) Kim et al (2003) reported that

some minor elements (e.g., Br and Sr) could be good tracers

of the fresh water and marine water mixing Andreasen and

Fleck (1997) used the ratios of Br to Cl in the water

com-position to differentiate saline water of marine and non-marine

origins Additionally, the ratios in groundwater under the

influence of seawater intrusion were reported to be similar

to those in seawater (Morris and Riley, 1966; Richter and

Kreitler, 1993) Groundwater samples from the study area

exhibited Br:Cl ratios ranging from 0.0033 to 0.0037, with

an average of 0.0035, and the ratio came very close to that

of normal seawater when Cl concentrations increased (Fig

3), indicating that the salinization of groundwater occurred

mainly through mixing with seawater Additionally, wells 7,

8, and 9, located along the side of the Saigon River,

exhib-ited higher TDS values than did other inland wells, such as

wells 3 and 10, implying that groundwater salinization could

be occurring along riverbank areas

In the Ho Chi Minh City area, two masses of saline

ground-water, in the south and in the west, are presently separated

by a mass of fresh groundwater in the central area (Fig 2)

The water types (Na-Cl) and Br:Cl ratios indicated that both

saline masses originated from seawater Considering that

the study area is a part of the Mekong River deltaic aquifer

system (Nguyen and Tran, 2003), the fresh groundwater body

in the central area was probably formed by precipitation

recharge in the deltaic lobe area This fresh groundwater body

could have then been surrounded by saline water bodies in

the west and south that formed during marine transgression

in geologic history Finally, groundwater over-exploitation

could have initiated saline water movement from the

out-side of the western boundary toward the central area However,

as for the inland saline groundwater in the western part of

the city, more detailed future studies are warranted to

elu-cidate its formation and impact on the surrounding areas

4.2 Stable Isotope Signatures of Groundwater

Oxygen (δ18O) and hydrogen (δ2H) isotopic data provided important information for evaluating the salinization process of the water resource in the study area The isotopic compo-sitions of the groundwater ranged from –7.9‰ to –2.0‰ for δ18O and from –56.3‰ to –19.0‰ for δ2H (Table 2) Considering the confined system of the main aquifer (n22), the results indicate a clear mixing process between fresh ground-water and seaground-water with different isotopic ratios (Fig 4) Both river water and groundwater were seriously affected by the intrusion of seawater Most samples taken from near the saline boundary (samples 6, 8, 11, 12, and 13) had mixing ratios

of 10–25% seawater Of particular note was sample 16, located near the coastal zone, which had a mixing ratio of ~75% seawater Samples 14 and 15 (river water) also showed strong mixing, with seawater ratios of 22% and 43%, respectively Given that the aquifer is located at a depth of greater than

100 m and is covered by three other shallower aquifers as well as confining layers, it probably has no direct interaction with river water Seawater may have intruded directly through aquifer sections that are exposed to the seafloor

Fig 3 Groundwater sampling locations and Br:Cl ratios of the

samples in relation to the chloride concentrations of water samples from the main aquifer (n22)

4.3 Long-term Changes in Groundwater

From 1950 to 2010, the local population of Ho Chi Minh

City increased by about 3.5 times, from fewer than two million

to approximately seven million (Fig 5) To satisfy the water demand of the city, based on the water supply standard of

120 liters/day/person in Vietnam (TCXDVN33, 2006), the total amount of groundwater abstraction has increased by

Table 2 Bromide and chloride concentrations and isotopic compositions of groundwater and surface water in the study area

Sample No Sample Type Sample depth (m) Temp (°C) EC (μS/cm) pH Cl (mg/L) Br (mg/L) Br:Cl ratio δ18O (‰) δ2H (‰)

GW: groundwater, RW: river water, SW: seawater

BDL: below detection limit

(–) indicates that no measurement was taken

Fig 4 Plot of δ2H vs δ18O of water samples from Ho Chi Minh City, indicating the mixing of fresh groundwater and surface water with seawater GMWL = the global meteoric water line (Craig, 1961)

about seven times, from less than 100,000 m3/day to more

than 700,000 m3/day (Ho Chi Minh City, 2010b) Presently, the

water demand for domestic use has reached up to 850,000

m3/day The rapid increase in groundwater pumpage since

1996 probably reflects the impact of the development of 12

industrial parks in the city since 1990, which consume more

water resources (Ho Chi Minh City, 2010a)

The long-term trend in water table changes, if any, was

delineated based on the monitoring data observed at four

national monitoring wells from 2000 to 2009 (Figs 1 and 6a)

and was tested statistically using the Mann-Kendall test (Mann,

1945; Kendall, 1975) The results of the Mann-Kendal test

(Table 3) clearly show a declining trend in monitoring wells

A, B, and C, located in the central and northern parts of the

city, corresponding to the area of groundwater exploitation

(the freshwater zone) At stations B and C, the rates of

water-level decline were greater than 1 m/year (Fig 6a)

However, no trend was identified at monitoring well D,

located in the coastal area close to the Can Gio Sea (Fig 6a)

The amount of annual precipitation did not change significantly

over this period Furthermore, the sea level data at the Vung

Tau monitoring station, located near the southwestern coast,

show that the mean sea level has also risen about 9 cm in

the last 28 years, from 1980 to 2007, at an average rate of 3.2 mm/year (Fig 6b) Therefore, the long-term water level decline in inland areas could potentially be attributed to the reduced recharge to the aquifer as a result of the paved land surface during urbanization and industrialization of the city and/or to the increased pumping of groundwater to satisfy water demand

From the potentiometric surface map of the main aquifer (n22) in 2004, a large cone-shaped depression was identified occupying the entire central area, with a water level of about –24 m at the lowest point (Fig 7a) In 2009, the depression cone became even wider and deeper, with a water level of –30 m at its deepest point (Fig 7b), and the center of depression cone moved to the south, probably because of increased abstraction of groundwater to meet the water demands of new residential towns in the south-central area Consequently, the saline boundary line of 1,000 mg/L TDS in the aquifer moved toward the city’s central area from both the west and the southeast of Ho Chi Minh, with the farthest dis-tance being about 3.2 km (Fig 7c) The rate of saline water intrusion through the aquifer appeared to be approximately

640 m/yr

Fig 5 Increase in groundwater abstraction according to population growth in the Ho Chi Minh area (Ho Chi Minh City, 2010b).

Table 3 Results of the Mann-Kendal test for water level trends in a monthly time series

No Station name Data length (months) Mann-Kendal test statistic (ZM-K) Trend observation

Fig 6 (a) Change in the water level from 2000 to 2009 in the main aquifer (n22) (m/month) (b) Change in sea level at the Vung Tau monitoring station, located near the southwestern coast (m/year) (database from the Sub-institute of Hydrometeorology and Environment

of South Vietnam)

Fig 7 Maps showing the water level and saline boundary of the main aquifer (n22) in (a) April 2004 and (b) April 2009, and (c) the movement of the saline water boundary

4.4 Groundwater Sustainability

The sustainability of Ho Chi Minh City from the perspective

of water resources was evaluated based on the groundwater

capacity of the area using four GWSIs, including (1) total

groundwater abstraction/exploitable groundwater resources;

(2) groundwater depletion; (3) groundwater quality; and (4)

groundwater salinization

4.4.1 Total groundwater abstraction/exploitable

ground-water resources (%)

This indicator aims to evaluate the sustainability of

ground-water abstraction and is expressed as the percentage of

groundwater abstracted from the exploitable groundwater

resources The exploitable groundwater resources are defined

as the volume of groundwater that can be abstracted under

the current socio-economic constraints, political priorities,

and ecological conditions (Vrba and Lipponent, 2007)

Taking into consideration that the amount of

groundwa-ter abstraction should not cause any adverse effects on

long-term water resource development and utilization, the

exploitable groundwater resources of the main aquifer (n22)

should be the same as the amount of renewable

ground-water Groundwater renewable resources (GWRR) consist

of the recharge from precipitation (recharge), surface water

that infiltrates into the groundwater (seepage), groundwater

that discharges into surface water (base flow), the flow of

groundwater from and to neighboring areas (inflow and

outflow), and artificial recharge The equation can be

writ-ten as follows:

GWRR = Recharge + Seepage – Baseflow + Inflow

The statistical information of stratigraphy from boreholes

and previous studies indicated that the main aquifer (n22)

located in Ho Chi Minh area is quite deep, with an average

depth of more than 100 meters, and is also isolated relatively

well from the other overlying aquifers by existing continuous

and impermeable clay layers between them Therefore, it

cannot be recharged directly from precipitation (recharge),

surface water (seepage) or discharges into surface water

(base flow) Additionally, since the study area is a large

ground-water exploitation area without any artificial recharge

activ-ities, all water flows tend to flow into the central area (Fig 8)

Consequently, we assumed that there was no recharge from

precipitation, no seepage, no baseflow, and no (or

unremark-able) outflow The volume of inflow (considering only fresh

water) comes from the northwest and was estimated using

Darcy’s law, with an average hydraulic gradient (i) of 0.01,

a mean hydraulic conductivity (K) of 14.2 m/day, and an

area of cross section (A) of 556,640 m2 These parameters,

including the hydraulic gradient and the width and height of the

cross section were estimated directly from Figure 8 Therefore,

the GWRR of the n22 aquifer was estimated as follows:

GWRR = Inflow = K × i × A = 79,042 m3/day (2) The Department of Natural Resources and Environment

of Ho Chi Minh City (2009) estimated groundwater pump-ing from this aquifer to be about 272,480 m3/day Conse-quently, the city appears to over-exploit the groundwater resources of the main aquifer n22 by more than three and a half times (approximately 345%) its renewable capacity This is an incredible number compared with results from both Finland and the Republic of South Africa (Vrba and Lipponent, 2007), which have pumping values of only 10% and 17.1%, respectively, at the national scale (Table 4) However, the results from Finland and the Republic of South Africa reflect the average level of groundwater abstraction for the whole country, and the population density and the stress on aquifers varies considerably among local areas Some previous stud-ies have also concluded that the best scale for applying GWSIs is the aquifer scale (Girman, 2007; Hirata et al., 2007; Lavapuro et al., 2008; Lambán et al., 2011) There-fore, the continuous pumping of groundwater from this aqui-fer could cause a significant water level decline and induce saline water intrusion through the southeastern seawater boundary

Fig 8 Map showing the movement characteristics of the Upper

Pliocene aquifer (n22)

4.4.2 Groundwater depletion

Maps of water levels in 2004 and 2009 with two-meter

intervals were built by interpolating groundwater monitoring

data using the Kriging method Then, two maps of water

levels were overlaid to identify water-depletion zones (Fig

9) In this study, water-level decline of at least 1 m between

in 2004 and in 2009 was set up as the criteria for the water

depletion zone The result was calculated as follows:

(Σ areas with a groundwater depletion problem/total

studied area)*100% = (823 km2/2,095 km2)*100%

The result indicates that 39% of the total area has a

ground-water depletion problem This depletion zone occupies the

entire center area covering 823 km2, and it tends to spread

to neighboring areas It corresponds with the areas in Ho

Chi Minh City that have very high populations and thus,

high water demands (Fig 9) Additionally, recent monitoring

data of water levels have also confirmed the rapid declining

trend in water levels during 2000–2009, especially at stations B

and C, where the rate was greater than 1 m/year (Fig 6) It

is obvious that the long-term abstraction of groundwater has greatly exceeded the renewable capability of the aquifer This depletion has possibly caused the change in groundwater qual-ity by increasing the possibilqual-ity of saline water intrusion

4.4.3 Groundwater quality

The quality of groundwater is controlled by natural and anthropogenic factors that include the geological structure and mineralogy of the aquifers, the residence time, and the reactions that take place within aquifers or in the mixing processes with surface water sources (Mendizabal and Stuy-fzand, 2009; Alexakis, 2011) Based on the particular char-acteristics of the groundwater, which has a low pH and high

Fe concentrations, and the widespread existence of saline groundwater in Ho Chi Minh City, the typical parameters of

pH, iron, and chloride were chosen as evaluating indicators

of groundwater quality The evaluation of groundwater quality was based on WHO guideline values (WHO, 2011) This aqui-fer is quite deep and lies under other shallower aquiaqui-fers and

Table 4 The results of the Total groundwater abstraction/Exploitable groundwater resources (EGWR) indicator, compared with data for

Finland and the Republic of South Africa

Ho Chi Minh city (aquifer scale) (national scale)Finland Republic of South Africa(national scale) References Total abstraction 0.895  109 m3a–1 0.306  109 m3a–1 1.771  109 m3a–1

Lavapuro et al (2008); Girman (2007) Exploitable groundwater 0.289  109 m3a–1 2.979  109 m3a–1 10.353  109 m3a–1

Fig 9 (a) Map showing the population density of Ho Chi Minh City (b) Map showing the groundwater depletion zone