Numerical modeling of changes in groundwater storage and nitrate load in the unconfined aquifer near a river receiving reclaimed water.

Ruixue Jiang,Fandong Zheng,Xianfang Song,Dongmei Han

doi:10.1007/s11356-022-18597-1

Abstract

Reclaimed water (RW) has been widely used as an alternative water resource to recharge rivers in mega-city Beijing. At the same time, the RW also recharges the ambient aquifers through riverbank filtration and modifies the subsurface hydrodynamic system and hydrochemical characteristics. To assess the impact of RW recharge on the unconfined groundwater system, we conducted a 3D groundwater flow and solute transport model based on 10years of sequenced groundwater monitoring data to analyze the changes of the groundwater table, Cl- loads, and NO3-N loads in the shallow aquifer after RW recharge to the river channel. The results show that the groundwater table around the river channel elevated by about 3-4m quickly after RW recharge from Dec. 2007 to Dec. 2009, and then remained stable due to the continuous RW infiltration. However, the unconfined groundwater storage still declined overall from 2007 to 2014 due to groundwater exploitation. The storage began to recover after groundwater extraction reduction, rising from 3.76 × 108 m3 at the end of 2014 to 3.85 × 108 m3 at the end of 2017. Cl- concentrations varied from 5-75mg/L before RW recharge to 50-130mg/L in 2years (2007-2009), and then remained stable. The zones of the unconfined groundwater quality affected by RW infiltration increased from 11.7 km2 in 2008 to 26.7 km2 in 2017. Cl- loads in the zone increased from 1.8×103t in 2008 to 3.8 × 103 t in 2017, while NO3-N loads decreased from 29.8 t in 2008 to 11.9 t in 2017 annually. We determined the maximum area of the unconfined groundwater quality affected by RW, and groundwater outside this area not affected by RW recharge keeps its original state. The RW recharge to the river channel in the study area is beneficial to increase the groundwater table and unconfined groundwater storage with lesser environmental impacts.

Highlights

The increasing demands for water resources driven by a combination of population growth, socioeconomic development, rapid urbanization, and climate change have been led to water scarcity and quality deterioration (USEPA and USAID, 2012; WWAP, 2019)
To assess the impact of Reclaimed water (RW) recharge on the unconfined groundwater system, we conducted a 3D groundwater flow and solute transport model based on 10 years of sequenced groundwater monitoring data to analyze the changes of the groundwater table, Cl- loads, and NO3-N loads in the shallow aquifer after RW recharge to the river channel
Based on long timesequenced groundwater monitoring data, this study established a three-dimensional groundwater flow and solute transport model to evaluate the impact of the RW recharge on the groundwater table and storage change, and Cl− and NO3-N loads in the unconfined aquifer

Summary

Introduction

The increasing demands for water resources driven by a combination of population growth, socioeconomic development, rapid urbanization, and climate change have been led to water scarcity and quality deterioration (USEPA and USAID, 2012; WWAP, 2019). RW could be utilized for agricultural irrigation, landscape irrigation, industrial reuse, municipal water, and groundwater recharge (Angelakis and Gikas, 2014; De Gisi et al, 2017; Deng et al, 2019). In China, RW utilization was 2.17×109 in 2009, accounting for 0.36% of the total water supply amount (Zhu and Dou, 2018). It was up to 8.74×109 m3 in 2019, accounting for 1.5% of the total water supply amount (MWR, 2021). Over 90% of the RW was primarily used for purposes of recreation and ecological conservation (e.g. water supply for recharging rivers or lakes) (Beijing Water Authority, 2019). Groundwater may have potential health risks and environmental impacts as RW seeps into the aquifer by river leakage (Asano and Cotruvo, 2004; Bekele et al, 2018)

Objectives

Methods

Results

Discussion

Conclusion