The impacts of a linear wastewater reservoir on groundwater recharge and geochemical evolution in a semi-arid area of the Lake Baiyangdian watershed, North China Plain

https://doi.org/10.1016/j.scitotenv.2014年02月13日0 Get rights and content

Highlights

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    An unlined wastewater reservoir caused the deterioration of groundwater quality.
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    An evaporation fraction was estimated by Rayleigh distillation theory of isotopes.
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    73.5% of wastewater recharge to groundwater by leakage and irrigation infiltration.
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    The region influenced by wastewater was divided into four subzones.
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    Mixing, ion exchange, and carbonate precipitation are major geochemical processes.

Abstract

Sewage leakage has become an important source of groundwater recharge in urban areas. Large linear wastewater ponds that lack anti-seepage measures can act as river channels that cause the deterioration of groundwater quality. This study investigated the groundwater recharge by leakage of the Tanghe Wastewater Reservoir, which is the largest industrial wastewater channel on the North China Plain. Additionally, water quality evolution was investigated using a combination of multivariate statistical methods, multi-tracers and geochemical methods . Stable isotopes of hydrogen and oxygen indicated high levels of wastewater evaporation. Based on the assumption that the wastewater was under an open system and fully mixed, an evaporation model was established to estimate the evaporation of the wastewater based on isotope enrichments of the Rayleigh distillation theory using the average isotope values for dry and rainy seasons. Using an average evaporation loss of 26.5% for the input wastewater, the estimated recharge fraction of wastewater leakage and irrigation was 73.5% of the total input of wastewater. The lateral regional groundwater inflow was considered to be another recharge source. Combing the two end-members mix model and cluster analysis revealed that the mixture percentage of the wastewater decreased from the Highly Affected Zone (76%) to the Transition Zone (5%). Ion exchange and redox reaction were the dominant geochemical processes when wastewater entered the aquifer. Carbonate precipitation was also a major process affecting evolution of groundwater quality along groundwater flow paths.

Introduction

With industrialization and accelerated urbanization, municipal sewage leakage has become an important source of groundwater recharge, resulting in adverse effects on groundwater quality (McArthur et al., 2012, Schirmer et al., 2013). This is especially true for aquifers located in arid/semi-arid climate regions in which global warming and anthropogenic activities have led to decreased runoff, drying of rivers and declining groundwater levels. The major non-agricultural sources of groundwater contamination include leakage from water supply and disposal networks such as evaporation ponds, on-site sewage disposal, and contaminated land and rivers (Wakida and Lerner, 2005). Among these sources, evaporation ponds have been widely used in arid regions for the storage and disposal of wastewater (Geophysics Study Committee, Geophysics Research Forum NRC, 1984, Al-Kharabsheh, 1999). Although these ponds are often lined, many are unlined and therefore have the potential to impact groundwater quality via leakage. To effectively manage water resources within a basin, it is important to investigate the impacts of polluted rivers and surface wastewater systems on groundwater recharge and to recognize the geochemical evolution in groundwater.
Groundwater contamination is a major water problem in the Lake Baiyangdian watershed near Beijing, China (Fig. 1(a)). In this region, rivers are typically polluted, which has greatly threatened the quality of groundwater resources. Among the eight rivers that flow into Lake Baiyangdian, the only one that has perennial flow is the Fu River, which is mainly sourced by municipal sewage with or without primary treatment from Baoding (Qiu et al., 2009). The Tanghe Wastewater Reservoir (TWR) is a large linear wastewater reservoir located 20 km east of Baoding in the Lake Baiyangdian watershed. The TWR was constructed parallel to the Tang River to store industrial effluent from Baoding in 1975. A sluice gate was set in the east end of the channel to prevent the effluent from flowing into Lake Baiyangdian. Industrial wastewater drained to this reservoir is not treated, which leads to concentrations of water soluble chemicals that are much higher than those in other sewage and has resulted in the TWR becoming a linear source of regional groundwater contamination. Therefore, there is an urgent need to investigate the impacts of the wastewater reservoir on groundwater.
To study the impacts of polluted surface water on groundwater contamination, increasing attention has been paid to the interactions of groundwater–surface water (Petelet-Giraud et al., 2007, Kumar et al., 2009, Guggenmos et al., 2011, Al-Charideh and Hasan, 2012). Indirect methods, based on water balancing and solute balancing, are suitable methods for larger scale assessments but suffer from a significant uncertainty (Rieckermann et al., 2005, Chisala and Lerner, 2008). Direct methods such as tracer tests are less uncertain and have been applied to investigate the groundwater recharge sources and determine the migration pathways of the pollutant (Rieckermann et al., 2005). The most widely applied tracers include heater, environmental isotopes, and solute concentrations. In recent years, the multivariate statistical methods combined with geochemical processes of major ions have been testified as the effective approaches to interpret the present water chemicals characteristics and evolution (Belkhiri et al., 2010). Uncertainties in each approach to estimating recharge underscore the need for application of multiple techniques to increase reliability of recharge estimates (Scanlon et al., 2002).
This study investigated the TWR and the groundwater surrounding it in the Lake Baiyangdian watershed, China using multiple techniques. The specific goals of this paper were to: (1) evaluate the influences of the TWR on groundwater (i.e., extent and range), (2) estimate the quantity and percentage of groundwater recharge from the TWR and (3) elucidate the hydrogeochemical evolution along the water flow path.

Section snippets

Site description and hydrogeological characterization

The study area is located in the plains area of the Lake Baiyangdian watershed (Fig. 1(b)). The topographic features of the region include the lake and related depressions. The TWR is an unlined wastewater reservoir and with a length of 17.5 km and a width of 100 m, giving a maximum storage capacity of 8 ×ばつ 106 m3. An alluvial flood plain and ancient river channels are distributed in the south and west of the study area (Wu, 2008). The region is characterized by a temperate continental monsoon

Sampling and analytical procedures

A field survey and sampling were mainly conducted in June, 2009. Two wastewater samples were collected from the TWR in Sept., 2008. Water table, pH, electrical conductivity (EC) and temperature (T) were measured in situ using a portable meter (WM-22EP) (DKK, TOA Corporation, Japan). Groundwater is divided into shallow groundwater (SGW) with depth less than 100 or 120 m and deep groundwater (Deep GW) with depth greater than 100 or 120 m (Wang et al., 2013). Water samples were also collected from

Water chemical characteristics

The means of field observations, major ions, heavy metals and isotopic components of water samples from different water bodies are listed in Table 1. An increasing trend in EC value and SO42 −, Ca2 +, Fe and Al ions was observed as follows: deep groundwater < upstream SGW < downstream SGW < TWR. The low concentrations of major ions (except Na+) and smaller isotope components of deep groundwater verified the existence of an aquitard, which reduces the hydraulic connection between shallow and deep

Conclusions

The impacts of a man-made wastewater reservoir channel on the local shallow groundwater were revealed by comparing the characteristics of the wastewater reservoir channel to those of groundwater. When the cluster analysis was combined with the mixture percentage of wastewater identified in a previous study, the local groundwater could be further divided into a Highly Affected Zone, Medium Affected Zone, Low Affected Zone and Transition Zone, which had wastewater contributions ranging from 76 to

Conflict of interest

There are no known conflicts of interest associated with this publication and there has been no significant financial support for this work that could have influenced its outcome.

Acknowledgments

The study was supported by the Key Program of National Natural Science Foundation of China (No. 40830636), the State Basic Research Development Program (973 Program) of China (No. 2010CB428805) and the "Support program of AGSST for youth research" of Chiba University of Japan. The authors greatly thank reviewers for their good comments and suggestions on this manuscript. The authors greatly thank Dr. Jun Yang from University of Texas at Austin, USA for his kind help on the English revision of

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