Groundwater development, use, and its quality in Korea: tasks for sustainable use

Groundwater use in the Republic of Korea (hereafter Korea) has been gradually increasing, thereby increasing frequent groundwater problems regarding quantity and quality (Lee et al., 2018). Therefore, in 1994, the Korean government implemented the ‘Groundwater Act (Law)’ to control groundwater development and use in the private and public sectors. Under this law, the Korean government (provincial governments) initially collected data on groundwater development and use. According to the law, to use groundwater with an abstraction amount greater than one, (100 m³/day for domestic and industrial uses, 150 m³/day for agricultural use), an official permit should be obtained from the local governments. It requires a tough and strict ‘Groundwater Impact Survey’, in which potential adverse effects on groundwater and surrounding environments are evaluated (Cha & Lee, 2020). In addition, the law obliges the government to establish nationwide groundwater monitoring networks to determine the status and changes in groundwater quantity (water levels) and quality (Lee et al., 2007; Lee & Kwon, 2016).

Although the Ministry of Environment is a key administrative authority to control and manage groundwater resources, there are several government entities controlling the usage of groundwater resources. The Korea Rural Community Corporation (KR) under the Ministry of Agriculture, Food, and Rural Affairs is in charge of groundwater affairs for agricultural use, and the Ministry of the Interior and Safety is in charge of groundwater used for hot springs. The groundwater used for drinking is controlled by the Ministry of the Environment. The Ministry of Defense is in charge of groundwater wells and their affairs in military facilities. Notably, scattered governing authorities are not efficient in tackling diverse groundwater problems.

Furthermore, groundwater use charges were not imposed on all groundwater facilities. They are applied only to groundwater for commercial and industrial purposes, golf courses, and large baths. The majority of groundwater wells used for domestic, agricultural, military, and academic facilities are exempted from these charges, with only 35% of local governments (80 of the total 226 local governments in the country) collecting the charges. Furthermore, the charge (price) is very low (0.76 US$/10 m³), amounting to only 50% of that of the river water charge. As of 2018, only 12.5 million USD of the charges were collected across the country, thereby resulting in immense shortage of appropriate groundwater management projects.

Although a separate law regulating groundwater resources (the Groundwater Act in Korea) was implemented earlier compared to other countries, still there are many groundwater problems to be resolved in the future. Thus, the present study examines the status of groundwater development, use, and groundwater contamination in Korea and suggests essential tasks for sustainable groundwater use.

To review the status of groundwater development and quality in Korea, we collected official groundwater data from government authorities. The Korean government publishes annual reports of groundwater development and use for the entire country since 1994. The data includes well location, groundwater use, well diameter, well depth, and usage. The groundwater data are publicly available on the website (www.gims.go.kr) and can be downloaded free of charge (Kang et al., 2020).

In addition, we collected groundwater quality data from exclusive groundwater quality monitoring stations distributed nationwide, operated by the Ministry of Environment (Jeon et al., 2020; Kim et al., 2020). Quality monitoring stations are generally installed in relatively clean areas that are free from anthropogenic contamination. Government authorities measure and analyze physicochemical groundwater quality parameters, including water level, water temperature, pH, dissolved oxygen (DO), oxidation–reduction potential (ORP), electrical conductivity (EC), and many organic and inorganic contaminants. Data were retrieved from the same website, and the number of datasets steadily increased from 140 in 2008 to 2,764 in 2017 (well depth = 10–80 m). Thus, in this study, to determine the overall status of groundwater quality, we mainly considered the field-measured parameters due to many undetected values of laboratory-analyzed contaminants.

In Korea's history, groundwater development by mechanical equipment traces back to the 1960s. In addition, the Groundwater Development Corporation was established by the Korean government in 1969 to manage nationwide groundwater development. Groundwater has been developed primarily in rural areas for agricultural purposes. Until the early 1990s, there were few concerns about groundwater use and contamination. However, in later years, public grievances increased regarding groundwater deficit and quality deterioration. Thus, the Korean government established the Groundwater Act in 1993 that enforced the collection of nationwide groundwater data (usage, water levels, and quality) and devised groundwater management plans at national and local levels for sustainable use (Lee et al., 2018; Jeon et al., 2020; Kang et al., 2020).

Figure 1 shows the land-use changes in the country over the last four decades (1980–2019). With increasing population and economic development, the buildings and roads have steadily increased from 3,121 to 6,542 km² during this period, whereas green areas (forest and crop fields) have continuously decreased. In particular, the proportion of crop fields (paddy and dry fields) are markedly decreasing, predicting a decrease in the groundwater use, at least for the agricultural sector; however, reality is the contrary.

Figure 2 shows the number of groundwater wells, annual groundwater use, and usage per well across the whole country from 1994 to 2018. The number of groundwater wells steadily increased from 637,285 in 1994 to 1,640,374 in 2018 (an increase of 157%). With an increase in the number of groundwater wells, the annual groundwater pumping also substantially increased for the period, except for the two most recent years (2017–2018). However, the amount of groundwater pumping per well is steadily decreasing, which indicates that the newly developed wells are mostly small which can pump only a very small quantity of groundwater (<10 m³/day) small pumps. In addition, it is a known fact that the farmers favor separate private groundwater wells for water supply, as the agricultural groundwater usage is free of charge.

Moreover, the usage of groundwater for different purposes, especially for agricultural activities, has been thoroughly examined (Figure 3). Before 2009, groundwater usage for livelihood (for households) was the prevailing purpose (47.6–51.3%); however, agricultural groundwater development later predominated (47.7–52.2%) among total usages. With the increasing implementation of municipal water sourced from large rivers, the residents in cities no longer depend on groundwater for their daily activities (Yun et al., 2014; Kim et al., 2016). This is one of the major reasons for the decrease in groundwater use for household activities. However, in the case of the agricultural sector, the scenario is completely different. Despite the steady decrease in cropland area, agricultural groundwater usage gradually increased until 2016. Regardless of decreasing amounts of total and agricultural groundwater usage during 2017–2018, the proportion of agricultural groundwater usage was still highly sustained.

Figure 4 shows the trends in the well diameters during 1994–2018. The well diameter is closely associated with the pumping rates of each well. That is, a large well diameter indicates high amount of pumping (r = 0.88) and deep well depth (r = 0.91). Among the well diameters, the smallest wells (diameter: <100 mm = 4 inches) are predominating (74.1–82.6%), whereas the larger ones exhibit smaller proportions of 7.5–20.6% (100–200 mm), 0.7–1.5% (200–300 mm), and 0.2–0.4% (>300 mm). During this period, the proportion of wells with the smallest diameter gradually decreased by 8.5% p, whereas that of relatively larger wells with diameters of 100–200 mm steadily increased by 13.1% p. This transition can be attributed to the substantial development of mechanical drilling technology with lower costs (Lee et al., 2018). However, these larger and deeper drillings elevated the possibility of groundwater contamination in deep bedrock aquifers due to inappropriate well completion and poor well management.

Along with the changing trends of the well diameter, the well depths exhibited similar variation (Figure 5). Although shallowest wells with depths less than 40 m were predominant (73.3 – 85.3%), their proportion steadily decreased by 12% p for the period. Owing to advanced drilling technology, deeper wells have been installed at a lower cost. The second shallowest wells (40–80 m) accounted for 6.7–10.4% of the total wells. However, unlike the shallowest wells, these wells have gradually expanded their proportion by 3.7% p during the period despite a slight decrease in the total number of groundwater wells in 2018. Although the number of groundwater wells at 80–120 m depth was less than those at 40–80 m depth before 2010, they outnumbered the latter by 2.4% p in 2018. Even though the deeper wells located at 120–160 m and over 160 m depths have gradually increased with each year, their proportions are still low (less than 3.5%). Thus, it can be inferred that the farmers prefer the shallowest wells of less than 40 m depth or deeper wells of approximately 100 m depth. The imprudent installation and maintenance of many shallow wells aggravate the quality of alluvial groundwater in Korea (Yi et al., 2007).

The field-measured parameters were examined to understand the progress of groundwater quality (Figure 6). The average values of groundwater water levels ranged from 4.44 to 4.9 m below the ground surface, and they have been continuously lowering. Although the groundwater-level decline is not substantial, its steady decreasing trends are of great concern regarding potential groundwater depletion. The increasing groundwater temperature is evident during the monitoring period (2008–2017), which indicates that even the groundwater has been affected by the increasing air temperature of the country (Park et al., 2011). Even though the rate of increase has lessened recently, the average increasing rate is + 0.19 °C/year (r² = 0.83), with remarkably high values, considering the increasing rate of air temperature (0.06 °C/year) for the same period.

In addition to decreasing water levels and increasing groundwater temperatures, the groundwater pH exhibited a statistically significant decreasing trend (p < 0.05), though the exact reasons for this variation are unclear. However, it may be inferred that increasing air and groundwater temperatures would decrease the solubility of O₂ gas in shallow groundwater, which may cause increased accumulation of carbonic acid and lower its pH (Riedel, 2019). The marked decrease in DO supports this interpretation. Along with the decreasing DO, the ORP also displayed a decreasing trend, which indicates the transition of groundwater conditions from oxic to anoxic. However, the marked decrease in DO cannot be fully explained by the increasing groundwater temperatures. The distinctive increase in EC indicates gradual groundwater contamination by organic contaminants, which can be reasonably inferred from the decreasing DO and lowering ORP (Choi & Lee, 2011; Gesels et al., 2021).

Table 1 shows the most relevant contaminants typically found in the groundwater quality monitoring stations. They include nitrate-nitrogen (NO₃-N), ammonia nitrogen (NH₃-N), arsenic (As), zinc (Zn), toluene (C₇H₈), xylene (C₈H₁₀), chloroform (CCl₄), and fluoride (F). Nitrate is one of the most frequently detected species in agricultural groundwater, originating from agricultural activities. The high amount of As is typically of geogenic origin, especially in alluvial aquifers (Lee et al., 2010). Petroleum contaminants such as toluene, xylene, and CCl₄ frequently occur in urban and industrial areas, as well as in military facilities (Choi & Lee, 2011; Lee, 2011; Kim et al., 2016; Lee et al., 2018). Irrespective of the source being anthropogenic or natural, a threatened groundwater environment is detected in Korea, which has not improved due to passive and inactive governmental measures.

Table 2 presents some current issues regarding groundwater contamination in Korea. Owing to the Groundwater Act of 1994, the contaminated groundwater should be remediated by polluters. When the polluter is not clearly known, the Ministry of Environment may initiate the cleanup of contaminated groundwater. Jeju Island, the largest island in Korea, where groundwater is the sole source of water, has suffered from nitrate contamination (>10 mg/L NO₃-N) from fertilizers, manure, and livestock farms (Koh et al., 2005, 2017). Although every administrative effort has been exerted to control nitrate contamination, the result is not significantly effective until now.

Cadmium (Cd) contamination of groundwater in a smelting site is a current controversial environmental issue in Korea. Inappropriate wastewater management during the manufacturing processes resulted in Cd contamination of groundwater, up to 2.204 mg/L (Korean standard 0.02 mg/L for industrial groundwater). High public concern was raised with regard to the Nakdong River, the upper branch of the river, which flowed very close to the smelting company, and its migration may cause a severe threat to the river, on which over 10 million people are dependent for water supply. Thus, the company started a contaminated groundwater remediation project, including slurry walls, which cost 38 million US$. However, the resident and environmental authorities do not trust the measures undertaken by the company. Many military facilities have suffered from groundwater contamination by organic contaminants, including total petroleum hydrocarbons, benzene, xylene, and PCE. This contamination causes public grievance and economic burden due to the high remediation costs (Lee, 2011).

We have briefly reviewed the current state of groundwater development and use, groundwater quality using a few field parameters, and major groundwater contaminants. Based on this evaluation, some essential tasks were discussed for sustainable groundwater use in the country.

Until now, the Korean government has focused on the management and control of individual groundwater wells, and no interest has been shown with perspectives of larger scale, well field, or watershed, regarding groundwater quantity and quality. As mentioned earlier, the installation of a groundwater well with a large capacity (100 m³/day for domestic and industrial uses, 150 m³/day for agricultural use) requires the conducting of the ‘Groundwater Impact Survey’, and an official permit must be obtained from the local governments for the well development. The survey includes an evaluation of the potential impacts of the new well on the surrounding environment, especially groundwater quantity and quality.

The survey is generally conducted on the individual well; thus, the installation of an additional well next to the existing well is treated separately as a single well. The combined effects on the surrounding environment are not considered, even though the combined and simultaneous pumping by the two wells may cause serious groundwater depletion or deterioration of groundwater quality, thereby further complicating groundwater contamination. Oliveira et al. (2019) have reported that unequal distribution of the wells and the extraction water from multiple wells in some points can contribute to overexploitation of groundwater and deteriorated groundwater quality. In many cases, well owners are trying to resolve contamination problems by simply closing the wells and not using contaminated groundwater (Baek & Lee, 2011). This solution is common, and thus, active remediation of contaminated groundwater is not prevalent in this country, leaving the groundwater contaminated. In addition, the remediation activity on the contaminated well is neither effective nor efficient for achieving the cleanup goal across the entire contaminated aquifer.

Thus, the paradigm of groundwater management in Korea needs to be changed, from individual well to well field, or watershed and sustainable watershed management should be adopted. In the USA (California), groundwater recharged has been enhanced by using sustainable watershed management (Levy & Christian-Smith, 2011). Also, the Cohasset's Ailing Water System has been rehabilitated by the development and implementation of extended range plans for distribution, treatment, and watershed protection (McNabb, 2010). The area closure and participatory watershed management at Abraha Atsebaha and Negash watersheds in Ethiopia has resulted in adequate recharge of groundwater and is being used for irrigation, livestock, and domestic water supply (Ouessar et al., 2012). Groundwater development should be considered from the perspective of sustainability of the watershed, and the combined effects of new wells and existing wells should be evaluated together. Presently, administrative convenience should be abandoned by focusing on individual wells. Until now, the Korean government has exerted its efforts to control point sources such as wells, above and underground storage tanks, and gas stations, and it should expand its interest even on nonpoint sources like fertilizers, pesticides, and herbicides by agricultural spraying to appropriately manage groundwater resources.

For a long period, groundwater and surface (stream) water have been treated as separate water sources. The different governmental authorities are dealing with two water resources; hence, academic communication and cooperation between researchers dealing with two water resources are not very common. However, this has necessitated conjunctive use and combined management of the two water bodies. A large number of greenhouses, along with the four major rivers of the country, consume a large quantity of groundwater to cultivate watermelons, melons, strawberries, pumpkins, and cucumbers and to keep them warm using water curtains in cold seasons (Kwon et al., 2020). Therefore, the impacts of heavy groundwater pumping on river (surface water) sustainability and dam (reservoir) construction on the surrounding groundwater are seriously considered (Kang et al., 2020; Lee et al., 2020).

Many rivers and streams in urban and metropolitan areas, with substantial water flows in the past, have recently gone dry. This is attributed to heavy groundwater pumping during deep underground building construction. In addition, a large quantity of groundwater is routinely pumped from subway lines and underground facilities to maintain low groundwater levels (Kim et al., 2005; Lee et al., 2005). Dried streams and rivers have poor esthetic effects on citizens and calls for running streams are accumulated from them. The combined management of groundwater and stream water is essential for tackling this problem.

An increasing number of severe droughts necessitate the conjunctive use of the two water resources. Conventionally, the central and local governments are repeatedly installing new groundwater wells as a temporary measure to mitigate droughts (Lee & Kwon, 2016); however, this imprudent and unmanaged groundwater development aggravates stream water depletion and causes rapid groundwater contamination through abandoned wells following the droughts (Yi et al., 2007). Groundwater and stream water are hydraulically interconnected; thus, conjunctive use and integrated management are essential for the sustainable use of both water resources.

The World Health Organization presents Singapore as an exemplary integrated water management model (Chen et al., 2011). Integrated water management can be achieved with political will, good governance, and a coherent water policy (Tortajada et al., 2013). Australia has adopted integrated water management strategies and revealed some progress in conjunctive use of water resources (Ross, 2018). The Western USA, especially California State, is also adopting the integrated surface and groundwater management and paving its way toward sustainable water resource management (Farrelly & Brown, 2011; Ross, 2018). The Korean government should implement integrated surface and groundwater management approaches, including proper land-use planning, judicial investments in infrastructure for water supply and used water, groundwater recharge by watershed management, licensing of groundwater use, pollution control measures, and use of technology and public education regarding water resource management.

Many different government entities control the usage of groundwater (Lee et al., 2007). Generally, the quantity and quality of groundwater affairs are governed by the Ministry of Environment (K-water) under the Groundwater Act; agricultural groundwater use is managed by the Ministry of Agriculture, Food, and Rural Affairs and its affiliated organization, Korea Rural Community Corporation (KR) under the law ‘Rearrangement of Agricultural and Fishing Villages Act’. However, the groundwater wells in military bases and facilities are governed by the Ministry of National Defense via the Act on the Military Facilities Project. In addition, the usage of hot groundwater for public baths is controlled by the Ministry of the Interior and Safety via the Hot Spring Act. Thus, many scattered government authorities result in inefficient groundwater management, with insufficient cooperation (Kang et al., 2020). Therefore, an integrated single authority is required for efficient and effective groundwater management. Australia has single centralized water planning and management systems. The groundwater and surface water at the highest level are managed together, while it is managed separately at lower levels. The primary authority for water management is usually a single lead government agency. Conjunctive water management usually involves multilevel governance interactions between many individuals, groups, organizations, and institutions, including governments (Ross, 2018). Decision-making is a complex process that involved the interaction of participants from various groups or organizations. Therefore, the communication among the organization working at a lower level should be strong enough for good decision-making and to formulate sound policy and planning.

Local government officials collect a variety of groundwater data regarding groundwater development and use, along with groundwater quality, complying with the enforcement of the Groundwater Act. However, most of them lack any expertise and relevant knowledge in groundwater affairs; thus, when dealing with groundwater data, the errors are not determined accurately. Consequently, a few erratic values and errors are observed in the measurement values in the groundwater data reported by local officials, questioning the integrity of the data. Therefore, the transition of data collection and management works from local officials to groundwater experts such as K-water and/or KR is of utmost importance.

As there are still many unlawful groundwater wells in Korea, harsh punishments or penalties must be imposed on unreported groundwater use. It is very important to educate the public regarding groundwater being a public asset, not a private property. Groundwater is the last resort to water resources in the era of aggravating climate change. The intensity of severe droughts and their frequency are increasing; thus, securing clean and sufficient groundwater is critical for the sustainable development of this country.

We have examined groundwater development and use over the last few decades and revealed some important facts and implications for the sustainable use of groundwater resources in Korea.

1. The number of groundwater wells and the quantity of groundwater pumping have been steadily increasing, except for the past 2 years. In addition, the number of large and deep wells is increasing with the development of drilling technology.

2. Agricultural groundwater use has been predominant since 2009, whereas domestic groundwater use has been dominant before 2009.

3. The decreasing groundwater levels, DO, and ORP, and increasing water temperature, pH, and EC represent aggravating groundwater environment conditions. In addition, frequently occurring hazardous contaminants, including NO₃, As, and organic petroleum pollutants, require considerable attention for the progress of the groundwater environment.

4. For sustainable groundwater development and use, there is a paradigm shift in groundwater management from individual wells to well fields or watersheds. Thus, we need to develop a strategy for conjunctive use and combined management of both groundwater and stream water. In addition, it is necessary to control and manage groundwater resources via an integrated single government authority. Moreover, groundwater data should be collected and managed by groundwater experts, rather than unprofessional local officials.

This work was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (No. 2019R1A6A1A03033167) and by Korea Environment Industry & Technology Institute (KEITI) through Measurement and Risk assessment Program for Management of Microplastics Program, funded by the Korea Ministry of Environment (MOE) (No. 2020003110010).

All relevant data are included in the paper or its Supplementary Information.