AGSO Journal of Australian Geology & Geophysics, 14 (213), 207-211 © Commonwealth of Australia 1993

The groundwater quality situation in alluvial aquifers of the Kathmandu Valley, Nepal Mohan Singh Khadka 1

Surveys of groundwater quality have been carried out in alluvial aquifers of the Kathmandu valley, Nepal, and a wide range of parameters studied . The natural groundwaters are characterised by high concentrations of iron, manganese, ammonia and carbon dioxide. The presence of coliform bacteria in many wells indicates

Introduction The Kathmandu valley covers an area of about 500 km2, centred on 2r 42' N, 85° 22' E. The average altitude of the valley floor is about 1350 m above sea level (a.s.!.) and the surrounding hills are about 2800 m a.s.!. The average summer temperatures are: maximum 27° C, minimum 1 r C; and the average winter temperatures: maximum 19° C, minimum 2° C. The annual average rainfall is 1300 mm, 80% of which occurs in the monsoon season, from June to September.

There is a high population growth rate in this region . The population of Kathmandu increased from 235 000 in 1981 to 414 000 in 1991, a linear growth rate of 5.83%. The population of the whole valley increased from 364 000 in 1981 to 593 000 in 1991, a linear growth rate of 4.03%.

Hydrogeology The geology of the Kathmandu valley is shown in Figure 1.

The Kathmandu valley comprises fluvio-lacustrine depos•its of Quaternary age. To the south, east and west it is bordered by a sequence of unmetamorphosed to slightly metamorphosed sedimentary rocks of Palaeozoic to Pre•Cambrian age. To the north, the valley is bordered mainly by granitic rocks. The thickness of the Quaternary deposits varies from place to place from 0 to greater than 500 m.

According to Sharma (1977) and Stocklin & Bhattarai (1977), Kathmandu is a tectonic valley of the synclinorium type. By magnetic surveys, it has been observed that the valley is controlled by trough faults in the central zone (Sharma, 1977). A drill hole at Lagan tole (Nautiyal & Sharma, 1961; Sharma, 1977) shows the following se•quence:

Depth range Strata (in m) 0-10 Sand, very coarse to fine-grained, mi•

caceous with occasional quartzite pebbles.

10-221 Clay, black, with light greenish clay inter•calations often in laminated form, occasion•ally gritty, with green phyllitic shale pieces and peat and lignite bands.

221-230 Sand, coarse to medium-grained with peaty to ignitic clay bands.

Ground Water Resources Development Board, Babar Mahal, Kathmandu, Nepal

the need for pollution control. Rapid population growth and urbanisation, and an increasing concentration of industries, are contributing to degradation of groundwater quality. Monitoring programs leading to increased public awareness and management action are necessary at this stage in development.

230-283

283-286

286-313

313-325

325-355

355-361

361-367

367-376

Clay, black, plastic, gritty with sand, con•sisting of quartz, feldspar, muscovite gran•ite , phyllite chips. Sand as above, coarse-grained, with small gravel essentially quartzite-quartz and feld•spar with few schistose sandstone pieces.

Clay, black, very compact sandy, with sand fine-grained, micaceous and occasionally pebbles (resulting in angular quartz gravel on drilling).

Predominantly sand, very coarse-grained and pebbles with intercalations of clay, black compact, often gritty and carbona•ceous.

Gravel, small sized and sand very coarse grained of the same composition as above with or without lignite and peat.

Clay, black, as above, with some gravel in the bottom 2 m.

Sand, coarse to very coarse-grained, grani•tic in composition with thin gravel and clay intercalations.

Clay and sand, as above, intercalated.

The above lithological log shows two aquifers, the upper one from 0 to 10 m and the lower from 313 to 367 m. The upper one is the unconfined shallow aquifer and the lower is considered as the confined deep aquifer. The porosity of these aquifers is about 20% (Sharma, 1977). Thus, the upper aquifer may contain 6.5 x 108 m3 of water, assuming thickness of 10 m, area of 325 km2 and porosity of 20%. Likewise, the lower aquifer may contain 32.5 x 108 m3 of water, assuming thickness of 50 m, area of 325 km2 and porosity of 20%.

More recently, the section through the valley has been explored by deeper drilling. Some 549 m of alluvium was intersected at Bhrikuti Mandap (Fig. 2) with nine water•bearing sand and gravel units below 170 m.

Beneath the alluvial deposits are some karstic limestone aquifers, and their groundwater prospects require further investigation .

Present groundwater quality situation in Kathmandu valley The groundwater resources of the Kathmandu valley are summarised below. Total groundwater abstraction in the valley is about 50 000 m3Jd according to recent consult-

208 MOHAN SINGH KHADKA

85' 20' E

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CHINESE - - '------. REPUBLIC

, _NEPAL '--- __ -t:,;--- , KathmandU.Q... __ J_~~T!-t::ll

> l --, BANGLADESH-

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QUARTERNARY

1- _I Alluvium

CAMBRIAN -- DEVONIAN FT=9 Limestone, quartzite, I::::::::r::l shale and dolomite

LATE PRE-CAMBRIAN -EARLY CAMBRIAN

• . . . . Phyllite, meta sandstone and minor limestone

PRE-CAMBRIAN o Granitic and gneissic rocks

o Built-up area

Fault

Geological boundary

Water catchment boundary

Rivers 19/05/6

Figure L Geology of the Kathmandu valley (after Stocklin & Bhattarai, 1977).

ant's reports (Salzgitter GmbH, 1993). Of this, about 37000 m3/d is derived from wells belonging to the Nepal Water Supply Corporation, which has 22 production wells in operation. About 13 000 m3/d is derived from private wells; there are 334 private wells in operation, of which 188 are shallow wells and 146 are deep wells. The natural recharge of groundwater in the valley is variously esti•mated at about 30 000 to 40 000 m3/d (Binnie & Partners, 1989), about 15 000 m3/d (JlCA, 1990), and about 13000 m3/d (Gautam & Rao, 1991).

Stone spouts Stone spouts fed by groundwater sources were used in the old days to meet the water demand. Some of them are still in operation, although most have dried up and their drainage systems have been disturbed by construction activities in the course of urbanisation.

Physical parameters of the remaining stone-spout supplies are within the drinking water standards, but detection of coliform bacteria and E.coli in large numbers indicate that these sources have been polluted with sewage. This is further confirmed by high concentrations of chloride, ammonia and phosphate.

Maximum and minimum concentrations of different water quality parameters in stone-spout supplies, are tabulated below.

Parameters

pH Turbidity Electrical Conductivity (us/cm) Colour (Hazen) Total hardness

as CaC03 (mg/L) Free ammonia (mg/L) Orthophosphate

(mg/L) Chloride (mg/L) Iron (mg/L) Manganese (mg/L) Total coliform /

100 ml E.coli / 100 ml

Springs

minimum value

6.0 <1

395 <5

80 <1 <1

21 0.01 0.07

20

0

maximum value

6.6 2

1180 20

300 10 15

144 0.15 0.20

1000

480

About five natural springs originating from limestone have been tapped in the southern part of the valley for water supply. The quality of this water is good; i.e. it is potable from physical and chemical points of view. It remains almost the same throughout the year. However, total coliform and faecal coliform organisms have been detected in concentrations of a few per 100 ml in some samples, possibly due to human activities around the intake points.

Depth I LITHOLOGY DATA (m) Log I Top soil Discriotion

· *. .. Coarse grained sand which is 5ubangular to subrounded in shape • • : •• *. consisting of quartz, feldspar and mica 20m

1= --•~ ---

100 -t f ~ ~ ~reenish gr~y clay, sticky in nature, with Carbonaceous matter =- =- = ~ In some portion

[~~~ t73m

Medium grained sand angular to subrounded in shape 179m

F-=--=--:..: :::--==-':::-.=-1 Greenish grey clay with Carbonaceous matter

200 ---E =-:=-~ 207m

o •• 0 . . ... • • O. Coarse sand with fme gravel conslstmg mamly quartz and feldspar •0 •• angular to subangular in shape 0-0.- 228m

~~ ~;- Greenish grey clay with Carbonaceous matter

••• -: .:. -I Coarse sand consisting of quartz, feldspar and biotite • • .: subangular to subrounded In shape

[~~ ~ Greenish grey clay with Carbonaceous matter

0: . 0 • • 0 •

300-1·: 0 .·~

246m

258m

282m

<> o . 1 0 • O. 1 Coarse sand with fine gravel consisting of quartz, feldspar and mica, •• • subrounded to subangular in shape o· ~·o· . .

I.c • 0 • • • <> .;=0 •• •• O.·.ad 353m

Greenish arev clav 359m .--....-00 ~~~ mm

Coarse sand consisting of quartz, feldspar and mica, subrounded to subangular in shape

377m

400 400m Greenish grey clay 406m .: :.·1 Coarse sand consisting of quartz, feldspar and mica,

• •••• subrounded to subangular In shape 418m

r~~ ~ Greenish grey clay with Carbonaceous matter in some portion

436m • 0 ••

•• • •• 0 · ... : .: •••• : I Medium to coarse sand .... · .. . • .·0 .• ~. .-.:. -= G Greenish grey clay ~ •. : : ·:.~I Medium to coarse sand

500 -t -=--=- .::-:: 1=-::::: ~ =-] Greenish grey clay

'0 '. ~ "00 " : ... : 0': ~' .. ~ .

'0: 0:0; Gravel with sand

~ Weathered Rock (Green phyllite)

~~ B"dAocliIGreen pliYflite

478m 484m 490m

517m

549m

570.13m 576m 19/05/5

Figure 2. Lithologic log of well no DMGG, Bhrikuti Mandap, Kathmundu, drilled by the Kathmundu Gas Project in 1988.

GROUNDWATER QUALITY, NEPAL 209

The stable yield of good quality water from these sources indicates that there are good prospects of groundwater being available in limestone aquifers beneath the alluvial deposits in the valley.

The maximum and mInlmUm concentration of different parameters in spring waters is tabulated below.

Parameters minimum value maximum value

pH 7.2 8.1 Electrical

conductivity (uS/em) 195 260 Turbidity NTU <1 3 Colour (Hazen) <1 3 Langelier Index -0.055 +0.16 Total alkalinity as

CaC03 (mglL) 98 148 Total hardness as

CaC03 (mglL) 115 225 Iron (mg/L) <0.01 0.13 Manganese (mg/L) <0.01 0.11 Free ammonia (mglL) <0.01 0.01 Phosphate (mg/L) <0.01 <0.01 Total coliform / 0 60

100 ml E.coli per 100 ml 0 6

Tube wells The number of shallow wells is increasing rapidly in the valley, as this is the cheapest means of getting supplemen•tary water. The municipal water being supplied is intermit•tent and not adequate . The number of deep wells is also increasing slowly with the increasing number of industries and hotels.

Waters from shallow wells in densely populated areas contain high concentrations of total coliform and faecal coliform organisms, indicating contamination from human wastes. Deep tube-well waters were found to be free from coliform organisms in the past, but recent analyses have indicated that these waters contain coliform organisms in low concentrations - possibly owing to pollution at the well sites.

The chemical quality of the deep tube-well groundwater is illustrated in Figures 3 to 6.

Concentrations of iron, manganese, silica and dissolved gases, such as NH3 and CO2, are found to be high in the deep-well waters, (Figs. 4 and 5) which are not potable without treatment. Organic matter deposited in the allu•vium beneath the valley floor could be the source of the dissolved gases. Other possible causes may be the corro•sive hydrochemical environment in the well water (the Ryznar Index is 10 to 12) or microbiological activity due to iron bacteria and manganese bacteria.

Biological oxygen demand values in deep tube-well waters are generally low (average 1 mg/L). Chemical oxygen demand values of deep wells used for water supply by the Nepal Water Supply Corporation are generally low (1 to 5 mg/L), but some of the private wells have appreciable values (up to 16 mg/L). Dissolved oxygen values vary at different well fields from 1 to 8 mg/L (Fig. 6). Nitrate and nitrite values are generally low (N03 <1 mg/L,

210 MOHAN SINGH KHADKA

1000

-800 ....J 0, E ~500 0

~400 Q) u co 0 0200 U o ::::

A

70

50 ....J 0,50 E ~ 40 .2 ~ 30 co Q)

§ 20 0

10

A

Btl 1.":".X,d

ESJ

Electric conductance

(~,

.~{

C 0 E G Well Fields

C 0 Well fields

NWSC ( 1985-88)

Binnie & Partners - 1988

Turbidity

G

• JICA-1990

19105n

Figure 3_ Groundwater quality in deep tube-wells, Kathmandu valley: electrical conductance and turbidity values for well•fields at (A) Gorkana, (B) Manohara, (e) Dhobikhola, (D) Bansbari, (E) Bore-Thimi, (F) Pharping, and (G) private wells in Kathmandu city area.

w,---------------------------------------,

_40

~ -30 co o

.~

E20 g 8 10

80

_70

~60 E - w

! 40 ~ I""; ";;, i ~ 30 ~1

co '."'~ o . ~v 020 'c'

N' 10 TIl

WI $"

A

A

Bb?:~;; !\W. [2]

Ammonia concentration

C 0 Well Fields

C o Well fields

NWSC ( 1985-88)

Binnie & Partners - 1988

G

Silica concentration

J G

• JICA-1990 19/05/8

Figure 4. Groundwater quality in deep tube-wells, Kathmandu

N02 <0.01 mg/L).

Calcium, magnesium, sodium, potassium, chloride, sul•phate and other ions determined in deep well waters are within the drinking water standards. Calcium and bicarbon•ate are the dominant ions. The pH values are generally 6 to 7, i.e. slightly acidic.

The quality of water from the Pharping well field, on the southern side of the valley, is quite good in comparison to the other well fields. Iron, manganese, free ammonia and other minerals are low in concentration (Figs 4 and 5). Total coliform and faecal coliform organisms are nil.

The quality of water from private deep tube-wells is lower than that from deep tube-wells owned by the Nepal Water Supply Corporation. The private tube wells are located in densely populated areas of the city, while the tube wells for municipal water supply are located in rural areas.

Present situation and activities threaten•ing the aquifers in the Kathmandu valley Overdraft of groundwater According to Gautam & Rao (1991) , the total groundwater reserves (perennial plus nonrenewable) are insufficient to fulfil the water demand deficit in the valley. Even at present, it is a situation of overdraft of groundwater. All well fields of the Nepal Water Supply Corporation show a notable depletion of the water table of between 15 and 20 m since the completion of the wells in 1984/85.

Necessary management action should be taken, depending upon the outcome of detailed studies, before some disaster occurs. Management may involve artificial recharge and/or control of abstraction. The groundwater potential of underlying limestone aquifers needs to be studied .

Increase in population The rapid increase in population is due to rapid urbanisa•tion, the influx of people from other parts of the country, and an increase in the number of industries. This has, on the one hand, increased the water demand and, on the other hand, increased pollution. The possible solution is to shift the industries to other appropriate cities.

Waste disposal practices Generally, industrial effluents and sewage are being discharged into rivers without pre-treatment. Septic tanks are very common in areas not connected with the sewerage pipe network. It is believed that some industries inject their effluents into the aquifer. Sewerage pipe networks have to be extended, and efficient sewage treatment plants con•structed. Sewage treatment by the ' root-zone treatment system' needs to be studied .

Lack of safety measures There are no regulations which a company must follow regarding pollution of aquifers during drilling. Well sites are not protected adequately. No standards have been set regarding the use of chemical fertilizers, insecticides and pesticides.

valley: ammonia and silica concentrations for wellfields at (A) Lack of monitoring system Gorkana, (B) Manohara, (C) Dhobikhola, (D) Bansbari, (E) Bore-Thimi, (F) Pharping, and (G) private wells in Kathmandu The quality and quantity of groundwater are not being city area.

10

-8 --' a, E ';;6 0 .~

<=4 Q) g 0 0 2114

o ' .'. A

0.8

~O.6 E

·gO.4 ~ <= Q) u 50.2 0

JIl "'t 0

A

mE'

Iron concentration

C 0 G Well Fields

Manganese concentration

COG Well fields

NWSC ( 1985-88) • JICA - 1990

k\.\:\1 Binnie & Partners - 1988 19/05/9

Figure 5. Groundwater quality in deep tube-wells, Kathmandu valley: iron and manganese concentrations for wellfields at (A) Gorkana, (B) Manohara, (C) Dhobikhola, (D) Bansbari, (E) Bore-Thimi, (F) Pharping, and (G) private wells in Kathmandu city area.

~6-

~ c: i 4-Q) g 8 2 -

[I mI r 'r ~::. I::':. W

I I

m:·~ :::" A C 0

Well fields k(/H Binnie & Partners - 1988

D. O. concentration

G

• JICA - 1990

19/05/10

Figure 6. Groundwater quality in deep tube-wells, Kathmandu valley: dissolved oxygen concentrations for wellfields at (A) Gorkana, (B) Manohara, (C) Dhobikhola, (D) Bansbari, (E) Bore-Thimi, (F) Pharping, and (G) private wells in Kathmandu city area.

GROUNDWATER QUALITY, NEPAL 211

monitored regularly . In fact, there is no institution which has overall responsibility and authority for controlling the abstraction of groundwater and checking of groundwater pollution.

Acknowledgements Funding for the author's attendance at the 'Aquifers at Risk' Conference was provided by the Australian Internat•ional Development Assistance Bureau, under its Internat•ional Seminar Support Scheme.

References Binnie & Partners and MULTI Disciplinary Consultants,

1989 - Report on service improvement in Kathmandu , Lalitpur and Bhaktapur and management support to W.S.S.c.

Gautam, R. & Rao, G.K., 1991 - Groundwater resource evaluation of the Kathmandu Valley . Journal of Nepal Geological Society, 7,39-48.

Japanese International Cooperation Agency, 1990 -Report on Water Supply for Kathmandu Valley towns.

Nautiyal , S.P. & Sharma, P.N. , 1961- A geological report on the groundwater investigation of Kathmandu valley .

Salzgitter, GmbH, S.l.L.T. & MULTI Disciplinary Con•sultants, 1993 - Report on rehabilitation of water supply and sanitation .

Sharma, c.K., 1977 - Geology of Nepal. Mani Ram Sharma, Bishalnagar, Kathmandu.

Stocklin & Bhattarai , D.R. , 1977 - Geology of Kath•mandu area and Central Mahabharat Range, Nepal Himalaya. His Majesty 's Government/United Nations Development Program, Report .