using s and pb isotope ratios to trace leaching of toxic substances from an acid-impacted...
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Journal of Hazardous Materials 235– 236 (2012) 54– 61
Contents lists available at SciVerse ScienceDirect
Journal of Hazardous Materials
j our na l ho me p age: www.elsev ier .com/ locate / jhazmat
sing S and Pb isotope ratios to trace leaching of toxic substances from ancid-impacted industrial-waste landfill (Pozdatky, Czech Republic)
artin Novaka,∗ , Petra Pacherovaa, Lucie Erbanovaa, Alain J. Veronb, Frantisek Buzeka, Ivana Jackovaa,omas Pacesa, Lenka Rukavickovaa, Vladimir Blahaa, Jan Holeceka
Czech Geological Survey, Geologicka 6, 152 00 Prague 5, Czech RepublicCEREGE UMR CNRS, Universite Aix-Marseille, Europole Mediterraneen, BP80 Plateau Petit Arbois, 13545 Aix en Provence, France
i g h l i g h t s
S and Pb isotopes are useful tracers of polluted groundwater movement.Large ranges of found ı34S and 206Pb/207Pb ratios made source apportionment robust.ı34S values higher than 6.5 permil indicated contamination.Pb in stream sediment recorded landfill leaks, but was insensitive to air pollution.The front of polluted groundwater plume in fractured plutonic rocks spread unevenly.
r t i c l e i n f o
rticle history:eceived 18 January 2012eceived in revised form 8 June 2012ccepted 10 June 2012vailable online 22 July 2012
eywords:oxic waste
a b s t r a c t
Slightly elevated concentrations of toxic species in waters sampled in the surroundings of a leaky landfillmay be both a sign of an approaching contaminant plume, or a result of water–rock interaction. Isotopescan be instrumental in distinguishing between anthropogenic and geogenic species in groundwater. Westudied sulfur and lead isotope ratios at an abandoned industrial-waste landfill, located in a denselypopulated part of Central Europe. Stable isotope variability in space and time was used to follow themovement of a groundwater plume, contaminated with toxic metals (Cd, Cr, Be), in fractured granitoids.Toxic metals had been mobilized from industrial waste by a strong pulse of sulfuric acid, also deposited
34 206 207
sotopesulfureadeachingin the landfill. Both tracers exhibited a wide range of values (ı S between +2.6 and +18.9‰; Pb/ Pbbetween 1.16 and 1.39), which facilitated identification of mixing end-members, and made it possibleto assess the sources of the studied species. In situ fractionations did not hinder source apportionment.Influx of contaminated groundwater was observed neither in irrigation wells in a nearby village, nor atdistances greater than 300 m from the landfill. Combination of stable isotope tracers can be used as partof an early-warning system in landscapes affected by landfills.
. Introduction
Abandoned industrial-waste landfills may represent a long-erm threat to the environment [1]. Uncontrolled leaching of toxicolutes is often viewed as a time bomb [2], especially in denselyopulated industrial regions, such as the Czech Republic. This Cen-ral European country experienced 40 years of poorly managed,entrally planned economy (1948–1989), followed by “wild earlyapitalism” in the 1990s [3]. Typically, shallow monitoring wells
n the vicinity of abandoned landfills ceased to be functional sev-ral years after the closure of the operation. If no increasing trendn the concentrations of pollutants was detected, hydrochemical∗ Corresponding author. Tel.: +420 251085333; fax: +420 251818748.E-mail address: [email protected] (M. Novak).
304-3894/$ – see front matter © 2012 Elsevier B.V. All rights reserved.ttp://dx.doi.org/10.1016/j.jhazmat.2012.06.018
© 2012 Elsevier B.V. All rights reserved.
monitoring was also discontinued. Fears persevere that a contam-inated groundwater plume may reach nearby human settlements.
Various geochemical tracers, such as stable isotope ratios, canserve as early-warning tools in the vicinity of landfills [4–6]. Pre-vious studies have shown that the complexity of the movementof a polluted plume may require several tracers to resolve theorigin and transport pathways for individual contaminants [7].Stable isotope compositions provide another type of concentra-tion information, independent of the bulk pollutant concentration.Attempts have been made to use stable isotopes at more remotesampling sites around point sources of pollution to identify theapproaching pollutant plume [8]. The concentrations of pollu-
tants may still fall in the range of their natural abundances, butchanging isotope composition already signals approaching con-tamination. Water–rock interaction, especially at sites where thegroundwater residence time is relatively long, may enrich the
M. Novak et al. / Journal of Hazardous Materials 235– 236 (2012) 54– 61 55
Table 1Study site characteristics.
Site characteristics
Elevation (m) 465–496Location N 49◦11.75007′ , E 15◦56.83685′
Mean annual precipitation (mm) 560Mean annual temperature (◦C) 9.6Waste repository area (m2) 10,400Watershed area (m2) 106,000
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Table 2Amounts of toxic materials deposited at Pozdatky in 1994–1997.
Type of material Mass (t)
Green vitriol 8330Sulfuric acid 1470Asbestos 2280Leather processing residues 2430Crude-oil contaminated soil 1020Paints 230
Bedrock DurbachiteSoil Sandy loam
olute in potentially toxic ions [4]. These just slightly elevated con-entrations can be successfully identified as geogenic by isotopeeasurements. One prerequisite in such studies is that the mixing
nd-members of anthropogenic and geogenic origin have contrast-ng isotope signatures [9]. Also, we should be aware of possiblesotope fractionations in the ecosystem, these fractionations muste quantified. In situ isotope fractionation may hamper applicationf mixing models [10,11].
Here we present sulfur (S) and lead (Pb) isotope data collected atn abandoned industrial-waste landfill at Pozdatky (Moravia, Czechepublic, Central Europe). In a 6-year study, we used a combinationf isotope and concentration measurements to obtain an insightnto the spatial and temporal dynamics of the pollutant plume. Over
years of operation, 50 different types of toxic industrial waste hadeen deposited in the landfill, containing a number of acid-solubleetals and metalloids (e.g., Cr, Cd, Pb, Cu, Ni, Zn, As, Sb, Co, and Hg).
he extreme environmental impact of this site was caused by theact that metal-rich waste formed intercallations in sulfuric acidoaked green vitriol (FeSO4·7H2O), a residue from the productionf pigment white. Green vitriol represented over 40% of the entireass of the deposited waste. Following each precipitation event,
ome of the 1470 t of the deposited concentrated sulfuric acid wereobilized and facilitated leaching of toxic metals into groundwa-
er. Based on eyewitness reports, the construction of the landfilln 1993 was flawed. Coarse-grained regolith was used, instead oflay, as an isolating layer, and the plastic bottom liner had numer-us leaks. The bottom of the landfill was situated underneath theroundwater table. Bedrock was comprised of tectonically-affectedurbachite (an ultrapotassic plutonic rock). Groundwater move-ent in rocks with fracture-controlled permeability (in contrast
o sedimentary rock aquifers) is difficult to predict. Two villagesre located downgradient from the landfill in the distance of mere00–900 m. These features make Pozdatky an intriguing, complexite, potentially representing a serious threat to local community.
Our main objective was to test the usefulness of the stable iso-ope tracers as an early-warning tool in the vicinity of an abandonedandfill containing toxic industrial waste. Our second objective waso quantify the effect of sealing of the landfill’s surface on waterhemistry. We also drilled and studied several new wells in areasf suspected movement of the contaminated groundwater plume.
. Materials and methods
.1. Study area
The industrial-waste landfill Pozdatky (Table 1) is situated 4 kmoutheast of the city of Trebic, Moravia, southeastern Czech Repub-ic. The landfill was opened in July 1994, and closed in January 1997.n the mid-1990s, 23 thousand t of mainly industrial waste wereeposited at the site. The volume of the waste was 16 thousand
3. Table 2 gives the main types of the deposited waste material.he 1470 t of concentrated sulfuric acid were deposited in the land-ll illegally, and by mistake. Acidic waters spilled over the basin’sdge (10 m above ground) following major precipitation events in
Catalyzers 130Chromium-rich waste 290
December 1997 and September 2000, and state authorities repeat-edly declared State of Emergency. Since 1997, an area of 1500 m2
downslope has been covered by a 20 cm thick crust of Fe oxyhy-droxides, with no vegetation. The surface of the abandoned landfillwas covered by impermeable, sealed plastic sheets in 2004. Thebedrock (Variscan durbachite) is weathered to a depth of 1–2 m.
Fig. 1 shows the position of the landfill relative to nearby streamsand human settlements. The landfill is situated on a hill overlook-ing the stream of Prasinec, a tributary to Markovka just upstreamof the village of Dobra Voda (north of the landfill). A second vil-lage, Pozdatky, is located northeast of the landfill. Farmers in bothvillages use wells to irrigate fruit and vegetable gardens.
2.2. Hydrogeology
There are three main aquifers in the study area: (i) durbachiteweathering zone, plus neogene and quaternary sediments form ashallow aquifer with a high hydraulic conductivity. Near the land-fill, the shallow aquifer has a free water table at a depth of 0–6 m.The aquifer may be locally confined, due to occurrence of lenses ofNeogene clay. The water table level is highly variable. (ii) Subsur-face fractures form a second aquifer down to a depth of 50–100 m.Horizontal and subhorizontal fractures are common, but irregularlyspaced, in the topmost 50 m of durbachites. Both free and confinedwater table occurs, depending on the degree of openness of thefractures. The water table level is less variable compared to aquifer(i). (iii) A deep aquifer in the Trebic Massif is spatially related tolarge-scale permeable tectonic zones.
2.3. Geophysical investigations
In 2005, a geophysical survey was performed in the study area[12]. The used methods included symmetrical resistivity profiling(SRP), and vertical electrical sounding (VES). SRP was performed onan area of 400 by 500 m around the landfill, reaching a depth of 15 mbelow surface. Sites for VES were selected along the zones of shal-low groundwater movements, as indicated by SRP. The investigateddepth for VES was 40–50 m below surface. The results of the geo-physical survey are presented in a geological map in the ElectronicAnnex (Fig. S1). The main tectonic features agree well with previousgeological mapping [13]. A tectonically-affected, presumably morepermeable, zone was identified, passing the landfill 100 m downs-lope and extending to the northeast (Fig. 1b). The tectonic zone endsbetween village of Dobra Voda (north of the landfill) and the villageof Pozdatky (northeast of the landfill). In 2006, we positioned ournew boreholes on this tectonic zone (see below).
2.4. Previous hydrochemical research
The Environmental Protection Agency performed chemical anal-ysis of environmental waters in the area on several occasions priorto the beginning of our project. Following spill-overs of contami-nated landfill waters (years 2000 and 2001), the stream water at
56 M. Novak et al. / Journal of Hazardous Materials 235– 236 (2012) 54– 61
Markovka
Prasinec
Pozdatky
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forests
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Roofed
landfill
surface runoff
Prasinec
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CzechRepublic Pozdatky
Fig. 1. Location of the industrial-waste landfill.
Table 3Types of samples.
Sample type Sample description Number of sites Sample I.D.s
Atmospheric deposition Open area precipitation 1 AD 1Atmospheric deposition Spruce canopy throughfall 1 AD 2Solutes from the landfill drainage system In the proximity of the landfill 1 DS 1Solutes from the landfill drainage system Near surface concrete collectors downslope 4 DS 2–DS 5Pre-2002 monitoring wells Between landfill and Prasinec stream (fenced-off) 9 GW 1–GW 9Stream water Markovka and Prasinec up stream of the contamination source 2 SW 1, SW 4Stream water Prasinec downstream of the contamination source 2 SW 2, SW 3Stream water Markovka downstream of confluence with Prasinec 1 SW 5Groundwater from new monitoring wells (drilled in 2006) Farmland north of the landfill in the direction to village Dobra Voda 4 GW 10, 11, 12, 14
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samples for anion analysis were transported to the laboratoryunacidified. Sulfate concentrations were determined on a Knauer-1000 liquid chromatograph. Sulfur for ı34S determinations wasprecipitated from water as BaSO4 and converted to SO2 [16]. The
Table 4Depths of monitoring wells and levels of groundwater table.
Well I.D. Well depth (m) Water table depth (m)
GW 1 5.2 4.8 ± 0.1GW 2 4.5 2.4 ± 0.5GW 3 6.8 2.1 ± 0.3GW 4 15.5 2.5 ± 0.2GW 5 15.4 3.9 ± 0.3GW 6 6.1 2.6 ± 0.2GW 7 6.0 2.5 ± 0.1GW 8 11.2 1.4 ± 0.1GW 9 5.7 1.0 ± 0.1GW 10 5.5 4.0 ± 0.3
Groundwater from new monitoring wells (drilled in 2006) Upslope of the landfiMineral water (abandoned spa in Dobra Voda) 8 m deep well in theFarmer’s wells in the village of Dobra Voda Private well used to
he nearest point of Prasinec had a pH of 1.9–3. Over 40 mg L−1 ofO4
2− were detected in stream water [14].
.5. Sampling
Water sampling for the current study was performed between005 and 2010 on an area of 72 ha (Fig. 1). The following typesf samples were collected: atmospheric deposition, solutes fromhe landfill drainage system, groundwater from the shallow pre-002 monitoring wells in the fenced-off area, groundwater fromhe new monitoring wells drilled in 2006 on the surrounding farm-and, stream water, mineral water in a spa, and farmers’ wells inhe village of Dobra Voda. More detailed description of individualample types is given in Table 3.
In all, 125 water samples were analyzed for S isotope composi-ion (ı34S), and 35 samples for Pb isotope composition (206Pb/207Pbnd 208Pb/207Pb). Chemical analysis (major species and trace ele-ents) was performed on a total of 360 water samples.The collectors used for monthly cumulative sampling of rainfall
ere described by [15]. The total depths of all monitoring wells areiven in Table 4, along with depths of the groundwater table. Theewly drilled well GW 12 reached the depth of 56 m, groundwater
rom GW 12 was sampled from two depths, 40 and 50 m, separately.he average depth of the remaining 13 wells was 7.6 m. The aver-ge depth of the groundwater table in these wells was 2.7 m below
urface. Prior to sampling, water from each well was pumped andiscarded. Sampling of solutes for chemical and isotope analysisas performed 24 h later, 0.75 m above the bottom of each well, sohat the collected samples would correspond to the conditions in
1 GW 13e 1 GW 15te vegetable gardens 2 GW 16, GW 17
the aquifers. Stream sediments were sampled for Pb isotope anal-ysis near sites SW 3 (Prasinec), and SW 4 (Markovka) in 2006. In2007, redox potential was measured in 15 monitoring wells fol-lowing a 24-h equlibration. A total of 25 Eh measurements wereperformed in solutes dominated by Fe2+.
2.6. Analysis
Water samples for cation analysis were acidified in the field,
GW 11 5.9 2.2 ± 0.2GW 12 56.3 7.3 ± 0.3GW 13 5.8 2.8 ± 0.1GW 14 5.6 2.7 ± 0.1
M. Novak et al. / Journal of Hazardous Materials 235– 236 (2012) 54– 61 57
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ig. 2. Effects of sealing on water chemistry. Sealing of the surface by plastic liners iefore and following the sealing.
34S values were determined on a Finnigan MAT mass spectrometerith a reproducibility better than 0.3‰. The results were expressed
s a ‰ deviation of the 34S/32S ratio in the sample from the V-CDTtandard. Prior to Pb isotope analysis, water and stream sedimentamples were processed in a clean lab (class 7). The samples under-ent acid dissolution and pre-concentration using anion-exchange
olumns (BioRed-AG-1-x8 resin). Purified samples were loaded one-filaments with silica gel and phosphoric acid [9]. 206Pb/207Pbnd 208Pb/207Pb ratios were measured by TIMS (Finnigan MAT 262).or calibration, the NIST SRM981 standard was used. The RSD valuesere near 0.02%.
Concentrations of As, Be, Cd, Co, Cr, Cu, Mo, Ni, V, and Pb wereetermined using ETAAS. Concentrations of Na, K, Ca, Mg, Mn, Zn,nd Fe were measured by AAS. Further analyzed species includedH4 (photometry), F (ion-selective electrode), Cl and NO3 (HPLC),nd alkalinity (Gran-titration).
. Results
.1. Time-series of pollutant load
Fig. 2 shows temporal trends in the concentrations of selectedajor and trace constituents. The sampling sites included the wellW 1, situated 15 m north from the landfill in the direction of theigh-permeability zone, and two drainage collectors downslopeDS 2 and DS 3), located 15 and 200 m from the landfill, respec-ively (Fig. 1a). In Fig. 2, annual mean concentrations of SO4, Fe,d, Cr, V and Co are given. Two values are given for the year 2004,re- and post-sealing. GW 1 and DS 2 exhibited a clear-cut down-ard temporal concentration trend for all species. No decrease in
oncentrations of toxic species was observed at the more remoterainage site, DS 3. The DS 3 pollution load was lower compared toW 1 and DS 2 in 2002, but not in 2006.
Fig. S2 in the Electronic Annex shows a decrease in concentra-ions of Ni, Cu and Zn in GW 1 and DS 2, but not DS 3, following theealing of the surface of the landfill.
Sulfate concentrations peaked in 2003 (80 g L−1 in GW 1), and
ecreased 15 times by 2009. More detailed, monthly, SO4 concen-ration data are given in the Electronic Annex (Fig. S3). Dissolvedron concentrations peaked also in 2003 (14 g L−1 in GW 1), andecreased 7 times by 2009 (Fig. 2). As seen in a pH–Eh diagramked by a gray vertical band. Two mean values are given for the year 2004, for period
(Fig. S4), redox conditions in most monitoring wells led to precipi-tation of FeIII.
Table 5 summarizes the concentrations of sulfate and other con-stituents in 9 wells (six monitoring wells, mineral water in DobraVoda, and two village wells used for irrigation). Average values forthe 2006–2010 period are presented. SO4, FeII, Cd, Cr, Co, Ni, Be andV concentrations dramatically exceeded safety limits in GW 1 [17].With an increasing distance from the landfill, the number of ele-vated elemental abundances decreased. In the high-permeabilityzone northeast of the landfill, only one well (GW 10; 200 m fromthe landfill) exhibited elevated concentrations of one element (Fe).At all sampling sites more distant from the source of pollution thanGW 10, all species were within the safety limits. Downslope fromthe landfill, GW 7 was less polluted than the more distant GW 8and GW 9.
3.2. Sulfur isotope composition of water
A wide range of ı34S values between +2.7 and +18.5‰ wasobserved. The entire data set, along with sulfate concentrations,is given in Table S1. It has been shown that mixing of isotopicallydistinct end-members can be best illustrated by a ı34S vs. 1/[SO4]plot, where [SO4] is sulfate concentration [18]. In such plots, obser-vations at various sampling sites form a straight line whenever theyresult from mixing of two isotopically distinct end-members withconstant initial concentrations. An overall ı34S vs. 1/[SO4] plot isshown in Fig. 3, a more-detailed graph for high sulfate concentra-tions is in Fig. 4.
Atmospheric input had low ı34S values (as low as 2.7‰, meanof 5.6‰; Fig. 3; throughfall < open-area precipitation). In contrast,heavily polluted waters sampled downslope from the landfill hadhigh ı34S values (up to 9.1‰, mean of 8.1‰). Other groundwatersand stream waters had slightly lower ı34S values. The Dobra Vodamineral water, sampled in a well inside a dilapidated, early 20thcentury spa building, exhibited a peculiar pattern of a steep straightline in the ı34S vs. 1/[SO4] plot (Fig. 3). The mineral water samplewith the most diluted sulfate had the highest ı34S (18.5‰).
3.3. Pb isotope systematics
Fig. 5 depicts a three-isotope plot of 206Pb/207Pb vs. 208Pb/207Pbratios for waters and stream sediments. The entire data set is
58 M. Novak et al. / Journal of Hazardous Materials 235– 236 (2012) 54– 61
Table 5Contrasting concentrations of toxic trace elements in groundwater downslope of the waste repository and in broader environs. Mean concentrations between 2006 and 2010.Values exceeding by more than 10% of the safety limits for groundwater are given in bold.
GW 1 GW 6 GW 7 GW 8 GW 9 GW 10 GW 12 GW 14 GW 15 GW 17
pH 3.10 4.80 6.90 4.70 4.70 6.40 7.10 6.20 7.50 6.70SO4
2− mg L−1 5070 740 110 170 850 170 28.0 47.0 10.0 92.0Fe2+ mg L−1 1970 0.80 0.35 3.20 50.0 3.90 1.00 1.15 0.20 0.30Cd �g L−1 39.0 3.10 0.04 1.00 1.00 0.20 0.04 0.06 0.04 0.05Cr �g L−1 5540 5.70 1.90 6.20 2.20 3.65 1.20 9.20 1.10 2.20Co �g L−1 800 105 0.90 38.0 110 2.30 2.90 2.0 0.80 1.20Ni �g L−1 1650 180 19.0 74.0 15Be �g L−1 5.30 4.30 0.03 0.90
V �g L−1 3630 34.0 5.00 5.00
c11(h
40 and 50 m below surface. While the deep well GW 12 showed
Fig. 3. S isotopes systematics.
haracterized by a wide range of 206Pb/207Pb ratios, from 1.16 to
.39 (Table S2). A mixed sample of atmospheric depositions (AD+ AD 2) had the lowest (least radiogenic) Pb isotope signature1.16). GW 11 and GW 13, situated in the farmland in the zone of aigh-permeability (southwest–northeast; Fig. 1), had similarly low
Fig. 4. S isotopes systematics (a detail).
0 18.0 11.0 17.8 3.70 37.01.60 0.06 0.08 0.04 0.06 0.055.00 5.00 6.70 5.00 5.00 5.00
206Pb/207Pb. Groundwater samples collected close to the landfill fellin the middle of the observed range (1.25–1.30). GW 4 and GW 6had the highest 206Pb/207Pb ratio (most radiogenic Pb). Stream sed-iments collected from Prasinec and Markovka, just upstream fromconfluence, had contrasting 206Pb/207Pb signatures (1.23 and 1.36,respectively).
4. Discussion
4.1. Groundwater in the southwest–northeast tectonic zone
The geophysical survey, performed in 2005, had indicated thepresence of a southwest–northeast zone of fractured crystallinebedrock [12]. This zone, presently covered by farmland, runs justnorth of the landfill and approaches the villages of Dobra Voda andPozdatky (Fig. 1). Our new deep well GW 12, situated in this zone,yielded water in three separated depth intervals: near the surface,
no signs of contamination, the adjacent well GW 10 (depth of 8 m)had slightly elevated Fe concentrations (Table 5). Sulfate concentra-tions in GW 10 were 170 mg kg−1, which falls within the safety limit
2.40
2.45
2.50
2.55
2.60
2.65
1.10 1.15 1.2 0 1.2 5 1.3 0 1.3 5 1.40
Markovk a sediment Prasinec sediment
206 207Pb/ Pb
208
207
Pb/
Pb
anthropogenic
geogenic
Fig. 5. Pb isotopes systematics.
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M. Novak et al. / Journal of Hazar
300 mg kg−1), but is more than in many other wells (Tables 5 and3). The front of the contaminated groundwater plume, if indeedoving to the northeast, has not reached GW 11 and GW 14 (ca.
00 m from the landfill). In the worst-case scenario, assuming aonstant rate of the movement of the plume front, and no ground-ater dilution, the pollution might reach Dobra Voda in 50 years
fter the landfill operation started, i.e., around 2045 AD. In fact,resence of aquifers, and groundwater movement, in fractured dur-achite is highly unpredictable. Wells closer to the point source ofollution may be less impacted than wells that are more distant.his is illustrated, e.g., by less polluted GW 7, compared to GW 6, 8nd 9.
.2. Are there S isotope fractionations in the system?
An almost linear increase in ı34S with increasing 1/[SO4],bserved in the Dobra Voda mineral water (Fig. 3), is very likely aesult of dissimilatory bacterial sulfate reduction (BSR). This anaer-bic process commonly occurs in groundwater [19], and may haveeen triggered off in the spa aquifer. During BSR, isotopically lightulfur (32S) is preferentially incorporated in the product (H2S, FeSx,r organic matter [11]). Consequently, the residual sulfate becomesnriched in the heavier isotope 34S. The magnitude of the S iso-ope fractionation is large (13‰, Fig. 3), but consistent with similarystems described before [8]. We cannot rule out intermittent ini-iation of BSR in some monitoring wells. However, limited shiftsn ı34S (see the groundwaters field in Fig. 3) may mean that therocess has not greatly changed the SO4/H2S mass balance. At Poz-atky, BSR is not a mechanism of efficient removal of sulfate fromhe groundwater. In the groundwaters field in Fig. 3, S-isotope frac-ionation probably has not obscured S mixing.
.3. Mixing end-members for sulfate
Three main sources may have contributed to sulfate S. As seenn Fig. 4 (gray and black areas), these three sources are isotopicallyistinct. Sulfur isotope composition of one mixing end-member,tmospheric deposition, was measured directly (mean of 5.6‰).he ı34S values of the other two mixing end-members, bedrocknd the deposited waste, were inferred. We were not able to obtainermission to unseal the plastic cover and sample the sulfuric acidoaked green vitriol directly in the landfill. Instead, we repeatedlynalyzed sulfate in samples from DS 1, highly concentrated soluterom the vicinity of the landfill. The resulting ı34S signature of theollutant is close to 8‰ (Fig. 4, top left). The advantage of indirectetermination of ı34S of the pollutant is that the extremely polluteddjacent wells homogenize the end-member S isotope signal ofulk landfill. In case of isotope variability among different batchesf the pollutant, this approach may be even more appropriate thanrab sampling of solids near the landfill surface only.
Neither dissolution of S-containing minerals during the weath-ring, nor sulfate adsorption/desorption in soils fractionate Ssotopes [20]. We attempted to extract S from accessory sulfidesn the bedrock, but no S was recovered. Thus, instead of a directly
easured ı34Sbedrock, we use the average ı34S value of seven crys-alline rocks in the region (1.4‰ [16]) as the mixing end-memberFig. 4, bottom left).
A growing number of studies have shown that sulfide oxidationay account for a large proportion of bulk chemical weathering.
uch data are available from Alpine glacier meltwaters [21–25],arge catchments [26–28], and small headwater catchments [29].
edrock-derived S, however, may not be detected in natural watersn industrial regions with a high atmospheric S deposition. We hadreviously shown that across 13 Central European catchments sim-
lar to Pozdatky, the ı34S of runoff did not correlate with ı34S of
aterials 235– 236 (2012) 54– 61 59
bedrock and that the ı34S of bedrock did not correlate with ı34S ofindividual soil horizons [16]. The ı34S of runoff was closely corre-lated with ı34S of soil SO4
2−, which, in turn, was almost exclusivelyderived from rainfall [16]. Most natural ecosystem S in the pollutedparts of Central Europe is of anthropogenic origin.
In summary, ı34S of S sources at Pozdatky increased in theorder bedrock < atmospheric deposition < landfill. The ı34S differ-ence between each pair of mixing end-members was more that 10times greater than the reproducibility of S isotope analysis (0.3‰).
4.4. Polluted and unpolluted waters according to ı34S
Sulfur isotopes reflect a simple trend of mixing of landfill S withrainfall S, and possibly also with bedrock S. Dilution is accompa-nied by decreasing ı34S (Fig. 4), in addition to decreasing SO4
2−
concentration. In Fig. 4, we identified fields of polluted pre-2002monitoring wells (solid black line), unpolluted waters, includingnew boreholes in the farmland north of the landfill (gray solidline), and village irrigation wells (dotted line). The border lines ofthese fields envelope all data points of a particular type. As seenin Fig. 4, there was some overlap between these operationally-defined fields. Village wells plotted completely in the field of thenew boreholes in the farmland, the chemistry in neither placeexceeded safety limits. Less than a third of the field of pollutedwaters (pre-2002 wells) and of unpolluted waters (encompassingthe new boreholes and village wells) overlapped. In terms of S iso-tope composition, about 25% of data points from the fenced-off area(pre-2002 wells plus landfill drainage) overlapped with data pointsfrom the more remote wells (GW 10–14, GW 16–17). We note that,in Fig. 4, only data points very close to the y-axis exceeded the sul-fate concentration safety limit (300 mg L−1). 72% of the depictedsamples had sulfate concentrations below the safety limit.
The ı34S values of streams helped to distinguish between uncon-taminated and contaminated water (Table S1). Prasinec had ı34Sof ca. 6‰ upstream from the confluence with landfill runoff, and7.5‰ below the inflow of landfill runoff. Prasinec further down-stream had also higher ı34S (7.4‰). Sulfate contamination of thesurface water pushed its ı34S above 6‰. Sulfate concentrations inthe streams were on average below the safety limit of 300 mg L−1.The average SO4
2− concentrations in Prasinec upstream and down-stream from the discharge of landfill runoff (SW 1 and SW 2) weresimilar (170 and 180 mg L−1, respectively), whereas the S isotopedifference (on average +1.5‰ in the landfill-affected water rela-tive to the upstream water) was more pronounced: 1.5‰ is 5 timesmore than the reproducibility of ı34S determinations.
The new monitoring well GW 13, situated near the hill-topabove the landfill (Fig. 1), had one of the lowest ı34S values (3.4‰).Even though this sampling site was mere 10 m from the landfill, Sisotopes clearly showed that no contamination reached this well.Diffusion of sulfate down a concentration gradient did not play arole in this part of the studied area.
We note that two surface waters sampled in spring areas (SW 6and SW 7) had extremely contrasting ı34S values (10.1 and 3.5‰).Since there was a small wetland at SW 6, we can invoke BSR as amechanism that increased ı34S of residual SO4
2+ in this well.Importantly, none of the more-remote sampling sites (such as
irrigation wells) showed a temporal trend in ı34S (Table S1). Wepostulate that S isotopes can be used as an early-warning tool atsuch locations. In the Pozdatky region, increasing ı34S in the mon-itoring wells could signal approaching contamination, but, so far,such situation has not been observed.
Table S3 compares the chemism of Dobra Voda mineral waterand that of an irrigation well. Water in the irrigation well hadmore sulfate and other constituents (except for HCO3
−) than themineral water. At the same time, the chemistry of the irrigation
6 dous Materials 235– 236 (2012) 54– 61
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Well I.D. Conductivity (�S cm−1)
GW 1 8990GW 2 107GW 3 260GW 5 21,500GW 6 1621
0 M. Novak et al. / Journal of Hazar
ells meets all safety standards. If the mineral water in the valleyas the most dilute water in the entire area, is it possible that the
illage irrigation well signaled approaching landfill contaminationfter all? Based on a closer inspection of Table S3, we suggest thatlightly elevated concentrations of a number of species in the vil-age wells (e.g., NO3
−) may result from the application of fertilizersnd manure on the farmland overlooking the village, rather thanrom an approaching pollutant plume.
Sulfur in the studied waters may partly come from the appli-ation of fertilizers as well. Sulfate may constitute up to 50 wt.%f industrial N–P–K fertilizers [30]. Our unpublished data indicatehat cattle farm manure contains about 0.2 wt.% S. Isotopic compo-ition of S in fertilizers used in the Pozdatky region is not known.everal studies have reported ı34S values of fertilizers of around‰ (−3 to +1‰; [30]), but also higher values (up to 21‰, medianf 6‰, [31]). Sources of sulfate for synthetic fertilizers are sulfuriccid with a variable ı34S, and marine evaporites with a high ı34S.
.5. Use of Pb isotopes
Because Pb is a heavy element, isotope fractionations are neg-igible, and Pb isotope composition in present-day environmentan be altered only by mixing. Local durbachite has extremelyadiogenic Pb (a high 206Pb/207Pb of 1.40). The 206Pb/207Pb ration most crystalline crustal rocks does not exceed 1.22 [32]. Theeason for such high ratio in the Moravian durbachite is a rarerimary enrichment of the local lithosphere in uranium. In ourtudy, the higher the 206Pb/207Pb ratio, the more bedrock-derived,on-anthropogenic, Pb is present.
As seen in Fig. 5, Pb isotopes are a useful tool to distinguishetween contaminated and uncontaminated stream sediments.06Pb/207Pb in Prasinec was significantly lower than in Markovka.ven though the Pb concentrations in both sediments were below00 mg kg−1, only the detritic material from Prasinec showedpproaching contamination.
The 206Pb/207Pb ratios of rainfall and concentrated landfilleachates (DS 1) were relatively low (1.16), and indistinguishable.ollowing 800 years of Ag–Pb smelting (206Pb/207Pb of Variscanres is close to 1.16, [9]), atmospheric Pb had the same isotopic com-osition as industrial Pb in the landfill. Atmospheric 206Pb/207Pbas lower than that of natural crustal dust also because of the
ecent use of low-radiogenic Precambrian Pb in gasoline additives1930–2000, [9]). Similar influx of precipitation-derived Pb into
arkovka and Prasinec did not dominate the sediment. The sed-ment was influenced mainly by bedrock (Markovka) and landfilleachates (Prasinec).
Interestingly, groundwater just underneath the landfill (GW 5),ontained as much as one-third of non-anthropogenic, i.e., bedrock-erived Pb. Overall, Pb concentrations in the monitoring wells wereery low (mean of 0.8 mg L−1). This helps to explain the relativelyigh contribution of bedrock-derived Pb in otherwise highly con-aminated solutes mere 15 m from the landfill.
.6. Complementary character of the S and P isotope tracers
In some wells (e.g., GW 6), we found a combination of landfill-erived S with mostly geogenic Pb. These cases illustrate theomplexity of dispersion pathways of pollutants in fractured crys-alline bedrock. We would expect the same landfill leachate to bringoth anthropogenic S and anthropogenic Pb to the monitoring well.
e presently have no explanation to offer for the combination ofnthropogenic, landfill derived S with geogenic Pb in one well. Ineneral, a larger number of tracers reduces the possibility of missinghe first indices of approaching groundwater contamination.
GW 7 1300GW 8 8010GW 9 1630
4.7. Density-driven movement of contaminated groundwater
In general, if the concentration of the total dissolved solids ishigh, the contaminated groundwater plume may have a compo-nent of density-driven flow. A vertically stratified plume migratesdifferently from a less dense plume. As a rule, density-drivenflow becomes significant at electric conductivities greater than10,000 �S cm−1 [33]. Table 6 gives electric conductivities in 9 mon-itoring wells at Pozdatky. All but one (GW 5, situated about 20 mfrom the landfill) exhibited values lower than 10,000 �S cm−1. Weconclude that, in the broader environs of the landfill, the move-ment of the contaminated groundwater plume may not include asignificant density-driven component.
4.8. Export of pollutants
Knowledge of landfill runoff fluxes, and the chemistry of GW 6made it possible to estimate annual export of toxic substances fromthe landfill sub-catchment to the larger Prasinec catchments at thebeginning of our study. These fluxes amounted to 6 t of sulfate and700 kg of Fe2+ year−1. Annual export was estimated to be relativelylow for some other pollutants, e.g., 7 g Cd, 12 g Cr, 10 g Be, and 3 gPb. As seen in Figs. 2 and S2, sealing the surface of the landfill withplastic liners resulted in reduced export of pollutants.
5. Conclusions
We did not detect downgradient dispersion of contaminatedgroundwater in the high-permeability zone in the farmland north-east of the landfill. This direction represented the shortest routetoward nearby human settlements. Similarly, irrigation wells inthe village of Dobra Voda were not affected by the contaminantplume. At the same time, some surface water contamination mayhave reached the Markovka stream at the outskirts of Dobra Voda.Both S and Pb isotopes were instrumental in resolving the move-ment of the contaminated water bodies. Mixing end-members wereisotopically distinct in the case of S. Two types of anthropogenicPb (landfill and rainfall) had identical 206Pb/207Pb ratios. However,given the low Pb abundance in waters and sediments, Pb isotopesprovided a sensitive tool to discriminate between geogenic andanthropogenic Pb.
Clearly, there are limitations when analyzing isotope data frommonitoring wells in the vicinity of toxic-waste landfills. Pos-sible isotope fractionations must be quantified, multiple-tracerapproach is recommended, and sufficiently long time-series ofisotope data are needed. A sampling site may yield background val-ues for one isotope system, and anthropogenic values for anotherisotope system, even if both chemical elements are expected tooriginate mainly from the contaminant groundwater plume.
Acknowledgement
This work was funded by the Scientific Center “Advanced Reme-dial Technologies and Processes” (1M4674788502).
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ppendix A. Supplementary data
Supplementary data associated with this article can beound, in the online version, at http://dx.doi.org/10.1016/.jhazmat.2012.06.018.
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