THE HYDROGEOCHEMICAL ATLAS OF SRI LANKA C. B. DISSANAYAKE S. V. R. WEERASOORIYA - T+TVIPIv ~/.IT~R~~F~P~~ ,, . d . . d BU d b - i,-di J .d A"" . a Avr a, 'u ,& ST\.! 3ANKA C. B. DISSANAYAKE 1 B.Sc. (1lox:s.) Cevlon; D.Phil (Oxon) A#I.I.RI.h,I. (Lond) E'.I.Chem.C] Professor anti Heati, Ilepartment of Geology University of I'eradeniya SKI LIZNKA and S. V. R. WEERASQORIYA [R.Sc (Mons) Ceylon] [I1h.D. Sri Lanka] Ileparrment of Geology Lyniversity of Peradcniya SRI 1-ANKA A PhRRblCATAQN OF THE NATURAL RESOURCES ENERGY AND SCIENCE AUTHORlT't' OrC' SR! AANKA TI-IE COMPII.ATION AND PUBLICATION OF THIS ATLAS HAVE BEEN FUNDED BY THE, NATURAL RESOURCES ENERGY AND SCIENCE AUTHORITY OF SRI LANKA UNDER THE RESEARCH GRANT R.G.B.181120. All Rights Resenred, No part of this pubiication may be reproducecl, stored in a retrieval systenm, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior permission of the Fub!isher. Surveyor Cietleral, Pleputy Surveyor General ((viapping) arid Staff of Uepart~n~rzf, of Surveyor Gen~r;zl iov supplying colour separations of maps. {:over desigll ,md Cartography : S.M.B. Amunugama Ofk'sel atrci IPublisl~ed by Natural Resources, Energy 6( Science Authority of Sri Eanka, 4715, Maitland Place, Coioinbo 7, SRI LANKA. CONTENTS FOREWORD PREFACE REFERENCES MAPS APPENDIX Dr. R.P. Jayewardene, Director General Natural Resources, Energy and Science Authority of Sri Lanka C.B. Dissanayake and S.V.R. Weerasooriya THE PHYSICAL ENVIRONMENT OF SRI LANKA SAMPLING PROCEDURES ANALYTICAL TECHNIQUES PLOTTING OF DATA AND MAP MAKING TOTAL DISSOLVED SOLIDS (TDS) TOTAL HARDNESS NITRATES, NITRITES AND AMMONIUM IONS CHLORIDE FLUORIDE TOTAL DISSOLVED SILICA IRON AND MANGANESE VANADIUM, CHROMIUM, COPPER AND ZINC THE GEOCHEMICAL CLASSIFICATION OF GROUNDWATER OF SRI LANKA Page i FOREWORD Since water is a precious natural resource its conservation and proper management are extremely important. If this is to be done efficiently continuous monitoring over all parts of the country must be undertaken. ']The hydrogeochemical atlas fills a long standing gap in the geological field. Groundwater monitor in^ is essential. The knowledge so gained will indicate where goad water is available and also where pollution - natural or man made - is prevalent. 'The atlas is the result of the work done by the Environmental Geochemistry Research Group of the Department of Geology, University of Peradeniya. The geochemistry of potable water in Sri Lanka has been an important area of the research undertaken by this group. The importance of this work is evident when we reali~e that water borne diseases are w~despread in our country. These diseases are preventable. If our water resources are moni- tored and well managed these preventable &\eases may ultimately be controlled. Another important health hazard is the presence of large amounts of fluorine in the water. 'This has been found in the dry zone in the Eastern and North Central Region of the country. I-Iigh concentration of fluorides in grounwater in these areas cause dental fluorosis (tootlz mottling) especially in children living in those regions. The geochemical status of fluorine in the environment is extremely important in the study of this disease. The Natural Resources, Energy and Science Authority (NARESA) has awarded a research grant to Prof. Dissanayake for this research work. I am extremely happy that NARESA is contributing towards this research effort and to the preparation of this atlas which will be of great help to all those working with groundwater resources. Director-General Natural Resources, Energy & Science Authority PREFACE The need for clean water as one of the most essential commodities for mankind can never be over-emphasized. Groundwater monitoring is one of the most important aspects of management of groundwater resources and prevention of groundwater pollution. Resource conservation calls for comprehensive monitoring systems to protect groundwater resources from pollutants. Pollution, whether natural or man-induced, is not confined to industria- lized nations and administrative boundaries. However, most environmental research activities have been centered on rivers, lakes and atmosphere in developed nations. Very few case studies have been reported from developing countries, and for this rkason it is of interest to note the establishment of a Central Environmental Authority in Sri Lanka, and the active participation of many research organizations including the Environmental Geo- chemistry Research Group of the Department of Geology at the University of Peradeniya. 'This interdisciplinary work has, not surprisingly, revealed some unpleasant but hard truths. The geochemistry of potable waters of Sri Lanka is one important area of study, in view of the fact that the majority of the country's health problems are related to its aquatic environment. According to a government publication, only 10 - 15% of the people have access to piped water. The majority use small, unportected wells, and in rural settlements, reservoirs and water channels are the main sources of drinking water. The proper disposal of human and other wastes through sewage systems and latrines is also severely limited, less than a third of the population having satisfactory latrine facilities. The poor water supply and excreta disposal systems have resulted in 40% of the Sri Lankan population being affected by typhoid, amoebic and bacillary dysentery, infectious hepatitis, gastro-enteritis, colitis anti worm infections. Our research group has recently carried out a preliminary Island-wide survey of nitrates in drinking water from wells, since an excess of nitrates can cause bowel diseases and metha- emoglobinaemia in children. This study shows that some areas, such as Jaffna, do indeed have dangerous levels of nitrates above the W.H.0 recommended limits of 50 to 100 mg/l. Other areas that contain high nitrate levels in well waters are the coastal regions around Batticaloa. The study also revealed that there are close correlations between the nitrate content in the water and factors such as population density, fertilizer use, annual rainfall and the underlying geology. At present, the research group is conducting a similar survey on the distribution of nitrosoamines, which are known to be carcinogenic and which could be formed by the reduction of nitrates and nitrites in the natural environment. In another study, the incidence of heart disease was related to the hardness of water in Sri Lanka. Studies conducted in other countries have shown that in most cases, people living in areas containing "hard water" are less prone to heart diseases than those living in areas containing "soft water". The results of this Island-wide survey showed that the same correlation also exists in Sri Lanka. Areas underlain by soft water have higher incidences of heart ailments, whereas these are less common in the Jaffna district which is underlain mostly by limestones yielding hard water. Such geomedical studies are proving to be of extreme importance, since potential health hazard regions can be easily delineated and studied in detail. The water quality of recently constructed reservoirs in central Sri Lanka is also under inve~t~igation. In the Polgolla reservoir, for example, it was found that trace metal concentra- tions exert an influence on the quality of drinking water of wells in the vicinity. This is particularly so for the case of Mn, which exceeds the W.H.0 standard of 0.5 ppm by a factor of three. One of the major objectives of our research group is the production of geocilemical maps showing the distribution of elements or important chemical species in the surface and groundwater of Sri Lanka. A geochemical data bank is now being prepared with the assistance of the Water Supply and Drainage Board and the Water Resources Board of Sri Lanka. For example, in a preliminary survey carried out on the relationship between fluoride ions in drinking water and the incidence of dental diseases, areas with abundant fluoride concentrations in the water (> 3 ppnz) were identified. Dental fluorosis was found to be common in areas where mineral deposits such as apatite are found or where hot springs with exhalations of fluorine occur. In contrast, those areas with very little or no fluoride, such as the central region of Sri Lanka, had a high incidence of dental caries. The intensity of rainfall also plays a major role in the leaching of fluoride ions from soils and probably contributes to the formation of a low fluoride zone in the wet central region of Sri Lanka. Relationships between the geochemical environment and human health are particularly complex and progress in establishing association and causation, between geochemical factors, health and disease requires rigorous interdisciplinary research. The production of a hydrogeochemical atals has long been a national need for Sri Lanka. This atlas is the result of many years of work by us and it is hoped that this hydrogeochemical atlas would prove to be useful to hydrogeologists, agriculturists, town-planners and public health workers, epidemiologists and environmentalists of Sri Lanka. Many friends and colleagues, particularly those in the Water Supply and Drainage Board, Water Resources Board and the Government Geological Survey Department have, in various ways helped in the preparation of the atlas, and to them we are deeply indebted. The extremely valuable assistance rendered by the academic and technical staff of the Department of Geology of the University of Peradeniya is gratefully acknowledged. A-special word of thanks is due to Dr. R.P. Jayewardene, Director-General of the Natural Resources, Energy and Science Authority of Sri Lanka for his very kind Foreword. Finally I wish to thank 'Mr. Anil Ranasinghe and other staff members of the IVARESA Printing lJnit for technical assistance and excellent printing of this publication. Department of Geology, University of Peradeniya, 1985. 1. THE PHYSICAL ENVIRONMENT OF SRI LANKA Location and physiography 'The Island of Sri Lanka is geologically and physically a southern continuation of India, only recently separated from the mainland by the shallow sea covering the Palk Strait and Gulf of Mannar. It is an essentially compact island, 69450 km2 in extent lying off the southern tip of Peninsular India between latitudes 5' 55' - 9O 51' N and longitudes 79' 41' - 81° 53'E. It is separi~ted from the Indian sub-continent by a strip of sea which, at its narrowest, is about 25 milcs wide. 'The continental shelf is narrow around the southern part of the Island, but towards the north, it widens out and merges with the platform that surrounds India. The morphology arid morphotectonics of Sri 1,anka have been studied by Adams (1 92Y), Wadia (1945), Cook (1951) and Vitanage (1970). On the basis of height and slope charac- teristics, the Island can be divided into three main morphological regions (Vitanage, 1970). 1. The coastxl lowlar~ds with elevation from sea level to 305 rn with a few isolated inselbergs. The slopes in the coastal belt range from 0' to 15'. The striking feature of the lowlands is that they are very narrow, particularly in the southern margin of the Island where the width could bc as smaIl as 3.2 km. Towards the west however, the coastal lowlands become wider with the widest parts being seen in the north west (fig'. 1). 2. The uplands with elevations ranging from 305 m to 915 m consisting of riclge and valley topography and highly dissected plateaus. These areas comprise of narrow "arenas" or "amphitheatres" and domes occupying nearly three tenths of the Island. The average degree of slope varies frorn 10' to 35' along the upland ridges depending on the lithology and structure. 3. The highlands comprising of a series of well defined high plains dncl plateaus rimmed with mountain peaks and ridges. Their elevations range from 9 15 m to 2420 rrl arld these highlands characterise the central parts of Sri Lanka. These morphological features are not continuous and are separated from the intervening dissected lower plateaus and uplands by steep escarpments and deep valleys. Two distinct highland mountain massifs - knuckles Massif (2035 m), north east of Kandy and Rakwdna Massif (1488 m) qouth west of Sri Lanka occur detached from the main central highland area proper by the deeply eroded valleys carved out by the head streams o! the Mahawcli and Kelani rivers. Climate The climate of Sri Lanka is basically controlled by.its location within the tropics, its proxi- mity to the Indian sub-continent, its insularity and the presence within it of a centrally located mountain mass (Peiris, 1976). The t'ropical location of Sri Lanka ensures a uniform- ly high temperature, but maritime influences consequent upon its insularity makes it free f~om thermal extremes that are characteristic of continental interiors. The mean rnonthly temperatures in the lowlands of Sri 1,anka fall between 78' - 85' F with little seasonal and moderate diurnal variations. In the central highlands however, there is an orographically induced lowering of temperdture to rnonthly means that range from 55' 70' F, in the highe 35,000 brine In irrigation practices, the TDS content in water is an extremely important water quality consideration. The water uptake relation of plants is mainly controlled by the osmotic pressure differential between soil solution and plant solution. This osmotic effect is generally relat:d to the total concentration of TDS rathern thar, to the indivi*ylal concentre- tion oi speclfic iorlic constituents. As shown in map 1 the total dissolved solidconcentrationsrange widely in the groundwate; ol Sri Lanka. In much of the inland aieas, TDS range from 100 to 600 ppm, and ~wate- of this type can be conslderecl as fresh water. The relatively low amounts of total dissolved solids (eg. less than 200 ppm) in the waters of Kandy, Nuwara Eliya and Baduila suggest a lack of soluble material in the soil or a rapid flow rate or both. Distribution of TDS in the Northern Region of Sri Lanka In the northern coastal region of the Island, atleast a part of the Jaffra peninsular limestone aquifer is subjected to salt intrusion. The TDS content ranges from about 1200 to 1900 ppm, due to the presence of large quantities of Na and C1. In extreme cases, these values tend to increas- UF to 30000 ppm, nearly to the same level as in sea water. In this work, the surface expressed bj the 1900 ppm line of equal TDS concentration is defined as the salinity front. A zone of transitior e~ist.s between the salinity front an4 freshwate- r trle :or? of transition (TDS rizngir~g from 500 to 190D pprn), the aquirer contains water which has con- centrations predominantly intermediate between those of freshwater and saline water. In the Sothern coastal regions of the Island however, intermixing of freshwater and saline water is not marked, probably due to the higher rainfall in some parts and discharge of freshwater towards the sea in contrast to the converse in the Jaffna Peninsula. The only exception appears to be an elongated region around Hambantota where total dissolved solids of upto 800 pprn are found. The zone of transition broadens from a width of about 20 km in the northeastern sector to about 160 km along a north-south direction. The principal mechanism for developing a zone of transition is the backward motion of the saline water resultirlg from tidal action and the rise and fall of the potentiometric surface due to varia- tion in re-charge and other forces, including pumping. It should also be noted that during thc past few hundred to thousand years, the Island has been subjected to multiple cycles of sea levcl fluctuations. 'The observed distribution of dissolved conterlts - especially in the. northern region - may therefore reflect, in part, the effects of past sequences of intrusion and flushing of saltwater due to sea level changes. 'l'he effect of the climate on the TDS colltents of groundwater Groundwater is generally considered as being of fairly stable chemical quality, even thongh [he concentrations may vary. It would vary in response to climatic environments, including prccipitation, evaporation, temperature, the nature of the hydrologic system of the rcgion, etc. In the dry zone, high temperatures the year round pro~note high evaporation, which reduces the amount of water and which increases the TDS contents of the remaining water. The increase of T13S due to evaporation however, will be prorlounced in groundwater at shallow depths. As a rcsult of this, a general decrcasing trend of TDS contents with rainfall is observed in the dry zone of Sri Lanka. In the wet zone however, the TDS concentration shows a marked decrease with increasing rainfall. Relation of rock type to TDS contents in groundwater 'The correlation of rock type with the chemical character of water is rarely simple or obvious and in Sri Lanka, it is further complicated by the diversity of lithology present. Water, from basic and ultrabasic rock-bearing terrains tend to have high TDS contents, whereas water from quartzites, marble etc. are low in 'TDS. Mafic minerals weather to readily soluble pro- ducts whercas quartz and to a lesser extent feldspar, prove less tractable to the agents of chemical weathering. 'The TDS contents in water of charnockitic gneiss and biotite gneiss host rocks ranged from 200 to about 1200 ppm. Water from marble, quartzites and feldspathic rocks, on the otherhand contained TDS contents less than 200 ppm. Waters from wallostonitc, scapolite type host rocks in the southwest of Sri 1,anka are characterized by TDS contents of 200 to about 500 ppm. The lirnestone terrain of the northern sector yields water with more than 1900 ppnl TDS. However, at very high TDS levcls, the water chemistry is dominated by chloride ions, Hardness is an important characteristi: of water, related to the Fresence oT alkaline earths. Ca and Mg are principal alkaline earth elements present in natural waters. Sr and Ba, which are also alkaline earth elements, are present in very low coilcentrations in all except the most unusual water systems. The ions of Fe, Mn and Al are normally not present in suffi- cient concentrations in natural waters to effect hardness. The term hardness is used in many wdys, each with its own definition. "9. (1) Carbonate hardness : The amount of hardness clien~cal:~ equivalent to the amount of 13COQ- and ~1~~- in solution (2) Total hardness : Ca2+ plus Mg2+ hardness in solution. Based on hardness, water can be classified as follows: Hardness in ppln as CaC03 Classification Soft Moderately hard Hard Very hard Map 2 shows the spatial distribution oi hardness in groundwater in Sri Lanka. As shown In the map, co~~centrations of hardness display wide geological variations. High values (i.e. more thun 850 ppm zn CaCO.?) of total hardn-ss occur frequently in the water of the northern sedimentary formation of Sri Lanka. In much o$ the inland and in the Vijayan Complex of the Island, hardness concentration., In general fall in the range of 250 - 500 ppm in CaC03. Concentrations less than 250 ppm in CaC03 hardness are largely restricted to the Highldrid dreas of Sri Lanka. As shown in map No. 2 the Jaffna Peninsula has the highest water hardness in Sri Lanka, indicating a clear relationship between aquifer geology and groundwater chemistry. The well water from the red-brown earth soil in the dry zone of Sri Lanka is characterized by 250 - 500 ppm of CaC03 total hardness. These soils may be more enriched in Ca - rich materials than the wet zone. In the humid well drained wet zone of Sri Lanka, rainwater would selectively remove cations from weathered rocks and soils by leaching. On the other- hand, in the dry zone, with its limited rainfall and restricted stream activity, the continued addition of rainwater would only change the chemical composition of shallow groundwater by dissolving the accumulated salts during water table fluctuations. Thus, the amount of precipitation brings about a net dilution of the corlstituents of groundwater in the wet zone and in the dry zone, the secondary minerals wiaely present in the unsaturated zone tend to dissolve thereby increasing the mineral content of the water. 7. NITRATES, NITRITES AND AMMONIUM IONS (~ap NO!: 3,4,5) The study of nitrogeneous compounds in groundwater and potable water systems has recently assumed extreme importance. The potential health implications of the contamina- tion of drinking water by nitrates ha~~e attracted scientific attention since 1945, primarily in connection with methaemoglobinaemia. As Brooks and Cech (1979) have pointed out, attention is at present sharply focussed on the problem of the intake of excessive nitrates, as these compounds, on reduction, yield nitrites and secondary amines known to be carcino- genic (Magce and Barnes, 1967; Bogouski: 1972). Nitrites however, are unstable in the presence of oxygen and are tilerefore hardly present under aerobic conditions. The presence of nitrite in water is perl~aps an indication of organic pollution. Mdp 3 shows the distribut'on of nitrates in the well waters of Sri Lanka. In general, these average nitrate levels are below the danger level of 45 ppm as specified by the World Health Organization, with the , affna region being an e,.ception. High nitrate levels are found in and around the maln cities of Sri Lanka indicatiqg a possible relationship with the popula- tion density. Th~s clear11 shows the effect of human influence on the input and distribution ol nitrogeneous specles ill th: groundwater r-gime. The influence of climate on nitrate contents A feature worthy of note is the influence of the climate on the levels of nitrates in the grouncTwater of Sri Lanka. As shown in map 3, most of tie wet zonc of Sri Lanka has greater nitrate levels than the dry zone. The rainfall influences the distribution of nitrates in the groundwater by raising or lowering the groundwater table. In the wet zone of Sri Lanka, the water tablc as expected is shallow, and hence easy migration of the nitrates from the top soil into the relatively shallow water table results in a high nitrate content. In the dry zone of Sri Lanka howzver, ihe water tahle is deep and inspite of a high fertilizer input into the soil, the goundwater zontalns very low nitrates mainly due to the problems associated with the migration of thc. nitrogeneous species deep in the water table. The effect of atmospheric electric discharges c.1 :~i:rogen fixatior, and NOg-- production in the wet zone is also of ,great importance. Nitrates in the Jaffna Peninsula As shown in map 3 the Jaffna Peninsula has the highest nitrate contents in the groundwater of Sri Lanka. Geologically, the Jaffna Peninsula IS underlain by highly fraztured and karstified lirpestone of Miocene age. There is a thin soil mantle of the red/yeliow latosol type and in the spthern part of the Peninsula are 10 - 20 m of fine sand which overlie the limestone formation. According to Gunasekeram (1983) 80% of the groundwater of the Jaffna Peninsula is being extracted from the limestone aquifer. The water table in the Jaffna Peninsula is very shallow on account of the surface aquifers. Gunasekeram (1983) in his detailed study of the groundwater contamination in the Jaffna Peninsula found that 80% of the water wells yielded water of unacceptable bacteriological quality contaminated with faecal coliform. Among the major factors responsible for the poor water quality in the Jaffna Peninsula are: 1. Discharge of human excreta in the form of soakage pitlseptic tank effluents directly underground within densely populated urban areas. In some cases, due to limitations of available land, the distance bettvcen soakage pit and water well is only 6 rn. 2. Abundant use of agricultural fertilizers, mainly urea which contains 46% N. Excessive use of urea on crops such as chillies and onions is prevalent. In addition, cattle manure is commonly used. 3. The easy solubility of urea enables it to reach the very shallow groundwater table and under normal condit;ons about 75% cf the nitrates applied, reach the gloundwater and percolate\. The lact that in certdin locations in the Jaffna Peninsula, the nitrate levels exceed W.H.O. limits by 100 - 150% 1s mainly due to the abundant nitroge leous waste matter in the form of human excreta and s~rnthetic and animal fertilizer reach~ng the challow grountlwater table aided by the surface limestone aquifer. The geological conditions are therefore deal for the excessive accumulation of nitrates. The dangers associated with drinking water wells being placed very close to septic tanks have been highlighted in many case studies from other countries. Hutton and Lewis (1980) in their study ol nitrate pollution of groundwater in Botswana found nitrate levels as high as 603 ppm in several water supplies providing drinking water to many villages. A lithium chloride tracer injected into a pit latrine was detected in the supply borehole 25 m away after only 235 mins. The steep hydraulic gradient between the latrine and the borehole had obviously induced the rapid movement of nitrates occurring In open fissures. The case of Jaffna could even be worse bearing in mind the very short distance of 6 m from the pit latrines to the water well as observed in some cases. Distribution of nitrites (Map No. 4) Chemical analyses of water from wells in Sri Lanka indicate a wide range of concentrations of nitrite. Nitrite seldom appears in concentrations greater than 1 ppm. Even in waste water effluents and in fresh water, its concentration is well below 1 ppm (Sawyer and McCarthy, 1978). Out of the wells studied, 48% had lierite contents of less than 0.05 ppm. Only 3% of the wells studied had nitrite concentrations greater than 0.60 ppm in the groundwater. In eastern and southeastern regions of Sri Lanka, nitrite concentrations of more than 0.60 ppm. levels have been recorded. At Kurunegala and Ratnapura, nitrite concentrations of 0.30 ppm and 0.45 ppm respectively have been observed. The occurrence of high nitrites in r atural as no othe. dominating observed. waters at shallow depths is likely to be caused by point-pollution factdrs affecting the spatial distribution of nitrites have been ''[e fer~ilisers, human and animal sewage are usually enriched with high concentrations of n,trogeneQuf compounds brhich may enter into a groundwater boay as a result of infiltra- t oil "ne co,lv.xsio,. of am.no?ia to nitrate (nztrzfzcation) is brought about by highly specialized soil bacteria. Nitrifi~atlon takes place in two steps. In the first qtep, ammonia is oxidized to nitrite followed by further oxidation to nitrate. The accumulation of high con- centrations of nitrites in water is often attri~uted to inhibition oi ,litr;ficaiion at the nitrite stage. The specific environmental factors involved with this mechanism appears to be very complex. Under controlled conditions however, the oxidation of nitrite to nitrate by nitro- bacter is inhibited by cyanide and from ~pectroscopic studies it has been suggested that a cytochrome is also involved (Hughes, 19 75). ' he migration of these nitrogeneous species usually occur in several ways. Ammonium (AJFI~') being positiiely charged gets attached to clay particles and clay humus in soils which are negatively charged. On the other hand, nitrates and nitrites are not complexed by soils and therefore are frec to move and are leached and enter into the groundwater body. Nitrite is usually present in small amounts in well drained neutral or slightly acidic soils. However, accumulation of nitrite in appreciable quantities is observed in calcareous soils. The alkalinc pII in the soil is particuIarIy favourable for nitrite accumulation. The distributioi ,, occurrence and prevalence of nltriies in thc environment are ol utmost ~rnportancc since they may act as precursors of mdny cdrcinogeillc compounds. (7 1 he formation of N - nitroro cornpouiids i;y ilitcraction of nitrite with substances susceptible to N - nitrosatiorl has received much attation and substances forming carcino- geriic N - nitroso compound:: includc- secondary and tertiary anlines. Thc distribution of ammonium ion colltellts in the groundwater of Sri Lalika is shown in map No. 5. Puttalam and Amparai areas contain thl: highest ammonium ion concentrations in the groundwater of Sri Lanka. Aminoniurr ions generally enter groundwa.ier from the decomposition of nitro- geneous organic matter (eg. domestic sezuage) and from industrial effluents. Out of the wells studied, 74% had ammonium ion concentrations of less than 0.20 ppm. 3.6%, 10.6% and 7.4% of the wells studied had ammonium ion collcer~ration ranges of 0.20 - 0.30 ppm, 0.30 - 0.50 ppm and 0.50 - 1.00 ppm respectively. There is a marked correlation betwecn the distribution of ammonium ions and the macro- climatic regions of Sri Lanka. The occurrence of large concentrations of ammonium ions is observed in the groundwater of the dry zone whereas in the .,vet zone only low ammonium ion concentrations were noted. It is of interest to iiote that this is almost a reverse of the climatic zonal distribution of citrates. Although the extensive input of the ammonium ferti- lizers are high in the arable lands of the dry zone, the contents of ammonium ions leachable into the deep water table is very low and is severely limited by the scarcity of rainfall. On the otherhand, the extensive rainfall in the wet zone permits the easy migration of ammonium ions from the soils as a result of cation exchange. Apart from climatic features, others such as population density, landuse, application of fertilizers, etc. also govern the distribution of the ammonium ions in the groundwater. - 2 3 CHLORIDE (Map No. 6) Chlorine is the most abundant element in the hydrosphere, the ocean. being considered as the dominar,t part of the hydrosphere. It is generally conservative and travels through the hydrological cycle with little involvement in redox reactions, adsorption or the life processes of plants and animals. The large variation of 21 with time probably indicates the intrusion of aquifers by sea water, contamination of groundwater or surface water with industrial and domestic wastes. Periodic determination of chloride ions is therefore useful in water quality monitoring. The W. H. 0. recommended limits are: C1 PPm Maximum limit 6 00 Recommended limit 200 Action level 250 As shown in map 6, the groundwater of Sri Lanka is characterized by the occurrence of high C1- contents with widely differing concentrations among individual wells. The C1- concen- trations range from less than 100 ppm to above 2000 ppm with 54% of the studied wells containing water with less than 100 ppm C1-. Approximately 3% of the wells had more ~han 2000 ppm of Cl--. 'The occurrence and behaviour of Cl in groundwater is not yet completely understoo~ excepi where sea-~ater is overlain by cavernous freshwater limestone aquifers as in the case of Jaffna Peninsula. The freshwater aquifers in this area could possibly receive an increment of C1 by slow upward movement of brine where a potentiometric gradient favours such a movement. In places where wells are heavily overdrawn, cones of mineralized water get mixed up with the freshwater. A special case of freshwater - salt water interface is found in the Vavuniya region where the rocks are highly permeable and fresh groundwater floats in lens shaped configurations owing to density differences. A high concentration of C1 in groundwater is also observed along the Mahaweli shear Zone in Trincomalee and Polonnaruwa. In general, water in many fault zones contains higher CI and soq2- concentrations compared to the water in areas outside fauIt zones. It is worthy of note that regional occurrences of C1- - bearing rninerals such as scz 3olites have been reported away from Trincomalee along the minerali*d belt (Jayawardena, 1983). Further, the formation of scapolite is also reported to be due to the passage of normal groundwater (rich in C1) or thermal water through the host rock (Shaw, 1960). Thus the occurrence of high C1 water in the Mahaweli Shear Zone may well be due largely to mineralizing - perhaps a hydrothermal process. As seen in map-6, the distribution of chloride in the groundwater of Sri Lanka correlates with the climatic boundaries. The 100 ppm isoline for example, nearly coincides with such a climatic- boundary between the wet and dry zones. The existi ~g information on C1 in rocks does not suggest that weathering of rocks could supply the quantities of C1 normally found in the groundwater. However, the relatively high C1 level (> 300 ppm) observed in the southwestern region could probably be explained by the process of hydrolysis of scapolite or other C1- - bearing minerals (Frederickson, 1951). 111 this process, the 11' ions penetrate into the mineral lattice. At each penetration site the electrical neutrality of the molecule is destroye~ and an atom of one of the mineral const~tue-lts is displaced to compensate for each entring H'. A parallel, but different, reaction takes place where C1- ions occupy exchange si~es on minerals such as mica and hornblende. The OH- ion displaces the adsorbed C1- ions releasing the latter to solution. 9. FLUORIDE (~ap NO. 7) Compounds of fluorine are found in soil, water, food and in the human body il7 the form of chlorides. , They are also present in sea water, in some supplies of drinking water and in mineral deposits such as fluorspars (CaF2) or apatite. '?he environmental behavioc-* of fluoride is of great importance physiologically. Children are more susceptible to the effects of fluoride than adults in view of the fact that childrens' skeletal tissues are relatively free from fluorides and are therefore absorbed more readily. The intake of excessive quantitie: of fluoride (more than 1.5 ppm F) containing drinking water particularly during calcifica- tion, may cause discolouration of teeth of children. If the fluoride concentration in tile drinking water is less than 0.5 ppm, the incidence of dental caries may be high. As shown in map 7, the fluoride concentration ranges between 0.10 to 3.00 ppm. The low fluoride arcas (below 0.10 ppm) are mainly situated in the wet zone, whereas fluoride-rich areas lie mainly in the dry zone. It is collceivable that in the wet zone, where the average rainfall exceeds 300 cm in certain instances, the leaching of soluble salts is high, due to the tendency lor soluble ions to be leached and carried away in solution. Fluoride is known to be easily leached from primary and secondary minerals alld soils under the effect of high rainfall (Hawkes and Webb, 1962). In the dry regions, on the other hand, evaporation tends to bring soluble Ions upwards due to capillary action in soils. 'The composition of thc rocKs of the area concerned, particularly the easily leached constiturnts coupled with the climate, are the key fac~ors in the geochemical distribution of elements in a tropical region. The abundance of- fluoride in the rocks dnd the ease with which it is leached under the effect of 'groundwater ]lave an important bearing on the abundance of fluoride in the areas concerned and hence the prevalence of dental diseases. It is apparent from Map 7, that the high fluoride concentrations lie in the eastern and north central regions of the country. The central hill country and the southwest coastal regions habe relatively low fluoride concentrations. It is of interest to note that the high -- fluoride zone of Sri Lanka lies on a mineralized belt at the Highland - eastern Vijayan geological boundary. Munasinghe and Dissanayake (1982) in their plate tectonic model for the geologic evolution of Sri Lanka, suggested that the Highland-eastern Vijayan boundary is a mineralized belt and put forward a scries of evidence to substantiate their thcory. The discovery of a Cu - Fe deposit at Seruwila on this boundary provided further evidence to this theory. Fluorine being a volatile element is known to be abundant in such tectonic Lones and are enriched in rocks found at such loca- tions. Granites are generally rich in fluorine and such granites are found in abundance at the eastern Vijayan Complex. Mineralogically, 30 - 90% of the fluorine in calc-alkaline granites is usually located in biotite with lesser amounts in hornblende, muscovite, quartz and in accessories. However, accessory miner& - apatite, sphene, fluorite, mirolite, pyrochlore, topaz, tourmaline, spodumene, cryolite, etc. - occasiondly contribute more than 50% of the fluorine notably in F - rich magmatic and metasomatic roo: zones. Among the areas containing the highest fluoride concenLra+ions in well water, the regions around Eppawala and Anuradhapura are prominent. Fluoride concentrations as high as 9 pptn have been rqported from these areas. It is a well established fact that the fluoride ion can take the place of the hydroxyl ion and that an equilibrium could be maintained. The substitution of fluoride for hydroxyl ion is to be expected from similarity of ionic radii and charges. Extensive research has been carried out on the fluoride-hydroxyl exchange in geological materials. The presence of higher con- centrations of fluoride in water in areas bearing fluorine-rich rocks is therefore explained on the basis of F- + OH- interchange between minerals and water. Apatite in particular is known to exhibit this interchange of fluoride and hydroxyl ions. Fluorapatite, Ca5(P04)3F and hydroxyl apatite Ca5(P04)3011 are isomorphic end-members in the apatite solid - solution series. Human and other animal teeth are composed principally of hydroxyl- apatite, whereas fossil shark teeth are composed principally of fluorapatite. Geochemical basis for dental diseases High concentrations of fluoride in groundw~t-r supplies have been the cause of dental iluoros~s (tooth mottling) among persons who have lived in these areas and have ingested the water as children. According to W.H.O. standards a concentration of 1.5 mg/l in thc drinkins water is considered to be detrimental to health. Lack of fluoride in the drinking water on the otherhand, results in dental caries. Since fluorides enter the body mainly from the drinking water supplies, the geochemical status of fluorinr in a particular region or environment is of extreme importance in the study of the incidence of dental diseases in that region. Tooth enamel is composed principally of crystalline hydroxylapz tite when fluoride is absent in the water supply. However, when fluoride is present in the water supply, some of the ingested fluoride ions are incorporated into the apatite crystal lattice of tooth enamel during its formation causing the enamel to become harder and possibly discolour. The s~bstitution of fluoride for hydroxyl ion proceeds since fluora~atite is more stable than hydroxylapatite under most conditions. As noted by Zack (1980), fluoride substitution into tooth enamel is affected by thermo- dynamic activity and by the amount of fluoride complexes that form in the presence of certain other ions. The activity of fluoride decreases with increasing ionic strength of water, and fluoride complexes form more readily in heavily mineralized water than in dilute water. Zack (1980) made several important observations concerning the occurrence of dental fluorosis in areas of different levels of fluoride and total dissolved solids in the water supplies. As expected, where fluoride levels were relatively low, examples of tooth mottlirlg were low and, where fluoride levels were high, the incidence of tooth mottling was 1igL. However, where fluoride and total dissolved solids were both high, examples of dental fluorosis appeared to be low. Fluoride ions can be exchanged for ;~ydroxyl ions on tooth surfaces. However, for ion exchange to proceed, either fluoride iors must be abundant, or electrochemical require- ments as described by Hem (1970) on tooth surfaces would have to be different than they actually are in order to speed up the exchange reaction. The principle of ion exchange is applied by dentists on tooth surfaces when topicd fluoride treatment is prescribed against tooth decay. In areas where fluoride is low or non-existent in the water supply, a paste or a gel containing as much as 10% SnF2 is often applied to the teeth of dental patients (American Academy of Pedodontics, 1976). If ionization is complete, the solution contains enough fluoride (75,000 mg/l) to vastly speed up the exchange rate of fluoride ions for hydroxyl ions. An effective, but temporary barrier against dental decay is established on tooth surfaces. Most evidence shows that ionic substitution by systemic fluorosis (ingested and at- orbed ~hrough the digestiue system) rather than by topical t-luorosis (ion exchange on the tootlz surface) is the principal process by which fluoride is incorporated into tooth enamel. Electrochemical requirements on tooth surfaces are not normally suitable for ion exchange to take pIace (Zack,1980). The fact that fluoride ions are approximately the same size and have exactly the same ionic charge as hydroxyl ions suggests that systemic fluorosis is the principal mechanism by which tooth mottling occurs. Defluoridation of Public Water Supplies In view of the implications on dentaI health of children and the on set of skeletal fluorosis in adults, it is important that the optimum concentration of fluoride be present in public water supplies. In Sri Ianka however, dile to the fact that the vast majority of people use untreated water from dug wells, the problem of fluoride excess or deficiency may not be easily overcome. Defluoridation is generally more difficult than the removal of other ions, such as Ca or Fe, but Maier (1970) states that there are presently three methods that have proved to be practicable under varying conditions of raw-water quality and availability of treatment chemicals. The methods involve he usc of activated alumina, bone char or magnesium compounds. Uptake of fluoride by serpentine Serpentine, a hydroxyl magnesium silicate has the remarkable ability to take up fluoride from an aqueous solution. 'l'his material has been employed with considerable success in the defluoridation of natural water (Rao et. al. 1972, 1975). Fluoride uptake by serpentine depends on a number of parameters. viz. chemical composition of serpentine, its particle size, pH of the ~nediurn and time of contact. Rao et. al. (1975) presented excellent data indicating the existence of an equilibrium between the fluoride concentrations in the solution and that taken up by serpentine over a wide range of experimental conditions. The available evidence strongly suggests the proxy of F- for (OH- group as contributing to the principal mechanism of the process. The readers are referred to the papers of Kao et. al. (1 972; 1975) for detalis. The use of serpentine in defluoridating public water supplies is of considerable interest to Sri Lanka in view of the fact that serpentine deposits are abundant in Sri Lanka. Use c,f the seeds of clearing nct (BG~: Strychnos potatorum ltnn. Loganiclceae) (Sinh: Ing'ni eta.) These seeds have often been used by villagers to purify water. 7ven m~ddy water is known to settle dowr- rapidly when placed in pots the inside of which have Deen rubbed with the seeds. 'The effect of adding these seeds in the defluoridatlon of water reeds to be carefully investigated as this may provide a cheaper method of defluoridation that is acceptable to the rural folk. 10. TOTAL DISSOLVED SILICA (M~JI NO. 8) Silicon constitutes about 20% (atomzc) of the earths' crust, and is invariably associated with oxygen as Si02 and in silicate rocks, minerals and constituents. 'Thc transport of sillcon and its intimate association with living organisms must involve solubilisation of the massive forms of silica and silicate, a process requiring their depolymerisation. When silica or silicates are in contact with water, there is invariably some hydrolysis of Si-0--Si bonds and silicic acid is liberated in very small quantities into the aqueous phase. At neutral pH, the solubility'of silicic acid is qf the order of 100 ppm and at concentrations below this it exists as a monomer SiI~tl)~. 4t ~oncentrat~ons much aLove 100 ppm, monomeric silicic acid tends to polymerl~t, eventuaily forming colloidal silica. Map No. 8 shows the distribution of silica in the groundwater of Sri Lanka. The clay mineral provinces as described by Herath (1 975) closely follow the concentration of silica in groundwater of the Island and this feature points to the fact that the formation of clays have played an important role in the geochelni-3al transformations of silica in the aqueous phase. It has been observe? that silica concentration decreases exponentially in kaolinitic regions whereas it increases towards montmorillonite regions. A relatively constant concen- tration of silica in solution suggests a steady state of kaolinite += montmorillonite equili- .brium. This phenomeno,~ is well seen in the intermediate climatic zone of Sri Lanka. It has been ot)served that the silica content varies positively wit.h annual rainfall in the wet zone and negatively in the dry zone. In the wet zone as the water table is shallow, the secondary silic$, found in between soil particles easily migrates into the groundwater. The low value!: of pN-pli and p Si(OH)4 in the wet zone favour the exha~stive leaching of acid soils Elowever, in the dry zone, due to the deeper water table, most silicon found in the ground- water is probaoly derived from the decomposition or metamorphism of silicate minerals. 1 1.. IRON- AND MANGANESE (mp Nos. 9,10) It has been noted for nearly a century that trace elements exert a positive or negative influence on biological processes. However, it is only recently that great emphasis has been placed on the study of the behaviour of these elements in aquatic environments. The term 'trace element' is rather ill defined. It is used nowadays to explain the presence of elements occurring in minute quantities in the environment. In addition, other terms such as 'heavy metals', 'trace inorganics', 'trace n;-tals', 'micro elements', and 'micro-nutrients' are used synonymously with the term 'trace elements'. Iron and manganese compounds are of particular importance since they are redox sensitive elements in the environment, and can act as potential sinks for other trace elements. 'I'he sorption and co-precipitation phenomena of transition metals by colloidal compounds of iron and manganese are largely controlled by the pH and Eh of the media. Apart from those redox sensitive reactions of iron and manganese, organic matter, chiefly humic and fulvic acids may exert a positive influence on the complexation of Fe and Mn in water. In the aquatic phase, the essentially soluble forms of Fe and Mn are Fe2+ and ~n~+ which can occur largely under anoxic conditions. It has been shown that Mn4' and Fe3+,are the only oxidation states possible for iron and manganese respectively in oxygen containing waters. These forms can be reduced to the soluble ~e~' and ~n'' ions only under anoxic corrditions Further, the oxidation of ~n'' and ~e~+ may also be catalyzed by a wide range of micro-organisms. The occurrence of relatively high zoncentrztions of Fe and Mn in the groundwater of Sri Lanka is a wide-spread problem. The major4ty of drinking water wells are not used on account of their high Fe and Mn concentratiow. Iron in particular imparts a taste not acceptable to the majority of people using well water. The occurrence of Fe and Mn in the groundwater of Sri Lanka is largely controlled by the natural environmerlt. The rocks and so~ls of the area concerned play a significant role in the distribution of iron and manganese In the groundwater. As noted by Herath (1975), extensive bodies of laterites occur in the llstrict of Colombo and a10r.g the southwest coast down to Matara and Tangalle. Iron is a very common constituent of the laterites, and since it is geochemically mobile under acidic conditions, it may accumulate in thc groundwaters as a result of extensive leaching. Further- more, the water table in the lateritic terrains is very shallow and may fluctuate rapidly with rainfall. Rainwater may have an impact on groundwater by its own composition as well as by liberation of components from soil. Since the mobility of most trace elements'(eg. Fe, Mn, Zn) are pH dependent, the slightly acidic nature of wet zone Iateritic soils and the intensive rainfall favours the accumulation of Fe in the groundwater. In contrast, the water table in the dry zone of Sri Lanka is very deep - greater than 50 m in some cases. The alka- line soils in the dry zone largely immobilize the iron which form colloidal oxides and hydroxides. \ As shown in map No. 10, the highest manganese concentratioi-s of groundwater are recorded in areas around Trincomalee and Tabbowa. The distribution of manganese appears to be associatea with sedimentary environments. As noted by Laxen et. al. (1984) there are two main sources of manganese - one is a result of weathering processes which produce suspend-a partlcLlate sediments. The other is the influx of soluble reduced Mn2+ species in varying proportions. The mild reducing environments which usually prevail in Tabbowa and Andigama sedirrlentary basins and the Mahaweli delta at lrincomalee probably accounts for the highcr ~cachiug of ~n*' into the aqueous phase. The distribution of Pe, Mn and other elements in sediments of the sea of Okhotsk (Nissenbaum, 1972) further confirms that Fe is mainly incorporated into the residual fraction whereas Mn is more associated with the aqueous phase. (Map Nos. 11,12,13,14,15) Only few waters contain chromium derived from natural sources. Vanadium, cobalt, copper and zinc however occur freely in nature, in minerals, in alluvial deposits and in organic materials. Even so, most waters rarely contain more than traces of these elements. Zinc for cxample is abundant in rocks and soils but is only a minor constituent in natural waters on account of the low solubility of the free element and oxides. In the aquatic environment, chromium exists as chromate. The cr3' ion is hydrolyzed completely in natu~al waters and the chromium precipitates as the hydroxide leaving minor amounts In sol~ltlon. Solutio,.~ containing cobaltous ion- (20~') are relatively stable 3+ whereas cobaltic ions (Co ) are strong oxidizing agents and are therefore unstable in r~atural watcrs. Copper and zinc in the aqueous phase occur mainly in the lonlc forms, and In aquatic organisms and in soluble organic fractions. Vanadium occurs in the aquatic environment as V03- ion. When it comes into contact with organic substances, it may be rcadily converted to the cationic form vo2+ which may be trapped in t~le organic substrate. The distribution of V, Cr, Co, Cu and Zn in the groundwater of Sri Lanka is illustrated In maps 11, 12, 13, 14, 15 and table 1. Frequency histograms (fig. 2) for each element show that 15, 18 and 37 wells had > 24 ppb of total Cr > 120 ppb of Co and > 400 ppb of zinc respectiveiy, in the groundwdter of Sri Lanka. In the case of Cu and V only 12 and 29 rcspcctively had > 203 ppb concentrations. However with industrial development in Sri Ennka the problem of gioundwatcr pollution is receiving more attention. Field investiga- tions in the Ratrnalana arca confirm that some wells located near the industries (5 - 10 rn dzslnrlce bctwpen j'actory and well) are subjccted to pollution from industrial wastes. As a result of this, the Cr content of gloundwater in these areas is higher than the values recommended by W.H.O. The rocks and minerals of the areas under consideration also play a significant role in the distribution of some metals. The rocks in the arca covered by the boundary between the Highland Series and the eastcrn Vijayan Complex in particular, are known to be mineralized and one could therefore expect significant concentrations of metals in these areas. mmewa~mmtbrnfi+wb-mmowmNe- h at~a-bm ~tmmbt-mmhmha~m d r( NN3 3 m NNNN A Total V (ppb ) - Total Cr ( ppb Figure 2 : Frequency histograms for elemental distribution in well water in Sri Lanka. d THE GEOCHEMICAL CLASSIFICATION OF GROUNDWATER OF SRI LANKA (Map fro. 16) In Sri Lanka, a country of 15 million people, ~nly 15 - 25% of the people have access to piped water, and the majority of the cou 1tr;r's health problems are related to its aquatic environment. The majority use small, unprotected wells, and in rural settlements, reservoirs and water channels are the main sources of drinking water. The proper disposal of human and other wastes through sewerage zystems and latrines is also severely limited, less than a third of the popul~ion having satisfactory latrine facilities. The poor water supply and excreta disposal systems have resulted in 40% of the Sri Lankan population being affected by typhoid, amoehic and bacillary dysentery, infectious hepatitis, gastro-enteritis, colitis and worm infections. Tlfe need to carefully monitor the groundwater quality of Sri Lanka, is therefore of high priority and upto now this aspect has been neglected. Environmental geochemistry essentially deals with the geographical distribution of elements and forms the basis for a variety of interdisciplinary studies involving human and animal health, quality of groundwater, agriculture and nutrit~on, soil fertility, pollution and mineral exploration. 'The study of the abundance and distribution of some trace elements and the resulting biological manifestations involves geochemists, public health workers,soil scientists, ecologists and nutritionists. The chemical quality of groundwater is related to the geology of the area concerned. For example, areas underlain by acid igneous rocks such a, grani~e or arenaceous sedimentary rocks generally contain lower levels of essential trace e elnents -- particularly the first row transition elements - than areas underlain by ultrabasic and igneous rocks or sliale. Thes~ however, may somet:mes contain sufficient concentrations of potentially toxic elements (Thornton and Plant, 1980). This study presents for the first time, a chemical classification of the groundwater of Sri Lanka. It is hoped that this chemical classifjration would help not only the hydrogeo- chemist, but also others in a number of scientific d~sciplines. The Chemistry of the Groundwater of Sri Lanka The groundwater of Sri Lanka can be classified into the 'ollowing 4 main water types 1. Calcium type 11. Magnesium type . . . nq Sodium/potassium type iv. Non-dominant cation type Map 16 illustrates the distribution of these 4 major water types in Sri Lanka. Each type is further sub-divided into the C1, SO4, HC03 and NDA type: Table 2 shows the averages for the elements and ionic species. i. The Calcium 'Type Fig. 3 illustrates the Piper trilinear diagrams for tne caciurr- water type. In Sri Lanka, this type of water is -distributed mainly in the nothern, central and in some parts southern, eastern and north central regions. The CI type ?redominates in the northern parts whereas the HC03 type is prevale-t irl the central reglons 'The effect of salinity and the presence of carbonate rocks in the areas could possibly be attributed to such a distribution. Table 3 shows the correlation matrix for the elements and ionic species dnaly~ed for the calcium type of water in Sri Lanka. The total dissolves solids (TDS) show significant correlations with K, Ca, HC03 and C1. The transition elements however show no significant correlations for this type of water. ii. The Magnesium Type When compared to the other types of water, the magnesium type is distributed only in relatively smaller areas, the southern parts of the country around Embilipitiya having higher concentrations. In this type of water, only the C1 and SO4 sub-types cou:d be found. Tlle correlation matrix and the Piper trilinear diagram for the Mg water type are shown in Table 4 and Fig. 4 respectively. iii. The Sodium/Potassium Type This .type forms a major group and is distributed v:ldely in Sri Lanka, particularly around the central region. The north western, north central and the south eastern dry zones mainly contain this type of groundwater. From among the sub-types, the Cl type is predominantly found in these regions. Excessive evaporation and probable influence of salinity may havc contributed to the prevalence of this water type. l'able 5 shows the correlation matrix for the Na/K water type and Fig. 5 illustrates the Piper trilinear diagram. iv. The Non-dominant Cation Type As illustrated in map. 16, the non-dominant cation type of water is distributed mainly at the prephery of the central highlands and in some parts of the north cer:tral and southern --gions. Iht- HC03 and non-dominant anion sub-types predominate in these regions. Table 6 shows the correlation matrix for the non-dominant cation water type and fig.6 illustrates the Piper trilinear diagrams. Effect of Geology and Climate on the Chemistry of Groundwater A closer study of the distribution patterns of the groundwater types in Sri Lanka reveals that the underlying geology and the climatic factors affect the chemical quality of water to a great extent. The wet zone of Sri Lanka (see map. 16) consists for the most part of non- dorninant cation type, calcium - HC03 and non-dominant anion types. In the dry zone however, the Na/K type predominates and in this type of water, the C1 sub-type is found L covcring vast areas of the dry zone. Evaporation under the strong drought conditions as prevailing in the dry zone of Sri Lanka results in the accumulation of sodium salts in the soil Figure 3 : Piper trillrear cliagrams for the calcium water typ,. ~g$~~~$~~=~~"-"~"Oo NO0 ~N~oo~Noooo~~&~-oqq ddddddddd00~00~0~0, I/ /I I I 3g~g23z2hgrn: 0000,00-~0&q, o~~~~d~o~o~o~do~~ I Ill I I I1 ~N\O m-*$zz22$K$zz$:8 00T--99110409-000 000~0~00~000~00, I!! IIII Ill II *P.~N~~~N-*o~P.N gS-z$sN22$G22:S OoddoaXjddoddti: I II I I., \D-p.m\O~t.O- om,,, mm*zW:$g ?000-9?N.O 2-00 O0~0~oooog do, I I Ill , - d, 0 1 U 5 2 C 0 s V) G. ,- m w 5 '-3 5' m ! U a t-" 5 d 3 s . ... Yi U M 2 "J -5 L. o 'i X . - t.P.hNP.~P. P.o\Omoo ,~~zg~g&~~~~"o r. 0 ~z~8z~;8~z~X~;;zX~~~ I 1 I I I I N 0 II) * Nri-NmWN"-xOmOtmm mk020 OamW*Nh~t.mNhNNMmO 0 28';?z2;z222z?8X22z o IIIIII I I I I I I * OG.P.*Omimmot.In3mmmNO -22-e 0.88Z?,d,:, 1 I I mWmC3nG.riG.o G\~N~~wNG.O ""7"70 X~~~OODG- , , Plmm"aNNm0 rnr-~mmm~\IO m 0 "?"Z'??,-; 0 0 r; I -\ON >maz:$g m-d* mo joqdzdil IIII t***. %2$$28 ""22-2 3 0 0 .t** zsz:g mr-mrn9 0000- 3 .. NWWO MO1.O mmmo 000- Xt ZC;8 2 2 2 3 0 m o 0'9 0 - 0 0 9 - 0" * - lli MU o 6'6s .go I Z C 0 . - Y - E 0 0 I * U - il C- ' C r V LL - V ; m 0 U z 2 rd U 2 m 2, L \ 0" z ", 0 Z C N 3 U : > 0 V 13 0 Ill I I I! Ill Ill' Mh01bmNm\O\33-\OG.P.mO Wmm0~0~m~~~Ornrnm3 -43 *"28mm" dddod 0 0 .,z~~~;~ lII,I/ ,Ill \oP.~* *zmm "0'ey"m z%E:%%p$L2g ,,z,gZ-O ;ddoooo 0 2 I I I I1 ".3NP.*m*~3mml.-0 . :>*0mG.Nm-md*mO m-~-~t.~-mmmmtrnO z!g;g~v?~?*~~z 11 I I 177 I m#n~~g2~g$g?g 0 0 W~.-mwri~.bmmG OG.W~~~P.NONO 7"?2222?223 ^rpO I 11 91 1 mm\~\~m-mm~.o 'OmNW*- MAGNESIUM TYPE Mg -CL Figure 4 : Piper trilinear diagrams for the Illagile- sium water type. @ b! ;'able 5 - Correlation Matr~x for the Sod~umIPotass~um Water Type v Cu Zn NO 3 NO2 NH4 F SiO* TDS * Signif~cant at 9590 confidence level SODIUM / POTASSIUM TYPE oww~~Om~mwOar.O+0+N0 *OMN m\omo\ot-mmmnNbmO ;z?1m"""+;288zz28%5 ooooo~o I I Ill + Flgure 6 . Piper trillnear cl>agrams for the non- dorn~nant ca~ion ware, type. layers and this factor is largely responsible for the abundance of the Na/K type in the dry zone. Further, the northern parts of Sri Lanka are underlain by sedimentary limestones as a result of which the calcium type of water predominates in these parts. Increasing salinity has been observed in areas closer to the shore-lines and in the Jaffna PeninsuIa in particular, this is commonly sekn. The predominati~lg anion in this type of water in the dry zone is CI. When one considers the topography, the central highlands have groundwater of the Ca - HC03 type and with decreasing elevation, merges into the non-dominant cation type. In the lowlands the Na/K type predominates. Thus - a ~a* NDC'N~/K type of sequence is apparent with decreasing elevations from the highlands to lowlands. This sequence could well be due to the different geochemical mobilities of the elements concerned. Further, there are numerous shallow and deep seated fractures and lineaments withi11 the ccntral regions of Sri Lanka and these are mainly responsible for the migration of groundwater within the hardrock terrains. SEFERENCES Adams, F. D. (1929) The Geology of Ceylon. Can. J. Res. 1 : 425 - 5 11. American Academy of Pedodontics (1976) Fluorides : an update for dental practice : New York, 39p Berger, ,A. R. (1973) The Precambrian Metamorphic rocks of Ceylon : A Critique of a radical interpreta- tion. Geol. Rundsch. 62 : 342 - 347. Berger, A. R. and Jayasinghc, N. R. (1976) Precambrian structure and chrqnology in the Highland Series of Sri Lanka. Precambrian Res. 3 : 559 - 576. Bogovski, P. (1972) The importance of the analysis of I"-nitroso compounds in international research. In : N-nitroso compounds analysis and formation. Bogovski, R., Preussman, R. and Walker, E. J. (Eds.) Lyon InWrn. Agelacy for Res. on Cancer Sci. Pub. No. 3 : 1 - 5. Brooks, D. and Cech, I. C. (1979) Nitrates and bacterial distributioi~ irl rvral domestic water supplies. Water Kes. 13 : 33 - 41. Rrowrl, E., Sltougstad, M. N. and Fishman, M. J. ('970). Methods for collection and analysis of water samples for dissolved minerals and gases. Chapter A1 in Book 5. Techniques of water resources investigation of the U. S. Geological Surv. Govr. Printing Office, Washington D. C. 160p. Coatcs, J. S. (1935) The geology of Ceylon, J. Sci. Section R. 19 : 101 - 187 Cook, E. K. (1951) A Geograph,y ofCeylon Macmillan and Company Ltd., London 360p. Cook, Pn. 3. and Miles, D. L. (1980) Methods for rhe chemical analysis of ground water. Rept, Inst. Geol. Sci., No. 80/5, 55p. Coomaraswarny, A. K. (1906) lviap of part of the Kandy distrlct : Earth movements : in Ceylon Adm. Rpt. (iv) : I.-- 14. Cooray, P. G. (1967) An introduction to the Geology of Ceylon. In Spolia Zeylanica 31 Part I. Sllva., P. H. D. H. De (Ed.) National Museums of Ceylon. 329p. Cooray, 1'. G. 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I I I I I I I I I 80' 1 81 in groundwater of PP'" 0.15 - 0.3 - - - 6' Polonnaruwa * ./ - I I I I I I I I I 80" I 81° Distribution of Ammonium ions in groundwater of PPm 0.5 - 1 .O - - - Embilipitiya - - - 6' miles 10 0 10 20 6~ KiIometers 8 0' -0 81 ' I I 1 I I I I 1 I I Nuwara Eliya Ratnapura 1 Polonnaruwa 1 I I I I I I I I 1 t 80' I 81 Distribution of Chloride ions - in groundwater of Sri Lanka P Pm B < 100 TOO - 300 - 3" 300 - 500 r 500 -1000 Q*- - \ 1000 -2000 I--. 3 - - Nuwara Eliya Ratnapura 1 Colombo d I I I 1 I I I I 80 I I 87" ide ions - in groundwater of " 0.1 - 0.5 0.5 - 1 .O go- - - - - - - ( P"'+"I 1 8"- - Batticaloa - k Qh - - - - ~iegombo - 7O i" - - - - - rantota -6' 10 0 10 20 6* - Kilometers 10 0 10 20 30 8 o0 I 81' I I I I I I I I I J Nuwara Eliya I Ratnapura I I I 8 I I I I I 80 I 81 in groundwater of 0.75 - 1.75 1.75 - 2.75 2.75 - 3.25 - - -7O - - - - - 6' """' 4 miles 10 0 10 20 6o - Kilometers 10 0 10 20 30 aoO 81 * I I I 1 1 1 I I I I I Negombo u Vavuniya 81 a .M~P ~0.10 of Manganese ions in groundwater of 1 Sri Lanka PP" incomdee 1 Anuradhapura ,iles 10 0 10 20 Kilometers -0 I . Vavuniya Kurunegala I I I 1 I I I I I 80' I 81 Distribution of Vanadium ions in groundwater of P Pm - - 8O- .. - - - - - 6' miles 10 0 10 20 - Kilometers 10 0 10 20 30 8 0' 81 * I I I I I 1 I 1 1 I m Ratnapura 1 I I I I I I I 80' I I 1 81 O istribution of Cobalt ions - in groundwater of PPm 0.02 - 0.04 0.04 - 0.09 0.09 - 0.12 9O- - - 8'- 7"- - - - -6' 8 0' I 81' I I I I I I I I I A I - . Vavuniya 1 Anura Embilipitiya - PP'" 0.025 - 0.1 0.1 - 0.25 0.25 - 0.4 - - - - .' - 6' ,;Ies 10 0 10 20 60_ - Kilometers 10 0 10 20 30 80' 81 * I I I I I I I I I I - MAF - 9' - - - - a0 - - - 7* - - - - 6' I miles 10 0 lo 20 M atam - Kilometers 10 0 10 20 30 80' 81 * I I I I 1 I I I I APPENDIX Chemical Kesults of the Sampled We11 Water: Ca - C1 Subgroup Loca- tion No 33 86 88 92 100 104 117 197 273 404 42 1 428 442 452 " 3 454 45 5 456 457 458 48 3 26 76 120 i26 407 Na K IiC03 SO4 C1 TDS Total Hard- ness Chem~cal Results of the Samplea Well V'ater: Ca - SO Subgroup 4 otal Fe PP'] 2700 110 110 110 3200 3200 1110 3110 7 0 1330 170 320 400 400 170 700 170 460 640 820 800 3200 870 1100 110 170 ,.in Total Co Total Cu Zn Cr v ppb ppb p;>m ppb Topographic Sheet 28 79 21 140 Alutgama 111 11 14 700 Hapurale 110 7 12 200. " 310 15 2 2000 Buttala 70 12 2 40 Avissawella 122 11 8 450 " 127 11 11 300 Hatton 112 12 1 70 Dandagamuwa 10 312 12 40Nalanda 28 17 37 700 Medawachchiya 22 627 41 750 Vavuniya 17 175 73 500 Mantai 12 137 31 2800 Padaviya 120 175 75 1500 Tunukkai 72 175 60 500 Iranamadu 90 170 75 1000 " 91 100 60 750 " 30 17 92 500Murunkan 37 27 17 750 " 27 21 19 1000 " 120 I05 22 321 KalaOya 38 32 31 100 Ambalantota 27 1. 7 400 Ratnapura 900 10 22 190Hatton 117 7 18 20 Nuwaradliya 27 32 22 700 Horow~atana Chemical Results of the Sampled Well Water: Ca - HC03 Subgroup Loca- tion No. 34 35 36 41 4 3 4 5 46 5 3 78 102 114 121 122 124 134 137 143 145 151 154 155 157 158 159 160 161 162 163 165 166 TDS Tc;cal Hard- ness Total Fe PP~ 2900 2710 2170 2000 3720 110 700 110 110 3160 720 80 270 80 270 3 00 2720 2120 3000 1220 720 2120 820 710 810 820 700 2200 1720 720 Mn Total Co Cr Total Cu Zn v Topographic Sheet Alutgama Rakwana Kataragama Haputale Avissawell a Hatton Nuwara Eliya Potuvil Gampaha Kandy Cont; Ca - HC03 Subgroup Kandy Hangurankeca Tirrukovil Dandagamuwa Kurunegala Rangala Maha Oya nt; 40.08 120.24 70.03 220.20 148.1 1 80.16 40.08 96.05 128.11 40.08 80.16 80.16 10C.20 58.43 60.12 60.12 96.79 84.02 97.66 40.38 116.00 140.20 120.24 80.16 120.24 120.24 120.24 80 16 80.16 140.28 120.34 120.24 100.20 140.24 100.20 60.12 84.06 80.16 160.32 160.32 Ca - HC03 Subgroup; Topopaphic Sheet Maha Oya Kalmunai Wariyapola Nalanda Elahera Ruliam Polonnaruwa Vakaneri Anuradhapur~ Anuradhapura Chemical Results of the Sampled Well Water Ca - NDA Subgroup :.la K HC03 SO4 Cl TDS 1 'oral Hard- Total ness Fe ppm in ppb CaC03 Mn Total Zo Cr ~pb Toppgraphic Sheet K& Arnbalangoda 80 100 Morawaka 60 70 Marara 20 " 90 Alutgama 20 120 670 "ataragama 520 Yala 210 Haputale 400 5 60 380 A wissav~ella 170 Hatton 220 Passara 0000 ' 270 Zampaha 490 210 390 420 '700 Nllgala 30 MahaOya 230 tTalanda 40 Blahera 1100 KalaOya 400 100 cD m Chemical Results of the Sampled Well Water Mg - SO4 Subgroup Loca- tion No. 12 459 46 1 462 46 3 465 466 467 46: Na PP" 2.52 91.95 206.89 22.98 22.98 22.98 22.98 45.97 22.98 PP"' 187 SO 1200 00 3746.39 144 09 192 12 480 30 960.6? 516.33 982.70 TDS Total Hard- ness Total C- PP~ 18 12 14 12 12 19 17 8 7 Co Total Cu Zn NO3 v Topograph~c Sheer Morawaka Tibulketiya Chemical Results of the Sampled Well Water Mg - C1 Subgroup 148 6.75 24.31 22.98 2.02 121.4 4.41 17.00 200 117 2320 17 14 3 3 12 77 7000 70 .2 7 420 Gampaha 180 7.95 24.31 16.17 7.82 128.1 19.11 32.00 110 120 720 44 16 3 1 12 410 2100 127 221 30 130 Hanguranketa 186 19.92 60.50 9.19 12.51 305.0 3.57 28.00 152 300 170 42 7 3 7 70 27 270 47 792 7 3780 Nilgala 411 100.20 8.74 0.22 39.10 434.4 3.45 170.00 1510 610 120 28 7 47 27 270 70 12?0 82 17 17 1000 Horowpatana Chemical Results of the Sampled Well Water Na + K/CI Subgroup Loca- tion No. 3 4 5 2 3 28 29 3 1 3 2 47 50 51 5 2 55 56 5 9 30 t * 62 6 3 64 6 5 66 67 69 70 8 0 90 9 1 98 101 106 TDS PPm 372 340 371 317 82 89 137 170 192 47 8 375 501 248 399 242 370 252 257 292 382 47 1 274 190 142 Total Hard- ness ppm in CaCO; 250 270 273 365 692 617 46 7 2 176 164 180 47 0 360 100 42 9 2 35 5 8 48 47 3 2 22 4 1 52 4 1 19 7 5 50 2 2 94 3 5 Total Pin Fe Total Zo Cr PPb PP~ 17 27 10 10 20 it 3 1 1 17 7 12 7 7 10 3 8 2 17 3 12 3 1 1 17 2 1 21 1 30 3 35 8 27 2 28 12 21 12 21 17 22 3 19 2 20 7 20 8 13 1 12 7 3 32 21 36 3 27 8 Total v PP~ 17 12 27 10 2 2 11 7 17 145 142 140 127 200 11 2 7 7 8 8 7 7 10 11 10 1 17 7 721 17 7 Topographic Sheet Ambalangoda Ambalantota Hambantota Alutgama Rakvana Yala Panadura Haputale Buttala Colombo A~ssawella Na + K/CI Subgroup Topographic Sheer Passara Puttu~il Gampaha Kandy llanguranketa Jhilav: Kalmunai kttulr Oya Wariyapola K/CI Subgroup Topographic Sheet Polonnaruwa Vakaneri Kalpitiya Anuradhapura Kaudulla Kathiraveli k~arichchukkaddi Madawachchiya Horowpotana Trincornalee o"-~~.l-mNNr,rN3Nt. -t-INm*NN- 0 3 d i nil - N* t.\U.- N N cn- N2N sam 2 - d 13 CII g> g - e on* 2 - dot- gc g F- CDr. .? . a t. e - n '2 e o ?E R '2 f- N t- b "I'.N0Om-OlU P b~--.m-n-\f a - T-N N 1 a & 22 %ZN2867$= n P + - - 1 I -0 - L6 NNNrV-I.C3b rn C 5: - 3 a s s- N-t-b---L..N Y - - N Y - + 0- + d NN N03NNr.t-dm d - m N N z g 'ON 0000*0000 oo~mo~ooo 0dt-ojd5.ddt; cob N mom - - Chemical Results of the Sampled Well Water NDC - C1 Subgroup Loca- tion No. 2 19 21 2 2 54 5 7 77 87 93 9 7 103 135 139 149 219 227 255 278 305 318 319 321 32t 379 380 409 410 41. 5 414 415 422 433 484 HC03 PP" 61.9 128.8 61.7 105.0 199.0 122.0 0.6 7.0 10.3 59.7 43.3 348.9 122.0 56.1 60.4 7.3 450.2 195.8 263.5 263.5 196.4 250.7 366.0 313.1 330.C 355.0 434.4 433.8 682.7 470.4 610.1 629.6 189.7 TDS PPm 320 1000. 470 320 ??O 502 43 9 2 340 1200 114 1900 200 211 170 420 270 440 294 616 800 700 388 470 1700 1500 2150 2100 21 50 2010 20'30 Total Hard ness ppm in CaCO -1 200 1770 ;00 216 3 04 75 12 2 0 120 110 42 400 170 120 94 73 520 270 300 296 270 318 3 44 428 429 520 600 61 0 1200 720 1000 9 80 295 Total "e PP~ 2790 73 2700 1180 210 500 9 20 700 700 120 2210 3 10 6220 3000 720 710 110 110 170 560 480 320 110 210 110 270 170 410 230 130 400 800 1120 Total Co Total Cu Zn NOj Cr V Topographic Sheet i.mbalangoda Ambalantota Kataragama Yala Haputale Buttala Avissawella Potuvi! Negomho Gampaha Kuruncgala Xalmune Nalanda Kukm Puttalam Damhul!a Polonnaruwa Kaudulla Horowpatana Vavuniya Puliyankulam Kala Oya ,hemica1 Results of the Sampled Well Water NDC - SO4 Subgoup Ca Mg Na K HC03 SO4 C1 TDS Total Hard Toral Mn Total Co Total Cu Zn NO3 O2 NH4 S102 F ~oca- ness F- Cr V tion . . I- 0. ppm PP~ PP~ PP~ PP~ PP~ PPI~ PP~ pplnirl PP~ PP~ ?pb PP~ PP~ PP~ PP~ ppb PP~ PP~ PP~ PP~ Qther CaC0 Remarks 120 81 17 100 Arnbalangoda 10 82 68 . 210 Morawaka 21 80 63 10 Morawaka 70 17 2 1920 Ambalantota 120 1 2 400 Rakwana 420 21 12 70 Hatton 17 1 nd Timbolketiya 3 67 24 1100 KalaOya Chemical Results of the Sampled Well Water NDC - HC03 Subgroup :a hg Loca- tion NO. ppm PP~ .\a K HC03 SO4 Cl TDS TI stal Hard- 'I ness 'otal l'l- 1 Fe Total Cu Zn NO3 NO2 NH4 Si02 F v ppb pp:: PP~ ?pb ppb ppb ppb ppb ppm ppb Topographic Sheet pprn in CaC03 Hapurale Avissawella Nuwara Eliya Potuvil Kandy Nilgala Kumnegala Maha Oya Waiiyapola Elahe .,I 2 117 31 1,000 12 T27 28 2400 Padaviya 7 117 32 1,100 62 427 27 3000 " 1 117 70 1,210 17 426 37 2600 " 7 61 25 7,500 27 42 3 1200 Galgamuwa 3270 Rukarn 780 Horowupatarta 270 Anuradhapura 1200 Kaudulla 3000 " 2700 " 3200 " 1000 Medawachchiya 900 Vavuniya 950 " Chemical Results of the Sarnpted Well Water NDC - NDA Subgroup 'otal Hard- ness ppm 111 CaC03 412 617 3 2 17 120 270 8 5 3 6 53 68 76 42 61 320 120 170 200 127 200 145 100 100 111 92 94 70 520 210 127 122 131 100 3 40 320 140 Total Mn Fe 'Toral Co Total Cu Cr V NO. YO2 NH 4 S102 Loca- tion No. ppb Topographic Sheet PP" PP"' 300 Ambalantota 1800 Harnbantota 810 Haputale 270 " 3200 Buttala 1390 " 270 Av~ssawella 170 " 70 Ilatton 10 " 170 " 10 Nuwara Jlya 7 0 20 Pottuv11 20 Negombo 170 Garnpaha 980 Nllgala 1320 " 230 Dandagamuwa 920 " 990 " 90 Kurunegala 120 " 110 " 270 " 320 " 130 " 200 Yurunegala 120 Rangala 10 PTalanda 320 Elahera 20 " 100 " Location Number 13 14 20 71 8 1 96 112 189 215 228 235 247 249 254 274 311 315 320 329 331 336 TDS PPm 330 320 1100 3 0 1200 " 2 540 117 173 200 272 270 700 720 420 1512 700 720 6 70 811 Total Hard- ness PPm Ir CaC'O 317 312 4170 113 10 270 40 3 I0 211 97 44 440 240 5 40 340 422 712 217 356 342 268 Chemical Results of the Sampled Well Water (Un Classified data) Total Cr 7Pb 21 17 3 14 10 7 6 2 17 10 ,7 1 21 2 7 20 '2 8 Si02 Cu Total v PPm PPb PP~ Topographic Sheet Morawaka Ambalantota Ratnapura Haputale Burtala Hatton Tir~~kkovil Kurunegala Aangala hiaha Oya Kalmunai Nalanda Rukam Puttalam Dambulla Dolonnaruwa Polonnaruwa Vakaner~ 3 84 361 8 100 4300 440 422 21 nd 17 73 21 19e 2 3300 Kathirar- ell 397 40C9 Anuradhapura 398 3100 YalaOya 399 4500 406 1000 620 2 72 20 nd I? 21 2,110 91 ?7 27 77 3 500 Horowpatana 434 2130 700 3 1720 560 40 42 1 820 22 100 27 10 3 750 Pul~vankulam