Research in abandoned well questions the practice or well representativity criteria used in selecting for groundwater monitoring sites

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Research in abandoned well questions the practice or well representativity criteria used in selecting for groundwater monitoring sites
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  BIULETYN PAÑSTWOWEGO INSTYTUTU GEOLOGICZNEGO 456: 105–112, 2013 R. RESEARCH IN ABANDONED WELL QUESTIONS THE PRACTICE OR WELL REPRESENTATIVITY CRITERIA USED IN SELECTING FOR GROUNDWATER MONITORING SITES BADANIA W PORZUCONYM OTWORZE KWESTIONUJ¥ PRAKTYKÊ I/LUB KRYTERIA REPREZENTATYWNOŒCISTOSOWANE PRZY WYBORZE PUNKTÓW MONITORINGU WÓD PODZIEMNYCH D ARIUSZ  D OBRZYÑSKI 1 , J AN  M ITRÊGA 2 Abstract. TheobjectofresearchiswellNo.5p(UE_ID:PL06G110_004)locatedinSoko³owsko(theSudetes,SWPoland).Sincecom- pletingthewellin1980,ithasneverbeenincludedinwaterservicesduetopoorwaterquality,butsimplyabandoned.Theabandonment,las-tingalready32years,hasestablishedanunintendedlong-termexperimentinthewell.Ofthefourscreenedwater-bearinghorizons,twolower onesrunmorepressurizedsulphatemineralwater,whichhasgeneratedapermanentupwardflowwithinthewellandpollutionoffreshwater inupperones.Theconsequencesaremuchwider,asthecombinationofhydraulicandgeochemicalsettingsformedanin-holenaturallabora-tory in which bio-geochemical processes affect the water quality and the contamination by hydrocarbons enhanced by human activity. Thewellshouldultimatelybecloseddown.Becausethewellhasbeenincludedinthenationalmonitoringnetworkforover20years,theseresultsalsoimpeltopostulateforestablishing:1)amorestrongprocedurefortestingtherepresentativityofobservationpointsinthemonitoringnet-work,2)arevisionprogrammeforalreadyexistingpoints,and3)amendmentstotheregulationstoexplicitlysolvethecaseof“orphans”dueto the risk they may cause. Key words:  abandoned water well, in-well geochemical environment evolution, well screen clogging, groundwater monitoring, credibilityof observation well, Poland. Abstrakt.  Przedmiotem badañ jest otwór studzienny nr 5p (UE_ID: PL06G110_004) po³o¿ony w Soko³owsku (Sudety). Od wykonaniaw1980roku,zuwaginaz³¹jakoœæwody,nigdyniew³¹czonogodosieciwodoci¹gowej,iwkonsekwencjiporzucono.Brakeksploatacjiprzez32lataspowodowa³stworzeniesiêwnimwarunkówdoniezamierzonego,d³ugotrwa³egoeksperymentu.Zujêtychwotworzewspólnieczterechstrefwodonoœnych,dwiedolneprowadz¹wodymineralnepodwiêkszymciœnieniem,copowodujeichsta³ypionowyprzep³ywwotworzeiza-nieczyszczenie wy¿ej leg³ych wód zwyk³ych. Hydrauliczne i geochemiczne warunki w studni sprzyjaj¹ procesom biogeochemicznymwp³ywaj¹cymnajakoœæwodyiwzbudzoneprzezdzia³alnoœæcz³owiekazanieczyszczeniewêglowodorami.Otwórpowinienbyæniezw³oczniezlikwidowany.Zuwaginato,¿estudniaodoko³o20latjestwsiecimonitoringukrajowego,wynikitesk³aniaj¹równie¿dopostulowaniaustano-wienia:1)skutecznejproceduryocenyreprezentatywnoœcipunktówobserwacyjnychwsiecimonitoringu,2)programurewizjiistniej¹cychpun-któw, oraz 3) nowelizacji regulacji w celu rozwi¹zania problemu „osieroconych” otworów, ze wzglêdu na zagro¿enia jakie one stwarzaj¹. S³owa kluczowe:  porzucony otwór studzienny, geochemiczna ewolucja œrodowiska studziennego, kolmatacja filtru, monitoring wód pod-ziemnych, wiarygodnoœæ punktu obserwacyjnego, Polska. 1 Institute of Hydrogeology and Engineering Geology, Faculty of Geology, University of Warsaw, ul. ¯wirki i Wigury 93, 02-089 Warsaw; Poland;e-mail: d.r.dobrzynski@uw.edu.pl 2 unaffiliated specialist; e-mail: jmit@wp.pl  INTRODUCTION The object of research is well No. 5p (MONBADA No.1183; UE_ID: PL06G110_004; Groundwater Body No. 110)located in Soko³owsko (the Sudetes, SW Poland) (Fig. 1),the presumptive source of water supply to the town of Wa³brzych. Because the well was completed in 1980 and theinvestigations were oriented on water resource assessment, ithas never been included in water services due to poor water quality, and simply abandoned. Despite the poor water quali-ty in terms of drinking water standards, chemical composi-tionof mineral water attractedtheinterest onthiswell again.Research was made to assess the balneological potentialof mineral water, and included a wide set of geochemicalexaminations (Dobrzyñski, 2009). Preliminary goal of theresearch was to identify the srcin of water chemistry andwater age, to explain the spatial pattern of water chemistry,and to examine the technical condition of the well. The studyresults displayed changes in geochemical characteristics of in-well water, which were not predicted before. Since 2000,the research has focused on periodically repeated water co-lumn profiling and chemical analyses, which confirmed the 106 Dariusz Dobrzyñski, Jan Mitrêga Fig. 1. Location of the studied water well 5p (after Dobrzyñski, 2009; modified) Hydroizohypses and limit of hydrogeological unit after Wojtkowiak (2000, 2002) Lokalizacja badanego otworu studziennego 5p (wg Dobrzyñskiego, 2009; zmienione) Hydroizohipsy i granica jednostki hydrogeologicznej wed³ug Wojtkowiaka (2000, 2002)   progress in changes of the in-well water environment. Theseresults were the reason for extending the research by geo-microbiological examinations (Borkowski  et al  ., 2013). Theup-to-date research results raise concerns of the situationcaused by the well 5p. Primarily, an unplugged abandonedwell, such as “orphan”, becomes an artificial water conduit.It provides hydraulic communication between fresh and sali-ne water bodies (Fig. 2), leading to uncontrolled and uncon-sidered contamination of fresh water by saline intrusion.Another concern relates to formal aspects if they admit tosafe abandonment of the hole in unplanned manner and rank it to the position of observation point in the monitoring ne-twork. It is very important, as the well 5p has been functio-ning for almost 20 years as an observation point in chemicaland transboundary monitoring (http://www.psh.gov.pl). Inthis particular case, the selection was made for the study areathat belongs to the upper part of the Œcinawka River transbo-undary catchment (in the territory of Poland and Czech Re- public). It seems that only the geographical location decidedabout including this well to the nationwide monitoring net-work and transboundary projects, serving to reports requiredunder the Water Framework Directive (WFD).This case study of “orphan” is an attempt to highlight theconsequences of 32-year abandonment, which established anunintended long-term experiment in the well, and in fact, anin-hole natural laboratory. HYDROGEOLOGICAL SETTING Inthestudyarea,thebedrocksareCarboniferous–Permianterrestrial clastic rocks (mainly conglomerates, sandstonesand mudstones). In the S part of the area, Permian volcanoge-nic rocks occur. Groundwater flow within both the unconfi-ned and confined parts of the system is predominantly throughfissures. The fresh groundwater system has an irregular  Research in abandoned well questions the practice or well representativity criteria used in selecting for groundwater monitoring sites... 107 Fig. 2. Schematic diagram of initial near-hole environment and design of well 5p(mainly after D¹browski and Szafranek, 1982; Szafranek   et al. , 1986) Schemat pierwotnych przyotworowych warunków œrodowiskowych i konstrukcji studni 5p(g³ównie na podstawie D¹browski, Szafranek, 1982; Szafranek i in., 1986)  geometry and is relatively thin. Geochemical investigations(Dobrzyñski, 2009) revealed that the hydrogeological systemis chemically and isotopically diversified. These features alsohave a horizontal N–S orientation with a southward increasein: 1) salinity and chemical character from Ca-HCO 3 -SO 4 type to Ca-Na-SO 4  type (mineral water in well 5p), 2) meantritium-age (from 10–20 to 100–200 years). The sulphate mi-neral water from well 5p, with radiocarbon age of about 5.9ka BP, represents the most chemically evolved groundwater found in the area. The diversity is caused by water mixing,conditioned by both lithological and tectonic factors(op.cit.).The abandonment of well 5p made it a part of hydrogeo-logical setting, as the borehole disturbed the natural environ-ment of this area. The well construction includes four screensections opening confined water-bearing horizons, whichdiffer in terms of both pressure and chemical composition.The hydrodynamic conditions in the well are typical for a dis-charge area. There is a higher hydraulic head in deeper hori-zons (Fig. 2). Figure 2 shows initial conditions in the well.The two upper horizons yield fresh water, whereas the twodeeper ones yield mineral water. The borehole, bottomed atthe depth of 350 m, was made by a rotary flush boring tech-nique, mostly in mudstones, and therefore, the increasingwell efficiency actions were applied afterwards. The screenswere installed along four confined water-bearing zones, se- parated by aquitards. The upper part of the well, down to102.8 m b.s.l., is 14 inches in diameter, whereas the lower one is 238 mm. Hydraulic contact between water-bearing zo-nes was cut away by way of cementing (Fig. 2). Pilot pum- ping tests were performed when the borehole cut the nextwater-bearing zone, and finally, a multi-rate test to assess thewell’s safe yield (1980) and multiple pumping test (1985) incompleted well were made. Archival chemical analyses from pumping tests after completing the well provided data onlyon mixed-waters, as water sampled at outflow was a resul-tant mixture of waters coming from all screened inflow zo-nes. The drilling report noted that the overflow from an openhole below the lowest screened zone was 0.3 m 3 /h, and thewater level reached +0.25 m. At present, the hydraulic headin the well is balanced by the recharge-discharge systemwhich maintains it at a stable position of approx. 5.8 m b.s.l.Simultaneously, the entire water column in the well is pre-sently saline (Tab. 1). In Table 1, only the results obtained bythe authors are compiled. 108 Dariusz Dobrzyñski, Jan Mitrêga Table 1Selected physico-chemical characteristics of water from the well 5p (after authors’ studies) Wybrane parametry fizyczno-chemiczne wody z otworu 5p (wed³ug badañ autorów) Parameter Mineral water  1 In-well water  2 (VIII.2000) (IX.2009, 35 m b.l.s.) (IX.2009, 50 m b.l.s.) (X.2012, 38 m b.l.s.) (X.2012, 55 m b.l.s.) pH 7.71 9.76 7.81 9.70 8.34SEC 3 / PEW 3 [  S/cm] 1920 3070 3420 3030 3260E H  measured [mV] –167 –24 83 –72 –162H 2 S [mg/L] 0.44 1.00 1.30 0.60 0.85O 2  [mg/L] 0.60 3.00 3.07 0.24 0.25SO 4  [mg/L] 1061 1500 1680 920 1020F [mg/L] <0.10 0.95 0.96 1.00 1.45Ca [mg/L] 305.9 220.0 308.9 281.8 302.9Fe [mg/L] 0.25 0.054 0.033 0.097 0.078As [mg/L] 0.130 <0.006 <0.006 0.011 0.022Benzene [µg/L] n.a. 5.1 10 n.a. n.a.BTEX (sum) [µg/L] n.a. 178 325 n.a. n.a.Aliphatic hydrocarbons (sum) [mg/L] n.a. 0.07–0.10 0.10 n.a. n.a.PAH (WWA) (sum) [µg/L] n.a. 49 130 n.a. n.a. 1 sampledbyusingsamplerduringpumpingtestatthedepthof95mb.l.s.;opróbowanepodczaspompowaniaprzyu¿yciupróbnikanag³êbokoœci95mp.p.t. 2 sampled by using sampler in quasi-stagnant in-well water column; opróbowane przy u¿yciu próbnika w quasi-stagnuj¹cej kolumnie wody w otworze 3 specific electric conductivity; przewodnoœæ elektrolityczna w³aœciwan.a. – not analysed; nie badane  RESEARCH METHOD Long-term comprehensive geochemical and hydrogeolo-gical studies have been carried out in Soko³owsko and its vi-cinity. Geochemical research covered (Dobrzyñski, 2009;Borkowski  et al  ., 2013): 1) multiple chemical analysis of groundwater (2000–2012); 2) stable isotopes (  2 H,   18 O,  13 C,   34 S) in groundwater; 3) tritium and radiocarbon datingof groundwater; 4) chemical and isotopic (  18 O,   13 C,   34 S)composition of the most reactive minerals (carbonates, gyp-sum); 5) geochemical modelling of groundwater; 6) estima-tion of mineral reaction rates in the aquifer based on fielddata; 7) multiple chemical analysis of in-well water; 8) deter-mination of organic compounds in bedrocks; 9) mineralogyof well clogging; 10) microbiological and molecular analysisof water and microbial mat from the well 5p. In-hole physi-co-chemical profiling was periodically repeated in years2000–2012. The QA/QC programme applied indicated thatthe main solutes were investigated with a very good preci-sion and reflect the geochemical distribution in the aquifer.For this case study, archival data on pumping have beenre-examined, recorded during: 1) pilot pumpings and hy-draulic head positioning in open hole during the progress of drilling, 2) multi-rate pumping to assess the well safe yield,3) multiple pumping to test the interference among wellsmade for the regional water supply project, and 4) one step pumping, connected directly with the present study, to con-front the losses in well efficiency as a consequence of theabandonment time scale. The latest investigation (in 2000)included also the measurement of well depth prior to pum- ping, which displayed entire perviousness of the well to 329m b.s.l., i.e. 15 metres below the lowest screen. This log re-cord became a basic for choosing the interpretation methodof all results from the above-mentioned pumping tests, ascomparatively the most grounded. The method assumes thatchanges ongoing in the well’s hydraulics do reflect in timeseries of Q/S (specific capacity) terms, which expresses thewell’s efficiency evolution, while rock mass properties re-main constant. Under such constraints, a simple estimationof upward discharge and distribution of saline water intru-sion rates was applied. The bases of this approach are: 1) Q/S – specific capacity already reflects the formation and actualwell losses, 2) all hydraulic data acquired during the pro-gress of drilling represent the entire profile cut at the tempo-rary depth of hole, 3) estimates of intrusion rate distributiondirectly rely on records of excessive heads prevailing alongapparent sections of the hole and specific capacity terms cor-responding with them, 4) inflow to well is balanced by out-flow from it and the flows are in the steady-state, 5) chemicalcharacteristics of well water is always time-scale dependantaccording to the ratio between the volumes of intruded and pumped off water. Direct measurement of the vertical flowin the well 5p has not been performed, but an inspecting ca-mera (in 2008) displayed a sign of flow in the well. DISCUSSION The hydraulics of the system intersected by the wellforms a driving force for in-hole upward flow of mineral wa-ter and its intruding into the upper fresh water horizons.Abandonment of the 5p well in an unprepared way was anenvironmentally inappropriate action. As an “orphan”, thewell 5p exerted the measurable (a) in-well, (b) near-field,and (c) probable far-field consequences. The primary con-sequence observed in all scales is the intrusion of minerali-sed water into fresh water bodies (in terms of WFD – Qu-evauviller, 2008). In addition to the saline water intrusioninto fresh water horizons, periodically repeated analysesfrom the well also show the appearance of new geogenic pol-lutants (hydrocarbons).Monitoring studies of water quality do not include hydro-carbon determinations. At the first, the presence of hydrocar- bons in water from the well was macroscopically noticed andanalysed by the authors in 2009 (Tab. 1). There are indica-tions that the hydrocarbons have a natural, geogenic srcin.The equipment used for camera inspection and in-well water  profiling could not pose a threat.Terrestrial sedimentary rocks of the study area common-ly contain organic matter, including also interbeds of bitumi-nous limestones and shales. Petroleum products extractedfrom shale rocks sampled in the vicinity of Soko³owskorevealed the presence of alkanes as well as mono- and poly-cyclic aromatic hydrocarbons (Borkowski  et al  ., 2013),which considerably supports the hypothesis about the geoge-nic srcin of hydrocarbons in the groundwater.Chemical diversity of this groundwater system is created by the mixing of modern  3 H-bearing fresh water and older mineral water (Dobrzyñski, 2009), which was confirmed both by geochemical modelling and groundwater dating(Fig. 3). At the quantitative evaluation of the mixing ratio, itwas taken into account that mineral water from the well 5pconstitutes a mixture of pure sulphate mineral water withfresh water. In the case of deeper horizons, the percentage of the sulphate mineral water component is estimated at 65%.Mineral water is of Ca-Na-SO 4  type with pH  7.6,TDS  1.8–2.0 g/L, and increased levels of Mg, B, As, Fe andSr. It owes its chemical composition to a dedolomitization process driven by gypsum dissolution. The mineral water has a key importance for understanding the system, is plan-ned to be balneologically used, and it threatens the quality of the overlying fresh water aquifer.The camera inspecting the well 5p in 2008 revealed ad-verse phenomena, like in-hole upward flow, considerable Research in abandoned well questions the practice or well representativity criteria used in selecting for groundwater monitoring sites... 109
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