Geosciences Journal Vol. 17, No. 4, p. 479 − 488, December 2013 DOI 10.1007/s12303-013-0037-8 ⓒ The Association of Korean Geoscience Societies and Springer 2013

Estimation of shallow groundwater ages and circulation rates in the Plain, : CFC and deuterium excess methods

Wei-hong Dong Key Laboratory of Groundwater Resources and Environment, Ministry of Education, Jilin University, Changchun Bo Kang 130021, China Shang-hai Du* } College of Environment and Resources, Institute of Water Resources and Environment, Jilin University, Changchun Xu-fei Shi 130021, China

ABSTRACT: CFC age and deuterium excess methods were applied challenges (Liu et al., 2007; Guo et al., 2003; Yang et al., to the estimation of groundwater circulation rates in the Quaternary 2004). The chlorofluorocarbons (CFCs) method can be used shallow groundwater system of the Henan Plain. The results provide to date groundwater of less than 50 a, and has achieved good a basis for groundwater renewability evaluation. The spatial dis- tribution of CFC age shows that the groundwater system mainly results in research on dating young groundwater over the comprises modern water, less than 50 a. The groundwater of less past 20 years (Katz et al., 1995; Cook and Solomon, 1997; than 30 a was in the piedmont zone of the Taihang, Funiu, and Bockgard et al., 2004; Long et al., 2008; Qing, 2005; Happell Dabie Mountains, indicating short groundwater residence times, et al., 2006). and fast groundwater cycling, with circulation rates of 27–31 m/d. In addition to groundwater ageing methods, deuterium (D) Groundwater cycling along the Yellow River was also rapid because and the 18O stable isotope methods have been proven to of exchange with the Yellow River. The circulation rates were 34–54 m/d. In the areas around Tongxu, , Taikang, Xiangcheng, be effective tools for understanding groundwater circulation in the middle of the study area, and east of Huaxian-Changyuan (Xu, 2009; Sun, 2007; Horita et al., 2005; Wang, 1991). and Xixian, Gushi in the south, groundwater age was 30–40 a, sug- Because of the thermodynamic properties of water, which is gesting a longer groundwater residence time. The groundwater controlled by the molecular mass of oxygen and hydrogen, cycle in these areas was slower than in the piedmonts, and the area D and 18O undergo isotopic fractionation in the water cycle, along the Yellow River. The circulation rates were 15–26 m/d. In driven by environmental factors (such as evaporation and the areas of Luyi, , , Xincai and Huaibin, the groundwater age was older than 40 a, with the longest resi- water-rock interaction), and the water has different isotopic dence times and slowest circulation rates (~12 m/d). The correla- characteristics in different compartments of the water cycle tion between groundwater age and deuterium excess averages for (Yuan, 2006; Xu, 2009). the northern, central, southern shallow groundwater systems and The deuterium excess parameter is derived from the con- the <30 a, 30–40 a, >40 a groundwater age divisions was strong (R centrations of D and 18O stable isotope, and is defined as d = 0.9714), showing that the groundwater residence time embodied = δD – 8δ18O (Dansgaard, 1964). by the deuterium excess parameter was consistent with ground- water age estimated using the CFC method. The initial value of d in groundwater should be equal to its value in local precipitation, because groundwater is recharged Key words: groundwater age, deuterium excess, chlorofluorocarbons, by the infiltration of precipitation. Subsequently, the recharged groundwater circulation rate, Henan Plain water interacts with rocks and isotope exchange can occur (Yin et al., 2001; Zhou and Rao, 1997). Generally, concen- 1. INTRODUCTION trations of compounds with hydrogen are very low in aqui- fers. This cannot significantly affect the δD value of the Groundwater age is one of the most important issues in water whereas isotope exchange of O can increase δ18O by water cycle research, and information about it can help in water-rock interaction because of O rich compounds such as the quantitative evaluation of groundwater cycling rates and CaCO3 in aquifers. Accordingly, with extended groundwater form the basis of groundwater circulation research (Li, 2008; residence time, the isotope exchange level between water Liu et al., 2007). In the past 40 years, tritium has been used and rocks is enhanced, increasing the value of δ18O and as a tracer for dating young groundwater, but the global ban reducing the value of d (Yin et al., 2001; Zhou and Rao, on nuclear bomb testing has sharply reduced atmospheric 1997). Generally speaking, because the controlling factors tritium concentrations. Consequently, precipitation in main- (climate, latitude and elevation) are approximately the same land China has low tritium concentrations, and the applica- for a specific area, the value of d only varies with ground- tion of tritium groundwater dating techniques faces huge water residence time (Yin and Ni, 2001). Therefore, in areas where precipitation is the main recharge of groundwater, the *Corresponding author: [email protected] value of d can be used to indicate the groundwater residence 480 Wei-hong Dong, Bo Kang, Shang-hai Du, and Xu-fei Shi time; the larger the value of d, the shorter the residence time. water level, ground subsidence, and fissures have occurred Our study focuses on the Henan Province of China, an because of excessive pumping in , , , important agricultural region with the largest population in and Cities (Lan and Liu, 2005; Miao, China. Shallow groundwater is the main water supply source 2010; Shi et al., 2012). for industrial and agricultural production. Because of the In this paper, we compare two methods to evaluate ground- arid climate, and excessive groundwater mining in the past water circulation rates, thereby demonstrating the similarity decades, the regional groundwater circulation system has and validity of each. The CFC method has been applied to suffered significant change. A cone of depression in ground- the study of shallow groundwater age, furthermore evaluating

Fig. 1. Shallow groundwater flow field and groundwater sampling locations for D and 18O. Groundwater ages and circulation rates in Henan Plain, China 481 quantitatively the groundwater circulation rate, whereas the pumping amount from the water supply wells was limited deuterium excess parameter qualitatively indicates the ground- and mainly for daily living. water circulation rate by evaluating groundwater residence For CFCs sampling, a glass bottle with a capacity of 50 ml time. This assessment will allow us to identify the age struc- and its cap with the tin foil liner are put into a stainless steel ture of groundwater in the Henan Plain and the groundwater cup with the open mouth upward when sampling. The stain- circulation rate, which will contribute to improve manage- less steel cup is higher than the glass bottle so that the bottle ment of groundwater resources and plans to slow ground- can be immersed by the water in the cup. A copper tube water mining. about one meter long with an inner diameter of about 5 mm is needed to transport the groundwater from the pumping 2. STUDY AREA AND SAMPLING pipe to the glass bottle. One end of the copper tube must be inserted into the bottom of the glass bottle. When the bottle The Henan Plain is located in the east of Henan Province, is filled with groundwater, the groundwater can overflow and has an area of ~8.53×104 km2 (Shi et al., 2012) (Fig. 1). from the glass bottle to the stainless steel cup. The copper The average annual precipitation is 1000~1300 mm in the tube is removed slowly from the glass bottle when ground- south of Huai River, 700~900 mm in areas between Yellow water overflows from the stainless steel cup for about 10 min- River and Huai River and 600~700 mm in the north of Yel- utes. Then, the bottle is caped quickly in the water. If there low River in study area (Gao, 2008). The Henan Plains is is no bubble in the bottle, the bottle can be sealed quickly to overlain widely by the Quaternary period formations. Accord- prevent the air from polluting the sample. ing to the characteristics of aquifer media and the burial set- For D and 18O sampling, the groundwater is filled directly tings of groundwater, the Quaternary formation in the Henan into a pure plastic bottle with a capacity of 100 ml. All the Plains is classified as a shallow-buried aquifer (the confining samples were measured within 7 days after sampling. bed depth is about 40~160 m), middle-buried aquifer (the lower confining bed depth 100~400 m) and deep-buried 3. RESULTS AND DISCUSSION aquifer (the lower confining bed depth is 300~500 m). Most of the groundwater used in industry and agriculture comes 3.1. CFC Age in Shallow Groundwater from the shallow aquifer. Thus, the objective of this ground- water ages and circulation rates evaluation is focused on shal- The CFC method is based on Henry’s Law, and historic low groundwater. The shallow groundwater system can be atmospheric background CFC values can be used to deter- divided into three subsystems: northern plain groundwater mine groundwater age (Guo et al., 2003; Liu et al., 2007). system (I), central plain groundwater system (II), and south- Shallow porous groundwater media are often medium sand ern plain groundwater system (III), according to the charac- and fine sand bodies, and the infiltration of precipitation can teristics of the groundwater flow net and the watershed which be generalized as piston flow, such that water can mix during it belongs to (Fig. 1) (Shi et al., 2012). The shallow ground- the infiltration process (Andrew and Larry, 2006). water is mainly recharged by precipitation whereas dis- Groundwater CFC ages estimated using the piston model charged by pumping and a small amount of evaporation, are presented in Table 1, and the shallow groundwater of runoff to the down gradient and leakage to the deep-buried the Henan Plain was mainly recharged over the last 50 aquifer. years (Fig. 3). The distribution is controlled by topogra- In accordance with regional hydrogeological conditions, phy, the watershed (the line of the Yellow River bed, D, 18O and CFC samples from the three groundwater sys- Queshan, Zhengyang and Xincai), and the groundwater tems (northern plain groundwater system (I), central plain age gradually increases along the direction of flow. groundwater system (II) and south plain groundwater sys- Groundwater less than 30 a is located in the Taihang, tem (III)) were collected along the groundwater flow direc- Funiu, and Dabie Mountain areas, and the eastern side of tion (Fig. 2). Twenty-nine samples for CFCs were collected City along the Yellow River. These are the regional during March and April, 2009 (Table 1), and analyzed by groundwater recharge areas, and the small groundwater ages gas chromatography (GC Shimazu, type 8AIE) with elec- (GL1, GL6, GL7, GL27, GL30, GL34) indicate that the tron capture in the groundwater dating laboratory of the groundwater residence time is shorter, and the rate of Chinese Academy of Science, Institute of Geology and groundwater cycling faster than in other areas. Groundwater Geophysics. Twenty-six samples for D and 18O were collected of between 30 and 40 years is located around Lankao, Tongxu, in August 2009, analyzed by stable isotope mass spectrom- Taikang, Tuocheng, Huaxian, Changyuan, Xixian and Gushi eter (MAT253) at the Chinese Academy of Geological City. Groundwater older than 40 years is located near Luyi, Sciences Institute of Mineral Resources (Table 3). All the Yongcheng, Xincai, Huaibin and Zhumadian. The greater age samples were collected from domestic water supply wells (GL3, GL5, GL10, GL11, and GL12) indicates longer ground- installed in the shallow aquifer. The diameters of the wells water residence time, and slower groundwater cycling than were about 15 cm mostly with a depth of 15~30 m. The elsewhere. 482 Wei-hong Dong, Bo Kang, Shang-hai Du, and Xu-fei Shi

Fig. 2. Shallow groundwater flow field and groundwater sampling locations for CFC.

3.2. Groundwater Circulation Rate ties. To determine shallow groundwater circulation rates in different areas of the Henan Plain, seven flow paths were The groundwater circulation rate is defined by the ratio of selected for investigation (Fig. 4 and Table 4). length and age gradients along the groundwater flow path, Based on calculated CFC ages (Table 1), the circulation rate and provides a comprehensive indication of aquifer proper- along each path was estimated (Table 2). They were found Groundwater ages and circulation rates in Henan Plain, China 483

Table 1. CFC concentrations and ages of groundwater samples CFC concentrations/pmol·L–1 CFC concentration/pmol·L–1 Samples Age/a Samples Age/a CFC-11 CFC-12 CFC-113 CFC-11 CFC-12 CFC-113 GL1 4.84 2.65 0.99 16 GL19 1.84 0.95 0.26 35 GL2 1.54 1.06 0.77 35 GL20 1.58 0.10 0.05 36 GL3 1.27 0.56 0.02 41 GL21 1.80 1.00 0.16 35 GL5 0.77 0.47 0.06 41 GL22 1.57 0.24 0.15 37 GL6 4.47 1.64 0.36 23 GL23 1.46 0.22 0.11 37 GL7 2.19 1.38 0.15 27 GL25 0.99 0.81 0.05 38 GL8 1.66 0.64 2.55 37 GL27 3.84 2.10 0.20 25 GL9 3.28 1.45 1.11 27 GL28 1.86 1.32 0.07 34 GL10 0.62 0.14 0.02 43 GL29 1.30 1.42 0.06 35 GL11 0.34 0.34 0.23 44 GL30 4.83 2.84 0.28 24 GL12 2.45 0.25 0.23 46 GL32 4.83 2.51 0.29 23 GL13 1.87 2.32 0.13 24 GL33 2.80 6.57 0.56 30 GL15 2.78 1.97 0.82 31 GL34 2.87 1.76 0.24 26 GL16 1.74 1.84 0.16 31 GL35 1.62 1.58 0.12 28 GL18 1.69 1.27 0.05 36

Table 2. Shallow groundwater circulation rates Path selected Length Age variation Cycle rate Groundwater system Label Path (km) (a) (m/d) A GL27 → GL29 54.2 10 15 North system B GL32 → GL29 76.7 12 18 C GL21 → GL23 39.7 2 54 D GL35 → GL25 125.7 10 34 Central system E GL13 → GL15 78.2 7 31 F GL16 → GL18 47.3 5 26 GGL7 GL359.51412 South system HGL2 GL326.5612 IGL6 GL738.9427

Table 3. δD, δ18O and deuterium excess of groundwater samples 18 18 Samples DV-SMOW (‰) OV-SMOW (‰) d Samples DV-SMOW (‰) OV-SMOW (‰) d GL2 –50 –6.8 4.4 GL20 –55 –7.9 8.2 GL3 –44 –6.4 7.2 GL21 –66 –9.5 10.0 GL6 –42 –6.8 12.4 GL22 –63 –8.8 7.4 GL7 –44 –6.7 9.6 GL23 –64 –8.8 6.4 GL10 –57 –8.4 10.2 GL25 –59 –8.2 6.6 GL11 –46 –7.1 10.8 GL26 –53 –7.2 4.6 GL12 –26 –2.5 –6.0 GL29 –58 –8.9 13.2 GL14 –53 –7.8 9.4 GL30 –62 –8.5 6.0 GL15 –60 –7.8 2.4 GL31 –63 –9.0 9.0 GL16 –52 –7.2 5.6 GL32 –57 –8.3 9.4 GL17 –52 –7.7 9.6 GL36 –68 –9.8 10.4 GL18 –50 –7.5 10.0 GL37 –67 –9.7 10.6 GL19 –55 –8.5 13.0 GL38 –60 –8.7 9.6

to be higher in the south of the Yellow River (paths C and and Dabie Mountains (paths E and I, 31 m/d and 27 m/d, D, 34–54 m/d), and lower in the foothill zones of west Funiu respectively). The central plain area, Huaxian, Puyang, the 484 Wei-hong Dong, Bo Kang, Shang-hai Du, and Xu-fei Shi

Fig. 3. Shallow groundwater age zones. northern plain, the southern plains along the Huai River, and 3.3. Deuterium Excess and Groundwater Residence Time the area south of Huai River (paths F, B, A, G, and H), all had lower groundwater circulation rates (26, 18, 15, 12, and 12 m/d, Rainfall provides the main recharge of shallow ground- respectively; Table 2) than elsewhere. Thus, because of the water in the Henan Plain. The estimated values of d for the lateral recharge from the Yellow River, groundwater south of the samples collected are presented in Table 3. Average ground- Yellow River has the highest circulation rate. The shallow water ages in the three shallow groundwater systems, and groundwater circulation rates decreased from the recharge area the three groundwater age partitions (<30 a, 30–40 a, and (paths E and I) to the discharge area (paths F, B, A, G and H). >40 a), are presented in Table 5. The values of d in the northern, Groundwater ages and circulation rates in Henan Plain, China 485

Fig. 4. Calculation paths for shallow groundwater circulation rate. central, and southern groundwater systems are 8.80, 7.73 and respectively. The trend of groundwater ages in the three shal- 8.40, respectively; indicating that the groundwater residence low groundwater systems is consistent with the trend of time is the shortest in the northern plain, followed by the groundwater residence times calculated from d. Additionally, southern and central groundwater systems. Compared with the average groundwater ages are 24.3 a, 34.8 a and 43.0 a in the CFC ages, the groundwater ages of northern, central and the partitions <30 a, 30–40 a and >40 a, respectively, and the southern groundwater systems are 27.8 a, 35.4 a, and 30.9 a, corresponding values of d are 9.05, 8.24 and 5.55. Thus, the 486 Wei-hong Dong, Bo Kang, Shang-hai Du, and Xu-fei Shi

Table 4. Summary of the seven flow paths selected for estimation In the northern plain system (I), shallow groundwater flow of shallow groundwater circulation rates is from southwest to northeast, and a pattern of slowing cir- Path Groundwater sub-system Zone type culation from the piedmont to the plain area was observed. A & B I - northern plain discharge , , Xinxiang, and Fengqiu are located at the C Yellow River recharge (lateral) piedmont area of Taihang Mountain; the aquifer lithology D Yellow River (south of) runoff there is mainly fine sand and gravels. The groundwater hydrau- E II - central plain recharge lic gradient is about 1/1000–1/1500, and the local ground- F II - central plain discharge water is recharged by lateral flow from the mountain areas. The younger groundwater ages (GL27, GL30, GL32 and G & H III - southern plain discharge GL34) and larger d values (GL31, GL32, GL36 and GL37) I III - southern plain recharge indicate stronger groundwater circulation in these areas. As the groundwater flows into the northeastern plain of Huax- Table 5. Average groundwater age and deuterium excess for each ian, Puyang and Fanxian, north of the Yellow River Alluvial groundwater system and groundwater age division Fan, which has smaller size medium, groundwater hydraulic Average age/a Average d gradients decreasing to around 1/2500–1/4000 and ground- North 27.8 8.80 water circulation weakens to a rate of 15–18 m/d. Groundwater Central 35.4 7.73 In the central plain groundwater system (II), Kaifeng, Lankao, system Minquan and Qixian are located south of the Yellow River. South 30.9 8.40 The lithology of the aquifer medium is mainly fine sand, and <30 a 24.3 9.05 the area is affected by lateral recharge from the Yellow Groundwater age 30–40 a 34.8 8.24 River. The groundwater circulation rate is about 34–54 m/d. >40 a 43.0 5.55 Following the groundwater flow direction to Luyi, Shangqiu and Yongcheng, located on the Yellow River Alluvial Fan, the aquifer lithology is silt and loam, and the groundwater hydraulic gradient is 1/2500–1/4000. Here the groundwater CFC age increases to more than 40 a (Fig. 3), the groundwater residence time is longer, and the circulation rate is lower. In the central plain area, the lithology of the aquifer medium at the Funiu and Gaoqi Mountain areas, and , is mainly fine sand and gravel. The groundwater hydraulic gradient is around 1/1000–1/1500, the groundwater age is small, and the groundwater circulation rate is about 31 m/d. Moving downstream to Luohe and Xiangcheng, the lithology is silt and loam, and the groundwater circulation rate decreases to 25 m/d. The groundwater CFC age (GL15 and GL16) and d values (GL15 and GL16) indicate that the ground- water residence time is longer here. Fig. 5. Correlation of average groundwater age versus average deu- In the southerly-most part of the central plain area, south terium excess. of Shangcai-Xiangcheng and east of Zhumadian-Zhengyang, the alluvial fans of the Huai and Ru Rivers have lithology trend in groundwater ages in the three partitions is consistent that is mainly loam. The groundwater hydraulic gradient is with the trend of d in the groundwater system. Average about 1/3000–1/5000, the groundwater age is larger (GL12), groundwater CFC age and d values (Table 4) were highly and the d value is smaller (GL12) than elsewhere, indicating correlated (R = 0.9714) (Fig. 5), providing further confirma- that the groundwater circulation rate is lower in these areas. tion of the consistency between groundwater residence times In the southern plain groundwater system (III), estimated from d and groundwater CFC ages. and Huangchuan are located at the piedmont of Dabie Moun- tain. The lithology of the aquifer medium here is fine sand 3.4. Summary of Groundwater Circulation Rates in Dif- and gravel, the groundwater hydraulic gradient is about 1/ ferent Areas 800–1/1500, and the groundwater circulation rate is 27 m/d. The groundwater age (GL1, GL6 and GL7), and d values The groundwater CFC ages, circulation rates and d values (GL6 and GL7) indicate short groundwater residence times, in the Henan Plain indicate that groundwater circulation slows and the groundwater circulation conditions are good in these from piedmont to plain areas, and groundwater circulation areas. characteristics change with local hydrogeological conditions. In the very south of the Henan Plain, Xixian, Huaibin and Groundwater ages and circulation rates in Henan Plain, China 487

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