Accepted Manuscript

Research papers

Riverbank Filtration in China: A Review and Perspective

Bin Hu, Yanguo Teng, Yuanzheng Zhai, Rui Zuo, Jiao Li, Haiyang Chen

PII: S0022-1694(16)30483-8 DOI: http://dx.doi.org/10.1016/j.jhydrol.2016.08.004 Reference: HYDROL 21439

To appear in: Journal of Hydrology

Received Date: 29 January 2016 Revised Date: 5 July 2016 Accepted Date: 1 August 2016

Please cite this article as: Hu, B., Teng, Y., Zhai, Y., Zuo, R., Li, J., Chen, H., Riverbank Filtration in China: A Review and Perspective, Journal of Hydrology (2016), doi: http://dx.doi.org/10.1016/j.jhydrol.2016.08.004

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Riverbank Filtration in China: A Review and Perspective

Bin Hu, Yanguo Teng*, Yuanzheng Zhai, Rui Zuo, Jiao Li, Haiyang Chen

Engineering Research Center of Groundwater Pollution Control and Remediation of Ministry of Education, Beijing

Normal University, Beijing 100875, China

* Corresponding author. Teng YG; Tel & Fax: + 86 10 58802738; E-mail: [email protected]

Abstract

Riverbank filtration (RBF) for water supplies is used widely throughout the world because it guarantees a sustainable quantity and improves water quality. In this study, the development history and the technical overview of

RBF in China are reviewed and summarized. Most RBF systems in China were constructed using vertical wells, horizontal wells, and infiltration galleries in flood plains, alluvial fans, and intermountain basins. Typical pollutants

+ such as NH4 , pathogens, metals, and organic materials were removed or diluted by most RBF investigated. There have recently been many investigations of the interaction between groundwater and surface water and biogeochemical processes in RBF. Comprehensive RBF applications should include not only the positive but also negative effects. Based on a discussion of the advantages and disadvantages, the perspectives of China’s RBF technology development were proposed. To protect the security of water supply, China’s RBF systems should establish a management system, monitoring system and forecasting system of risk. Guidelines of RBF construction and management should also be issued on the basic of relevant fundamental investigations such as climate influence, clogging, and purification mechanism of water-quality improvement.

Key wards: Riverbank filtration, Groundwater, Security water supply, Removal of pollutants, Research perspective

1. Introduction

In nature, river water percolates through riverbeds into aquifers during high-flow conditions (Eckert and

Irmscher, 2006; Schubert, 2002). During the percolation processes, components of infiltrating water will be changed and purified by a series of physical, chemical, and biological reactions in the hyporheic zone, as well as aquifer materials, all of which contribute to filtration and attenuation of contaminants in river water (Grischek et al, 2002;

Kuehn and Mueller, 2000; Ray et al., 2002a). Thus, groundwater exploitation at riverbanks is gradually being conducted via riverbank filtration (RBF).

In RBF, the process of groundwater exploitation is similar to the capture of percolating water from production wells that are near the riverbank (Sheets et al., 2002; Sprenger et al, 2011; Ulrich et al, 2013). With the withdrawal of groundwater, differences in water levels between groundwater and river become greater, resulting in infiltration 2 / 37 of river water into aquifers and water into pumping wells (Wett et al, 2002; Derx et al, 2013).

For more than 150 years, RBF has been used in Europe to supply drinking water (Grischek et al., 2002; Kuehn and Mueller, 2000; Ray et al., 2002b; Sontheimer, 1980; Tufenkji et al., 2002), while RBF in the United States has been used for the water supply for more than 70 years (Ray et al., 2002b; Eckert and Irmscher, 2006). However, this technology has been used for less than 20 years in other countries such as Korea (Lee and Lee, 2010), India (Sandhu et al., 2011), Egypt (Hamdan et al., 2013), and Brazil (Freitas et al., 2012). During these times of high water-security risk (Voeroesmarty et al., 2010), the RBF system has been proven in a number of studies to be effective and has shown worldwide potential for supplying water (Ray, 2008; Schiermeier, 2014).

Compared with the development and application of RBF in the western countries, the history of RBF use in

China is short; current use and future prospects are low. In recent years, the concerns of RBF in China concentrated on sustainable yield of water exploitation and water quality improvement after infiltration process at specific areas.

Scientific summarization of the development history and comprehensive review of characteristics of RBF system in

China are still lack. Accordingly, the objective of this article is to: 1) review the history of development of RBF in

China; 2) summarize the technical overview; 3) discuss the advantages and disadvantages of China’s RBF application; and 4) discuss the prospects of China’s RBF technology development.

2. Overview of RBF in China

According to the statistics data of China Water Resources Bulletin, 2014, the quantity of groundwater supply was 111.7 billion cubic meters, 18.3% of China total water supply. The surface water infiltration quantity was 49 billion cubic meters, 43.9% of China total groundwater supply. It has created favorable conditions for development of RBF in China.

2.1 Development of RBF in China

Knowledge on the exploitation and utilization of groundwater had a long history in ancient China. The oldest well discovered in Zhejiang Province was built before 5700-3710 years BC (Han and Chen, 2013).

While, the first RBF facility was constructed in northeast China in the 1930s, and it has since been widely used in other areas (Table 1). China’s RBF facilities are mainly in the north. More than 50 RBF sites are located along the

Yellow River. Additionally, there are more than 15 well fields pumping groundwater in the Hai River and Luan

River basins for public water supply of RBF. Although most RBF projects are located in north or northwest cities,

Sichuan province, Hubei province, Shanghai and a few other places in southern China also have the water pre-treatment works that utilize infiltrating water for urban drinking water supplies.

Table 1 3 / 37

Exploitation of infiltration water is an effective approach for reducing environmental problems caused by excessive exploitation of surface water and groundwater. As a typical method for conjunctive regulation of surface water and groundwater, RBF contributes to the sustainable yield of water supply, while reducing damage to the stability of aquifers, cost of water treatment, and the pressure of meeting increasing water supply demands. The proportion of water supplied by RBF in water supply systems is shown in Table 2. The quantities of infiltrating water exploitation at RBF sites are various.

Table 2

In the Yellow River basin, five provinces along the Yellow River have developed RBF into supply water for urban drinking in varying degrees. In these arid or semi-arid regions, the application of RBF can effectively solve the shortage of water resource and maintain the sustainable development and utilization of groundwater. RBF can also be a meaningful water-intake technology for the cities in south and northeast China, where water resources are relatively rich.

Rely on the practice of RBF establishment, the experience of RBF operation, and the improvements of groundwater exploitation technology, the development of RBF in China has been laid a certain foundation.

2.2 Classification of RBF

In view of the infiltration process, RBF can be divided into direct bank filtration and indirect filtration. The hydraulic connection between groundwater and river water is controlled by variations in river hydrodynamic conditions. Decreased seepage (less than the exploitation quantity), increased groundwater withdrawal (more than river flow), and formation of the riverbed clogging zone (low infiltration rate) can accelerate development of a water-unsaturated zone beneath the riverbed or in the aquifer, eventually leading to indirect filtration of river water

(Fox and Durnford, 2003; Hubbs, 2006; Brunner et al, 2009). The formation of clogging zone beneath the riverbed is caused by the continuous infiltration of river water because of well pump age (Schubert, 2006). The clogging phenomenon of parts of riverbed is principally unavoidable during long-term RBF wells operation, which accompanies with infiltrate-rate decreasing, reduction of permeability in the infiltration area, the formation of unsaturated zone, and results in water yield continuous reducing (Mucha et al., 2006). Conversely, with the formation of clogging zone, filtration in an aerated zone of water-unsaturated aquifer material can improve the infiltrated-water quality more efficiently (Su et al, 2007; Zhang et al, 2011). In contrast, direct bank filtration provides higher infiltrated-water quantity, whereas the capacity for improving infiltrated-water quality may not be as 4 / 37 great (Schubert, 2002).

Another method of classifying RBF sites is based on the landforms of water source fields. In China, most riverside groundwater sources are constructed in flood plains, alluvial-proluvial fans or intermountain basins located along riverbanks. According to these various landforms in which RBF facilities are constructed, China’s RBF sites are classified into four types: intermountain valley, intermountain basin, alluvial-proluvial fan, alluvial-lacustrine and coastal plain (Table 3). Aquifer particles size becomes finer from intermountain valleys to alluvial-lacustrine and coastal plains, while the distribution of the aquifer becomes wider. Vertically, aquifers commonly mix with thin layer of granular aquifers (clay or silty sands), which are distributed in the middle or bottom of the whole aquifer.

When compared with coarse particle aquifers, the content of total carbon and organic carbon in granular aquifers is greater.

Table 3

2.3 Types of RBF wells

Generally, application of RBF wells can be classified into three types in China (Fig. 1):

(a) Vertical well (a): A large-scale tubular well is drilled downward into aquifers near the river. Vertical wells are

typical water intake structures that have been widely applied in China for groundwater exploitation.

Withdrawal of high quantities of groundwater, simple construction and low economic cost are the main

advantages of vertical wells used in RBF.

(b) Horizontal well (b and c): Horizontal wells consist of a vertical well and horizontal lateral well screens

distributed in the aquifer to collect groundwater and percolating water. In China, horizontal wells are often

applied to areas in which the hydraulic conductivity and exploitation quantity are lower. Thus, these wells can

be used for RBF in low-permeability aquifers.

(c) Infiltration gallery for water-collection (d and e): These systems consist of horizontal water collection

structures that also can be applied to low-permeability aquifers. At a certain depth, the infiltration gallery will

collect water from riverbank and riverbed percolating water or phreatic water. Because of their simple

structure, low operating cost and convenient maintenance, infiltration galleries are used for industrial and

agricultural production, and daily life.

Fig. 1 Types of RBF wells in China

5 / 37

2.4 Optimization of RBF wells

The distribution of pumping wells is a key factor influencing the quantity and quality of water. Well optimization involves reasonable design of well distributions, which will ensure the sustainable operation of RBF. In

China, there are two kinds of well arrangements for withdrawal of groundwater along rivers: line and five points

(Fig. 2).

Fig. 2 Well arrangements in China’s RBF systems

Line RBF systems run parallel to the flow direction of the river. In contrast, five points systems are scattered.

Line arrangements are widely applied to withdrawal of groundwater for different types of water source fields. The boreholes are parallel to rivers within a certain distance, and well distance is another specific distance for reduction of well group interference. This method is currently widely applied for groundwater exploitation in China. The five-point method is an ideal approach. High cost of investment and complicated construction process cause this design become a utopian distribution way.

Table 4

The purpose of optimizing wells is to guarantee the quality and quantity of water supply in riverside groundwater sources. To achieve this goal, it is important to explore the factors influencing optimization of boreholes. The location of boreholes in RBF sites varies based on the various demands for water and different hydrogeological conditions (Table 4). In Matan, after analysis of local hydrogeological conditions, the minimum distance of boreholes location was determined to be 50 m. To protect the water intake structure from floods, the reasonable distance of wells from the Wei River was suggested to be more than 50 m. Because of the Fen River’s seasonal variations, the distance between pumping wells and the river ranges from 750 m to 2150 m. Differences in well completion technologies may also influence the wells’ location. For vertical wells, the general distance between the well and the river is 50–1000 m. Compared with vertical wells, the completion technology for horizontal wells is more complex, the cost of drilling is greater, and the location of horizontal wells at the RBF site is depend on wells’ length in horizontal direction and geomorphology.

In riverside groundwater sources, a reasonable residence time of infiltrated-water will satisfy the demands imposed by urban development, while assuring the stability of aquifers and reducing the environmental problems caused by groundwater withdrawal. It also contributes to remove surface water contaminants during infiltrating into 6 / 37 groundwater through the riverbed. An appropriate distance back-calculated by residence time provides sufficient space and time for soil sorption, sedimentation in pores, inactivation and colloidal filtration.

Well spacing also must be considered. When wells exploit groundwater, the water levels and flow may interfere with each other, which can lead to two results: 1) when water table drops to a certain degree, the single well-yield of the interfered-well will be reduced, 2) drawdown of the interfered-well will be larger than normal if the well ensures the normal yield. Thus, reasonable spacing of wells can decrease interference, guaranteeing water table and sustainable yield of groundwater. Conversely, unreasonable well spacing may aggravate the drawdown of groundwater in RBF systems, which will induce land subsidence or other geo-environmental problems at RBF sites; therefore, the influence of drawdown with well spacing also needs to be considered.

However, ensuring reasonable well spacing may increase the capital costs associated with construction and management of RBF sites because of the need for increased water pipes, transmission lines, and monitoring. Thus, economic factors are also important to consider during development of RBF.

2.5 RBF Designs

Numerous factors must be considered when managers design RBF systems (Moore et al., 2012). The principles for designing China’s RBF systems are as follows:

(a) When analyzing the present utilization of water, data on the degree of regional water resource

development (surface water, groundwater) are prerequisite for RBF systems construction.

(b) The feasibility of the RBF facility must be estimated while considering the quantity and quality of surface

water and groundwater.

(c) The physiographic conditions and hydrogeological condition of RBF sites must be considered so managers

can choose appropriate districts for RBF systems construction. The new RBF systems should be located

upstream to reduce other industrial sewage and domestic sewage pollution of RBF systems.

(d) The success of designing RBF systems is tied to reasonable distribution of boreholes.

(e) The impact of groundwater exploitation on regional environmental quality must also be considered when

designing RBF systems.

To achieve reasonable designs in China’s RBF systems, the following conditions must be considered:

(a) Physiographic conditions: physiographic conditions must be surveyed as the first step in designing RBF

systems. Climate, rainfall, landforms, elevation, river characteristics (perennial or intermittent), stratum

lithology, and other geologic conditions all influence riverside groundwater sources. Generally, RBF

systems are near perennial rivers in China which recharges aquifers during RBF site operation. For

intermittent rivers (such as the Tarim River in Xinjiang Province), RBF well operation consumes aquifer 7 / 37

storage during the dry season, while the consumption can be recovered during the wet season.

(b) Hydrogeological conditions: RBF systems must be designed based on scientific exploration of

hydrogeological conditions. Ascertaining the hydrogeological conditions benefits the design schemes of

groundwater exploitation at riverside groundwater sources. It is also necessary to assess the aquifer

stability. The lithology of aquifers, hydraulic conductivity, thickness, recharge, and drainage source of the

groundwater system, groundwater dynamics and other factors must be considered. In China, aquifers are

primarily gravel, coarse sand or sand, all of which have relatively larger pores than other media. The

objective aquifers of groundwater exploitation are primarily phreatic aquifers, and the thickness of the

aquifers is generally more than 10 m. This ensures hydraulic connections between aquifers and nearby

rivers.

(c) Impact on regional environment: when designing RBF systems, the properties of aquifers, variation in

geotectonic stress in aquifers, drawdown of groundwater and other geo-environmental problems induced

by groundwater withdrawal at riverside groundwater sources must be considered. The impact on the

regional environment is a comprehensive index that must be determined through a comprehensive

assessment of these impact factors.

2.6 Maintenance and management

Maintenance and management of RBF systems guarantee a sustainable water supply. Management principles are designed to meet the requirements of water supply in the locality. According to the water supply demands, efforts should be made to (1) establish and classify the RBF water resource area, (2) develop monitoring specifications and targets, and (3) reduce environmental impacts (John et al., 2006; Galatchi, 2006).

In China, there are two basic rules used for division of groundwater protection zones:

(a) The total times required for pathogens to penetrate from riverbed to aquifers (t1), and from aquifers to

well screens (t2) must be greater than the residence time (t0).

(b) According to the distance request of groundwater resources protection zone in Technical Guideline for

Delineating Source Water Protection Areas (HJ/T338-2007), the distance between wells and riverbanks

should not be shorter than the distance of the groundwater drinking-water health protection zone of 30 m.

According to the Technical Guideline for Delineating Source Water Protection Areas (HJ/T338-2007), from the national policy, there are five principles of establishing the China’s RBF water resource areas: primacy of protecting, integrated prevention and treatment, water quality security, reasonable range, and adaptation to local conditions.

Experience formula method (a standard method for determining radius of protection areas in China, proposed from

Technical Guideline for Delineating Source Water Protection Areas (HJ/T338-2007) ) and solute transport numerical 8 / 37 simulation method are widely used to decide the range of RBF water resource area in China.

Establishment of effective long-term monitoring measures enables sustainable utilization of RBF systems.

Such measures are essential to the development of strategies for responses to environmental emergencies and emergency programs as well as to reducing the risk of pollution in RBF water resource conservation. For China’s

RBF systems, monitoring capacity deficiency is still the main weakness of environmental management of water sources. The distribution of monitoring wells, construction of monitoring information platforms, and establishment of warning systems are necessary measures for perfecting monitoring systems of RBF.

Reducing environment impacts is also vital to maintenance management of riverside groundwater sources.

Managers should pay attention to the influence of extreme climate (such as drought and flood) on RBF systems.

Land subsidence, saline invasion and other environmental geological problems caused by groundwater overexploitation, as well as deterioration of water quality caused by human activities will affect the RBF operation.

To protect the safety and security of RBF systems, some response measures are necessary, including modulating exploitation schemes according to the environmental change, designing alternatives for RBF and strengthening the cooperation of departments.

However, management of China’s RBF systems still faces many challenges. Compared to guidelines of RBF construction and management published worldwide, the specifics in China are still missing. There are no unified standards of classification. Additionally, there is no unified management precept for generalized analysis at the national level. Regional diversity and discrepant constraint conditions cause administrative vulnerability in China.

The management targets are also limited. In addition to the quality and quantity of groundwater in RBF systems, the influence of river hydrodynamic conditions should be considered. Conversely, ambiguity of monitoring specifications will obstruct management in China’s RBF systems and weaken the capacity for emergency response.

Third, maintenance of China’s RBF systems is not widely accepted by the managers. The traditional concept of maintenance is confined to boreholes inspection which is lack of scientific and systems guidance.

Thus, maintenance and management of China’s RBF systems require further studies to develop unified management specifications, confirm the monitoring specifications, further refine delineation of water resource protection zones and establish technological standardization and processes of maintenance.

3. Water-quality improvement with RBF in China

According to the conclusion of China Water Resources Bulletin, 2014, the quality of surface water was moderate; more than 85% of water quality of groundwater resource was poor. Compared to pump surface water/groundwater directly, the advantage of RBF is infiltrated-water quality improvement and pollutants dilution in aquifer (Wu et al., 2007). As an effective pre-treatment step for water supply, RBF can promote the guarantee of 9 / 37 water supply quality and security in water low-quality areas.

The pollutant removal/dilution rate depends on the raw-water composition, porous filtration medium properties, and biogeochemical processes during infiltration (László and Literathy, 2002). Studying pollutant removal/dilution processes is helpful to understanding the characteristics of riverside groundwater sources, assessing sustainability of

RBF, and putting forward feasible suggestions for RBF systems management (see Table 5).

Table 5

+ 3.1 Removal of NH4

+ RBF is an effective method of removing ammonia nitrogen (NH4 ) during surface water infiltration process.

+ + Excessive NH4 in surface water of China is a universal phenomenon. The source of NH4 pollution is caused by release of sewage water from factories, agricultural runoff, and domestic sewage (Krüner and Rosenthal, 1983; Sun

+ et al., 2015). Through RBF, NH4 can be removed by sorption, redox reaction or nitrification at the hyporheic zone

(interface riverbed/aquifer). A three-year successive field observation at the Xucun and Huangqiao sections of the

Kui River showed that the RBF in the saturated percolation had the potential to remove the nitrogen through biochemical processes, the nitrogen removal rates were more than 95% over the monitoring period (Wu et al.,

2007).

3.1.1 Sorption

+ When compared with physical sorption, cation exchange (chemical sorption) of NH4 -N by soil particles in riverbed or aquifer medium is more common.

+ 2+ 2NH4 + CaX Ca + (NH4)2X

+ 2+ 2NH4 + MgX Mg + (NH4)2X

+ NH4 -N can be temporarily transferred to soil colloid medium (negatively charged). For RBF systems, the

+ + sorption process increases the residence time of NH4 -N, which benefits nitrification. However, NH4 -N will be released from soil colloid medium when environmental conditions in RBF systems have changed. The release of

+ NH4 -N will increase with pH decreasing, temperature decreasing or salinity increasing, which affected by seasonal variation, surface runoff, and infiltrated-water salinity (Wang et al., 2000; Regnery et al., 2015; Lee et al., 2009).

Besides, during the sorption process, the concentration of Ca2+ and Mg2+ will increase, which poses the risk of increasing infiltrated-water hardness in RBF systems.

3.1.2 Nitrification and denitrification

+ Nitrification plays a leading role in removal of NH4 -N that infiltrates into RBF systems from surface water. 10 / 37

+ Under aerobic conditions, active nitrobacteria are essential to nitrification to remove NH4 -N from filtration soil:

+ - + NH4 +32O2 NO2 +H2O+2H

- - NO2 +12O2 NO3

With the development of nitrification, the consumption of oxygen increases, which changes the riverbed and aquifer to become anaerobic, leading to denitrification:

- + - 2NO3 +10H N2+4H2O+2OH

- + - 2NO2 +6H N2+2H2O+2OH

- + N2O +2H N2+2H2O

- - The reaction products (NO3 and NO2 ) can be transformed into N2 by denitrification, which decreases the secondary pollution risk of nitrate. Moreover, denitrification is beneficial to consumption of DOC and TOC in infiltrated-water (Wu et al., 2007). DOC and TOC are not only the main nutrients utilized by denitrifying bacteria,

- - but also provide electron donors for reduction of NO3 and NO2 .

3.2 Removal of Pathogens, Surrogates and Indicators

RBF is also an effective method of removing pathogens and surrogates during the surface water infiltration process. In China, Microcystins, Escherichia coli, Cryptosporidium, and Giardia are common microbial pathogens.

RBF can reduce these pathogens during the infiltration process, which will lower water treatment costs.

3.2.1 Microcystins

Cyanobacteria can produce cyanotoxins in surface water, with the most common being Microcystins (MCYST).

Most MCYST are highly hepatotoxic, causing liver hemorrhage within a few hours of acute dose (Sivonen et al.,

1999). MCYST may accumulate in surface scum and enter surface water or groundwater systems by rainfall; therefore, they pose a risk to groundwater source field.

Studies in China have suggested that RBF is an effective method for removal of microbial pollutants. The removal of MCYST through RBF is a comprehensive process that involves straining, inactivation, sedimentation in pores and colloidal filtration. Sampling and subsequent laboratory analyses revealed that the removal rate of

MCYST was more than 94% in Jiuwutan near the Yellow River. The removal rate is closely connected to soil properties. From August to September, the removal rate of MCYST was found to be more than 73%. The removal rate differs among samples of pumping wells because of differences in soil organic carbon content and pore media.

According to concentration of MCYST in Yellow River consistent with cyanobacteria’s change trend in seasons, the concentration-gradient curves speculate that MCYST comes from cyanobacteria rupture, then being released into river. 11 / 37

3.2.2 Escherichia coli

Sampling analyses of percolating water in pumping wells and surface water have verified the removal of

Escherichia coli (E. coli) in RBF systems (Table 6).

Table 6

After the surface-water penetration process, the removal rate of E. coli reached more than 99.99% in Santan well field. Groundwater average residence time was 70 days and the average elimination rate of E. coli was more than 0.1 log unit per day in Santan well field. Moreover, the removal rate of E. coli can be improved with infiltration distance of RBF systems. In the riverbank source field of Qingpu River, the groundwater average residence time was

148 days (distance from river to wells was 200 m) and average elimination rate of E. coli was more than 0.03 of log unit per day.

3.2.3 Cryptosporidium and Giardia

Cryptosporidium and Giardia removal with RBF is just beginning to be evaluated in China since pollution by oocysts and cysts is attracting increasing concern (Table 7).

Table 7

The primary investigations of oocysts and cysts have concentrated on removal after water treatment, especially in finished water (Table 7). In contrast, pollution of oocysts and cysts in groundwater systems has not been thoroughly investigated. When compared with water treatment plants, the removal of oocysts and cysts by RBF is more effective because it occurs via attachment to the aquifer grains, colloidal filtration, and inactivation through aquifer media. RBF can also lower the water treatment cost. However, oocysts and cysts in groundwater are often covered or replaced by the concept of the total number of colonies. Thus, it is difficult to identify the specific removal rate.

3.3 Removal of other pollutants

In addition to the pollutants discussed above, several other pollutants can be removed by RBF after surface water infiltrating into the groundwater system. A large number of regulated inorganic and organic chemicals accompanied with suspended particles will lower the riverbed permeability by attaching on the sediment (Xia et al.,

2013), pollute surface water and infiltrate groundwater systems via withdrawal of groundwater in riverbanks. Here, we will discuss the main types of these chemicals to reveal water-quality improvements in response to RBF in 12 / 37

China.

3.3.1 COD

Chemical oxygen demand (COD) is a typical factor reflecting groundwater quality, with a higher COD indicating greater contamination by organic pollutants. Accordingly, COD is important to evaluation of groundwater water security at RBF sites. Forecasting of the COD by numerical modeling in Puyang city (north of China) has indicated that more than 90% COD can be removed by RBF via aquifer grains sorption. In southwestern China, the

COD removal rate by RBF is also high. Within the water-rock interaction and microbial reactions in the riverbed of the Yangtze River in Baisha, the COD removal rate reaches 75% at local riverside source fields. In the RBF site of the Taipu River, microbial degradation has resulted in a COD removal rate of more than 80%. Moreover, the removal rate of COD is greater than 95% in a RBF site located along the Kui River, in Xuzhou (Wang et al., 2007).

Microbial degradation in saturated seepage systems plays an important role in COD removal.

CODMn measures COD using KMnO4 as an oxidizing agent, while CODCr uses K2Cr2O7 as the oxidizing agent.

It has been reported that CODMn removal can exceed 80%. After analyzing variations in CODcr levels in surface water and groundwater, CODcr can be effectively removed by RBF (Wang et al, 2007). When percolating water passes through subsoil passages, soil sorption and microbial degradation improve the quality of percolating water.

3.3.2 Heavy metals

In some areas of China, background values of specific heavy metals (for example, Fe and Mn) in groundwater systems are very high. However, RBF utilizes river-borne water to recharge aquifers and dilute natural contaminants, resulting in pre-treatment of infiltrating water. Based on field sampling analysis, more than 50% of heavy metal pollutants were lower by RBF in Shanghai. With the infiltration of large quantities of river water, the concentration of heavy metals in groundwater systems can be diluted.

Moreover, percolation may disrupt the redox environmental balance with infiltrated water containing oxygen.

This leads to more active redox reactions and microbial degradation, which are suggested to be effective methods for the removal of heavy metals. The removal of Fe ions in infiltrated-water was more than 90% with the RBF in

Xishui City. The filtration, absorption, microbial degradation of sand gravel surface contributed to remove Fe ions.

4. Specific research regarding RBF in China

Most specific studies of RBF in China have focused on the interaction between groundwater and surface water and biogeochemical processes.

4.1 Surface water–groundwater interaction

Withdrawal of groundwater from RBF systems can be generalized as a process of capturing surface water that infiltrates into groundwater systems in riverbanks. This is essentially a phenomenon of surface water–groundwater 13 / 37

(SW-GW) interaction. To understand the characteristics of RBF, it is necessary to investigate the interaction between groundwater and surface water. Although many studies have investigated the SW-GW interaction in China, there is no specific definition of the concept. Because RBF induces the infiltration of surface water into groundwater systems, the concept of SW-GW interaction in RBF can be concluded as follows: under the influence of surface water infiltration, groundwater quantity and redox environment in groundwater systems are changed, and in the meantime, redox reactions (chemical behaviors), biodegradation, biological attenuation, nitrification or denitrification, and other biogeochemical reactions (biogeochemical behaviors) are active in the riverbed (or hyporheic zone), infiltration zone, and aquifers.

Hydraulic connections, water chemistry connections, and water quality response between surface water and groundwater are the essential to the SW-GW interaction. These factors represent the possibility of interactions, processes and consequences. According to these characteristics, the SW-GW interaction researches in China’ RBF are enriched gradually.

Without a certain hydraulic connection between river and groundwater, the occurrence of SW-GW interaction is less frequent. Various hydraulic connection conditions of the SW-GW interaction zone in RBF fields have been described according to regional hydrogeological surveys. The establishment of numerical simulation models has enabled researchers to explore changes in the rule of hydrodynamics and contaminant migration in riverside source fields. A 1-D flow hydraulic coupling model of stream-aquifers interaction was used to study the transformation law of SW-GW; however, the simulation results were not accurate. Accordingly, field experiments and laboratory simulation tests are vital to investigation of the hydraulic connections involved in SW-GW. The results of such experiments reflect the SW-GW transformation relationship in the process of RBF. Some researchers have used

HydroGeoSphere, Processing Modflow, Visual Modflow and other simulation software to calculate the exchange capacity of SW-GW in various hydrodynamic fields of RBF sites.

The hydrochemistry connection between surface water and groundwater is another important composition of

SW-GW interactions in RBF. Hydrochemistry connections are the result of hydraulic connections, so analysis of hydrochemistry connections can also be utilized to identify the hydraulic connection and reflect SW-GW interaction at riverside groundwater source. 2H and 18O are considered to be conservative and stable in the natural water cycle, which can be utilized as a tracer of water movement, and help ascertain hydraulic connections in RBF sites with estimation of the concentration correlation. This method has been widely applied in different river basins, including those of the Malian, Wuyuer, Fuyang, Xilin and Second Songhua rivers. Conventional ions in groundwater (K+, Na+,

2+ 2+ - 2- - - Ca , Mg , Cl , SO4 , HCO3 , NO3 ) are also indicators of SW-GW interaction that can be utilized to confirm the

SW-GW interaction relationship of RBF systems. Moreover, TDS, conductivity, and some specific ions are regarded 14 / 37 as representative of the hydrochemistry connection between surface water and groundwater at RBF sites. Sample analysis can be utilized to evaluate the hydrochemistry connection of SW-GW, which also plays an important role in identification of the hydraulic connection.

RBF can impact the hydrodynamic conditions of SW-GW, which not only influences the hydraulic connection, but also changes the degree of SW-GW pollution. To enhance regional water resource protection in China under the influence of SW-GW interaction, studies of water quality response are necessary. Pollution levels, distribution of pollution plumes, and influence of pollution range are important for estimating the degree of pollution. Researchers focused on studying the influence of contaminants infiltration from surface water into aquifers, especially for quality of shallow groundwater along the riverbank. The degree of pollution of different RBF sites can be estimated by the combination of sampling analysis and various evaluation methods (e.g., plug flow model, DRASTIC, fuzzy evaluation method). Investigation of the contaminants migration process is an important part of water quality response. Researchers tried to explore migration mechanisms of contaminants infiltrating into aquifers from surface water during continuous exploitation of groundwater at RBF sites; however, establishment of simple contaminants migration models cannot always reflect the migration in these systems (Wang et al., 2002). In contrast, a flow-solute coupling model has been developed to simulate contaminant migration under complicated hydrodynamic conditions.

Some researchers have used various mathematical methods and different types of simulation software to simulate specific contaminant migration rules at RBF sites. Moreover, in-site tests, leaching tests, column tests, and some other laboratory experiments were used to analyze the law of contaminant concentration changes, as well as study the contaminant migration mechanism. The combination of experiments and numerical modeling is beneficial to improving understanding of the contaminant migration process. Based on the experimental data, a 1-D solute migration model and multicomponent migration 3-D coupling mathematic model were applied to explore the migration mechanism. Investigation of water quality is one aspect of pollution process research. Sampling analysis and numerical modeling revealed that the contaminants concentration in both seepage and raw-water were positively correlated, indicating that the hydraulic connection is closed at the riverside groundwater source and the pollution process can be predicted. Numerical modeling has also been applied to estimate the water quantity response between surface water and groundwater in RBF systems. For arid regions in China, estimation of the capture quantity of infiltration water is important to guarantee a sustainable yield of groundwater at RBF sites. Thus, when compared with traditional sustainable yield calculation, researchers preferred to estimate the capture water quantity of infiltration from surface water.

4.2 Biogeochemical investigation of contamination

The process of surface water infiltration and solute transportation is accompanied by a series of biochemical 15 / 37 reactions that may influence the quantity and quality of groundwater withdrawal. In RBF systems, biogeochemistry refers to the activities of chemical migration and transformation in the environment by microbial community behaviors. Biogeochemistry is controlled by temperature, pH, Eh, humidity, chemical concentration gradient and other factors.

Investigation of biogeochemical behavior in China’s RBF systems started relatively late. Such studies focused on migration and transformation of agricultural non-point source contaminants (nitrogen and phosphorus), which occurred at the interface of surface water and subsoil. The influence of biogeochemical behaviors on metalloid or heavy metals migration and transformation in the hyporheic zone has also drawn the attention of hydrogeologists. In addition, biogeochemical investigation of microorganisms has become increasingly popular.

+ - - The removal of NH4 , NO3 , NO2 , total nitrogen (TN), and COD were related to nitrobacteria, denitrifying bacteria and other bacteria. Saturation conditions of the seepage system influenced contaminants removal efficiency by percolating water passing through media in the RBF system. When compared with the saturated seepage system,

+ unsaturated seepage systems were beneficial in that they removed NH4 , increased microbial growth, and induced aerobic degradation of contaminants. In contrast, the saturated seepage system contributes to degradation by aerobes and anaerobes because of consumption of dissolved oxygen (DO). Microbial oxidation degradation plays an important role in removal of total phosphorus by RBF.

Heavy metals pollution can be decreased through effective biogeochemical behaviors, which occur frequently in the SW-GW interaction zone (hyporheic zone) and infiltration passage. Biogeochemical behavior for removing heavy metals contaminants from the hyporheic zone can be divided into three processes: attenuation of contaminants in aquifers, the cycle of diffusible contaminants and attenuation of point source pollutants. Summarizing the related studies has revealed that the biogeochemical behavior of aerobic bacteria helped removing heavy metal contaminants during the percolation process. After sampling analysis, the purification capacity of the riverside groundwater source in the Taipu River was confirmed, with removal rates of Cr6+ and As3+ of about 90%, and Zn2+,

Cu2+, Ni2+, Mn2+ removal rates of more than 50%. Sorption and microbial degradation contributed to prevention of contaminants migration, especially in an oxidation environment.

Few studies of removal of pathogenic microorganisms in RBF systems in China via biogeochemical behaviors have been conducted. In recent years, some researchers have conducted related studies and provided personal opinions regarding removal of microbial contaminants. The removal rate of E. coli was found to be greater than 98% at the RBF site of the Yellow River. Accordingly, researchers have focused on analyzing the removal mechanism by sampling analysis and laboratory experiments. The results showed that total bacterial counts of surface water decreased dramatically after infiltration. Sorption, natural attenuation, and the food chain of microflora were 16 / 37 considered to be the mechanisms of pathogenic microorganism removal in the Baisha waterworks, Chongqing province. Interception by strata, microbial phagocytosis and microbial degradation also contribute to removal of pathogenic microorganisms by RBF systems. The pathogen removal mechanism can be divided into two major aspects, physical filtration interaction and soil microbial phagocytosis. The residence time and the percentage of bank-filtered water in pumped groundwater are crucial parameters for all compounds in the process of RBF. Thus, these factors cannot be ignored when exploring the removal mechanism of pathogens in RBF systems.

5. Disadvantages of RBF

Despite the many advantages of RBF, it also has some limitations. For example, the efficiency of removal of microbial contaminants with RBF can be impaired by short flow paths, high heterogeneity, high hydraulic gradients and accompanying high flow velocities (Schijven et al. 2002). An important benefit of RBF processes is that they can remove pollutants and dilute contaminant concentrations during infiltration process. However, temporary RBF failure to completely remove pathogenic microorganisms could result in difficulty recognizing the short period of moderate contaminant concentrations (Schijven et al. 2002).

The capacity of RBF systems is limited by local hydraulic and hydro-geological conditions, which may not be favorable for the desired system performance. Although RBF systems are effective at removing or reducing the concentrations of some contaminants (including many compounds of emerging concern), others are resistant to removal. When water pollution incidents occur, the purification capacity of RBF systems can not satisfy primary standards, which increases treatment difficulties for waterworks. The potential public health risk is great when the

RBF water only receives regular disinfection. Due to the weakness of hydraulic connection between groundwater and surface water, the upstream mountain of Nalinguole River (Qinghai Province) was unsuitable for RBF application.

Seasonal variations in river water levels and flow in arid and semiarid lands limit the application of RBF in

China. Significant perennial freshwater resources are not available in most arid and semiarid lands. When river flow significantly decreases during dry season, the infiltration rate of river water is less than the groundwater exploitation rate, resulting in consumption of aquifer storage, damage to the original stability of aquifers, and a variety of negative environmental effects such as land subsidence and decreased safety of the water intake structure. In the

Hotan River non-flood season, the river was completely dry up or riverbed frozen, and forms a desert zone of

5-10km wide, which were unsuitable for the concentration of RBF site.

RBF is also influenced by climate change. Temperature, and the natural organic, dissolved organic and particulate organic matter composition of surface water, as well as seepage travel times, may influence the redox milieu during RBF and result in decreased quantity and quality of water (Doussanet al, 1997; Greskowiak et al, 2006; 17 / 37

Maeng et al, 2008). Temperature directly influences redox processes by influencing microbial activity, the solubility of various components and redox reactions (Matsunaga et al, 1993). Moreover, extreme climate conditions (e.g., drought and flood) also influence the redox conditions in RBF systems, which is reflected in infiltration rate, seepage residence time, oxygen consumption, and variations in pollutants concentrations in surface water

(Doussanet al, 1997; Massmann et al, 2006; Diem et al, 2013b). Thus, the removal efficiency of RBF systems is influenced by climate and climate change. Under the influence of temperature and frozen ground, the aquifers of

RBF along the Xunbiela River, frigid area of northeast of China, were not recharged by surface water infiltration; meanwhile, the decrease of water quality was obvious caused by redox reactions and microorganism inactivity.

During the operation of RBF, clogging of the riverbed and infiltration area is unavoidable (Riesen, 1975; Ray and Prommer, 2006; Schubert, 2006). Continuous infiltration of river water that contains suspended particles, chemicals and microbial components will induce clogging at the riverbed/aquifer interface and infiltration zone

(Hubbs, 2006). After mechanical sorption, chemical reaction (e.g., redox reaction, ion exchange), and microbial reaction (e.g., microbial activity, degradation, biofilm growth), the grain size of percolating medium will increase and the pore size will decrease. The infiltration rate of river water and purification capacity of RBF systems will be affected by the increase in resistance between rivers and aquifers. Clogging of riverbed in Yangzi River at Baisha

County has affected RBF operation.

Although the removal efficiency of pollutants by RBF is remarkable, it cannot replace waterworks treatment processes. When compared with water treatment by traditional waterworks, the main disadvantages of RBF are limitation of the specific pollutants removal capacity and requirement for seepage residence time. Moreover, variations in external conditions (e.g., changes in river hydrodynamics, climate, and river quality) also limit the purification capacity of RBF. Thus, in public water supply systems, RBF is only used as a pre-treatment step for water supply.

6. Perspective of RBF in China

Because of the continuous development of urban and rural areas, the demand for water resources is increasing.

However, the contradiction between urban development and water supply safety has become increasingly significant in China. The popularization of RBF technology may partly relieve China’s water resource issues and promote drinking water safety.

6.1 Reduction of risk associated with water supply

The available data indicate that abrupt water quality pollution accidents are often not stopped in China.

Conventional water-supply modes limit emergency treatment patterns and time for handling abrupt water quality pollution accidents. Chemicals, sewage and oil are the main types of pollutants involved in emergency water 18 / 37 pollution accidents, which are expensive to remove using traditional treatment facilities. Excessive water treatment will influence the quality of water supply (e.g., pH, smell, taste, chlorinity), and cause panic among consumers.

The filtration fields of RBF can act as an important buffer reducing the risk of water pollution. The delay in contaminant travel time in RBF systems is significantly greater than in the direct intake systems, and the hysteresis of water quality response in the interaction process between pumped water (groundwater) and the river nearby in filtration fields offers a relatively processing time for water utilities to respond to an emergency event.

However, the development of RBF in China prefers exploitation of quantity assurance to pre-treatment of percolating water with RBF technology. The purification capacity of RBF and response to water pollution incidents should receive increased attention. Thus, it is essential to enhance awareness of water quality pre-treatment ability and emergency disposal capacity of RBF to improve the development of China’s RBF. Alternative schemes for groundwater resource exploitation in RBF also should be designed. It is beneficial to providing the time required to formulate an effective contingency plan to deal with river water pollution incidents.

6.2 Drinking water security with RBF

The application of RBF in China can help ensuring drinking water safety. RBF can partly guarantee the quality and quantity of infiltrating water in natural attributes (water safety), and improve the water quality and quantity in social meaning (water security).

RBF can effectively remove pollutants via percolating-water when surface water infiltrates into groundwater at riverbanks. Under physical, chemical and biogeochemical reactions, RBF projects purify pollutants from infiltrating water through subsoil passage. This is an efficient pre-treatment process that improves water quality and reduces the treatment cost of waterworks at riverside groundwater sources.

Reasonable residence time will be beneficial to reaction conditions and time required for removal of pollutants that infiltrate into groundwater systems through the bottom of the riverbed (Table 4). When accidental pollution events occur, the distance will delay the pollutants migration and decrease direct pollution risk. It also provides additional response time for managers to develop emergency prediction schemes of pollution prevention and control, helping to ensure the water supply security.

RBF systems also improve surface water infiltration recharge. Continuous pumping at riverside groundwater sources aggravates differences in water tables and increases the hydraulic gradient between surface water and groundwater. The increased hydraulic gradient can increase the quantity of surface water captured, ensuring sustainable yield at RBF sites.

Thus, RBF projects improve the reliability of source water and ensure the security of drinking water. Effective removal of pollutants and response times safeguard drinking water safety. 19 / 37

6.3 Future of China’s RBF

Compared to achievements of management and construction of RBF in Western hemisphere, there is still a large gap in China. Because of lacking specific management standards, operation technology guidelines, water works construction standards for riverside groundwater source, the government management responsibility is ambiguous. Thus, the application of RBF in China has only just begun.

The China National Urban Drinking Water Health Safety and Security Plan (2011–2020) set a goal of ensuring urban water-supply health and safety, and protecting public health. To accomplish this, the following additional research is needed:

(a) Additional studies of urban water-supply safety and security with RBF technology should be conducted.

For RBF systems, the key points of guaranteeing safety and security of public water supply can be divided

as follows: investigation of the SW-GW interaction mechanism; the pathogen removal mechanism,

surrogates and indicators by RBF system; and clogging during continuous RBF operation. In China’s RBF

systems, the contaminants removal mechanism and efficiency are closely connected with SW-GW

interaction and clogging. Ascertaining these mechanisms will help ensure the quantity and quality of

sustainable water supply in riverside groundwater sources.

(b) The influence of riverbank groundwater systems capturing surface water on river ecosystem stability

should be investigated (Wang et al., 2014). Having a reasonable estimate of the proportion of water

infiltration of river runoff is important to determining sustainable yield of RBF. The relationship between

decreasing river water and the river channel ecosystem at riverside groundwater sources is important to

management of river ways and groundwater systems along the river and will ensure the sustainability and

security of the riverbank source field.

(c) Establishment and perfection of RBF management system. The establishment of a reasonable management

system helps reducing the negative effects of drinking water on health, and improves the security of the

public water supply by appropriate water-intake approach selection in RBF, well arrangement optimization,

and other measures. Additionally, establishment of these systems is in conformity with the long-term

objectives of the 13th Five Year Plan in China (2016–2020). Within confirming responsible department,

determining RBF management targets and mission, establishing the specific evaluation system, and

formulating contingency plans, management system of RBF can be effectively operated.

(d) Strengthen the construction of monitoring network at RBF sites. The construction of a drinking water

safety monitoring network and information-shared platform is beneficial not only to the evaluation and

prediction of health risk associated with drinking water but also to the establishment of methods for 20 / 37

handling drinking water pollution emergencies at RBF sites.

(e) Reinforcement of legal protection. According to the comprehensive evaluation of existing drinking water

health standards and drinking water safety protection laws, the government should revise and unify related

standards. Perfecting principles and standards of protection zone of riverbank source field.

The development perspective of China’s RBF is promising. With the establishment of a management system, improvement of the monitoring system, reinforcement of legal protection, and promotion of civic awareness,

China’s RBF will play an important role in development of the water resource industry. The specific prospective planning is shown in Fig. 3.

Fig. 3 Prospects for RBF in China

7. Conclusion

RBF is a successful strategy for improving the quality of water supply by natural infiltration process. The feasibility of RBF has been validated in Europe and the United States by an array of experiments under different settings and conditions. In contrast, the application of RBF in China is still in the early stages. For China, RBF is an effective technology for relieving the shortage of water, especially in arid or semi-arid regions. After reviewing development of RBF in China, the technical overview of RBF’s classification, well types, wells optimization, designs, and maintenance and management has been summarized.

Compared with traditional water resource development modes, the advantage of RBF is water-quality improvement by percolation. Components of infiltrating water will be changed and purified by a series of physical, chemical, and biological reactions in the hyporheic zone (or riverbed) during the percolation process. Moreover, filtered-water will dilute the concentration of typical pollutants after infiltrating into aquifers. The water-quality improvement capacity of RBF (purification and dilution) can help reducing water treatment costs and increasing the water quality security. However, RBF has some disadvantageous. For example, climate change, local hydraulic and hydro-geological conditions, purification capacity limitations, clogging and other factors can affect RBF systems operation to different degrees. Thus, studies investigating the reaction mechanism are necessary to promote the development of RBF in China. Improvement of China’s RBF systems is vital to development of the water resource industry. Continuous exploration and concern should be placed on safeguarding the water supply security, interaction regions, and environmental protection measures in China’s RBF sites.

Acknowledgment 21 / 37

This study was supported by the National Key Scientific and Technological Project of China (No.

2014ZX07201-010).

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Figures Fig. 1 Well types of RBF in China Fig. 2 Well arrangements of China’s RBF systems Fig. 3 Perspective of RBF in China

Fig. 1 Well types of RBF in China

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Fig. 2 Well arrangements of China’s RBF systems

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Unity of water quality standards

Determine standards of Reinforcement of delineating protection zone legal protection of RBF

Expedite construction of relative laws

Confirm responsible department

Determine standards of delineating protection zone Perspective Establishment of of RBF Promotion of civic development of management system awareness China’s RBF Formulate contingency plans of RBF

Establish the specific evaluation system

Water quantity

Improvement of Water quality monitoring system

Ecosystem/ Environmental geology

Fig. 3 Perspective of RBF in China

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Tables Table 1 Development of RBF in China Table 2 Capacity of Public-Water Supply with RBF in China (Parts) Table 3 Classification of China’s RBF Systems Table 4 Influence Factors of China’s RBF Systems (Distribution of Boreholes in some China’s RBF Sites) Table 5 Removal of Pollutants in China’s RBF Systems (Incomplete Statistics) Table 6 The monitoring results of Escherichia coli at Santan well field (Liang and Shi, 1997) Table 7 The Study of Oocysts and Cysts’ Pollution in China’s RBF systems

Table 1 Development of RBF in China Time Location Development References 1930s Northeast China Infiltration galleries were utilized for groundwater withdrawal Gao, 2012 Hydrogeological investigations of RBF locations had begun, and a number of Wang and Shen, 1983; 1950s Northeast China RBF sites had been constructed Chen and Zhang, 1983 Evaluation of groundwater exploitation potential of RBF in northwest China had Duan and Wang, 1984; been carried out. Peng, 1988; 1980s Northwest China The survey results demonstrated the feasibility of RBF construction schemes Han, 1988; that guarantee high quantity and quality of infiltrating water for water supply, Guo, 1988 which promoted the application of RBF technology in China 1987 Heinan Province Horizontal wells were first applied in RBF Su and Zhao, 1989 Along the Yellow Chen and Zhou, 1995; 1990s River; Infiltration gallery was regarded as a type of RBF application in China Xu et al., 2001 Xinjiang Province Dong et al., 2005 2002 About 300 RBF facilities were present in China s Wang and Kong, 2002

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Table 2 Capacity of Public-Water Supply with RBF in China (Parts) RBF Sites Alongside River Exploitation Quantity Reference

Baoji City Wei River 20.40×104 m3/d Wu, 2001 Shanxi Ba River 20.00×104 m3/d Li and Wang, 1997 Northern suburb of Zhengzhou Yellow River 20.00×104 m3/d Qian et al., 1997 Northwestern suburb of Xi'an Wei River 15×104 m3/d Yan, 2010 Puzhou Yellow River 4.80×104 m3/d Li et al., 1997 Liguanbao Hun River 12.59×104 m3/d Yi et al., 2006 Matan; Cuitan; Yinmentan Yellow River 15.15~20.38×104 m3/d Liang and Shi, 1997 East of Changchun Yinma River 12.16~12.99×104 m3/d Liu et al., 1995 Ta'er City Beichuan River 12.35×104 m3/d Li and Wang, 1994 Jiuwutan Yellow River 10.00×104 m3/d Lin et al., 2003 Qingqu district of Shanghai Taipu River 10.00×104 m3/d Zhang, 2009 Weibin of Xi'an Wei River 9.81×104 m3/d Wu, 2000a Xianyang City Wei River 28.80×104 m3/d Wu, 2001 Wugong County Qishui River 7.92×104 m3/d Zhang et al., 2000 Mianyang City Fu River 3×104 m3/d An et al., 2013 Nenjiang County Nenjiang River 3.15×104 m3/d Li, 2011 Baisha Town Yangtze River 3.00×104 m3/d Li et al., 2004 Xiaolangdi Yellow River 2.67~3.87×104 m3/d Zhao et al., 2005 Xindian of Sanmenxia City Yellow River 2.50×104 m3/d Cao et al., 2009 Chuandao City Yue River 2.07×104 m3/d Li et al., 2001 Xishui County Xishui River 2.00×104 m3/d Song et al., 2011 Chengde City Luan River 1.91×104 m3/d Liu, 2006 Pinglu County Yellow River 1.44×104 m3/d Cao, 2010 Hua County Wei River 1.37×104 m3/d Xu, 2011 Shache County Ye'erqiang River 0.98×104 m3/d Gao, 2012 Shaowu City Futun Stream 0.60×104 m3/d Zhang et al., 2010

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Table 3 Classification of China’s RBF Systems Classification RBF Sites Province Characteristic References

Aquifer medias are consist of gravel or coarse sand. The Li and Ta’er Qinghai Intermountain capacity of regulation and storage is weak due to aquifers Wang,1994 Valley Dagu River Shandong distribution along the river nearby is narrow. Sustainable Xu, 2013

Xilipu Hebei yield shall less than minimum flow in dry season. Han, 1997 Shalingzi power plant Hebei Aquifer medias are composed of coarse sand and sand and Han, 1997

Intermountain Hanzhong Shanxi aquifers have the capacity of regulation and storage. Xia, 2003 Basin Sustainable yield in basin shall less than flow of basin exit Yumenkou Shanxi Zhao, 2003 in dry season. Matan Aquifer particles are composed of sand gravel, coarse Cuitan sand and sand. Because of the wide aquifers’ distribution, Alluvial-proluvial Liang and Shi, Gansu aquifers have the strong capacity of regulation and Fan 1997 Yinmentan storage. Sustainable yield shall satisfy the condition of water levels limits. Jiuwutan Aquifer particles are consisted of sand or fine sand. Lin et al., 2003 North Suburb of Henan Paleochannel which is the enrichment zone often exists in Alluvial-lacustrine Liao et al., 2004 Zhengzhou such kind of water source field. Aquifers have the strong and Coastal Plain Northwest Suburb of capacity of regulation and storage. Sustainable yield has Shanxi Wu, 2000b Xi’an periodicity.

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Table 4 Influence Factors of China’s RBF Systems (Distribution of Boreholes in some China’s RBF Sites) Percentage of Distance from Wells Wells RBF Sites Wells Types River-borne References River to Wells Distance Arrangement Water Shanxi (Wei river) 200 line vertical >75.99% Zhang, 1992 Hubei (Xishui River) 96 line vertical >65.34 Song et al., 2011

Lanzhou (Matan) 50,100,150 100~500 line vertical 96.00% Gao, 1991 Zhengzhou (Jiuwutan) 300~800 >500 line/well group vertical 82.60% Ma et al., 1994 Xi'an (Ba river) line/five points vertical 73.39% Li and Wang, 1994

Zhengzhou (North first line: 250, >500 line vertical 70.18% Qian et al., 1997 suburbs) second line: 750 Shanxi (Puzhou) 250 275 line/five points vertical 76.00% Li, 1996 Shanxi (Qi River) 150~850 800~1000 line vertical 78.81% Zhang et al., 2000 Shanxi (Fen River) 750~2150 line vertical >60.00% Jia et al., 2003

Hejin (Yellow River, Fen River, 300~3000 line veritcal >70.00% Zhao et al., 2002 Shushui River, Shanxi) Nanyang (Tang River, 320 50 well group vertical/horizontal >60.00% Fu et al., 2004 Henan) Douluo (Muma River, 100~600 500 line vertical 82.56% Xue, 2006 Shanxi) Chengde (Luan River, 80 120 line vertical 76.00% Shu et al., 2006 Hebei) Heilongjiang (Songhua 500 50 line/well group vertical 74.42% Liu et al., 2008 River) Chengdu (Yinma River) 300 Line vertical 80.00% Liu et al., 1995 Qingpu (Taipu River, Zhang et al., 2008; 200 300 line vertical 70.00%~80.00% Shanghai) Zhang, 2009 Binzhou (Yellow River) 50 line horizontal >80.00% Zhang and Wu, 2004 Jilin (Di'er Songhua River) 2000 vertical >70.00% Sun, 2002 Fujian (Futun Stream) single horizontal 74.40% Zhang et al., 2010

Shanxi (Yellow River) 0-1000 250 line vertical >80.00% Liu, 2000

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Table 5 Removal of Pollutants in China’s RBF Systems Pollutant Concentration Percentage Purificat Refere RBF Sites Paramet River of Bank-filtrated Well Water ion Rate nces er Water Water

Liang Matan Escherich 6000/ml <100 >98.33% 96.00% and Shi (yellow river) ia coli (1997) Turbidity 1,000-7,000 3 >99.99% Total 10,000 /ml <100 /ml >99.90% bacteria Baisha Town 72 mg/l <2.0 >97.22% Wang COD >82.10% (Yangtze river) 17 <0.5 >97.06% (2004) BOD 12 <1.0 >91.67% TOC 9,86 <1.0 >89.86% - NO3

CODMn 4.79 mg/l 1.24 mg/l 70.75%

UV254 0.13 0.03 79.91% TP 0.27 mg/l 0.13 mg/l 56.12% Jiuwutan Wang + NH4 0.81 mg/l 0.43 mg/l 51.50% 82.60% (Yellow River) (2009) Algae 11.10×106 /l 0.33×106 /l 93.51% Cell 0.59~0.71μ Non-detected~ 66.89%~

MCS g/l 0.196 μg/l 100%

NH4+ 0.94 mg/l 0.19 mg/l 80.00% COD 15.90 mg/l 1.59 mg/l 90.00% Zhang BOD 2.71 mg/l 0.68 mg/l 75.00% Qingpu district 70.00%~80.0 et al. Fe 0.84 mg/l 0.42 mg/l 50.00% (Taipu river) 0% (2008, TP 0.14 mg/l 0.05 mg/l 60.00% 2009) TN 2.60 mg/l 0.26 mg/l 90.00% KMnO4 5.02 mg/l 2.01 mg/l 59.94%

Wu et TN 15.54 mg/l 0.31 mg/l 97.99% Xuzhou al. COD 379.00 mg/l 3.80 mg/l >98.99% >80.00% (Kui River) (2002, + NH4 17.09 mg/l 0.14 mg/l 99.18% 2005) Chengdu COD 7.83 mg/l 2.10 mg/l 73.18% Liu et 80.00% + (Yinma River) NH4 57.50 mg/l 2.00 mg/l 96.52% al. (1995)

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Table 6 The monitoring results of Escherichia coli at Santan well field (Liang and Shi, 1997) Distance from River to Escherichia Residence Time Sampling Location Well Depth Wells (m) Coli (MPN/L) (d) Yellow River 6000 Matan No.2 97.20 32 <3 89 Matan No.3 45.00 71 <3 197 Matan No.4 98.80 31 <3 86 Matan No.5 58.75 27 <3 75 Matan No.6 98.00 26 <3 72 Matan No.7 47.00 10 <3 28 Matan No.8 45.20 206 <3 572 Matan No.9 46.70 460 <3 1278 Cuitan No.3 65.00 272 <3 756 Cuitan No.5 65.00 112 <3 311 Yantan No.3 42.50 58 <3 161 Yantan No.5 60.00 26 <3 72 Yantan No.9 50.00 34 <3 94 Average hydraulic conductivity of 25m/d, average hydraulic gradient of 4.3‰，aquifer effective porosity of 0.3 (Li et al., 2010; Lv et al., 2014)

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Table 7 The Study of Oocysts and Cysts’ Pollution in China’s RBF systems Referenc Place Research Comments e

Nanjing and Oocysts and cysts detection in Han et al., Oocysts and cysts are detected in China first time. Anhui surface water first time 1987 Examination of oocysts and cysts in Fan et al., Macao raw water from reservoir 2001 More than 66% sewage water from After treatments, the residual of microbial pathogens Yu et al., Shenzhen sewage treatment works is polluted by in sewage water still can’t be ignored. 2003 oocysts and cysts

The concentration of Oocysts and cysts are 0-0.6/L Removal of microbial pollutant after Zhou et Shanghai and 0-0.8/l. The concentration may be higher than treatment of water works al., 2007 Standards For Drinking Water Quality in China (0.1/L).

Detection of oocysts and cysts for 19 In finished water, oocysts and cysts are not detected. Zhang, Shenzhen water supply enterprises in the finished It shows that treatments of water works are effective. 2009 water after treatment. Survey of oocysts and cysts in south Countries in of China countries. Occurrence of It proves that faultiness treatments and substandard Wang et South of China microbial pathogens is 36.67% and management of water works in southern China countries. al., 2014 28.33%.

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High lights <1> A comprehensive review of riverbank filtration engineering in China was proposed firstly. <2> The technical overview of riverbank filtration in China was systematic summarized firstly. <3> The hot spots of China’s riverbank filtration researches were comprehensive generalized and summarized. <4> The perspectives of China’s RBF technology development were proposed in the view of risk reduction of water supply, water security protection, and fundamental researches support