EVOLUTION OF GROUNDWATER CHEMISTRY ON SHALLOW …geologic-risk.ft.ugm.ac.id/fresh/jsaag/vol-3/no-2/jsaag-v3n2p116.pdf · EVOLUTION OF GROUNDWATER CHEMISTRY ON SHALLOW AQUIFER OF YOGYAKARTA

J. SE Asian Appl. Geol., Jul–Dec 2011, Vol. 3(2), pp. 116-124

EVOLUTION OF GROUNDWATER CHEMISTRYON SHALLOW AQUIFER OF YOGYAKARTACITY URBAN AREA

Doni Prakasa Eka Putra*

Department of Geological Engineering, Faculty of Engineering, Gadjah Mada University

Abstract

Since 1980s, accelerated by urbanization, Yo-gyakarta City was shifting to many directionsdefined by main road networks and service cen-tres. Urbanization has transformed rural dwellingsto become urban settlements and generated ur-ban agglomeration area. Until now, new businesscentres, education centres and tourism centres aregrowing hand in hand with new settlements (formalor informal) without proper provision of water sup-ply and sanitation system. This condition increasethe possibility of groundwater contamination fromurban wastewater and a change of major chemistryof groundwater as shallow unconfined aquifer islying under Yogyakarta City. To prove the evolu-tion of groundwater chemistry, old data taken on1980s were comparing with the recent groundwaterchemistry data. The evaluation shows that nitratecontent of groundwater in 1980s was a minor anion,but nowadays become a major anion, especially inthe shallow groundwater in the centre of YogyakartaCity. This evidence shows that there is an evolutionof groundwater chemistry in shallow groundwaterbelow Yogyakarta City due to contamination fromun-proper on-site sanitation system.Keywords: urbanization, Yogyakarta city, ruraldwellings, settlements, agglomeration, contamina-tion, groundwater.

*Corresponding author: D.P.E. PUTRA, Departmentof Geological Engineering, Faculty of Engineering, Gad-jah Mada University. Jl. Grafika No.2 Bulaksumur, Yo-gyakarta. E-mail: [email protected]

1 Introduction

Yogyakarta City is located on the central-part ofJava Island. It is a capital city of YogyakartaSpecial Province and one of the most impor-tant cultural centres in Indonesia (Figure 1).Based on the regional context, Yogyakarta Cityand its agglomeration area are sited on aquiferswhich are part of the Merapi Aquifer System(Figure 2). MacDonald & Partners (1984) andHendrayana (1993) differentiated the MerapiAquifer System into two major Formations; Yo-gyakarta Formation as the upper aquifer andSleman Formation as the lower aquifer. Theresults of the lithostratigraphy correlation fromborehole data within the study area shows thatthere are actually five quarternary layers or suc-cessions, which build the multilayer aquifers ofthe Merapi Aquifer System beneath YogyakartaCity. Each layer consists of a heterogeneouscomposite of gravel, sand, clayey sand, andclay facies, and they are separated by later-ally uncontinuous sandy silt to clay layers.The laterally uncontinuous semi-permeable toimpermeable layers make incomplete separa-tion between the aquifers and cause hydraulicwindows. As a consequence, the aquifers ofthis multilayer system are connected directly toeach other in some places (Putra, 2007). Thus,it is possible that any contamination on the up-per aquifer can induced to the deeper aquiferlayers.

Historically, in 1930s, Yogyakarta was just asmall town in the interior of Java with the pop-ulation of approximately 60.000 populations

116

EVOLUTION OF GROUNDWATER CHEMISTRY ON SHALLOW AQUIFER OF YOGYAKARTA CITY

URBAN AREA

Figure 1: Yogyakarta City and its urban agglomeration area

Figure 2: Concept of aquifer system underlying Yogyakarta City area (Putra, 2007)

© 2011 Department of Geological Engineering, Gadjah Mada University 117

PUTRA

(Baiquni, 2004). Since 1980s accelerated byurbanization, Yogyakarta City settlement pat-tern was shifting to many direction defined bymain road networks and service centres. Ur-banization has transformed rural dwellings tobecome urban settlements and generated urbanagglomeration area. Until now, new businesscentres, education centres and tourism centresare growing hand in hand with new settlements(formal or informal) without proper provisionof water supply and sanitation system. Ac-tually, in the first half of the twentieth cen-tury, sanitation system in Yogyakarta City wasserved by a main sewerage system built byDutch engineers. This old system was supple-mental by a new one in 1998. However, thesewage system with the old and new sewagesystem can serve only 9 % of the city population(Sukarma and Pollard, 2002). As a result, morethan 90 % of the population (total populationca. one million peoples) are using on-site sani-tation systems. The other characteristics of ur-banization in Yogyakarta City is the wide use ofshallow infiltration wells, as alternative way todispose domestically non human body waste oreven small workshops wastewater directly intothe ground. The practice of infiltration wells isgood in terms of maintaining recharge; how-ever, it turns to become a potential source ofgroundwater contamination. Nevertheless, thispractice of shallow infiltration wells occurs dueto lack of an integrated sewerage system. Onits relation with the lack of sewerage systemand the wide usage of on-site sanitation sys-tems i.e. septic tank systems, latrines, togetherwith the direct disposal of waste water to theground, it is reasonable to assume that watertaken from domestic dug wells are potentiallycontaminated and thus can harm the humanhealth. It is known that water quality surveysof domestic wells in unsewered areas have re-vealed a widespread chemical (i.e. nitrate) andmicrobial (i.e. faecal coli) contamination of shal-low groundwater (Sinton, 1982, Morris et al.,1994, GWMAP, 2000). Based on above facts, theobjective of this study is to recognize the evo-lution of groundwater chemistry in upper shal-low aquifer of Yogyakarta City and its agglom-

eration area and to correlate the changes withthe urbanization aspect.

2 Literature review

2.1 Urbanization and groundwater

One of the most important issues of the grow-ing city is the interaction between urban devel-opment and groundwater, especially on citieslocated above shallow unconfined aquifer. Theinteraction between urban development andgroundwater may be explained in the relationwith the pattern and stage of city evolution onaffecting the quantity and quality of ground-water. Two important studies of the impact ofurbanization on groundwater have been wellreported by Foster et al. (1993) and Morris etal. (1994). From both studies, two main issuescan be concluded, which are; 1) urbanizationchanges groundwater recharge or cycle, withmodification to the existing recharge and theintroduction of the new sources, 2) the intro-duction of new sources of recharge in urban-ization cause extensive but essentially diffusegroundwater contamination. Another issues re-lated to the changes in the quantity and qualityof groundwater in urbanized areas are the un-controlled aquifer exploitations, fluctuation ofgroundwater levels and problems with the un-derground structure (Chilton, 1999, Vásquez-Suné et al., 2005).

It is often thought that urbanization reducesinfiltration to groundwater due to the imper-meabilisation of the catchment by paved areas,buildings and roads. However, the reserve isoften true and recharge beneath cities is usuallysubstantially greater than the pre-urban values(Foster et al., 1993). The increase of ground-water recharge is closely related with the oc-curence of three main sources of recharge whichexist in urbanized area: rainwater, wastewaterand main leakage from water supply system.Lerner et al. (1990) mentioned that in humidareas, leakage recharge (waste water and wa-ter supply system) may balance the loss of pre-cipitation recharge caused by the impermeableareas and the overall effect of urbanization willbe small. However, in arid and semi arid ar-eas, leakage recharge will always significant-

118 © 2011 Department of Geological Engineering, Gadjah Mada University


URBAN AREA

tly larger than precipitation recharge. In fact,Lerner (2002) mentioned that in cities, whereno sewers are present to take waste water away,the most important recharge route would be theinfiltration of waste water from large numbersof septic tanks, latrines, and soakaways.

The sources and pathways for groundwaterrecharge in urbanized area are more numerousand complex than in rural environments. Nev-ertheless, the increase of groundwater rechargein this area is known to be closely relatedto three main sources: rainwater, wastewaterand main leakage from water supply networks.In cities where waste water is not exported(cities without sewers for waste water trans-port), as much as 90 % of abstracted and/orimported water may return as groundwaterrecharge (Lerner et al., 1990). In these cities, themost important recharge source would be theinfiltration of waste water from large numbersof septic tanks, latrines, and soakaways (Lerner,2002).

According to Lerner et al. (1990), the effectof urban recharge sources will be always sig-nificantly larger than precipitation recharge insemi arid and arid regions. But in humid ar-eas, urban recharge may only balance the loss ofprecipitation recharge caused by the imperme-able areas, and the overall effect of urbanizationwill be small. On the other hand, cities whichuse the local groundwater for their water sup-ply, the effects of urbanization on recharge arein general smaller than in cities that import wa-ter. Therefore, it can be also concluded that al-most all urbanization processes can potentiallyincrease the rate of infiltration to groundwater.In contrast to the effect of urbanization on thequantity of recharge, the net effect of urban-ization on the quality of recharge is generallyadverse, especially if waste water is an impor-tant component (Table 1). From Table 1, it canbe seen that the quality of recharge water fromwaste water (e.g. on site sanitations, leakagesewers, etc) is commonly poor. This table alsoshows that the causes of groundwater qualitydeterioration in urbanized area are complex, in-volving a combination of contaminants. Fromall possible contaminant in the groundwaterunder urban area, nitrate is the main important

contaminants that are derived from on-site san-itation (Foster and Hirata, 1988). Therefore, ni-trate is commonly used as a marker species forgroundwater contamination from urban on-sitesanitation.

2.2 Background value of Yogyakarta’s

groundwater chemistry

According to MacDonald and Partners (1984),the inorganic chemical quality of the ground-water in the study area was very good forirrigation, drinking and most industrial pur-poses (see Table 2). Physical-chemical charac-teristics of water ranged between less than 100µS/cm for Specific Electric Conductivity (EC)or 70 mg/L for Total Dissolved Solid (TDS)in spring water and 600 µS/cm for EC or 500mg/L for TDS in near geological boundariesof south, east and west. In fact, nitrate con-centration, which is commonly used as markerspecies for agricultural practice and urban on-site sanitation, was less than 2.8 mg/L. Thedegradation of inorganic chemical quality ofshallow groundwater due to human activitiesin the study area was recognized in the late 80sand early 90s as reported by Sudharmaji (1991)and Hendrayana (1993). Both studies statedthat groundwater quality degradation was indi-cated to occur in the central-part of YogyakartaCity. However, the groundwater quality at thattime was generally good, and only in few localareas, the nitrate concentration was greater than10 mg/L.

3 Methodology

In order to prove the evolution of groundwaterchemistry in the shallow groundwater systemunder Yogyakarta City and Its AgglomerationArea, old data of groundwater chemistry takenin 1980s was compared with the recent data.On this comparison, major cations (Na+, K+,Ca2+ and Mg2+) and major anions (Cl−, SO2−

4 ,HCO−

3 ) including NO−

3 (as common markerspecies for groundwater contamination fromurban on-site sanitation) of groundwater iscompared. To show the difference betweennitrate content of shallow groundwater of Yo-gyakarta City in 1980s and recent condition, a


PUTRA

Table 1: Impact on groundwater quality from various sources of urban recharge (Morris et al., 2003)

Table 2: Summary of hydrochemical analyses of groundwater from Merapi Aquifer (MacDonaldand Partners 1984)



URBAN AREA

distribution map of nitrate content in shallowgroundwater is developed. More over, to eval-uate the impact of population density (urban –rural area) to nitrate content in shallow ground-water, a XY-graph is developed between nitrateconcentration in groundwater and number ofpopulation.

4 Results and Discussion

For this research, 10 groundwater samples weretaken for the routine water analysis and about152 samples were taken for nitrate content anal-ysis. Routine water analysis involves mea-suring the concentration of the standard testof constituents of major ions such as Ca2+,Mg2+, Na+, K+, HCO−

3 , SO2−4 , Cl− and NO−

3

as well as pH, total dissolved solid and elec-tric conductivity. Result of the analysis showsthat almost all major components meet the Na-tional Drinking Water Standard, except onesample which contains nitrate concentrationgreater than 50 mg/L (Table 3). The comparisonbetween the recent average concentrations ofprinciple groundwater quality and their back-ground values based on the data from MacDon-ald and Partners (1984) does reveal dramaticchanges in water quality, especially for the an-ions group. Based on its anions content, thehydrochemistry of the shallow groundwater inYogyakarta City and its agglomeration area canbe differentiated into 3 water types: 1) HCO3–SO4 to HCO3– Cl–SO4 water, 2) HCO3–NO3 wa-ter and 3) NO3–HCO3–SO4 water. By its rela-tion to the urbanization process and assumingthe homogeneity of the shallow groundwatersystem beneath the study area, type 1 (MI-01,MI-02, MI-03, MI-04, MI-07, MI-08, MI-09, MI-10) is the dominant type of groundwater foundbeneath sub urban/rural areas (less developedarea). Whilst due to limited data, type 2 (MI-06) may the type of groundwater found in theboundary between sub urban and urban area(moderate developed area). Type 3 (MI-05) mayrepresent the type of groundwater found in thecentral-part of urban area (old developed area).A composite map of the shallow groundwatertype and the major land use in the study area isshown in Figure 3.

Despite the reservation of the limited data,a comparison between the recent groundwa-ter chemistry (Table 3) and the backgroundgroundwater chemistry in the study area (Ta-ble 2) shows clearly that the concentration ofsulphate and nitrate have increased over time.These changes in groundwater composition ofthe study area should have occurred during thelast 20 years or more, presumably parallel to theevolution of the urban development/land usechange in the study area. Besides due to suburban/urban contamination sources, the salin-ization process of the shallow groundwater inthe study area may also occur due to naturalcondition. Sample MI-03 that was taken onthe south geological boundaries of the studyarea is a good example of this anomaly. It con-tains the highest concentration of Ca2+, Mg2+,HCO−

3 , Cl− and SO2−4 of all groundwater sam-

ples (see Table 1) although it was sampled fromthe shallow groundwater beneath sub urban-rural area. This condition occurs presumablydue to water mixing processes between the up-per aquifer (predominantly HCO3 water) andthe lower aquifer (predominantly Cl–SO4 wa-ter) together with the influence of dissolvingCa-Mg-Carbonate of the Tertiary Rocks Forma-tion (non-aquifer). This process reveals higherconcentration of EC and TDS in groundwaternear the geological boundaries as also alreadymentioned by MacDonald and Partners (1984).

For the nitrate contaminant in groundwater,a total 152 secondary data of nitrate contentwere used. The data were taken on 2005. Ac-cording to Sudharmaji (1990), the nitrate back-ground value on shallow groundwater of Yo-gyakarta City in 1985 was found to be 0.03 –12.92 g/L (mean value 2.82 mg/L), while olderdata showed that nitrate content on ground-water of Merapi aquifer was between 0.00 –2.8 mg/L (MacDonald & Partners, 1984). Therecent data shows that the nitrate content onshallow groundwater of Yogyakarta City andits surrounding area are between 0.28 – 151.70mg/L (see Figure 4).

Figure 4 shows the nitrate content in shallowgroundwater under Yogyakarta City on year1985 and 2005. From this figure, it can beconcluded that for about 20 years, the nitrate


PUTRA

Table 3: Physical-chemical characteristics and major ions of shallow groundwater in the study area.Unit: mg/L, except for EC (µS/cm) and pH

Figure 3: Composite map of shallow groundwater type and major land use in the study area



URBAN AREA

Figure 4: NO3 concentration of shallow groundwater in central part of Yogyakarta City area

content was increasing dramatically in shallowgroundwater of Yogyakarta City. Moreover, bycomparing the population density and nitratecontent in shallow groundwater in the researcharea according to the cross-section from Northto South across central-part of Yogyakarta City.It is reasonable to conclude that the denser thepopulation the higher the nitrate concentrationin shallow groundwater (see Figure 5). Thisfact reveals due to high possibility of existingsources of contamination and loading of nitratefrom improper on-site sanitation system on theurban area.

5 Conclusions

Based on this research, it can be concludedthat the shallow groundwater chemistry of up-per aquifer Yogyakarta City is change withtime due to the impact of urban wastewaterfrom improper on-site sanitation. As a re-sult, the groundwater beneath highly urban-ized area contains extremely high nitrate com-pare to groundwater in sub-urban/rural area,which contains lower nitrate. If about 20 yearsago, bicarbonate and sulphate ions are the dom-inant anion of shallow groundwater chemistry,nowadays, nitrate ion becomes a major anion ingroundwater of upper aquifer especially belowthe central part of Yogyakarta City.

References

Baiquni, M. (2004), Urbanization and Urban Set-tlement Dualism: A case study and researchof Yogyakarta, Indonesia, Proceeding of Inter-national Workshop on Asian Approach TowardSustainable Urban Regeneration, September 2004,The University of Tokyo, Japan. http://csur.t.u-tokyo.ac.jp/ws2004/papers/B1-Baiquni.pdf

Bedient, P.B., Rifai, H.S., and Newell, C.J. (1999),Ground Water Contamination: Transport and Re-mediation, 2 nd ed., 604 p, Prentice-Hall.

Chilton, J., (1999), (ed), Groundwater in the urbanenvironment, International Contributions to Hy-drogeology Vol. 21, 342 p, IAH, A.A. Balkema,Rotterdam.

Foster S.S.D., Morris B.L., and Lawrence A.R. (1993),Effects of Urbanization on groundwater recharge,in Wilkinson, W.B., (ed), Groundwater Problemsin Urban Areas, Proceeding of Institution of CivilEngineers, June 1993, London, p. 43 – 63.

GWMAP (2000), Groundwater quality underthree unsewered subdivisions in Minnesota,Minnesota Pollution Control Agency, Ground-water and Toxics Monitoring Unit, Environ-mental Monitoring and Analysis Section, En-vironmental Outcomes Division, Minnesota.http:www.pca.state.mn.us/water/groundwa-ter/gwmap/gwq-unseweredsub.pdf

Hendrayana, H. (1993), Hydrogeologie undGroundwassergewinnung Im YogyakartaBecken, Indonesien, Dissertation, RWTH-Aachen.


PUTRA

Figure 5: Relations between changes of population density and nitrate groundwater content in theresearch area from north to south across central-part of Yogyakarta City

Lerner D.N. (2002), Identifying and quantifying ur-ban recharge: a review, Hydrogeology Journal,Volume 10, p. 143 – 152, Springer-Verlag.

Lerner, D.N., Issar, A.S., and Simmers. I. (1990),Groundwater Recharge: A Guide to Understand-ing and Estimating Natural Recharge, Interna-tional Contributions to Hydrogeology Vol. 8,IAH, Verlag Heinz Heise, Hannover, Germany.

MacDonald and Partners (1984), Greater Yo-gyakarta Groundwater Resources Study Volume3: Groundwater, 116 p, Directorate General ofWater Resources Development Project (P2AT),Ministry of Public Works, Government of TheRepublic of Indonesia.

Morris B.L., Lawrence A.R., and Stuart M.E. (1994),The Impact of Urbanization on GroundwaterQuality (Project Summary Report), TechnicalReport WC/94/56, British Geological Survey.

Morris, B.L., Lawrence, A.R., Chilton, P.J.C., Adams,B., Calow, R.C., and Klinck, B.A. (2003), Ground-water and its susceptibility to degradation: Aglobal assesment of the problem and options formanagement. Early Warning and Assesment Re-port Series, RS.03-3. United Nations EnvironmentProgramme, Nairobi, Kenya.

Putra, D.P.E. (2007), The Impact of Urbanizationon Groundwater Quality, A Case Study in Yo-gyakarta City – Indonesia, Mitteilungen zur Inge-nieurgeologie und Hydrogeologie, Heft 96, 148 S,Okt 2007, Herausgegeben vom Lehrstuhl fuer In-genieurgeologie und Hydrogeologie, Univ.-Prof.Dr. R. Azzam, RWTH Aachen, Germany.

Sinton, L.W. (1982), A groundwater quality surveyof an unsewered semi – rural area, New ZealandJournal of Marine and Freschwater Research, Vol.16, p. 317 – 326.

Sudarmadji (1991), Agihan geografi sifat kimiawiairtanah bebas di Kotamadya Yogyakarta, diser-tasi, Universitas Gadjah Mada, Yogyakarta.

Sukarma, R., and Pollard, R. (2002), Overview ofSanitation and Sewerage Experience and PolicyOptions, Urban Development Sector Unit, In-donesia Country Management Unit, East Asiaand Pacific Region, World Bank.

Vazquez-Sune, S., Sanchez-Vila, X., and Carrera,

J. (2005), Introductory review of specific fac-

tors influencing urban groundwater, an emerg-

ing branch of hydrogeology, with reference to

Barcelona, Spain, Hydrogeology Journal, Volume

13, p.522 – 533, Springer-Verlag.


Documents

EVOLUTION OF GROUNDWATER CHEMISTRY ON SHALLOW …geologic-risk.ft.ugm.ac.id/fresh/jsaag/vol-3/no-2/jsaag-v3n2p116.pdf · EVOLUTION OF GROUNDWATER CHEMISTRY ON SHALLOW AQUIFER OF YOGYAKARTA