Jul 21, 2010 - Alluvial Aquifers from Delta Plains, Eastern India: Options ..... 200 000 is served by a full-scale conventional treatment plant for the removal of.
This article was downloaded by: [202.53.173.194] On: 31 March 2014, At: 10:38 Publisher: Routledge Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
International Journal of Water Resources Development Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/cijw20
Occurrence of ArseniccontaminatedGroundwater in Alluvial Aquifers from Delta Plains, Eastern India: Options for Safe Drinking Water Supply Prosun Bhattacharya , Debashis Chatterjee & Gunnar Jacks Published online: 21 Jul 2010.
To cite this article: Prosun Bhattacharya , Debashis Chatterjee & Gunnar Jacks (1997) Occurrence of Arsenic-contaminatedGroundwater in Alluvial Aquifers from Delta Plains, Eastern India: Options for Safe Drinking Water Supply, International Journal of Water Resources Development, 13:1, 79-92, DOI: 10.1080/07900629749944 To link to this article: http://dx.doi.org/10.1080/07900629749944
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information.
Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content.
Downloaded by [202.53.173.194] at 10:38 31 March 2014
This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http://www.tandfonline.com/page/terms-andconditions
W ater R esources D evelopm ent, V ol. 13, N o. 1, 7 9± 92, 1997
O ccurren ce of A rsenic -conta m inate dG roundw ate r in A llu via l A quifers from D elta Pla ins, Easte rn India: O ptions for Sa fe D rinkin g W ate r Supply
PRO SU N BH AT TA C H A RYA 1, D E BA SH IS C H AT TE RJEE2 & GU N N A R JA C KS 1
Downloaded by [202.53.173.194] at 10:38 31 March 2014
1
D iv ision o f Land a nd W ater Resources, D ep a rtm ent of C ivil and E nv iro nm enta l E ngineering ,
R o ya l Institute o f Technolog y , S-10 0 4 4 Sto ckh o lm , Sw ed en; 2 D epa rtm ent o f C hem istry, U niv ers ity of Ka ly a ni, Ka ly a ni 74 1 2 3 5, W est B eng al, Ind ia
A BSTRACT A rsenic contam ination in ground w ater used for drinking purposes has been envisaged as a problem of global concern. Exploitation of ground w ater contam inated w ith arsenic w ithin the delta plains in W est Beng al has caused adverse health effects am ong the population w ithin a span of 8± 10 years. The sources of arsenic in na tural w ater are a function of the local geology, hydrology and geochem ical characteristics of the aquifers. The retention and m obility of different arsenic species are sensitive to varying redox cond itions. The delta plains in W est Beng al are characterized by a series of m eand er belts form ed by the ¯ uv ial processes com prising different cycles of com plete or trun cated ® ning up w ard sequences (sand± silt± clay). The arseniferous groun dw ater belts are m ainly located in the up per delta plain and in aband oned m eand er channels. M ineralogical investigations have established that arsenic in the silty clay as w ell as in the sandy layers occurs as coatings on m ineral grains. C layey sedim ents intercalated w ith sandy aquifers at depths betw een 20 and 80 m are reported as a m ajor source of arsenic in ground w ater. Integrated kno w ledge on geological, hydrological and geochem ical characteristics of th e m ulti-level aquifer system of the up per delta plain is therefore necessary in predicting the origin, occurrence and m obility of arsenic in groun dw ater in W est Beng al. This w ould also provide a basis for dev elop ing suitable low -cost techniques for safe drink ing w ater supply in the region.
Introduction A rsen ic (A s) contamination of natural orig in in ground w ater has been env isaged as a w orld w ide problem . Several accounts of the presen ce of arsen ic at elev ated levels have been reported from various parts of the U SA such as Arizona, C alifornia, M ontana, N evada, O klahoma and W ash ington in relation to iss ues on arsenic in groundw ater (Robertson , 1986, 1989; M oncure et al., 1992; Schlottmann & Breit, 1992; Frost et al., 1993). Similar cases have also been reported from many other countries including C hile, Bangladesh and the Taiw an province of C hina. G lobal perspectives on the problem of arsen ic occurren ces in groundw ater and treatm en t strategies have recen tly been rev iew ed by H erin g & Elim elech (1995). In India, the problem of the occurren ce of high A s in ground w ater has been 0790-0627/97/010079± 14 $7.00
Ó
1997 Jou rnals O xfor d Ltd
Downloaded by [202.53.173.194] at 10:38 31 March 2014
80
P. Bhattacharya et al.
detected for a decade in some areas of W est Beng al located in the Ind oGangetic delta plains affecting the districts of N adia, M ursh idabad, M alda, Bard dhaman, N orth and South 24-Paraganas. The mid-1970s saw a large-scale exploitation of groundw ater, resources for irrig ation purposes. A s a consequence of the w ar in Bangladesh in 1971, the exodus of 80± 90 m illion people from Bangladesh increased the number of settlem en ts in the borderin g districts of W est Beng al, thereb y sign i® cantly increasin g the demand for w ater. A dverse health effects due to the consumption of groundw ater w ith excess arsenic content w ere manifested am ong the population w ithin a time span of 8± 10 years (Goriar et al., 1984; Chakraborty et al., 1987; Guha M azumder et al., 1988; Das et al., 1994). The source of As in groundw ater as w ell as in surface w ater is most often leaching of geological materials, in puts from geoth erm al sources, mining w astes and land® lls (Welch et al., 1988; Korte & Fern and o, 1991). Uncontrolled anthropogenic activities such as sm eltin g of metal ores, use of arsen ical pesticid es and w ood preservative agen ts may release arsen ic directly to the env iron ment (Bhattacharya et al., 1995c). Occurren ce of arsenic in natural w ater depen ds on the local geolog y, hy drology and geochemical characteristics of the aquifer m aterials. Furth erm ore organic content in sed im en ts as w ell as the land-use pattern may also be important factors controllin g the natural m obility of arsenic in alluvial aquifers. In spite of the reported occurren ce of high As in groundw ater in W est Beng al, the people of the area are solely depend ent on the groundw ater resources in this region. The resea rch carried out so far has concern ed the quantitative determ ination of the level of arsen ic in groun dw ater and epidemiological studies among the population in the in fested zone. Geochemical in vestigations pertaining to the occurrenc e of As in ground w ater in W est Beng al sh ould receiv e priority to evaluate overall quality of the groundw ater and quanti® cation of geochem ical processes that control groundw ater chem istry. The examination of the presen t nature of hyd rological conditions in the aquifer sys tem is essen tial to understand the impacts of groun dw ater development. The chemistry of the solid phase, i.e. soils , m inerals and und erly ing bedrocks togeth er considered as aquifer materials, and their interaction w ith the aqueous phase play a key role in controlling the reten tion and /or m obility of As und er differen t red ox conditions w ithin the subsurface en viron ment (Bh attacharya et al., 1995a,b). The occurren ce and origin of A s in groundw ater depend on severa l factors such as adsorption± desorption as w ell as precipitation± disso lution of uns table A s minerals, subsurface red ox condition, grain size of aquifer materials, ion-ex change capacity of the aquifer, m ineralogy of the aquifer, organic contents, biological activity and aquifer characteristic s (Roberts on, 1989). The presen t contrib ution therefore aim s to high ligh t the need for proper und erstan ding of the problem in order to predict the possible prim ary mechanism s resp onsib le for reten tion or mobility of various As species through adsorption/desorption phen omen a in groundw ater under the prevailin g red ox condition. The red ox conditions are likely to play a key role in determ inin g the m obilization of arsenic (Robertson , 1986). A ny phen omen on affecting the red ox conditions such as the pumping rate and the land -use pattern is of interes t in revealing the mechanism s behind the excess arsen ic content in groun dw ater.
Downloaded by [202.53.173.194] at 10:38 31 March 2014
O ccurrence of A rsenic-contam inated G round w ater in A quifers
81
Figure 1. M ap of W est Ben gal, sh ow ing the areas w ith high arsenic in ground w ater in the delta plains of Eastern India.
N atural A rsenic C ontam ination in the Indo -G ange tic D elta Plains G eographical D istribution H igh arsen ic in groundw ater has been encountered in N adia, M ursh idabad, M alda, Barddhaman and the N orth and South 24-Paraganas districts of W est Beng al, restric ted betw een latitudes 21 30 9 and 27 10 9 N and longitudes 86 and 2 90 E (Figure 1). The total affected area covers around 34 000 km , represen ting nearly 39% of the total area of the state. The geographical extent of the arsenic-infested area is about 450 km from the district of M alda in the north to the 24-Paraganas district in the south, affecting about 35% of the total population of the state. Table 1 summ arizes the present status of geographical distrib ution, demography and epidem iological impacts of elevated As concentration in six districts of the state. A nalytical data on elevated A s concen tration of tubew ell w ater samples (June± July 1995) from N adia district indicate that 143 villages are affected out of 221 situated in the arsen ic-prone area (Table 2).
°
°
°
°
Epidem iological Im pacts A pproximately 175 cases of arsen ical derm atosis w ere reported durin g 1983± 84, from the borderin g districts of N adia, M ursh idabad and M alda, w hile a few cases w ere also reported from the districts of N orth and South 24-Paraganas and Bard dhaman (Guha M azumder et al., 1988). Symptoms such as hyperk eratosis and hyperpigm entation in palms and soles, and non-cirrh otic portal ® brosis w ere clinically observed among the affected population. Epidemiological studies have show n evid en ce of arsenical derm atosis and hepatomagaly among nearly
10.02 5.72 30
3
10
54
10± 460
12± 160
T otal num b er of arsen icaffected blocks
Percen tage of arsen ic occurren ces in th e blocks
T otal num b er of affected villages
Range of arsen ic con cen tration in ground w ater (in m g/l)
Range of depth of arsen iccon tam in ated w ells
2
24-Pargan as (South)
T otal area (*10 km ) 6 T otal population (*10 ) T otal num b er of blocks
3
A rsenic-affected d istricts
12± 125
10± 490
50
41
5
4.13 7.28 22
24-Pargan as (N orth )
12± 85
10± 410
75
33
2
3.73 2.65 15
M ald a
20± 95
10± 450
20
6
2
7.02 6.05 34
B ard d ham an
12± 85
10± 560
92
35
9
5.52 4.74 26
M ursh id abad
12± 150
10± 590
143
76.5
13
3.93 3.85 14
N adia
Ð
Ð
434
Ð
41
34.34 30.3 144
T otal
T able 1. Geographical distribution, demographic parameters and epidemiological impacts of arsenic contaminated groundw ater from tubew ells in Bengal Delta Plains (data incorporated up to July 1995)
Downloaded by [202.53.173.194] at 10:38 31 March 2014 82 P. Bhattacharya et al.
T otal
K arim pur I K arim pur II T eh atta I T eh atta II K aligan j N akash ipara N ab adw ip H an skh ali K rish nagan j H arin ghata C hakdah San tipur C hapra
B lock
119
3 26 3 8 6 10 8 5 9 11 14 15 1
N o. of sub division s covered in th e stud y
66
2 13 3 3 5 6 6 3 3 4 10 7 1
N o. of h am lets affected w ith A s ( , 50 m g/l)
221
11 24 36 28 33 6 36 6 3 7 10 17 4
N o. of sam ples an alysed from A s affected villages
143
6 15 34 8 6 6 20 5 3 5 10 9 4
N o. of sam ples w ith elevated level of A s ( , 50 m g/l)
Ð
10± 7± 10± 10± 10± 10± 10± 20± 10± 0± 10± 10± 10±
185 188 485 185 300 240 175 70 90 70 220 57 60
Ran ge of A s con cen tration ( m g/l)
Table 2. Analytical data on A s concentrations in groundw ater extracted from the alluvial aquifers of Bengal Delta Plains at different blocks of N adia D istrict, W est Bengal
Downloaded by [202.53.173.194] at 10:38 31 March 2014
O ccurrence of A rsenic-contam inated G round w ater in A quifers 83
84
P. Bhattacharya et al.
92.5% of the population exposed to arsenic in the concentration of 0.2± 2.0 m g/l in contrast w ith about 6.25% of the population w ith # 0.05 mg/l in drin kin g w ater (Goriar et al., 1984; Chakraborty et al., 1987; Guha M azumder et al., 1988). Laboratory investigations of the urine, nails, hair and sk in-scales as w ell as the analysis of biopsy sam ples collected from a cross-section of the affected people of the area revealed sig ni® cant concentrations of As (Chatterjee et al., 1995; Das et al., 1995). The evid en ce of bio-accumulation of A s has also been observed among cattle (Das et al., 1995) due to the consum ption of 40± 50 l/day of arsenic-contaminated groun dw ater.
Downloaded by [202.53.173.194] at 10:38 31 March 2014
Physiographic and G eom orphologic Fram ew ork The m ajor phy siog raphic and geom orphic domains in the state of W est Ben gal and their geographic locations are presen ted in Table 3. The area en circled by the rivers Padm a and Bhagirathi and the Bay of Ben gal in the south represents the Gangetic delta. Th e delta plain com prises a thick succession of sed iments deposited by the Ganga± Brahmaputra riv er system s w ith a typical southw ard gradien t. The delta plain is typically of moribund character and formed due to siltin g of the old river levees. The Gang a has sh ifted eastw ard s from its origina l course and is branched in to tw o distributaries, Bhagirath i± H ooghly and Padm a± M egh na. The causes of shiftin g of the Gang a and the m eandering beh aviour of the riv er have not been properly understood . A mong the possib le explanations for the changes in the riv er courses are alluviation at the heads of successive m ain spillw ays, resp onse to neotectonism and eustatic sea-level changes. Secular sw ing in the course of the Teesta tow ard s the east is a recen t manifestation (PH ED , 1991). The upper delta plain (UD P) w ith a gen tle southerly slope is characterized by a series of meander belts form ed by the ¯ uvial processes as a resp onse to varying hyd rodyn amic conditions . The w avelen gth s and amplitudes of the various segm ents of the m eander belts vary w idely and are often characterized by detached loops of ox-bow lakes and alluvial rid ges. O ther geom orphic form s are levees and sw amps in betw een inter-distrib utary levees. The basin -® lled deposits are ¯ uvial deposits and com prise stacks of differen t cycles of upw ards ® ning sequences (sand± silt± clay). Such cyclic sed imentation (sym metrical and asy mmetrical) in the form of festoon-bedding are found w ith coarse to medium sand, ® ne sand, clay and silt resp ectively . The arsen iferous belts are located in the upper delta plain and in the aband oned m eand er channels as w ell as scrolls (Figu re 2). The plain betw een the m orib und delta in the north and the Sundarbans (the coastal part) is consid ered as the low er delta plain (LD P). The rivers ¯ ow w ith a gen tle slope tow ards the south. The Sundarbans is the curren tly active delta and is covered w ith tidal mang rove forests.
Sed im ento logical Characteristics A thick pile of ¯ uvial sed iments pertaining to the Quaternary age constitutes the Beng al delta plains . The U DP com prises a composite seq uence of meanderin g riverin e deposits of the Proto-Padm a Meand er Belt (PPM B) w ith a N N E± SSW trend . The belt merg es w ith the lateritic pied mont plain tow ard s the north-east. The PPM B is transected by four younger meander belts of the Padma
O ccurrence of A rsenic-contam inated G round w ater in A quifers
85
T able 3. M ajor phy siog raphic and geomorphic domains of W est Ben gal, Eastern India
Downloaded by [202.53.173.194] at 10:38 31 March 2014
Geog raph ic location
Ph ysiographic d om ain
Geom orph ic d om ain
D arjeeling an d n orthern parts of Jalpaiguri d istrict
M ountainous terrain
H im alayan and subH im alayan ranges
C ooch B ihar, Jalpaiguri and n orthern part of W est D inajpur
Sub-m on tan e terai
Sub-m on tan e terai
M alda and W est D inajpur
Pa ra delta
T errace of old er lateritic alluvium
B irb hum , Ban kura, Pu rulia an d part of M idnapur
L aterite upland
L aterite pied m on t plain
M urshidabad , N ad ia and parts of B ardd ham an and N orth 24-Pa rganas
Gang etic d elta
U pper d elta plain of m eand er belt
B ardd ham an, H oogh ly and parts of M idnapur
Gang etic d elta
M arginal fan and valley m argin fan
C alcutta, H ow rah , South 24-Pa rganas an d parts of N orth 24-Pa rganas
L ow er Gan getic d elta
L ow er d elta plain
Figure 2. Diagrammatic sketch sh ow ing the deposition of m utually truncating ® ning upw ard sequences in a typical cross-section of the arsen iferous alluvial sed iments of the U DP.
Downloaded by [202.53.173.194] at 10:38 31 March 2014
86
P. Bhattacharya et al.
Figure 3. Section show ing the disposition of the various aquifers along a N N W ± SSE transect of the UD P. N ote: The sedimen ts are classi® ed into three units among w hich U nit 2 is arsen iferous.
river (PMB) tow ard s the south-east of the upland plain. The River Bhagirathi also in dicates development of three consecutive m eand er belts in the w estern part of the PPM B. These meander belts are discontinuous in nature and often preserv ed as festoons or show truncated character. U pw ard-® ning cycles of various thicknesses constitute the meander belts (Saha & C hakraborty, 1995). Abrupt changes in lithology could be explained in term s of ¯ uctuations in the hyd rodyn amic conditions and the result of the eros ion of the older sed iments as w ell as the deposition of younger sed imen ts. The sed im en ts are in gen eral sand, silt and clay in the young er meand er belt sequen ces, w hile the older ones are m ore sand y and und erlain by gravel beds that ind icate the existence of high-en ergy streams during their form ation (PH ED, 1991). The oldest gravel beds of large dim en sions w ere form ed possibly during the rapidly rising stage of the Flandrian trans gress ion. The extensive clay beds of the Tertiary period are observed in the subsurface at depths of about 150 m and sh ow unconformable relation to the younger ¯ uvial cycles. N o strong evid en ce of older Quaternary deposits w as found at this depth possibly due to erosion durin g the falling stage of the sea level (PH ED, 1991).
H ydrogeological C haracteristics The northern part of the Ben gal basin is characterized by extensive near surface aquifers of uncon® ned nature. The lith ology is prim arily dominated by intercalations of sand , silt and clays of Quaternary age. Subsurface rid ges of basements demarcate the hy drological boundary to the low er and deeper parts of the basin in the south. The basin is, how ever, open tow ards the south-east into the Tertiary form ations of Bang ladesh. C on® ned aquifers occur at depths of about 300 m, w ith possibilities of zonal in ter-conn ection w ith the upper group of uncon® ned aquifers especially along the tectonic trough s through w hich the m ajor riv ers ¯ ow . Groundw ater occurs under uncon® ned condition particularly in the N adia,
87
Downloaded by [202.53.173.194] at 10:38 31 March 2014
O ccurrence of A rsenic-contam inated G round w ater in A quifers
Figure 4. Simpli® ed lith ological column togeth er w ith the disposition of arsen iccontaminated aquifers at a borehole site in N adia D istrict, W est Beng al, India.
M ursh idabad and M alda districts and in sem i-con® ned condition in Barddhaman, and the N orth and South 24-Paraganas districts. Thus the aquifers change gradually from open to sem i-con® ned character tow ard s the south (Figu re 3). The closed aquifers are genera lly inter-connected w ith the upper groups of open aquifers. Fluvial sand and gravel are the principal deposits form ing the major aquifers. The rech arg e areas are located in upland and sub-mountain fronts. The deposits in the aquifers are ® ne, m edium and coarse sand w ith gravel. Clayey intercalations are darker in colour, possibly re¯ ecting elevated contents of organic m atter.
88
P. Bhattacharya et al.
Downloaded by [202.53.173.194] at 10:38 31 March 2014
Sandy clay mixed w ith kankar and coarse, medium to ® ne sand characterize the open hyd rological system s. The sem i-con® ned sys tems are deposits w ith ® ne w hite sand w ith clayey intercalations and medium to coarse sand w ith gravels tow ard s the bottom. Fine-grained deposits are also accumulated in the bottom of the aquifer overlain by a pure ® ne w hite sand. The lith ological succession of a w ell site in N adia district is given in Figu re 4. The aquifers in the low er delta plain and coastal tracts of M idnapur districts normally lie deeper ( . 200 m) under a blank et of a w idespread aquiclude in the near surface zone (Saha & C hakraborty, 1995). The groun dw ater in the w estern part of the basin is restric ted to localized zones found both in con® ned and uncon® ned conditions. The eastern margin of the ground w ater basin is formed from the fractured and w eathered parts of the old rocks and in m inor channel® lled sed im en ts of some streams. M ineralogical and G eochem ical Constraints Investigations have revealed that w ithin the meand er belt the As contaminated groundw ater is mainly con® ned to the interm ediate aquifer (20± 80 m), w hile the occurrence of A s in the sh allow and deep aquifers (90± 150 m ) is quite lim ited . The absen ce of impervious clay parting s betw een the interm ediate and deeper aquifers seem s to play an important role for the occurren ce of As. The analytical data ind icate that the m ajor ions are calcium, magn esium and bicarbonate w ith elevated contents of iron , phosphate and arsen ic. Contents of sulphate, chlorid e and ¯ uoride are low . D istin ct tren ds of increasing arsen ic have been docum en ted during pumping , sugg esting a release of As ¯ ow in g in from distant sources (PH ED, 1991; C hatterjee et al., 1995; D as et al., 1995). M ineralogical inv estigations by SEM and EDX of aquifer materials have establish ed that arsenic occurs in the silty clay as w ell as in the sand y layers as coating on mineral grains. The impersisten t clay horizons separating the shallow and in term ediate aquifers have yield ed a relatively high arsen ic content w ith occasional distin ct grains of arsen opyrite observ ed (PH ED, 1991). Arsenic in groundw ater is con® ned to the meander belt zone of the UD P comprising Late Quaternary sedimen ts. Ground w ater extracted from older sed iments of Barind and Ilambazar Form ations in the area w est of the UDP do not in dicate As occurren ce. C layey sed imen ts intercalated w ithin the sandy aquifers at depths betw een 20 and 80 m m ight act as a major source of A s in groundw ater. It has been inferred that the sed im en ts w ere transported from the source terrains located in the C hhotanagpur± Rajmahal high lands in eastern Bihar and deposited by sluggish meandering streams in the Ben gal ¯ ood plain under red ucing conditions. A lterna tives for Safe D rink ing W ater Sup ply Groundw ater contamination is a priority en vironm en tal issue particularly in the context of a safe drin king w ater supply for the sem i-urban and rural population in developing countries such as India, C hina, C hile and Bangladesh . Occurren ce of arsenic in groundw ater can be attributed to natural sources or be in duced by anthropogenic activities or through a combined effect. Several options for the supply of safe drin king w ater w ere sugg ested by the join t investigators to the planners and a few of them w ere adopted durin g
Downloaded by [202.53.173.194] at 10:38 31 March 2014
O ccurrence of A rsenic-contam inated G round w ater in A quifers
89
subsequent action plans (PH ED , 1991, 1993). Extraction of w ater from deeper aquifers (150± 300 m) has so far rem ained the most viable altern ative to safeguard the drin king w ater supply, as long as concentrations of arsen ic rem ained below the perm issible lim it ( , 50 m g/l). This expen sive operation has not been successful as elevated levels of arsen ic have been noted in recent groundw ater sam ples. This could be due to leaching and dow nw ard m ovem en t of soluble arsen ic from the overly ing sed iments resulting from forced extraction of groun dw ater. Recen t observations sugges t that the problem of high As contents in groundw ater has affected aquifers at several depths as w ell as spread to new er areas, emerging as the greatest natural arsen ic calamity in the w orld (PH ED , 1993). C hem ical treatm en t using coagulation, ¯ occulation, sed im en tation, ® ltration and disinfection is consid ered as another suitable option for the rem oval of A s from ground w ater for drin kin g purposes (Bellack, 1971; Gulled ge & O ’C onnor, 1973; Shen , 1973; Gupta & C heng , 1978; Sorg & Legs don, 1978; H athw ay & Rubel, 1987; H arper & Kin gh am , 1992; Brew star, 1994; C hen g et al., 1994; Edw ard s, 1994; Scott et al., 1994; H sia et al., 1994). In C hile, a population of nearly 200 000 is served by a full-scale conven tional treatm en t plant for the rem oval of A s. Th is experien ce suggests that for source w ater w ith high As concen trations, m ore strin gen t standards for A s ( , 20 m g/l), now bein g consid ered , could not be m et by conven tional coagulation (Sancha, 1995). Th e problem of chemical treatm en t of groundw ater in W est Bengal is dif® cult to solve by conven tional practice ow ing to the occurren ce of As in variable oxidation states, As(III) and A s(V) and distin ct variations in their ratio. Th e red ox speciation of As has sign i® cant implications for the ef® ciency of treatment processes (H erin g & Elim elech, 1995). Transform ation of As species from a low er to high er oxidation state can be achieved by using a suitable ox idizing agent before coagulation (M azumdar et al., 1993). Effectivity and maintenance of such high -cost, full-scale treatm en t plants are not viable altern atives for municipal w ater supply schemes in rural and sem i-urb an areas in develop ing countries like India w ith poor in frastructural facilities. A nother m ajor aspect of the applicability of such processin g plants concern s the safe disposal of sludges containing high A s. Action plans suggested by state planners during 1993± 94 recommend ed distribution of surface w ater from distant sources in selected areas of M alda district, amend m en t of ground w ater in domestic as w ell as tubew ells by attached ® lter units or dugw ells ® tted w ith hand -pumps (PH ED, 1993). The merits of these options for safeguardin g the supply of drin kin g w ater in the arsen ic-infested zone are yet to be establish ed. The econom y of long-range trans portation of surface w ater, further handlin g and disposal of used ® lter units and bacteriological contamination of w ater from the dugw ells are the possible lacunae of these options . A ssessm ent of the techn ical feasibility , social acceptability and cost-bene® t analysis of these options w ould therefore be im portant w hile implem en ting these techn iques for future plannin g of safe drin king w ater supply in rural and sem i-urban areas of W est Ben gal.
D iscus sion N one of the proposed rem edies has been proved to solve the problem for the rural and sem i-urban drin kin g w ater supply. M oreover the m echanism s of A s m obilization are not unequivocally explained . The possibility of localizing
Downloaded by [202.53.173.194] at 10:38 31 March 2014
90
P. Bhattacharya et al.
groundw ater of acceptable quality depend s on an integrated kn ow led ge of the geology, hyd rogeology and hyd rochem istry of the aquifers and their settin g. Even rem edies such as rein ® ltration of iron ous, As-containing groundw ater m ust be based on a sound interpretation of the mechanism inv olved in the m obilization of the A s. The developm en t of the problem is likely to be closely associated w ith the red ox cond itions in the aquifers (Robertson , 1986, 1989). C urrently it is not know n w hether the arsenic concen trations in the groundw ater have alw ays been high in the second aquifer or w hether the concentrations have increased as a consequ en ce of ground w ater development. The bedrock source of the arsenic is in ferred to be a source rock in eastern Bihar in the C hhotanagpur± Rajmahal hills. The arsen ic contained in pyrite or arsenop yrite has been deposited in the sed imen ts and partly red istributed there. The part contained in clays may have rem ained in its initial form w hile in the sand y sed iments it has oxidized and been adsorb ed onto ferric coatings on the sand grains. W e can infer that arsen ic is mobilized mainly by tw o processes: (1) oxidation of pyrite and/or arsenop yrite in clayey interc alations; (2) red uction of ferrous coatings on sand grains releasin g arsen ic and adsorbed phosphate. M ost of the arsen iferous groundw ater is high in ferrous iron and phosphate as w ell. This seem s to support the second mechanism . M oreover the gen erally low level of sulphate contents in the ground w ater indicates that the oxidation of pyrite may not be the source of the arsenic. Thus anaerob ic conditions leading to red uction of ferric iron seem s to be the m ost plausib le mechanism for the form ation of the observed hyd rochemical cond itions in the U DP. An important issue is w hether groun dw ater extraction has affected quality. The experiences from the pumping of the deeper aquifers w hen the arsen ic content increased w ith time indicate that the pum ping rate m ay in¯ uen ce the quality . The land-use pattern may also affect the w ater quality by creating more or les s anaerobic soil conditions. W etland cultivation such as paddy ® eld s may give a sh ift to more red ucing conditions. Drainage of sw am ps m ay act in the other direction , increasing the oxyg en diffusion into the ground. The in¯ uence of land -use changes and pumping rates may be rev ealed by time-series analysis of accumulated data. The measurem en t of red ox potentials in pumped ground w ater is a means of de® ning the redo x conditions prev alent in the aquifers. The measured potential could be correlated w ith the potential in ferred from the ferrous/ferric and arsen ate/arsen ite red ox couples (H olm & C urtiss , 1989). A sim ple batch test for sed iments to test the potential for arsenic mobilization could be help ful. Enclosing sed iment and w ater along w ith an easily deg radable organic com pound such as glucose may be a possible model system for the sim ulation of arsen ic m obilization und er red ucing conditions. Laterite could be a possible ® lter medium for som e of the A s contaminated groundw aters, notably those in w hich the arsen ate dominates over the arsen ite. The laterite could be manipulated in a number of w ays to achieve good physical form and m axim um adsorption capacity. Rein ® ltration of iron ous ground w ater high in As may be an option if perm eable surface sed imen ts are present. In particular, arsen ate may be rem oved by
O ccurrence of A rsenic-contam inated G round w ater in A quifers
91
adsorption of the ferric precipitates. The rem oval and safe disposal of the ® lter bed must be undertaken.
A cknow ledge m ents The authors w ould like to thank Jon Petter Gustafsson and Sune N ordqvist for several stim ulating discussion s and com men ts on the prelim in ary drafts of this m anuscript. One of the co-authors (D C ) w ould lik e to thank KTH for provid ing the travel grants and all the facilities at the Division of Land and W ater Resources.
Downloaded by [202.53.173.194] at 10:38 31 March 2014
R eferences B ellack , E . (1971) A rsen ic rem oval from potable w ater, Jou rna l of A m erica n W a te r W o rks A ssociatio n, 63(7), pp. 554± 558. B h attach arya, P., C h atterjee, D. & Jacks, G. (1995a) A rsen ic con tam ination in ground w ater w ithin m ultilevel aquifer system of In do-G an getic d elta plains: a case study fr om W est B en gal, eastern In dia, in: 5th Sem inar on H yd rog eolo gy an d E n viro nm ental G eoch em istry , B . B oÈ lviken S em ina r-95 ; N o v em ber 9± 10 , 1 9 95 , N org es G eolo giske U nd erso È k else, Report 95.138, pp. 8± 9. B h attach arya, P., Ch atterjee, D . & Jacks, G. (1995b) Sign i® cance of contam ination stud ies: case ex am ples fr om In d ia, in: A bstra cts an d p ap ers (Se ssio n 3 ), N eed s fo r E n vironm ental D ata an d H u m an R esou rces D ev elop m en t. K T H -T N A U S em ina r o n S afeg ua rd ing W ate r R esou rces U tility by C atch m ent O riented P olicies: L esson s L earned from C u rrent A p proa ch es, Ku n glig a T ekniska H oÈ g skolan, A ugust 1995. B h attach arya, P., N ordq vist, S. & Jack s, G. (1995c) Status of arsen ic con tam ination in the soils around a form er w ood preservation facility at K ons terud , K ristineh am ns M un icipality, V aÈ rm land s C ounty, W estern Sw ed en, in: 5th Sem inar o n H y drog eolo g y a nd En v iron m enta l G eochem istr y, B. B oÈ lviken S em ina r-9 5 ; N o vem ber 9± 10 , 1 9 95 , N o rg es G eolog iske U nd erso È k else, Report 95.138, pp. 70± 72. B rew star, M .D . (1994) Rem oving arsen ic fr om con taminated w aste w ater, W ater E n vironm en ta l T ech no lo g y, 4(11), pp. 54± 57. C h akraborty, A .K., B anerjee, D ., Ghosh al, S. & Barm an, P. (1987) A rsen ical d erm atitis from tubew ell w ater in W est Ben gal, In d ia n Jo urna l o f M edica l Research , 85, pp. 326± 334. C h atterjee, A ., D as, D ., M and al, B .K., C h ow dh ury, T .R., Sam an ta, G. & C h akrab orty, D . (1995) A rsen ic in ground w ater in six d istricts of W est B en gal, In d ia: the biggest arsen ic calam ity in the w orld, Part 1: A rsen ic species in d rinking w ater and urine of the affected people, A na ly st, 120, pp. 643± 650. C h en g, R.C ., Liang, S., W ang , H .C . & B euh ler, M .D . (1994) E n h anced coagulation for arsen ic rem oval, Jou rna l o f A m erican W ater W orks A sso cia tion , 86(9), pp. 79± 90. D as, D ., Ch atterjee, A ., Sam anta, G., M and al, B .K., Ch ow d hury, T .R., C h ow dh ury, P.P., C h and a, C ., B asu, G., L odh , D., N and i, S., C h akrab orty, T., M and al, S., B h attach arya, S.M . & C hakraborty, D . (1994) A rsen ic in groun dw ater in six districts of W est B en gal, In d ia: the biggest arsen ic calam ity in the w orld, A na ly st, 119, pp. 168N ± 170N . D as, D ., C h atterjee, A ., M and al, B .K., Sam anta, G., Ch akraborty, D . & C h and a, B . (1995) A rsen ic in groun dw ater in six d istricts of W est B en gal, Ind ia: T h e biggest arsen ic calamity in the w orld, Pa rt 2: A rsen ic con cen tration in d rinking w ater, hair, nails, urine, skin-s cale an d liver tissue (biopsy) of the affected people, A na ly st, 120, pp. 917± 924. E d w ard s, M . (1994) C hem istry of arsen ic rem oval d uring coagulation and iron± m ang anese ox idation, Jou rna l o f A m erican W ater W orks A sso cia tion , 86(9), pp. 64± 78. Frost, F., Fran k, D ., Pierson , K ., W ood ruff, L ., Raasina, B., D avis, R. & D avies, J. (1993) A season al stud y of arsen ic in groun dw ater, Sn oh om ish C ounty, W ashington, U SA , En v iron m enta l G eoch em istry a nd H ealth, 15, pp. 209± 214. Goriar, R., C h akrab orty, K. & Py n e, R. (1984) C hronic arsenic poisoning from tubew ell w ater, Jo urna l o f the In d ia n M ed ical A ssocia tion , 82, pp. 34± 35. Guh a M azum d er, D .N ., C h akraborty, A .K., Gh ose, A ., Gupta, J.D ., C h akrab orty, D .P., D ey, S.B. & C h attopadh yay, N . (1988) C h ronic arsen ic toxicity from d rinking tubew ell w ater in rural W est B en gal, B ulletin of th e W o rld H ealth O rg an iz atio n, 66(4), pp. 499± 506. Gulledge, G.H . & O ’ C onn or, G.T . (1973) Rem oval of arsen ic(V ) fr om w ater by ad sorption of alum inium and fer ric hy d roxides, Jou rna l o f A m erican W ater W orks A ssocia tion , 65, pp. 548± 552.
Downloaded by [202.53.173.194] at 10:38 31 March 2014
92
P. Bhattacharya et al.
Gupta, S.K. & C h eng , K .Y. (1978) A rsen ic rem oval b y ads orption, Jou rnal o f W a te r P ollutio n C on tro l F ederation , 50, pp. 493± 506. H arper, T .R. & K ingh am , N .W . (1992) Rem oving arsen ic fr om w aste w ater using ch em ical precipitation m ethod s, W a te r E nv iron m enta l R esearch, 64, p. 200. H athw ay, S.W . & Rubel, F., Jr (1987) Rem oving arsen ic from d rinking w ater, Jo u rnal of A m erica n W ater W orks A ssocia tion , 79(8), pp. 61± 65. H ering, J.G . & E limelech, M . (1995) In ternational perspectives on arsen ic in groun dw ater: problems an d treatm ent strategies, Pr o ceed ings of th e A m erican W ater W orks A ssocia tio n , A n n ua l C on ference, 18± 22 June 1995 (Pr eprint). H olm , T.S. & C urtiss, C .D . (1989) A com parison of ox idation-r ed uction poten tials calculated from the A s(V )/A S(III) and Fe(III)/ Fe(II) couples w ith m easured platinum -electrod e potentials in ground w ater, Jo u rnal o f C o ntam ina n t H y d rolog y , 5, pp. 67± 81. H sia, T.S., L o, S.L ., L in, C .F. & L ee, D .Y. (1994) C h aracterization of arsen ate ad sorption of h yd rous iron ox ide using ch em ical an d ph ysical m ethod s, C ollo id Surfa ces A , 85, pp. 1± 7. K orte, N .E . & Fern and o, Q . (1991) A review of arsen ic (III) in groun dw ater, C ritica l R eview o f E n v iron m enta l C o ntro l, 21, pp. 1± 39. M azum d ar, A ., K ahali, B . & N ath, K .J. (1993) Rem oval of arsen ic by ch em ical precipitation in d rinking w ater, Jou rna l of In dian P u blic H ealth En g ineers, 62, pp. 103± 106. M on cure, G., Jan kow ski, P.A . & D rever, J.I. (1992) Th e hy d roch em istry of arsenic in reservoir sedim en ts, M illtown , M on tana, U SA , in: Y.K. K h araka & A .S. M aest (E ds ) W a te r± R ock In te ractio n, V ol. 1: L o w Te m peratu re E nv iron m ents (R otterdam , A .A . Balkem a), pp. 513± 516. PH E D (1991) N ational D rinking W ater M ission: Sub m ission Project on A rsenic P ollu tio n in G rou n dw a ter in W est B eng al, Final Report by Steering C om m ittee, A rsenic Inv estigation Project, Governm en t of W est Ben gal, 57pp. PH E D (1993) First phase A ction Plan Report on A rsenic P ollu tio n in G rou nd w ater in W est B enga l, A rsen ic Inv estigation Project, Govern m en t of W est Ben gal, 46pp. Robertson , F.N . (1986) O ccurren ce an d solub ility con trols of trace elem ents in groun dw ater in alluvial basins of A rizona, in: T .W . A nd erson & A.I. John son (E ds ) R eg io na l A qu ifer S yste m s o f U n ited States , S o uthw est A lluv ia l B asins of A rizo na , A m erican W ater Resources A ssociation M on ograph , Series 7, pp. 69± 80. Robertson , F.N . (1989) A rsenic in ground -w ater und er ox idizing con d itions, south-w est U n ited States, E n vironm en ta l G eochem istr y a n d H ealth , 11, pp. 171± 185. Saha, A .K. & Ch akraborty, C. (1995) Geolog ical and geochem ical b ackgroun d of the arsen ic b earing groun dw ater occu rrences of W est Ben gal, Pr o ceed ings, In te rnatio na l C o n ference o n A rsenic in G rou nd w a te r, C alcutta, In dia. Sanch a, A .M . (1995) Rem oval of arsen ic in d rinking w ater: C hile ex perience at full-scale w ater treatm en t plants and at point of use treatm ent d evice, P roce ed ing s, Inter na tion a l C o nference o n A rsenic in G rou nd w ater , C alcutta, Ind ia. Sch lottmann , J.L . & B reit, G.N . (1992) M obilization of A s and U in the C entral Ok lah om a aquifer, U SA , in: Y.K. K haraka & A .S. M aest (E d s) W ater ± R o ck Inter action , V ol. 1: Lo w T em p eratur e E n v iron m ents (R otterd am , A .A . B alkema), pp. 835± 838. Scott, K .N ., Green , G.F., D ow e, H .D . & M acL ean , S.G. (1994) A rsenic rem oval b y coagulation, Jo urna l o f A m erica n W a te r W o rks A ssociatio n, 87(4), pp. 114± 126. Sh en , Y.S. (1973) Stud y of arsen ic rem oval fr om d rinking w ater, Jou rna l o f A m erican W ater W orks A ssociatio n, 65(8), pp. 543± 547. Sorg, T .G. & Log sd on , G.S. (1978) T reatmen t tech nolog y to m eet the interim primary drinking w ater regulation for inorgan ics, Pa rt 2, Jou rna l of A m erica n W a te r W o rks A ssocia tio n , 70, pp. 379± 393. W elch , A .H ., Lico, M .S. & H ugh es, J.L . (1988) Ar sen ic in ground w ater of the W estern U nited States, G rou n d W ater , 26, pp. 333± 347.
