Groundwater Monitoring Requirements for managing aquifer response and quality threats

Transcription

1 GW MATE Briefing Noe Series world bank Susainable : Conceps and Tools Susainable Conceps & Tools Briefing Noe Series Noe 9 Monioring Requiremens for managing aquifer response and qualiy hreas 2006 Auhors (GW MATE Core Group) Alber Tuinhof 1 Sephen Foser 1 Karin Kemper 2 Hécor Garduño Marcella Nanni ( 1 lead auhor 2 main supporing auhor) Wha are he aims, benefis and challenges of groundwaer monioring? is an exensive, concealed and inaccessible resource (Briefing Noes 1 and 2), and (in conras o surface waer) changes in quaniy and qualiy are ofen very slow processes occurring below large land areas. These changes canno be deermined by simple one-off snapsho surveys alone, and require more elaborae monioring neworks and daa inerpreaion. The primary goal of aquifer managemen is o conrol he impacs of groundwaer absracion and conaminan loads, and monioring aquifer response and qualiy rends provide key inpus for his goal. The evaluaion of groundwaer issues and he implemenaion of managemen soluions require hydrogeological daa ha are in par baseline and in par ime-varian in characer (Table 1) he collecion of he ime-varian componen is wha is usually considered groundwaer monioring. Table 1: Types of daa required for groundwaer managemen TYPE OF DATA Occurrence and Aquifer Properies Use Supporing Informaion BASELINE DATA (from archives) waer well records (hydrogeological logs, insananeous groundwaer levels and qualiy) well and aquifer pumping ess waer well pump insallaions waer-use invenories populaion regisers and forecass energy consumpion for irrigaion climaic daa land-use invenories geological maps/secions TIME-VARIANT DATA (from field saions) groundwaer level monioring groundwaer qualiy monioring waer well absracion monioring (direc or indirec) well groundwaer level variaions riverflow gauging meeorological observaions saellie land-use surveys 1

2 monioring hus comprises he collecion, analysis and sorage of a range of daa on a regular basis according o specific circumsances and objecives. The ype and volume of daa required will vary considerably wih he managemen issue being addressed, bu is also ineviably dependen upon available financial resources. Figure 1: inflow and consrucion deails of (a) nesed monioring piezomeers wih (b) producion waer well for comparison A he hear of all groundwaer invesigaion and monioring are wells, of he wo basic ypes indicaed below. They represen keyholes o aquifers, which allow groundwaer pressure and qualiy measuremens o be made and hus furnish informaion from which he healh of he aquifer sysem can be judged. Absracion Wells. When waer wells are drilled hey provide one-off unique in-siu daa on he groundwaer resource and is variaion wih deph and daa acquired during drilling (borehole logging) and iniial es pumping form key baseline reference informaion on groundwaer quaniy and qualiy, in addiion o heir value for he deerminaion of absracion well poenial. However, daa colleced from waer wells once operaional are normally more difficul o inerpre, because groundwaer levels are affeced by he drawdown-recovery cycle and pumped-sample qualiy reflecs he variable mixing of groundwaer from a wide range of aquifer dephs and residence imes (Figure 1). Observaion Wells. These are dedicaed monioring saions, sied and designed o deec poenial changes in groundwaer flow and qualiy design parameers include selecion of deph for he inake screen, frequency of measuremen (if no coninuous) and selecion of qualiy parameers. To overcome he widespread presence of deph variaion in hydraulic head and/or groundwaer qualiy, nesed piezomeers (Figure 1) or well clusers can be used. Piezomeer ness are more cos effecive han observaion well clusers, bu should only be used if proper sealing can be achieved o preven verical flow beween heir screens. (a) (b) 2

3 A suie of observaion wells coupled wih a selecion of absracion wells normally comprise a monioring nework, which should be designed so as o provide he required access o he groundwaer resource. Monioring neworks and sysems are classified ino hree main (bu no muually exclusive) groups (Table 2), and are specifically designed and operaed o: deec general changes in groundwaer flow and rends in groundwaer qualiy, and bridge gaps in scienific undersanding of he groundwaer resource base (Primary Sysems) assess and conrol he impac of specific risks o groundwaer (Secondary and Teriary Sysems). Table 2: Classificaion of groundwaer monioring sysems by funcion SYSTEM Primary (Reference Monioring) Secondary (Proecion Monioring) Teriary (Polluion Conainmen) BASIC FUNCTION evaluaion of general groundwaer behavior: rends resuling from land-use change and climaic variaion processes such as recharge, flow and diffuse conaminaion proecion agains poenial impacs of following: sraegic groundwaer resource wellfields/springheads for public waer supply urban infrasrucure from land subsidence archaeological sies agains rising waer able groundwaer-dependen ecosysems early warning of groundwaer impacs from: inensive agriculural land use indusrial sies solid wase landfills land reclamaion areas quarries and mines WELL LOCATIONS in uniform areas wih respec o hydrogeology and land use around areas/ faciliies/ feaures requiring proecion immediaely downand up-hydraulic gradien from hazard How can we ensure ha groundwaer monioring is cos effecive? Effecive groundwaer monioring is characerized by wo key requiremens: i should be driven by a specific objecive monioring for is own sake ofen leads o inefficien use of manpower and budges he daa colleced should be sysemaically sored for fuure use here are far oo many cases of monioring daa being los along he way. monioring is ofen considered expensive he main componens of expendiure include he capial cos (of nework insallaion), sampling coss (for insrumenaion, personnel and logisics) and analyical coss (for laboraory, daa processing and sorage). Moreover, he reurn on iniial invesmen is no likely o be eviden immediaely. Ye, in he longer run, his reurn can be subsanial where monioring represens an inegral par of a managemen process and avoids loss of valuable groundwaer sources, he inroducion of cosly reamen or he need for expensive aquifer remediaion. Awareness of hese facors increases if cos-benefi analysis is included in he design phase of groundwaer monioring programs. 3

4 The effeciveness of groundwaer monioring can be considerably increased by careful aenion o nework design, sysem implemenaion and daa inerpreaion (Table 3), and also by: making bes use of daa colleced by pas monioring aciviies selecing monioring saions ha, as far as possible, are easily accessible making fulles use of indicaor deerminans o reduce analyical cos promoing complemenary self-monioring amongs waer users incorporaing qualiy conrol and qualiy assurance procedures. Table 3: Basic success rules for groundwaer monioring programs NETWORK DESIGN SYSTEM IMPLEMENTATION DATA INTERPRETATION objecives mus be defined and program adaped accordingly groundwaer flow sysem mus be undersood sampling locaions and monioring parameers mus be seleced by objecives appropriaely-consruced observaion and absracion wells mus be used field equipmen and laboraory faciliies mus be appropriae o objecives a complee operaional proocol and daa handling sysem mus be esablished groundwaer and surface waer monioring should be inegraed where applicable daa qualiy mus be regularly checked hrough inernal and exernal conrols decision makers should be provided wih inerpreed managemen-relevan daases program should be periodically evaluaed and reviewed modified afer UN-ECE Task Force on Monioring & Assessmen (2000) How should he responsibiliy for groundwaer monioring be shared? legislaion should make provision for monioring of groundwaer use and saus by assigning faces of his ask o he waer resources adminisraion and o waer users. To be effecive his legislaion should se realisic requiremens ha ake accoun of exising insiuional capaciy (Briefing Noe 4). A ypical division of responsibiliies is: Cenral Governmen/Naional Waer Auhoriy basic reference nework Regional/Basin/Aquifer Waer Resource Agency resource regulaion and proecion funcions Waer well Conracors/Drilling Companies obligaions for well logs and pump esing Large Absracors records of meered well absracion and waer levels Small Absracors general feedback on well characerisics and performance Poenial Polluers defensive qualiy monioring a sie level. The sorage of groundwaer monioring daa (including ha generaed by privae secor sakeholders) is an imporan issue, ofen no properly coordinaed beween naional and local agencies involved. Clear daa collecion and sorage proocols need o be agreed beween all agencies, and a sysemaic daabase and arrangemens for daa sharing via he Inerne esablished. Daa sorage a he lower erriorial level will be more effecive, alhough i will be useful for represenaive daases o be held naionally a he Waer Auhoriy or he Geological Survey. Some daa needed for groundwaer managemen (Table 1) are usually archived by he Meeorogical Service and he Geological Survey, and public access o hese daa sysems needs o be ensured. 4

5 I is no possible wihin he space available for his Briefing Noe o provide a complee caalogue of groundwaer monioring echniques nor a comprehensive guide o groundwaer monioring nework design (bu hese can be found in he Furher Reading secion). Two common and classic applicaions are provided below which will serve o illusrae he fundamenals of he approach required. (A) MEASURING GROUNDWATER USE & AQUIFER Behavior How can groundwaer and aquifer monioring improve he evaluaion and managemen of groundwaer resources? The primary goal of aquifer managemen is o develop groundwaer resources on he basis of a policy plan, and o monior and conrol he impacs of absracion on he groundwaer sysem. The developmen and evoluion of policy requires good hydrogeological undersanding and will benefi from a monioring nework deecing changes in aquifer waer level due o groundwaer absracion. Since groundwaer flow is relaed o groundwaer levels, changes in flow regime can be deermined from he observed changes in aquifer waer levels. Monioring groundwaer absracion and aquifer waer levels hus provides key informaion for groundwaer resource managemen. is developed hrough drilling absracion wells, ofen in groups as wellfields. Such wellfields are designed on he basis of an accepable prediced aquifer response (change in groundwaer levels and flow) for a cerain level of absracion. These predicions are usually made using numerical models, which simulae he aquifer response o differen absracion scenarios. Wellfield consrucion and absracion licenses are issued on he basis of such predicions. Aquifer monioring plays an imporan role in his conex because: hisoric daa are imporan for he calibraion of numerical aquifer models, and as such form he basis for reliable simulaions of fuure absracion scenarios measuring (and archiving) he reference siuaion for new absracion wells is imporan o provide baseline informaion for he evaluaion of fuure changes observaions of groundwaer levels and pumping raes during wellfield operaion provide informaion o verify he prediced aquifer response and, if necessary, ake imely acion o reduce absracion he informaion colleced can also play a key role in increasing awareness of waer users, o faciliae he inroducion of required groundwaer demand managemen measures. Which echniques are available o measure and o monior groundwaer absracion and use? Direc monioring of groundwaer absracion in individual waer wells by means of meers normally gives accurae measuremens, bu (especially in developing naions) can be cosly o operae and difficul o susain wihou he full cooperaion of waer users. Waer meer readings are usually made by he waer user and submied o he regulaory auhoriy. The auhoriy also carries ou periodic inspecions, providing ha hey have adequae manpower and ranspor. 5

6 I is also possible o obain valuable daa by indirec monioring of groundwaer absracion hrough: collecion of indicaive daa for example irrigaion groundwaer use can be esimaed indirecly using hours of pump operaion (from energy consumpion) muliplied by average pumping rae use of remoe sensing saellie or airborne sensors can provide objecive measuremens a poenially large scales, wih quasi-coninuous cover a low cos per km 2 Convenional applicaions include mapping Quaernary geology, land use, crop ypes, soil salinizaion and land subsidence. These have recenly been complemened by inerpreaion of hermal energy sensor daa o esimae acual evaporaion raes. If sufficien frequency of adequae images is available, and land-surface relief is no oo abrup, hen boh daily and oal dry-season acual evaporaion a farm and aquifer level can be deermined, and used for checking daa on groundwaer use and focusing effors on ground inspecion. The required images can be obained from: commercial saellies (such as LandSa), wih high resoluion images bu passing only every 16 days and may no generae sufficien daases in regions wih frequen overcas specialized meeo-saellies, passing more frequenly bu generaing images ha may no always be of adequae resoluion. This echnique is subjec o increasing measuremen error a low vapor fluxes, however, and hus canno be used direcly o deermine cumulaive acual evaporaion, soil moisure defici or aquifer recharge raes for a naural arid-zone vegeaion cover. Neverheless, saellie imagery and airborne surveys show much fuure poenial o broaden he coverage and reduce he cos of groundwaer invesigaion and monioring. esimaes of change in regional groundwaer absracion can also be obained hrough informaion on demographic changes and random checks on per capia waer use. Wha problems can be encounered in he monioring of groundwaer level flucuaions and rends? level measuremens (in observaion, unused and absracion wells) can be made manually or auomaically (Figure 2). Manual waer-level recorders give a visual or audio signal when heir probe is immersed in waer. Auomaic recorders are small probes (divers) insalled in observaion or absracion wells, which sore waer-level and emperaure daa a pre-se inervals, and can be downloaded o a daa-logger during inspecion visis or elemerically ransmied enabling remoe monioring. monioring neworks mus be designed by specialiss on he basis of managemen requiremens (Table 2), bu financial consrains are ofen a problem and require choices o be made. The inclusion of producion and disused wells will help increase he number of monioring poins. Bu i may also be imporan o idenify he presence of areas wih marked verical variaion in groundwaer head, which end o occur below groundwaer recharge or discharge areas and in layered sysems. 6

7 Operaion of a monioring nework requires manpower and logisical resources, ogeher wih clear procedures o assure he coninuous generaion of reliable daa. Lack of hese resources is ofen a consrain in mainaining he necessary level of daa collecion and qualiy conrol. Delegaion of monioring responsibiliy o he local level wih self-monioring by waer users will help o overcome his problem. daa sorage, evaluaion and rerieval are essenial componens of effecive monioring. The flow of daa from he field saions o cenral sorage faciliy (daabase) should be assured, and qualified personnel be available o review daa colleced. level changes observed hrough monioring may have widely differing causes and should be carefully evaluaed o deermine he correc managemen acion required. (B) DETECTING GROUNDWATER QUALITY CHANGES Why does groundwaer monioring require special sampling procedures? The process of well pumping and sample handling causes major sample modificaion hrough such processes as air enry, degassing and volaile losses (poenially inroducing more significan errors han acual sample analysis), which need o be addressed hrough appropriae sampling procedures (Table 4). Table 4: Summary of sampling procedures and precauions for specific groups of groundwaer qualiy parameers Deerminand group Sampling procedure preferred maerials sorage ime/ TEMPERATURE operaional difficuly/cost Major Ions Cl, SO 4, F, Na, K 0.45 µm filer only no acidificaion any 7 days/4 C minimal Trace Meals Fe, Mn, As, Cu, Zn, Pb, Cr, Cd, ec. sealed 0.45 µm filer acidify (ph <2) avoid aeraion hrough splashing/head space plasic 150 days moderae N Species NO 3, NH 4 (NO 2 ) sealed 0.45 µm filer any 1 day/4 C moderae/low Microbiological TC, FC, FS serile condiions unfilered sample on-sie analysis preferred dark glass 6 hours/4 C moderae/low Carbonae Equilibria ph, HCO 3, Ca, Mg unfilered well-sealed sample on-sie analysis (ph, HCO 3 ) (Ca/Mg a base laboraory on acidified sample) any 1 hour (150 days) moderae Oxygen saus pe(eh), DO, T on sie in measuring cell avoid aeraion unfilered any 0.1 hour high/moderae Organics TOC, VOC, HC, ClHC, ec. unfilered sample avoid volailizaion (direc absorpion in carridges preferred) dark glass or eflon 1 7 days (indefinie for carridges) high 7

8 Wha are he requiremens and limiaions of groundwaer qualiy monioring a mains waer-supply sources? A primary focus for qualiy monioring is he surveillance (or qualiy conrol) of waer wells and springheads being used for public waer supply via piped disribuion sysems, and he collecion of pumped samples from such sources is he mos commonly praciced groundwaer sampling mehod. The range of deerminands under analysis iniially will include all hose lised in he WHO poable waer qualiy guidelines, alhough a reduced lis of parameers will usually be moniored on a long-erm basis, wih fuller analyical checks underaken periodically and immediaely afer any significan change is deeced. This funcion is essenial for produc conrol o confirm he accepabiliy of raw (pumped) waer and/or he effeciveness of reamen processes, and as such presens few problems specific o groundwaer. The resuls of his ype of monioring do no normally correspond o he condiion of groundwaer in siu essenial for aquifer monioring programs which have o define he subsurface disribuion of groundwaer of inferior qualiy, is variaion wih ime and in response o managemen miigaion measures. This is because of variabiliy and uncerainy of sample origin, given ha producion wells faciliae he enry of groundwaer over a large deph range of he aquifer and ha he proporion derived from a given deph can vary widely boh wih pumping rae and pumping period (Figure 1). These obsacles can be cosly o overcome, and serious limiaions in groundwaer sampling someimes have o be acceped. Bu such limiaions mus always be recognized in he inerpreaion of resuls, and consideraion given o inroducing improved sampling mehods where jusified economically or on public healh grounds. How can an early warning of poenial hreas o aquifer and groundwaer supply qualiy be obained? In many cases he criical requiremen is o obain an early warning of poenial qualiy problems ha may hreaen he groundwaer source and he aquifer sysem on which i depends. For his purpose i is necessary o design monioring neworks which relae o he hree-dimensional spaial variaion of groundwaer flow and qualiy (Figure 2), so as o obain samples represenaive of he qualiy of he more recen recharge (replenishmen) of he aquifer in quesion. This will ofen be markedly differen Figure 2: Deecion of groundwaer qualiy rends in aquifer replenishmen in he viciniy of a public-supply waer well 8

9 Figure 3: Processes causing major verical variaions in groundwaer qualiy wihin an aquifer sysem which need o be deeced hrough monioring spillage of ligh hydrocarbon fuel which floas on waer able wih some dissolving ino groundwaer flow peneraion of immiscible heavy organic solven afer sorage ank rupure wih accumulaion a base of aquifer and wih some dissolving ino groundwaer flow classical wedge of saline inrusion in a coasal aquifer wih mixing zone developing along fresh waer/saline waer inerface from he average qualiy of groundwaer in aquifer sorage as a resul of he very large sorage volumes and long residence imes of many groundwaer sysems. Oher facors which can also cause marked verical variaion in groundwaer qualiy will require a similar monioring approach (Figure 3). The rapid growh of urban and indusrial wase disposal o he ground and he widespread inensificaion of agriculural culivaion in recen decades is necessiaing a major expansion of focused groundwaer qualiy managemen monioring, using sampling piezomeers designed and insalled for a specific applicaion (Figure 4) wih he following ypes of objecive: Figure 4: Schemaic represenaion of groundwaer qualiy monioring nework design for specific managemen objecives (a) offensive deecion monioring (b) defensive deecion monioring 9

10 o faciliae he early warning of he onse of groundwaer polluion from a given aciviy and allow he imely inroducion of any necessary conrol measures o provide advance warning of he arrival of pollued waer a an imporan groundwaer supply source and hus make provision for reamen or oher miigaion o idenify any conaminaion reaching an aquifer from a poenial major polluion source and hus ake early remedial acion o esablish evidence o deermine legal liabiliy for groundwaer polluion incidens. The complexiy of groundwaer flow and qualiy regimes is ofen such ha specialis hydrogeological experise will be required in many applicaions boh o design monioring neworks and o inerpre heir resuls. Furher Reading - ASTM Sandard Pracice for Design and Insallaion of Ground Waer Monioring Wells in Aquifers. American Sociey for Tesing and Maerial Sandards. Philadelphia, USA. - UN-ECE Task Force on Monioring & Assessmen Guidelines on Monioring and Assessmen of Transboundary. RIZA Publicaion. Lelysad, The Neherlands. - Foser, S. and Gomes, D Qualiy Monioring An Appraisal of Pracices and Coss. WHO-PAHO-CEPIS Publicaion, Lima, Peru. - Foser, S., Hiraa, R., Gomes, D., D Elia, M. and Paris, M Qualiy Proecion: A Guide for Waer Uiliies, Municipal Auhoriies and Environmen Agencies. World Bank Publicaion. Washingon, D.C., USA. - Meijerink, A Remoe Sensing in Hydrology & Waer 27 (eds. Schulz, G. A. and Engman, E. T.). Springer Verlag. New York, USA. - Nielsen, D Pracical Handbook of Monioring. Lewis Publishers. Chelsea, Michigan, USA. Publicaion Arrangemens The GW MATE Briefing Noes Series is published by he World Bank, Washingon D.C., USA. I is also available in elecronic form on he World Bank waer resources websie ( and he Global Waer Parnership websie ( The findings, inerpreaions, and conclusions expressed in his documen are enirely hose of he auhors and should no be aribued in any manner o he World Bank, o is affiliaed organizaions, or o members of is Board of Execuive Direcors, or he counries hey represen. Funding Suppor GW MATE ( ) is a componen of he Bank-Neherlands Waer Parnership Program (BNWPP) using rus funds from he Duch and Briish governmens. 10