water

Article Protection of the Liuzheng Water Source: A Karst Water System in Dawu, ,

Henghua Zhu 1,2, Yanan Dong 3, Liting Xing 3,*, Xiaoxun Lan 3, Lizhi Yang 2, Zhizheng Liu 2 and Nongfang Bian 4 1 School of Environmental Studies, China University of Geosciences, Wuhan 430074, China; [email protected] 2 Institute of Geological Survey, 250000, China; [email protected] (L.Y.); [email protected] (Z.L.) 3 School of Water Conservancy and Environment, University of Jinan, Jinan 250022, China; [email protected] (Y.D.); [email protected] (X.L.) 4 Administrative Department of Dawu Water Source Area of Zibo, Zibo 255400, China; [email protected] * Correspondence: [email protected]; Tel.: +86-531-8276-9233

 Received: 5 March 2019; Accepted: 2 April 2019; Published: 4 April 2019 

Abstract: The Dawu water source is a rare, large-scale groundwater source located in northern China. The water supply function from this water source has, however, been lost due to anthropogenic pollution. In order to fully utilize valuable groundwater resources, a new water source of urban domestic water in Liu Zheng is planned. In this study, a tracer test and a numerical simulation method are used to examine the hydraulic connection between the Liuzheng water source and the Wangzhai industrial park; to optimize the exploitation layout of the Liuzheng water source and Dawu water source; and to propose the extent of the Liuzheng water source protection area. Results indicate that: (1) Karst development in the study area is uneven, and the Wangzhai area is a recharge area of the Liuzheng water source; (2) it is predicted that the groundwater flow field will not be significantly changed when a groundwater volume of 150,000 m3/day is exploited from the Liuzheng water source; (3) it is predicted that the proposed chemical park in Wangzhai will gradually pollute to the groundwater in the northern area of Liuzheng; and (4) results using the empirical formula method and the numerical simulation method indicate that the area of the primary protection area of the Liuzheng water source is about 0.59 km2, and the area of the secondary protection area is about 14.98 km2. Results from this study provide a certain technical basis for the exploitation and protection of groundwater in the Liuzheng water source.

Keywords: tracer test; numerical simulation; pollution; division of protection areas; Liuzheng water source

1. Introduction The karst landforms are widely distributed around the world, and karst water provides drinking water to nearly a quarter of the world’s population. In China, the total area of bare limestone is about 1.3 million square kilometers, accounting for 13.5% of the total area of the country, and covered limestone buried underground is more extensive. During the long geological history evolution, landforms such as gully, dissolved depression, dry valley, blind valley, falling water cave, and skylight are formed. The soluble rocks can be dissolved and eroded by groundwater along the layers, joints or structural fractures, and formed underground passages, rapidly moving through karst fissures, karst conduits, etc. Groundwater in the karst area is extremely easy to be polluted, which means that karst aquifer has a high degree of vulnerability [1–3]. The multiple conduit flow of karst medium leads to rapid contamination, while the diffuse flow forms persistent contamination [4]. Due to the

Water 2019, 11, 698; doi:10.3390/w11040698 www.mdpi.com/journal/water Water 2019, 11, 698 2 of 14 uneven development of karst as well as the complex and variable movement of groundwater flow, people try to study the migration of pollutants in karst water from different scales using different methods, such as isotopes [5], tracer test [6], pumping test [7], numerical simulation [8–10], indoor experiment [11], and so on. For example, Hamdan et al. [12] revealed the characteristics of groundwater vulnerability to pollution with the method of combining the stable isotopic (oxygen and hydrogen) and data of water temperature, discharge, and turbidity. Morales et al. [13] depicted the transport characteristics along preferential flow paths in karst aquifers by analyzing data obtained in 26 tracer tests in Basque.Maloszewski et al. [14] combined the application of lumped-parameter models to establish a measurement model for 18O and tritium in precipitation and springs, and obtained mean values of hydraulic parameters. Therefore, in order to effectively manage vulnerable karst water systems, specific exploration techniques and modeling methods are required to master, studying the media characteristics and hydrodynamic field characteristics of the karst area [15,16]. Previous studies have indicated that the majority of water in karst areas with intense anthropogenic activity has been contaminated to different degrees [17–19]. Pollution sources are derived mainly from industrial, agricultural and domestic pollution [20], with industrial and agricultural pollution being the main source points. For example, industrial production activities produce refractory organic pollutants, heavy metals, etc., which cause different degrees of pollution to groundwater systems [21]. Currently, water pollution in karst areas has certain universality in the north and south of China, as well as in other karst areas around the world. Water pollution associated to the chemical industry in karst areas is a notably serious issue [22–24]. In order to protect groundwater resources and prevent groundwater pollution risks, methods suitable for the division of groundwater source protection areas have been examined [25–27]. For example, Andreo et al. [28] used karst water replenishment conditions combined with groundwater flow rate to delineate the risk zone for karst water pollution. With the rapid development of computer science, numerical methods have been widely used. Numerical methods can not only simulate large-scale karst water movementand evaluate karst water resources [1], but also predict groundwater pollution processes [29]. For instance, Rudakov et al. [8] used two-dimensional and three-dimensional flow to simulate the migration of pollutants in groundwater. The migration of characteristic pollutants in aquifers was investigated by Saghravani using FEFLOW [9], and Rao Lei et al. [10] used the Visual Modflow to simulate and study the migration of pollutants in groundwater after the leakage of sewage from an industrial park in Jiangjin District, Chongqing. In order to delineate groundwater protection zones, a large number of studies have been undertaken [30–33], with the majority using empirical methods to determine the extent of protected areas [34]. In order to predict the spread of pollutants over long-term scales [35], the numerical method has advantages over traditional empirical formula methods, however the numerical method requires more hydrogeological exploration work. The Dawu water source is a rare large-scale karst water source. However, an oil spill by the Qilu Petrochemical Company in the mid-1980s resulted in groundwater pollution in this water source [36]. In order to control karst water pollution in this area, hydraulic interception measures were implemented in the upper reaches of the Dawu water source in 1992. However, these measures have not protected the Dawu water source as petroleum pollutants in some areas still exceed standard guideline values. At present, the Dawu water source has lost its water supply function. In order to alleviate water supply issues in this area, new water sources are urgently needed. According to previous analysis, the Dawu water source area and the upstream Liuzheng area belong to the same hydrogeological unit; the Liuzheng section in the runoff area has a large output capacity from a single well and it has good water quality [37]. It is therefore proposed that a new water source is created in the Liuzhen area. As a new petrochemical park is proposed in the Wangzhai area, it is important to study the impact this park may have on the groundwater environment of the Liuzheng water source. Therefore, this paper uses the tracer test to reveal the characteristics of medium field, uses numerical simulation to grasp the characteristics of groundwater flow field, and combines the tracer test, empirical formula and numerical simulation to divide the protection area of karst water source area. Water 2019, 11, 698 3 of 14

2. Study Area The study area belongs toa warm temperate continental monsoon climate. The annual average temperature is 12.3–13.1 ◦C, and the average annual precipitation is 640.50 mm. The rivers in the area are all rain-source type, and the terrain is high in the south and low in the north. The terrain in the south is a low mountain and hilly, and the highest elevation is 380 m. The northern part is connected to the sloped plain in front ofa mountain, and the lowest elevation is 40 m. carbonate rocks are exposed in the southern high mountains, central limestones are exposed in the low hills and Ordovician limestones are concealed to the north in the - sand sheets. Below the rock strata, Quaternary loose rock stratais widely distributed in the piedmont plain in the north, and the Carboniferous-Permian coal-bearing strata constitutes the water-blocking barrier of fractured karst water in the north. The fault structure is developed in the area. The central Zihe fault zone is the largest concealed fault zone in this area, which constitutes the water-conducting zone from the south to the north. The Liuzheng water source is located in the middle of this fault zone (Figure1). The carbonate fractured karst aquifers in the southern region and the Quaternary loose-rock-porous aquifers in the northern region are the main aquifers in the study area. The Quaternary loose-rock-porous aquifer is mainly distributed in the floodplain of the Zihe River and along its two sides, the plain area in the north and the alluvial fan of the Zihe River. The carbonate fractured karst aquifer is mainly distributed Water 2019, 11, 698 4 of 15 in bare mountainous areas to piedmont concealed zones.

FigureFigure 1. 1. GeologyGeology of the study study area. area. 1: 1: Village; Village; 2: 2:Source Source well; well; 3: Observation 3: Observation well; well; 4: Simulation 4: Simulation zone zoneboundary; boundary; 5: Fault; 5: Fault; 6: Geological 6: Geological boundary; boundary; 7: River; 7: River;8: Tracer 8: Tracertest area; test 9: area; Dawu 9: Dawuwater watersource sourceexploitation exploitation area; 10: area; Liuzheng 10: Liuzheng water water source source exploitation exploitation area; area; 11: 11:Quaternary Quaternary loose loose layer; layer; 12: 12:Ordovician Ordovician limestone; limestone; 13: 13:Cambrian Cambrian limestone; limestone; 14: 14:Magmatic Magmatic rock; rock; 15: Carboniferous-Permian 15: Carboniferous-Permian sand sandshale. shale.

3. MethodsWater recharge in the study area is mainly by atmospheric precipitation and water extraction is mainly due to artificial exploitation. Total water resources in the region are about 410,000 m3/day, 3.1. Tracer Test Arrangement In order to examine the hydraulic connection between the Wangzhai, Hougao and Liuzheng areas, WK01 and W512 were used as source wells for field tracer tests (Figure 1). On 7March 2017, 210 kg of ammonium molybdate was injected into the WK01 well in the Wangzhai experimental area, and 27 monitoring wells were established. A total of 379 water samples were collected from the following day until 20June 2017. On 16November2017, 200 kg of ammonium molybdate was injected into the W512 well in the Hougao experimental area, and 25 monitoring wells were established. A total of 350 water samples were collected from the following day until 9March 2018. For both experiment sites, the aquifers of the source and sampling holes are Ordovician limestone aquifers.

Prior to the open tracer test, molybdenum ion background values from the Wangzhai and Hougao experimental areas were recorded.After the tracer was injected, in the encrypted observation area within 2 km from the source point, the monitoring frequency was once a day; the area outside the encryption area was sampled once every three days. Monitoring holes close to the source well were sampled first.As the tracer migrated, the sampling frequency of the surrounding area was gradually encrypted.The atomic absorption spectrophotometer-graphite furnace method was used to measure molybdenum ion concentrations, and the detection limit is 0.5 ppb. The water level measurement at the monitoring points was synchronized during the tracer test.

3.2. Groundwater Flow Model

Water 2019, 11, 698 4 of 14 of which artificial groundwater exploitation is mainly concentrated in the northern region, with exploitation volume accounting for about 350,000 m3/day [38]. However, groundwater pollution in this area caused by the oil spill in the 1980s has rendered it not suitable for domestic use. It is therefore necessary to optimize the exploitation layout of the Dawu and Liuzheng areas, and to divide the Liuzheng water source protection area with the aim to maximize the benefits of groundwater resources.

3. Methods

3.1. Tracer Test Arrangement In order to examine the hydraulic connection between the Wangzhai, Hougao and Liuzheng areas, WK01 and W512 were used as source wells for field tracer tests (Figure1). On 7March 2017, 210 kg of ammonium molybdate was injected into the WK01 well in the Wangzhai experimental area, and 27 monitoring wells were established. A total of 379 water samples were collected from the following day until 20June 2017. On 16November2017, 200 kg of ammonium molybdate was injected into the W512 well in the Hougao experimental area, and 25 monitoring wells were established. A total of 350 water samples were collected from the following day until 9March 2018. For both experiment sites, the aquifers of the source and sampling holes are Ordovician limestone aquifers. Prior to the open tracer test, molybdenum ion background values from the Wangzhai and Hougao experimental areas were recorded.After the tracer was injected, in the encrypted observation area within 2 km from the source point, the monitoring frequency was once a day; the area outside the encryption area was sampled once every three days. Monitoring holes close to the source well were sampled first.As the tracer migrated, the sampling frequency of the surrounding area was gradually encrypted.The atomic absorption spectrophotometer-graphite furnace method was used to measure molybdenum ion concentrations, and the detection limit is 0.5 ppb. The water level measurement at the monitoring points was synchronized during the tracer test.

3.2. Groundwater Flow Model According to the hydrogeological conditions of the study area, the aquifer in the study area was generalized into a heterogeneous, anisotropic, three-dimensional unsteady groundwater flow model. The mathematical model of groundwater flow can be written as [39]:    ∂  ∂H  ∂ ∂H ∂  ∂H  ∂H  Kxx + Kyy + Kzz + W = µ ...... (x, y, z) Ω  ∂x ∂x ∂y ∂y ∂z ∂z ∂t  ∈  H(x, y, z, t) = H0(x, y, z) ...... (x, y, z) Ω (1)  |t=0 ∈  ∂H ∂H ∂H  Kxx + Kyy + Kzz = q(x, y, z, t) ...... (x, y, z) Γ ∂x ∂y ∂z |Γ2 ∈ 1 where Kxx, Kyy and Kzz are values for hydraulic conductivity (m/day) along the x, y, and z axes, respectively; µ is the specific storage or specific yield; H (m) is the potentiometric head; H0 (m) is the potentiometric head at the initial moment; W is a volumetric flux per unit volume representing sources and/or sinks of water; Ω is the simulation area; and Γ1 is the boundary. According to the drilling data and hydrogeological conditions, the model was divided into three layers in the vertical direction: (i) The Quaternary pore aquifer; (ii) the relatively weak aquifer; and (iii) the fractured karst aquifer. The planar area was divided by a discrete method of rectangular finite difference and the cell size was 500 m 500 m. The east-west boundary of the calculation zone was the × water-blocking boundary; the north was the lateral runoff discharge; and in the south, the west side of the Taihe Reservoir was the lateral runoff recharge. The main recharge items in the study area were the recharge of precipitation infiltration, and other recharges include the lateral runoff recharge, river leakage recharge, and recharge of reservoirs during the flood season. The main extraction process is artificial exploitation. The initial flow field used the groundwater flow field on 1September 2018. Water 2019, 11, 698 5 of 14

3.3. Solute Transport Model In order to predict the pollution impact of the proposed chemical park on the groundwater of the Liuzheng water source, the mathematical model of solute transport is as follows [39]:

 qs P  ∂C = ∂ (D ∂C ) ∂ (V C) + C + R (x y z)  ∂t ∂x ij ∂x ∂x i n s k ...... , , Ω  i i − i ∈ (2)  C(x, y, z, t) = C (x, y, z) ...... (x, y, z) Ω |t=0 0 ∈ 2 where C (mg/L) is the concentration of pollutants; Dij (m /day) is the hydrodynamic dispersion coefficient; Vi(m/day) is the groundwater permeation flow rate; t (day) is time; n is the porosity; 3 Cs (mg/L) is the concentration of source sink item; qs (m /day) is the unit flow; ΣRk is the chemical reaction term; C0 (mg/L) is the initial concentration of pollutants; and Ω is the simulation area. Based on the water flow model, the solute transport model was established. Combined with the composition of pollutants discharged from various chemical enterprises in the plant area [40], the conventional component Cl− was selected as the simulation predictor. Assuming the initial concentration of the region was 0, the pollution source was assumed to be a point source. Leakage was 3 set to 5000 m /day, and the concentration of the pollutant Cl− was set to 3000 mg/L.

4. Results and Analysis

4.1. Anisotropy of Karst Development

4.1.1. Anisotropy of Runoff Channels Tracer detection values were set at concentrations 5-times greater than background values at the observation wells. Molybdenum tracer was detected in eight observation wells in the Wangzhai test area and in ten observation wells in the Hougao experimental area. The tracer concentration curves form the observation wells in Wangzhai and Hougao were divided into single peak, double peak and triple peak types (Table1), and the three major categories were subdivided into di fferent specific forms. The single-peak curve was divided into slightly symmetrical and asymmetric types; the double-peak curve was divided into high-low and low-high types; and the three-peak curve was divided into high-low-low and low-high-low types. Single peak concentration curves accounted for the majority of tracer curves (62.5%) from wells in the Wangzhai test area, followed by triple peak curve (25%) and double peak curve (12.5%). Results from observation wells in the Hougao test area recorded double peak (50%) and single peak (40%) as the dominant tracer concentration curves; the triple peak curve type accounted for 10%. The various types of curves reflect the difference in the degree of aquifer fissure development, with a single channel and two or three main channels [41]. The concentration curve obtained by the tracer test indicates that karst development in the Wangzhai and Hougao areas of Zibo are characterized by the coexistence of karst pores, karst fissures, fractures and pipelines. The range of tracer diffusion suggest that the main direction of the Hougao experimental area is northward and eastward, and the mainstream of the Wangzhai experimental area is to the southeast (Figure2). Therefore, the Wangzhai section is a supply area of the Dawu and Liuzheng water sources. Water 2019, 11, 698 6 of 15 Water 2019, 11, 698 6 of 15 formWater 2019the ,observation 11, 698 wells in Wangzhai and Hougao were divided into single peak, double peak6 ofand 15 formtripleWater 2019the peak ,observation 11 , types698 (Table wells 1), in and Wangzhai the three and major Hougao categories were divided were subdivided into single peak,into differentdouble peak specific6 ofand 15 tripleforms.formWater 2019 thepeak The ,observation 11 ,types single-peak698 (Table wells curve1), in and Wangzhai was the dividedthree and major Hougaointo caslightlytegories were dividedsymmetrical were subdivided into singleand asymmetric peak,into differentdouble types; peak specific6 ofandthe 15 forms.Waterdouble-peakformtriple 2019the peak The , observation11 , types698single-peak curve (Table was wells dividedcurve1), in and Wangzhai was theinto dividedthree high-low and major Hougaointo and caslightlytegories low-highwere dividedsymmetrical were types; subdivided into and singleand the asymmetric peak,three-peakinto differentdouble curvetypes; peak specific6 ofwasandthe 15 double-peakdividedtripleforms.form thepeak The into observation types single-peakhigh-low-lowcurve (Table was wells dividedcurve1), inand and Wangzhai low-high-lowwas theinto dividedthree high-low and major Hougao intotypes. and caslightly tegories low-highwere dividedsymmetrical were types; subdivided into and single and the asymmetric peak,three-peakinto differentdouble curvetypes; peak specific wasandthe form the observation wells in Wangzhai and Hougao were divided into single peak, double peak and dividedforms.double-peaktriple peak The into types single-peak high-low-lowcurve (Table was dividedcurve1), and and low-high-lowwas theinto dividedthree high-low major intotypes. and caslightly tegories low-high symmetrical were types; subdivided and and the asymmetric three-peakinto different curvetypes; specific wasthe tripledouble-peakdividedforms. peak The into typessingle-peak high-low-lowcurve (Table wasTable dividedcurve1), and and1.Tracer low-high-lowwas theinto concentrationdividedthree high-low major intotypes. and curve caslightlytegories low-high type symmetricalof were observation types; subdivided and andwell. the asymmetric three-peakinto different curvetypes; specific wasthe forms.double-peak The single-peak curve wasTable dividedcurve 1.Tracer was into concentrationdivided high-low into and curveslightly low-high type symmetrical of observation types; and and well. the asymmetric three-peak curvetypes; wasthe divided intoPeak high-low-low Type and low-high-low Curve Type types. Observation Well double-peakdivided into high-low-lowcurve wasTable divided and 1.Tracer low-high-low into concentration high-low types. and curve low-high type of observation types; and well. the three-peak curve was Peak Type Curve Type Observation Well Waterdivided2019, 11, 698into high-low-lowTable and 1.Tracer low-high-lowasymmetric concentration type types. curve type of observation well. 6 of 14 Peak Type Curve Type Wangzhai Observation：W43, Well W36 Table 1.Tracerasymmetric concentration type curve type of observation well. Peak Type Table 1.Tracer Curve concentration Type curve type of observationWangzhai Observation well.：W43, Well W36 asymmetric type Hougao：W77 Peak TypeTable 1. Tracer concentration Curve Type curve type of observationWangzhai Observation well. ：W43, Well W36 Peak Type asymmetric Curve Type type Observation： Well Single peak WangzhaiHougao：W43,W77 W36 Peak Typeasymmetric Curve Type type ObservationHougao：W77 Well Single peak slightlyasymmetric symmetrical type type Wangzhai： ：W43, W36 asymmetric type Wangzhai W10,：： W45, W45 Single peak slightly symmetrical type WangzhaiHougao W43,W77 W36 WangzhaiWangzhai:：W10, W43,： W45, W36 W45 Single peak slightly symmetrical type HougaoHougao：W98, W96,W77 W95 Single peak WangzhaiHougaoHougao:：W10,： W77W77 W45, W45 Single peak slightly symmetrical type Hougao：：W98, W96, W95 Single peak Wangzhai W10, W45, W45 slightlyhigh-low symmetrical type type Hougao：：W98, W96, W95 slightlyslightly symmetrical symmetrical typetype WangzhaiWangzhaiW10,： W45,W8 W45 high-low type WangzhaiWangzhai:Hougao：： W10,W98,W10, W45,W96, W45, W45 W95 W45 Wangzhai：W8 high-low type HougaoHougaoHougao:：： W98,W76,W98, W96, W90, W96, W95 W101 W95 HougaoWangzhai：W98,： W96,W8 W95 high-low type ： Double peak high-low type HougaoWangzhaiW76, W90,：W8 W101 high-low type Hougao：W76, W90, W101 Double peak high-lowlow-high type WangzhaiWangzhai:： W8W8 Double peak HougaoHougao:Wangzhai： W76,W76, W90, ：W90,W8 W101 W101 Double peak low-high type Hougao：W75, W529 low-high type Hougao：W76, W90, W101 Double peak HougaoHougao：W76,：W75, W90, W529 W101 low-high type Double peak low-high type Hougao：W75, W529 Double peak low-high type Hougao: W75, W529 high-low-low type Hougao：W75, W529 low-high type Wangzhai：W16 high-low-low type Hougao：W75, W529 high-low-low type HougaoWangzhai：W75,：W16 W529 high-low-low type Hougao：W531 WangzhaiWangzhai:： W16W16 high-low-low type ： TripleTriple peak peak WangzhaiHougaoHougao: W531：W531W16 high-low-low type Hougao：W531 Triple peak high-low-lowlow-high-low type Wangzhai：W16 low-high-low type WangzhaiHougao：：W531W16 Triple peak low-high-low type WangzhaiHougao：：W531W4 low-high-low type Wangzhai: W4 Triple peak HougaoWangzhai：：W531W4 Triple peak low-high-low type Water 2019, 11, 698 Wangzhai：W4 7 of 15 Triple peak low-high-low type Wangzhai：W4 Single peak concentration curveslow-high-low accounted type for the majority of tracer curves (62.5%) from wells Wangzhai：W4 in theSingle Wangzhai peak testconcentration area, followed curves by tripleaccounted peak forcurve the (25%) majority and ofdoubleWangzhai tracer peak curves： curveW4 (62.5%) (12.5%). from Results wells infrom theSingle observation Wangzhai peak testconcentration wells area, in followedthe Hougao curves by tripletestaccounted area peak recorded curvefor the (25%) majoritydouble and peak ofdouble tracer (50%) peak curves and curve single (62.5%) (12.5%). peak from (40%) Results wells as fromthein the dominant Singleobservation Wangzhai peak tracer testconcentration wells concentrationarea, in followedthe Hougao curves curves; by tripletestaccounted areathe peak triple recorded forcurve peak the (25%) majoritydouble curve and typepeak ofdouble tracer accounted (50%) peak curves and curve forsingle (62.5%) 10%. (12.5%). peak The from (40%) variousResults wells as thetypesinfrom the dominantSingle observation Wangzhaiof curves peak tracer reflecttestconcentration wells concentrationarea, inthe followedthe difference Hougao curves curves; by tripletestaccountedin the thearea peak degrtriple recorded curveforee peak thofe (25%) aquifermajoritydouble curve and type peakfissure ofdouble traceraccounted (50%) development, peak curves and curve for single (62.5%) 10%. (12.5%). peakwith The from (40%) a variousResults single wells as Single peak concentration curves accounted for the majority of tracer curves (62.5%) from wells typeschannelfromthein the dominant observation Wangzhaiof andcurves two tracer reflecttest wellsor concentrationarea,three inthe followed themain difference Hougao channels curves; by tripletestin the [41].areathe peak degrtriple recordedThe curveee peakconcentration of (25%) aquiferdouble curve and typepeakfissure double curve accounted (50%) development, obtainedpeak and curve for single by10%. (12.5%). thepeakwith The tracer (40%) a variousResults single test as in the Wangzhai test area, followed by triple peak curve (25%) and double peak curve (12.5%). Results channelindicatesthetypesfrom dominant observationof and curvesthat two karsttracer reflect wellsor development concentrationthree inthe themain difference Hougao channelsin curves; the test inWangzhai the [41].thearea degrtriple recordedThe anee peakconcentrationd of Hougao aquiferdouble curve areas type peakfissure curve ofaccounted (50%) Zibodevelopment, obtained and are for characterizedsingle by10%. the peakwith The tracer (40%) avarious bysingle testthe as from observation wells in the Hougao test area recorded double peak (50%) and single peak (40%) as indicatescoexistencetypeschannelthe dominant of and curvesthat of two karsttracerkarst reflect or developmentpores, concentrationthree the karstmain difference fissures, channelsin curves; the inWangzhai fractures the [41].the degrtriple The andanee peakconcentrationd of pipelines.Hougao aquifer curve areas typeThefissure curve rangeofaccounted Zibodevelopment, obtained of are tracer forcharacterized bydiffusion10%. thewith The tracer asuggestvarious bysingle testthe the dominant tracer concentration curves; the triple peak curve type accounted for 10%. The various coexistencethatchannelindicatestypes the of and maincurvesthat of two karstkarst direction reflect or developmentpores, three the of karstmain differencethe fissures, channelsHougaoin the inWangzhai fractures theexperime[41]. degr The and aneental concentrationd ofpipelines. Hougao areaaquifer is areas Thenorthwardfissure curve range of Zibodevelopment, obtained of and aretracer characterized eastward, bydiffusion thewith tracer andasuggest bysingle testthe types of curves reflect the difference in the degree of aquifer fissure development, with a single thatmainstreamindicatescoexistencechannel the and mainthat of oftwo karstkarst directionthe or development pores, Wangzhaithree of karstmain the fissures, experimental Hougaochannelsin the Wangzhai fractures experime[41]. area The andan ntal isconcentrationd pipelines.Hougaoto area the is southeastareas Thenorthward curve rangeof Zibo obtained(Figure of and aretracer characterized eastward,2). bydiffusion Therefore,the tracer and suggest by testthe channel and two or three main channels [41]. The concentration curve obtained by the tracer test mainstreamWangzhaicoexistencethatindicates the mainthat section of of karstkarst directionthe is developmentpores, aWangzhai supply of karst the area fissures, experimental Hougaoin of the the Wangzhai fracturesDawu experime area and and an ntalLiuzhengisd pipelines. Hougaoto area the iswatersoutheast areas Thenorthward range sources.of Zibo (Figure of and aretracer characterized eastward,2). diffusion Therefore, and suggest by the indicates that karst development in the Wangzhai and Hougao areas of Zibo are characterized by the Wangzhaithatmainstreamcoexistence the main section of of karst directionthe is pores, aWangzhai supply of karst the area fissures, experimentalHougao of the fracturesDawu experime area and and ntalLiuzhengis pipelines.to area the iswatersoutheast Thenorthward sources.range (Figure of and tracer eastward,2). diffusion Therefore, and suggest the coexistencemainstreamWangzhaithat the main section of of karst directionthe is pores, aWangzhai supply of karst the area fissures, experimentalHougao of the fractures Dawu experime area and and ntalLiuzhengis pipelines.to area the iswatersoutheast Thenorthward rangesources. (Figure of andtracer eastward,2). diffusion Therefore, andsuggest the thatWangzhaimainstream the main section of directionthe is aWangzhai supply of the area experimentalHougao of the Dawu experime area and ntal Liuzhengis to area the iswatersoutheast northward sources. (Figure and eastward,2). Therefore, and the mainstreamWangzhai section of the is aWangzhai supply area experimental of the Dawu area and Liuzhengis to the watersoutheast sources. (Figure 2). Therefore, the Wangzhai section is a supply area of the Dawu and Liuzheng water sources.

Figure 2. TheThe range range of of tracer tracer diffusion. diffusion. 1: 1: Observation Observation well; well; 2: 2:Source Source well; well; 3: 3:Water Water level level line/m; line/ m;4: Fault;4: Fault; 5: 5:Tracer Tracer diffusion diffusion zone zone in inWangzha Wangzhai;i; 6: 6:Tracer Tracer diffusion diffusion zone zone in in Hougao. Hougao.

4.1.2. Anisotropy of Dispersion Coefficient Assuming that the instantaneous injection of tracer in the steady flow field forms a two- dimensional dispersion, tracer migration will mainly be affected by mechanical dispersion, ignoring the influence of molecular diffusion [42]. The concentration distribution expression of a point (x, y) on the plane will therefore be:

M(xut)1 − 2 y 2 c =−+−exp λt π ×  (3) 4n ααLTt 4ut ααLT where c (mg/L) is the tracer concentration at (x, y) point; n is the porosity; u (m/day) is the average pore flow velocity of the groundwater, and αL (m) and αT (m) are longitudinal and transverse dispersion, respectively.

According to the test data, it was possible to determine the peak moment of molybdenum ion concentration in the observation well (tm), to organize the measured data with (tm2/t+t) as x and (lnCt+tm/t) as y, and to the identify slope (B) and intercept (lnA) of the fitted line using linear regression. Similarly, the source hole data was collated and a scatter plot with t as x and lnCt as y was drawn. The intercept (lna) of the fitted straight line was obtained. Then, these values were substituted into Formula 4, which can give the vertical and horizontal dispersion [43].

 x2 y 2 − = 4u()Bt 2 + t α α m m  L T  x ln A − ln a =  α (4)  2 L  u B = + λ  α  4 L

Water 2019, 11, 698 7 of 14

4.1.2. Anisotropy of Dispersion Coefficient Assuming that the instantaneous injection of tracer in the steady flow field forms a two-dimensional dispersion, tracer migration will mainly be affected by mechanical dispersion, ignoring the influence of molecular diffusion [42]. The concentration distribution expression of a point (x, y) on the plane will therefore be:     2 2   M  1  (x ut) y   c = exp  − +  λt (3) 4nπ √αL αTt −4ut αL αT  −  × where c (mg/L) is the tracer concentration at (x, y) point; n is the porosity; u (m/day) is the average pore flow velocity of the groundwater, and αL (m) and αT (m) are longitudinal and transverse dispersion, respectively. According to the test data, it was possible to determine the peak moment of molybdenum ion 2 concentration in the observation well (tm), to organize the measured data with (tm /t+t) as x and (lnCt+tm/t) as y, and to the identify slope (B) and intercept (lnA) of the fitted line using linear regression. Similarly, the source hole data was collated and a scatter plot with t as x and lnCt as y was drawn. The intercept (lna) of the fitted straight line was obtained. Then, these values were substituted into Formula 4, which can give the vertical and horizontal dispersion [43].

 2    x2 y 2  = 4u Btm + tm  αL − αT  ln A ln a = x (4)  2αL  −  B = u + λ 4αL where x (m) and y (m) are the transverse distance and longitudinal distance from the observation hole to the source hole, respectively; u (m/day) is the average pore flow velocity of the groundwater; and tm (day) is the time when the tracer concentration reached the peak time. The Equations are solved to obtain the longitudinal and transverse dispersion, which are substituted into the Equations DL = αLv and DT = αTv to obtain the longitudinal and transverse dispersion coefficients (Table2).

Table 2. Calculation results of the dispersion coefficient.

Observation Longitudinal Dispersion Transverse Dispersion Source Well Direction Well Coefficient (m2/day) Coefficient (m2/day) Southeast W36 3.71 0.25 WK01 Southeast W45 6.41 0.83 (Wangzhai) Southwest W43 2.38 0.52 Northeast W8 5.76 0.79 North W31 12.83 0.93 W512 East W101 3.06 0.4 (Hougao) East W75 2.71 0.22 Southeast W95 4.56 0.62

The dispersion coefficient in all directions of the test area is anisotropic, and it has no obvious correlation with the flow rate and tracer concentration. Therefore, the hydrodynamic field in this area is simulated using a three-dimensional flow model.

4.2. Water Level Prediction of the Liuzheng Water Source According to the exploration data of the Liuzheng water source [38], the identification and inspection stage of the model was completed using data spanning June 2017 to September 2018. The permeability coefficient, elastic drainable porosity, specific yield and rainfall infiltration coefficient of each division of the study were also determined. Since the Liuzheng area is considered as a new water supply source, exploitation layout was appropriately adjusted according to previous regional groundwater exploitation volume. Therefore, the amount of exploitation in the northern Water 2019, 11, 698 8 of 14 part of the Dawu area was reduced and the amount of artificial exploitation in the Liuzheng areawas increased. Precipitation data from 2008–2017, including the dry water series, was selected for our study. After debugging the exploitation capacity of the Dawu water and Liuzheng water sources several times, the dynamic change of the groundwater level in the Liuzheng area over the next 10 years was predicted based on an exploitation rate of 150,000 m3/day. Results indicate that when the total volume of the karst water system is kept constant, water extraction in the Liuzheng area is about 150,000 m3/day, and 200,000 m3/day in the Dawu water source. In this case, although the groundwater level of the Liuzheng is reduced in dry years, groundwater is quickly replenished and the water level is able to increase in wet years (Figure3). The groundwater system can maintain a dynamic equilibrium for many years. Figure4 showed the groundwater flow field of the Liuzhengarea during the wet season after adjusting the mining layout. There is no significant change in the regional natural groundwater flow field. The average water level in the mining center droppedfrom about 27m adjusting the mining layout to about 22mafter adjusting the mining layout, that is, the mean water level drop was about 5 m, and no hydrogeological problems willWaterWater appear, 20192019,, 1111 such,, 698698 as karst collapse. 99 ofof 1515

FigureFigureFigure 3. 3.3.PredictionPrediction curve curve ofof waterwater levellevel level changechange change inin in thethe the LK11LK11 LK11 well.well. well.

FigureFigureFigure 4. 4.4.Groundwater GroundwaterGroundwater plane planeplane flow flowflow field. field.1field.1 1:::village;village; village; 2:2: 2: miningmining mining well;well; well; 3:3: 3: grgr groundwateroundwateroundwater levellevel level contourcontour contour (m).(m). (m).

AfterAfter optimizingoptimizing thethe exploitationexploitation layout,layout, explexploitationoitation ofof high-qualityhigh-quality groundwatergroundwater inin thethe LiuzhengLiuzheng areaarea increased,increased, andand thethe sourcesource ofof infeinferiorrior groundwatergroundwater inin thethe northnorth ofof thethe DawuDawu waterwater sourcesource waswas intercepted,intercepted, therebythereby greatlygreatly improvingimproving thethe utilizationutilization efficiencyefficiency ofof groundwater.groundwater. TheseThese resultsresults indicateindicate thatthat thethe exploitationexploitation ofof 150,000150,000 mm33/day/day ofof waterwater fromfrom thethe LiuzhengLiuzheng waterwater sourcesource isis feasiblefeasible forfor domesticdomestic use.use.

4.3.4.3. PollutionPollution PredictionPrediction BasedBased onon thethe groundwatergroundwater flowflow simulationsimulation whenwhen ththee amountamount ofof groundwategroundwaterr exploitationexploitation inin thethe LiuzhengLiuzheng waterwater sourcesource isis 150,000150,000 mm33/day,/day, thethe regionalregional pollutantpollutant transporttransport afterafter 10,10, 3030 andand 5050 yearsyears ofof continuouscontinuous wastewaterwastewater dischargedischarge (Figure(Figure 5),5), andand thethe concentrationconcentration curvecurve ofof ClCl−− inin thethe miningmining wellwell locationlocation ofof LiuzhengLiuzheng waterwater sourcesource (Figure(Figure 6)6) werewere modeled.modeled.

Water 2019, 11, 698 9 of 14

After optimizing the exploitation layout, exploitation of high-quality groundwater in the Liuzheng area increased, and the source of inferior groundwater in the north of the Dawu water source was intercepted, thereby greatly improving the utilization efficiency of groundwater. These results indicate that the exploitation of 150,000 m3/day of water from the Liuzheng water source is feasible for domestic use.

4.3. Pollution Prediction Based on the groundwater flow simulation when the amount of groundwater exploitation in the Liuzheng water source is 150,000 m3/day, the regional pollutant transport after 10, 30 and 50 years of

Watercontinuous 2019, 11, wastewater698 discharge (Figure5), and the concentration curve of Cl − in the mining10 wellof 15 location of Liuzheng water source (Figure6) were modeled. Water 2019, 11, 698 10 of 15

(a) (b) (c) (a) (b) (c)

Figure 5. Plane range of solute migration. ( a)) 10 years, ( b) 30 years, (c) 5050 years;years; 1:1: Concentration of Figure− 5. Plane range of solute migration. (a) 10 years, (b) 30 years, (c) 50 years; 1: Concentration of Cl− (mg/L);(mg/L); 2: 2: Village; Village; 3: 3: Liuzheng Liuzheng water water source source mining mining well; well; 4: 4: Fault; Fault; 5: 5: River. River. Cl− (mg/L); 2: Village; 3: Liuzheng water source mining well; 4: Fault; 5: River.

− − FigureFigure 6.6.TheThe concentration concentration curve curve of of Cl Cl . −. .

ForecastsForecasts indicate that that thethe solute solute will will mainly mainly mi migratemigrategrate in in a asoutheast southeastsoutheast direction, direction,direction, before before gradually gradually movingmoving to to thethe northnorth inin thethe mainmainmain direction.direction. AfteAfte Afterr r continuouscontinuous discharge discharge discharge for for for 21 2121 years, years, LK02 LK02 in in the the LiuzhengLiuzheng area area will be the first first wellwell toto bebe affected. affected. affected. Wi Wi Withthth an an increase increase in in time, time, solutes solutes will will then then gradually gradually affectaaffectffect groundwatergroundwater in in some some areas areas northnorth north of of of the the the Liuzheng Liuzheng Liuzheng water water water source. source. source.

4.4.4.4. DeterminationDetermination of Water Source ProtectionProtection Areas Areas

4.4.1.4.4.1. EmpiricalEmpirical Formula Method TheThe scopescope of the protection areaarea ofof thethe LiuzhengLiuzheng water water source source is is calcul calculatedated using using the the empirical empirical formulaformula providedprovided by the Technical guidelineguideline for for delineating delineating source source water water protection protection areas areas[44]:[44]:

R =α× K ×J ×T/n (5) R =α× K ×J ×T/n (5) where R (m) is the radius of the protection zone, αis the safety factor, it is generally 150%; K (m/day) is where R (m) is the radius of the protection zone, αis the safety factor, it is generally 150%; K (m/day) is the aquifer permeability coefficient; J is the hydraulic gradient; T (day) is the horizontal migration time the aquifer permeability coefficient; J is the hydraulic gradient; T (day) is the horizontal migration time of the pollutant; and n is effective porosity. According to the literature [44],when T takes 100, R is the of the pollutant; and n is effective porosity. According to the literature [44],when T takes 100, R is the

Water 2019, 11, 698 10 of 14

4.4. Determination of Water Source Protection Areas

4.4.1. Empirical Formula Method The scope of the protection area of the Liuzheng water source is calculated using the empirical formula provided by the Technical guideline for delineating source water protection areas [44]:

R = α K J T/n (5) × × × where R (m) is the radius of the protection zone, α is the safety factor, it is generally 150%; K (m/day) is theWater aquifer 2019, 11 permeability, 698 coefficient; J is the hydraulic gradient; T (day) is the horizontal migration11 of 15 time of the pollutant; and n is effective porosity. According to the literature [44],when T takes 100, Rradiusis the of radius the primary of the primary protection protection area, and area, when andT takes when 1000,T takes R is 1000,the radiusR is the of the radius secondary of the secondaryprotection protectionarea. area. AccordingAccording to to the the identification identification and verificationand verifica of groundwatertion of groundwater flow simulation; flow thesimulation; permeability the coepermeabilityfficient of thecoefficient aquifer of in the the aquifer Liuzheng in the area Liuzhe is aboutng area 250 mis/ aboutday. The 250 averagem/day. The hydraulic average gradient hydraulic in thegradient Liuzheng in the area Liuzheng is about area 0.00035, is about the safety0.00035, factor the safety is 150%, factor and is the 150%, effective and the porosity effective is 0.15. porosity Using is this0.15. information, Using this information, results from results Equation from (5) Equation show the (5) radius show of the the radius primary of protectionthe primary zone protection to be 87.5 zone m, andto be the 87.5 radius m, and of thethe secondaryradius of the protection secondary zone protection to be 875 zone m. to be 875 m.

4.4.2. Numerical Simulation Method 4.4.2. Numerical Simulation Method Using the MODPATH module for backtracking, 10 tracer particles were set for each production Using the MODPATH module for backtracking, 10 tracer particles were set for each production well to predict the capture range of tracer particles passing through 100 and 1000 days (Figure7). well to predict the capture range of tracer particles passing through 100 and 1000 days (Figure 7). The The maximum migration distance of the tracer particles for 100 day is about 90 m (Figure7a), and the maximum migration distance of the tracer particles for 100 day is about 90 m (Figure 7a), and the maximum migration distance of 1000 day outside the fault is about 760 m (Figure7b). maximum migration distance of 1000 day outside the fault is about 760 m (Figure 7b).

(a) (b)

Figure 7. Tracing trajectory of tracer particles. (a) 100 day, (b) 1000 day; 1: Village; 2: Fault; 3: River; Figure 7. Tracing trajectory of tracer particles. (a) 100 day, (b) 1000 day; 1: Village; 2: Fault; 3: River; 4: 4: Migration trajectory. Migration trajectory. 4.4.3. Comparative Analysis 4.4.3. Comparative Analysis For the division of the primary protection zone, the maximum migration distance obtained by theFor numerical the division simulation of the primary method protection is slightly zone larger, the than maximum the radius migration calculated distance by the obtained empirical by formulathe numerical method. simulation For the division method ofis slightly the secondary larger than protection the radius zone, calculated the maximum by the migration empirical distance formula calculatedmethod. For by the numericaldivision of simulation the secondary method prot isection slightly zone, smaller the thanmaximum the radius migration calculated distance by thecalculated empirical by formulathe numerical method. simulation The distance method of theis slightly secondary smaller protection than the zone radius calculated calculated using by thethe empirical formula method. The distance of the secondary protection zone calculated using the numerical simulation method is slightly smaller than the radius of the protection zone calculated using the empirical formula method. This finding is due to the calculation of the empirical formula method, where hydraulic gradient takes the average hydraulic gradient in the Liuzheng area. In the numerical simulation method, the hydraulic gradient near the mining location is greater than the hydraulic gradient away from the mining well location. The numerical method not only simulates the actual situation of the groundwater flow field, it also shows the anisotropy of karst development in the partition of permeability coefficient, water storage coefficient and dispersion. For example, when the permeability coefficient near the fault zone is large, the radius of the protection zone is therefore also slightly large. Our results indicate that the numerical method is relatively accurate recording the area of the primary protection area of the Liuzheng water source to be about 0.59 km2, and the area of the secondary protection area to be about 14.98 km2 (Figure 8).

Water 2019, 11, 698 11 of 14 numerical simulation method is slightly smaller than the radius of the protection zone calculated using the empirical formula method. This finding is due to the calculation of the empirical formula method, where hydraulic gradient takes the average hydraulic gradient in the Liuzheng area. In the numerical simulation method, the hydraulic gradient near the mining location is greater than the hydraulic gradient away from the mining well location. The numerical method not only simulates the actual situation of the groundwater flow field, it also shows the anisotropy of karst development in the partition of permeability coefficient, water storage coefficient and dispersion. For example, when the permeability coefficient near the fault zone is large, the radius of the protection zone is therefore also slightly large. Our results indicate that the numerical method is relatively accurate recording the area of the primary protection area of the Liuzheng water source to be about 0.59 km2, and the area of the Watersecondary 2019, 11, protection 698 area to be about 14.98 km2 (Figure8). 12 of 15

Figure 8. The scope of the protected area of the Liuzheng water source. 1: Mining wells; 2: Villages; Figure 8.The scope of the protected area of theLiuzheng water source.1:Mining wells; 2:Villages; 3: 3: Faults; 4: Group well outsourcing line; 5: Primary protection area (experience formula method); Faults; 4:Group well outsourcing line; 5:Primary protection area (experience formula method); 6: Secondary protection area (experience formula method); 7: Primary protection area (numerical 6:Secondary protection area (experience formula method); 7:Primary protection area (numerical simulation method); 8: Secondary protection area (numerical simulation method). simulation method); 8. Secondary protection area (numerical simulation method). 5. Conclusions 5. Conclusions 1. The tracer test results show that karst development in the Wangzhai and Hougao areas of Zibo 1. Theare tracer characterized test results by show the coexistence that karst developmen of karst pores,t in the karst Wangzhai fissures, and fractures Hougao and areas pipelines, of Zibo andare characterizedthat the degree by the of developmentcoexistence of iskarst uneven. pores, Thekarst runo fissures,ff channel fractures and and the pipelines, dispersion and coe thatfficient the degreeare anisotropic, of development and the is uneven. overall The dispersion runoff channel coefficient and isthe less dispersion than 15 coefficient m2/day. In are addition, anisotropic, the andtracer the concentrationoverall dispersion curve co canefficient be divided is less intothan three15 m2 types:/day. In Single addition, peak, the double tracer peak concentration and triple curvepeak. can The be Wangzhai divided into experimental three types: area Single is one pe ofak, the double recharge peak areas and triple of the peak. Dawu The and Wangzhai Liuzheng experimentalwater sources. area is one of the recharge areas of the Dawu and Liuzheng water sources. 2. Using the numerical simulation optimization calculation, when extraction of the Liuzheng water 2. Using the numerical simulation optimization calculation, when extraction of the Liuzheng water source reaches 150,000 m3/day, it will not only change the regional groundwater flow field in source reaches 150,000 m3/day, it will not only change the regional groundwater flow field in the the Dawu karst water system, it will also make full use of groundwater resources. The solute Dawu karst water system, it will also make full use of groundwater resources. The solute transport transport model predicts that the proposed Wangzhai Chemical Industrial Park will have a certain model predicts that the proposed Wangzhai Chemical Industrial Park will have a certain potential potential pollution impact on the northern part of the Liuzheng water source area. pollution impact on the northern part of the Liuzheng water source area. 3. The empirical formula method and the numerical method can be used to divide the protected area 3. Theof theempirical Liuzheng formula water method source, and and the to comparenumerical and method analyze can results be used of to the divide protection the protected area division area of the Liuzheng water source, and to compare and analyze results of the protection area division of the two methods. Our results indicated that the numerical simulation method is suitable for use in this area. The area of the primary protection area is recorded as being 0.59 km2, and the area of the secondary protection area is 14.98 km2. Corresponding anti-pollution protection measures should therefore be implemented for all levels of the protected areas in accordance with relevant national regulations.

Author Contributions: Conceptualization, H.Z.; Investigation, X.L. and N.B.; Methodology, Y.D. and L.X.; Resources, L.Y. and Z.L.; Writing—original draft, H.Z. and Y.D.; Writing—review & editing, L.X.

Funding: This article is supported by the National Natural Science Foundation of China (41772257) and the Doctoral Fund of Jinan University (XBS1817).

Water 2019, 11, 698 12 of 14

of the two methods. Our results indicated that the numerical simulation method is suitable for use in this area. The area of the primary protection area is recorded as being 0.59 km2, and the area of the secondary protection area is 14.98 km2. Corresponding anti-pollution protection measures should therefore be implemented for all levels of the protected areas in accordance with relevant national regulations.

Author Contributions: Conceptualization, H.Z.; Investigation, X.L. and N.B.; Methodology, Y.D. and L.X.; Resources, L.Y. and Z.L.; Writing—original draft, H.Z. and Y.D.; Writing—review & editing, L.X. Funding: This article is supported by the National Natural Science Foundation of China (41772257) and the Doctoral Fund of Jinan University (XBS1817). Acknowledgments: We acknowledge Guangyao Chi and Xinyu Hou of University of Jinan for their extensive input of ideas on this research. This project would not have been possible without the cooperation of the Shandong Institute of Geological Survey. Conflicts of Interest: The authors declare no conflict of interest. The founding sponsors had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, and in the decision to publish the results.

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