Upload
others
View
1
Download
0
Embed Size (px)
Citation preview
ARTICLE IN PRESS
Available at www.sciencedirect.com
WAT E R R E S E A R C H 4 0 ( 2 0 0 6 ) 7 5 3 – 7 6 7
0043-1354/$ - see frodoi:10.1016/j.watres
�Corresponding aTel.: +852 2241 5479;
E-mail address: ch
journal homepage: www.elsevier.com/locate/watres
Heavy metal and trace element distributions ingroundwater in natural slopes and highly urbanized spacesin Mid-Levels area, Hong Kong
Chi-Man Leung�, Jiu Jimmy Jiao
Department of Earth Sciences, The University of Hong Kong, Pokfulam Road, Hong Kong, China
a r t i c l e i n f o
Article history:
Received 30 May 2005
Received in revised form
24 November 2005
Accepted 2 December 2005
Keywords:
Groundwater
Heavy metals
Trace elements
Urbanization
Leakage from service pipes
Pollution
nt matter & 2006 Elsevie.2005.12.016
uthor. Rm 206, James Lefax: +852 2517 [email protected]
A B S T R A C T
The lower slope of the Mid-Levels area, Hong Kong, is one the most heavily urbanized
coastal areas in the world. A comprehensive groundwater heavy metal and trace element
study was conducted in the Mid-Levels area aiming to investigate the impacts of
urbanization on the aqueous distributions of these chemicals. Groundwater samples were
collected in the upper natural slopes and the lower highly urbanized spaces in the area in
different seasons, and analyzed for heavy metal and trace element contents.
Compared to the results from natural slopes, groundwater samples in the developed
spaces did not exhibit significant elevated levels in Zn, Cr, Cu, Cd, Pb and Fe, which are
commonly found in stormwater. On the other hand, the samples were found to have
elevated contents in Mn, V, Co and Mo, minor stormwater-related heavy metals, suggesting
that stormwater drains may be leaking to some extent. However, the results suggested that
the vadose zone could remove many of the heavy metals, protecting groundwater from
being contaminated seriously. Statistical analysis suggested that a certain amount of Mn
and Co was likely to be re-mobilized from natural soils due to the changes in local redox
conditions, while Mn, V, Co and Mo may also be derived from steel corrosion as a result of
prolonged submergence. Besides, the average B concentration in the developed spaces was
about eight times higher than that in the natural slopes, indicating the presence of sewage.
The mean Se concentration in the developed spaces was about 100 times higher than that
in the natural slopes. About 40% of samples in the developed spaces contained Se level
higher than the drinking water guideline value proposed by the World Health Organization.
Se was found to be positively correlated with B and SO42� (R ¼ 0.534 and 0.631, respectively),
suggesting that Se may also be related to leakage from sewage pipes. Part of the Sr may
come from leakage of flushing water and/or sewage as Sr was strongly correlated with Cl�
(R ¼ 0.929). According to the measured results, deep groundwater samples collected from
piezometers (410 m in depth) in the urbanized spaces appeared to be virtually free from
any anthropogenic contaminations.
This study may shed important light on the identification and evaluation of leakage
from service pipes in a particular area based on aqueous distributions of heavy metals and
trace elements. Moreover, the above findings may be instructional for other coastal cities
with a similar level of urban development to understand the potential threats to their
groundwater resources.
& 2006 Elsevier Ltd. All rights reserved.
r Ltd. All rights reserved.
e Science Building, The University of Hong Kong, Pokfulam Road, Hong Kong SAR, China.
k (C.-M. Leung).
ARTICLE IN PRESS
WA T E R R E S E A R C H 4 0 ( 2 0 0 6 ) 7 5 3 – 7 6 7754
1. Introduction
In Hong Kong, thousands of cut slopes have been created
in the process of urbanization because of the rugged
topography. Groundwater samples from the weepholes or
drains installed in these slopes, which are otherwise
extremely difficult or expensive to collect, provide a unique
and economical chance to understand the physical and
chemical natures of the subsurface flow system in
the intensively urbanized hillslopes and the impacts of
urbanization on groundwater chemical systems. Previous
studies were mainly concerned about the impacts of
urbanization on the groundwater flow and major element
chemical systems in the highly urbanized coastal
areas in Hong Kong (Jiao et al., 2006; Leung and Jiao, 2005;
Leung et al., 2005). In this paper, heavy metal and trace
element distributions in groundwater samples collected
from natural slopes and urbanized spaces in the Mid-Levels
area are discussed. The data collected from the natural
slopes could be regarded as the background trace element
concentrations in the natural environment of this area. These
data are employed to evaluate the extent of heavy metal and
trace element contamination in groundwater in the urba-
nized spaces. In our knowledge, this is the first comprehen-
sive study of heavy metals and trace elements in groundwater
in Hong Kong. The results may be instructional for other
coastal cities with similar levels of urban development
to understand the potential threats to their groundwater
resources.
Fig. 1 – Overview of the study area. The shaded area represen
bounded by the gray line is the Mid-Levels area. Dotted lines re
rock. Black lines represent the locations of normal faults.
2. Geology and hydrogeology of the study area
The Mid-Levels area, approximately 1.5 km2 in size, is situated
on the northern slope of the Victoria Peak [550 m above
Principle Datum (mPD)] on Hong Kong Island (Fig. 1). The
study area can be divided into two parts with significantly
different modes of development. The upper part of the area
(4170 mPD) is essentially a natural slope with minimum
development. In contrast, the lower part of the area has been
extensively urbanized and is regarded as one of the most
heavily urbanized areas in the world.
The geology and hydrogeology of the area has been
described elsewhere in Geotechnical Control Office (GCO)
(1982). The geology is dominated by two rock types, acidic
volcanic rocks and a granitic intrusion. The volcanic rocks
have been subject to low grade regional metamorphism and
deformation and affected by contact metamorphism where
close to the granite. Both lithologies have been subsequently
intruded by basaltic dykes. The irregular contact between the
granite and volcanic rocks crosses the area and is disrupted
by normal faults in several locations (Fig. 1).
In general terms, colluvium overlies several meters of
decomposed rock above the bedrock. The granite underlies
most of the developed spaces, composed of quartz (23–42%),
potassium feldspar (31–42%), plagioclases (16–35%) and biotite
(�5%) according to Allen and Stephens (1971). Volcanic rock
underlies the upper undeveloped slopes.
Although it is likely that the lithologies in the subsurface
are very heterogeneous and anisotropic, GCO (1982) have
ts the natural slope with minimum development. The area
present the contact between granite and volcanic
ARTICLE IN PRESS
Table 1 – Summary of geochemistry of rock samples collected within and near the Mid-Levels area, Hong Kong (GEO, 2001)
Sample 1 2 3 4 5 6 7 8 9
Ref. no. 2189 2228 2457 2857 4258 11027 2230 4237 11028
Rock type (a) (a) (a) (a) (a) (a) (b) (c) (d)
SiO2 67.75 71.61 72.90 73.67 72.47 74.40 75.77 77.01 80.33
TiO2 0.49 0.56 0.49 0.26 0.26 0.23 0.13 0.13 0.10
Al2O3 14.92 15.39 15.30 13.05 13.43 13.23 12.74 12.09 10.52
Fe2O3 4.16 4.80 4.18 2.26 2.83 2.17 1.61 1.52 1.01
MnO 0.10 0.03 0.05 0.07 0.06 0.07 0.09 0.07 0.02
MgO 0.99 0.84 0.75 0.34 0.23 0.27 0.13 0.11 0.08
CaO 2.85 0.06 0.06 1.67 1.57 1.29 0.74 0.90 0.53
Na2O 3.07 0.09 0.04 3.01 2.88 3.80 3.72 2.77 1.58
K2O 4.92 5.27 5.51 4.87 5.61 4.09 5.14 4.76 5.80
P2O5 0.17 0.03 0.04 0.06 0.07 0.06 0.01 0.02 0.01
LOI 0.35 1.19 0.30 0.77 0.23 0.23 0.29 0.72 0.10
Total 99.77 99.87 99.62 100.00 99.64 99.84 100.40 100.10 100.10
Cr 21 28 20 12 23 3 15 30 6
Ni 9 7 4 1 10 4 14 o1 5
Co 3 4 4 5 5 3 o1 na 3
V na na o1 13 na na na na na
Cu o1 o1 o1 o1 o1 1 4 o1 1
Pb 16 102 23 31 44 14 33 31 21
Zn 19 116 23 56 33 36 103 30 12
Sn na na o1 2 o1 na 10 2 Na
W 10 5 7 2 8 6 7 4 2
Rb 244 238 204 193 263 241 320 241 343
Ba 548 640 801 464 228 483 83 140 555
Sr 148 158 205 189 100 133 32 86 83
Ga 16 16 17 15 17 15 16 13 15
Nb 21 19 16 19 25 18 29 19 13
Zr 147 150 165 174 194 148 193 152 136
Y 54 41 32 37 49 43 57 46 29
Th 33 29 30 29 42 34 39 33 35
U 5 8 7 7 6 5 5 8 5
La 53 43 52 49 90 25 40 30 17
Ce 111 107 111 70 200 58 97 70 36
F 1881 1686 1686 na 1813 1130 1585 na 905
Remarks: 1. Rock type (a) represents coarse ash crystal tuff; (b): eutaxitic fine ash vitric tuff; (c): medium-grained granite; (d): microgranite.
2. Major element in %wt; Trace element in ppm; na: not analyzed.
WAT ER R ES E A R C H 40 (2006) 753– 767 755
grouped them into three aquifer units corresponding to (a)
colluvium, (b) decomposed volcanic and granite rocks, and (c)
volcanic and granite bedrocks. The colluvium contains
transient and permanent perched water tables, whereas, as
recently demonstrated by Jiao et al. (2003, 2005), and the
highly decomposed rock or saprolite below the colluvium is
relatively impermeable due to its clay-rich content. The
bedrock zone along the uppermost part of parent rocks may
be fairly permeable with confined groundwater contained
within a well-developed fracture network.
Geotechnical Engineering Office (GEO) conducted a geo-
chemical survey for some major rock types in Hong Kong
(GEO, 2001). In the Mid-Levels area, seven volcanic rock
samples (coarse ash crystal tuff and eutaxitic fine ash vitric
tuff) and two granitic rock samples (medium-grained granite
and microgranite) were collected and analyzed. Table 1 shows
their whole rock composition results. From Table 1, it seems
that no significant difference in the compositions could be
observed among those samples.
3. Field and analytical methods
Groundwater samples were collected in natural and cut
slopes, and piezometers in the study area in September
2002 (wet season) and January 2003 (dry season). The
sampling locations are showed in Figs. 2 and 3, respectively.
At each site, the pH, temperature, electrical conductivity
(EC) and dissolved oxygen (DO) of water samples were
measured. Sampling and analytical techniques followed
the suggestions by APHA (1998) and are described in
detail in Leung (2004). In brief, water samples for chemical
analysis were filtered through a hand-held Hanna filter
system using a 0.45mm cellulose filter paper (Advantec MFS
Inc.) and collected in a 500 mL clean HDPE bottle. Two 125 mL
aliquots were collected at each site, one unacidified and the
other acidified to pHo2 using ultrapure nitric acid. The
samples were then refrigerated at 4 1C before chemical
analysis.
ARTICLE IN PRESS
Fig. 2 – Sampling location in the wet season in 2002 in and around the Mid-Levels area. Squares represent water samples
collected from seepage or a spring from natural or cut slopes. Circles represent water samples collected from
piezometers. Shaded area represents the natural slopes.
Fig. 3 – Sampling location in the dry season in 2003 in and around the Mid-Levels area. Triangles represent water samples
collected from seepage or a spring from natural or cut slope. Circles represent water samples collected from
piezometers. Shaded area represents the natural slopes.
WA T E R R E S E A R C H 4 0 ( 2 0 0 6 ) 7 5 3 – 7 6 7756
Acidified aliquots were analyzed for heavy metals and trace
elements by inductively coupled plasma mass spectrometry
(ICPMS) except for boron (B) which was analyzed by induc-
tively coupled plasma atomic emission spectrometry (IC-
PAES). Unacidified aliquot was analyzed for major anions by
Ion Chromatography. Detailed analytical results are listed in
Leung (2004). The pH values, DO content, heavy metal and
trace element concentrations of groundwater samples are
ARTICLE IN PRESS
Table 2 – Heavy metals that are found in variouscomponents of a motor vehicle
Component Heavy metal
Exhaust Al, Sb, Ba, B, Cr, Co, Cu, Fe, Pb, Li, Ni, Se, Sr, V, Zn
Engine Cd, Cr, Cu, Fe, Ni, Zn
Brakes Al, Sb, Ba, Cr, Cu, Fe, Mo, Sn, Zn
Tires Cd, Pb, Ti, W, Zn
References: Kiem (2002), Valcav and Valcav (1992), Ball et al. (1998)
WAT ER R ES E A R C H 40 (2006) 753– 767 757
listed in Appendices A and B in this paper. Sample batches
were regularly interspersed with standards and blanks, and
all data were corrected for instrument drift. A three-point
calibration curve was constructed for each element. National
Institute of Standards and Technology (NIST) Standard
Reference Material (SRM) 1640 was employed to check the
reliability of the analysis. The measured values of SRM 1640
were all within 5% of the certified values. The results of three
replicate analyses indicated that the precision of cation
measurements was generally better than 5%.
and Friedlander (1973).
Table 3 – Typical concentration of some heavy metal (inppb) in stormwaters from literatures
Element Typical literature values
Al 17089–17760e
Fe 18368–19742e
V 7–2200a
Cr 1–2300b, 51.1–58.73e
Mn 7–3800b
Co 1.3–5.4a, 6.7d
Ni 53c, 93d, 248–266e
Cu 52c, 274d, 1–54.3f, 267–283e
Zn 498c, 208d, 50–1462f, 2548–2792e
Mo 20d
Cd 5c, 14.1d, 3.02–4.42e
Sb 3.5–23b
Pb 1558c, 81d, 1–199.5f, 2548–2792e
a Dannecker et al. (1990).b Cole et al. (1984).c Yousef et al. (1984).d Hares and Ward (1999).e Kiem (2002).f Barbosa and Hvitved-Jacobsen (1999).
4. Sources of heavy metals and trace elementsin the study area
Heavy metals and trace elements in subsurface environments
come from natural and anthropogenic sources. The weath-
ering of minerals is one of the major natural sources. As
shown in Table 1, no significant difference in heavy metal and
trace element concentrations between the bedrocks is
observed in the study area. Anthropogenic sources include
fertilizers, industrial effluent and leakage from service pipes.
In the area, industrial and agricultural activities are unlikely
to be the major contamination sources because of the
absence of these activities. The main features of urbanization
in the area are (1) high density of residential and commercial
buildings, (2) extensive areas of impervious surfaces and (3)
extensive construction of subsurface drainage systems such
as flushing water pipes, sewers and stormwater drains.
High traffic rate is common in the study area. Table 2 lists
the heavy metals present in various car components. Thus,
motor vehicles are likely to be the contributor to the
pollutants on roads. Pollutants accumulated on road surfaces
could be washed by storm or street cleansing as road runoff
and finally collected into the nearby stormwater drainage.
These pollutants include heavy metals (Ball et al., 1998;
Dannecker et al., 1990), organic chemicals (Cole et al., 1984;
Krein and Schorer, 2000) and organic compounds (Blumberg
and Bell, 1984). In this paper, focus is placed on heavy metals
and trace elements. Many studies have investigated the
concentrations of heavy metals in stormwater (Dannecker
et al., 1990; Cole et al., 1984; Yousef et al., 1984; Hares and
Ward, 1999; Kiem, 2002; Barbosa and Hvitved-Jacobsen, 1999).
Table 3 shows the typical concentrations of heavy metals in
stormwater from the literature. It should be noted that the
heavy metal concentrations in stormwater are controlled by
various factors such as average daily traffic, the type of
vehicles, the nature of fuels used and climate, etc.
It is commonly accepted that stormwater contains high
levels of heavy metals, especially aluminum, iron, zinc,
copper, chromium, cadmium, nickel and lead (if leaded petrol
is still in use). In Hong Kong, although the actual heavy metal
contents in road runoff have not been studied, some studies
measured heavy metals in dusts collected in urban areas
including streets (Yim and Niu, 1987; Tong and Lam, 2000;
Poon et al., 1999; Ng et al., 2003). These data may help to
assess the heavy metal compositions of road runoff in Hong
Kong. In this paper, the results from Ng et al. (2003) are
employed mainly because their results reflect the most recent
heavy metal compositions of dusts in urban environments in
Hong Kong. In their study, a total of 89 dust samples were
obtained from 62 urban playgrounds and parks of various
sizes and types from November 2000 to February 2001. The
dust samples were then analyzed with heavy metals (Zn. Cu,
Cd, Cr, Pb, Fe, Mn) and organic carbon (OC) contents. The
analytical results are listed in Table 4. Although the dust
samples were collected in playgrounds and parks located in
urban areas, Ng et al. (2003) successfully demonstrated the
significant traffic related inputs of heavy metals by the
presence of tire fragments, metallic debris and sand grains
with a tar coating. The results presented by them could be
used as a reference for the heavy metal contents of road dusts
in Hong Kong. It is believed that the heavy metal concentra-
tions in dust samples collected from roadsides may be even
higher than that from urban parks because the former are
closer to the source (motor vehicles).
Ng et al. (2003) concluded that roadside dusts in Hong Kong
are characterized by high concentrations of Zn, Cu and Cr.
This finding agrees with Yim and Niu (1987), Poon et al. (1999)
and Tong and Lam (2000). Since road runoff is collected by
ARTICLE IN PRESS
Table 4 – Chemical composition of playground dust (n ¼ 89) (Ng et al., 2003)
Chemical variables Mean Maximum Minimum Std. dev.
Zn (mg/g) 1883 6658 159 1309
Cu (mg/g) 143 859 17.0 109
Cd (mg/g) 7.0 13.7 4.6 1.9
Cr (mg/g) 263 2681 11.8 408
Pb (mg/g) 77.3 263 1.8 39.4
Fe (mg/g) 22,991 159,596 4826 19,554
Mn (mg/g) 518 1359 216 179
OC (%) 11.6 25.8 2.1 4.8
Table 5 – Trace element (in ppb) statistics of groundwater in the natural and developed areas in the wet season
Element Natural slope (n ¼ 18) Developed area (n ¼ 20)
Min Median Mean Max SD CV Min Median Mean Max SD CV
Al 0.78 3.20 8.19 43.72 11.15 136.14 0.01 0.26 1.02 6.17 1.58 154.90
Fe 2.23 3.68 5.57 19.13 4.60 82.59 1.73 3.87 4.89 16.18 3.54 72.39
Mn 0.85 2.20 2.72 7.34 1.92 70.59 0.37 5.55 89.87 789.36 188.90 210.19
Cu 0.00 0.00 0.14 1.42 0.35 250.00 0.00 0.10 1.33 14.95 3.35 251.88
Zn 8.11 46.18 40.83 73.75 26.23 64.24 7.39 26.91 33.69 92.39 23.34 69.28
Sr 14.72 28.16 28.18 47.47 9.32 33.07 75.82 325.90 412.01 1477.00 323.24 78.45
Se 0.00 0.01 0.07 0.37 0.10 142.86 0.56 5.62 8.60 23.25 7.22 83.95
Li 0.20 1.34 2.04 6.79 1.80 88.24 0.00 1.00 3.31 15.83 4.69 141.69
Be 0.04 0.39 0.45 1.12 0.35 77.78 0.00 0.02 0.18 1.71 0.41 227.78
V 0.27 0.55 0.55 1.06 0.21 38.18 1.21 3.65 4.77 14.61 3.21 67.30
Cr 0.00 0.10 0.54 5.12 1.19 220.37 0.60 1.45 1.58 4.31 0.83 52.53
Co 0.00 0.02 0.02 0.07 0.03 150.00 0.00 0.18 0.34 2.54 0.58 170.59
As 0.12 0.33 0.42 1.78 0.37 88.10 0.00 1.81 2.65 17.49 3.65 137.74
Rb 2.61 6.15 6.39 11.38 2.79 43.66 2.22 33.21 35.70 81.92 20.03 56.11
Mo 0.00 0.06 0.12 0.88 0.21 175.00 0.02 1.03 1.60 5.72 1.66 103.75
Ag 0.68 2.90 3.16 7.10 1.39 43.99 0.52 1.48 1.90 6.10 1.46 76.84
Cd 0.01 0.06 0.07 0.18 0.04 57.14 0.01 0.09 0.14 1.18 0.25 178.57
Sb 0.00 0.02 0.03 0.10 0.03 100.00 0.00 0.18 0.28 0.81 0.27 96.43
Ba 8.07 32.52 31.51 55.79 13.07 41.48 11.18 39.75 57.15 195.99 47.22 82.62
Pb 0.03 0.15 0.54 3.34 0.89 164.81 0.06 0.35 0.95 6.67 1.59 167.37
B 12.54 18.41 18.84 31.22 4.81 25.53 46.70 123.05 146.07 433.54 99.20 67.91
Remarks: ‘‘SD’’ represents standard deviation; ‘‘CV’’ (in %) represents coefficient of variation.
WA T E R R E S E A R C H 4 0 ( 2 0 0 6 ) 7 5 3 – 7 6 7758
nearby stormwater drainage, any leakage from the drains
could bring heavy metals into the surrounding environments,
which may in turn pollute groundwater. Besides, leakage
from other service pipes may also bring additional trace
elements into the environment.
5. Results and discussions
5.1. Heavy metal and trace element distributions ingroundwater samples in the Mid-Levels area
The main objective of this study is to evaluate the impacts of
urbanization on groundwater in terms of heavy metal and
trace element contaminations. Groundwater samples in the
natural slopes are assumed to be free from any anthropogenic
contaminations and thus they could be used to evaluate the
degree of heavy metal and trace element contaminations in
the urbanized spaces. Tables 5 and 6 present the statistical
summary of heavy metal and trace element concentrations in
groundwater samples collected in wet and dry seasons.
According to Appendices A and B, in general groundwater
samples collected in the natural slopes were slightly more
acidic and of higher DO content than that in the developed
spaces for both seasons. Most of the groundwater samples in
the study area are weakly acidic (pH ranged from 5 to 7) and
oxic (DO above 5 mg/L) in nature.
Since the developed spaces are located downhill to the
natural slopes, the distribution of heavy metals and trace
elements may be modified by natural processes such as
water–rock interactions. For most of the heavy metals and
trace elements measured, their average concentrations in
the developed spaces were higher than that in the natural
slopes. This may be the results of natural processes and/or
ARTICLE IN PRESS
Table 6 – Trace element (in ppb) statistics of groundwater in the natural and developed areas in the dry season
Element Natural slope (n ¼ 12) Developed area (n ¼ 14)
Min Median Mean Max SD CV Min Median Mean Max SD CV
Al 2.31 7.02 10.06 27.74 8.27 82.21 0.00 0.92 2.41 16.21 4.28 177.59
Fe 3.63 8.43 12.52 63.25 16.27 129.95 1.61 5.72 7.84 26.86 6.55 83.55
Mn 0.36 1.28 1.76 6.07 1.57 89.20 0.20 3.42 138.62 1192.00 335.79 242.24
Cu 0.28 0.76 1.16 4.53 1.19 102.59 0.23 0.88 1.05 2.45 0.67 63.81
Zn 1.50 2.10 4.62 12.65 3.96 85.71 1.56 5.23 9.08 39.60 11.09 122.14
Sr 5.82 18.81 20.03 35.13 7.80 38.94 46.17 280.15 308.71 742.20 211.18 68.41
Se 0.00 0.36 0.38 0.70 0.21 55.26 0.52 5.64 7.92 18.96 6.63 83.71
Li 0.61 1.46 1.79 4.71 1.27 70.95 0.06 0.53 1.19 5.01 1.49 125.21
Be 0.03 0.32 0.34 0.82 0.26 76.47 0.00 0.01 0.18 1.36 0.37 205.56
V 0.00 0.20 0.021 0.49 0.15 714.29 0.11 1.91 2.24 4.69 1.58 70.54
Cr 0.25 0.47 0.71 2.34 0.61 85.92 0.35 1.34 1.44 2.90 0.798 55.42
Co 0.00 0.00 0.0008 0.01 0.0029 362.50 0.00 0.05 0.28 1.95 0.53 189.29
As 0.00 0.18 0.24 0.97 0.27 112.50 0.00 0.45 0.75 3.27 0.91 121.33
Rb 2.39 5.07 5.05 9.09 2.00 39.60 1.45 25.39 30.30 78.24 23.50 77.56
Mo 0.04 0.19 0.29 0.86 0.28 96.55 0.13 0.58 1.03 4.45 1.30 126.21
Ag 0.00 0.00 0.0033 0.01 0.0049 148.48 0.00 0.01 0.05 0.30 0.09 180.00
Cd 0.01 0.03 0.05 0.16 0.0465 93.00 0.00 0.03 0.0743 0.31 0.087 117.09
Sb 0.01 0.04 0.05 0.20 0.05 100.00 0.03 0.09 0.14 0.63 0.17 121.43
Ba 11.57 27.27 27.63 39.54 8.38 30.33 6.18 36.26 39.38 95.60 22.47 57.06
Pb 0.01 0.24 1.84 12.10 3.59 195.11 0.01 0.35 1.09 6.85 1.81 166.06
Ni 0.00 0.67 1.78 7.66 2.44 137.08 0.00 1.36 3.81 35.53 9.20 241.47
Remarks: ‘‘SD’’ represents standard deviation; ‘‘CV’’ (in %) represents coefficient of variation.
WAT ER R ES E A R C H 40 (2006) 753– 767 759
anthropogenic pollution. In the following parts, the degree of
heavy metal contamination in groundwater in the urbanized
spaces are discussed. As stated, one of the major heavy metal
and trace element sources in the area may be leakage from
service pipes.
5.1.1. Leakage from stormwater drainsIn Hong Kong, road dusts are characterized by high concen-
trations of heavy metals such as Zn, Cr and Cu. It is thus
reasonable to assume that stormwater may also contain
high concentrations of these heavy metals. According to
Tables 5 and 6, no significant difference in the concentrations
of Zn, Cr, Cu, Cd, Pb and Fe in groundwater can be
observed between the developed spaces and the natural
slopes in both seasons. This suggests that groundwater in the
developed spaces was almost unaffected by the major heavy
metals found in stormwater. Two possible reasons may
account for this: (1) there is no significant leakage from
stormwater drains; (2) Heavy metals in leaked stormwater
cannot reach groundwater. Owing to the fact that the storm-
water drainage in the study area was built decades ago, zero
leakage is hardly possible. In this sense, it may be more
reasonable to suspect that heavy metals in the leaked
stormwater cannot reach groundwater. This possibility will
be discussed in detail.
The impacts of leakage from stormwater drains on ground-
water quality were controlled by factors such as pollutant
abundance in stormwater and pollutant mobility in the
vadose zone (Pitt et al., 1999). In the study area, the amount
of pollutants in stormwater would possibly be large because
of the dense traffic. Heavy metal concentrations in ground-
water would, therefore, be mainly controlled by pollutant
mobility in the vadose zone.
Many studies demonstrated that most of the heavy metals
are removed, degraded or accumulated with little downward
movement in the vadose zone (Hathhorn and Yonge, 1995; Ku
and Simmons, 1986; Hampson, 1986; Nightingale, 1987; Legret
et al., 1999; Dierkes and Geiger, 1999; Mikkelsen et al., 1997).
Crites (1985) suggested five metal removal processes by soil.
They are (1) soil surface association, (2) precipitation, (3)
occlusion with other precipitates, (4) solid-state diffusion into
soil minerals and (5) biological system or residue incorpora-
tion. Table 7 lists the possible removal mechanisms of some
of the common heavy metals in soil.
Dissolved heavy metal ions are removed from stormwater
during infiltration mostly by adsorption onto the near-surface
particles in the vadose zone (Ku and Simmons, 1986). The
particulate heavy metals are readily filtered out at soil
surfaces or as water infiltrates into the soil (Ku and Simmons,
1986; Pitt et al., 1995). In some cases, the direct physical
removal mechanisms are more important than chemical
removal mechanisms for most heavy metals (Pitt et al., 1995).
It appears that most of the heavy metals from the leakage of
stormwater drains are generally not important groundwater
contaminants because of their affinity for soils. However, it
may be possible that the contaminants accumulate in the
subsurface materials in the built-up areas to environmentally
critical levels.
According to Tables 5 and 6, some heavy metals, including
Mn, V, Co and Mo, in groundwater in the developed spaces
were at significantly higher concentrations than that in the
natural slopes. A few sites were even found to have Mn levels
ARTICLE IN PRESS
Table 7 – Metal removal mechanisms in soil
Element Principal removal mechanisms
Arsenic Strong associations with clay fractions of soil
Barium Precipitations and sorption onto metal oxides and hydroxides
Cadmium Ion exchange, sorption, and precipitation
Chromium Sorption, precipitation, and ion exchange
Cobalt Surface sorption, surface complex ion formation, lattice penetration, ion exchange, chelation, and precipitation
Copper Surface sorption, surface complex ion formation, ion exchange, and chelation
Iron Surface sorption and surface complex ion
Lead Surface sorption, ion exchange, chelation, and precipitation
Manganese Surface sorption, surface complex ion formation, ion exchange, and chelation, precipitation
Mercury Volatilization, sorption, and chemical and microbial degradation
Nickel Surface sorption, ion exchange, and chelation
Selenium Ferric-oxide selenite complexation
Silver Precipitation
Zinc Surface sorption, surface complex ion formation, lattice penetration, ion exchange, chelation, and precipitation
Source: modified from Crites (1985).
WA T E R R E S E A R C H 4 0 ( 2 0 0 6 ) 7 5 3 – 7 6 7760
higher than the drinking water guideline value of 500 ppb
recommended by WHO (1993). Some of these heavy metals
could be derived naturally. For example, Edmunds and
Smedley (2000) and Edmunds et al. (2002) suggested that Mn
could be released by incongruent or disproportionation
reactions from silicate or oxide minerals and emerge as
potential residence-time indicators. Besides, some elements
are redox-sensitive and local chemical conditions could affect
their availability and mobility in groundwater (Zachara et al.,
1995; Abrams et al., 1998; Kedziorek et al., 1998; Davis et al.,
2000). Statistical analysis indicated that Mn and Co are
negatively correlated with DO in both seasons (with R40.7).
Certain groundwater samples from the lower part of the
developed spaces (e.g. sites ‘‘27’’ and ‘‘LLR’’) contained
relatively high Mn and Co concentrations, which may
possibly be related to their low DO contents. This suggests
that the concentrations of some heavy metals could be
affected by local redox conditions. On the other hand, the
concentration of Mo is found to be positively correlated with
pH (R40.65 for both seasons). For most of the other heavy
metals, only weak statistical correlations with pH were
observed in both seasons.
However, natural processes alone may not be able to
account for the observed concentrations. Mn, V, Co and Mo
may be related to vehicles (Table 2) and present in stormwater
(Table 3). Loranger et al. (1994) found that the ambient
manganese concentrations are significantly correlated with
traffic density. Moreover, it is shown that vadose zones may
be less effective at removing certain heavy metals under
certain circumstances. For example, Wilson et al. (1990) found
that manganese was mobile in the vadose zone and showed
up in the groundwater at elevated concentrations at a
residential site in Arizona. Therefore, it appears that the
occurrence of Mn, V, Co and Mo in groundwater in the
developed spaces was partially related to the leakage from
stormwater drains.
Besides, Mn, V, Co, Mo could also be derived from steel
corrosion. Leung et al. (2005) demonstrated that groundwater
in the study area was highly aggressive. These heavy metals
are used as additives on steel production. Manganese
improves the rolling and forging qualities, strength, tough-
ness, stiffness, wear resistance and hardness of steel.
Vanadium foil is used as a bonding agent in binding titanium
to steel. Molybdenum contributes to the hardenability and
toughness of quenched and tempered steels. Almost all ultra-
high strength steels contain molybdenum in amounts from
0.25% to 8%. Much of the in situ materials in the urbanized
spaces have been replaced by subsurface engineering struc-
tures which consist of steels. Heavy metals may be leached
out from steels as a result of the prolonged submergence
under highly aggressive groundwater. If this is the case, the
structures of some of the buildings may be adversely affected.
5.1.2. Leakage from sewage pipesBoron is a good indicator of the presence of sewage. In the
developed spaces, the concentration of boron in groundwater
ranged from 46.70 to 433.54 ppb with average of 146.07 ppb. In
the natural slopes, it ranged from 12.54 to 31.22 ppb with an
average of 18.84 ppb. The average boron concentration in the
developed spaces was about eight times higher than that in
the natural slopes, indicating that groundwater in the
developed spaces was likely to be contaminated by the
leakage from sewage pipes to some degree. Boron is also
found to be positively correlated with sulfate (R ¼ 0.921)
(Leung, 2004), suggesting that boron and sulfate may be
derived from the same source, possibly from sewage.
Groundwater samples in the developed spaces appeared to
be commonly contaminated by selenium (Se). The average Se
concentration in the developed spaces was about 100 times
higher than that in the natural slopes. Moreover, about 40% of
the samples collected in the developed spaces contained Se
levels higher than the drinking water guideline value of
10 ppb recommended by WHO (1993). Se is used in the
production of photocells, semiconductor, stainless steel and
glass. However, none of the above industrial activities exists
in the Mid-Levels and the surrounding areas. Instead, the area
is crowded by residential buildings with a high population
density. Selenium sulfide is one of the additives in anti-
ARTICLE IN PRESS
WAT ER R ES E A R C H 40 (2006) 753– 767 761
dandruff shampoo with concentrations of 1% (non-prescrip-
tion) and 2.5% (prescription) (Pierard et al., 1997; Greer, 2000;
McKenzie, 2000). Being one of the shampoo ingredients,
selenium could be found in the sewage pipes after bathing
of local residents. Statistical analysis indicated that selenium
is correlated with boron and sulfate (with R ¼ 0.534 and 0.631,
respectively) (Leung, 2004). This further supports the
speculation that selenium may be related to leakage from
sewage pipes. Given that anti-dandruff shampoos generally
contain at most 2.5% of selenium sulfide, the highest
selenium concentration measured in the developed spaces
was relatively low (�20 ppb). This may imply that only small
scale leakage from sewage pipes occurred in the developed
spaces.
5.1.3. Leakage from flushing water pipesGroundwater in the developed spaces may also be affected by
leakage from flushing water pipes (Leung et al., 2005).
Flushing water samples were collected and analyzed for trace
element contents. It was found that flushing water contained
an exceptionally high strontium (Sr) concentration of about
9334 ppb. The leaked flushing water may contribute trace
elements, especially Sr, to groundwater in the urbanized
spaces. Groundwater samples in the developed spaces con-
tained Sr concentrations ranging from 75.82 to 1477 ppb with
an average of 412.01 ppb, which is significantly higher than
that in the natural slope. Sr is also found to be statistically
correlated with chloride (R ¼ 0:929) (Leung, 2004), indicating
that Sr may be related to the flushing water. Besides
contribution from natural sources such as the weathering of
plagioclase feldspar, it seems that a large part of the
Table 8 – Seasonal differences of trace element concentrations
Element Dry season
Min Mean Max SD
Al 2.31 9.417 27.74 8.346
Fe 4.39 13.328 63.25 16.809
Mn 0.36 1.366 2.71 0.820
Cu 0.28 1.118 4.53 1.238
Zn 1.50 4.906 12.65 4.023
Sr 13.58 21.325 35.13 6.695 1
Se 0.00 0.375 0.70 0.218
Li 0.61 1.851 4.71 1.319
Be 0.03 0.352 0.82 0.267
V 0.00 0.206 0.49 0.159
Cr 0.25 0.736 2.34 0.634
Co 0.00 0.001 0.01 0.003
As 0.00 0.260 0.97 0.276
Rb 2.39 4.995 9.09 2.086
Mo 0.04 0.3091 0.86 0.285
Ag 0.00 0.003 0.01 0.005
Cd 0.01 0.052 0.16 0.047
Sb 0.01 0.056 0.20 0.053
Ba 11.57 28.525 39.54 8.168
Pb 0.01 1.986 12.10 3.727
Remarks: % difference is calculated by the mean trace element level by (E
measured Sr in groundwater was contributed from leakage
of flushing water. As sewage pipes contain flushing water, a
certain amount of Sr may also come from leakage from
sewage pipes.
5.2. Seasonal differences of trace element contents in thestudy area
Seepage samples collected both in wet and dry seasons are
compared to examine the seasonal effects on groundwater
heavy metal and trace element contents. Samples collected
only in one season are omitted. A total of 11 and 12 sites in
the natural slopes and urbanized spaces, respectively, are
selected for comparison. According to Appendices A and B, in
general, for both the natural slopes and the developed spaces,
groundwater samples collected in wet season were slightly
less acidic and of lower DO contents than that in dry season.
The seasonal comparisons of trace element contents in the
natural slopes and the developed spaces are presented in
Tables 8 and 9, respectively.
From Tables 8 and 9, for both the natural slopes and the
developed spaces, the average concentrations of most of the
heavy metals and trace elements are higher in wet
season than in dry season. It is suggested by Vaze et al.
(2002) that the concentrations of heavy metals in road runoff
are particularly high when short duration, intense summer
storms follow a long dry period during which pollutants have
accumulated on the road surface. However, as discussed, the
impacts of leakage from stormwater drains on the heavy
metals and trace elements in groundwater appear to be
insignificant. Another explanation is that more heavy metals
(in ppb) in the natural slope in the Mid-Levels area (n ¼ 11)
Wet season % difference
Min Mean Max SD
0.78 5.356 17.94 5.653 �75.82
2.23 4.758 10.06 2.375 �180.12
0.85 2.258 7.34 2.031 39.50
0.00 0.060 0.51 0.153 �1763.33
8.11 48.564 73.75 25.074 89.90
5.31 29.867 47.47 10.302 28.60
0.00 0.064 0.37 0.116 �485.94
0.20 2.369 6.79 2.083 21.87
0.10 0.476 1.03 0.361 26.05
0.27 0.483 0.77 0.166 57.35
0.00 0.772 5.12 1.488 4.66
0.00 0.031 0.07 0.027 96.77
0.12 0.466 1.78 0.467 44.21
2.61 5.396 9.85 2.554 7.43
0.00 0.154 0.88 0.260 �100.71
0.68 2.662 4.20 1.063 99.89
0.01 0.073 0.18 0.047 28.77
0.00 0.036 0.08 0.028 �55.56
8.07 29.298 47.89 11.127 2.64
0.03 0.503 3.34 0.978 �294.91
lementwet�Elementdry)/Elementwet� 100%.
ARTICLE IN PRESS
Table 9 – Seasonal differences of trace element concentrations (in ppb) in the developed space in the Mid-Levels area(n ¼ 12)
Element Dry season Wet season % difference
Min Mean Max SD Min Mean Max SD
Al 0.00 1.294 4.98 1.721 0.05 0.917 6.17 1.758 �41.11
Fe 1.61 6.622 13.65 3.796 2.02 3.796 7.48 1.725 �74.45
Mn 0.20 62.38 536.7 155.9 0.37 83.11 789.36 227.1 24.94
Cu 0.23 0.990 1.82 0.553 0.00 0.373 2.91 0.850 �165.42
Zn 1.56 7.125 27.76 7.213 7.39 29.87 92.39 25.39 76.15
Sr 61.40 323.2 742.2 213.3 75.82 361.6 722.9 184.0 10.62
Se 0.52 7.589 17.79 6.015 0.56 9.862 23.25 7.076 23.05
Li 0.06 1.176 5.01 1.591 0.00 1.369 4.17 1.609 14.10
Be 0.00 0.091 0.41 0.152 0.00 0.221 1.71 0.493 58.82
V 0.43 2.363 4.69 1.576 1.21 4.087 6.64 1.742 42.18
Cr 0.35 1.428 2.90 0.743 0.60 1.542 4.31 1.006 7.39
Co 0.00 0.158 0.84 0.233 0.00 0.295 2.54 0.714 46.44
As 0.00 0.829 3.27 0.960 0.00 3.045 17.49 4.669 72.78
Rb 1.45 28.243 72.05 19.74 2.22 36.72 81.92 23.96 23.09
Mo 0.13 1.148 4.45 1.368 0.02 1.395 5.72 2.003 17.71
Ag 0.00 0.047 0.30 0.091 0.96 1.991 5.55 1.267 97.64
Cd 0.00 0.069 0.31 0.088 0.01 0.083 0.24 0.076 16.87
Sb 0.03 0.149 0.63 0.177 0.00 0.193 0.72 0.225 22.80
Ba 6.18 35.31 60.4 16.91 11.18 46.19 95.16 24.09 23.55
Pb 0.01 0.686 2.19 0.766 0.07 0.665 3.19 0.880 �3.16
Remarks: % difference is calculated by the mean trace element level by (Elementwet�Elementdry)/Elementwet�100%.
Table 10 – Depths of piezometers with water samplescollected
Piezometer Depth (m)
HW1 15.00
HW2 20.00
B3 Unknown
AB1 11.00
NPZ 17.84
MLS66 19.50
MLS66H 32.00
WA T E R R E S E A R C H 4 0 ( 2 0 0 6 ) 7 5 3 – 7 6 7762
and trace elements could be leached out in wet season
because of the generally higher water table during the season.
In addition, more chemicals may be washed out directly from
the vadose zone by infiltrated rainwater during the wet
season.
5.3. Trace element concentrations of groundwater collectedfrom deep piezometers
A few deep groundwater samples were collected from piezo-
meters installed in the urbanized spaces in the study area
(Figs. 2 and 3). The depths of piezometers are shown in Table
10. Many of the heavy metals and trace elements in these
samples showed similar concentrations as that in the natural
slopes. However, certain trace elements showed obviously
higher concentrations than that in the natural slopes or even
the developed spaces.
The total iron (Fe) concentration of HW2 was about
2755 ppb, which was significantly higher than the other
samples in the area. The sources from anthropogenic
activities appear to be unlikely because of the low concentra-
tions of other heavy metals. Instead, the high Fe content may
be related to the weathering of mineral grains (such as biotite
and feldspar). The primary reaction through which Fe3+
oxides are formed is the hydrolytic and oxidative decomposi-
tion of Fe2+ containing primary minerals (mainly Fe2+
silicates) through the reaction (Awoleye, 1991):
Fe2þFOFSiþH2Oþ ½O� !FFe3þOHþFSiOHþ e�;
ðFe2þ silicateÞ ðFe3þ oxideÞ(1)
Once formed, the Fe3+ oxides can be dissolved either through
(microbial) reduction to Fe2+ or through complexation by
organic ligands (Awoleye, 1991). Ruxton (1987) collected over
80 soil samples from the Mid-Levels area and found that 20 of
them showed significant quantities of iron cemented grains
(45% of iron cemented grains in fine sand). A few of the
samples even show 50% of iron cemented grains of the whole
sample. This may explain the high Fe content observed in the
groundwater sample. Ruxton (1987) further suggested that
deeper materials usually contain higher percentage iron
cemented grains.
Some water samples (for examples, AB1, B3, MLS66 H and
MLS66) contained relatively high lead (Pb) concentration.
Owing to the low concentrations of other heavy metals (such
as Zn, Cr and Fe, etc.) and the usage of unleaded petrol in
Hong Kong several years ago, it appears that contamination
ARTICLE IN PRESS
WAT ER R ES E A R C H 40 (2006) 753– 767 763
from stormwater is unlikely. Lead could be found naturally in
galena (lead sulfide, PbS), anglesite (lead sulfate, PbSO4),
minim (a form of lead oxide with formula Pb3O4), cerussite
(lead carbonate, PbCO3) and other minerals. Galena may be
the most important natural source. Water samples HW1 and
HW2 contained high barium (Ba) concentrations. Barium
could be derived from the weathering of minerals such as
barite and witherite. The host rocks also contained a
relatively high concentration of barium. Some water samples
showed elevated Mn contents, which may be related to the
corrosion of steel, as discussed. The boron concentration of
water samples from deep piezometers ranged from 13.47 to
34.24 ppb, which were comparable to that in the natural
slopes. This may indicate the absence of sewage contamina-
tion.
As limited by equipment, manpower and the scope
of study, only few groundwater samples from piezometers
were collected. Better evaluation of the heavy metal
contamination of deeper groundwater environment would
be achieved if more samples from piezometers can be
collected.
6. Conclusion
This paper presents the heavy metals and trace element
concentrations in groundwater samples in the natural slopes
and the highly urbanized spaces in the Mid-Levels area, Hong
Kong. The results from the natural slopes were used to
evaluate the impacts of urbanization on the heavy metal and
trace elements contents of groundwater in the developed
spaces.
The extents of leakage from service pipes and their effects
on heavy metal and trace element contents in groundwater
were investigated. Although it is believed that leakage from
stormwater drains would be common in the study area,
groundwater samples in the developed spaces did not contain
elevated levels of major heavy metals found in stormwater
(including Zn, Cr, Cu, Cd, Pb and Fe). This shows that the
vadose zone could effectively remove many of the heavy
metals and thus protect the underlying groundwater from
contaminations. On the other hand, groundwater samples in
the developed spaces were found to contain elevated levels of
minor, stormwater-related heavy metals including Mn, V, Co
and Mo which may support the occurrence of leakage from
stormwater drain. These heavy metals may also be derived
from remobilization from natural soils due to the changes in
local redox conditions and the corrosion of subsurface
engineering structures due to prolonged submergence
under acidic groundwater. More attention should therefore
be paid to investigate this corrosion process that could
possibly affect the stability of high-rise structures in the
study area. The average B and Se concentrations in the
developed spaces was about 8 times and 100 times higher
than that in the natural slopes, respectively, indicating the
presence of sewage in the groundwater in the developed
spaces. B and Se were statistically correlated to each other,
which further suggested that they may be derived from the
same source (leaked sewage). Besides, it is found that a large
part of the strontium (Sr) in groundwater may come from the
leakage of flushing water and/or sewage. These results
demonstrated that leakage from service pipes was
common in the developed spaces and they affected the heavy
metal and trace element distributions in groundwater to
different extents.
Although limited in number, the deep groundwater samples
collected from piezometers showed similar heavy metal and
trace element levels as that of the samples in the natural
slopes. Some trace elements with elevated levels were
considered to be mainly the result of natural processes such
as the weathering of minerals.
This study suggested that the vadose zone could filter many
of the heavy metals in leaked stormwater. Further heavy
metal studies are suggested to investigate the subsurface
materials (especially sediments and soils) in order to have a
more comprehensive picture about the impacts of urbaniza-
tion on the subsurface environment. The proposed studies
would be crucial for further modeling studies in the Mid-
Levels area or other areas with a similar level of urbanization.
The reason is that if soils collected in the developed spaces
are found to be insignificantly affected by heavy metals, this
may suggest that leakage from stormwater drains is minimal.
Then it is reasonable to assume that there is minimum
rainwater infiltration in the urbanized spaces in the Mid-
Levels area or other areas with a similar degree of urbaniza-
tion.
Acknowledgement
This study is partially supported by the Hong Kong Research
Grants Council (RGC) (HKU 7013/03) of the Hong Kong Special
Administration Region, China, the Seed Funding within the
Faculty of Science in The University of Hong Kong, and the
Development Budget for Area of Excellence in Water Environ-
ment Engineering, the University of Hong Kong.
Appendix A
Summary of chemical results (in ppb) of samples in the Mid-
Levels area in the wet season (DO is expressed as mg/L; ‘‘—’’
represents not measured; ‘‘nd’’ represents not determined
(Table A1).
Appendix B
Summary of chemical results (in ppb) of samples in the Mid-
Levels area in the dry season (DO is expressed as mg/L; ‘‘—’’
represents not measured; ‘‘nd’’ represents not determined
(Table B1).
ARTICLE IN PRESS
Ta
ble
A1
Sa
mp
lep
HD
OA
lFe
Mn
Cu
Zn
Sr
Se
Li
Be
VC
rC
oA
sR
bM
oA
gC
dS
bB
aP
bB
Natu
ral
slop
es
13
6.9
55.5
94.9
14.3
61.3
5n
d64.0
028.0
40.0
61.2
80.1
10.5
70.1
30.0
50.3
56.4
70.0
62.9
00.0
60.0
827.8
50.1
522.5
6
15
6.7
15.6
826.3
614.2
74.3
3n
d65.3
829.1
40.1
41.4
00.1
70.5
50.3
10.0
70.6
13.8
50.1
33.2
00.0
70.0
616.8
00.2
418.4
3
16
6.8
35.6
317.9
410.0
67.3
40.5
164.7
028.2
70.0
91.1
70.1
30.5
40.0
70.0
70.4
16.7
90.0
63.9
60.0
80.0
629.6
40.9
622.2
8
17
6.7
15.6
314.2
17.8
64.7
90.1
466.2
627.7
0n
d1.1
70.1
30.5
50.0
60.0
70.3
45.6
70.0
61.6
80.0
50.0
624.9
60.4
322.0
9
18
6.1
65.3
41.8
72.6
32.3
2n
d64.5
933.7
3n
d2.7
40.7
00.3
50.6
90.0
50.2
54.2
50.0
54.2
00.1
00.0
233.6
70.0
812.5
4
19
6.3
35.3
81.2
13.3
70.8
7n
d66.7
838.8
6n
d5.0
81.0
10.3
20.8
30.0
41.7
83.3
60.3
62.8
80.1
20.0
332.7
30.0
513.9
5
20
6.4
15.7
82.0
25.6
70.8
9n
d73.7
547.4
7n
d3.9
00.4
50.4
50.7
20.0
40.5
13.7
50.8
82.7
40.1
80.0
834.1
70.2
513.1
2
21
6.1
65.3
81.6
74.6
91.4
0n
d61.7
243.5
7n
d6.7
90.8
20.3
90.8
80.0
30.6
93.9
70.1
23.3
60.0
60.0
438.3
10.0
918.3
9
22
6.1
45.7
22.7
33.1
86.3
1n
d62.5
333.5
20.1
84.0
11.1
20.3
00.3
60.0
30.1
98.1
90.0
32.8
10.0
90.0
255.7
90.0
616.4
4
23
6.7
15.6
843.7
219.1
32.0
9n
d24.5
233.1
5n
d0.7
40.0
40.5
00.5
0n
d0.3
111.3
80.1
37.1
00.1
00.1
014.8
20.5
019.5
9
24
6.8
15.9
22.9
33.6
51.3
6n
d24.1
418.5
30.3
72.1
51.0
30.2
7n
dn
d0.1
29.6
80.0
11.3
60.0
50.0
232.3
00.0
321.9
6
26
6.7
55.7
26.5
84.9
31.3
50.0
230.6
419.2
6n
d0.4
60.1
00.3
85.1
2n
d0.1
42.9
60.0
20.6
80.0
20.0
28.0
70.1
031.2
2
D009
4.8
85.4
96.7
52.5
11.7
10.4
48.4
318.8
90.1
10.4
40.4
30.6
8n
dn
d0.2
610.3
90.0
22.2
70.0
4n
d38.0
30.8
324.2
4
D012
4.7
35.5
24.7
92.2
32.3
0n
d9.5
115.3
10.1
80.2
00.3
40.7
7n
dn
d0.2
09.8
50.0
72.6
40.0
8n
d47.8
93.3
420.5
9
D116A
5.1
14.9
60.7
82.8
80.8
5n
d8.1
127.8
00.0
21.1
20.4
10.7
4n
dn
d0.3
22.6
1n
d2.8
90.0
1n
d12.6
90.0
618.3
2
D118
5.0
95.3
62.5
52.7
63.3
2n
d10.4
428.8
40.0
91.7
20.5
21.0
6n
dn
d0.3
98.4
80.0
34.3
40.0
5n
d53.3
20.1
114.9
9
Dra
in4.6
6—
3.2
32.3
14.0
3n
d8.7
114.7
2n
d0.8
80.1
90.6
10.0
6n
d0.2
07.5
60.0
14.0
50.0
3n
d34.3
72.2
814.3
0
PS
#1
6.3
35.7
43.1
73.7
12.3
31.4
220.6
920.3
6n
d1.4
60.3
60.8
4n
dn
d0.4
35.8
30.0
93.7
50.0
6n
d31.8
10.1
414.0
3
Dev
elop
edsp
ace
s
77.3
95.2
73.6
216.1
86.8
71.8
873.8
7170.9
00.6
512.1
50.0
12.9
51.7
30.1
91.7
819.5
72.9
16.1
00.1
30.5
111.3
90.1
746.7
0
30
—5.9
71.2
85.8
90.7
0n
d24.5
475.8
20.5
64.1
70.3
91.8
60.6
0n
d1.1
02.2
21.0
80.9
80.0
40.0
455.3
80.0
747.1
2
35
7.0
55.6
60.3
22.5
5220.2
7n
d26.4
289.7
82.0
40.8
00.0
62.1
10.7
90.2
70.6
834.0
41.4
61.0
50.1
00.1
040.9
60.3
2115.7
8
36
5.6
34.0
30.5
04.8
0352.6
7n
d57.8
8312.0
05.1
03.8
20.7
52.8
11.4
61.1
40.8
759.8
50.1
31.1
51.1
80.0
3161.7
10.1
075.3
1
37
6.8
05.5
11.1
49.0
84.2
30.6
826.8
5134.1
02.0
32.3
80.0
82.7
01.0
90.0
81.9
118.4
52.6
21.0
20.0
60.7
038.5
30.3
957.1
0
39
6.8
05.2
90.6
59.6
945.2
53.3
144.4
5329.7
01.7
91.0
60.0
25.9
22.3
60.4
33.8
129.8
02.1
60.5
20.1
00.8
130.0
80.6
593.8
2
43
6.5
95.3
90.1
33.7
62.5
6n
d29.0
0322.1
020.4
00.6
80.0
53.5
51.1
30.0
32.9
728.9
70.7
91.8
60.1
80.1
753.6
40.3
6144.9
3
44
6.7
05.6
30.1
44.1
00.7
4n
d26.9
6340.0
011.5
40.6
10.0
23.3
71.0
90.0
51.1
132.3
80.9
71.7
50.1
70.2
164.2
50.3
4129.4
4
No
.26.9
45.3
10.1
55.3
60.7
1n
d7.3
9192.7
01.5
3n
dn
d1.2
11.7
50.0
3n
d11.2
20.4
53.2
40.0
2n
d11.1
80.3
548.6
8
87.5
25.6
70.6
37.4
81.9
20.9
863.9
9518.1
06.7
13.0
00.0
16.3
82.3
50.3
12.6
245.9
45.7
25.5
50.1
30.5
864.8
90.2
980.7
9
27
5.7
53.1
76.1
72.7
2789.3
62.9
192.3
9391.9
023.2
52.3
81.7
14.4
60.6
12.5
417.4
981.9
20.1
51.4
90.2
40.0
695.1
63.1
960.0
3
42
6.3
54.9
51.9
52.0
2162.1
20.2
040.9
1219.3
015.1
24.1
60.4
44.7
51.0
00.1
12.6
665.0
80.4
81.9
80.0
80.1
938.0
31.4
9150.8
6
45
6.9
65.5
60.1
43.9
70.3
7n
d8.5
8443.2
05.4
00.2
1n
d3.6
91.4
30.0
50.8
917.9
50.6
91.5
80.0
20.1
421.2
60.1
0116.6
6
46
6.3
44.8
30.0
52.0
40.5
0n
d8.3
8246.0
05.6
70.0
1n
d3.1
01.3
2n
d0.6
313.6
80.0
21.2
80.0
10.0
223.6
10.2
2179.2
2
47
7.1
15.6
13.0
35.9
198.9
40.2
611.9
3564.0
05.5
70.9
40.0
24.1
22.2
90.4
01.3
528.9
71.3
91.7
50.0
70.6
633.9
66.6
7141.3
6
48
6.2
03.9
40.1
32.2
120.4
3n
d12.1
2270.0
05.2
30.1
10.0
13.6
01.1
00.0
41.8
334.1
30.2
00.9
60.0
30.0
863.2
40.6
6232.9
0
28
7.1
55.6
90.1
43.7
40.9
80.3
921.4
6722.9
011.7
40.7
00.0
16.6
44.3
10.1
83.5
754.0
65.5
41.7
50.0
50.7
236.5
50.2
8230.9
5
29
6.9
55.6
30.1
02.2
816.9
0n
d22.6
6597.5
011.2
00.3
80.0
16.4
61.8
20.1
81.6
553.1
30.6
61.4
70.0
30.1
127.1
20.6
3259.5
1
38
7.0
25.7
30.0
11.7
34.1
91.0
827.6
41477.0
021.1
312.8
90.0
114.6
11.5
40.3
52.6
639.0
51.5
91.1
60.1
10.2
1195.9
90.0
6433.5
4
40
6.9
35.1
60.2
02.2
767.6
714.9
546.3
7823.1
015.4
315.8
30.0
111.0
71.8
10.4
43.3
943.5
43.0
91.2
70.1
10.3
676.1
32.7
4276.6
1
WA T E R R E S E A R C H 4 0 ( 2 0 0 6 ) 7 5 3 – 7 6 7764
ARTICLE IN PRESS
Ta
ble
B1
Sa
mp
lep
HD
OA
lFe
Mn
Cu
Zn
Sr
Se
Li
Be
VC
rC
oA
sR
bM
oA
gC
dS
bB
aP
bN
i
Natu
ral
slop
es
13
6.4
39.0
721.6
914.3
22.3
00.4
91.5
018.1
90.3
30.6
80.0
40.2
00.2
6n
d0.1
95.1
00.1
2n
d0.0
10.0
425.
20
0.2
2n
d
16
6.4
38.9
212.9
69.1
81.1
20.4
21.5
617.8
50.5
80.6
70.0
40.4
02.3
4n
d0.1
55.1
20.4
7n
d0.0
10.0
826.
91
12.1
0n
d
17
6.3
68.6
69.9
79.0
50.4
90.4
91.6
817.6
90.3
20.6
10.0
30.2
00.2
7n
d0.1
94.9
50.1
1n
d0.0
20.0
324.
17
0.0
6n
d
18
5.1
46.6
02.8
14.3
92.1
32.1
36.5
221.1
9n
d2.0
10.5
00.0
50.8
2n
d0.2
25.0
40.7
80.0
10.1
00.2
034.
76
0.1
67.6
6
19
5.2
15.9
02.3
14.9
40.8
40.8
55.6
322.4
10.3
23.3
90.6
30.0
80.7
3n
d0.9
72.9
20.3
80.0
10.0
90.0
827.
62
0.3
24.9
3
20
5.6
27.4
46.1
411.0
20.5
40.6
612
.65
35.1
30.5
02.7
90.2
90.3
90.5
1n
d0.3
13.0
30.8
60.0
10.1
60.0
436.
53
0.2
63.0
7
21
5.2
07.5
14.9
610.1
01.0
11.0
32.2
430.7
70.0
54.7
10.5
40.2
01.0
1n
d0.5
33.1
90.2
2n
d0.0
20.0
434.
55
3.0
90.7
6
24
5.9
18.4
14.4
57.8
02.1
00.2
810
.67
13.7
30.7
01.3
20.8
2n
d0.2
8n
dn
d7.0
00.0
4n
d0.0
40.0
132.
67
0.0
10.7
0
26
6.5
2—
27.7
463.2
52.7
14.5
37.6
519.4
20.4
61.5
90.1
50.4
90.3
60.0
10.1
37.1
10.2
1n
d0.0
20.0
420.
25
0.5
20.5
6
D012
5.5
08.3
17.8
95.6
91.4
30.8
81.9
513.5
80.5
80.7
20.3
50.1
80.2
5n
dn
d9.0
90.0
4n
d0.0
50.0
139.
54
0.0
30.6
4
D116A
5.2
26.9
72.6
76.8
70.3
60.5
41.9
124.6
10.2
81.8
70.4
80.0
81.2
7n
d0.1
72.3
90.1
7n
d0.0
50.0
411.
57
5.0
83.0
5
LFS
4.6
36.3
517.1
73.6
36.0
71.5
71.5
15.8
20.3
81.1
60.2
40.2
80.4
2n
d0.0
15.6
40.0
90.0
10.0
10.0
117.
82
0.2
0n
d
Dev
elop
edsp
ace
s
27
6.3
14.2
53.0
27.5
1536.7
00.5
68.2
7328.5
04.7
50.5
20.2
81.2
40.9
40.8
40.4
044.1
50.4
70.0
10.0
80.0
732.
01
2.1
90.5
7
28
7.0
16.7
2n
d5.5
81.4
51.5
33.9
8718.3
010.6
30.4
5n
d3.8
41.7
00.2
10.5
036.2
33.5
20.0
20.0
30.3
627.
60
0.3
51.8
6
29
6.7
37.3
9n
d2.9
325.7
21.1
16.2
0742.2
012.8
30.4
6n
d4.6
92.1
50.2
8n
d46.5
50.7
40.0
10.0
20.0
931.
41
0.8
61.8
9
30
6.4
47.8
12.5
613.6
50.5
50.2
31.5
661.4
00.5
23.4
10.3
20.4
30.3
5n
d0.3
91.4
50.7
3n
d0.0
20.0
340.
51
0.0
1n
d
42
5.8
4—
4.9
81.6
1158.3
01.6
327
.76
361.2
017.6
95.0
10.4
14.5
52.2
90.1
51.0
272.0
50.4
20.3
00.3
10.1
160.
40
1.2
935.5
3
43
6.3
57.4
9n
d5.3
23.8
60.9
49.6
6280.3
017.7
90.7
00.0
61.8
51.5
00.0
43.2
723.6
41.0
50.1
40.1
40.1
544.
23
2.0
70.3
2
44
6.4
87.2
3n
d5.8
60.8
30.8
17.6
4280.0
08.5
00.6
40.0
11.9
61.2
50.0
41.7
326.0
40.9
60.0
80.1
20.1
556.
01
0.3
50.2
5
45
7.1
07.2
91.5
28.8
80.2
00.3
71.8
7155.3
01.6
10.1
8n
d1.0
80.6
10.0
10.1
77.9
30.5
4n
d0.0
30.1
06.1
80.0
43.3
0
46
5.9
06.1
6n
d3.6
10.7
20.6
32.2
9278.6
06.2
60.0
6n
d2.0
71.2
60.0
5n
d14.9
50.1
5n
dn
d0.0
327.
97
0.3
30.3
8
48
5.9
54.9
4n
d2.8
013.1
70.5
71.8
2164.1
04.3
40.1
3n
d1.7
90.7
70.0
50.7
224.7
40.1
3n
d0.0
30.0
442.
89
0.0
83.7
7
87.0
77.8
83.1
311.7
34.0
51.6
84.2
6376.9
05.0
12.4
60.0
14.3
61.4
10.2
01.5
931.8
24.4
5n
d0.0
40.6
347.
32
0.1
91.6
9
LLR
5.6
42.3
316.2
13.3
81192.0
02.4
539
.60
397.3
018.9
62.0
21.3
62.8
42.5
61.9
50.5
178.2
40.3
50.1
60.1
80.0
895.
60
6.8
52.1
7
MM
5.8
58.2
02.0
326.8
60.2
00.3
12.0
846.1
70.8
00.5
40.0
70.1
10.4
7n
dn
d7.0
00.2
6n
d0.0
30.0
331.
99
0.1
71.0
3
No
.26.6
6—
0.3
29.9
92.9
71.8
210
.19
131.6
01.1
40.0
9n
d0.5
02.9
00.0
30.1
69.3
60.6
2n
d0.0
10.0
37.1
60.4
70.6
4
WAT ER R ES E A R C H 40 (2006) 753– 767 765
ARTICLE IN PRESS
WA T E R R E S E A R C H 4 0 ( 2 0 0 6 ) 7 5 3 – 7 6 7766
R E F E R E N C E S
Abrams, R.H., Loague, K., Kent, D.B., 1998. Development andtesting of a compartmentalized network model for redoxzones in contaminated aquifer. Water Resour. Res. 34,1531–1541.
Allen, P.M., Stephens, E.A., 1971. Report on the GeologicalSurvey of Hong Kong. Institute of Geological Sciences,London.
American Public Health Association (APHA), 1998. AmericanWater Works Association and Water Environment Federation.Standard Methods for the Examination of Water and Waste-water, 20th ed. American Public Health Association, Wa-shington, USA.
Awoleye, O.A., 1991. Weathering and iron oxide mineralogy ofHong Kong Granite. Ph.D. Thesis, University of Glasgow.
Ball, J.E., Jenks, R., Aubourg, D., 1998. An assessment of theavailability of pollutant constituents on road surfaces. Sci.Total Environ. 209, 243–254.
Barbosa, A.E., Hvitved-Jacobsen, T., 1999. Highway runoff andpotential for removal of heavy metals in an infiltration pond inPortugal. Sci. Total Environ. 235, 151–159.
Blumberg, M.S., Bell, J.M., 1984. Effect of various hydrologicalparameters on the quality of stormwater runoff from a WestLafayette, Indiana Urban watershed. NTIS PB84-207380, U.S.Environmental Protection Agency.
Cole, R.H., Frederick, R.E., Healy, R.P., Rolan, R.G., 1984. Prelimin-ary findings of the priority pollutant monitoring project of thenationwide urban runoff programme. J. Water Pollut. ControlFed. 57 (7), 898–908.
Crites, R.W., 1985. Micropollutant removal in rapid infiltration. In:Takashi, A. (Ed.), Artificial Recharge of Groundwater. Butter-worth Publishers, Boston, pp. 579–608.
Dannecker, W., Au, M., Stechmann, H., 1990. Substance load inrainwater runoff from different streets in Hamburg. Sci. TotalEnviron. 93, 385–392.
Davis, J.A., Kent, D.B., Coston, J.A., Hess, K.M., Joye, J.L., 2000.Multispecies reactive tracer test in an aquifer with spatiallyvariable chemical conditions. Water Resour. Res. 36 (1),119–134.
Dierkes, C., Geiger, W.F., 1999. Pollution retention capabilities ofroadside soils. Water Sci. Technol. 39 (2), 201–208.
Edmunds, W.M., Smedley, P.L., 2000. Residence time indicators ingroundwater: the East Midlands Triassic sandstone aquifer.Appl. Geochem. 15, 737–752.
Edmunds, W.M., Carrillo-Rivera, J.J., Cardona, A., 2002. Geochem-ical evolution of groundwater beneath Mexico City. J. Hydrol.258, 1–24.
Friedlander, S.K., 1973. Chemical element balances and identifi-cation of air pollution sources. Environ. Sci. Technol. 7,235–240.
Geotechnical Control Office (GCO), 1982. Mid-Levels Study—-
Report on Geology, Hydrology and Soil Properties. Geotechni-cal Control Office, Hong Kong.
Geotechnical Engineering Office (GEO), 2001. Geochemical Datafor Hong Kong Rocks, OG60 GR4/2001. Geotechnical Engineer-ing Office, Civil Engineering Department, Hong Kong SARGovernment.
Greer, D.L., 2000. Successful treatment of tinea capitiswith 2% ketoconazole shampoo. Int. J. Dermatol. 39 (4),302–304.
Hampson, P.S., 1986. Effects of Detention on Water Quality of TwoStormwater Detention Ponds Receiving Highway SurfaceRunoff in Jacksonville, Florida. US Geological Survey WaterResources Investigations Report 86-4151, Prepared in coop-eration with the Florida Department of Transportation. USGS,Denver, CO.
Hares, R.J., Ward, N.I., 1999. Comparison of the heavy metalcontent of motorway stormwater following discharge into wetbiofiltration and dry detention ponds along the London Orbital(M25) motorway. Sci. Total Environ. 235, 169–178.
Hathhorn, W.E., Yonge, D.R., 1995. The Assessment ofGroundwater Pollution Potential Resulting from StormwaterInfiltration BMP’s. Final Technical Report, Research ProjectT9902, Task 3, Washington State Transportation Center(TRAC), Washington State University, Pullman.
Jiao, J.J., Leung, C.M., Ding, G.P., 2003. Confined groundwater at No.52, Hollywood Road, Hong Kong. In: Proceedings of theInternational Conference on Slope Engineering, 8–10 Decem-ber 2003, Hong Kong.
Jiao, J.J., Wang, X.S., Nandy, S., 2006. Preliminary assessment ofthe impacts of deep foundations and land reclamation ongroundwater flow in a coastal area in Hong Kong, China.Hydrogeol. J. 14 (1–2), 100–114.
Jiao, J.J., Wang, X.S., Nandy, S., 2005. Confined groundwater zoneand slope instability in weathered igneous rocks inHong Kong. Engineering Geology 80, 71–92.
Kedziorek, M.A.M., Duputy, A., Bourg, A.C.M., Compere, F., 1998.Leaching of Cd and Pb from a polluted soil during thepercolation of EDTA: laboratory column experiments modeledwith a non-equilibrium solubilization step. Environ. Sci. Tec.32, 1609–1614.
Kiem, S., 2002. Heavy metal pollution of waterways from roadrunoff. Bachelor Degree Thesis, School of Engineering, JamesCook University, unpublished thesis.
Krein, A., Schorer, M., 2000. Road runoff pollution by polycyclicaromatic hydrocarbons and its contribution to river sedi-ments. Water Res. 34 (16), 4110–4115.
Ku, H.F.H., Simmons, D.L., 1986. Effects of Urban StormwaterRunoff on Groundwater Beneath Recharge Basins on LongIsland, New York. US Geological Survey Water ResourcesInvestigations Report 85-4088. Prepared in cooperation withLong Island Regional Planning Board, Syosset, New Your.USGS, Denver, CO.
Legret, M., Nicollet, M., Miloda, P., Colandini, V., Raimbault, G.,1999. Simulation of heavy metal pollution from stormwaterinfiltration through a porous pavement with reservoir struc-ture. Water Sci. Technol. 39 (2), 119–125.
Leung C.M., 2004. Groundwater chemistry in the urban environ-ment: a case study of the mid-levels area, Hong Kong. M.Phil.Thesis, The University of Hong Kong, Hong Kong, unpublishedthesis.
Leung, C.M., Jiao, J.J., 2005. Change of groundwater chemistryfrom 1896 to present in the Mid-Levels area, Hong Kong.Environmen. Geol. DOI:10.1007/s00254-005-0133-9.
Leung, C.M., Jiao, J.J., Malpas, J., Chan, W.T., Wang, Y.X., 2005.Factors affecting the groundwater chemistry in a highly-urbanized coastal area in Hong Kong: an example from theMid-Levels area. Environ. Geol. 48 (4–5), 480–495.
Loranger, S., Zayed, J., 1994. Manganese and lead concentrationsin ambient air and emission rates from unleaded and leadedgasoline between 1981 and 1992 in Canada: a comparativestudy. Atmos. Environ. 28, 1645–1651.
McKenzie, R.C., 2000. Selenium, ultraviolet radiation and the skin.Clin. Exp. Dermatol. 25 (8), 631–636.
Mikkelsen, P.S., Hafliger, M., Ochs, M., Jacobsen, P., Tjell, J.C.,Boller, M., 1997. Pollution of soil and groundwater frominfiltration of highly contaminated stormwater: a case study.Water Sci. Technol. 36 (8–9), 325–330.
Ng, S.L., Chan, L.S., Lam, K.C., Chan, W.K., 2003. Heavy metalcontents and magnetic properties of playground dust in HongKong. Environ. Monit. Assess. 89, 221–232.
Nightingale, H.I., 1987. Water quality beneath urban runoffwater management basins. Water Resour. Bull. 23 (2),197–205.
ARTICLE IN PRESS
WAT ER R ES E A R C H 40 (2006) 753– 767 767
Pierard, G.E., Arrese, J.E., Pierard-Franchimont, C., De Doncker, P.,1997. Prolonged effects of antidandruff shampoos: time torecurrence of Malassezia ovalis colonization of skin. Int. J.Cosmetic Sci. 19 (3), 111–117.
Pitt, R., Clark, S., Field, R., 1999. Groundwater contaminationpotential from stromwater infiltration practices. Urban Water1, 217–236.
Pitt, R.E., Field, R., Lalor, M., Brown, M., 1995. Urban stormwatertoxic pollutants: assessment, sources, and treatability. WaterEnviron. Res. 67 (3), 260–275.
Poon, C.S., Liu, P.S., Li, X.D., 1999. Heavy Metal Levels in Countryand Urban Park Soils in Hong Kong: A Preliminary Database.Construction Industry Development Studies and ResearchCentre (CIDARC), The Hong Kong Polytechnic University,Hong Kong.
Ruxton, B.P., 1987. Iron cementation in boulder colluvium matrixunder Hong Kong city. The Role of Geology in UrbanDevelopment, Geological Society of Hong Kong Bulletin No. 3,October 1987.
Tong, S.T.Y., Lam, K.C., 2000. Home sweet home? A case study ofhousehold dust contamination in Hong Kong. Sci. TotalEnviron. 256, 115–123.
Valcav, S., Valcav, V., 1992. Lubricants and Special Fluids. Elsevier,Amsterdam.
Vaze, J., Chiew, F.H.S., 2002. Experimental study of pollutionaccumulation on an urban road surface. Urban Water 4,379–389.
Wilson, L.G., Osborn, M.D., Olson, K.L., Maida, S.M., Katz, L.T.,1990. The groundwater recharge and pollution potential of drywells in Pima County, Arizona. Groundwater Monit. Rev. 10,114–121.
World Health Organization (WHO), 1993. Guidelines for DrinkingWater Quality, vol. 1. Recommendations. World Health Orga-nization.
Yim, W.W.S., Niu, P.S., 1987. Distribution of lead, zinc, copper andcadmium in dust from selected urban areas of Hong Kong.Hong Kong Eng., 7–14.
Yousef, Y.A., Wanielista, M.P., Hvitved-Jacobsen, T., Harper, H.H.,1984. Fate of heavy metals in stormwater runoff from highwaybridge. Sci. Total Environ. 33, 233–244.
Zachara, J.M., Smith, S.C., Kuzel, L.S., 1995. Adsorption anddissociation of Co-EDTA complexes in iron oxide-containingsubsurface sands, Geochim. Cosmochim. Acta 59 (23),4825–4844.