The Relationship of Geology and High Lev

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The Relationship of Geology and High Level of Manganese Concentration in Groundwater

Case Study in Kaikoli and its Surrounding Areas, Dili, Timor-Leste 2017.

Mafaldo Jose Faria Graduate Internship Program

Marҫal Ximenes Supervisor Geohazard Division

2017.

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Foreword

Instituto do Petróleo e Geologia – Instituto Público (IPG) as an Institution of Government which is established in 18^th of July 2012 with decree law of no. 33/2012. The main objective of the institute is to conduct scientific investigation and collect geological data in Timor-Leste territory, including gas, petroleum, mineral resources such metallic and non-metallic, hydrogeology, geological risk and other geological resources.

Graduate Internship Program (GIP) is one of the IPG’s plan in this year to give an opportunity for new geologist graduate to develop them in their specialized area. The GIP are required to demonstrate their capacity through a scientific work like report study and/or desk study. This report study is one of them.

This report is intended to identifying the health concern of manganese and also the relationship of geology and its high concentration in groundwater. The Geo-Hazard Division of IPG hopes this report study will be useful and valuable for the public (the readers) in their understanding of the high level of manganese concentration in groundwater in Kaikoli and its surrounding areas either from the formation of manganese concentration processes and also its health concern as well. The contents of this report discusses about the concentration process of manganese chemical characteristics in groundwater based on geological and hydrogeological approaches and also manganese effect in drinking water for health to the community.

Dili, September, 2017

Helio C. Guterres The President of IPG-IP

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Preface

The Hydrogeology Unit of Geo-Hazard Division is fully responsible for this report of study in particular terms of geological and hydrogeological approaches for manganese concentration in groundwater. In this opportunity, the Hydrogeology Unit would like to express our deepest gratitude to all the IPG staff especially the Geo-Hazard Division who have involved in providing ideas and support in this report study.

The results of this report study are expected to be made as base valuable guiding for manganese concentration in groundwater and its health concern which will be a solution in the future.

Furthermore, the authors realize that the results of this study has many shortcomings especially in hydrogeological data where it is due to the limitation of laboratory analyses equipment therefore, further study is expected.

Acknowledgment

In this opportunity, I as a Graduate Internship Program (GIP) would like to expand my profound gratitude to:

• IPG who has given me the opportunity to internship here for six months.

• Mr. Eugenio Soares, Director of Geo-Hazard Division, all staff of Geo-Hazard Division and also my all GIP colleagues as well in providing ideas and support in this report study.

• Mr. Marcal Ximenes as my supervisor who have already guide me during this report study.

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ABSTRACT

In Kaikoli and its surrounding areas there was a high concentration of manganese. The distribution of the highest manganese concentration is 0.7 to 13.2 mg/L that has far exceeded the limit of manganese concentration in drinking water which established by WHO to 0.5 mg/L as standards.

One of the objectives of this study is to investigate more deeply about the formation of manganese concentration in the study area based on geological approach and hydrogeological of field investigation parameters as well as to know its health concern for local community.

It assumes that the distribution of high manganese concentrations in the study area was controlled by the swamp condition. Hence, the expected result of this study is to determine the swamp dissemination be based on the manganese concentration in study area.

In conclusion, the high level of manganese concentration in groundwater is caused by the geological condition factor. Kaikoli and its surrounding areas is a puddle or swamp area which geologically can accumulate the distribution of downstream river sediment that carried manganese later on dissolved into groundwater through catchment erosion, leaching and weathering of rock. Moreover, only with the swamp conditions can occur the chemical characteristics of high manganese concentration in water. In addition, landfill leachate from human activity is also considered as additional factor for the distribution of high manganese concentration in study area.

Keyword: High Concentration of Manganese, Manganese Distribution, Chemical Characteristics of Manganese in Water, Swamp Area, Health Concern of Manganese.

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Manganese (Mn) usually occurring with iron, those are one of the most abundant metals in Earth’s crust. In general, manganese never occurs as the free metal and always be found in more than 100 minerals including various sulfides, oxides, carbonates, silicates, phosphates, and borates (ATSDR, 2000). The concentration of manganese in groundwater can range up from < 0.001 mg/L to values occasionally in excess of 0.5 mg/L (WHO, 2004). One of the causes of the excessive number of manganese concentration is due to the organic circulation by plants and leaves (Longe, E.O., and Enekwechi, L.O., 2007) and it also makes water distasteful to drink with no specific toxic effects (BIS, 2003). The excessive distribution of the highest manganese concentration in study area is 0.7 to 13.2 mg/L.

In general, the main source of manganese concentration is from weathering of sediment rocks fragments and from metamorphic minerals such as mica, biotite, amphibole and hornblende (Purwanto Sudadi, 2003). Furthermore, manganese naturally occurs in groundwater as a trace element, mostly in groundwater that has little or no oxygen (in chemically-reducing conditions), in areas where groundwater flow is slow, and in areas where groundwater flows through soils rich in organic matter. Additionally, high manganese concentrations will also quickly form in acidic conditions or in water sealed environments such as swamp and lake.

Based on the geological engineering map 1:25.000 of Dili area (see Figure 2.2) shows that the manganese concentration is in swamp area. Therefore, it assumes that the distribution of high manganese concentrations in the study area was controlled by the swamp itself.

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I.2. Description of the Study Area

The study area of manganese concentration lies in Nain Feto Administrative Post of Dili Municipality from UTM projected coordinate system between 781000 to 785500 N and 9052500 to 9054000 S. Apart from this, the area consists of nine (9) villages like Kaikoli, Beira Mar, Nazare, 7 Dezembro, 28 Novembro, Solo, Santa Cruz, Bemori and Talera Hun. The occurrence of groundwater in study area has been observed through the dug wells as shallow unconfined aquifer in intergranular aquifer system. The fifteen (15) dug wells of high level of manganese concentration ranging at varies depth between 0.5 to 4.3 meters or 1.61 meters average from ground surface. Generally, the groundwater flows follow the topographic with direction from South to North. Moreover, the study area is flat plan and covered by Quaternary age of alluvium deposits which contains of fluvial sediments where is dominated by unconsolidated material such as gravel and sandy soil. In adition, groundwater discharge considered directly relate to rainfall and the height of groundwater level is likely linked strongly to seasonal fluctuations.

I.3. Purpose and Expected Result

The purpose of the study is to investigate the relationship between geology and high level of manganese concentration in groundwater. Thus, the expected result of this study is to determine the swamp dissemination be based on the manganese concentration in study area.

II. LITERATURE REVIEW

II.1. Geological and Hydrogeological Maps of Study Area II.1.1. Geology

According to the geological map of Dili sheet (IPG, 2014), the geological unit of lithology in the study area is dominated by alluvium deposits which is consist of fluvial sediments and marine terrace sediments. The fluvial sediments composed of sandy soil and gravels and some areas mixed with marine terrace sediments, like generally occur along river terrace and low mountain slope. At the Southern part of the study area is formed by metamorphic rock such as metasandstone black greenish phyllitic schist and black phyllitic schist (see Figure 2.1).

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Figure 2.1. Geological map of study area, IPG, (2014).

On the other hand, built upon of the geological engineering map of Dili and surrounding area (Djadja, N.R. Sutarto 1989), the geological engineering unit of study area are organic clay, clay silt and black clay (I), grey blackish sand and yellow whiteness sand (II), brown blackish of sand, gravel and pebble (III), white yellowish of silt clay and clay silt (IV) and grey brownish of

Study Area

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pebble, gravel and sand (V). Hereafter, at the Southern part of the study area is controlled by metamorphic rock such as schist and slate (VI) where composed a lot of quartz vein. In addition, the study area that covered by organic clay, clay silt and black clay (I) is a puddle area or swamp area which is the main factor of causing the high level of manganese concentration in groundwater (see Figure 2.2).

Figure 2.2. Geotechnical map of Dili and surroundings area, Djadja N.R. Sutarto, (1989).

III.1.2. Hydrogeology

The study area is located among the coastal area and foothills of Nain Feto Administrative Post of Dili Municipality, which is high intergranular aquifer that composed by sediments. The sediments have been mapped as Quaternary age of alluvium. The composition of alluvium deposit that ranges throughout the study area is reflecting the surroundings geology.

The texture of these sediments are varies, but is typically unconsolidated and moderately poorly sorted clays to pebbles. These sediments is constituent material of shallow unconfined aquifer in

Study Area

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intergranular aquifer system which is considered to be predominantly supplied by the Maloa and Bemori Rivers then deposited as a delta (Wallace et al., 2012).

Figure 2.3. Hydrogeological map of Timor- Leste, (Wallace et al., 2012).

Study area

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II.2. Basic Principles of Manganese Chemistry in Groundwater II.2.1. Redox Reactions (Eh) and pH

The water’s pH and its redox reactions or oxidation/reduction potential (ORP) are the two most important environmental conditions that control manganese chemistry in groundwater. pH is a measure of the acidity or alkalinity of a solution. It is presented as a range from 1 to 14, with pH of 7 considered neutral. The acidity of most groundwater is dominated by the bicarbonate content when the pH range <6.5. The dominance of bicarbonate decreases as pH goes up further, and once pH exceeds 8.5, CO32- becomes the dominant form of alkalinity. Hereafter, at very high pH (>11), OH^_ dominates the total alkalinity. Once in a while, other dissolved components contribute significantly to the alkalinity; e.g. dissolved hydrogen sulfide (HS-) is common in deep groundwater which totally devoid of oxygen (Younger, P. L., 2007).

ORP expressed in voltage, indicates the relative presence of oxidants, such as dissolved oxygen, and describes the oxidizing or reducing tendency of a water. It determines the direction and rate of redox reactions. Hereinafter, ORP is also interpreted as the transfer of electrons between atoms, molecules, or ions, where oxidation is defined as the loss of electrons (positive values are more oxidizing) and reduction is defined as the gain of electrons (negative values are more reducing). The change of the transference of manganese electrons will affect directly its solid properties and solubility in water (MGWA, 2015).

In most cases, groundwater constantly has neutral pH; therefore, ORP, also known as redox potential (Eh), generally drives manganese behavior. The Eh-pH diagram describes these two variables of water’s pH and its redox reactions as a graphical, it means the diagram can show the effect of changing redox potential and pH on manganese solubility in aqueous systems.

Moreover, the diagram of Eh-pH is also describing the stability of solid “(c)” and aqueous phases of manganese as a function of redox potential and pH, at standard temperature (25°C) and pressure (1 atmosphere). Manganese precipitates and forms as insoluble compound in the solid of stability fields. The boundaries at a concentrations of 0.01 ppm (parts per million) dissolved manganese (0.01 mg/L) represent the solid lines. Whereas the dashed lines represent the boundaries of dissolved Mn⁺² concentrations at 0.10, 1.0, 10, and 100 ppm.

In addition, manganese in the solid phase is released to the aqueous phase when Mn oxides become reduced to Mn (II) which is relatively soluble because the increase in redox potential is due to the decrease in dissolved oxygen of groundwater along its flow path at greater

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depths (Freeze and Cherry 1979 in Singhal and Gupta, 2010). Hence, redox potential (Eh) is a strong indicator of the ability for manganese to be released in to solution where at low pH and Eh the dissolved manganese concentration will increase (Hem, 1985). As for Eh values for the reduction of Mn oxides (IV) to Mn reduces (II) is tended to be around 1.2 V to 0.2 V (Dixon and Schulze, 2002; WHO, 2011 in Elizabeth C.G., 2014).

Figure 2.4. Diagram of Eh-pH (Hem, 1985 in MGWA, 2015).

As it was mentioned above, manganese concentrations in groundwater can be high when the aquifer has reducing conditions. Under these conditions, manganese converts to its more soluble form (Mn (II)). In consequence, much higher dissolved manganese concentrations commonly are found in groundwater that has low amounts of oxygen such as deep or isolated aquifers (Nadaska and Michalik, 2010; Mitsch and Gosselink, 2007, in MGWA, 2015).

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In summary, manganese concentration in water is controlled primarily by pH and redox conditions, where solubility increases under acidic as well as under anaerobic conditions. The redox potential has a stronger influence on manganese mobility than pH when water’s pH is in neutral conditions. Under aerobic conditions the concentration of manganese, typical of shallow aquifers and surface water is generally low and as a rule do not reach detection limits. The reason is that, in aerobic conditions manganese is found in its stable oxidized form, mostly as MnO2, which is highly insoluble. As water infiltrates downwards through soils and aquifers, the soil environment becomes more anaerobic and more reducing. The reduction reactions follow a sequence in which oxygen is removed first, then later followed by nitrate and manganese. The more reducing conditions increasingly lead to the reduction of iron followed by sulfate. In these anaerobic conditions, manganese is released from minerals and reduced to its more soluble form (Mn⁺²). This form is apparently the most soluble one in most waters. Therefore, much higher manganese concentrations are commonly found in anaerobic ground waters than in aerobic surface waters or shallow ones.

II.2.2. Bacteria and Microbial Activity

In General, the bacteria and microbial use redox-sensitive compounds (oxygen) as a source of energy for their metabolism. In groundwater systems many redox reactions are microbially mediated and kinetically controlled. Other than that, microbial are also learned in the subsurface to investigate whether pathogenic bacteria is present in groundwater or to determine the role of microbial activity in predominantly redox processes (UNESCO, 2004).

In anaerobic groundwater often contains high levels of dissolved manganese. At pH 4–7 the Mn²⁺ dominates in most water, however at higher pH values or from microbial oxidation result may generate more highly oxidized forms of manganese (ATSDR, 2000, in US EPA, 2004).

There are over 200 species microbes of Mn reducers that can be found in the soil. The presence of microbes will increase the rate of manganese reduction from Mn oxides (IV) to Mn reduces (II) (Gounout, 1994). The presence of organic matter which produce CO2 in soil and changes in temperature alongwith seasonal and daily humidity control the activity of soil micro- organisms, because elevated levels of organic matter drive microbial activity to reduce Mn (IV) to Mn (II), then allowing Mn²⁺ to be released into groundwater. Moreover, the increase of

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organic matter decomposition by microorganism in saturated conditions will also create a potential for Mn (IV) reduction (Gounot, 1994 in Elizabeth C.G., 2014).

In groundwater, once manganese oxides are reduced many factors may prevent the movement of Mn²⁺. For instance, Mn (II) may re-partition in the solid phase in secondary precipitates, such as MnCO3 (Gounot, 1994). Plants may also take up dissolved Mn in the groundwater (Intawongse and Dean, 2006 in Elizabeth C.G., 2014). The microbial or abiotic oxidation of Mn (II) may remove Mn from the aqueous phase, but this tends to be a slower process compared to the reduction of Mn oxides (Gounot, 1994; Sly et al., 1990 in Elizabeth C.G., 2014). An example of dissolved manganese becoming immobile is when bodies of water such as streams or swamps become aerated and Mn (II) becomes oxidized (Gounot, 1994 in Elizabeth C.G., 2014). Sometimes areas that contain less vegetation and coarser grained sediments above the water table will allow for more aerated conditions and permit the oxidation of Mn (II) (Gounot, 1994 in Elizabeth C.G., 2014).

In finding out how big the influence of bacterial and microbial activity towards manganese concentration in groundwater is required TOC analysis by quantifying the overall concentration of organic compounds in a groundwater.

II.3. Chemical Characteristics of Natural Groundwater Approach for Manganese Concentration

II.3.1. Major Cations and Anions

The major cations which are present in the greatest concentrations (constantly greater than 1 mg/L) in most groundwater are calcium (Ca²⁺), magnesium (Mg²⁺), sodium (Na⁺) and potassium (K⁺). Low concentrations of all four elements are obtained from rainwater to aquifers, even though evaporative concentration during the recharge process of rainwater increases infrequently approximately above 20 mg/L. The major natural source of all four dissolution minerals are from soil and bedrock.

Calcium and magnesium are predominantly sourced from dissolution of carbonate minerals, especially calcite (CaCO3, which can also contain significant quantities of Mg) and dolomite (CaMg (CO3)²), both of which are abundant in limestone terrains. Calcite is also a common cementing phase in many sandstones. In some sedimentary sequences, beds comprising of the highly soluble minerals gypsum (CaSO4 2H2O) and anhydrite (CaSO4) can act as important sources of dissolved Ca. Many silicate minerals are also important sources for Ca²⁺

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and Mg²⁺ in groundwater. For instance, acidic igneous rock such as rhyolite tuffs and granites, and in the many sedimentary rocks derived from them, common sources for Ca and Mg include hornblende (Ca2Mg4Al2Si7O22 (OH) 2) and biotite mica (K (Mg,Fe)3(Si3Al)O10(OH)2). Ultrabasic and basic igneous rocks (including basalt lavas), dissolved Ca and Mg are derived from the weathering of anorthic plagioclase (CaAl2Si2O8), diopsidic pyroxene (CaMgSi2O6), and forsteritic olivine (Mg2SiO4).

The formation of clay minerals effectively traps nearly all of the aluminum (and much of the SiO2) in solid form. Silicate weathering is also a common source for dissolved Na⁺ and K⁺. Most plagioclase and potassium feldspars contain a lot of Na⁺and K⁺. They are also abundantly present in the minerals halite (NaCl) and sylvite (KCl), which are both common constituents of ancient evaporate (i.e. salt lake) deposits, formed under hyper-arid conditions. When such minerals gain access to modern groundwater, they tend to dissolve so vigorously that they yield many thousands of mg/L of Na⁺ and/or K⁺ to solution (Hem, 1985 in Younger, P. L., 2007).

The major anions which are present in the greatest concentrations (all > 1 mg/L) in most groundwater are bicarbonate (HCO3-), sulfate (SO42-) and chloride (Cl^-). Although modest concentrations of all three anions are introduced to aquifers in rainwater, even after evaporative concentration during the recharge process their rainwater-derived concentrations seldom exceed about 20 mg/L.

Bicarbonate dissolved in groundwater is derived from two principal natural sources:

Biogenic: CO2 is released into the soil atmosphere, and thus into waters draining through the soil, both directly from plant roots and (more importantly) by the microbial degradation of soil organic matter. At circum-neutral pH, CO2 dissolves in water to form bicarbonate as follows:

CO2 (d) + OH^-(aq) ↔ HCO3-(aq). Mineral: the dissolution of the same carbonate minerals which release Ca²⁺ and Mg²⁺ to solution also yield abundant dissolved HCO3-.

Sulfate dissolved in groundwater has two principal natural sources: Weathering of sulfide minerals, most commonly pyrite. Weathering of gypsum and/or anhydrite, as already mentioned in relation to Ca²⁺ release.

Chloride is one of the least reactive solutes found in groundwater systems, and as such it has very few natural mineral sources. Clearly where the evaporate minerals halite and sylvite are encountered by flowing groundwater very high concentrations of Cl^- can result. In many hydrogeological settings, concentrations of Cl^- much greater than can be accounted for by

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evaporative concentration of rainwater to indicate that the groundwater in question actually represents a mixture of different water sources. Sea water is also very rich in chloride (averaging 18,980 mg/L), so that Cl^- concentrations can be a sensitive indicator of the intrusion of marine groundwater into terrestrial aquifers (Younger, P. L., 2007).

II.3.2. Chemical Equivalence

Positively charged cations and negative anions combine and dissociate in definite weight ratios. By expressing ion concentrations in equivalent weights, these ratios are readily determined because one equivalent weight of a cation will exactly combine with one equivalent weight of an anion. The combining weight of an ion is equal to its formula weight divided by its charge. When the concentration in milligrams per liter is divided by the combining weight, an equivalent concentration expressed in milliequivalents per liter (meq/L) results. Table 2.1 shows the lists of the reciprocals of combining weight of cations and anions; concentrations in milligrams per liter can be converted to mill equivalents per liter by multiplying the appropriate conversion factor.

If the chemical analysis of the various ionic constituents indicates a difference from this balance, it may be concluded either that there are other undetermined constituents presents or that errors exist in the analysis.

Table 2.1. Conversion factor for chemical equivalence, concentrations in mg/l times the conversion factor yields concentration in meq/l (Hem, 1985 in Todd and Mays, 2005).

Chemical Constituent Conversion Factor Bicarbonate (HC03-) 0.01639

Calcium (Ca+2) 0.04990

Carbonate (CO3-2) 0.03333 Chloride (Cl-) 0.02821

Hydroxide (OH-) 0.05880

Iron (Fe+3) 0.05372

Magnesium (Mg+2) 0.08226

Manganese (Mn+2) 0.03640

Potassium (K+) 0.02557

Sulfate (SO-4-2) 0.02082

Sodium (Na+) 0.04350

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II.3.3. Hydro-chemical Facies of Groundwater

The major ion chemistry of groundwater is a powerful tool for revealing the origin of solutes and processes that generated an observed water. In general, a gradual increase of the mineralization of groundwater and shift from the dominant anion HCO3 by way of the SO4 to Cl^- are observed in waters moving from shallow to greater depth, due to decreasing groundwater circulation and increasing water-rock interaction. Furthermore, the major ion chemistry can also determine the trace element such as Fe, Mn, Zn, Pb, Ni, Cr, Cu, etc. in groundwater. Such variations in chemical character are used to subdivide formation water into hydro-chemical facies. Therefore, the concept of hydro-chemical facies is to denote the diagnostic chemical character of water solutions in hydrologic systems. The facies reflect the effects of chemical processes occurring between the minerals within the lithologic framework and the groundwater (Back, 1966). Other than that, the hydro-geochemical facies is to define different sedimentary by means of specific mineral indicators of oxidation-reduction potentials and pH.

The concept of hydro-chemical facies has been also used for explaining the changes in water quality from recharge to discharge areas and along the flow paths in a given lithology (Back, 1966 in Singhal and Gupta, 2010). Some of the main inferences are: (i) Bicarbonate content is low in recharge areas and high in discharge areas; (ii) Sulphate content decreases in the direction of flow and bicarbonate increases, as a result of sulphate reduction; and (iii) The ratio of sulphate to chloride decreases in the direction of flow.

As water flows through an aquifer it assumes a diagnostic chemical composition as a result of interaction with lithologic framework. The term hydro-chemical facies is used to describe the bodies of groundwater, in an aquifer that differ in their chemical composition. The facies are a function of the lithology, solution kinetics, and flow patterns of the aquifer (Back, 1966 in Fetter, 2001). Hydro-chemical facies can be classified on the basis of the dominant ions in the facies by means of the trilinear diagram. A trilinear diagram can show the percentage composition of the major cations and anions to be displayed. Piper’s diagram forms the basis of classification of waters into various hydro-chemical facies (Figure below).

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Figure 2.5 Piper’s diagram (Piper, 1944 in Singhal and Gupta, 2010) of hydro-chemical facies classification. The ionic concentration is in percent of total meq/L.

According to Piper’s diagram indeed if the yield of groundwater facies is bicarbonate type it means that the abundant of dissolved HCO3 is released by the dissolution of carbonate minerals including carbon dioxide in groundwater. Groundwater that containing a number of manganese is always deficient in dissolved oxygen and contains high amounts of carbon dioxide.

High levels of carbon dioxide indicate the presence of extensive organic oxidation by bacteria, whereas the absence of dissolved oxygen suggests the development of anaerobic conditions.

Therefore, high level of Mn²⁺ concentrations in groundwater are influenced by complexation with bicarbonate ions (Hem, 1972 in Alan M. MacDonald et al 2010).

Given that manganese accumulated in plant material also provides a source for dissolution during decomposition. In aquatic systems manganese solubility increases at low pH as well as under low oxidation-reduction potential, and is most commonly in the Mn (II) and Mn

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(IV) oxidation states. The presence of high concentrations of chlorides, sulfides and nitrates may increase manganese solubility, raising both aqueous movement and uptake by plants (Morje J.W, 1991 in Gabriela NADASKA, et al 2005).

II.4. Health Concern of Manganese

Manganese is a common compound that found everywhere on earth. Manganese absorption by the human body mainly occurs through drinking water and food which is then transported through the blood to the liver, kidneys, pancreas and endocrine glands. High manganese contamination especially in drinking water can have a major impact on health.

Manganese effects often occur mainly in the respiratory tract and the brain. The toxicity of its poisoning is forgetfulness, hallucinations and nerve damage. Manganese can also cause Parkinson's, lung embolism and bronchitis. When people consume large quantities of manganese through drinking water or food for a long time they become impotent. A syndrome caused by manganese has symptoms such as schizophrenia, muscle weakness, stupidity, insomnia and headaches.

Source of manganese contaminated in groundwater generally come from natural occurrences of manganese in rock and from anthropogenic activity. By reason of manganese dissolves in water, it can get into drinking water by catchment erosion, leaching and weathering of rock, and dissolution of manganese from dust sediment as well as from human activity including landfill leachate, industrial effluent, and underground injection (US EPA, 2004).

III. METHODOLOGY AND MATERIALS OF STUDY

This study is based on a desk study and field observation. In the desk study, the necessary data were collected from various sources later on interpreted, organized, identified a method for fieldwork, preparation of reports and presentation. Furthermore, information of dug wells, production wells, water level and physical properties (pH) of groundwater will collect directly from field observation and on the other hand the geological data (stratigraphical correlation from hand digging sampling) will obtain from primary and some secondary data. The information of chemical parameters (manganese, major cations and anions) will refer to the Laboratory Nacional dá Saúde, Timor-Leste analyses from the chosen samples. Nevertheless, some modifications can be made during the fieldwork be based on field information and inventory of

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laboratory analysis. In addition, of all available data is processed by using ArcGIS and Surfer software afterwards to create groundwater flow map and manganese distribution map.

Figure 3.1. Flow chart of study

The field equipment that request for this study is shown in table below.

Table 3.1. Materials for field observation

No. Materials Unit

1 Hanna Instrument H19811-5 Portable: pH-EC-TDS Meter 1

2 ORP/Eh Meter 1

3 GPSMap 60 CSx 1

4 Brunton Compass 1

5 Digital Camera 1

6 Stationery 1

7 Geological Hammer 1

8 Water Level Meters Model 101 1

9 Bottle Sample ± 20

10 Hand Auger 1

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IV. RESULT AND DISCUSSION

IV.1. Manganese Distribution in Study Area

As it was explained before, the distribution for the highest manganese concentration in Kaikoli and its surrounding area is 0.7 to 13.2 mg/L. This distribution of manganese has far exceeded the limit of manganese concentration in drinking water which established by WHO (2004) to 0.5 mg/L as standards.

Figure 4.1. Manganese Distribution Map of Dili and Surroundings Areas (2016).

IV.2. Potential of Hydrogen Distribution in Study Area

From the 15 existing well points, then the average distribution of pH in the study area classified as Neutral with values ranging from 6.2 to 8.3. It assumes that groundwater facies in Kaikoli and surrounding areas are controlled by major anions of all three of bicarbonate, chloride and sulfide types. Groundwater facies of bicarbonate type reflects the abundant of dissolved HCO3 which is released by the dissolution of carbonate minerals including carbon dioxide in groundwater. Groundwater that containing a number of manganese is always deficient in dissolved oxygen and contains high amounts of carbon dioxide. High levels of carbon dioxide

STUDY AREA

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indicate the presence of extensive organic oxidation by bacteria which can increase the rate of manganese reduction from Mn oxides (IV) to Mn reduces (II) later on released into groundwater.

Whereas the presence of chlorides and sulfides may increase manganese solubility, raising both aqueous mobility and uptake by plants where manganese accumulated in plant material also provides a source for dissolution during decomposition.

Figure 4.2. Potential of Hydrogen Distribution Map of Dili and Surroundings Areas (2016).

IV.3. Watershed Analyses for Manganese Distribution in Study Area

As it is known that the main source of manganese concentration is from weathering of sediment rocks fragments and from metamorphic minerals such as mica, biotite, amphibole, and hornblende. Geologically, the lithology of the southern part of the study area is composed by metamorphic rock units such as Black Greenish Phylitic Schist, Meta Sandstone, Meta Claystone and Meta Peridotite which entirely consist of those minerals above. In general, from the source of manganese will be streamed through the existing watershed later on distributed to the main river (Maloa and Bemori River) which flows through the study area. Because of the study area is a puddle or swamp area, so geologically it is composed of fine grained sediments which is

Study Area

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impermeable towards water. Hence, the distribution of manganese is all accumulated in the swamp areas. Moreover, only with the swamp conditions can occur the chemical characteristics of high manganese concentration in water. This condition differs from the surrounding areas such as the Comoro region where it is composed of coarse grained sedimentary material (sand and gravel) which has a high permeability levels to the fluid so that there is no significant manganese concentration in that areas.

Figure 4.3. Watershed analysis and anthropogenic influences for manganese distribution in study area

On the other hand, human activity (anthropogenic) is also considered as an additional factor of manganese distribution. From a dense population accompanied by geological factors, the leachate landfill which is also a source of manganese especially from the food chain must be taken into account.

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IV.4. Groundwater Flow Model in Study Area

It assumes that under normal geological condition of unconfined aquifer systems, groundwater generally flows from high to lower areas.For instance, in coastal aquifers where the downstream from the direction of groundwater usually flows towards the lower shore. In this case, the direction of groundwater should be flow towards the coast (North direction) but the flow pattern shows the irregular pattern. From the irregular pattern of groundwater flow model (Figure 4.4.), it is estimated that the aquifer in the study area is an isolated aquifer (swamp area) which has its own aquifer system to the surroundings area.

Figure 4.4. Model of groundwater flow in study area

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V. CONCLUSIONS AND RECOMMENDATION V.1. Conclusions

Refer to the previous pages of explanation on this study concluded that the high level of manganese concentration in groundwater in study area is caused by the geological condition factor. Kaikoli and its surrounding areas is a puddle or swamp area which geologically can accumulate the distribution of downstream river sediment that carried manganese later on dissolved into groundwater through catchment erosion, leaching and weathering of rock.

Furthermore, landfill leachate from human activity is also as additional factor for the distribution of high manganese concentration in study area.

V.2. Recommendations

 Groundwater sample is highly required for laboratory analysis in determining the value of Eh and TOC thereby the concentration of manganese in the study area which is hydrogeologically caused by swamp conditions will be detected.

 Considering also that it is necessary to know groundwater facies and then be reconnected to manganese concentrations in study area. Therefore, the laboratory analysis for major cations (Ca²⁺, Mg²⁺, Na⁺, K⁺) and major anions (HCO3-, SO42-, Cl^-) are required.

 Because Kaikoli and its surrounding is a puddle or swamp area, hence it is required hand auger equipment to take soil samples from hand digging sampling (± 10 m) later on will make a model of stratigraphic correlation to manganese concentration in order to determine the manganese concentration to the depth and also the dissemination of swamp area.

 It is also required to check the health department's data on study area then related to diseases caused by manganese in order to provide solutions in the future.

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REFERENCES

Alan M. MACDONALD et al. (2010), Manganese concentrations in Scottish groundwater, Science of the Total Environment.

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The Relationship of Geology and High Lev

The Relationship of Geology and High Level of Manganese Concentration in Groundwater

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