## 1 Introduction  
Various factors have led to the depletion and shortage of freshwater resources. The shortage of water resources is one of the most severe challenges facing humanity in the 21 st century. Almost half of the world's population is expected to live in areas with water shortages by 2030 without stable water supplies [1], and this could trigger severe crises in terms of not only the natural environment and ecosystem, but also the quality of life and human health. As such, securing a stable, safe, and clean water supply has become a major focus of both governmental and nongovernmental organizations. Developing measures towards achieving such a resource is perceived as a key agenda for the sustainable development of the human race [2]. Clean and safe water is now considered a fundamental factor of human rights protection [3,4]. Currently, many countries are struggling to establish and implement national policies to secure stable, clean, and safe water resources [5]. Korea has been facing water shortages for many years due to frequent climate and weather anomalies, such as local and sporadic torrential downpours and repeated droughts. The Korean government has been making efforts to resolve this issue. In particular, extensive resources have been used to develop various policies and measures for using river water, as a means of preventing water shortages during droughts. In addition, substitutes for water resources, including groundwater, are being explored not only at the national government level, but also at the local government level. However, coping with this tough problem requires more fundamental solutions. Around the world, many improvements have been made in the development of various policies and technologies for securing clean water resources, and related regulatory and institutional infrastructures have been established. To keep up with such trends, Korea has been investigating various water resources at the national level, such as seawater desalination, groundwater dams, rainwater harvesting, artificial rainfall, riverbank filtrate, and deep sea water, all of which may assist the country in securing a stable supply of clean water [5,6]. Recently, Korea has been implementing the Aquifer Storage and Water Quality Enhancement (ASWQE) project in an effort to find reliable alternatives for water resources. This project, as a promising approach to managing various water resource issues emerging in Korea, can ensure water supply to a certain extent by making optimal use of the natural state of aquifers while also improving water quality. It is a positive and active technology that links surface water and groundwater in a complementary manner, and thus can help balance the pros and cons of using surface water and groundwater resources, such as by providing proactive measures for disasters and accidents due to water shortage and water quality deterioration, promotion of water security by diversifying water resources, elimination of social conflicts due to interregional water disputes, and cost reduction measures to secure clean water resources. Therefore, it is considered to be fundamentally different from the existing short-term technologies, which are considered negative and passive, for linking surface water and groundwater [7]. Many countries all over the world, such as the US, Australia, and some European, Asian and African countries, have been adopting various types of management of aquifer recharge (MAR) technologies as an effective alternative water management strategy to cope with water shortages due to climate change or global/regional environmental change [8]. In particular, many countries are showing great interest in aquifer storage and recovery (ASR)/aquifer storage transfer and recovery (ASTR) as part of an overall strategy to manage and use large-scale water resources [9, 10, 11]. For example, as of March 2010, the usage capacity of ASR (including ASTR) was 1 billion gallons per day (3.79 million m\({}^{3}\)/d), and this value is expected to increase to 5 billion gallons per day by 2020.