Geosciences JournalVol. 18, No. 1, p. 115 − 123, March 2014DOI 10.1007/s12303-013-0050-yⓒ The Association of Korean Geoscience Societies and Springer 2014

REVIEW

Use of environmental and applied tracers for groundwater studies in Korea

ABSTRACT: With a growing demand for fresh water, mainly dueto the rapidly developing economy, their interests focus on securingplentiful groundwater resources for drinking, domestic, agriculturaland industrial purposes. In addition, remediation of contaminatedgroundwater has become another main interest. Hence, manyenvironmental tracers, such as CFCs, Ra, Rn, CH4, δ18O, δD, 3H,He, δ13C, δ37Cl, and applied tracers, such as Cl–, Br– and rhodamineWT, have been widely used in the country for groundwater studieswith different purposes. The main purposes include estimations ofsubmarine groundwater discharge pathways and their quantifica-tion in coastal regions, especially in Jeju (volcanic island), as wellas examinations of groundwater origin and mixing with streamwater, groundwater age dating, tracing (apportioning) the contam-ination sources of chlorinated solvents (e.g., TCE, PCE) in indus-trial areas, and identification of reservoir (large dam) leakage. Thispaper reviews the use of environmental and applied tracers in Koreangroundwater studies and provides perspectives on their use.

Key words: environmental tracers, submarine groundwater discharge,age dating, source apportionment, conservative tracers

1. INTRODUCTION

Groundwater is one of the main fresh water supply sourcesin the Republic of Korea (hereafter referred to as Korea)and it accounts for about 11.5% of the total annual watersupply (Lee, 2011). With increasing demand of water supplyfor drinking, domestic, agricultural and industrial usages,groundwater development has been largely expanded. Thusthe number of groundwater wells in the country has graduallyincreased from 640,000 in 1994 to 1.36 million in 2009, andthe corresponding annual groundwater use has also largelyincreased from 2,570 million to 3,806 million m3 for thesame period (MLTM, 2010). Also, sales of bottled water(permitted only from groundwater sources in Korea) havegreatly increased from 25 million US$ in 2004 to 39 millionUS$ in 2011. All these circumstances combined have causeda widespread awareness of potential groundwater problemsin the future.

In Korea, an official groundwater management strategyof the government was started when the “Groundwater Law”was enacted in 1994 (Lee et al., 2007d). The law enforcesan obligatory report of any groundwater development (wellinstallation) to a relevant authority, as well as an environ-

mental impact assessment for groundwater wells whosedaily pumping is greater than 100 m3 (150 m3/day for agri-cultural purposes). The law also required the establishmentand operation of a nation-wide groundwater monitoring net-work. Construction started on the first groundwater moni-toring station in 1995, and today the network consists of334 stations, at which groundwater level, water temperatureand electrical conductivity are being automatically mea-sured every hour (Lee et al., 2007d; Park et al., 2011). Fur-thermore, the law enforced a basic groundwater investigationfor the entire the country, which is still underway.

In coincidence with the “Groundwater Law” in 1994, theKorean Society of Groundwater Environment was also estab-lished in the same year (merged into the Korean Society ofSoil and Groundwater Environment in 2000). Members ofthe society mostly originated from Departments of Geologyor Geological Sciences of Korean universities and fromnation-run or nation-assisted research institutes, such as KoreaInstitute of Geoscience and Mineral Resources, a stateagency with a similar range of roles of the USGS. The soci-ety largely contributed to the development of groundwaterstudies by stimulating R&D investment by governmentagencies and environmental companies, and by disseminat-ing research data to the members of the society, as well asto the public.

In the early period of the groundwater studies in Korea,the focus was largely on the application of basic ground-water theories and field tests (to Korean hydrogeologic con-ditions) which were already widely developed in manycountries. These studies include estimations of water leveldistribution by some kriging methods (Chung, 1993; Chungand Lee, 1995) and performance of pumping and slug testsin fractured aquifers (Hamm, 1994; Hamm et al., 1998; Leeand Lee, 1999). With an increasing usage of groundwaterand rapid urbanization, a number of groundwater problemswere perceived, including a large decline in the groundwa-ter level in a number of regions (Booh and Jeong, 2000; Leeet al., 2004, 2007c; Lee, 2011; Park et al., 2011; Choi andLee, 2012) and groundwater contamination (Hahn et al.,1991; Chung, 1995; Lee et al., 2001b, 2003b, 2005; Hammet al., 2006; Jeon et al., 2008; Lee, 2011). Concern for thewater level decline triggered detailed investigations of itscause and preparation of mitigation measures (Lee et al.,

Jin-Yong Lee* Department of Geology, College of Natural Sciences, Kangwon National University, Chuncheon 200-701, Republic of Korea

*Corresponding author: hydrolee@kangwon.ac.kr

116 Jin-Yong Lee

2007c, 2007d; Park et al., 2011), as well as in-depth isoto-pic and environmental tracers studies in order to enhanceour understanding of hydrologic cycles, as a base of securinggroundwater resources, especially on Jeju volcanic island,where groundwater is practically the sole freshwater source.

Issues of groundwater contamination also drew attentionwithin the academic community. Hydrogeologists increasedtheir efforts to determine methods of characterization andsource apportionment for groundwater contamination. One ofthe most frequently occurring contaminants in groundwaterswithin Korea is trichloroethylene (TCE) (Park et al., 2005;Baek and Lee, 2011; Lee, 2011; Yang and Lee, 2012). Thus,characterization of TCE contaminated aquifers and identifi-cation of its origins (source) is now a hot research topic withinKorea, as are follow up studies relating to remediation of

the contaminated groundwater (Park et al., 2013). The objec-tives of this paper are to review some important ground-water studies within the country, where environmental andartificial tracers were used for specific and appropriate pur-poses, and to draw some perspectives on their use in thefuture.

2. USE OF ENVIRONMENTAL AND APPLIED TRACERS IN KOREA

Groundwater studies using environmental and appliedtracers in Korea (Fig. 1; Tables 1 and 2) can be summarizedinto three main categories. The first, and main one, is toreveal submarine groundwater discharges (SGD) and asso-ciated nutrients fluxes into estuaries of coastal areas using

Fig. 1. Location of the Republic of Korea and the studies sites where the environmental and applied tracers were used. One symbol (filledrectangular or circle) does not mean a single study, rather means multiple studies (or tests).

Use of environmental and applied tracers for groundwater studies in Korea 117

environmental tracers, including 222Rn, 223Ra, 224Ra, 226Ra,228Ra, 18O, CH4 and their combinations (Kim et al., 2003,2005; Hwang et al., 2005; Lee and Kim, 2007; Lee et al.,2009). Tracer studies have been dominated by the efforts ofa research team of Prof. Guebuem Kim of Seoul NationalUniversity. The other main research team for the islandusing δ2H, δ18O, 3H, 3He, CFCs, SF6 and their combination,has been mainly led by Dr. Dong-Chan Koh of Korea Insti-tute of Geoscience and Mineral Resources (KIGAM), andthey have tried to examine groundwater age, groundwatermixing with rainfall and saline water, and sources of nitrateand sulfate in coastal areas and inland areas of the country(Kim Y. et al., 2003; Koh et al., 2005, 2006, 2007a, 2007b;Kawon et al., 2009a, 2009b; Koh et al., 2012).

The second main category is to identify contaminationsources of TCE and other daughter products, includingdichloroethylene (DCE) and vinyl chloride (VC) in groundwater(Lee, 2013; Park et al., 2013). In Korea, unlike remediationof contaminated soils, remediation activity of contaminatedgroundwater is mainly hampered to then inherent difficultyin ascertain the origin of the groundwater contamination(Baek and Lee, 2011). The “Groundwater Law” enforces theremediation of the contaminated groundwater at the expense of

the polluters based on the “Polluter Pays Principle”. If thereis no appropriate apportionment for the remediation costamong the polluters, then enforcement is not possible. Withinthis context, tracer studies mainly using δ13C and δ 37Cl forthe identification of the groundwater contamination sourcehave been recently used at a TCE contaminated aquifercontaining an industrial complex (Park et al., 2013). The studieshave been led by Prof. Kang-Kun Lee of Seoul NationalUniversity (Lee, 2013).

The last main category is the use of artificial tracers suchas Br−, Cl− and rhodamine WT, in examining hydrodynamicdispersion characteristics of aquifers of interest (Table 2).Specifically, attempts have been made to reveal groundwa-ter flow pathways and to estimate the dispersivity of aqui-fers through conventional tracer tests (natural and forcedgradient tests) (Lee et al., 2001a, 2002, 2003a, 2007a, 2007b;Kim Y. et al., 2005; Chung et al., 2006a, 2006b; Kang et al.,2006, 2007; Lee M.J. et al., 2007). Generally, the estimateddispersivity (mostly longitudinal) was used as an inputparameter for various numerical groundwater models usingVisual and GMS MODFLOW software. Unlike most of theenvironmental tracer studies above, the applied tracer stud-ies were mostly conducted in inland alluvial and fractured

Table 1. Summary of important groundwater studies in Korea using environmental tracersEnvironmental tracers Case studies (ref.) Main purposes Location; aquifer

δ2H, δ18O

Lee and Kim (2007) Groundwater recharge Inje; not knownLee and Cho (2008) SGD Incheon; bedrock aquiferLee et al. (2013) Groundwater mixing Yanggu; weathered rock aquiferLee K.S. et al. (2007) Water movement Jeju: unsaturated soil

δ18O Cho et al. (2008) Groundwater recharge estimation Boeun; alluvial aquiferδ2H, δ18O, 3H Koh et al. (2005) Nitrate origin, age dating Jeju; coastal aquifersδ2H, δ18O, 3H, CFCs Koh E.H. et al. (2012) Flow path, groundwater mixing, age dating Jeju; coastal aquiferδ2H, δ18O, 3H, 3He, CFCs Kaown et al. (2009a) Groundwater recharge, nitrate source Chuncheon; weathered rock aquifer3H, 3He, CFCs Koh et al. (2006) Groundwater mixing, age dating Jeju: coastal and inland aquifers3H, CFCs, SF6 Koh et al. (2007b) Groundwater mixing, age dating Jeju; basaltic aquifer3H, CFC-12, Cl- Hagedorn et al. (2011) Recharge estimation, age dating Jeju; fractured aquiferCFCs Koh et al. (2007a) Age dating Jeju; fractured aquifer

δ2H, δ18O, δ13CKoh et al. (2001) Groundwater recharge Yeosu; fractured aquiferKim J.H. et al. (2003) Origin of groundwater Gimje; coastal shallow sandy aquifer

δ2H, δ18O, δ34S, 87Sr/86Sr Kim Y. et al. (2003) Origin of saline groundwater Jeju; coastal aquifer δ2H, δ18O, δ15N Koh et al. (2012) Groundwater recharge, nitrate source Jeju: inland aquifers222Rn, 226Ra, 228Ra, 18O Kim et al. (2003) SGD, nutrient flux Jeju; coastal aquifer222Rn, 224Ra, 226Ra Hwang et al. (2005) SGD, nutrient flux Jeju; coastal aquifer223Ra, 224Ra Lee and Kim (2007) SGD, source of excess nutrients Yeosu; coastal shallow aquifer226Ra, 228Ra Kim et al. (2005) SGD, silicate flux Yellow sea226Ra Lee et al. (2009) SGD, nutrient flux Masan; coastal aquifer234U/238U, 87Sr/86Sr Ryu et al. (2009) Source of solutes Han River basinδ15N Min et al. (2002) Nitrate source Changwon; alluvial aquiferδ15N, δ18O, δ34S Kaown et al. (2009b) Nitrate and sulfate sources Chuncheon; weathered rock aquiferδ13C, δ37Cl Lee (2013) Apportionment of TCE source Wonju; weathered rock aquifer

118 Jin-Yong Lee

aquifers by research teams of Prof. Jin-Yong Lee of Kang-won National University (Lee et al., 2001a, 2002, 2003a,2007a, 2007b, Lee M.J. et al., 2007) and Prof. Sang YongChung of Pukyong National University (Chung et al., 2006a,2006b; Kang et al., 2006).

More details of the studies described above and otherimportant tracer studies (e.g., Koh et al., 2001; Min et al.,2002; Kim J.H. et al., 2003; Lee and Kim, 2007; Lee K.S.et al., 2007; Lee and Cho, 2008; Cho et al., 2008; Ryu et al.,2009; Hagedorn et al., 2011; Koh E.H. et al., 2012; Lee etal., 2013) are given in the following sections.

3. ENVIRONMENTAL TRACERS

3.1. SGD and Nutrient Fluxes

Submarine groundwater discharge SGD is groundwater,which is discharging into the sea through coastal aquifers,and is known to control nutrient fluxes, then affecting thequality of coastal seawater (Kim et al., 2003, 2005; Hwanget al., 2005; Lee and Cho, 2008; Lee et al., 2009). Thus, theoccurrence and quantification of the SGD and associatednutrients fluxes are major interests in coastal areas. The Jejuvolcanic island and western and southern coastal areas ofthe country are the most frequently studied sites (see stud-ied locations in Fig. 1). Kim et al. (2003) measured the con-tents of 18O, 228Ra, 226Ra and 222Rn in basal groundwater andpristine seawater in Jeju island and seepage rates of ground-water along the coast (50–300 m3/m2·yr), and they con-cluded that fresh groundwater and recirculated seawater hada great impact on the mass budget of the nutrients in thisisland. Hwang et al. (2005) also conducted a detailed inves-tigation in the eastern coast (Bangdu Bay) of the island, onSGD and nutrients N, P and Si, using environmental tracers,including 226Ra, 224Ra and 222Rn, together with Si for seawater,pore water and coastal groundwater. Based on the mass bal-ance of the environmental tracers, they estimated 120–180 m3/m2·yr of SGD in this bay and concluded that the nutrient

fluxes from SGD explain approximately 90, 20, and 80% ofthe total input of dissolved inorganic nitrogen, dissolvedinorganic phosphorus and dissolved inorganic silicate, respec-tively, into the bay. Thus, they inferred that the excess nutrientinput from SGD might be responsible for benthic eutroph-ication in the semi-enclosed bay.

The SGD study was extended to western coasts of Korea,facing the Yellow Sea (see Fig. 1). Kim et al. (2005) evaluatedSGD into the sea using 226Ra and 228Ra isotopes, together withSi, in coastal groundwater and seawater. According to theirstudy, advective fluxes of 226Ra and Si through SGD wereapproximately 270×1012 dpm/yr and 23×109 mol/yr, respec-tively, in the Yellow Sea. In addition, based on 226Ra fluxand its activity in coastal groundwaters, they suggested thatSGD was 1.0–6.7×1011 m3/yr, which is equivalent to about40% of the river water input. The occurrence and magni-tude of SGD were examined in the southern coast of thecountry (Yeosu and Masan; see locations in Fig. 1). Lee andKim (2007) analyzed levels of radium isotopes (223Ra and224Ra), nutrients and photosynthetic pigments in coastalgroundwater and seawater in Yeosu. They found that red tides(harmful dinoflagellate blooms) occurred when dissolvedinorganic nitrogen and phosphorus were depleted and con-cluded that the outbreaks of red tides might be acceleratedby sufficient groundwater-derived nutrients.

Another study by Lee et al. (2009) of the same southerncoast (Masan Bay) highlighted a role of SGD as a conveyorof nutrients into seawater using 226Ra tracer. Based on a226Ra mass balance, they estimated 4.8×106–5.7×106 m3/dayof SGD and 2–3 times the nutrients fluxes via GSD comparedto that of stream water. In addition, another notable SGDstudy was carried out in the western coast of the country(Incheon) by Lee and Cho (2008). They revealed the occur-rence of SGD using water chemistry and stable isotopes(δ2H and δ18O) of coastal groundwater, borehole water obtainedfrom a man-made undersea LPG cavern and seawater. Theisotopic compositions of the borehole waters of the under-sea LPG cavern fell on a mixing line between the fresh

Table 2. Summary of groundwater studies in Korea using artificial (applied) tracersApplied tracers Case studies (ref.) Main purposes Location; aquifer

Br−

Lee et al. (2001a) Migration pathway and dispersivity Uiwang; shallow sandy aquiferLee et al. (2002) Landfill leakage Changwon; weathered aquiferLee et al. (2003a) Dispersivity, pore velocity Yeosu; fractured aquiferChung et al. (2006a) Dispersivity, pore velocity Busan; fractured aquiferKang et al. (2006) Dispersivity, pore velocity Ulsan; fractured aquifer

Cl− Kim Y. et al. (2005) Fracture connectivity Geumsan; fractured aquiferKang et al. (2007) Dispersivity, pore velocity Gimhae; shallow gravelly aquifer

Br−, rhodamine WT Lee et al. (2007b) Dam leakage path Gunwi; earth core damBr−, rhodamine WT, uranine Lee M.J. et al. (2007) Migration pathway Chuncheon; alluvial and fractured aquifersRhodamine WT, uranine Lee et al. (2007a) Flow path Taebaek; karst aquiferRhodamine WT Chung et al. (2006b) Dispersivity, pore velocity Busan; shallow sandy aquifer

Use of environmental and applied tracers for groundwater studies in Korea 119

groundwater and seawater, which indicated that the freshwater in the cavern originated from land through SGD.

3.2. Age Dating, Groundwater Mixing and Recharge

The knowledge of (parts of or whole) hydrologic cycles,such as groundwater residence time (groundwater age), recharg-ing and its mixing characteristics in a specific site of inter-est are essential for sustainable use. Koh et al. (2007b) triedto determine groundwater age through the analysis of CFC-12, 3H and SF6 from basaltic aquifers (coastal aquifers) inJeju volcanic island. From the analysis based on a lumped-parameter dispersion model, they determined that ground-waters in the basaltic aquifers consist of young water (<15years), old water (20–30 years) and their mixture, and sug-gested that terrigenic SF6 can affect the whole dating rangeof groundwater. Another study by Dr. Koh (Koh et al., 2007a)using CFCs also revealed groundwater ages of 15–25 yearsfor coastal and somewhat inland aquifers of the island.They also indicated that the small variation in groundwaterage and annual temperature might be due to a fast flow in thevery permeable aquifers. A later study by Koh et al. (2012)using 18O, 2H, 3H and CFCs asserted that the groundwaterof Jeju Island is composed of binary mixtures of youngwater (15–25 years) and relatively old water (>60 years).All the groundwater ages suggested by the above studiesare very young (even though they stated as “old”), which ismainly derived from very fast recharge and groundwater flowdue to the highly permeable hydrogeological features of theisland (Won et al., 2005). Another notable study of ground-water age using δ18O, δD, 3H/3He and CFCs was conductedby Kaown et al. (2009a) for a shallow unconfined aquifer(well depth mostly approximately 30 m) of a main inland ofthe country (Chuncheon; see location in Fig. 1). Groundwaterages, determined based on dispersion models of CFC-113and 3H levels, were 13 to 31 years, which were quite a sim-ilar to those of groundwaters in the Jeju volcanic island.

Kim Y. et al. (2003) attempted to identify the reason forsaline groundwater in the eastern region of Jeju Island usingconservative ions ratios of Br/Cl and I/Cl, as well as iso-topic data (δ18O, δ34S and 87Sr/86Sr). Based on these analysisdata, they concluded that the saline water in the coastalregion resulted from the mixing of fresh groundwater frominland and seawater that intruded inland up to 2.5 km fromthe coast. Lee et al. (2013) examined the water circulation(groundwater and stream water) for a small basin in Yanggu(a mountainous region in northeast Korea) using stable iso-topes (δ18O, δD). The isotopic compositions of unconfinedgroundwaters and stream waters were very similar for bothwet and dry seasons. This finding indicated that the two waterbodies have a good hydraulic connection and that they arecirculated rapidly (Yun et al., 2009).

One of the most important reasons for using environmen-tal tracers in groundwater studies is to enhance our under-

standing of groundwater recharge in various hydrogeologicalsettings (Koh et al., 2001; Lee and Kim, 2007; Lee K.S. et al.,2007; Cho et al., 2008; Hagedorn et al., 2011). Koh et al.(2001) conducted an investigation of groundwater rechargecharacteristics for a weathered rock aquifer of a small water-shed in Yeosu, southern part of Korea using stable isotopes(18O and 2H) of rainfall, stream water and groundwater. Fromthe study, they identified that the stream water and ground-water were directly affected by rainfall and that 16.5% ofrainfall percolated into the subsurface, becoming ground-water, according to mixing equations of stream water andgroundwater. Lee and Kim (2007) determined the season-ality of groundwater recharge using stable isotope tracers(δ18O, δD) in the upper North Han River basin (northeasternpart off Seoul). They suggested that little difference of betweenisotopic compositions of stream water and groundwater isindicative that the former is mainly originated from the lat-ter. Unlike previous studies, Lee K.S. et al. (2007) carriedout an interesting isotopic study of the “unsaturated soilzone” in Jeju Island. They monitored temporal variations in18O and 2H isotopes of rainfall and soil water. Based on thefact that the isotopic compositions of the soil waters were acombination of water parameters for summer and winterrainfalls, they concluded that the soil waters were rechargedfrom precipitations throughout the whole year, not duringsome specific period.

Hagedorn et al. (2011) conducted a comparison of ground-water recharges rates estimated from a groundwater tablefluctuation method, chloride mass balance, groundwater CFC-12 ages and 3H residence times, which produced differentmean recharge values of 687, 429, 423 and 394 mm/yr, respec-tively. Thus, they insisted that depending on a single methodfor estimating groundwater recharge rates can be misleading.In the meanwhile, Cho et al. (2008) conducted a hydrographseparation study for estimating base flow (groundwaterrecharge) using 18O tracer in a central mountainous region(Boeun) of Korea. The percentages of the base flow for theregion were estimated as 7–21% with a spatially averagedvalue of 17%. They demonstrated the usefulness of 18O as amethod of hydrograph separation with enhanced reliability.

3.3. Nitrate Source

Nitrate is one of the most frequent elements to occur at alevel which deems it to be a contaminant in groundwater ofrural areas in Korea (Min et al., 2002; Kaown et al., 2009b).Thus, revealing the origin of the nitrate is a main interest forthe appropriate management of groundwater resources, espe-cially in agricultural areas, because urban groundwater hasrelatively simple nitrate sources such as leaked sewage andlandfill (Wakida and Lerner, 2005). Koh et al. (2005) exam-ined the nitrate contamination for basaltic and hydrovolca-nic sedimentary aquifers in Jeju Island using 3H, 18O and Dtracers. They revealed that young groundwater was associ-

120 Jin-Yong Lee

ated with higher nitrate contamination and suggested that3H can be used an indicator for the nitrate contamination inthis island. Another interesting study of nitrate contamina-tion was conducted in the Gosan area of Jeju island (west-ern part) by Koh E.H. et al. (2012) using δ18O, δD and δ15N.They suggested, based on δ15N and δ18O values, that the mainsource of nitrate contamination in both perched and regionalaquifers is synthetic fertilizers.

Kaown et al. (2009b) identified nitrate and sulfate originsin groundwater for an agricultural area in the northeasternpart of the country (Chuncheon) using δ15N and δ34S trac-ers. Based on the major ion chemistry and the stable isotoperatios, they asserted that low δ34S of SO4 and δ15N of NO3(6–10‰) were highly related to a mixture of chemical fer-tilizers and manure in the western part but elevated δ15N ofNO3 was associated with the manure. Min et al. (2002) car-ried out an extensive investigation of nitrate contaminationfor alluvial groundwaters in the Nakdong River basin (nearChangwon in Fig. 1), southern part of Korea. They collected137 groundwater samples and analyzed them for their ionicchemistry including NO3

− and nitrogen isotopes. Thus, theyfound two main sources: one is nitrate from synthetic fertilizers(δ15N = 4.3–6.2‰) and the other is from animal manure andanthropogenic waste (δ15N = 15.0–19.9‰). All these stud-ies above suggested the potential use of environmental tracers,especially δ15N, as a nitrate contamination indicator, eventhough there are still some technical problems for distinc-tive separation (identification), like overlapping of isotoperanges from different origins.

3.4. TCE Studies

Environmental studies for TCE contaminated aquifers arefew, even though TCE is the most frequently occurring con-taminant in most urban groundwaters (Baek and Lee, 2011;Lee, 2011; Yang et al., 2012). Very recently, an isotope studywas undertaken by Prof. Kang-Kun Lee of Seoul NationalUniversity to allow for the identification (apportionment) ofTCE contamination of groundwater in an industrial com-plex in Wonju, Korea (Lee, 2013). The contamination his-tory can be traced up to 1995 when a groundwater well wasfound to be contaminated with TCE (Baek and Lee, 2011).A following investigation (Yu et al., 2006) indicated that anasphalt laboratory, located up-gradient of the complex, wasa main source for the contamination, as the asphalt labora-tory had used TCE for determinations of asphalt quality,and waste TCE was inappropriately dumped in the yard ofthe laboratory (Yu et al., 2006; Baek and Lee, 2011). How-ever, active remediation for the contaminated groundwaterwas not enforced by the relevant authorities as there werealso many other facilities, as potential sources, in the com-plex, including electronic and vehicle maintenance compa-nies where TCE had been used as a solvent in their variousproduction processes (Jo et al., 2010). Thus, the debate on

the source apportionment (liability) of the contamination isstill undergoing (Baek and Lee, 2011; Yang and Lee, 2012).Lee (2013) tried to reveal the contamination source usingdual isotopes (δ13C and δ37Cl) and found that there are mul-tiple contamination sources (eight source areas) in the site,which is expected to yield another debate on the remedia-tion liability for the contaminated groundwater.

4. APPLIED TRACERS

There are two main reasons for using artificial tracers,such as Br−, Cl− and dyes, for groundwater studies in Korea(Table 2). The first one is to estimate (mainly longitudinal)dispersivity of aquifers using various natural and forcedgradients tracer tests. The second one is to identify flow (orleakage) paths of aquifers or dams. Some details are as fol-lows.

4.1. Evaluation of Hydrodynamic Dispersion

Kang et al. (2006) conducted the single well injection andwithdrawal tracer tests in a horizontally fractured aquiferusing a conservative tracer, Br−. From the tests, they esti-mated the average pore velocities of 4.31×10−4–8.08×10−4

m/sec and longitudinal dispersivity of 18.49–28.73 cm. Chunget al. (2006a) examined the hydrodynamic characteristics ofa fractured aquifer in Busan, using a natural gradient bro-mide ion (Br−) tracer test. Using the breakthrough curvesobtained, they estimated an effective porosity of 0.105 anda longitudinal dispersivity of 0.85 m. Another tracer test byChung et al. (2006b) was carried out for a multi-soil layerdeposit. They continuously injected a solution of rhodamineWT for 160 h. From the test, they obtained effective porosity,longitudinal dispersivity and transverse dispersivity of 10.49–10.50%, 0.80–1.98 m and 0.02–0.04 m, respectively. Kanget al. (2007) performed a convergent tracer test (test scale2–5 m) for a very permeable alluvial aquifer in Gimhae city.They instantaneously injected chloride tracer under con-verging radial flow condition. From the test, estimated lon-gitudinal dispersivities were 0.41 m to 3.2 m, showing a testscale effect (Gillham et al., 1984).

Lee et al. (2001a) also conducted a natural gradient tracertest for an alluvial sandy aquifer using bromide ion. Esti-mated longitudinal dispersivities were 0.96–2.6 m at adistance of 5 m and 7.5–8.5 m at a distance of 10 m,which is also showing the scale effect due to heteroge-neity of the aquifer (Pickens and Grisak, 1981; Gelhar etal., 1992). Lee et al. (2003a) carried out a combinedpumping and tracer test for a highly fractured aquiferusing bromide ion, which was injected into an observa-tion well under stable conditions. Analysis of the break-through curve yielded a longitudinal dispersivity of 0.3m. This value well matched those reported in literature,considering the scale of the test (Gelhar et al., 1992).

Use of environmental and applied tracers for groundwater studies in Korea 121

4.2. Identification of Flow Path

Lee et al. (2007b) carried out 15 tracer tests at a largerockfill dam in Gunwi, in which they tried to reveal largewater seepage paths after several sinkholes developed on thedam crest, which threatened the dam’s stability. Repeatedand sequential tracer tests at different injection points and26 observation wells using rhodamine WT and bromide ionsrevealed that the most probable leakage path and damagearea were in the left side of the dam crest, that is the tonguewing zone. This finding greatly helped in mitigating the damleakage and enhancing the stability of the dam.

Another notable tracer study was conducted for a karstterrain in Taebaek city, Korea (see location in Fig. 1) (Leeet al., 2007a). In this karst area, a small dam, which was tobe used as a drought mitigation measure, was planned, butthe plan caused a public concern that the dam constructionwould dry a pond (called Hwangji pond), located in thecenter of the city. Because this pond is a cultural asset,which should be preserved, determining any hydraulic con-nection between the pond and the dam construction site wasessential prior to advancing plans for the dam. Lee et al.(2007a) injected a tracer solution of fluorescent (uranine) inand around the dam construction area, which is approxi-mately 1 km from the pond. When 2.2 days after the tracerinjection, the tracer reached the pond and the pond waterbecame blue in color, which demonstrated the connectionbetween the two areas (Kim et al., 2006).

Application of artificial tracers was also carried out toexamine potential groundwater contamination through aban-doned (unmanaged) wells (Lee M.J. et al., 2007). Lee M.J.et al. (2007e) applied a variety of tracers including rhodamineWT, uranine and bromide ion under various conditions suchas surface impoundment, open (bare) hole and partly back-filled (with natural soil) holes for alluvial and bedrock aqui-fers. From the multiple tests, they found that the open holeand the partly backfilled hole were very vulnerable to ground-water contamination and thus that the two kinds of holesshould be managed with some appropriate technical measures,especially for shallow alluvial aquifers. Lee et al. (2002)conducted a tracer test examining landfill leakage in the coastalarea of Changwon using bromide ions. They detected a bro-mide ion peak at a monitoring well outside of the landfill.However, they also determined that the use of bromide ionsas an applied tracer in the coastal areas might be inappro-priate because seawater generally has a substantial level ofbromide.

5. CONCLUSIONS

Many groundwater studies using various environmentaland applied tracers have been conducted in Korea. Withadvancements of analytical methods and equipment, appliedfields are expanding, bringing about advancements in our

understanding of water cycles and identification of variouscontamination sources. However, tracer studies are not for aguaranteed method of solving all such environmental problems.Consequently, an integrated approach, combing hydrologic,ionic and isotopic methods, is more plausible to appropriatelyaddress many issues. Especially, source identification ofchlorinated solvents (TCE, PCE, CT) using environmentaltracers is promising, by which remediation of the contaminatedgroundwater can be activated, in a similar manner to soilremediation, which is already a widespread practice in Korea.

ACKNOWLEDGMENTS: This research project was supported bythe Korea Ministry of Environment under “The GAIA project (No. 173-092-010)”. I appreciate helpful comments by Prof. S.-Y. Hamm (editor)and two anonymous reviewers.

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Manuscript received June 1, 2013Manuscript accepted August 26, 2013