## 2 Study Area  
### Geographical, Climate, and Water Management Overview  
The study area is located on the northeast coast of the Iberian Peninsula, at Port de la Selva valley. The valley covers an area of 10.5 km\({}^{2}\), and mainly extends over the north and east slope of the Rodas Mountains (with a peak elevation of 670 m above sea level) until they reach the Mediterranean Sea. The area is characterized by a Mediterranean climate with a warm thermal regime in summer and moderate cold in winter. Average monthly temperatures have varied from 8.8 \({}^{\circ}\)C in February to 23.7 \({}^{\circ}\)C in July over the period 2007-2016. The annual rainfall is moderate, with an average of 570 mm/year, but below 450 mm/year in dry years. Rainwater is distributed irregularly during the year. Maximum rain values are recorded in the October-November period (more than 160 mm on average) and the driest month is July (below 20 mm), coinciding with the highest potential evapotranspiration values [34]. The rainfall is assumed to be mainly incorporated into surface run-off (60%) while evapotranspiration (25%) and aquifer infiltration (15% or equivalent to 2000 m\({}^{3}\)/day) completed the water balance of the Port de la Selva basin [35]. Similar to other Mediterranean coastal areas, Port de la Selva municipality has experienced extensive urbanization and an associated shift away from an agricultural and fishing economy to one governed by the growth of tourism from the 1950s to the present (Figure 1). Water demands and wastewater effluents in the area have therefore greatly increased--due to the rise of water consumption for recreational uses and tourists--especially in summer, when its population reaches 10,000 inhabitants compared to 1000 inhabitants during winter or non-tourist season. The average annual supply water abstraction in El Port de la Selva basin is about 400,000 m\({}^{3}\), while the average annual volume of treated wastewater is in the range of 220,000 m\({}^{3}\). Both abstraction and wastewater volumes have large fluctuations between summer and winter [36]. Furthermore, chloride concentrations in water abstracted from the municipal well were recurringly above the regional drinking water limit of 250 mg/L [37]--during the autumn months--probably triggered by saltwater intrusion after summer's high water demand period (Figure 2). To increase the security of water supplies and to improve the water quality, Port de la Selva's town council have constructed an SAT--pioneering in Europe in the usage of recycled wastewater for recharging an aquifer dedicated to human consumption--and joined the European Commission DEMOWARE project. The DEMOWARE project involves the public perception in water reuse, artificial recharge of water into aquifers and disseminate investigations related to wastewater recycling. The innovation and significance of the project were to demonstrate the SAT commissioning without the need for advanced treatment such as ozonation or reverse osmosis, relying on the natural treatment capacity of the soil and aquifer only. The used waters of the municipality of Port de la Selva are connected to the sanitation system consisting of a wastewater treatment plant (WWTP) with biological flocculation, tertiary double-filtration, and UV disinfection treatments. Most of the water entering the WWTP receives biological treatment with nitrogen removal (approximately 70%) and the effluent is discharged into the Romanyac stream (during the period October to May) or directly into the sea through the marine emissary (the months of June, July, August, and September). The Romanyac stream outlets to the mid part of the beach and the point of discharge of the effluent of the WWTP is about 300 m from the coastline. DEMOWARE project proposes that wastewater, after receiving an appropriate tertiary treatment could be reused for aquifer recharge SAT system.