Assignment 6 pages

Evaluation of organic contamination in urban groundwater surrounding a municipal landfill, Zhoukou, China D. M. Han &X. X. Tong &M. G. Jin & Emily Hepburn &C. S. Tong &X. F. Song Received: 9 February 2012 / Accepted: 23 July 2012 / Published online: 8 August 2012 # Springer Science+Business Media B.V. 2012 AbstractThis paper investigates the organic pollution status of shallow aquifer sediments and groundwater around Zhoukou landfill. Chlorinated aliphatic hydro- carbons, monocylic aromatic hydrocarbons, halogenat- ed aromatic hydrocarbons, organochlorine pesticides and other pesticides, and polycyclic aromatic hydrocar- bons (PAHs) have been detected in some water samples.

Among the detected eleven PAHs, phenanthrene, fluo- rine, and fluoranthene are the three dominant in most of the groundwater samples. Analysis of groundwater sam- ples around the landfill revealed concentrations of PAHsranging from not detected to 2.19μg/L. The results show that sediments below the waste dump were low in pollution, and the shallow aquifer, at a depth of 18– 30 m, was heavily contaminated, particularly during the wet season. An oval-shaped pollution halo has formed, spanning 3 km from west to east and 2 km from south to north, and mainly occurs in groundwater depths of 2– 4 m. For PAH source identification, both diagnostic ratios of selected PAHs and principal component analy- sis were studied, suggesting mixed sources of pyro- and petrogenic derived PAHs in the Zhoukou landfill.

Groundwater table fluctuations play an important role in the distribution of organic pollutants within the shal- low aquifer. A conceptual model of leachate migration in the Quaternary aquifers surrounding the Zhoukou landfill has been developed to describe the contamina- tion processes based on the major contaminant (PAHs).

The groundwater zone contaminated by leachate has been identified surrounding the landfill.

KeywordsLandfill.

Organic contamination.

Hydrogeology.

PAHs.

Conceptual model Introduction Groundwater, used mostly for irrigation, drinking water, and municipal water supplies, is essential to the econom- ic viability and livability of many cities in China.

Groundwater contamination caused by human activities is universal, with extensive pollutant sources such as Environ Monit Assess (2013) 185:3413–3444 DOI 10.1007/s10661-012-2801-z D. M. Han :X. F. Song Key Laboratory of Water Cycle & Related Land Surface Processes, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing 100101, China D. M. Han e-mail: [email protected] X. X. Tong (*) School of Water Resources & Environment, China University of Geosciences, Beijing 100083, China e-mail: [email protected] M. G. Jin :C. S. Tong School of Environmental Studies, China University of Geosciences, 430074 Wuhan, China E. Hepburn School of Earth Sciences, The University of Melbourne, Parkville 3010, Australia wastewater, landfill leachate, storage and disclosure of petroleum products, and pesticide and herbicide use.

Unsuitable disposal of organic products can result in unreasonable emissions and harmful byproducts entering the geological environment, causing groundwater con- tamination. The burial of municipal solid waste in land- fills is the most common disposal alternative in most countries. According to the investigation in Henan part of Huaihe River Basin, the total amount of domestic garbage from 17 primary cities is up to 3,640 × 10 3m3, with approximately 80 landfill sites in major towns (Tong2012). Most of early established landfills do not have an engineered liner, leachate collection system, or engineered cover system. Thus, landfill leachate could have the potential to pollute soil and water system directly.

The current policies surrounding landfill management in China are guided by the Standard for Pollution Control on the Landfill Site of Municipal Solid Waste (GB 16889- 2008), which is released by Ministry of Environmental Protection of the People’s Republic of China.

Organic contamination issues resulting from landfill in many urban areas are of particular concern to local authorities and scientists, since agricultural activities are carried out close to near these cities and since ground- water is a major supply of both irrigation and domestic water. Most volatile halogenated compounds, even at low concentrations, are probably carcinogens or muta- gens (Baudoin et al.2002). These have been paid inter- national attention and are strictly controlled by water and air quality standards. Substantial research on the environment, such as polycyclic aromatic hydrocarbons (PAHs), organochlorine pesticides (OCPs), and tetra- chloroethylene (Nielsen et al.1995; Persson et al.

2006; Eggen et al.2010), has theoretical significance and applicability to field based studies of landfills such as those located throughout the numerous small urban centers in China (Zhou and Maskaoui2003). Due to PAHs ubiquitous occurrence, recalcitrance, bioaccumu- lation potential, and carcinogenic activity, the PAHs have gathered significant environmental concern.

PAHs have a detrimental effect on the flora and fauna of affected habitats, resulting in the uptake and accumu- lation of toxic chemicals in food chains, which cause serious health problems and/or genetic defects in humans. The major potential environmental impacts related to landfill leachate are pollution of groundwater and surface water. The leaking of strongly reduced landfill leachate, high in organic matter, into a shallow, presumably aerobic aquifer creates a very complicatedenvironment owing to redox processes, biodegradation, dissolution/precipitation, complexation, ion exchange, and sorption processes (Christensen1992).

This research focuses on one municipal landfill in Zhoukou city, which is located at the Huaihe River Basin (Fig.1). The results of an investigation into seven big rivers in China in 1993 showed that the main pollu- tion type in Huaihe River was organic contamination (Cui and Fu1998). Huaihe River has the highest popu- lation density of these rivers and, with rapid develop- ment of economic society, gradually increasing water demands will conflict with water shortages in many cities, including Zhoukou city. Groundwater is the main source of water supply for industrial, agricultural, and, locally, domestic water in Zhoukou city, and it is facing groundwater quality problem. There is a major concern that urban pollution can affect the production wells in this and other similar settings in Northern China. It is therefore both necessary and urgent to develop reason- able groundwater utilization practices and effective pro- tection of the resource. If no successful measures are taken for reducing the leakage and transport of pollu- tants in urban soils and groundwater, the accumulation of contaminants can not only degrade soil quality but also pose a health risk to humans and the ecosystem.

This study investigated the hydrogeological conditions and the status of organic pollution in groundwater and soil in a typical landfill around Zhoukou city. The objectives of this study were therefore (1) to investigate the extent of chlorinated aliphatic hydrocarbons (CAHs), monocylic aromatic hydrocarbons (MAHs), halogenated aromatic hydrocarbons (HAHs), OCPs and other pesticides, and polycyclic aromatic hydrocar- bons (PAHs) in aquifer sediments and surface and groundwater around Zhoukou landfill, and (2) to deter- mine the potential sources and pathways of PAHs as the main contaminant in polluted groundwater. Finally, some suggestions are put forward for the reasonable development of water resources and better protection of the eco-geological environment. These can provide a basic framework and scientific foundation for protecting and managing groundwater resources.

Study area description Landfill background The landfill is located in the north of Zhoukou city in Henan province, China. The study area lies between 3414Environ Monit Assess (2013) 185:3413–3444 longitudes 114°36.7′and 114°40.8′E and latitudes 33° 37.1′and 33°39.8′N, and has an area of 18 km 2.Itis an alluvial depositional plain, bordered by LuDong Trunk Canal to the north, Ying River to the south, Jialu River to the west and the Low-lying Gully to the east (Fig.1). Elevation ranges between 45 and 51 m a.s.l. with land surface gradient ranging from 1/3,000 to 1/6,000. The area has a continental monsoonal climate, with an annual mean air temperature of 14.6 °C, a mean rainfall of 790.8 mm (averaged be- tween 1951 and 2004) and a mean potential evapora- tion of 1,736 mm. As much as 54 % of yearly precipitation is concentrated in July, August, and September. The main rivers flowing through the study area include Ying River and Jialu River, which are both perennial rivers and belong to the Huaihe River network. The Ying River and Jialu River arecharacterized by small bed slope and big changes of water table and flux. During flood season, surface water recharges local groundwater. After the conflu- ence of Ying River and Jialu River, the stream flows towards the southeast and into Huaihe River. Ying River and Jialu River converge at the south of Zhoukou city and flow towards the southeast. Only during the devastating floods, the river water recharges groundwater, and river receives groundwa- ter discharge in most cases.

Landfilling operations at the Zhoukou site spanned a period of 13 years, from 1998 to 2010. The landfill site was the borrow pits of the Beijiao brickworks before 1998. The activities for excavating soil at the former brickworks have resulted in the formation of pits and trenches with different sizes and depths. In 1998, the brickworks were closed and began piling up Fig. 1Map of the sampling sites around the Zhoukou landfill, China.1residential area,2landfill,3farmland,4orchard,5 waters,6groundwater monitoring wells (sampling wells with labels in Table1),7surface water sampling sites,8shallowgroundwater table contours (m.a.s.l),9major groundwater-flow direction,10flow direction of surface water,11sewage ditch,12 local factory. Thedashed linedelineates the pollution range.

Groundwater contours from December 2009 Environ Monit Assess (2013) 185:3413–34443415 household and construction waste, ceasing in 2010.

The length of the landfill site measures 200 m from southtonorthand90mfromeasttowestandis currently surrounded by the city planning area. The depth of the solid waste disposal ranges from 6 to 9 m.

The waste generated by city life has been stacked in the landfill since 1998, and the landfill was closed in 2010. The accumulative amount of municipal solid waste, mainly composed of household waste, is now up to approximately 140 × 10 3m3, including garbage, trash, and septic tank waste, derived from houses, apartments, hotels, campgrounds, and picnic grounds (Tong2012). The construction of this landfill has no design features intended to prevent movement of leachate into the ground water. The landfill does not have an engineered liner, leachate collection system, or engineered cover system. There is a wastewater discharge canal to the east of the landfill. The landfill leachate and wastewater discharge have resulted in serious contamination to the ambient groundwater and surface water. This landfill with a life of over 10 years was managed by the Zhoukou City Environmental Sanitation Management Office.Hydrogeological setting The hydrogeological conditions play an important role in controlling the distribution of groundwater organic contamination. Zhoukou city is located in the southern part of the Yellow River alluvial–diluvial fan. The vadose zone is characterized by coarse grains.

Generally, there are two aquifers within 55 m depth around the Zhoukou landfill. Figure2shows the char- acterization of the hydrogeology based on drilling around the landfill. The shallow aquifer at the depth of 11–25 m, mainly consists of fine sand and silty sand, is the major aquifer exploited for local irrigation.

The thickness of the aquitard on top of the first aquifer is approximately 11 m. The deep aquifer consists of interbedded fine sand and silty sand is distributed at the depth of 45–52 m, with a hydraulic conductivity of 12–16 m/day (Qu2010). One weak permeable layer composed of silt and silty clay with 20 m thickness is distributed between the two aquifers. Aquifer sand thickness becomes slightly thinner towards the Ying River. From pumping testing at the field site (Tong 2012), the hydraulic conductivity was determined to Fig. 2Simplified hydrogeological sections of the Zhoukou landfill. ZKE, ZKW, ZKN, and ZKS are the groundwater mon- itoring wells. ZKC is located at the center of the landfill. ZKS′islocated at some 150 m south of the landfill. The hydraulic parameters of the aquifers are obtained from the results of the pumping test (Tong2012) 3416Environ Monit Assess (2013) 185:3413–3444 be in the range 1.2–63.4 m/day. The main recharge sources of the shallow aquifer include vertical precip- itation infiltration, lateral recharge by rivers and canals, and irrigation return flows. The groundwater discharge also includes human exploitation and drain- age to rivers. Local groundwater flow under natural conditions is towards the southeast with a gradient of 1/3,000 to 1/5,000.

One control bore (17 m depth) has been drilled in the center of the landfill. The garbage layer, composed of domestic waste material, is located between 0 and 9.3 m. The strata intersected by the drilled bore can be seen in Fig.2. According to drilling data, the depth of waste dump at the center of the landfill reached 9.3 m.

There is a silty clay layer of 2–3 m thickness below the depth of 9.4–13.8 m, which has a certain protective function for the shallow aquifer. However, the silt and fine sand below the silty clay layer is less protective (more permeable). In the east, west, south, and north of the landfill, four bores, namely, ZKE, ZKW, ZKS, and ZKN, respectively, have been drilled at a depth of 27 m in order to monitor the groundwater table and sample for organic pollutants. The mean groundwater table depth around the landfill was 3.6 m in May 2009 and 3.9 m in December 2009.Some criss-crossing ditches and scattered ponds were constructed due to the irrigation and drainage needs of the region. These ditches, channels, pits, and ponds can store precipitation and surface water during the rainy season and become receivers of wastewater emission in the dry season; this is one of the sources of potential pollution of shallow groundwater. The N–S drainage ditch passes through the eastern landfill and probably provides local recharge to groundwater. Artificial exploitation makes the surrounding water level slightly lower than that in the position of nonexploitation areas. A water-table mound exists beneath the landfill in response to the rainfall infiltration, and this has diffused into the surroundings.

Different types of pollution, such as waste from the local winery, food factory, pesticide factory, gas station, municipal landfill, and garbage pollution treatment plant (locations in Fig.1), may be potential pollution sources to the shallow aquifer. Pollution sources may also in- clude sewage, municipal wastewater, and agricultural fertilizers. Previous investigation (Tong2012) shows that groundwater pollution away from urban areas and villages are relatively mild in this area; hence, the major source of groundwater pollution is likely to be the municipal landfill and possibly sewage ditches, which receive wastewater discharge.

Fig. 3Sediment distribution in the core profile located at the center of the landfill, and the main organic pollutants’concentrations in the sediment samples. The water depth is about 3.5 m Environ Monit Assess (2013) 185:3413–34443417 Material and methods Sample collection Field investigations were carried out around the land- fill site in the north of Zhoukou city.

Sediment sampling in the shallow aquifer Seven sediment samples from different depths were collected by drilling the control bore in May 2009.

The bore was located at the center of the landfill, where depth to water was 3.5 m. Sediment sample depths were 9.3, 9.3–9.5, 9.7–9.9, 10.1–10.3, 10.5– 10.7, 10.9–11.1, and 11.3–11.5 m (Fig.3). Within 3 min, 5 g of sediment was collected in an amber bottle (40 mL), with 5 mL NaHSO 4(20 %) and sub- jected to one magnetic stirring, which was ultrasoni- cally cleaned by methanol in advance. The collected samples were sealed tightly, placed upside down slow- ly and stored at 0–4 °C in the freezer. Sample analysisbegan as soon as possible after returning to the labo- ratory. The measured results are shown in Table1.

Water sampling During three main sampling campaigns in December 2008, May 2009, and December 2009, 40 wells and 10 surface water sites were investigated for organic mat- ter analysis (Table2).The locations of the sampling stations are shown in Fig.1. The wells, including production and observation wells, were purged before sampling, and groundwater was sampled by pumping after constant values of conductivity and redox poten- tial had been established. Most selected sampling points for groundwater were situated near the landfill.

Seven sampling sites were selected for surface water (sampling depth 0.5 m below surface) (Fig.1). A fresh sample tube was used for each piezometer to prevent cross contamination. All samples were filtered through GF/Fs (Whatman, Brentford, UK) to separate the par- ticulate from the dissolved fraction. The samples were Table 1Concentrations of organic compounds in the sediment samples in the Zhoukou landfill Compound name Sampling depth (m) 9.3 9.3–9.5 9.7–9.9 10.1–10.3 10.5–10.7 10.9–11.1 11.3–11.5 Phenol-D5 1.54 1.59 1.30 1.83 1.80 0.71 1.37 Phenol,2-fluoro 1.53 1.62 1.34 1.74 1.73 0.66 1.42 Phenol 0.06–––0.05–– Phenol,3-methyl 0.00–––––– Nitrobenzene-D5 1.36 1.48 1.11 1.78 1.93 0.69 1.26 Naphthalene a 0.06––0.03 0.04–0.04 Naphthalene,1-methyl a 0.06–––––– 1,1-Biphenyl ss 1.41 1.42 1.16 1.51 1.69 0.69 1.27 Dibenzofuran a 0.04 0.03––0.03–– Fluorene a 0.04–––––– Phenanthrene a 0.11–––––– Anthacene a 0.14–––––– Dibutyl phthalate 0.00–––0.16–– p-Terphenyl-d14 2.05 1.82 1.57 1.85 2.44 0.87 1.23 1,2-Benzenedi acid ,disooctyl ester 1.42–––––– Benzo(b)fluoranthene a 0.54–––––– ∑All compounds 10.35 7.97 6.48 8.75 9.87 3.77 6.58 ∑PAHs 0.99 0.03 0.00 0.03 0.07 0.11 0.04 Units are in nanograms per milligram (–)“not detected” aPAHs 3418Environ Monit Assess (2013) 185:3413–3444 Table 2Physico-chemical values of water samples around the landfill Location siteSampling timeWell depth (m)Water depth (m)UtilizationT(°C) pH Turbidity EC (μS/cm)Eh (mV) DO (mg/L) ZA December 2008 30 3.4 Agricultural irrigation 16.6 7.7 0.4 964 256 6.38 ZB December 2008 50 3.5 Domestic water 14.6 7.7 0.9 1,086 195 5.46 ZC December 2008 SU Sewage water 19.6 7.7 90.1 1,602−208 4.03 ZD December 2008 SU water from pond 13.9 8.1 82.5 638 138 3.06 ZE December 2008 SU Waste leachate 11.1 7.9 79.2 3,255−184 5.76 ZF December 2008 18 3.3 Agricultural irrigation 16.8 7.3 0.5 3,365 328 1.54 ZG December 2008 20 3.3 Domestic water 17.3 7.3 0.7 2,235 283 4.97 Z6A December 2008 16 3.0 Domestic water 17 7.1 0.3 1,734 149 5.59 Z6 December 2008 20 2.6 Domestic water 17 7.3 0.2 1,770 160 8.67 SW29 December 2008 9 4.0 Domestic water 16.3 7.5 0.1 1,255 60 6.1 SW49 December 2008 14 5.0 Domestic water 18.3 7.0 1.9 1,231 137 0.48 SW59 December 2008 6 3.0 Domestic water 17.5 7.5 1.6 1,325−5 0.54 ZK1 December 2008 300 Urban water supply 22 8.5 0.1 893 72 2.41 ZKE May 2009 27 3.4 Observation well ZKW May 2009 27 3.6 Observation well 18.3 8.9 3.5 396 98 1.07 ZKS May 2009 27 3.5 Observation well 18.4 7.5 10.3 961 3 1.98 ZKN May 2009 27 4.0 Observation well 19.3 6.9 17.2 3,644 115 1.92 ZF May 2009 18 4.1 Agricultural irrigation 17.6 7.6 0.9 1,316 151 2.55 ZG7 May 2009 9 Observation well ZG9 May 2009 9 Observation well ZG10 May 2009 9 2.0 Observation well 18.9 7.5 9.6 1,076 73 2.29 ZG11 May 2009 9 3.7 Observation well 18.7 6.8 4.6 3,430 25 2.29 ZG12 May 2009 9 Observation well Z16 May 2009 30 4.3 Agricultural irrigation Z34 May 2009 28 3.9 Agricultural irrigation 17.6 7.6 4.3 1,809 194 2.35 Z40 May 2009 30 4.1 Agricultural irrigation 17.2 7.6 4.1 1,162 189 1.98 DW09 May 2009 16 3.9 Domestic water 18.9 7.4 4.8 1369 153 1.85 DW18 May 2009 30 4.1 Domestic water 21.5 8.0 1.8 2,930 106 2.05 DW23 May 2009 18 4.1 Domestic water 18.4 7.5 3.2 1,671 198 2.06 DW25 May 2009 30 3.9 Domestic water 20.5 7.5 6.2 1,332 171 2.13 ZC May 2009 SU Sewage water ZD May 2009 SU Water from pond SUJL May 2009 SU River water 22.7 7.8 SULG May 2009 SU Sewage water 22.4 7.9 SUY May 2009 SU River water 18.9 7.9 SULD May 2009 SU Agricultural irrigation 20.5 7.8 ZKE December 2009 27 4.0 Observation well 17.8 7.3 1,676−91.3 ZKW December 2009 27 3.6 Observation well 16.6 7.2 1,652 ZKS December 2009 27 4.1 Observation well 17.5 7.4 1,353−87.2 ZKN December 2009 18 3.9 Observation well 18.4 6.6 3,999 ZF December 2009 18 4.2 Agricultural irrigation 16.1 7.4 1,502 ZG9 December 2009 9 3.7 Observation well 18.5 7.4 1,219 Z06 December 2009 15 2.8 Agricultural irrigation 16.8 7.3 1,378 Z16 December 2009 30 3.2 Agricultural irrigation 17.4 7.7 787 Environ Monit Assess (2013) 185:3413–34443419 taken using precleaned, brown glass bottles, trans- ported under anaerobic conditions in refrigerated box- es to the laboratory, and stored in the dark under water at 4 °C until the time of analysis. Water chemistry characteristics of the samples are given in Table2, including temperature (°C), pH, turbidity, specific electrical conductivity (EC), redox potential (Eh), and dissolved oxygen (DO). These parameters and water table depth were measured in the field.

In each instance, duplicate water samples for volatile organic compound (VOC) measurement were collected and placed in precleaned 40 mL amber glass bottles with Teflon-lined rubber septa. Samples for semivolatile or- ganic compound (SVOC) and OCP measurement were collected in 1-L amber glass bottles. The bottles were carefully filled to overflowing, without passing air bub- bles through the sample or trapping air in the sealed bottles. Preparation of bottles included washing with detergent, rinsing with tap water, ultrapure water (Millipore: Milli-Ro 5 plus and Milli Q plus 185), and acetone (Mallinckrodt Chemical Works St. Louis), and placing in an oven at 150 °C for 2 h. At each site, HCL (4 drops 6 N/40 mL) was added to the water sample in order to bring the solution’s pH down to 2 and prevent bio- degradation and dehydrohalogenation (APHA1992).

Analytical procedure The analysis of organic pollutants in the sediment samples was performed at the National Research Center for Geoanalysis. PAHs (US EPA Method 8310) were tested by high performance liquid chro- matography–mass spectrometry (HPLC-MS), OCPs (US EPA Method 8081A) were measured by gas chro- matography with electron capture detector (ECD), and VOCs (US EPA Method 8260B) were analyzed bypurge and trap extraction systems followed by gas chromatography/mass spectrometry (P&T-GC-MS).

Only SVOCs could be detected in the sediment sam- ples and were quantified by HPLC equipped with a variable wavelength fluorescence detector and a Supelcosil LC-PAH (250 × 4.6 mm i.d., 5μm particle size, Supelco) column. The injection volume was 5.0μL, and the column temperature was 30 °C. The gradient elution program consisted of 65 % water and 35 % acetonitrile for 2 min, then 100 % acetonitrile for 12 min at a flow rate of 2.0 mL/min.

All organic pollutants in the water samples, includ- ing VOCs, SVOCs, and OCPs, were analyzed in the Ministry of Land and Resources P.R.C. Huadong Mineral Resources Supervision and Testing Center (Research Center of Nanjing Institute of Geology and Mineral Resources).

VOCs in water samples were analyzed by P&T-GC/ MS, derived from US EPA method 524.2 (Eichelberg and Bundle1989). The Tekmar 3000 Purge and Trap autosampler device, operated with Helium as a carrier (gas flux, 50 mL/min; purge time, 11 min), was connected to a GC-MS system (HP 6980). A Carbopack C and B (Supelco) trap was used at a desorption temperature of 225 °C and a desorption time of 4 min. An HP 5.5 % phenyl methyl siloxan GC column was used for the separation of the target compounds (film thickness, 0.25μm; interior diame- ter, 0.25 mm; length, 60 m). The mass spectrometer was operated at 315 °C in the selected ion mode. A stock solution of 2,000μg/mL (EPA 524, Supelco) of both fluorobenzene and 1,2-dichlorobenzene-d4 in methanol was diluted to 200μg/mL and used as an internal standard for calibration.

SVOCs (mainly PAHs) in water samples were de- termined by HPLC-MS, derived from US EPA method Table 2(continued) Location siteSampling timeWell depth (m)Water depth (m)UtilizationT(°C) pH Turbidity EC (μS/cm)Eh (mV) DO (mg/L) Z34 December 2009 28 4.0 Agricultural irrigation 15.6 7.2 1,985 Z40 December 2009 30 4.4 Agricultural irrigation 16.5 7.3 1,494 ZB December 2009 50 4.0 Domestic water 10.1 7.6 1,164 50.7 DW09 December 2009 16 3.2 Domestic water 15.8 7.0 1,726 DW25 December 2009 30 4.0 Domestic water 7.6 7.6 1,412 SUJL December 2009 SU River water 6.9 7.9 1,085 SUsurface water,ECspecific electrical conductivity,Ehredox potential,DOdissolved oxygen 3420Environ Monit Assess (2013) 185:3413–3444 610. PAHs in the water samples were analyzed using an HPLC (Waters 5890) with UV detector and a Waters 3.9 × 300 mmμBondapak C18 reverse phase column. The HPLC was operated under the following conditions: a flow rate of 1.8 mL/min, an injection volume of 15μL, a wavelength of 254 nm, and a mobile phase of acetonitrile to water of 80:20, and with isocratic flow conditions. The concentrations of 11 PAHs were quantified in this study. According to their elution orders, they were acenaphthene (Acp), fluorene (Flu), phenanthrene (Phe), anthracene (Ant), fluoranthene (FLT), pyrene (Pyr), benzo(a)anthracene (BaA), chrysene (CHR), benzo(b)fluoranthene (BbF), and benzo(k)fluoranthene (BkF).The detection limits for these congeners are 0.2, 0.01, 0.005, 0.01, 0.01, 0.005, 0.002, 0.001, 0.001, 0.002, and 0.001μg/L, respectively.

OCPs and other pesticides in water samples were detected by GC using a Hewlett Packard Gas Chromatograph 5890 Series II, supported by a 63Ni ECD, derived from US EPA Method 8081A. A 30 m × 0.53 mm i.d. × 0.5μm film thickness fused silica cap- illary column HP-608 was used for the chromato- graphic separation of pesticides. Helium was used as the carrier gas and nitrogen as the makeup gas, and the injection technique was split/splitless. The detection limit for OCPs is 0.01μg/L.

Detailed procedures for sample collection, transpor- tation, extraction, and cleanup were referenced from the Geological Survey Standard of Groundwater Pollution (China Geological Survey 2008). Quality control samples were prepared and analyzed for each batch of samples. The QC results showed that the deviation between duplicates was within 20 % and the recovery of laboratory control standards was between 80 and 120 %.

Results and Discussion Concentration variation of organic pollutants in the core profile Sixteen SVOCs (Table1) have been detected in the sediment samples, including phenol-d5, (phenol, 2- fluoro), phenol, (phenol, 3-methyl), nitrobenzene-d5, naphthalene, (naphthalene, 1-methyl), (1,1-biphenyl ss), dibenzofuran, fluorene, phenanthrene, anthacene, dibutyl phthalate,p-terphenyl-d14, (1,2-benzenediacid, disooctyl ester), and benzo(b)fluoranthene. The concentrations of SVOCs in the sediments varied to a great extent at different sampling depths. The total concentration of∑SVOCs in sediments sampled in May 2009 ranged between 3.8 and 10.4 ng/mg. As the bottom of the waste disposal site is at 9.3 m depth, the detected types of SVOCs and their total concen- trations are greater at this depth than at others. The core was taken from the base of the landfill (starting at 9.3 m depth) for 2.2 m into silty clay (Fig.3).

Therefore, as a whole, the concentrations of different SVOCs are characterized by a decrease with depth. It can be seen from Table1that phenol-d5, phenol,2- fluoro, nitrobenzene-d5, 1,1-biphenyl ss, andp-ter- phenyl-d14 were continually detected at all seven depths. Figure2shows the vertical variation of these five compounds in the core profile. The total concen- trations of the five compounds are highest (≥9.6μg/kg) at 10.5–10.7 m depth, and lowest (≥3.6μg/kg) at 10.9–11.1 m depth. The silty clay, 3.2 m thick, exists from 9.4 to 12.6 m depth and can be regarded as a natural barrier for preventing direct pollution from the landfill into underlying material.

There are seven PAHs in the detected 16 SVOCs, namely, naphthalene, (naphthalene, 1-methyl), diben- zofuran, fluorene, phenanthrene, anthacene, and benzo (b)fluoranthene. The total PAH concentrations (Table1) at the different depths range from 0 to 990μg/kg. According to the classification standards of Maliszewska-Kordybach (1996), sediments with PAH concentrations close to 1,000μg/kg at 9.3 m depth, namely, at the bottom of the landfill, are heavily contaminated. Conversely, the detected PAH concen- trations below 100μg/kg (∑PAHs) at the remaining six depths could be indicative of low pollution in sediment.

Surface and groundwater General characteristics The physicochemical characteristics of the water sam- ples can be seen in Table2. EC values range from 0.4 to 4 mS/cm in groundwater samples, with total dis- solved solid (TDS) between 0.4 and 3.9 g/L, pH 6.6 and 8.9, DO 0.5 and8.7 mg/L, and turbidity 0.1 and 17.2. EC values range from 0.6 to 3.3 mS/cm in surface water samples, with TDS between 0.6 and 1.1 g/L, pH 7.7 and 8.1, DO 3.1 and 5.8 mg/L, and Environ Monit Assess (2013) 185:3413–34443421 turbidity up to 90. The groundwater sample (ZKN) in the north of the landfill shows a high mineral content (EC≥4mS/cm),whichisduetoalarge number of anthropogenic sources. The pHs of the groundwaters at the Zhoukou landfills were slightly alkaline (Table2). The mean pHs of groundwaters were 7.57 and 7.40 in May 2009 and December 2009, respectively.

The pulse of oxygen introduced by lowering the water table likely causes a partial and temporal oxidation of previously reduced species. The dissolved oxygen (DO) values of the wells with 9 m depth are >1 mg/L, indicat- ing the condition is aerobic. The phenolic compounds generally degrade readily under aerobic conditions, while nitrification of ammonium can also occur if oxy- gen is present. However, as nitrifying bacteria grow slowly relative to heterotrophic bacteria responsible for degradation of organic compounds, available oxygen may be utilized in the degradation of organic substances thereby preventing nitrification (Keener and Arp1994).

Nitrification has also been observed to be inhibited in the presence of phenols due to their toxicity (Stafford1974; Dyreborg and Arvin1995).

In the interior of the Zhoukou landfill, levels of alkalinity were very high (average 1,025 mg/L as CaCO 3), and they decreased along flow path to about 155 mg/L at ZKW. Excess of the alkalinity relative to calcium (Ca) is likely to be derived from the biodeg- radation of organic matter (Borden et al.1995; Basberg et al.1998; Lee et al.2001). The alkalinity values of groundwater samples in the Zhoukou landfill ranged between 155 and 2,045 mg/L in May 2009. As expected, the nearest well (ZG11) to the landfill showed the highest values of alkalinity (2,045 mg/L), which indicates that groundwater near landfill site is being significantly affected by leachate percolation.

Thirty-one organic compounds (out of 92 analyzed) exceeded detection limits. Table3shows the detectionrate of the CAHs, MAHs, HAHs, OCPs and other pesticides, and PAHs in water samples. The detected results of these organic compounds in the water sam- ples are shown in Tables4and5. The relative percent- age of the total concentration of the detected pollutants can be seen from the pie map in Fig.4, showing PAHs are the main organic contaminants in shallow aquifers around the Zhoukou landfill.

CAH, MAH, and HAH in water samples Seven CAHs (out of 29 analyzed) were detected in the water samples, namely, dichloromethane, chlo- roform, 1,2-dichloroethane, 1,2-dichloropropane, cis-1,2-dichloroethylene,tetrachloroethylene, and 1,1,2,2-tetrachloroethane. Besides groundwater samplesZKN,ZG7,andZG11(all≤0.2μg/L) from May 2009, CAHs were mainly detected in surface water samples with concentrations ranging between 0.2 and 2.8μg/L. Comparing these concentrations with the drinking water quality standards (GB5749- 2006) (e.g., chloroform, 60μg/L; 1,2-dichloropro- pane, 5μg/L; tetrachloroethylene, 5μg/L), the CAH concentrations in these water samples are not above the standards, indicating low levels of contamination, probably by industrial discharge in sewage water.

Nine MAHs (out of 14 analyzed) were detected, including benzene, toluene, ethylbenzen, ortho- xylene,m+p-xylenes, 1,2,4-trimethylbenzene, isobu- tylbenzene, styrene, and isopropylbenzene.

Concentrations of the total MAHs ranged from 0.57 to 8.96μg/L in surface water (highest in sewage water ZC), and 0.12μg/L (Z34, depth 28 m) to 1.14μg/L (ZG7, depth 9 m) in groundwater samples (mainly from May 2009). Only one HAH (out of 9 analyzed), namely 2-chlorotoluene, was detected in the water sample ZG12. Table 3Frequency of detection (%) in water samples GWgroundwater samples,SU surface water samplesSampling time Number of samplesCAHs MAHs HAHs OCPs + other pesticidesPAHs December 2008 10 (GW) 0 20.0 0 0 40.0 3 (SU) 66.7 66.7 0 66.7 66.7 May 2009 17 (GW) 23.5 58.8 5.9 5.9 76.5 6 (SU) 83.3 50.0 0 0 16.7 December 2009 13 (GW) 0 0 0 0 76.9 1 (SU) 0 0 0 100 3422Environ Monit Assess (2013) 185:3413–3444 Table 4CAH, MAH, and HAH concentrations in water samples Location siteSampling timeCAHs (μg/L) MAHs (μg/L) HAHs (μg/L) DCM (0.2) aTCM (0.1) a1,2-DCA (0.2) a 1,2- DCP (0.2) a cis-1,2- DCE (0.1) a PCE (0.1) a1,1,2,2- PCA (0.1) a ∑CAHs B (0.2) aT (0.1) aE (0.1) ao-X (0.1) am+p-X (0.2) a 1,2,4- TMB (0.1) a IBB (0.1) aStyrene (0.1) a IPB (0.1) a∑MAHs 2-Chlorotoluene (0.1) a ZA December 2008--- -- -- - - - - -- - -- -- - ZB December 2008--- -- -- - - - - -- - -- -- - ZC December 20080.41 0.63 0.66 0.47 - 0.63 - 2.8 - 8.15 0.17 0.22 0.42 - - - - 8.96 - ZD December 2008--- -- -- - - - - -- - -- -- - ZE December 2008- - 1.3 - - 0.25 - 1.55 - 1.33 0.16 - - - - - - 1.49 - ZF December 2008--- -- -- - - - - -- - -- -- - ZG December 2008--- -- -- - - - - -- - -- -- - Z6A December 2008--- -- -- - - - - -- - -- -- - Z6 December 2008--- -- -- - - - - -- - -- -- - SW29 December 2008- - - - - - - - - 0.51 - - - - - - - 0.51 - SW49 December 2008--- -- -- - - - - -- - -- -- - SW59 December 2008--- -- -- - - - - -- - -- -- - ZK1 December 2008- - - - - - - - - 0.44 - - - - - - - 0.44 - ZKE May 2009 - - - - - - - - - - - - - - - - - - - ZKW May 2009 - - - - - - - - - 0.13 - - - - - - - 0.13 - ZKS May 2009 - - - - - - - - - - - - - - - - - - - ZKN May 2009 - - - - 0.15 - - 0.15 0.44 - - - - - - - 0.13 0.57 - ZF May 2009 - - - - - - - - - - - - - - - - - - - ZG7 May 2009 - - - - 0.19 - - 0.19 0.97 - - 0.17 - - - - - 1.14 - ZG9 May 2009 - - - - - - - - - 0.19 - - - - - - - 0.19 - ZG10 May 2009 - - - - - - - - - - - - - - - - - - - ZG11 May 2009 - - - - - - 0.16 0.16 0.55 - - - - - - - - 0.55 - ZG12 May 2009 - - - - - - - - 0.37 - - - - - - - - 0.37 0.26 Z16 May 2009 - - - - - - - - - 0.24 - - - - - - - 0.24 - Z34 May 2009 - - - - - - - - - 0.12 - - - - - - - 0.12 - Environ Monit Assess (2013) 185:3413–34443423 Table 4(continued) Location siteSampling timeCAHs (μg/L) MAHs (μg/L) HAHs (μg/L) DCM (0.2) aTCM (0.1) a1,2-DCA (0.2) a 1,2- DCP (0.2) a cis-1,2- DCE (0.1) a PCE (0.1) a1,1,2,2- PCA (0.1) a ∑CAHs B (0.2) aT (0.1) aE (0.1) ao-X (0.1) am+p-X (0.2) a 1,2,4- TMB (0.1) a IBB (0.1) aStyrene (0.1) a IPB (0.1) a∑MAHs 2-Chlorotoluene (0.1) a Z40 May 2009 - - - - - - - - - 0.2 - - - - - - - 0.2 - DW09 May 2009 - - - - - - - - - - - - - - - - - - - DW18 May 2009 - - 0.97 1.25 - - - 2.22 0.5 - - - - - - - - 0.5 - DW23 May 2009 - - - - - - - - - - - - - - - - - - - DW25 May 2009 - - - - - - - - - - - - - - - - - - - ZC May 2009 - 0.26 0.38 0.38 - 0.61 - 1.63 - 5.43 1.14 - 1.45 0.13 0.13 0.59 - 8.87 - ZD May 2009 - - - - - 0.22 - 0.22 - - - - - - - - - - - SUJL May 2009 - 1.33 - - - - - 1.33 - - - - - - - - - - - SULG May 2009 - - - - - - - - - 1.07 - - - - - - - 1.07 - SUY May 2009 - 1.81 - - - - - 1.81 - - - - - - - - - - - SULD May 2009 - - 1.11 - - - - 1.11 - 0.57 - - - - - - - 0.57 - No CAH, MAH and HAH has been detected in water samples collected in December 2009 CAHschlorinated aliphatic hydrocarbons (includingDCMdichloromethane,TCMchloroform,1,2-DCA1,2-dichloroethane,1,2-DCP1,2-dichloropropane,cis-1,2-DCEcis-1,2- dichloroethylene,PCEtetrachloroethylene,1,1,2,2-PCA1,1,2,2-tetrachloroethane),MAHsmonocylic aromatic hydrocarbons (includingBbenzene,Ttoluene,Eethylbenzen,o-X ortho-xylene;m + p-X m+p-xylenes;1,2,4-TMB1,2,4-trimethylbenzene,IBBisobutylbenzene,IPBisopropylbenzene),HAHshalogenated aromatics hydrocarbons aDetection limit 3424Environ Monit Assess (2013) 185:3413–3444 Table 5OCP and PAH concentrations in water samples Location siteSampling timeOCPs (μg/L) PAHs (μg/L) BHC (0.01) a γ-chlordane (0.01) a Endosulfan-I (0.01) a Endosulfan sulfate (0.01) a Nap (0.2) a Acp (0.01) a Flu (0.005) a Phe (0.01) a Ant (0.01) a FLT (0.005) a Pyr (0.002) a BaA (0.001) a CHR (0.001) a BbF (0.002) a BkF (0.001) a ∑PAHs ZA December 2008- - - - - 0.38 0.682 0.519 0.168 0.261 0.158 0.0181 - - - 2.19 ZB December 2008-- - - ------------ ZC December 2008- 0.058 - - - - 0.0477 0.125 - 0.0323 0.0306 - - - - 0.24 ZD December 2008-- - - ----------- ZE December 2008- 0.014 - - - - 0.0184 0.043 - 0.0097 0.007 - - - - 0.08 ZF December 2008- - - - - 0.215 0.362 0.452 0.079 0.153 0.0815 0.0086 - - - 1.35 ZG December 2008- - - - - - 0.0241 0.033 - - - - - - - 0.06 Z6A December 2008-- - - ------------ Z6 December 2008-- - - ------------ SW29 December 2008-- - - ------------ SW49 December 2008- - - - 0.6 - - - - - - - - - - 0.60 SW59 December 2008-- - - ------------ ZK1 December 2008-- - - ------------ ZKE May 2009 0.18 - - - - 0.147 0.3642 0.8299 0.174 0.2984 0.1763 0.0334 0.0396 0.0131 0.0042 2.08 ZKW May 2009 - - - - - - 0.2793 0.645 0.122 0.3549 0.1691 0.029 0.0363 - - 1.64 ZKS May 2009 - - - - - 0.144 0.2971 0.5953 0.117 0.2096 0.1224 0.0139 - - - 1.50 ZKN May 2009 - - - - - 0.06 0.177 0.2833 0.038 0.0531 0.0295 - - - - 0.64 ZF May 2009 - - - - - 0.212 0.4391 0.7569 0.168 0.2753 0.1578 0.0214 0.0207 - - 2.05 ZG7 May 2009 - - - - - - 0.0259 0.028 - - - - - - - 0.05 ZG9 May 2009 - - - - - - 0.02 0.024 - - - - - - - 0.04 ZG10 May 2009 - - - - - - 0.0338 0.028 - - - - - - - 0.06 ZG11 May 2009 - - - - - 0.02 0.0395 0.0312 - - - - - - - 0.09 ZG12 May 2009 - - - - - - 0.0215 0.0189 - - - - - - - 0.04 Z16 May 2009 - - - - - 0.115 0.2596 0.3552 0.075 0.1474 0.097 0.0093 0.0099 - - 1.07 Z34 May 2009 - - - - - 0.129 0.2818 0.452 0.104 - 0.0943 0.0118 0.0098 - - 1.08 Environ Monit Assess (2013) 185:3413–34443425 Table 5(continued) Location siteSampling timeOCPs (μg/L) PAHs (μg/L) BHC (0.01) a γ-chlordane (0.01) a Endosulfan-I (0.01) a Endosulfan sulfate (0.01) a Nap (0.2) a Acp (0.01) a Flu (0.005) a Phe (0.01) a Ant (0.01) a FLT (0.005) a Pyr (0.002) a BaA (0.001) a CHR (0.001) a BbF (0.002) a BkF (0.001) a ∑PAHs Z40 May 2009 - - - - - - 0.0137 - - 0.0818 0.1471 0.0095 - - - 0.25 DW09 May 2009 - - - - - - - - - - - - - - - - DW18 May 2009 - - - - - - - - - - - - - - - - DW23 May 2009 - - - - - - - - - - - - - - - - DW25 May 2009 - - - - - - - - - - - - - - - - ZC May 2009 - - - - - - 0.0465 0.1189 - 0.0581 0.0348 0.0077 0.0134 - - 0.28 ZD May 2009 - - - - - - - - - - - - - - - - SUJL May 2009 - - - - - - - - - - - - - - - - SULG May 2009 - - - 0.088 - - - - - - - - - - - - SUY May 2009 - - - - - - - - - - - - - - - - SULD May 2009 - - 0.021 - - - - - - - - - - - - - ZKE December 2009 - - - - - - 0.0322 0.017 - 0.016 0.0097 - - - - 0.07 ZKW December 2009 - - - - - - 0.0311 0.066 0.015 0.0327 0.0213 - - - - 0.17 ZKS December 2009 - - - - - 0.025 0.0869 0.103 0.041 0.1135 0.057 0.0077 0.0076 - - 0.44 ZKN December 2009 - - - - - 0.014 0.0491 0.108 0.023 0.0339 0.026 - - - - 0.25 ZF December 2009 - - - - - 0.013 0.0506 0.142 0.027 0.0272 0.0491 0.0344 0.0053 - - 0.35 ZG9 December 2009 - - - - - - 0.0916 0.196 0.028 0.0301 0.0195 - - - - 0.37 Z06 December 2009 - - - - - - - - - - - - - - - - Z16 December 2009 - - - - - - 0.0625 0.156 0.026 0.0457 0.0361 0.0033 0.0033 - - 0.33 Z34 December 2009 - - - - - - - - - 0.0323 0.0466 - - - - 0.08 Z40 December 2009 - - - - - - 0.0732 0.171 0.033 0.0661 0.0525 0.005 0.0058 - - 0.41 ZB December 2009 - - - - - - - - - - 0.006 - - - - 0.01 DW09 December 2009 - - - - - - - - - - - - - - - - DW25 December 2009 - - - - - - - - - - - - - - - - SUJL December 2009 - - - - - - - - - - 0.008 - - - - 0.01 aDetection limit OCPsorganochlorine pestcides (BHCbenzene hexachloride),PAHspolycyclic aromatic hydrocarbons (Napnaphthalene,Acpacenaphthene,Flufluorine,Phephenanthrene,Ant anthracene,FLTfluoranthene,Pyrpyrene,BaAbenzo(a)anthracene,CHRchrysene,BbFbenzo(b)fluoranthene,BkFbenzo(k)fluoranthene) 3426Environ Monit Assess (2013) 185:3413–3444 BTEX compounds (benzene, ethylbenzene, tolu- ene, and three isomers of xylene) of MAHs are clas- sified as environmental priority pollutants, which may not exceed 10, 700, 300, and 500μg/L in drinking water, respectively, according to the National Chinese (NC) standards (GB-5749-2006). They are commonly found together in crude petroleum and petroleum products such as gasoline and diesel fuel. The pres- ence of these hydrocarbons in the environment is a hazard to public health and an ecological concern, due to their toxicity and ability to bioaccumulate through the food chain (Brigmon et al.2002). BETX are prominent components of gasoline, and their presence in water is usually an indication of gasoline contami- nation. The contaminants in this study do not exceed the defined limits for Chinese drinking water stand- ards, which is the same with the World Health Organization (WHO) guidelines for drinking water quality (WHO2006).Toluene is mainly detected in the water samples from the Low-Lying Gully and sewage ditch (ZC), xylene detected in the sewage ditch (ZC), and benzene mainly detected in ground- water samples (such as ZG7, ZKN, ZG11, and ZG12 at 9 m depth) close to the landfill.The detection rate of BTEX in May 2009 is higher than that in December 2009. BTEX concentrations at individual boreholes were highly variable over time.

These temporal variations appeared to result from not only hydraulic variations and seasonal groundwater flow variations but also preferential dissolution and biodegradation. In particular, systematic decreases in SO 42− concentrations, increases in HCO 3− concentra- tions, and the presence of degradation products in regions of the plume where BTEX concentrations are relatively high are indicative of degradation processes (Grbic-Galic and Vogel1987; Wiedemeier et al.

1995). Ranking the hydrocarbon compounds by the plume-scale degradation rate estimate, from highest to lowest rate gave the order: toluene,o-xylene, naphtha- lene,m-andp-xylene, trimethylbenzene, ethylben- zene, and benzene (Davis et al.1999). For an aerobic, nitrate-rich BTEX contaminated aquifer, Daniel and Borden (1997) found highest degradation rates near the source of their plume, with decreasing degradation rates with distance down the plume.

During biodegradation, microorganisms transform available carbon into forms useful for energy and cell production. This results in oxidation of the electron Fig. 4Total frequency of the detected organic com- pounds in the groundwater samples, like CAHs, OCPs, MAHs, and PAHs Environ Monit Assess (2013) 185:3413–34443427 donor (such as organic matter) and reduction of elec- tron acceptor [such as DO, nitrate, iron (III) or Mn (III), sulfate, and carbon oxide] (Essaid et al.1995;Lu et al.1999). The aquifer near the landfill is character- ized by elevated BTEX concentrations in May 2009, relatively low concentrations of nitrate, and sulfate. In contrast, the distribution area of low BTEX concen- trations (Fig.5e) under aerobic condition (DO detected over 1 mg/L) and nitrate (Fig.5b), sulfate (Fig.5c), and manganese (Fig.5d) concentrations is high. The in situ microbes seem to be using fuel hydrocarbons as their carbon and energy sources, thereby contributing to the natural removal process.

OCPs and other pesticides in water samples From Table5, it can be seen that only one OCP (out of 11 analyzed), namely, benzene hexachloride was detected in the groundwater sample ZKE (27 m depth) with a concentration of 0.18μg/L, which is far below the Chinese drinking water standard of 5μg/L. With the exception of well ZKE, groundwater samples are not contaminated by OCPs and other pesticides, which have been detected in drainage canals in the east of the landfill and in water from the LuDong Trunk Canal and the Low-Lying Gully. This indicates that, exceptfor local point polluted by OCPs in the eastern part of the landfill, there is less pesticide contribution to the shallow aquifer. Three kinds of common pesticides (out of 13 analyzed), includingγ-chlordane (detected in ZC and ZE), endosulfan-I and endosulfan sulfate, were detected in water sample from the sewage ditch with concentrations varying from 0.021 to 0.088μg/L, indicating that local agricultural activities contribute irrigation return flows to the sewage water. This is also a potential source for some shallow groundwater pol- lution due to the untreated bed of the sewage ditch.

The sources of pesticide residues in the waters studied are agricultural practices within the study area, in combination with rainfall. Maximum concentrations of this compound were detected in May, possibly due to surface run-off. The spatial and temporal dis- tribution of pesticides obtained from the monitoring network shows no clear trends for prediction of future concentrations. Nitrate–N concentrations and pesticide detections show no clear relationship, suggesting dif- ferent source, transport, or degradation pathways.

PAHs distribution in water samples PAHs are the main contaminants of concern detected in the water samples. Unlike CAHs, MAHs, HAHs, Fig. 5Concentration contours for the chloride (a), nitrate (b), sulfate (c), manganese (d), BTEX (e), and PAHs (f) of groundwater samples in May 2009. Units are micrograms per liter for BTEX and PAHs and milligrams per liter for the rests 3428Environ Monit Assess (2013) 185:3413–3444 and OCPs, most groundwater samples contained PAHs in the summer and winter 2009 samples, with a high detection rate of more than 75 % (Table3).

PAH concentrations in nine representative wells (Fig.6) varied from 0.04 to 2.08μg/L in May 2009 and from 0.07 to 0.44μg/L in December 2009, indi- cating that rainfall can enhance contaminant leakage from the waste disposal site into groundwater during the summer. It is clear that PAH concentrations in summer are higher than those in winter. Many of the PAH compounds in water samples were present at concentrations in excess of 1μg/L, suggesting that water in this area was heavily contaminated (Zhou and Maskaoui2003), especially in May 2009. In this study, the heavily contaminated water samples, such as ZA and ZF sampled in December 2008, and ZKE, ZKS, ZKW, ZF, Z16, and Z34 sampled in May 2009, mainly occur at water depths of 18–30 m, in some cases with concentrations of total PAHs (in ZKE and ZF) beyond 2μg/L (Fig.7). The detectable propor- tions of three- and four-ring PAHs were the highest, with two- and five-ring PAHs the lowest (Fig.6).

Univariate Pearson correlation matrix (Table6) shows a good correlation among all PAHs except BaA.

Higher Pearson coefficients of different PAHs under the 0.01 significant level can reflect the similar pollu- tion sources, e.g., Acp, Ant, FLT, and Pyr.

Eleven PAHs (out of 16 analyzed) were detected, including Nap, Acp, Flu, Phe, Ant, FLT, Pyr, BaA, CHR, BbF, and BkF. No six-ring PAHs were detected in water samples. The detected concentrations in wateris 0.6μg/L for two-ring PAHs (Nap), ranged 0.01– 1.75μg/L for three-ring PAHs (Acp, Flu, Phe, and Ant), 0.01–0.59μg/L for four-ring PAHs (FLT, Pyr, BaA, and CHR), and 0.02μg/L for five-ring PAHs (BbF and BkF). The total concentrations of these 11 PAHs in water ranged from 0.01μg/L at well ZB to 2.19μg/L at well ZA, with a mean concentration of 0.62μg/L (Table5). The three dominant PAHs found in most groundwater samples are Phe, Flu, and FLT in the study area (Fig.8). They formed 0–52 (mean, 35) %, 0–46 (mean, 19) %, and 0–40 (mean, 17) % of the total PAHs, respectively. The lower molecular weight (LMW, two to three rings) PAHs dominate in all samples with the exception of Z40.

Generally, PAHs from a petrogenic source show a depletion of higher molecular weight (HMW, four to six rings) PAHs relative to LMW PAHs, while pyrogenic sources are abundant in HMW PAHs (Zakaria et al.2002). Most groundwater around the Zhoukou landfill not only contains a consider- able amount of LMW PAHs but is also abundant in HMW PAHs, indicating the input of both petrogenic and pyrogenic origins.

Source and degradation of PAHs Source diagnosis by diagnostic ratios of PAHs Inferring the sources of PAHs is widely considered to be very important to study the transport and fate of PAHs in environment (Wan et al. 2006). Generally, ratios of various PAH concentrations have usually been undertaken to diagnose the possible sources of PAHs (Fernandes et al.1997; Yunker et al.2002).

When the concentrations of different PAHs in water Fig. 6Non-outlier range, interquartile range (IQR), and median concentrations (box-and-whisker plots)of∑11PAHs in shallow groundwater samples (ZKE, ZKS, ZKW, ZKN, Z16, Z34, Z40, ZF and ZG9) during the two sampling campaigns Fig. 7Plots (a) of PAHs concentrations corresponding to groundwater sampling depth Environ Monit Assess (2013) 185:3413–34443429 samples reaches the quantitation limit, some selected diagnostic ratios have been calculated and shown in Table7. Most of the water samples detected PAHs in this study show these ratios intermediate betweenpyrogenic and petrogenic values, compared with the reported values for particular processes (Table8).

Petroleum often contains more thermodynamically stable compounds such as Nap, Flu, Phe, and CHR, Table 6Pearson coefficient of different PAHs in the groundwater samples (n026) around the Zhoukou landfill Acp Flu Phe Ant FLT Pyr BaA CHR PAHs Acp 1 Flu 0.99 a 1 Phe 0.69 b 0.86 a 1 Ant 0.80 a 0.90 a 0.95 a 1 FLT 0.76 b 0.80 a 0.92 a 0.93 a 1 Pyr 0.75 a 0.71 a 0.94 a 0.96 a 0.91 a 1 BaA -0.10 0.28 0.51 0.47 0.51 0.51 1 CHR 0.60 0.71 b 0.88 a 0.84 a 0.94 a 0.94 a 0.67 b 1 PAHs 0.88 a 0.95 a 0.97 a 0.98 a 0.93 a 0.84 a 0.47 0.86 a 1 aCorrelation is significant at the 0.01 level (two-tailed)bCorrelation is significant at the 0.05 level (two-tailed) Fig. 8Distribution of organic compound groups identified in water samples around the landfillain May 2009 andbin December 2009. Results are based on GC peak areas of theGC-MS full scan analysis.∑PAHs denotes total PAH concen- tration, i.e., the sum of the individual mass concentrations of the 11 PAH congeners 3430Environ Monit Assess (2013) 185:3413–3444 while FLT and Pyr are usually the most abundant compounds for pyrolytic PAHs (Doong and Lin 2004). The FLT/Pyr and FLT/(FLT + Pyr) ratios can be useful tools to check PAHs pollution origin (Gschwend and Hites1981; Gogou et al.1998;Magietal.2002).

Values of FLT/Pyr <1, FLT/(FLT + Pyr) <0.5, Phe/ Ant >15, and CHR/BaA >1 indicate a petrogenic origin of contamination (De Luca et al.2004). In this context, Z40 (May), Z34 (December), ZF (December) show a strong petrogenic character and that FLT/Pyr and FLT/(FLT + Pyr) ratios are much below 1 and 0.5, respectively, where the rests show ratios compatible with pyrogenic sour- ces of contamination, probably originate mainly from grass, wood, and coal combustion.

Similar results were observed for the CHR/BaA ratios. CHR and BaA are both derived from the com- bustion processes with CHR/Pyr ratio lower than 1.

This ratio in this study ranges between 0.15 and 1.74, indicating combustion processes and petroleum hydro- carbons are the possible main source of PAHs in water samples in this study. The ratio Ant/(Ant + Phe) hasbeen suggested as diagnostic indicator for distin- guishing between pyrogenic and petrogenic sources with values >0.1 indicating pyrolytic souces, where- as <0.1 suggest petrogenic (Budzińskietal.1997).

In this study, this ratio is >0.1 for the water samples (e.g., ZA, ZF, ZKE, and ZKS in Table6)whereAnt and Phe are detectable, indicating dominance of fuel combustion and coal burning processes in these sample sites. Most samples with Phe/Ant <10 and FLT/Pyr <1 were characterized as a mixture of py- rolytic and petrogenic contamination, which is in good agreement.

The distribution of LMW and HMW PAHs is also a tool for identifying the petrogenic/pyrolytic origin of PAHs (Sicre et al.1987; Budziński et al.1997). The higher the LMW/HMW ratio is, the higher the preva- lence of petrogenesis on pyrolytic origin of PAHs is (De Luca et al.2004). The LMW/HMW ratios of the collected water samples range from 0.06 to 8.34 with mean value of 3.24. Except for Z34 (May) and Z40 (December), Table3also shows that LMW are clearly predominant over HMW, suggesting a definite Table 7Diagnostic ratios used with their typically reported values for particular processes PAH ratio Value range Source Reference This study ∑LMW/∑HMW <1 Pyrogenic Zhang et al.2008; Budziński et al.19970.06–8.34 >1 Petrogenic Flu/(Flu + Pyr) <0.5 Petrol emissions Ravindra et al.2008b0.09–0.86 >0.5 Diesel emissions Ant/(Ant + Phe) <0.1 Petrogenic Pies et al.20080.12–0.29 >0.1 Pyrogenic FLT/(FLT + Pyr) <0.4 Petrogenic Gogou et al.1998;DeLa Torre-Roche et al.20090.36–0.68 0.4–0.5 Fossil fuel combustion >0.5 Grass, wood, coal combustion FLT/Pyr <1 Petrogenic Sicre et al.1987; Baumard et al.1998a;b0.55–2.1 >1 Pyrogenic BaA/(BaA + CHR) <0.2 Petrogenic Akyüz and Çabuk2010; Yunker et al.2002; Wang et al.20100.37–0.87 0.2–0.35 Coal combustion >0.35 Combustion CHR/BaA <1 Pyrogenic Soclo et al.20000.15–1.74 >1 Petrogenic Phe/Ant <10 Pyrogenic Baumard et al.1998a; b; Cao et al.20052.51–7.46 >15 Petrogenic Environ Monit Assess (2013) 185:3413–34443431 petrogenic origin of PAHs. The low solubilities of LMW PAHs compared to the HMW compounds (Lee and Lee2004; Sahu et al.2004) may also be responsible for the high ratios in water, as opposed to source material alone (Tobiszewski and Namieśnik 2012). These results showed that the PAHs contami- nation in this study was probably from mixture sour- ces of petroleum and combustion products.

Source apportion by principal component analysis To provide insight into the accuracy and quantification of source apportion, principal component analysis (PCA) was applied to analyze the data set. PCA reduces the number of variables in the original data set into principal components without significant loss in the total variance of the data. The loading that each variable in the original data contributes to the principal components enables grouping of data with similar behaviors. Values below the detection limit were replaced by half of the method detection limits for the statistical analysis. The score and loading plots(Fig.9) obtained by PCA can show the similarities or dissimilarities between ambient PAH profiles.

After autoscaling, two significant components were identified, giving account for 62.5 and 16.3 % of the total variance, respectively. The third component takes into account only 8.9 % of the total variance and was not considered in the present analysis. Figure9a shows the loading plot and substantiates that the first component is mainly related to Phe, FLT, Ant, Pyr, Acp, Flu, and BaA, whereas the second component is mainly related to BkF, BbF, and CHR. High loads of Pyr, Phe, and FLT might be an indication of diesel combustion (Ravindra et al.2008a). There are also three groups identified on the factor score plot (Fig.9b). Group 1 clusters samples (such as ZG7, ZG9, and ZG10) mostly collected around the landfill in Decemeber; group 2, samples collected from ZKN, ZKW, Z16, and Z34 in May and ZF in December; and group 3 only contains one sample, which collected from the ZA. The discrimination in three groups was confirmed by hierarchical cluster- ing analysis (Fig.10).

Table 8PAH characteristics and diagnostic ratios from water samples around the Zhoukou landfill ID∑PAHs LMW/ HMWLMW% HMW% Phe/ AntFlu/ (Flu + Pyr)FLT/ PyrFLT/ (FLT + Pyr)CHR/ BaAAnt/ (Ant + Phe)BaA/ (BaA + CHR) Water samples in May 2009 ZKE 2.08 2.68 72.8 27.2 4.77 0.67 1.69 0.63 1.19 0.17 0.46 ZKS 1.50 3.33 76.9 23.1 5.09 0.71 1.71 0.63 0.16 ZKW 1.64 1.89 64.0 33.8 5.29 0.62 2.10 0.68 1.25 0.16 0.44 ZKN 0.64 6.76 87.1 12.9 7.46 0.86 1.80 0.64 0.12 ZC 0.28 1.45 59.2 40.8 0.57 1.67 0.63 1.74 0.36 ZF 2.05 3.32 76.8 23.2 4.51 0.74 1.74 0.64 0.97 0.18 0.51 Z16 1.07 3.17 75.3 23.7 4.74 0.73 1.52 0.60 1.06 0.17 0.48 Z34 1.08 8.34 89.3 10.7 4.35 0.75 0.83 0.19 0.55 Z40 0.25 0.06 5.4 94.6 0.09 0.56 0.36 Water samples in December 2009 ZG9 0.37 6.36 86.4 13.6 7.00 0.82 1.54 0.61 0.13 Z34 0.08 0.00 0.0 100.0 0.69 0.41 ZF 0.35 2.01 66.7 33.3 5.26 0.51 0.55 0.36 0.15 0.16 0.87 ZKN 0.25 3.24 76.4 23.6 4.70 0.65 1.30 0.57 0.18 ZKE 0.07 1.91 65.7 34.3 0.77 1.65 0.62 ZKS 0.44 1.38 57.9 42.1 2.51 0.60 1.99 0.67 0.99 0.28 0.50 ZKW 0.17 2.08 67.5 32.5 4.40 0.59 1.54 0.61 0.19 Z40 0.41 2.24 68.2 30.4 5.18 0.58 1.26 0.56 1.16 0.16 0.46 Z16 0.33 2.87 73.4 25.6 6.00 0.63 1.27 0.56 1.00 0.14 0.50 3432Environ Monit Assess (2013) 185:3413–3444 Fig. 9Principal component analysis (PCA) loadings for PAHs in groundwater samples in the Zhoukou landfill site:aPrincipal components loading plot andbcomponent score plot. Principalcomponent 1 and 2 (PC1 and PC2) account for 62.5 and 16.3 % of the variance in the data set, respectively (ZKE not reported here because located outside the graph b) Fig. 10Hierarchical clus- tering of the PAHs concen- trations from water samples around the Zhoukou landfill Environ Monit Assess (2013) 185:3413–34443433 The samples circled in the group 1 contain similar contaminants, particularly Nap, with a high contribu- tion relative to the other PAHs. The samples in the group 1are mostly those collected around the landfill.

Samplesingroup2weremostlycollectedinMay 2009 and show similar characteristics, which may be related to the origins of contamination and timing of the sampling. These samples are characterized by pos- itive loading in the PC2 and negative loading in PC1, so have more contribution from Phe, Ant, FLT, Pyr, Flu, and Acp the than other samples. Although the sample of ZA of the group 3 was collected from the shallow aquifer west of the landfill with the highest total PAHs concentration (up to 2.19μg/L); CHR, BaA, and Flu make up a relatively high contribution to ZA.

Degradation of PAHs Although PAH may undergo adsorption, volatiliza- tion, photolysis, and chemical degradation, microbial degradation is the major degradation process (Zaidi and Imam1999; Christensen et al.2001; Haritash and Kaushik2009). Sorption of leachate organic matter on to aquifer material seems to be of only minor signifi- cance according to column experiments reported in the literature (Christensen1992; Rügge et al.1995). The biodegradation of PAHs has been observed under both aerobic and anaerobic conditions (Haritash and Kaushik2009), which depends on the environmental conditions, number and type of the microorganisms, and nature and chemical structure of the chemical compound being degraded. In this study, the DO con- centrations of most groundwater samples in excess of 1.0 mg/L are identified that the aquifer is aerobic. The value of 1.0 mg/L is defined in order to minimize the presence of nitrate-reducing microenvironments in the aerobic aquifer (Lyngkilde and Christensen1992).

The pH values are lower in winter season than that in summer season. Although altering the pH of water from neutral to pH 6.0 and 8.0 had very little or no effect on Phe (Zaidi and Imam1999), the increasing pH values of water in summer season may have effect on reducing the other PAHs degradation.

The monitoring results show the water table is higher in December than that in May, due to the reduction in groundwater exploitation over the winter season. Little is known about the effects of fluctuations of the watertable on organic contaminant degradation under field situations. From laboratory experiments, it was demon- strated that fluctuating the water table enhanced the degradation of diesel oil (Rainwater et al.1993). It can be expected that the dynamics regime imposed by a fluctuating water table and the resulting differences in unsaturated zone (e.g., soil aeration), not only affect the microbial and chemical reactions that organic pollutants undergo but also the transport of gases and solutes through the aquifer (Sinke et al.1998).

Some studies showed that some LWM PAHs are biosusceptible and can be biodegraded more rapidly than the HMW PAHs (Hinga2003;Rothermichet al.2002). PAHs are known to dissipate under nitrate- and sulfate-reducing conditions; sometimes, HMW PAHs after LMW PAHs have been utilized/ degraded (Meuller et al.1989), while the presence of phenanthrene is reported to inhibit degradation of pyrene (McNally et al.1999). Because HMW PAHs (such as Pyr, BaA, and BbF) are more resis- tant to microbial degradation processes, they tend to persist longer in contaminated environments (van Brummelen et al.1998; Neilson and Allard1998; Bosma et al.2001), and their degradation pathways are less well understood.

The Gibbs free energy for oxidation of organic carbon decreases at neutral pH in the order: O 2, NO 3−,MnO 2, Fe(OH) 3,SO 42− ,andCO 2(van Breukelen2003; Wilson et al.2004). Therefore, aero- bic degradation followed by nitrate reduction oxidizes organic carbon at the fringes of plumes. Figure11 shows the chloride levels and the concentrations of redox-sensitive parameters with BTEX and PAHs con- centrations along the NS and WE cross-sections in the Zhoukou landfill. A combination of geochemical data, in terms of changes in solute concentrations along the flowpath, and the PAHs concentrations in each well can be used to describe contaminated extent in the shallow aquifer system. As groundwater moves away from the landfill the following changes occur:

1. Chloride is not considered to undergo any chem- ical or physico-chemical reactions in the aquifers and as such is considered inert or conservative (Christensen1992). For this reason, chloride can be used to study dispersion and dilution of a contaminant plume. Measured chloride concentra- tion in groundwater samples was 239 mg/L 3434Environ Monit Assess (2013) 185:3413–3444 ranging between 51 and 976 mg/L in May 2009.

There was a definite attenuation pattern observed in wells down gradient of the landfill site (Fig.4a).2. Sulfate concentrations increase as groundwater moves outside the sulfate reduction zone. A de- cline of sulfate near the landfill is noted due to Fig. 11Chloride and redox sensitive species with main organic contaminants along the NS and WE cross-sections in the Zhou- kou landfill.1Middle and fine sand,2silt,3silty clay,4fill soil(clayey silt),5landfill,6groundwater table,7groundwater flow direction,8monitoring well with well screen Environ Monit Assess (2013) 185:3413–34443435 sulfate reduction. Sulfate concentration in landfill leachate (<200 mg/L at the monitoring wells of 27 m depth) is generally too low to maintain a degradation potential equal to iron reduction.

3. Groundwater near the landfill contains elevated concentrations of dissolved Fe and Mn, mainly mobilized under reducing conditions from landfill leachate.

4. The presence of ammonium (NH 4+) in groundwa- ter has biochemical significance as a useful indi- cator of organic pollution (Chapman1992).

Ammonium appears to give way downstream to a narrow zone in which elevated concentrations of nitrite are detected (e.g., at Z40, ZKW, and Z16).

This may be interpreted as partial nitrification of the ammonium plume due to infiltrating oxic wa- ter. Downstream of the nitrite well, nitrate becomes the dominant species, suggesting further nitrification. Nitrate reduction causes disappear- ance of nitrate with depth upstream from the land- fill (e.g., Postma et al.1991), such as the monitoring wells at 9 m depth (ZG10, ZG11, and ZG12). Nitrate reduction is a likely process at the mixing zone of landfill leachate and shallow ni- trate containing groundwater.

Nitrate >1 mg/l (with a maximum of 487 mg/L at DW18) was encountered downstream of the landfill, and nitrate <0.1 mg/L water samples were found near the landfill at wells ZG10, ZG11, ZG12, ZKE, ZKN, and ZF, especially ~9 m depth, indicating that denitri- fication is likely a dominant redox process at the downstream fringes of the plume. The contribution of aerobic and nitrate-reducing zones to natural atten- uation of a plume increases with the O 2and NO 3− concentrations in pristine groundwater and the extent of mixing with the leachate plume (van Breukelen 2003). Figure4cshows lower NO 3− concentrations near the landfill, and there are higher Phe concentra- tions detected in ZKE, ZKW, ZKN, etc (Table4), which are the monitoring wells near the landfill. This is consistent with that the idea that a lack of N may slow down the biodegradation of phenanthrene (Zaidi and Imam1999) and cause it to accumulate in the groundwater.

Most groundwater samples (such as ZKN, ZKE, ZF, and Z16) in December have higher NO 3− concen- trations and lower pH values than in May. These will enhance degradation of PAHs due to the addedinorganic nitrogen under aerobic conditions and result in lower PAHs concentrations in winter season. In addition, the higher HCO 3− concentrations (mean val- ue, 926 mg/L at 27 m depth) in December than in May (mean value, 487 mg/L) support this conclusion, as HCO 3− is probably a by-product of PAHs degradation.

Characteristics of organic pollution in water bodies Horizontal distribution of organic pollution No organic compounds were detected in samples from wells ZB, Z6A, Z6, SW59, DW23, DW09, DW25, and Z06. The contamination plume is identifiable by the dashed oval-shaped line in Fig.1and is distributed across the area where groundwater depth is 2–4m.In the horizontal direction, the extent of pollution around the landfill is 2 km from south to north and 3 km from east to west. In the contaminated area, relatively fewer organic compounds are detectable in December as opposed to May. Theoretically, VOCs are not often found in surface waters (especially lakes, e.g., Nikolaou et al.2002) because of their high volatility; however, they are the most common groundwater contaminants (Golfinopoulos et al.2001). In the north- east of the landfill, surface water samples from ZC, located in a sewage ditch, yielded similar results over two sampling periods. MAHs accounted for 78 % of the total organic compounds, CAHs for 19 %, and PAHs for <2 %. In the pond surface water sample ZD, near the southeast of the landfill, fewer CAHs were detected (only tetrachloroethylene, 0.22μg/L) in the summer period, with no organic pollutants detected in the winter. In the southwest of the landfill, the leachate sample ZE showed CAHs to account for 50 % of the total organic compounds, MAHs for 48 %, PAHs for <3 %, and OCPs for only 0.4 %. Figure12 shows that PAH concentrations of groundwater char- acterized by a declining trend with increasing distance from the landfill center. According to the exceedance of 1μg/L, the contaminated distance can be estimated to be 1,200 m from this map. Pollutant concentrations vary greatly in different directions (Fig.13). Towards the east and south direction, the concentration decreases very significantly away from the landfill. By contrast, there is no obvious decreasing trend of the pollutant concentrations in the north direction. Combined with the variation of the different chemical composition and pollutants in shallow aquifers (Fig.5a–f), it indicates 3436Environ Monit Assess (2013) 185:3413–3444 that leakages from the landfill into the aquifer have developed in different directions and to different extents.

Generally, as the groundwater table rises in the winter season, pH lowers and the concentration of organic compounds (especially PAHs) increases, compared to those in the summer season. Large fluctuations in PAHs and BTEX concentrations in individual boreholes were shown to be largely attributable to seasonal groundwater flow variations, which can affect microbial and chemi- cal reaction that organic pollutants undergo and the transport of gases and solutes through aquifer.

The sediments towards the north of the landfill, belonging to the southern margin of the Yellow River paleo-alluvial fan, are composed of coarse grains, including medium-fine grained sand and are known to bear better quality water. This groundwater has been utilized for vegetable planting by local farm- ers, and as a result of groundwater exploitation, the natural flow field has changed, causing wastewater from the landfill to flow towards the north. The lower chloride concentrations (Fig.5a) of groundwater in south portions of the aquifer relative to the leachate plume are consistent with mixing of leachate withuncontaminated groundwater. The natural attenuation and/or mixing with fresh water can be shown from the chloride variation. In contrast, the sediments in the south of the landfill belong to the bank of Huaihe River and are characterized by fine grains, including silty clay and clay, which can prevent contamination from spreading due to lower permeability. The farmers in the south of the landfill must plant wheat because there is less groundwater available for irrigation. As a result, there is little groundwater abstraction. Local anthropogenic pollution input may have caused the high NO 3− and SO 42− in east–south of the study area (such as DW18). In the western part of the study area, groundwater discharges into the Jialu River. The dis- tribution characteristics of PAHs and BTEX are dif- ferent from other inorganic chemical composition. The highest concentration of PAHs is distributed some 300 m SE of the landfill, while BTEX is highest at the NW corner of the landfill.

Only CAHs were detected in the river water sam- ples (SUJL and SUY) in May 2009. This indicates that river water can become contaminated during the sum- mer period. CAHs, MAHs, and OCPs, with the excep- tion of PAHs, were detected in the sewage water samples (SULG and SULD) to different extents during the multiple sampling campaigns. Lower detection frequencies of CAHs, MAHs, and OCPs and higher PAHs concentrations in groundwater than that in river and sewage ditch suggest that there is no inflow of polluted groundwater into the stream, and the contam- inated river and waste water from sewage ditch are generally not recharging the groundwater body. That is, the interaction between groundwater and the sur- face water is likely weak. The municipal waste water emission and the agricultural irrigation return flow into the river and the sewage ditch could be sources of surface water pollution upstream; however, the Fig. 13Variation of different contaminants in different directions Fig. 12Variations of PAHs concentrations with distances from the landfill center Environ Monit Assess (2013) 185:3413–34443437 landfill body is the main pollution source for ground- water contamination in the study area.

Vertical distribution of organic pollution In the contaminated area (dashed line, Fig.1), the waste dump is immersed in groundwater. A ground- water mound has formed at the landfill site and dif- fused into the surroundings. Local water table gradients just below and around the landfill may differ from the general gradients because the landfill may have a different hydrogeology than the surrounding strata (Christensen1992). The unlined Zhoukou land- fill without any top cover may result in a larger infil- tration than in the surrounding soil, and if leachate is not removed quickly, this may result in a local water table mound potentially affecting the local gradients.

Local mounding effects are enhanced lateral spreading of the leachate plume and to downward directed hy- draulic gradients in the groundwater zone beneath the landfill. The enhanced lateral spreading of the plume may increase the volume of contaminated groundwa- ter and its spatial extent, but provides increased dilu- tion of contaminants.

Controlled by aquifer heterogeneity, contaminated groundwater has reached the shallow aquifer to depths of 13–25 m, which is composed of fine and middle sand with hydraulic conductivity of 11–12 m/day (Qu 2010). The results show that, near the landfill, the shallow aquifer within 25 m depth has been contami- nated, but not the deeper aquifer at 50 m depth. Thedeepest well, ZK1 at 300 m depth, was not contami- nated by organic pollutants, with the exception of 0.44μg/L toluene, which may have resulted from regional groundwater flow. Additionally, water sam- ples from the monitoring wells (such as ZKW and Z16) near the gas station (Fig.11b) were not detected to have higher Phe and Nap, which are plentiful in fresh fuels (Colombo et al.2005a,b;Iturbeetal.

2005). Therefore, their nonprevalence in groundwater seems to show no recent leaks of petroleum products from tanks and pipelines.

The main conclusion can be drawn that based on the organic contaminants distribution of different wa- ter bodies, the interaction between groundwater and the surface water (including water from the river, gully, and sewage ditch) is probably weak in this area.

The landfill body is hence the main pollution source for groundwater contamination. However, Municipal waste water emissions and agricultural irrigation re- turn flow into the river and the sewage ditch could be the source of surface water pollution upstream.

Quality assessment and conceptual model River water and groundwater monitoring together with the analysis of the organic pollutants demonstrated that the landfill leachate is significantly impacting on the surrounding aquatic environments. PAHs are the major pollutants in groundwater surrounding the Zhoukou landfill and can be used to evaluate ground- water quality. Compared with PAHs concentrations Table 9PAHs concentrations in surface water reported in the world YearNRange(ng/L) Mean ± SD(ng/L) References River water:

Jialu and Ying River December 2009 6 nd–10 60 ± 107.3 This study Hai River, Tianjin, China 16 115 ± 58.2 Shi et al.2005 Tonghui River, Beijing, China 2002.Apr 16 193–2,651 762 ± 777 Zhang et al.2004 Middle and lower Yellow River, China 2004.Jun 15 179–369 248 ± 78 Li et al.2006 Xihe River, China 2006,Aug. 11 26–384 151 ± 22 Song et al.2007 Gaoping River, Taiwan, China 1999/2000 16 10–9,400 430 Doong and Lin2004 Lower Mississippi River, USA 1999 13 5.6–68.9 40.8 ± 32.9 Mitra and Bianchi2003 Elbe River, Hamburg, Germany 1992/1993 16 107–124 116 ± 12 Götz et al.1998 Lower Seine River, France 1993.Oct 11 4–36 20 ± 13 Fernandes et al.1997 Lower Brisbane River, Australia 2001/2002 15 5–12 8.2 ± 3.0 Shaw et al.2004 Malaysian River, Malaysia 2009 3,925–5,126 4,682 ± 238 Geik et al.2009 Nnumber of PAH compounds analysed in each study 3438Environ Monit Assess (2013) 185:3413–3444 reported for other contaminated rivers in China, USA, Germany, Australia, and other countries (Table9),Jialu and Ying river water in this study area are char- acterized by relatively lower PAHs concentrations Fig. 14Conceptual diagram of leachate migration in the Qua- ternary aquifers surrounding the Zhoukou landfill. The data of geological background is referenced from Qu (2010). The groundwater zone contaminated by leachate is determined bythe distribution of the total PAHs concentrations in groundwater samples. The boundary line of the contaminated zone is the contour of total PAHs concentration 0.1μg/L, which is the maximum permissible value of the WHO standard Environ Monit Assess (2013) 185:3413–34443439 (<0.01μg/L), indicating light organic contamination in river water. The groundwater close to the river bed should be diluted with lower PAHs concentrations if this was a major recharge source in the wet season.

However, Z16 is featured by higher PAHs concentra- tion (1.07μg/L) in May 2009 than that (0.33μg/L) in December 2009, suggesting that the groundwater re- charge from river water is horizontally very limited within short distances and that the dominant driver of groundwater flow and contaminant migration is the groundwater mound surrounding the landfill.

Figure14shows the conceptual model of leachate migration in the Quaternary aquifers surrounding the Zhoukou landfill. There is a groundwater mound dif- fused into the surroundings at the landfill site. The levels of PAHs were generally higher in the vicinity of the landfill. Based on the distribution of PAHs concentra- tions in groundwater along the NS and WE hydrogeo- logical cross-sections (Fig.14a-b), the groundwater zone contaminated by leachate can be circled by the contour of total PAHs concentration 0.1μg/L, which is the maximum permissible value of the WHO standard.

The results suggest that groundwater beneath the Zhoukou landfill and within 50 m depth is not suitable as a drinking water source, and pollution control should be improved and enhanced in this area (for example, with the construction of artificial liner or providing impermeable clay cover to reduce water infiltration into the waste site). The groundwater contaminated zone varies from May to December. From Fig.14,itcanbe seen that the zone becomes smaller in the W–E direction but has little change in the N–S direction between these times, suggesting anisotropy in the local permeability distribution.

Due to the complexityof leachate migration through landfills, fundamental aspects of subsurface contaminant transport include the thickness of the unsaturated zone, the permeability and moisture con- tent of the earth materials within the unsaturated zone, and the hydraulic conductivity and local hydraulic gradient of geological units in the saturated zone (Taylor and Allen2006). Poorly conductive units un- derlying the landfill, e.g., clay-rich material or the presence of an installed artificial liner can reduce leachate migration. On the other hand, discontinuities of the landfill bottom such as fissures and joints in the subsurface or faults or holes in a liner, dramatically increase leachate flow. Access to hydrogeological in- formation is thus vital for situation assessments anddesigning lining systems both beneath and down- stream of landfills. With the gradual expansion of the Zhoukou city area, the landfill has been surrounded by urban planning area. If the local government does not take preventive measures, the existing waste will con- tinue long-term groundwater contamination. Long- term detailed monitoring programs are essential to develop conceptual models of natural attenuation, and studies need to allow the recognition that our understanding of microbial transformation pathways is constantly changing.

Conclusions and environmental implications The investigation of organic contamination around Zhoukou landfill shows the present status of pollution in sediments and surface and groundwater. This paper has provided important data on parent PAH levels and other organic contaminants in the water and sediments of the Zhoukou landfill in Henan Province, China.

Some conclusions can be drawn as follows:

1. The main source and pathway for organic contam- ination is infiltration of rainfall in the vicinity of the landfill, which has created a local groundwater mound.

2. Detected organic contaminants include MAHs, CAHs, OCPs, and PAHs. The concentrations of these compounds are affected by seasonal ground- water table fluctuations. PAHs are the main organ- ic contaminant in this study area. Among the detected eleven PAHs, Phe, Flu, and FLT identi- fied by PCA are the three dominant in most of the groundwater samples. PAH diagonostic ratios, in- cluding FLT/Pyr, FLT/(FLT + Pyr), Phe/Ant, and CHR/BaA, suggest the mixture of petrogenic and pyrolytic contaminations of groundwater near the Zhoukou landfill.

3. Higher NO 3− concentrations and lower pH values under aerobic conditions enhance degradation of PAHs in December, resulting in lower PAHs and HCO 3-concentrations.

4. The organic contaminants detected from different water bodies show that the interaction between groundwater and the surface water (including wa- ter from the river, gully, and sewage ditch) is weak in this area. The landfill body is the main pollution source for groundwater contamination in this 3440Environ Monit Assess (2013) 185:3413–3444 study area. The municipal waste water emission and the agricultural irrigation return flow into the river and the sewage ditch could be sources of surface water pollution upstream.

5. Based on the PAHs concentrations distribution, a conceptual model of leachate migration in the Quaternary aquifers surrounding the Zhoukou landfill has been developed to describe the con- tamination processes. The groundwater zone con- taminated by leachate has been identified surrounding the landfill. An oval-shaped pollution halo has formed, spanning 3 km from west to east and 2 km from south to north, and mainly occurs in the area with groundwater level depths of 2– 4 m. High detection rates of contaminants (espe- cially PAHs) in groundwater from the shallow aquifer at 18–30 m indicate that it has been heavi- ly contaminated. The deeper aquifer at depths >50 m has not yet been contaminated by organic pollutants. The existence of clay and silty clay layers with stable thicknesses at about 20 m (30– 50 m depth) may contribute to these results.

In order to comprehensively evaluate groundwater quality and protect drinking water, it is important to investigate spatial and temporal distributions of organ- ic pollution in the subsurface environment. The find- ings point to an urgent need to establish a robust monitoring procedure for persistent organic pollutants such as PAHs, not only in water bodies and sediments but also in the relationships between microorganisms, and in regards to aquifer physico-chemical parameters.

Any exceedance in organic pollutant concentrations over the environmental quality standards should be rapidly reported and the necessary actions taken to mitigate the effects. Additionally, it is necessary to improve urban sewage facilities, such as establishing underground sewage pipes and implementing antisee- page treatments along the sewage ditches, in order to reduce leakage of landfill leachate. AcknowledgmentsThis research was financially supported by the Exploratory Forefront Project(no. 2012QY007) for the Strategic Science Plan in the Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, and was un- dertaken as part of a groundwater survey project titled“Investiga- tion and evaluation of typical contaminated sites in Zhoukou region of Huaihe River Plain”(no. 1212010634505). The authors are grateful to Mr. Xie Shiyong and Qu Zewei from School of Envi- ronmental Studies, China University of Geosciences, for their help and support during water sampling in the field and data collection. References Akyüz, M., & Çabuk, H. (2010). Gaseparticle partitioning and seasonal variation of polycyclic aromatic hydrocarbons in the atmosphere of Zonguldak, Turkey.Science of the Total Environment, 408, 5550–5558.

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