Integration of Artificial Recharge and Recovery Systems for Impaired Water Sources in Urban Settings: Overcoming Current Limitations and Engineering Challenges Julia Regnery, 1,2 Jonghyun Lee, 1,3 Peter Kitanidis, 1,3 Tissa Illangasekare, 1,2 Jonathan O. Sharp, 1,2 and Jo ¨ rg E. Drewes 1,2, * 1 Engineering Research Center for Re-Inventing the Nation’s Urban Water Infrastructure (ReNUWIt), National Science Foundation, Stanford, California. 2 Department of Civil & Environmental Engineering, Colorado School of Mines, Golden, Colorado. 3 Department of Civil & Environmental Engineering, Stanford University, Stanford, California. Received: May 8, 2012 Accepted in revised form: April 23, 2013 Abstract Utilization of underlying local aquifers to treat, store, and recover locally produced reclaimed water provides the potential to reduce costs, energy, and infrastructure requirements of water supplies in urban areas. However, water quality issues, limited design and operational guidance, and physical footprint requirements are impeding the implementation of artificial recharge and recovery (ARR) systems in urban water infra- structure configurations. This article reviews the current practice of ARR and proposes approaches to improve the integration into urban settings regarding (1) feasibility of a reduced physical footprint of ARR systems, while maintaining water quality benefits and maximizing yield; and (2) manipulating subsurface hydrological, geochemical, and biological conditions to increase attenuation of key contaminants. The contribution of this interdisciplinary review article is to outline ways to achieve improved design and control strategies of ARR systems that ensure cost-effective water supply and consistent water quality by leveraging current under- standing and technology. Key words: artificial recharge and recovery; hydrogeology; managed aquifer recharge; urban water infrastructure; water reuse Introduction G roundwater resources have long played a central role in both agricultural and municipal water supplies. For example, almost half of the Americans obtain their drinking water from groundwater resources (National Groundwater Association, 2012). However, the reliability of groundwater supplies for urban centers is threatened by three develop- ments: (1) the gradual depletion of local aquifers; (2) the re- duction of natural recharge to aquifers due to surface sealing or the consumptive use of surface water; and (3) long-term uncertainties on water resources posed by climatic changes. Several major aquifers in the United States and throughout the world are undergoing an inexorable process of depletion due to overextraction (Bartolino and Cunningham, 2003; Konikow and Kendy, 2005). The effects of depletion include rising pumping costs, deteriorating water quality, damaged ecosystems, and land subsidence. Today, an increasing degree of surface sealing in urban areas has decreased the rate of direct recharge, while contamination through anthropogenic activities, such as seepage from leaking sewers or septic tanks and seawater intrusion due to overextraction, has limited the use of unconfined shallow groundwater for drinking water supplies (Foster, 2001; Lerner, 2002). A third challenge is due to potential effects of global climate change on water supply. Among the possible consequences of ongoing climatic changes in many regions, more precipitation is expected to occur in the form of rain rather than in the ac- cumulation of snow packs (IPCC, 2001). This will reduce the reliability of water supplies unless surface storage is increased or subsurface storage is more widely utilized. At the same time, the warmer and wetter winters that are expected will result in higher volumes of peak runoff. If not effectively captured, this will reduce the availability of conventional water supplies. Using natural treatment systems to augment local groundwater resources in urban settings via managed aquifer recharge (MAR) has been practiced for more than five de- cades in North America and over a century in Europe (Ray et al., 2008). Utilizing the subsurface to both increase stor- age capacity and to augment local water supplies with reclaimed water (treated municipal wastewater) is becoming *Corresponding author: Department of Civil and Environmental Engineering, Colorado School of Mines, Golden, CO 80401-1887. Phone: (303) 273-3401; Fax: (303) 273–3413; E-mail: jdrewes@mines .edu ENVIRONMENTAL ENGINEERING SCIENCE Volume 30, Number 8, 2013 ª Mary Ann Liebert, Inc. DOI: 10.1089/ees.2012.0186 409