Natural Isotopes of
18O,
2H and
3H to Study
Leachate Contamination in Bantar Gebang Landfill to Its Shallow Groundwater
E. Ristin Pujiindiyati*
Center for Isotopes and Radiation Application –National Nuclear Energy Agency Jl. Lebak Bulus Raya No.49, Jakarta 12440, Indonesia
A R T I C L E I N F O A B S T R A C T AIJ use only:
Received date Revised date Accepted date Keywords:
Deuterium Tritium Groundwater Leachate
Bantar Gebang Landfill
Municipal landfill located in Bantar Gebang district – Bekasi regency was constructed in 1986 by Jakarta authority that covered area of 108 ha. During its operation, this landfill had often come up some social impacts to local people who claimed for closing it permanently because of pollution generated by waste landfill activities. To confirm whether shallow groundwater surrounding landfill had contaminated by leachate, it was conducted an investigation to trace leachate movement using natural isotopes of 18O, 2H and 3H. Those stable isotopes consisted of leachate are quite unique relative to the aquous media found in most native groundwater such that they can be utilized as tracers. Isotopic value of 2H varied considerably not only between landfills but also seasons. Leachate collected from treatment pond of IPAS-3 in Bantar Gebang landfill had highly enriched in 2H with values as high as +10,3 ‰ in dry season due to the extensive methane production in the limited reservoir of landfill. The recent fill area of Sumur Batu exhibited less enrichment in 2H value of –18.9 ‰. Those values were more enriched 2H in dry season rather than rainy season because of high evaporation and less rainwater input remaining more 2H in leachate. In the other hand, shift of 18O in leachate from local meteoric line was influenced by evaporation process. The highest tritium activity in leachate was 493.89 TU, seemly, it was too high to be explained from previous meteoric water recharging.
Luminescent paints buried in landfill were most probably supposed as source of high tritium content. Based on calculation using deuterium from rainwater and leachate, monitoring well in IPAS -3 with 6m depth had the highest leachate mixing of 32.99% and followed by same location with 15m well depth which had 30.22% mixing. Besides, three people’s pumped wells might have been indicated by leachate impact because of their higher tritium and more enriched deuterium.
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INTRODUCTION
Clean water is one of basic needs for human beings. Mostly, people who live in developing country take groundwater for their daily need from shallow aquifer. Shallow groundwater is generally recharged from local precipitation and surface water such that its availibility and quality strongly depend on the human activities. Since three decades ago, it is indicated that the quality of this water sources decrease gradually as taken place in many metropolitan city like Jakarta and its some
Corresponding author.
E-mail address: [email protected]
supporting areas. The rapid growth of industries and population might have caused in decreasing groundwater qualitiy. Besides shallow groundwater, some people used the water sources from river which had been treated and distributed by Local Drinking Water Company. Survey that was conducted in 2009 by Health Ministry concluded that 48 % of 300 groundwater samples collected in Jakarta, Depok, Bogor, Tangerang, Bekasi and Bandung had been contaminated by coliform bacteria and 50 % of those had lower pH [1].
Other problem relating to rapid population growth as taken place in Jakarta is siting for landfill.
Mostly, local people refuse if their area will be
constructed for solid waste disposal, not only they will inhale polutted air from gas released by organic material decay but also they get afraid if their groundwater will be contaminated by leakage of leachate water. Moreover, they will also have a health problem as impact of landfill activity.
Novotny and Olem (1994) revealed that solid waste disposal is major source after septic tank leakage that contaminates to groundwater in the world and only 6 % of sanitary landfills in USA which was managed well such that they did not impact to enviromental pollution [2].
Bantar Gebang landfill was constructed in Bekasi regency in 1986 by municipal city of Jakarta to load as much as 6500 ton/day solid organic disposal produced by 10.931.207 Jakarta people.
The landfill area is around 108 ha which is consisted of 5 zones and applies a sanitary landfill system where waste is isolated from environmental until it is safe. Although it has equipped with a multi protecting system, local people still doubt of their environmental health whether groundwater in surrounding of landfill that they withdraw for daily needs has been contaminated by leachate [3].
The leachate formed in landfills can be dangerous because of many hazardous substances contained in these areas. For instance, if rain washes over a stack of discarded heavy metals such as Pb, Fe, Cu, Cd, Hg etc, it can transfer those contaminants from the objects to people, plants and animals if those are consumed or contacted. The other secondary pollutions generated from landfills are gases, bacteria content, NO3, SO42-, flies and pets. Decomposition and dissolution of organic waste in landfill site will released some gases such as CH4, H2S, NH3, CO2 because of rapid growth of bacteria under decreasing oxygen content [4]. The offensive odor can be smelled in the distance of 10 km away from Bantar Gebang landfill.
The utilization of area in Bantar Gebang district is 52,6 % for settlements and the rest is for agricultures, rice fields and industries. The rapid growth of industries which taken place in Bekasi increased population as also happened in Bantar Gebang such that as much as 13 % of agriculture areas and 11,6% rice fields of Bantar Gebang change over for settlements. Moreover, the rate of urbanization increased significantly since economic crisis occurred in 1997 and these urban poor built some irregular settlements around landfill area. It is predicted that in 2013 there are more than 7200 scavengers who work by picking some unused things such as plastics, metals, papers from waste disposal of Bantar Gebang landfill [5].
Investigation toward chemical contents (Fe, NO2-, NO3-, Mn, Pb), COD, BOD, and pH in Bantar
Gebang groundwater was carried out by Matahelumual [6] and Environmental Management Centre [7]. They were concluded that the quality of groundwater surrounding landfill was very worst.
This unhealthy environment directly impact to the decreasing local people health. According to profile data recorded in Center for Public Health of Bantar Gebang I, during 2006 -2008 the number of under five-year-old children who suffered diarrhea increased as much as 1.547 cases and totally became 2.980 cases [8]. This disease could be caused by the groundwater they consume had been contaminated by bacteria from leachate leakage of Bantar Gebang landfill.
The investigations to know chemical contents in groundwater and river surrounding Bantar Gebang landfill have been conducted whereas the use of natural isotopes for studying pollutant movement is rarely applied. However, natural isotopes can provide independence means for corroborating and refuting information based on traditional investigations [9,10]. Applications of isotopes in hydrology are based on the general concepts of “tracing”, in which naturally occurring.
Natural isotope (either radioactive or stable) techniques are used to study hydrological processes on large temporal and spatial scales through their natural distribution in a hydrological system. Thus, natural isotope methodologies are unique in local studies of water resources to obtain integrated characteristics of groundwater system. The most frequently used natural isotopes include those of the water molecules, hydrogen (ratio of 2H/1H expressed with 2H or D- also called deuterium and 3H also called tritium), oxygen (ratio of 18O/16O expressed with 18O). 2H and 18O are stable isotopes of the respective elements whereas 3H is radioactive isotopes [10,11]
One of the most important areas where natural isotopes are useful in groundwater applications is fate and transport pollutants like leachate. Pollution of shallow or deep aquifer by anthropogenic contaminants is one of central problems in the management of water resources.
Natural isotopes can be used to trace the pathways and predict the spatial distribution and temporal changes in pollution patterns for assessing pollution migration scenarios and in planning for aquifer remediation. In the case of landfill study, 18O and 2H isotopes were applied to trace a flow pattern of leachate water [10,12,13]. Previously, both isotopes were applied to study the origin and migration of nitrate pollutant in the shallow groundwater of Bantar Gebang landfill [14]. Both isotopes and electrical conductivity were also utilized to trace
leachate movement streamed through Cibitung river and nearest groundwater from that river [15].
This investigation prolonged to previous investigation which was conducted in 2011 but sampling points were selected mainly for shallow groundwater with distances approximately 1-2 km away from landfill sites. The purpose of this investigation is to observe leachate movement to local people wells by tracing their natural isotopes of 18O, 2H and 3H. This investigation is possible to be done because the extreme condition taking place in leachate water will enrich in heavier isotope of 2H.
The positive shifting of 2H is due to hydrogen isotopic changes with methane gas which is produced intensively in leachate ponds. It means that 2H values from leachate fall outside of the ranges associated with natural groundwater [10].
Besides its stable isotopes, tritium activities were also observed in both leachate water and shallow groundwater. Some investigations reported that tiritum content in landfill sites were much higher than natural groundwater such that the anomalous tritium concentration together with 2H value can be used as indication of leachate migration in groundwater surrounding landfill sites [16,17].
EXPERIMENTAL METHODS Location and Sampling Method
Sampling locations for shallow groundwater were selected in radius approximately 1-2 km away from Bantar Gebang landfill and collected from local people bore wells. For having refference values of isotopes, leachate water from Bantar Gebang landfill and Sumur Batu landfill were also collected. Observations were done in March 2013 representing for rainy season and October 2013 representing for dry season. A suite of 18 samples from groundwater, 5 samples from leachate water and 2 samples from river were collected in this observation. Figure 1 showed the sampling location map with dot symbol as groundwater and triangel symbol as leachate water. Some phisical parameters such as electrical conductivity, pH, temperature and Total Dissolved Solid (TDS) were measured as soon as possible in the field.
For sampling 18O and 2H isotopes in water, following steps must be done because water molecules are sensitive to physical process such as evaporation. About 20 mL of water samples were filled into plastic bottle, submerse under the surface of sampled water. Air bubbles must be prevented by flowing the water sample slowly. The bottle are closed carefully until the no air bubble were formed.
Water sampling for tritium analysis didn’t need any
special preparations. One liter of water sample were placed into plastic bottle and capped tightly. All water samples were analyzed in Hydrology laboratorium in Center for Isotopes and Radiation Application – National Nuclear Energy Agency (BATAN)
Analysis Method
18O and 2H analysis
18O and 2H isotopes is measured by liquid water stable isotope analyzer LGR (Los Gatos Research) DLT-100 which is connected to CTC LC- PAL Auto sampler through PTEE transfer line.
Water sample (filtered previously if it is cloudy or countains of sediment) was shaked to equilibrate.
Using the pipette and a fresh tip for every sample, as much as 1 ml water sample was dispensed into appropriate vial glass on the autosampler tray. It is the best to only fill vials at a time, then cap the filled vials (and next sample was open). The same manner was also treated to three kinds of water working standards which each of them had different isotopic composition starting from depleted to enriched 18O and 2H values. Those standard solutions and samples were arranged in a certain order in auto sampler tray such that every three working standards were followed by five samples.
When all the vials were filled and capped, double check that the logbook matched what was the tray.
Principle of liquid water stable isotope analyzer LGR is that a laser beam is directed to vapor sample and a mole fraction of gas is determined from measured absorption using Beer’s Law as a conventional spectroscopy. The molecular concentration of 2HHO, HH18O and HHO are calculated by measuring the amount of absorbance at wavelength of 1390 nm. Each sample is measured six times to obtain good reproduciblity values [18]
and the measurement results are calculated by excel programme.
Isotope ratio value was expressed with delta
(delta) notation in per mill (0/00) and defined as follow:
VSMOW VSMOW measured
R R
R
, “R” notation
is, in the case of water, the 18O/16O or 2H/1H. A reference for oxygen and deuterium in water is used an international standard of VSMOW (Vienna Standard Mean Ocean Water) [10,11,18].
Tritium analysis
The water samples from the field were distilled first to remove any interfering minerals. A 600 mL of sample was weighed and transferred into electrolytic cell. As much as 14 electrolytic cells
were placed in cooling water bath at 0 0C. Each cell was connected in series and flow with electric current. After 10 days, the volume of sample would only left about 20 mL, which mean the tritium content were 30 times enriched. After that, each sample was neutralized using CO2 and distilled to remove Na2O. Exactly 10 mL of each sample was pipetted into vial glass and mixed with 11 mL of ULTIMA Gold Llt (scintillator) and counted using Liquid Scintillation Counter (LSC).
Tritium concentration (expressed in TU) which decreases exponentially is calculated according to the following decay formula [10,19], where T is decay time in year, t1/2 =12,34 years (halflife of tritium), Co is initial concentration of tritium, Ct is tritium concentration of groundwater.
t T
t
C e
C
12693 . 0 0
RESULTS AND DISCUSSION
In previous investigation applying isotopes of
18O and 2H, Syafalni concluded that an evaporation processes generally had been taken place in the shallow groundwater sorrounding Bantar Gebang landfill [14]. In his investigation, more detail process involving on enrichment of 2H from leachate water that could be as a finger printing tool was not discusssed. The investigation toward Cibitung river that was utilized to discard the treated leachate water through some drainage ditches was also conducted [15].
This investigation was stressed on observation of some natural isotopes either radioactive like 3H (called tritium) and natural isotopes such as 2H and 18O toward shallow groundwater in the radius range of 2 km from Bantar Gebang landfill. The term of shallow groundwater referred to the unconfined aquifer system with the depth scale around 0-40 m [20].
Selected sites of Bantar Gebang shallow groundwater were mapped at Figure 1 while water sample depths and their coordinates were shown at Table 1.
TTable 1. Sampling locations for leachates and shallow
groundwater
No. Sample ID Sample type - depth Coordinates
Longitude Latitude 1 BG-1a groundwater - 9m 06o20’58” 106 2 BG-1b 6m Groundwater- 6m 06o21’9.3” 106o 3 BG-1b 15m groundwater – 15m 06o21’9.3” 106o 4 BG-1c river water - surface 06o20’42.6” 106o 5 BG-1d leachate outlet-BG1 06o21’9.3” 106o 6 BG-1e leachate inlet-BG1 06o21’9.3” 106o 7 BG-1f leachate effluent-BG 06o20’50.1” 106o 8 BG-2 groundwater – 10m 06o20’55.2” 106o 9 BG-3 groundwater – 12m 06o20’28.9” 106o 10 BG-4a groundwater – 5m 06o20’32.1” 107o 11 BG-4b groundwater – 15m 06o20’32.7” 107 12 BG-4c leachate outlet-SB2 06o20’32.7” 107 13 BG-4d river water – surface 06o20’32.7” 107 14 BG-4e leachate inlet-SB2 06o20’35.1” 107o 15 BG-5 groundwater -15m 06o20’59.6” 107o 16 BG-6 groundwater – 18 m 06o21’32.9” 106o 17 BG-7 groundwater – 12 m 06o21’15.1” 106o 18 BG-8 groundwater - 20 m 06o20’48.5” 106o 19 BG-9 groundwater – 20 m 06o20’9.7” 106o 20 BG-10 groundwater -18 m 06o19’58.6” 106o 21 BG-11 groundwater -12 m 06o20’1.1” 107 22 BG-12 groundwater - 15 m 06o20’25.8” 107o 23 BG-13 groundwater -12 m 06o20’54.1” 107o 24 BG-14 groundwater -12 m 06o21’25.5” 107o 25 BG-15 groundwater -10 m 06o21’50.4” 106o BG: treatment pond in Bantar Gebang
SB: treatment pond in Sumur Batu
FIGURE 1
Groundwater Quality
Electrical conductivity (EC) is the measure of water’s ability to conduct electrical current and is closely related to total dissolved solids (TDS) in the water. Conductivity value of water increases with the increase in the amount of dissolved solid in the water. Both tests can be used to monitor the consistency of quality of the groundwater as they indicate the total inorganic mineral content in the water. As seen at Table 2, it was observed that the average of electrical conductivity for shallow groundwater in rainy season was 489 µS/cm. The highest value was 3070 µS/cm which was measured in monitoring well of BG-1b with depth of 6m (open dug well), that could be an indication of leachate infiltration to this well. Seemly, the downward movement of leachate coming from Bantar Gebang landfill was still detected at BG-1b with depth of 15 m (bore well) with EC value of 3100 µS/cm which was observed at rainy season.
Both wells are still located in IPAS-3 area with distance around 3 m from inlet pond which has extremely high EC value of more than 20.000 µS/cm.
Table 2. Measured physical parameters in the field Table 2
Table 2
Different case to Sumur Batu landfill, leachate movement was not detected at monitoring well of BG-4a (open dug well with depth of 5m and the distance is approximately 10 m from inlet pond) which still represented common natural groundwater based on EC value. However, leachate movement could be observed at BG-4b (bore well with depth of 10m and 3 m distance from inlet ponds) which had EC value rather higher than other shallow groundwater. But, the extent of EC value at this well was still much lower than that of bore well of BG-1b at IPAS-3 area.
EC value of most shallow groundwater in surounding Bantar Gebang landfill was in the range of 0.16 to 0.73 µS/cm (TDS is 70 mg/L to 360 mg/L) in rainy season except monitoring wells in landfill area. Seemly, those EC values did not significantly change for water samples collected in rainy season. The leachate from inlet ponds in
Figure 1. Map of sampling location for shallow groundwater in Bantar Gebang landfill
Bantar Gebang Landfill had a highest TDS of more than 10.000 mg/L while leachate in Sumur Batu landfill had TDS value of 4730 mg/L. The higher TDS value in Bantar Gebang landfill might be caused by its longer operation which has been active since 1986 than Sumur Batu landfill starting for operation since 2002. Thus, the rate of organic waste decomposition in Bantar Gebang landfill which produced CO2, H2S, NH3, dissolution cation and anion, redox reaction was extremely higher.
Most pH values for shalow groundwater, except monitoring wells, fell at acid scale with average of 5.68 and the lowest was 4.54 in BG-15 as observed in rainy season. The average pH tended to decrease
slightly at 5.36 in dry season. The low pH of native groundwater primarily because of the law pH of rainfall and the lack of other soluble minerals in the aquifer material. The significantly higher pH (> 7.1) in leachate is somewhat surprising because large amounts of CO2 generated from degradation of organic materials should lower pH. However, the pH is increased by generation of ammonium and by fermentation reactions which consume hydrogen and CO2 during the formation of methane.
According to Health Minister Regulation as recorded at No.492/Menkes/Per/IV/2010, save drinking water for TDS level is 500 mg/L and pH range is 6.5 to 8.5 [1]. Although most shallow groundwater had lower TDS than that was required by Menkes, its pH values were beyond scale of save drinking water such that most shallow groundwater should not be utilized for drinking water supply.
Groundwater interrelationship Deuterium and Oxygen-18
There are some physical and chemical processes which effect the isotope composition of the water subsequent to precipitation and can cause deviation from the meteoric line. The Figure 2 shows the Meteoric Water Line (MWL) and how isotopes of the water are effected by certain physicochemical processes such as evaporation, high and low temperature exchange reactions with rock minerals, hydration of silicates, CO2 exchange reactions, H2S exchange reaction and methanogenesis [11].
The results for 18O and 2H are expressed in part per mill (‰) with a difference ratio of 18O to
16O (denoted as 18O) and ratio of 2H to 1H (denoted as 2H), respectively, relative to SMOW (Standard
Mean Ocean Water). Those results were represented at Table 3 whereas plotting stable isotopes of 18O and 2H was displayed at Figure 3 and Figure 4 for water samples collected in rainy season and dry season, respectively. Wandowo et.al (2002) indicated that relationship between 18O and 2H for Local Meteoric Water Line (LMWL) was 2H = 7.8 18O +13 which was found from collecting monthly rainfalls at different elevations starting from Tongkol-Jakarta (at elevation of 10 m) to Puncak-Bogor (at elevation of 1020 m) [20].
Characterizing 18O and 2H in meteoric waters in local area is essential in determining the input function or as base line to trace groundwater recharge.
Figure 2
Table 3. Result of 18O, 2 H and 3 H isotopes from water samples collected in rainy and dry season
No Rainy season Dry season
18O ( ‰)
2H (‰)
3H (TU) 18O (‰)
2H (‰)
1 -5.96 -37.42 14.92 -6.26 -37.9
2 -6.02 -29.80 76.66
3 -5.81 -30.6
4 -6.14 -30.93 8.43 -3.04 -23.1
5 -5.43 -21.87 50.90 -0.42 -3.6
6 -5.93 +7.86 493.89
+
0.67 +10.3
7 -5.65 -17.51 116.07 -4.89 -5.0
8 -6.68 -45.00 7.23 -7.23 -44.1
9 -6.06 -41.24 6.93 -6.92 -43.1
10 -6.64 -42.66 8.65
11 -6.31 -36.57 19.29 -6.71 -37.6
12 -5.32 -25.68 9.55 -0.98 -21.1
13 -6.13 -28.96 33.49 -4.97 -25.6
14 -5.98 -23.92 10.65 -2.37 -18.9
15 -5.40 -33.95 7.83 -6.82 -39.3
16 -6.31 -40.72 7.59 -7.20 -42.5
17 -5.73 -37.94 7.05 -7.16 -42.8
18 -6.26 -41.09 n.a -7.28 -43.1
19 -7.20 -46.58 n.a -7.27 -48.3
20 -5.59 -35.34 16.76 -7.39 -46.6
21 -6.07 -40.25 5.19 -6.62 -43.8
22 -6.22 -38.66 n.a -6.26 -41.8
23 -6.50 -43.49 6.96 -6.38 -41.7
24 -6.15 -39.71 6.59 -6.58 -41.2
25 -6.62 -41.54 n.a -6.83 -46.2
na: not analyzed
As seen at Figure 3, most shallow groundwater collected in rainy season were distributed along the line of 2H = 7.38 18O + 6.38. The slope of 7.4 had shifted closed to LMWL (slope= 7.8) because the little evidence of
Figure 2. Plot of Meteoric Water Line showing the effects of certain physicochemical processes on the isotopic composition of the water
evaporation occured during rainy season. The extent of shifting slope was clearly performed in water samples collected in major dry season as illustrated at Figure 4 where points distributed along the line of
2H = 6.98 18O +5.54. The more decreasing slope showed a strong evaporation area. A mixing process between direct rainwater infiltration and evaporated water due to hot landscapes during dry season had influenced to more enriched value of both isotopes in groundwater samples. Evaporation could occur from surface water during run off prior to infiltration, from the unzaturated zone itself or from the water table.
Results for 2H in leachate collected during rainy season from inlet pond, outlet pond and leachate run off in Bantar Gebang municipal landfill showed an enriched value that ranged from -21.87
‰ to +7.86 ‰ and -5 to +10.3 ‰, for rainy season and dry season, respectively. Significant enrichment in deuterium of leachate water was also observed in Sumur Batu landfill which had range values from -25.68 ‰ to -23.92‰ and -21.1‰ to -18.9 ‰ for rainy season and dry season, respectively. Seemly, the extent of deuterium enrichment in both active landfills increased significantly for the leachates sampled in dry season compared to rainy season;
that was probably caused by strong evaporation due to hot atmosphere and minimal influence from groundwater and surface water. Deuterium values for leachate varied considerably between two active landfills, where leachate from Bantar Gebang landfill was much higher and had a wider range than those of Sumur Batu landfill. The more enriched isotopic values at Bantar Gebang were likely due to one or a combination of two reasons. The first reason is a pure leachate sample that might be without any contribution from river water which is located at the distance of more than 1 km whereas leachate from Sumur Batu is approximately 5m- distance from the river as seen at Figure 1. The second is an increased methanogenesis activity caused by gradual enrichment of existing organic source since 1986 when Bantar Gebang landfill started for operation. In contrast to older landfill of Bantar Gebang covering total area of 108 ha, Sumur Batu landfill has operated since 2002 and covered less than 10 ha area. Cibitung river which streamed along two active landfills had also enriched deuterium values either in rainy season or dry season. However, increasing deuterium values were significantly exhibited at samples collected in dry season that were probably caused by not only strong evaporation but also less contribution of water flow while leachate effluent streamed to this river was relatively constant.
The highly enriched of deuterium in leachate compared to most natural groundwater was mainly effected by generation of huge methane by microbes (or methanogenesis) at landfill sites as described at Figure 2 above. This process requires a fully saturated environment that excludes atmospheric O2 and high content of organic carbon subtract which is most closely matched by landfill site. Microbes playing important role in isotopic fractionation of 2H preferentially utilize the lighter hydrogen isotope (or 1H) when producing CH4 such that 2H composition of remaining water is highly enriched. Another process assosiated with enrichment of 2H isotope in landfill site is isotopic exchange between H2O and H2S which would be generated during SO4 reduction in landfill.
However, the major effect in producing enriched deuterium of leachates is methanogenesis process [10, 12,13,16].
Isotopic composition of oxygen in leachates was not influenced by microbial activity in landfill.
The more enriched oxygen values in leachate than those of most natural groundwater might have been
18O
2 H
Figure 3. Relationship between 18O and 2H from water samples collected in rainy season
18O
2 H
1b-6m
1b-15m
Figure 4. Relationship between 18O and 2H from water samples collected in dry season
caused by evaporation effect in a closed system of leachate ponds as described at Figure 2. Moreover, the effect of evaporation in shifting oxygen isotope clearly appeared in leachates taken during dry season as seen at Table 3. The 18O values in both active landfills showed the narrow range from -5.32
‰ to -5.98 ‰ and from 0.67 ‰ to -4.89 ‰ for rainy season and dry season, respectively. Similar case in enrichment of 18O, the river seemed to have the higher 18O values in dry season than those of rainy season. It was mainly caused by hot atmosphere in dry season and more stagnant river flow such that evaporation process would occur more strongly.
Tritium
Tritium (or 3H) concentrations are expressed as Tritium Unit (TU) where 1 TU is 1 tritium atom per 1018 hydrogen atoms. The result for tritium collected in leachate from Bantar Gebang and Sumur Batu landfill as well as its surounding groundwaters were listed at Table 3. It showed that tritium contents in leachate samples were higher levels than that of native groundwater. Tritium content of leachates from Bantar Gebang landfill varied in a wider range from 50.90 TU to 493 TU and it was much higher values than those of Sumur Batu landfill. It was probably due to the older municipal landfill of Bantar Gebang such that the portion of soluble materials in leachate was relatively larger. Those tritium level was even higher than the peak of concentration reached in 1963 of around 180.2 TU in Jakarta, the nearest station from studied area, that was attributed to the atmospheric 3H bomb tests between 1954-1963 [19].
Tritium content in shallow groundwater samples were in large variation from 5.49 TU to 76.66 TU.
The high level of tritium up to 5.5 TU in 1978 and 1.9 TU in 1987 in precipitation [19] infiltrating in some groundwater samples might be as an indication of leachate contribution.
Measured tritium content of leachate in samples from the Breitenau Exprimental Landfill in Austria were up to about 2000 TU with a few leachate samples showing 3000. The tritum content from leachate from three different municipal landfill in Illinois ranged from 227 TU to 8000 TU [16] and 150 to 820 TU in municipal landfill in Metro Manila-Philippines [17]. Seemly, too high tritium contents in leachate is very difficult to be explained solely by tritium input from local precipitation after termonuclear bomb test in 1952-1962, because tritium from precipitation in Jakarta station has decreased to 5.3 TU since 1978 [19]. Thus, the most probable source of tritium in leachate is from gaseous tritium light devices (GTLDs), luminescent
paints used in watch dials, compasses, lights for map reading, in self-illuminated exit signs and clocks as well as other luminescent dials that could easily be disposed of in municipal landfills. These luminescent paints contain tritiated hydrocarbons that could biodegradable in landfill and add to overall tritium contents [10,16].
Mixing between leachate and groundwater
General equation for mixing between two water sources with different isotopic contents is expressed as follow:
18O = a 18Ox + b 18O(1-x)
Where a and b are types of two solution, x and (1-x) are mole fraction of a and b, and 18O is a measured isotope value [21,22]. In the case of leachate migration to groundwater, solution a is leachate as source of contaminant and solution b is pure water of rainwater. Table 4 showed the results for estimated percentage of leachate contribution to some shallow wells based on the equation above.
Tritium activity as one of qualitatively parameter for leahate migration were also listed in this table in order to compare that some water samples had been quantitatively mixed with leachate. In this calculation, 2H value which was used as input rainwater recharging to local groundwater was -39.3
o/oo [19], it was nearest value to -39.53 o/oo for 2H average value of shallow groundwater in Bantar Gebang. The average of 2H value in leachate was with assumption that the nearest leachate run off and ponds were as main source except for river which its average of 2H was calculated from all input leachates.
Table 4. Result for mixing percentage of some supposed wells contaminated by leachate in rainy season
Sample ID Average of
2H in leachate (o/oo)
2H (o/oo)
3H (TU)
Mixing with leachate
(%) BG-4d
(river)
-17.66 -28.96 33.49 47.77
BG 1b-6m -10.51 -29.80 76.66 32.99
BG 1b-15m -10.51 -30.60 n.a 30.22
BG-1c (river)
-10.51 -30.93 8.43 29.07
BG-4b -24.80 -36.57 19.29 18.83
BG-5 -10.51 -33.95 7.83 18.58
BG-10 -10.51 -35.34 16.65 13.75
BG-1a -10.51 -37.42 14.92 6.53
n.a = not analyzed
As seen at Table 4, the highest percentage to 32.99% of leachate contribution to groundwater was 6m-monitoring well in IPAS-3 located approximately 3m from leachate ponds. Moreover, mixing leachate to this monitoring well was also
performed by highest tritium content. Seemly, downward leachate movement as much as 30.22 % was also observed in 15m-pumped well collected in dry season. Although it was not as high as mixing leachate in Bantar Gebang, 15m-pumped well in Sumur Batu landfill area might have contaminated by 18.83 % leachate that was also supported by lower tritium than that of Bantar Gebang monitoring wells. Thus, qualitatively mixing of leachate to groundwater that was calculated by deuterium clearly confirmed to electrical conductivity (EC) data as seen at Table 2. Cibitung river of BG-4d collected nearest to Sumur Batu had much higher mixing portion than that of BG-1c, this difference could be observed physically by its rather black water. Some people’s wells which might have been contaminated by leachate with their mixing percentage were BG-5, BG-10 and BG-1a as shown at Table 4.
CONCLUSION
Deuterium from leachate treated in pond in Bantar Gebang landfill showed highest value of +10,3 ‰ in dry season that could be caused by more extensive methane production and isotopic exchange with H2S generated in leachate. While, the more recent landfill area of Sumur Batu exhibited less enrichment deuterium of –18.9 ‰. The extent of deuterium enrichment in both active landfills was much stronger in dry season than that of rainy season because of high evaporation and less rainwater input. In the case of 18O shift from its local precipitation, strong evaporation in dry season solely influenced in increasing 18O value in leachate.
Tririum from leachate collected in both landfills also gave significant level compared to most natural grundwaters. The highest tritium level in leachate was 493.89 TU in older landfill of Bantar Gebang, that was impossible to be derived from precipitation even after nuclear bomb tests between 1952 and 1962. Therefore, tools using luminescent paints buried in solid waste were most probably sources of high tritium level in leachate. In mixing calculation which utilized deuterium parameter, monitoring well of IPAS-3 with 6 m depth might have been contaminated by leachate as much as 32.99%, even the leachate migration had reached to pumped well with depth of 15 m in same location. Besides, three people’s wells which could be indicated leachate contamination were BG-5, BG-10 and BG-1a.
Tritium concentration for those wells was also sufficiently high to indicate the effect of leachate.
ACKNOWLEDGMENT
This study was supported by Center for Iso- topes and Radiation Application – National Nuclear Energy Agency (BATAN). The author would like to acknowledge the Godang Tua Jaya Company as the executor for Bantar Gebang Landfill for its permis- sion in leachate sampling and local people for their sincere assistances in groundwater collection. The author also greatly expressed the thanks to Agus Martinus in his charge to analyze tritium and Hy- drology staffs in Industrial and Environmental Divi- sion.
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Table 2. Measured physical parameters in the field
No Rainy season Dry season
T
(oC) pH EC
(mS/cm) TDS (ppt) T
(oC) pH EC
(mS/cm) TDS (ppt)
1. 29.7 6.21 0.30 0.13 30.8 6.37 0.33 0.16
2. 30.6 5.77 3.07 1.53 *
3. n.a 30.4 5.88 3.10 1.54
4. 31.3 7.18 0.38 0.19 30.6 7.22 0.73 0.37
5. 31 7.14 6.72 3.36 30.5 7.61 10.88 5.45
6. 37.2 8.13 >20 >10 35.2 8.04 >20 >10
7. 33.4 8.07 11.62 5.80 32 8.00 >20 >10
8. 31.1 5.19 0.73 0.36 30.5 5.28 0.63 0.31
9. 30.8 5.10 0.18 0.09 35.1 5.32 0.23 0.11
10. 28 6.05 0.08 0.04 *
11. 31.2 6.65 1.30 0.05 32.2 6.34 1.39 0.69
12. 30.5 7.88 2.30 1.17 31 8.58 1.89 0.94
13. 29.9 7.72 3.01 1.52 33.2 7.99 8.04 4.03
14. 29.8 8.16 4.73 2.36 34.1 8.18 4.09 2.04
15. 29.4 6.64 0.36 0.18 30.2 5.90 0.35 0.17
16. 29.8 5.08 0.17 0.08 30.2 4.36 0.20 0.09
17. 30.1 5.2 0.22 0.10 30 4.55 0.14 0.07
18. 30.2 6.3 0.34 0.17 29.7 6.58 0.30 0.15
19. 30.2 5.49 0.23 0.11 30 4.55 0.14 0.07
20. 30.4 6.24 0.22 0.11 30.3 5.31 0.12 0.06
21. 30.9 5.85 0.37 0.18 29.9 5.48 0.33 0.26
22. 30.5 5.78 0.16 0.07 29.5 5.07 0.15 0.07
23. 27.6 5.20 0.20 0.10 29.5 5.51 0.20 0.10
24. 29 5.19 0.13 0.06 30.8 5.79 0.18 0.08
25. 29.6 4.54 0.25 0.12 29.2 4.40 0.22 0.11
n.a= not analyzed
*.=drought
Deuterium shift due to methanogenesis
to Water / Rock interactionEvaporation CondensationSilicate Hydra-2H-Exchange with Hydrocarbon GMWL
CO2-Exchange
Figure 2. Plot of Meteoric Water Line showing the effects of certain physicochemical processes on the isotopic composition of the water
