groundwater nitrate contamination and risk assessment in an agricultural area, south korea
TRANSCRIPT
ORIGINAL ARTICLE
Groundwater nitrate contamination and risk assessmentin an agricultural area, South Korea
Jae-Yeol Cheong • Se-Yeong Hamm •
Jeong-Hwan Lee • Kwang-Sik Lee •
Nam-Chil Woo
Received: 26 September 2010 / Accepted: 13 August 2011 / Published online: 30 August 2011
� Springer-Verlag 2011
Abstract The nitrate of groundwater in the Gimpo
agricultural area, South Korea, was characterized by means
of nitrate concentration, nitrogen-isotope analysis, and the
risk assessment of nitrogen. The groundwaters belonging to
Ca–(Cl ? NO3) and Na–(Cl ? NO3) types displayed a
higher average NO3- concentration (79.4 mg/L), exceeding
the Korean drinking water standard (\44.3 mg/L NO3-).
The relationship between d18O–NO3- values and d15N–
NO3- values revealed that nearly all groundwater samples
with d15N–NO3- of ?7.57 to ?13.5% were affected by
nitrate from manure/sewage as well as microbial nitrifica-
tion and negligible denitrification. The risk assessment of
nitrate for groundwater in the study area was carried out
using the risk-based corrective action model since it was
recognized that there is a necessity of a quantitative
assessment of health hazard, as well as a simple estimation
of nitrate concentration. All the groundwaters of higher
nitrate concentration than the Korean drinking water stan-
dard (\44.3 mg/L NO3-) belonged to the domain of the
hazard index \1, indicating no health hazard by nitrate in
groundwater in the study area. Further, the human exposure
to the nitrate-contaminated soil was below the critical limit
of non-carcinogenic risk.
Keywords Nitrate � Groundwater � Nitrogen isotope �Agricultural area � Geochemistry � Risk assessment
Introduction
Nitrate, one of the most common pollutants in groundwater,
causes a significant water-quality issue worldwide, espe-
cially in agricultural regions. Nitrate can originate from
various anthropogenic sources, such as fertilizers, animal
manure, domestic waste water and septic tanks, as well as
organic nitrogen from soil (Aravena et al. 1993; Fogg et al.
1998; Kim et al. 2002; Min et al. 2002; Lee et al. 2008).
Nitrate in groundwater originates from non-point sources
(chemical fertilizers) and point sources (septic tanks, sew-
age system, and animal/human manures) (Appelo and
Postma 1994). The excess loading of nitrogen can cause
eutrophication of surface waters (Bohlke and Denver 1995).
Nitrate is typically found in oxygenated groundwater in a
relatively stable state (Hamilton and Helsel 1995).
Numerous studies (Bohlke and Denver 1995; McMahon
and Bohlke 1996; Mengis et al. 1999) have been carried out
to determine the origin of nitrate contamination and to
evaluate the factors controlling the nitrate concentration in
groundwater. Recently, several studies using d15N–NO3-
J.-Y. Cheong
Technology Development Center, Korea Radioactive
Waste Management Corporation, 105-1, Duckjin-Dong,
Yusong-Gu, Daejeon 305-353, Republic of Korea
S.-Y. Hamm (&) � J.-H. Lee
Division of Earth Environmental System, Pusan National
University, San 30, Jangjeon-Dong, Geumjeong-Gu,
Busan 609-735, Republic of Korea
e-mail: [email protected]
K.-S. Lee
Korea Basic Science Institute, 52 Eoeun-Dong,
Yuseong-Gu, Daejeon 305-333, Republic of Korea
K.-S. Lee
Graduate School of Analytical Science and Technology,
Chungnam National University, Daejeon 305-764,
Republic of Korea
N.-C. Woo
Department of Earth System Sciences, Yonsei University,
134 Shinchon-Dong, Seodaemun-Gu, Seoul 120-749,
Republic of Korea
123
Environ Earth Sci (2012) 66:1127–1136
DOI 10.1007/s12665-011-1320-5
and d18O–NO3- (Burns and Kendall 2002; Mayer et al.
2002; Pardo et al. 2004; Li et al. 2010) have been conducted
to verify the origin of nitrate contamination. However, it is
not easy to differentiate various nitrate–nitrogen sources
based on only nitrogen-isotope values because a significant
overlap occurs in the nitrogen isotopic compositions of
atmospheric deposition, synthetic fertilizer, soil organic
nitrogen, and sewage/manure (Bedard-Haughn et al. 2003).
In agricultural areas of Korea, the use of nitrogen fer-
tilizer ([250 N kg/ha) (Kim et al. 2002) poses a significant
potential of water pollution by nitrate. It was also reported
that 32–42% of the groundwaters in the Iljuk region,
Gyeonggi province (Kim and Woo 2003) exceeded the
Korean drinking water standard for nitrate (\44.3 mg/L
NO3-, Korean Ministry of Environment 2008). High-nitrate
concentrations in groundwater may cause cyanosis (a dis-
ease caused by the increase in methemoglobinemia in the
blood, often referred to as ‘blue-baby syndrome’). Thus, the
risk assessment of groundwater by nitrate becomes
increasingly important. For instance, groundwater nitrate
contamination risk assessment in the Piedmont area in Italy
was carried out by the simulation of parametric systems
(Sacco et al. 2007). In another case, groundwater nitrate risk
assessment was conducted for diffuse agricultural sources
in the Upper Bann Catchment, Northern Ireland, by using an
improved GIS-based D-DRASTIC approach (Wang and
Yang 2008). Consequently, it is important to assess health
hazard quantitatively, as well as to estimate groundwater
contamination with nitrate simply based on its concentra-
tion in circumstance that rural areas in Korea consume
groundwater as drinking water and contain a great sector for
agricultural activity.
In this study, the characteristics of nitrate contamination
in the agricultural area of Gimpo City in Gyeonggi prov-
ince were examined using chemical and nitrogen-isotope
analyses. Nitrate risk assessment for groundwater was also
undertaken using the risk-based corrective action (RBCA)
tool kit for chemical releases v.2.5 (Groundwater Services
2005).
Study area
The study area, Gimpo City (Fig. 1), is located along the
Han River, the largest river in South Korea in terms of river
discharge and watershed area. The study area that is mostly
composed of agricultural land is well known as an impor-
tant rice field (‘‘Gimpo Field’’) in South Korea. Gimpo rice
field has a long history of rice production since
5,300–4,600 BP (Agriculture Technology Center of Gimpo
City 2011). In the study area, a significant amount of
chemical fertilizers and sewage/manure have widely been
used in the agricultural area even though the total
agricultural land has been continuously decreasing from
53% (11,488 ha) of the total land in 1999 to 45% (9,638 ha)
of the total land in 2007 (Statistical Yearbook of Gimpo
City 2007). Today, this area is changing with the continuous
expansion of industrial districts, the rapid increase in pop-
ulation, and the over-exploitation of groundwater to meet
the water demand due to insufficient water supply through
systematic waterworks. Annual precipitation ranged from
953.0 to 2,365.4 mm with an average of 1,326.4 mm and an
annual average air temperature ranging from 9.9 to 12.0�C
with an average of 11.0�C in the period between 1978 and
2007 (Korea Meteorological Administration 2008). An
annual precipitation of \1,000 mm was recorded in 1982
(992.2 mm) and 1988 (953.0 mm) because of drought,
whereas heavy rain storms occurred in 1987 with 1,738 mm
rainfall, 1990 with 2,365 mm, 1998 with 2,116 mm, 1999
with 1,542 mm, and 2003 with 1,642 mm (NIDP 2008).
The geology of the study area is mainly composed of
Precambrian Gyeonggi metamorphic complex, Jurassic
Daedong Group, Jurassic Daebo intrusive rocks and qua-
ternary alluvium (Lee et al. 1999). Precambrian Gyeonggi
metamorphic complex is composed of banded gneiss and
schist (Fig. 2). Gneiss is the most extensive bedrock in the
study area. Schist originating from sedimentary rocks is
distributed in the northern and southern parts of the study
area. Consisting of sandstone and shale-bearing abundant
iron, Tongjin formation, belonging to the Jurassic Daedong
group, occurs in the north-western part on a small scale. A
small body of gabbro is present in the middle part of the
study area at a small scale. A small granite body occurs in
Fig. 1 Location of sampling sites and land use (modified from NGII
(National Geographic Information Institute) 2008) of the study area
1128 Environ Earth Sci (2012) 66:1127–1136
123
the north-western part of the study area. Quaternary allu-
vium is located along the eastern boundary of the study
area. Quaternary alluvium in the floodplain around the Han
River consists of gravel, sand, and mud and has an average
thickness of 11.8 m (MIFAFF 2007).
The study area can be divided into 11 land use areas:
woods area, rice field, agricultural area except rice field,
grass land, greenhouse area, bare ground, industrial area,
residential area, business area, road, and freshwater body
(NGII 2008). The largest part (64.5 km2 or 45.3%) of the
total area (142 km2) is occupied by rice field which
includes five wells (G15, G18, G19, G22, and G24)
(Table 1). The second largest area comprises a wood area
of 29.4 km2 (20.6%) containing ten wells (G1–G4, G6, G9,
G12, G13, G21, and G25) and the third largest area is a
residential area of 27.3 km2 (19.2%) with 15 wells (G5,
G14, G20, G23, G26–G32, and G35–G38). The water wells
were drilled to a depth of 60–200 m with an average depth
of 112 m. The depth to groundwater ranged from 0.54 to
14 m with an average value of 4.05 m (MIFAFF 2007).
The water wells are mostly used for agriculture and partly
for drinking and domestic purposes.
Methods of sampling and chemical analyses
The field measurement, the laboratory analysis, and the
nitrogen-isotope analysis were carried out on the water wells.
Groundwater sampling was conducted twice in July 2007
and September 2008. The first sampling was performed on
38 wells (G1–G38) and the second sampling on 16 wells (G2,
G7, G8, G12, G15, G16, G18–G20, G24, G25, G27, G29,
G31, G35, and G36) (Fig. 1). The wells were purged by at
least three well volumes before the measurements of water
temperature, pH, electrical conductivity (EC), and alkalinity
in the field. The groundwater temperature was measured
using a digital thermometer manufactured by Sato Co., Japan
(model SK-1250MC); pH was measured using a portable pH
meter made by Orion Co., USA (model 250A); and EC was
measured using a portable EC meter made by Orion Co.,
USA (model 115). Alkalinity, expressed as bicarbonate
(HCO3-), was analyzed in situ using a portable photometer
(MultiDirect meter by Lovibond Co.). Samples for cation,
anion, and nitrogen-isotope analyses were filtrated using
0.45-lm cellulose membranes. In addition, the filtered
samples for the cation analysis were treated with 0.05 N
nitric acid to maintain the cation species in the state of a
pH \ 2. All samples for laboratory analysis were stored
below 4�C in an icebox and samples for nitrogen-isotope
analysis were preserved in a frozen state before the analysis.
Cations (Na?, K?, Ca2?, Mg2?, SiO2, Al3?, Fe2?, Mn2?,
and Zn2?) were analyzed using an inductively coupled
Fig. 2 Geological map of the study area (Lee et al. 1999)
Table 1 Various landuse areas
in the study areaLanduse type Area, km2 (%) Well no.
Rice field 64.5 (45.3) G15, G18, G19, G22, G24
Wood area 29.4 (20.6) G1–G4, G6, G9, G12, G13, G21, G25
Residential area 27.3 (19.2) G5, G14, G20, G23, G26–G32, G35–G38
Agricultural area excepting rice field 5.01 (3.52) G11, G34
Greenhouse area 3.06 (2.15) G16
Grass field 2.00 (1.40) G17
Industrial area 1.23 (0.86) G7, G8, G10, G33
Fresh water 5.15 (3.61) –
Bare ground 2.47 (1.74) –
Road 1.90 (1.33) –
Business area 0.05 (0.32) –
Total area 142 (100)
Environ Earth Sci (2012) 66:1127–1136 1129
123
plasma atomic emission spectrometer (Thermo Jarrell Ash
Co. model ICP-IRIS) and anions (SO42-, Cl-, NO3
-, F-)
were analyzed using an ion chromatography (Dionex Co.
model ED40) at the Busan Center of the Korea Basic Sci-
ence Institute (KBSI). Ion balance errors for the analyses
were within ±10%. The Fe, Al, and Mn ions were presented
as Fe3?, Al3?, and Mn2?, respectively, and were considered
as the dominant species in the study area. d15N–NO3-
and d18O–NO3- values were analyzed at the University
of Waterloo, Canada. For d15N–NO3- and d18O–NO3
-
analysis, a concentrated HgCl2 solution was added to
groundwater samples to prevent microbial activities which
can cause significant N and O isotopic fractionation of
nitrate. d15N–NO3- values were determined by a Thermo
Instruments Deltaplus elemental analyzer-isotope ratio mass
spectrometer (EA-IRMS) using the modified AgNO3
method following Silva et al. (2000). d18O–NO3- values
were determined by a VG PRISM IRMS using the CO2
breakseal method (Chang et al. 1999; Silva et al. 2000;
Drimmie et al. 2006). The analytical reproducibility was
±0.3% for d15N–NO3- and ±0.5% for d18O–NO3
-. All
stable isotope analysis data were represented in the con-
ventional d notation relative to the international standard
(i.e., V-SMOW for oxygen isotope and air for nitrogen
isotope), i.e., d = [(Rx/Rs) - 1] 9 1,000, where Rx is the
isotopic ratio 18O/16O or 15N/14N of the samples and Rs is
the isotopic ratio 18O/16O or 15N/14N of the standard.
Results and discussion
Nitrate contamination and origins of the groundwater
A plot on a piper diagram revealed that the groundwaters
belonged to Ca–HCO3, Na–HCO3, Ca–(Cl ? NO3), and
Na–(Cl ? NO3) types (Fig. 3). The groundwaters (G1, G3–
G10, G22, G23, G26, G28, and G37) belonging to
Ca–HCO3 and Na–HCO3 types displayed a lower average
concentration of NO3- (13.6 mg/L), which was likely to
represent a natural condition and the groundwaters (G2,
G11, G14, G15, G19, G25, G27, G29, G31, G34, G36, and
G38) belonging to Ca–(Cl ? NO3), and Na–(Cl ? NO3)
types displayed a higher average NO3- concentration
(79.4 mg/L), which might be affected by anthropogenic
pollution. Nitrate (NO3-) concentration ranged from 0.15 to
174 mg/L with an average of 36.7 mg/L (Table 2). Nine
sites (G2, G15, G19, G25, G29, and G33–G36) exhibited an
NO3- concentration of 44.3–174 mg/L, which exceeded the
Korean drinking water standard (\44.3 mg/L NO3- by
Korean Ministry of Environment 2008) (Fig. 1). No rapid
increase in nitrate with time may be anticipated from a
slight variation of nitrate concentration (e.g. 149 mg/L in
July 2007 and 159 mg/L in September 2008, on the well
G29). Calcium (Ca?) ranged from 3.80 to 661.1 mg/L
(Table 2). Sodium (Na?) and potassium (K?) ranged from
31.3 to 223 mg/L and from 0.71 to 14.6 mg/L, respectively.
On the other hand, chloride (Cl-) and sulfate (SO42) ranged
from 0.74 to 403 mg/L and from 0.19 to 74.3 mg/L,
respectively. The chloride concentration (403 mg/L) at G31
exceeded the Korean drinking water standard of 250 mg/L
and this appeared to be from domestic waste (Fig. 1). The
nitrate concentration did not show any distinct correlation
with other inorganic components. According to an R-mode
factor analysis, NO3- was uniquely linked to factor 3 with
a loading of 0.81, accounting for 11.3% of the total vari-
ance with an eigenvalue of 2.18. In contrast, factor 1 was
loaded to EC, Cl-, Mg2?, and Na? (C0.89), accounting for
34.4% of the total variance with an eigenvalue of 5.14;
factor 2 was loaded to SO42-, Mn2?, and K? (C0.69),
accounting for 15.9% of the total variance with an eigen-
value of 2.33; factor 4 was loaded to F- (0.66) and SiO2
(0.57), accounting for 8.26% of the total variance with an
eigenvalue of 1.56.
The nitrate concentration of nine groundwater wells
(G2, G15, G19, G25, G29, and G33–G36) in the rice field
(the largest land use area), woods area, residential area,
industrial area, and agricultural area except for the rice
field (Fig. 1; Table 1) were proven to exceed the Korean
drinking water standard (\44.3 mg/L NO3-). Higher
nitrate concentrations (8.69–174 mg/L) of groundwater in
the rice field than in other areas were marked by manure/
sewage during agricultural activities.
Nitrogen-isotope analysis was adopted to identify nitrate
origins of groundwaters collected from the thirteen wells
Ca
20
40
60
80
Na+K
20
40
60
80
Mg
80 60 40 20 20 40 60 80Cl+NO3
80
60
40
20
SO4
80
60
40
20
CO 3
+HC
O 3
Ca+M
g20
40
60
80
SO4+C
l+N
O 3
80
60
40
20
Fig. 3 Piper diagram of groundwater samples from the first (filledcircle) and second (open circle) suryeys
1130 Environ Earth Sci (2012) 66:1127–1136
123
(G2, G7, G8, G12, G15, G18, G20, G24, G25, G27, G29,
G35, and G36) in the study area (Table 3). The d15N-NO3-
values of groundwater ranged from ?5.94 to ?13.5% with
an average of ?10.3% (Fig. 4). In Fig. 4, ten wells (G2,
G7, G8, G12, G15, G18, G20, G27, G29, and G36) with the
d15N–NO3- of ?7.57 to ?13.5% displayed the origin of
manure/sewage while the remaining three wells (G24, G25,
and G35) displayed an undefined origin. The heavier iso-
tope composition that resulted from the storage and appli-
cation of animal manures was accompanied by ammonia
(NH3) volatilization so as to preferentially remove 14N
isotope, and to then enrich heavier 15N isotope in the
residual ammonium (Appelo and Postma 1994). When 15N-
enriched animal manures are applied to soil, ammonium
(NH4?) is converted to nitrate by bacterial nitrification.
Thus, the d15N value is used to reveal the origins of nitrate,
using different values between different nitrate sources:
chemical fertilizers (-4 to ?4%), soil organic nitrogen
(?3 to ?8%), and manure/sewage (?10 to ?20%) (Fre-
yer and Aly 1974). As a result, the nitrate in groundwater in
the study area was mostly derived from manure/sewage.
Based on the plot of d18O–NO3- values versus d15N–
NO3- values, it is also evident that most nitrate in the
groundwaters was affected by microbial nitrification before
entering the groundwater system in the study area. In
general, denitrification exponentially increases with the
d15N–NO3- and d18O–NO3
- values and decreases with
nitrate concentration (Mariotti et al. 1988; Kendall 1998;
Min et al. 2002). Conversely, in this study area, the d15N–
NO3- values versus log-transformed nitrate concentrations
exhibited a positive linear relationship (r2 = 0.43) (Fig. 5),
which suggested negligible denitrification.
On the plot of NO3- versus Cl- (Fig. 6a), two groups
were distinguished: group 1 represented a linear relation-
ship between NO3- and Cl- that indicated anthropogenic
impact mainly due to manure/sewage; group 2 represented
the mixing of the fresh groundwater affected by manure/
sewage and the paleo-brine originated from ancient coastal
environment at least 6,000 years ago (Ryu et al. 2005).
According to Ghabayen et al. (2006), the Na/Cl ionic ratio
of 0.86 is a criterion for the discrimination of seawater
intrusion. However, in the study area, Na/Cl ionic ratios
lower than 0.86 (Fig. 6b) indicated the existence of paleo-
brine in the sediments of the Gimpo coastal region in the
ancient time since the study area is not currently under the
influence of seawater intrusion. In addition, the ground-
waters in the upper left region in Fig. 6b showed a heavier
fraction of nitrogen isotopes than that of the other
groundwaters that represented a longer residence time of
the groundwaters. Based on the cluster analysis (Fig. 7),
groundwater samples could be explained by paleo-brine
(clusters 1) and nitrate-contaminated fresh groundwater
(cluster 2) which were correspondent to groups 1 and 2,
respectively, as interpreted by the relationship between
NO3- and Cl- (Fig. 6a). Further, cluster 3 was represented
by manure/sewage sources as comprising the well G31 in
residential area.
Table 2 Descriptive statistics of chemical constituents in the groundwater samples
Temp.
(�C)
pH EC
(lS/cm)
Ca2?
(mg/L)
K?
(mg/L)
Mg2?
(mg/L)
Na?
(mg/L)
SiO2
(mg/L)
Cl-
(mg/L)
NO3-
(mg/L)
SO42-
(mg/L)
HCO3-
(mg/L)
Maximum 23.0 7.92 1,679 66.1 14.6 47.3 223 18.5 403 174 74.3 323
Minimum 15.5 5.41 66.2 3.80 0.74 1.77 3.13 1.25 0.74 0.15 0.19 8.58
Mean 18.0 6.60 328 25.1 3.17 10.2 26.4 11.2 43.2 36.7 10.8 84.4
Median 18.0 6.58 284 22.5 2.24 8.89 15.4 11.2 23.0 16.7 6.75 62.5
SD 1.58 0.52 276 16.5 3.23 8.33 37.2 3.74 71.2 50.9 14.1 62.2
Kurtosis 1.21 0.57 15.3 -0.07 6.96 10.2 22.5 0.16 18.5 2.30 11.1 4.60
Skewness 0.86 0.14 3.31 0.66 2.64 2.57 4.37 -0.25 3.95 1.85 2.94 1.74
SD standard deviation
Table 3 d15N–NO3- and d18O–NO3
- isotopic compositions of
groundwater samples in the study area
d15N–NO3- (%) d18O–NO3
- (%)
G2 11.1 5.51
G7 11.6 6.61
G8 8.54 2.28
G12 8.94 7.53
G15 13.1 3.15
G18 7.57 5.57
G20 9.96 4.17
G24 5.94 8.43
G25 11.0 19.8
G27 10.7 3.80
G29 8.70 4.71
G35 13.5 15.5
G36 12.9 5.62
Maximum 13.5 19.8
Minimum 5.94 2.28
Mean 10.3 7.13
SD 2.27 5.04
Environ Earth Sci (2012) 66:1127–1136 1131
123
Risk assessment of nitrate in groundwater
As mentioned in the introduction, the high nitrate con-
centration in groundwater at the sites of G2, G15, G19,
G25, G29, G33, G34, G35, and G36 was required to be
evaluated not only by a simple analysis of nitrate con-
tamination, but also by health risk assessment because an
increase in nitrate over time may cause cyanosis. In gen-
eral, quantitative risk assessment is conducted to determine
an acceptable exposure level of toxic chemicals and to
estimate risks from exposure to the toxic chemicals in food,
drinking water, air, soil, groundwater, etc. (Chen et al.
2003). In this study area, a risk assessment of nitrate for
groundwater was undertaken using the RBCA tool kit for
chemical releases v.2.5 (Groundwater Services 2005).
Originally, RBCA tool kit was developed for assessing the
risk of chemicals at the stages of Tier I, Tier II, and Tier III.
The risk assessment analysis using RBCA accounts for
several factors, such as exposure pathways (surface water,
groundwater, soil, and air), concentration of pollutants, air,
groundwater, soil, and transport models.
In the study area, the main exposure pathway of nitrate
was identified as groundwater. The factors of non-carcin-
ogens, exposure frequency, dermal exposure frequency,
soil dermal adherence factor, soil ingestion rate, swimming
exposure time, swimming event frequency, and swimming
water ingestion rate were followed the US EPA guideline
(1995) because these factors are not specified in Korea’s
statistics (Tables 4, 5). However, body weight, fish con-
sumption rate, exposed surface area of skin, surface area of
body skin, exposed skin area during swimming, vegetable
ingestion rate, and water ingestion rate are specified in the
-2 0 2 4 6 8 10 12 14
δ15N-NO3- (o/oo)
0
10
20
30
40
50
60
δ18O
-NO
3- (o
/ oo) Atmospheric deposition
δ15N-NO3- = -15 ~ +15O/OO
δ18O-NO3- = +25 ~ +75O/OO (AgNO3 method)
δ18O-NO3- = >60O/OO (Denitrifier method)
Microbial nitrification(δ18O-NO3
- = -10 ~ +10O/OO)
G25
G35
G24 G18
G8G29
G12
G20 G27G2
G7 G36
G15
Synthetic fertilizer
Soil organic matter
Manure & sewage
Fig. 4 Plot of d18O–NO3- values versus d15N–NO3
- values for
groundwaters in the study area, with the indicative range of microbial
nitrification (Mayer et al. 2002; Michalski et al. 2004; Kendall 1998)
0 2 4 6
ln NO3- (mg/L)
-4
0
4
8
12
16
20
δ15N
-NO
3- (o/ o
o)
G35G36 G15
G7G27
G20G12 G8
G18G24
G2G25
G29
r2 = 0.43
Fig. 5 d15N–NO3- values versus log-transformed NO3
- concentra-
tions in groundwaters
Cl -(mg/L)
0
40
80
120
160
200
NO
3-(m
g/L
)
Mixing
line
1st survey2nd survey
(a)
Group 1
Group 2
0 100 200 300 400 500
0 100 200 300 400 500
Cl - (mg/L)
0.1
1
10
100
Na+ /
Cl-
1st survey2nd survey
(b)
Na+/Cl- = 0.86
Fig. 6 Plots of NO3- versus Cl- (a) and Na? versus Cl- (b) using
data from the first and second surveys
1132 Environ Earth Sci (2012) 66:1127–1136
123
Korean standards (Table 5). The ASTM model was applied
for the soil to groundwater leachate process (ASTM 1995).
In addition, the Domenico model (1987) with dispersion
only was introduced to estimate the dilution attenuation
factor (DAF) which represented the ratio of the source
concentration to the receptor point concentration. Hence, a
value of DAF = 1 (the meaning of no dilution or attenu-
ation) indicates that the concentration at the receptor point
is the same as that in the soil leachate. Accordingly, a high
DAF value corresponds to a high degree of dilution and
attenuation.
The risk assessment of nitrate in the study area was
undertaken for the sites of G2, G15, G19, G25, G29, G33,
G34, G35, and G36 showing higher nitrate concentration
than 44.3 mg/L (Fig. 8). Hydraulic conductivity of
9.67 9 10-5 cm/s (MIFAFF 2007), the effective porosity
of 0.26 for medium sand (Fetter 2001), and an average pH
(6.60) of the groundwater were used for the nitrate risk
assessment (Table 4). The thickness of the surface soil
layer was regarded as 11.8 m, the area of contaminated soil
was estimated as 7.1 9 107 m2, the thickness of the con-
taminated soil layer was 6.5 m, and the soil type was
medium sand (MIFAFF 2007). As a result of the risk
analysis, the non-carcinogenic risk of human exposure to
the contaminated soil was lower than the critical risk level
for the risk, indicating no risk of the non-carcinogenic
component (nitrate). On the other hand, the hazard index
(HI) induced by nitrate in groundwater was eventually 0.75
which was also lower than the critical value (1) of non-
carcinogenic risk. HI \ 1 implies there is no need of
remediation work to the contaminant, while HI C 1
implies that remediation work is required. The site-specific
target level (SSTL) for corrective action was determined as
245 mg/L, comparing to 44.3 mg/L of nitrate (the standard
for both Korea and USA drinking water) correspondent to
1.6 mg/kg/day of the oral reference dose (or the threshold
Fig. 7 Dendrogram from the
cluster analysis of groundwater
wells in the study area
Table 4 Site-specific input
parameters for soil and
groundwater necessary for
nitrate risk assessment
Soil Groundwater
Depth to water (1.29 m) Groundwater Darcy velocity (9.70 9 10-7 cm/day)
Depth to top of affected soils (1.29 m) Groundwater seepage velocity (3.70 9 10-6 cm/day)
Depth to base of affected soils (6.20 m) Hydraulic gradient (0.01)
Affected soil area (2,025 m) Hydraulic conductivity (9.67 9 10-5 cm/s)
Precipitation (1,486.7 mm) Effective porosity (0.26)
Fraction of organic carbon (0.01) Fraction of organic carbon in saturated zone (0.001)
Soil/water pH (6.60) Groundwater pH (6.60)
Groundwater plume width at source (45 m)
Plume thickness at source (2 m)
Longitudinal dispersivity (15 m)
Transverse dispersivity (4.95 m)
Vertical dispersivity (0.75 m)
Environ Earth Sci (2012) 66:1127–1136 1133
123
for certain toxic effects) (US EPA 1990). Therefore, the
SSTL for the study area is *5 times higher than Korea’s
drinking water standard of nitrate, and this is related to the
characteristics of the exposure pathway and concentration
of nitrate in the study area.
Using the groundwaters at G2, G15, G19, G25, G29,
G33, G34, G35, and G36, the relationship between onsite
nitrate concentration and radial distance from the onsite
nitrate source was established for different HI values
(Fig. 8). In the figure, all the groundwaters belonged to the
domain of HI \ 1 in which no health hazard can take place
by nitrate in groundwater even when nitrate concentration
in the groundwaters exceeded the Korean drinking water
standard (\44.3 mg/L NO3-). As the nitrate contamination
at the source (onsite NO3- concentration) increases, the
radial distance to HI = 1 also increases. The regression
line between the onsite NO3- concentration (Y) and the
radial distance (X) from the onsite NO3- source relative to
HI = 1 (Fig. 8) is expressed by an empirical equation:
Y ¼ 0:000006 � X4 þ 0:0017 � X3 þ 0:20 � X2
� 1:39 � X þ 223ð1Þ
Thus, using Eq. 1, the critical limit of health hazard by
nitrate can effectively be determined in the study area.
In the future, the hazard index will be changed accord-
ingly if the Korean Ministry of Environment strengthens
the Korean drinking water standard of nitrate, even though
all the groundwaters of the study area, at present, exhibit no
health hazard by nitrate. Nitrate concentration in ground-
water in the study area can be decreased by applying an
autotrophic sulfur-oxidizing reactive barrier and con-
trolled-release molasses reactive barrier systems (Kim et al.
2009). Moreover, governmental policy should be estab-
lished for the proper use of nitrogen fertilizer on agricul-
tural land.
Conclusions
This study examined the nitrate contamination in the
Gimpo agricultural area using nitrate concentration, nitro-
gen-isotope analysis, and nitrogen risk assessment. The
groundwaters belonged to the Ca–HCO3, Na–HCO3,
Table 5 Exposure factors for
RBCA tool kitSource Exposure factors Values
Korean standard Exposure duration to carcinogens (KSIS 2010) 79.4 years
Body weight (MKE 2004) 63 kg
Exposed surface area of skin (Lee 2005) 3,247 cm2/day
Surface area of skin (MKE (Ministry of Knowledge Economy) 2004) 17,000 cm2
Exposed skin area during swimming (MKE 2004) 17,000 cm2
Vegetable ingestion rate (KSIS 2010) 1.892 kg/day
Recommended water ingestion rate 2 L/day
US (1995) Exposure duration to non-carcinogens 30 years
Exposure frequency 350 day/year
Dermal exposure frequency 350 day/year
Soil dermal adherence factor 0.5 mg/cm2
Water ingestion rate 2 L/day
Soil ingestion rate 100 mg/day
Swimming exposure time 3 h/event
Swimming event frequency 12 event/year
Swimming water ingestion rate 0.05 L/h
0 50 100 150
Radial distance (m)
0
500
1000
1500
2000
On
-sit
e N
O3
(mg
/L)
HI = 1
HI > 1
HI < 1
Fig. 8 Onsite NO3- concentration versus radial distances from the
center of the nitrate-contaminated groundwater source in the study
area, with different hazard index (HI) values. Dot (•) designates G2,
G15, G19, G25, G29, G33, G34, G35, and G36
1134 Environ Earth Sci (2012) 66:1127–1136
123
Ca–(Cl ? NO3), and Na–(Cl ? NO3) types, among which
the Ca–(Cl ? NO3) and Na–(Cl ? NO3) types displayed a
higher average NO3- concentration (79.4 mg/L), exceed-
ing the Korean drinking water standard (\44.3 mg/L
NO3-). Based on the plot of d18O–NO3
- values versus
d15N–NO3- values, 10 groundwater samples among a total
of 13 samples were linked to a manure/sewage source with
microbial nitrification. Further, d15N–NO3- values versus
log-transformed NO3- concentrations showed a positively
proportional relationship which suggested negligible deni-
trification. As a result of the risk analysis, the site-specific
target level (SSTL) was evaluated as 245 mg/L. The non-
carcinogenic risk of human exposure to the nitrate-con-
taminated soil was below the critical non-carcinogenic
level and the hazard index (HI) of nitrate in groundwater
was finally 0.75, which was also below the critical limit of
non-carcinogenic risk. In the study area, all the ground-
waters belonged to the region of HI \ 1 while some of the
groundwaters exceeded the Korean drinking water stan-
dard. Hence, no remediation action for nitrate-contami-
nated groundwater is needed at this time. In addition, the
line of HI = 1 displayed a positive relationship between
the onsite NO3- concentration and the radial distance from
the onsite NO3- source.
Acknowledgments This work was financially supported by the
Korea Ministry of Environment as ‘‘The GAIA Project’’.
References
Agriculture Technology Center of Gimpo City (2011) http://agri.
gimpo.go.kr. Accessed 2011
Appelo CAJ, Postma D (1994) Geochemistry, groundwater and
pollution. A.A. Balkema, Rotterdam, pp 271–279
Aravena R, Evans ML, Cherry JA (1993) Stable isotopes of oxygen
and nitrogen in source identification of nitrate from septic
systems. Ground Water 31:180–186
ASTM (American Society for Testing and Materials) (1995) Standard
guide for risk-based corrective action applied at petroleum
release sites. ASTM E-1739, pp 1–395
Bedard-Haughn A, van Groenigen JW, van Kessel C (2003) Tracing15N through landscapes: potential uses and precautions. J Hydrol
272:175–190
Bohlke JK, Denver JM (1995) Combined use of groundwater dating,
chemical, and isotope analyses to resolve the history and fate of
nitrate contamination in two agricultural watersheds, Atlantic
coastal plain, Maryland. Water Resour Res 31:2319–2339
Burns DA, Kendall C (2002) Analysis of d15N and d18O to
differentiate NO3- sources in runoff at two watersheds in the
Catskill mountains of New York. Water Resour Res 38:1–11
Chang CCY, Langston J, Riggs M, Campbell DH, Silva SR, Kendall
C (1999) A method for nitrate collection for d15N and d18O
analysis from waters with low nitrate concentrations. Can J Fish
Aquat Sci 56:1856–1864
Chen JJ, Chen Y-J, Teuschler LK, Rice G, Hamernik K, Protzol A,
Kodell RL (2003) Cumulative risk assessment for quantitative
response data. Environmetrics 14:339–353
Domenico PA (1987) An analytical model for multidimensional
transport of a decaying contaminant species. J Hydrol 91:49–58
Drimmie RJ, Zhang L, Heemskerk AR (2006) 15N/18O in dissolved
nitrate, Technical Procedure 12.0, Revision 03, Environmental
Isotope Laboratory: 9 pages. Department of Earth and Environ-
mental Sciences, University of Waterloo, Waterloo
EPA US (1990) Criteria document for nitrate/nitrite. Office of
Drinking Water, Washington, DC
Fetter CW (2001) Applied hydrogeology. Prentice-Hall, New Jersey,
pp 66–112
Fogg GE, Rolston DE, Decker DL, Louice DT, Grismer ME (1998)
Spatial variation in nitrogen isotope values beneath nitrate
contamination sources. Ground Water 36:418–426
Freyer HD, Aly AJM (1974) 15N studies on identifying fertilizer
excess in environmental systems, In: Isotope ratios as pollutant
source and behavior indicators. IAEA, Vienna, pp 21–33
Ghabayen SMS, Mckee M, Kemblowski M (2006) Ionic and isotopic
ratios for identification of salinity sources and missing data in the
Gaza aquifer. J Hydrol 318:360–373
Groundwater Services (2005) RBCA tool kit software guidance
manual for chemical releases, pp 1–34
Hamilton PA, Helsel DR (1995) Effects of agriculture on ground-
water quality in five regions of the United States. Ground Water
33:217–226
Kendall C (1998) Tracing nitrogen sources and cycling in catchment.
In: Isotope tracers in catchment hydrology. Elsevier, Amster-
dam, pp 519–576
Kim YT, Woo NC (2003) Nitrate contamination of shallow ground-
water in an agricultural area having intensive livestock facilities.
J Soil Groundw Environ 8:57–67 (in Korean)
Kim KH, Yun ST, Chae GT, Choi BY, Kim SO, Kim KJ, Kim HS, Lee
CW (2002) Nitrate contamination of alluvial groundwaters in the
Keum river watershed area: source and behaviors of nitrate, and
suggestion to secure water supply. J Eng Geol 12:471–484
(in Korean)
Kim YB, Song SH, Woo NC, Nam GP, Lee JM et al (2009)
Development of in situ remediation techniques for contaminated
groundwater with nitrate in rural area. Korea Rural Community
Corporation, Republic of Korea (in Korean)
Korea Meteorological Administration (2008) http://www.kma.go.kr.
Accessed 2008
Korean Ministry of Environment (2008) Korean drinking water
standard. Ministry of Environment, Republic of Korea (in
Korean)
KSIS (Korean Statistical Information Service) (2010) http://www.
kosis.kr
Lee JY (2005) A study on the body surface area of Korean adults.
Doctoral dissertation of Seoul National University
Lee BJ, Kim YB, Lee SR, Kim JC, Kang PC, Choi H-I, Jin MS (1999)
Geological map and explanatory note of the Seoul–Nam-
chonjeom sheet. Korea Institute of Geology Mining and
Materials, pp 1–64
Lee KS, Bong YS, Lee DH, Kim YJ, Kim KJ (2008) Tracing the sources
of nitrate in the Han River watershed in Korea, using d15N–NO3-
and d18O–NO3- values. Sci Total Environ 395:117–124
Li SL, Liu CQ, Li J, Liu X, Chetelat B, Wang B, Wang F (2010)
Assessment of the sources of nitrate in Changjiang River, China
using a nitrogen and oxygen isotope approach. Environ Sci
Technol 44:1573–1578
Mariotti A, Landreau A, Simon B (1988) 15N isotope biogeochemistry
and natural denitrification process in groundwater application to
the chalk aquifer of northern France. Geochim Cosmochim Acta
52:1869–1878
Mayer B, Boyer EW, Goodale C, Jaworski NA, Breemen NV,
Howarth RW, Seitzinger S, Billen G, Lajtha K, Nadelhoffer K,
Dam DV, Hetling LJ, Nosal M, Paustian K (2002) Sources of
Environ Earth Sci (2012) 66:1127–1136 1135
123
nitrate in rivers draining sixteen watersheds in the northern US:
isotopic constrains. Biogeochemistry 57–58:171–197
McMahon PB, Bohlke JK (1996) Denitrification and mixing in a
stream–aquifer system: effects on nitrate loading to surface
water. J Hydrol 186:105–128
Mengis M, Schiff SL, Harris M, English MC, Arvena R, Elgood RJ,
MacLean A (1999) Multiple geochemical and isotopic approaches
for assessing ground water NO3- elimination in a riparian zone.
Ground Water 37:448–457
MIFAFF (Ministry of Food, Agriculture, Forestry and Fisheries)
(2007) Report on groundwater management for agricultural area
(Gimgo district, Gimpo City), pp 347–421 (in Korean)
Min JH, Yun ST, Kim KJ, Kim HS, Hahn JS, Lee KS (2002) Nitrate
contamination of alluvial groundwaters in the Nakdong river
basin, Korea. Geosci J 6:35–46
MKE (Ministry of Knowledge Economy) (2004) http://www.mke.go.kr
. Accessed 2004
NGII (National Geographic Information Institute) (2008) http://www.
ngii.go.kr. Accessed 2008
NIDP (National Institute for Disaster Prevention) (2008) http://www.
nidp.go.kr. Accessed 2008
Pardo LH, Kendall C, Pett-Ridge J, Chang CCY (2004) Evaluating
the source of streamwater nitrate using d15N and d18O in nitrate
in two watersheds in New Hampshire, USA. Hydrol Process
18:2699–2712
Ryu E, Nahm WH, Yang DY, Kim JY (2005) Diatom floras of a
western coastal wetland in Korea: implication for late quaternary
paleoenvironment. J Geol Soc Korea 41:227–239 (in Korean)
Sacco D, Offi M, Maio MD, Grignani C (2007) Groundwater nitrate
contamination risk assessment: a comparison of parametric
systems and simulation modeling. Am J Environ Sci 3:117–125
Silva SR, Kendall C, Wilkinson DH, Ziegler AC, Chang CCY,
Avanzino RJ (2000) A new method for collection of nitrate from
fresh water and the analysis of nitrogen and oxygen isotope
ratios. J Hydrol 228:22–36
US EPA (1995) How to evaluate alternative cleanup technologies for
underground storage tank sites. EPA 510-8-95-005
Wang JL, Yang YS (2008) An approach to catchment-scale ground-
water nitrate risk assessment from diffuse agricultural sources: a
case study in the Upper Bann, Northern Ireland. Hydrol Process
22:4274–4286
1136 Environ Earth Sci (2012) 66:1127–1136
123