Design and Testing of Recharge Wells in a Coastal Aquifer: Summary of Field Scale Pilot Tests

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Article Design and Testing of Recharge Wells in a Coastal Aquifer: Summary of Field Scale Pilot Tests

Joseph Guttman *, Ido Negev and Genadi Rubin

Mekorot, Israel National Water Company, 9 Lincoln Street, P.O. Box 20128, Tel-Aviv 6713402, Israel; [email protected] (I.N.); [email protected] (G.R.) * Correspondence: [email protected]; Tel.: +972-3-623-0656

Academic Editor: Pieter Stuyfzand Received: 9 October 2016; Accepted: 10 January 2017; Published: 14 January 2017

Abstract: Surplus water from seawater desalination plants along the Israeli Coast can be injected underground for seasonal storage. Two pilot projects were established to simulate the movement of air bubbles and changes in the well hydraulic parameters during pumping and recharging. The study showed that it is impossible to remove the smaller air bubbles (dissolved air) that are created during the injection process, even when the injection pipe is fully saturated. The pumping tests showed that there were large differences in the well hydraulic parameters between the pumping and the recharge tests despite that they were conducted at the same well. Two mechanisms are responsible for the reduction in the aquifer coefﬁcients during the recharge event. The ﬁrst mechanism is the pressures that the injected water needs to overcome; the aquifer pressure and the pore water pressure it is supposed to replace at the time of the injection. The second mechanism is the pressure that the injected water needs to overcome the clogging process. It is expressed as the high water level inside the recharge well in comparison to the small rising of the water level in the observation wells. This research gives good insight into the injection mechanism through wells and is essential for any further development of injection facilities and for the operation and management protocols.

Keywords: recharge well; air clogging; well design; desalination; MAR (Managed Aquifer Recharge); IWRM (Integrated Water Resources Management); MARSOL

1. Introduction Artificial recharge is a common tool to increase the total available water in a study area. The use of recharge wells in MAR (Managed Aquifer Recharge) as a tool of IWRM (Integrated Water Resources Management) is widely known. The increasing demand for water in many regions around the world has led to the implementation of artificial recharge tools as part of the IWRM concept. There are many reasons to carry out artificial recharge methods [1,2] as listed below:

• to increase the water budget of the aquifer • to improve the water quality in the aquifer • to use the aquifer for seasonal storage • to prevent seawater intrusion by creating freshwater barriers • to inject surplus water during periods of low demand

There are two main techniques of injecting water underground. One technique is to spill water onto the surface through inﬁltration ponds, trenches, and similar methods. The second technique is to inject water through a single injection well or through a dual-purpose well. This article will deal with the well technique only and will focus on the new artiﬁcial recharge concept that is now being implemented in Israel.

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During the period between 1960 and 1980, dozens of wells were drilled in Israel for the injection of surplus water from the Sea of Galilee [3]. Some wells were designed as dual‐purpose wells, enabling the recharge of surplus water during the winter and pumping during periods of high demand [4]. Water 2017, 9There, 53 were many obstacles in the recharging process, and after a few years of operation most of 2 of 12 the recharge wells were abandoned. Since 2005, the water sector in Israel has changed dramatically. The incorporation of several sea water Duringdesalination the plants period along between the Mediterranean 1960 and 1980, coast dozens currently of produce wells wereabout drilled600 Million in IsraelCubic Meters/year for the injection of surplus(MCM/year) water fromof desalinated the Sea ofwater Galilee (Israel [3 Water]. Some Authority wells were data) designed that is transferred as dual-purpose to the Israel wells, National enabling the rechargeWater Carrier of surplus (NWC) water for drinking during thepurposes. winter Today, and pumping desalinated during water periods provides of up high to 50% demand of the [ 4]. annual drinking water supply. The additional water creates surplus conditions in the NWC during There were many obstacles in the recharging process, and after a few years of operation most of periods of low demand. Throughout these periods (mainly during the winter and weekends), there the rechargeis a surplus wells of desalinated were abandoned. water for short periods of time (hours) that the system does not have the Sincecapability 2005, to the store water in open sector surface in Israel reservoirs. has changed The surplus dramatically. volume varies The incorporationbetween a few ofhundred several sea waterthousand desalination cubic meters plants to along several the million Mediterranean cubic meters. coastFigure currently1 shows typical produce weekly about water 600 surplus Million in the Cubic Meters/yearNWC in an (MCM/year) average year. of desalinated water (Israel Water Authority data) that is transferred to the Israel NationalIn Israel, Water the Carriersurplus (NWC)water can for be drinking injected purposes.into a few Today,existing desalinated infiltration waterponds providesthat were up to 50% ofconstructed the annual specifically drinking to water inject supply. run‐off, in The several additional abounded water quarries creates that surplus were adjusted conditions to store in theand NWC duringto periodsinfiltrate ofsurplus low demand. water from Throughout the NWC, and these through periods injection (mainly wells. during the winter and weekends), The major advantage in using recharge wells is the ability to locate them in places where the there is a surplus of desalinated water for short periods of time (hours) that the system does not have subsurface geology is not suitable for infiltration ponds (for example, the existence of clay layers close the capability to store in open surface reservoirs. The surplus volume varies between a few hundred to ground surface), in small and dense areas, in confined aquifers, and in areas close to the water thousandsupply cubic networks. meters Yet, to severalthe main million disadvantage cubic is meters. the low Figure injection1 shows rate per typical well and weekly the need water for many surplus in the NWCrecharge in an wells average in the event year. the total injection amount is high (hundred thousand cubic meters per well).

Figure 1. Typical weekly surplus water in the Israel National Water system in an average year. Figure 1. Typical weekly surplus water in the Israel National Water system in an average year. 2. Artificial Recharge in Israel In Israel, the surplus water can be injected into a few existing infiltration ponds that were Previously, surplus water was injected into the sandstone layers of the coastal aquifer and into constructed specifically to inject run-off, in several abounded quarries that were adjusted to store and the limestone and dolomite layers of the Western Mountain aquifer (Yarkon‐Taninim Basin). Today, to infiltratethe injection surplus target water is the from coastal the aquifer NWC, only. and through injection wells. The majorBetween advantage the 1960s and in using the 1980s recharge the percussion wells is themethod ability was to the locate main them drilling in technique places where for the subsurfacerecharge geology wells in is the not coastal suitable aquifer. for infiltration Only a few ponds were drilled (for example, using the the reverse existence circulation of clay method. layers close to ground surface), in small and dense areas, in confined aquifers, and in areas close to the water supply networks. Yet, the main disadvantage is the low injection rate per well and the need for many recharge wells in the event the total injection amount is high (hundred thousand cubic meters per well).

2. Artiﬁcial Recharge in Israel Previously, surplus water was injected into the sandstone layers of the coastal aquifer and into the limestone and dolomite layers of the Western Mountain aquifer (Yarkon-Taninim Basin). Today, the injection target is the coastal aquifer only. Between the 1960s and the 1980s the percussion method was the main drilling technique for recharge wells in the coastal aquifer. Only a few were drilled using the reverse circulation method. Water 2017, 9, 53 3 of 12

Currently the drilling method of injection and production wells in the coastal aquifer uses the reverse circulation method only. The production sections of the dual-purpose wells and of the recharge wells that were drilled in the past showed a variety of differences in their technical proﬁles. There were differences in screen type and screen diameter: some were made from galvanized steel and others from stainless steel. 1 The diameter of the screen pipe varied between 8” and 12 4 ” with differences in the slot width. There were also differences in the type and size of the gravel pack. Some wells had only gravel pack outside their screen section and others contained a basket ﬁlled with gravel together with common gravel pack. In addition, the length of the open section was different. In some wells the open section was in the lower part of the well and in others the open section extended from the static water level down to the bottom of the well. There was no documentation that explains the considerations (geological, hydrological, technical) that were behind the decisions in the design and construction of each injection well. The water for injection through wells at that period came from two sources:

• Water from the National Water Carrier (surface water pumped from the Sea of Galilee). • Groundwater from the limestone-dolomite aquifer (Western Mountain aquifer).

Monitoring of the injection parameters show that the injection wells suffered from a decrease in their absorption rate (an expression that is equal to specific discharge in pumping wells) due to clogging on the screen slots [4]. In wells that injected water into the coastal aquifer (sand and sandstone layers with some clay beds [5]) the specific absorption capacity decreased up to one-third during the recharge season. In the limestone-dolomite aquifer the reduction in the specific absorption capacity was very small [6–8]. The injection results showed that dual-purpose wells were more effective than single-purpose injection wells because in dual-purpose wells redevelopment and backwashing from the accumulated solid and organic contaminants were relatively easy since the pump already existed in the well. Redevelopment of the recharge well at the end of the recharge season was the way to restore the specific discharge. However, on switching from recharge to pumping, the water pumped during the first few hours (in general 2–10 h) contained excessive bacteria growth from the screens. In some wells the amount of water that was pumped out during the redevelopment was greater than the amount that was injected into the wells. As mentioned above, between the 1960s and 1980s, the source of injection water was from the Sea of Galilee (Lake Kinneret). At that time, the lake water contained high percentages of suspended organic material. Today, there is a large, modern filtration plant for the National Water Carrier that removes organic matter before the water is supplied to the customers. Therefore, we presume that clogging by organic material will not be a problem any time in the near future. Throughout that period, the means to bypass reduction in the absorption rate in the injection wells in the Coastal aquifer was to use groundwater from the limestone dolomite aquifer as a source for the injection activities. This water was clean and without organic material. In order to keep the water balance in the limestone dolomite aquifer stable, water from the Sea of Galilee was injected into this aquifer. The changing of the injection water source enabled an increase in the absorption rate in the recharge wells at the Coastal aquifer. Looking at that data retrospectively, our opinion is that poor water quality (the effect of high organic matter in the water) and inadequate technical structure of the injection wells was why many wells were declared abandoned and the injection into the sandstone aquifer failed after a few years of operation. In order to re-evaluate the feasibility and profitability of recharge wells as part of a general MAR policy to handle excess water, “Mekorot; the Israel National Water Company Ltd. (Tel-Aviv, Israel)”, designed and built two full scale pilot sites. Each pilot contains production, recharge, and two observation wells in one yard. The recharge wells were designed specifically to enable high flow rates Water 2017, 9, 53 4 of 12 to maximize the volume that can be recharged during a relatively short period of time by a minimum number of wells. Attention was also given to the design of the recharge equipment and to the necessity to prevent air bubbles from entering the aquifer together with the recharged water [9,10]. Pumping tests were Water 2017, 9, 53 4 of 12 conducted to evaluate the hydrological conditions of the aquifer, the effect of the technical design of the rechargeAttention wells, was thealso rechargegiven to the capacity design of and the recharge its changes equipment with time, and to the the effect necessity of airto prevent bubbles on clogging,air bubbles as well from as the entering need forthe aaquifer back-flushing together with routine the recharged [9,10]. water [9,10]. Pumping tests were Inconducted parallel, to we evaluate carried the out hydrological an additional conditions pilot of in the an aquifer, open transparent the effect of the pipe technical that focused design of on the relationshipthe recharge between wells, flow the rate, recharge depth capacity of injection and point,its changes and creation with time, of airthe bubbles effect of and air theirbubbles movement on towardclogging, the screen as well (drainage as the need point for ata back the‐ bottomflushing of routine the transparent [9,10]. pipe). In parallel, we carried out an additional pilot in an open transparent pipe that focused on the 3. Pilotrelationship Test Description between flow rate, depth of injection point, and creation of air bubbles and their movement toward the screen (drainage point at the bottom of the transparent pipe). Recently in Israel, the water source for recharge has been surplus desalinated water. This water does not3. Pilot contain Test Description any organic matter, has very stable chemical composition, stable temperature, low turbidity, andRecently low in inorganic Israel, the suspended water source solids. for recharge We assume has been that surplus with this desalinated kind of water. water This quality, water we can ignoredoes the not appearance contain any of organic chemical matter, and biologicalhas very stable clogging, chemical and composition, can focus on stable the mechanicaltemperature, processes low such asturbidity, clogging and by low air inorganic bubbles. suspended solids. We assume that with this kind of water quality, we can ignore the appearance of chemical and biological clogging, and can focus on the mechanical 3.1. Airprocesses Bubble such Pilot as clogging by air bubbles.

A3.1. major Air Bubble form Pilot of mechanical clogging is air entrainment. The dissolved or suspended gas (air) has chemical and physical functions in the aquifer. The presence of small air bubbles inside the pores may cause blockageA major of form the aquifer of mechanical and reduce clogging water is air percolation entrainment. into The the dissolved aquifer. or suspended gas (air) has chemical and physical functions in the aquifer. The presence of small air bubbles inside the pores Therefore, we decided to build a pilot to simulate the movement of the air bubbles in a well. may cause blockage of the aquifer and reduce water percolation into the aquifer. The pilot consistsTherefore, of we a transparent decided to build pipe a 6-m pilot length to simulate and 6”the diameter movement (Figure of the air2) andbubbles several in a well. valves The at the bottompilot of consists the pipe. of Thea transparent valves represent pipe 6‐m length the screen and 6 section″ diameter and (Figure allow 2) control and several of the valves flow at discharge. the Insidebottom the 6” of transparent the pipe. The pipe, valves we represent inserted the the screen injection section pipe. and We allow constructed control of the two flow types discharge. of injection tubes:Inside the first the 6 was″ transparent a regular pipe, pipe we where inserted the the exit injection of the pipe. water We was constructed located attwo the types bottom of injection of the tube (Figuretubes:2), and the first the secondwas a regular had the pipe bottom where closedthe exit soof the water water was was located forced at to the exit bottom via aof number the tube of 1” pipes(Figure with the 2), openingsand the second facing had upwards the bottom (Figure closed2). so The the ideawater in was the forced second to tubeexit via was a number to enable of 1 the″ air bubblespipes to with move the upward openings in facing the opposite upwards direction (Figure 2). to The the idea water in the flow. second tube was to enable the air bubbles to move upward in the opposite direction to the water flow. The injection discharge was 6–10 m3/hour at a pressure of 4 atmospheres, which was the pressure The injection discharge was 6–10 m3/hour at a pressure of 4 atmospheres, which was the pressure in thein regional the regional water water system. system. The The temperature temperature waswas constant. The The air air was was injected injected artificially artificially into the into the systemsystem by a by compressor a compressor (Figure (Figure2). 2).

Figure 2. The air bubble pilot (schematic layout). Figure 2. The air bubble pilot (schematic layout). 3.2. Pumping and Recharge Wells Pilot 3.2. Pumping and Recharge Wells Pilot The objective was to construct a pilot on a larger scale that included production and recharge Thewells objective with some was observation to construct wells ain pilot between. on a larger scale that included production and recharge wells withThe some first observation stage was to wellsselect the in between.drilling technique, the screen diameter, length of the screen, and the monitoring system. Study of the failures of the “old” recharge wells in Israel and from other cases

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The first stage was to select the drilling technique, the screen diameter, length of the screen, and the monitoring system. Study of the failures of the “old” recharge wells in Israel and from other cases in the world [9,10] led to the decision to drill two separate wells (one for production and one for recharging).Water 2017 The, 9, 53 separation between the pumping and injection wells allowed us to continue5 of operating 12 the pumping well in the event the injection well became clogged (see Section2). Fundamentally,in the world [9,10] the led drilling to the proceduredecision to drill of a two recharge separate well wells is quite (one for similar production to that and of aone production for well whenrecharging). both of themThe separation are drilled between in the samethe pumping formation. and We injection would wells also expectallowed that us bothto continue wells would have similaroperating hydrological the pumping characteristics. well in the event In the practice, injection this well is became not the clogged case. The (see effectiveness Section 2). of a recharge Fundamentally, the drilling procedure of a recharge well is quite similar to that of a production well is often significantly lower than a production well. Recharge wells are more sensitive to clogging well when both of them are drilled in the same formation. We would also expect that both wells and a decreasewould have in similar the absorption hydrological rate characteristics. (an expression In practice, that is equalthis is tonot a the specific case. The rate effectiveness in pumping of wells). For thisa recharge reason, well it is is very often important significantly to lower design than the a production drilling profile well. Recharge of the recharge wells are wellsmore sensitive carefully, and thereforeto clogging we established and a decrease a drilling in the guideline absorption for rate a recharge (an expression well that that includes is equal to several a specific critical rate in points: pumping wells). For this reason, it is very important to design the drilling profile of the recharge • Drilling technique: Reverse circulation and/or percussion method. wells carefully, and therefore we established a drilling guideline for a recharge well that includes • Drillingseveral critical mud: points: In the aquifer section, to use water or biodegradable drilling fluids. • Diameter Drilling of pipes technique: Large: Reverse diameter circulation (14”) of and/or the casing percussion and method. the screen. Long screen section starting a few metersDrilling below mud: In the the static aquifer water section, table. to use water or biodegradable drilling fluids. • Gravel Diameter pack: Well of pipes sorted,: Large mainly diameter quartz (14″ with) of the very casing low and content the screen. of carbonate Long screen fragments. section Glass beadsstarting are highly a few recommended. meters below the static water table. • Observation Gravel pack point: Well in thesorted, recharge mainly wellquartz: Inserting with very alow small content diameter of carbonate pipe fragments. between theGlass outside beads are highly recommended. casing and the inside casing for water level measurement during the recharge.  Observation point in the recharge well: Inserting a small diameter pipe between the outside • Observationcasing and wells the :inside Drilling casing two for observation water level measurement wells. One well during located the recharge. about 3 m from the recharge well andObservation the second wells about: Drilling 10 m two from observation the recharge wells. well. One well The located pumping about well 3 m was from located the at a distancerecharge of about well 20 and m the from second the about recharge 10 m well from and the recharge acted as well. an additional The pumping monitoring well was located well during the rechargeat a distance tests. of The about two 20 observation m from the recharge wells were well drilledand acted to as the an same additional depth monitoring as the recharge well well and theirduring screens the recharge were located tests. The on thetwo sameobservation level aswells in the were recharge drilled to well. the same depth as the recharge well and their screens were located on the same level as in the recharge well. The production well was equipped with a 16” casing and screen. The length of the screen section The production well was equipped with a 16″ casing and screen. The length of the screen section in thein production the production well well is shorter is shorter than than in in the the rechargerecharge well well because because it takes it takes into into consideration consideration the the dynamicdynamic drawdown drawdown and the and depth the depth of the of pump. the pump. Figure Figure3 shows 3 shows the technical the technical profile profile of the of production the (pumping)production and the (pumping) recharge and wells the recharge in the pilot wells site. in the pilot site.

Figure 3. Technical and geological profile of the pumping and recharge well on the pilot site. Figure 3. Technical and geological proﬁle of the pumping and recharge well on the pilot site.

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4. Results 4. Results 4.1. Pumping and Injection Tests 4.1. Pumping and Injection Tests The field work in the pumping and recharge wells pilot began with the development of the The ﬁeld work in the pumping and recharge wells pilot began with the development of the pumping well followed by pumping tests. The water level in the recharge well and the nearby pumping well followed by pumping tests. The water level in the recharge well and the nearby observation wells were measured during the pumping test. observation wells were measured during the pumping test. The next step was to develop the recharge well and to conduct pumping tests similar to the The next step was to develop the recharge well and to conduct pumping tests similar to the pumping tests in the pumping wells. Afterwards, an injection test was carried out. The results of the pumping tests in the pumping wells. Afterwards, an injection test was carried out. The results of the tests are presented in Table 1. tests are presented in Table1.

Table 1. Major hydraulic parameters from the pumping and injectioninjection tests.tests. Pumping Test in the Injection Test in the Parameter Pumping Well Pumping Test in the Injection Test in the Parameter Pumping Well Recharge Well Recharge Well Recharge Well Recharge Well Max. discharge (m3/hour) 300 196 176 Max. discharge (m3/hour) 300 196 176 Drawdown/rising (m) 35.5 12.8 34 Drawdown/rising (m) 35.5 12.8 34 3 SpecificSpeciﬁc rate (m(m3/hour/m)/hour/m) 8.448.44 15.4 15.4 5.2 5.2 AquiferAquifer loss (B)(B) 1.131.13 ×× 1010−1− 1 5.465.46 ×× 1010−−2 2 1.461.46 ×× 1010−−1 1 WellWell loss loss (C) 1.651.65 ×× 1010−5− 5 5.25.2 ×× 1010‐5− 5 3.23.2 ×× 1010−4− 4 2 TransmissivityTransmissivity (T)(T) (m (m/day)2/day) 24922492 1357 1357 1128 1128 Storativity (S) 5 × 10−5 8 × 10−3 6 × 10−3 Storativity (S) 5 × 10−5 8 × 10−3 6 × 10−3

The resultsresults inin Table Table1 were1 were calculated calculated by by AQTESOLV AQTESOLV Pro Pro for Windowsfor Windows [ 11]. [11]. The The results results show show that, inthat, general, in general, there there are differences are differences in the in specific the specific rate between rate between the pumping the pumping and the and recharge the recharge wells. wells. What isWhat more is interestingmore interesting are the are differences the differences in the parameters in the parameters between between the pumping the pumping test and thetest injection and the testinjectionin the test recharge in the well rechargedespite well both despite being both conducted being conducted in the same in well.the same well. When wewe compare compare the the hydraulic hydraulic properties properties during during the pumping the pumping and injection and injection tests in thetests recharge in the well,recharge we seewell, that we the see rise that of the the rise water of levelthe water during level the during injection the test injection is greater test than is greater the drawdown than the duringdrawdown the pumpingduring the test pumping (Figures test4 and (Figures5) and the4 and specific 5) and rate the (absorption specific rate rate (absorption in the injection rate in test) the duringinjection the test) injection during test the injection was reduced test was sharply reduced (Figure sharply6) to (Figure about one 6) to third about of one the specificthird of the rate specific in the pumpingrate in the test. pumping test.

Figure 4. The drawdown test in the recharge well.

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FigureFigure 5. 5. TheThe recharge recharge test test in in the the recharge recharge well.well.

FigureFigure 6.6. 6. TheTheThe dynamicdynamic dynamic drawdowndrawdown drawdown againstagainst against thethe hourlyhourly the dischargedischarge hourly discharge fromfrom thethe drawdowndrawdown from the andand drawdown thethe rechargerecharge and tests.tests. the recharge tests. TheThe waterwater sourcesource forfor thethe injectioninjection testtest waswas waterwater fromfrom thethe regionalregional pipelinepipeline thatthat passespasses closeclose toto thethe wellwell yardyard fence.fence. TheThe waterwater isis aa mixturemixture ofof desalinateddesalinated waterwater andand waterwater fromfrom thethe WesternWestern MountainMountain The water source for the injection test was water from the regional pipeline that passes close to aquiferaquifer (dolomite(dolomite‐‐limestonelimestone aquifer).aquifer). TheThe electricalelectrical conductivityconductivity variedvaried betweenbetween 0.30.3 andand 0.80.8 mS/cm,mS/cm, butbut the well yard fence. The water is a mixture of desalinated water and water from the Western Mountain mostmost ofof thethe timetime itit waswas betweenbetween 0.60.6 andand 0.70.7 mS/cm.mS/cm. TheThe turbidityturbidity waswas 0.8–1.00.8–1.0 NTU.NTU. TheThe LangelierLangelier aquifer (dolomite-limestone aquifer). The electrical conductivity varied between 0.3 and 0.8 mS/cm, indexindex ofof thethe injectioninjection waterwater variedvaried betweenbetween 0.020.02 andand 0.20.2 (slightly(slightly corrosive).corrosive). but most of the time it was between 0.6 and 0.7 mS/cm. The turbidity was 0.8–1.0 NTU. The Langelier DuringDuring thethe injectioninjection testtest wewe alsoalso examinedexamined thethe effecteffect ofof thethe airair entrainmententrainment onon thethe injectioninjection raterate index of the injection water varied between 0.02 and 0.2 (slightly corrosive). byby checkingchecking thethe differencesdifferences inin thethe riserise ofof thethe waterwater levellevel duringduring injectioninjection withwith airair andand withoutwithout air.air. TheThe During the injection test we also examined the effect of the air entrainment on the injection rate by airair waswas introducedintroduced intointo thethe injectioninjection wellwell throughthrough thethe airair releaserelease valve.valve. checking the differences in the rise of the water level during injection with air and without air. The air OpeningOpening thethe valvevalve duringduring thethe injectioninjection createdcreated vacuumvacuum conditionsconditions (Venturi(Venturi effect)effect) andand aa mixturemixture was introduced into the injection well through the air release valve. ofof waterwater andand airair enteredentered thethe well,well, asas cancan bebe seenseen inin FigureFigure 7.7. IncreasingIncreasing thethe hourlyhourly dischargedischarge fromfrom 5050 Opening the valve during the injection created vacuum conditions (Venturi effect) and a mixture mm33/hour/hour toto 9595 mm33/hour/hour togethertogether withwith thethe openedopened airair valvevalve raisedraised thethe waterwater levellevel immediatelyimmediately byby of water and air entered the well, as can be seen in Figure7. Increasing the hourly discharge from approximatelyapproximately 2222 mm inin 9090 min.min. DuringDuring injectioninjection atat 103103 mm33/hour/hour thethe waterwater levellevel roserose byby aroundaround 1919 mm (Figure(Figure 5).5). ThisThis meansmeans thatthat thethe presencepresence ofof airair inin thethe injectedinjected waterwater addedadded aboutabout 33 m.m. SimilarSimilar resultsresults

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50 m3/hour to 95 m3/hour together with the opened air valve raised the water level immediately by approximately 22 m in 90 min. During injection at 103 m3/hour the water level rose by around

19Water m (Figure2017, 9, 535 ). This means that the presence of air in the injected water added about 3 m. Similar8 of 12 results were received when comparing the measurements at the same discharge (50 m3/hour) with thewere closed received valve when (Figure comparing7). In this the experiment, measurements the air at cloggingthe same added discharge about (50 2.6 m3 m/hour) to the with 6 m the rising closed at 3 50valve m /hour. (Figure 7). In this experiment, the air clogging added about 2.6 m to the 6 m rising at 50 m3/hour.

FigureFigure 7.7. The rise of the waterwater levellevel asas aa resultresult ofof thethe injectioninjection ofof aa mixturemixture ofof waterwater andand air. air.

Another point that we can learn from these results is in regards to the huge reduction in the Another point that we can learn from these results is in regards to the huge reduction in the hydraulic parameters during the injection test in comparison to the pumping test (Figure 6). hydraulic parameters during the injection test in comparison to the pumping test (Figure6). Calculating Calculating the weight of B (aquifer loss) and C (well loss) coefficients from the total dynamic the weight of B (aquifer loss) and C (well loss) coefficients from the total dynamic drawdown at drawdown at 150 m3/hour (Table 2) shows that during the pumping test the aquifer loss coefficient 150 m3/hour (Table2) shows that during the pumping test the aquifer loss coefficient contributed contributed 87.5% to the total drawdown, and only 12.5% came from the well loss coefficient. This 87.5% to the total drawdown, and only 12.5% came from the well loss coefficient. This indicates that indicates that the well was constructed properly. On the other hand, during the injection test the the well was constructed properly. On the other hand, during the injection test the “contribution” of “contribution” of the well loss coefficient increased to 25% from the total rising, and the aquifer loss the well loss coefficient increased to 25% from the total rising, and the aquifer loss coefficient was coefficient was reduced to 75%. reduced to 75%.

3 TableTable 2. 2.The The calculated calculated aquifer aquifer loss loss (B) (B) and and well well loss loss (C) (C) at at 150 150 m m3/hour./hour Parameter Pumping Test Injection Test Ratio Injection/Pumping TotalParameter drawdown (or rising) Pumping9.36 Test Injection29.1 Test Ratio Injection/Pumping Total drawdownAquifer (or loss rising) (B) 8.19 9.36 (87.5%) 21.9 29.1 (75%) 2.68 AquiferWell loss loss (B) (C) 8.191.17 (87.5%) (12.5%) 7.2 21.9 (25%) (75%) 6.09 2.68 Well loss (C) 1.17 (12.5%) 7.2 (25%) 6.09

4.2. Air Bubble Pilot Tests 4.2. Air Bubble Pilot Tests The air bubble pilot consisted of a six meter 6″ transparent pipe (Figure 2) and several valves at the bottomThe air of bubble the pipe pilot that consisted represented of a six the meter screen 6” section. transparent For the pipe injection (Figure 2tests) and we several used two valves types at theof injection bottom of tubes. the pipe The thatfirst representedinjection tube the was screen a regular section. pipe For where the injection the water tests exit we was used located two typesat the ofbottom injection of the tubes. tube, The while ﬁrst in injection the second tube injection was a regular tube the pipe bottom where was the closed water and exit the was water located exited at the via several 1″ pipes with the openings facing upwards (Figure 2). It was observed that during the flow, small dissolved air bubbles began to develop immediately at the beginning of the flow before we introduced air artificially. We also observed that there was a separation between large and medium‐sized bubbles, and smaller bubbles. The smaller air bubbles moved downward toward the valves and the large and medium‐sized air bubbles moved upward to the dynamic water table.

Water 2017, 9, 53 9 of 12 bottom of the tube, while in the second injection tube the bottom was closed and the water exited via several 1” pipes with the openings facing upwards (Figure2). It was observed that during the flow, small dissolved air bubbles began to develop immediately at the beginning of the flow before we introduced air artificially. We also observed that there was a separation between large and medium-sized bubbles, and smaller bubbles. The smaller air bubbles moved downward toward the valves and the large and medium-sized air bubbles moved upward to the dynamic water table. We saw that the separation of bubbles (large and small) was qualitatively better with the regular tube (water exit at the bottom). In the second tube (drainage points facing upward), the air bubbles at first were large to medium that rose upward. However, after a few minutes of flow, we could see small bubbles drop down and drain through the opening valves. This implies that the configuration of the injection pipe with the opening drainage points facing upward does not resolve the problem of the smaller air bubbles. We are concerned that in a real injection operation there would be an accumulation of the smaller air bubbles that can cause a clogging problem on the well screen. Therefore, we decided to continue the pilot with the first type of injection pipe during injection; we observed that when the water level dropped and reached a few centimeters above the bottom of the injection pipe, turbulent conditions developed and large amounts of air bubbles of all sizes were created. The amount of air bubbles increased when the water level continued to drop below the bottom of the injection pipe and large air bubbles reached the valves. On a practical level, this means that such an injection method begins to clog in a very short time on the screen and possibly in the gravel pack as well. The solution is to keep the injection pipe filled with water and saturated all the time (the water level should be a few meters above the bottom). The general way to achieve this is to install a control flow valve (an orifice valve type) at the bottom of the injection pipe. However, this will not totally eradicate the clogs created by the smaller air bubbles. The main outcomes from the experiences in the air bubble pilot are:

• There is a critical level of about 1.5 m above the injection point, where above it, the vortex effect and the creation of air bubbles is reduced to a minimum. • During the injection, different sizes (from larger to smaller) of air bubbles are created. • The larger air bubbles tend to move mainly upward but the smaller air bubbles move downward to the drainage valves with the injected water as dissolved air. • It does not appear possible to totally remove the smaller bubbles (the dissolved air). • Another important factor is the distance between the injection point and the top of the screen. If the injection point is too close to the top of the valves (the screen), the potential to have air clogging the screen and in the gravel pack increases.

5. Discussion During the injection period, the water levels in the recharge well and in the two nearby observation wells were measured continuously. The distance of the observation wells from the recharge well was 3 m and 10 m, respectively. With an injection rate of about 176 m3/hour, the water level inside the recharge well was raised by around 34 m, while in the observation wells it was raised by 2.67 m to 1.73 m, respectively. Figure8 shows the course of the water level in the recharge and observation wells during the recharge test. We can see that during injection, the rising cone (an expression similar to depression cone) is totally different to the theoretical cone of depression that we would expect in a regular pumping test. What we saw in the recharge test is that the major rising occurs inside the injection well, while in the observation wells (3 m and 10 m from the recharge well) the rising of the water level was very small (Figure9). Water 2017, 9, 53 10 of 12

Water 2017, 9, 53 10 of 12 The expression of these two mechanisms (injection pressure to overcome the aquifer pressure and theThe pore expression water pressure) of these twois the mechanisms high water (injectionlevel inside pressure the recharge to overcome well compared the aquifer to the pressure small waterand the level pore rise water in the pressure) observation is the wells high (Figures water level 8 and inside 9). the recharge well compared to the small waterIn level the riseair bubblein the observation pilot, we saw wells that (Figures it is not8 and possible 9). to eliminate the smaller air bubbles (dissolvedIn the air) air thatbubble are pilot,created we during saw that the injectionit is not process,possible evento eliminate when the the injection smaller pipeair bubblesis fully saturated.(dissolved Theair) injectionthat are createdtest with during opened the and injection closed valveprocess, indicates even when that thethe airinjection clogging pipe process is fully is 3 verysaturated. rapid, The as showninjection in testFigure with 7. openedInjection and of 95closed m /hour valve together indicates with that the the opened air clogging air valve process raised is thevery water rapid, level as shownimmediately in Figure by around7. Injection 22 m of in 95 90 mmin.3/hour Comparing together thewith rising the openedof the water air valve level raisedat the same discharge (50 m3/hour) in the closed valve (before and after the injection of 95 m3/hour together Waterthe water2017, 9 level, 53 immediately by around 22 m in 90 min. Comparing the rising of the water level10 at of the 12 3 withsame the discharge opened (50 air mvalve)3/hour) shows in the that closed air clogging valve (before added and about after 2.6 the m injection to the 6 ofrising 95 m in3/hour 50 m together/hour. with the opened air valve) shows that air clogging added about 2.6 m to the 6 rising in 50 m3/hour.

Figure 8. The behavior of the water level in the recharge well and the observationobservation wells during the rechargeFigure 8. testtest The (the(the behavior numbers of the inin redred water areare level thethe hourlyhourly in the discharge dischargerecharge atwellat eacheach and step).step). the observation wells during the recharge test (the numbers in red are the hourly discharge at each step).

Figure 9. A schematic cross section showing the water level (thick blue line) at the end of the injection test in the recharge well and in the observation well. Figure 9. A schematic cross section showing the water level (thick(thick blueblue line)line) atat thethe end of the injection

testtest inin thethe rechargerecharge wellwell andand inin thethe observationobservation well.well.

When comparing the aquifer and the well loss coefficients of the two tests in the recharge well (Table2), we can see that the aquifer loss coefficient (B) in the recharge test is 2.68 times greater than during the pumping test, and the well loss coefficient (C) is about 6.09 times greater than during the pumping test. We assume that the increases in the aquifer and in the well coefficients are a result of two processes that are occurring simultaneously. The high aquifer loss coefficient (B) in the recharge test is due to Water 2017, 9, 53 11 of 12 the injected water that flows from the inside of the well towards the aquifer layers. It requires an injection pressure to overcome the aquifer pressure and the pore water pressure that the injected water is supposed to replace during injection [12,13]. The high value of the well loss coefficient (C) indicates that the screen is partly clogged during the injection. Based on the air bubble pilot results and the injection tests, we assumed that the screen (and maybe part of the gravel pack) was partly sealed by air clogging during the injection. The expression of these two mechanisms (injection pressure to overcome the aquifer pressure and the pore water pressure) is the high water level inside the recharge well compared to the small water level rise in the observation wells (Figures8 and9). In the air bubble pilot, we saw that it is not possible to eliminate the smaller air bubbles (dissolved air) that are created during the injection process, even when the injection pipe is fully saturated. The injection test with opened and closed valve indicates that the air clogging process is very rapid, as shown in Figure7. Injection of 95 m 3/hour together with the opened air valve raised the water level immediately by around 22 m in 90 min. Comparing the rising of the water level at the same discharge (50 m3/hour) in the closed valve (before and after the injection of 95 m3/hour together with the opened air valve) shows that air clogging added about 2.6 m to the 6 rising in 50 m3/hour.

6. Conclusions The increasing demand for water in many regions around the world has led to the implementation of tools such as artificial recharge as part of IWRM (Integrated Water Resources Management). Since 2005, the water sector in Israel has changed dramatically due to the establishment of several seawater desalination plants along the Mediterranean Coast. During low demand periods (mainly in the winter and weekends), there is a surplus of desalinated water for short periods of time (hours) that the system does not have the capability to store. The surplus water can be injected in a few existing infiltration ponds that were specifically constructed to inject runoff, in several abandoned quarries, and through injection wells. The main advantages of using injection wells is the ability to locate them in places where the subsurface geology is not suitable for infiltration ponds, in confined aquifer, in small and dense areas, and in areas close to the water supply network. Most of the injection wells that were drilled in Israel in the past have been abandoned primarily because of the poor quality of the injection water, and secondly because of the problematic technical structure. Therefore, the new recharge wells were designed and constructed in a way that enable high flow rates and reduce the clogging effect. Two pilots were conducted in parallel. One pilot focused on the relationship between flow rate, depth of injection, and creation of air bubbles, and a second pilot included a pumping well, recharge well, and two nearby observation wells. The second pilot was conducted in order to evaluate the hydrological conditions of the aquifer, the effect of the new technical design on the injection rate, and the clogging process. Pumping and injection tests that were conducted in the recharge well showed a huge reduction in the hydraulic parameters in the injection test compared to the pumping test despite both tests being conducted at the same well. We assume that there are two mechanisms that are operating together that caused the reduction in the aquifer coefficients during the recharge event. The first mechanism is the injection pressure that needs to overcome the aquifer pressure and the pore water pressure, and the second mechanism is the pressure that the injected water needs to overcome the clogging process that occurs on the screen and in the gravel. The expression of these two mechanisms is the high water level inside the recharge well compared to the lower water level in the nearby observation wells. The air bubble pilot indicated that it is not possible to remove the smaller air bubbles (dissolved air) that are created during the injection process, even when the injection pipe is fully saturated. The injection test with opened and closed valves indicates that the clogging process is very rapid and appears just after injection. Water 2017, 9, 53 12 of 12

On a practical level, it is important to keep the injection pipe filled with water and saturated all the time (the water level should be a few meters above the injection point). The general way to achieve this is to install a control flow valve (an orifice valve type) at the bottom of the injection pipe. However, this will not totally eradicate the creation of the smaller air bubbles and the clogging caused by them. This research gives good insight into the injection mechanism through wells and is essential for any further development of injection facilities and for operation and management protocols.

Acknowledgments: The research was partly funded from the European Union’s Seventh Framework Program (FP7/2007–2013) under grant agreement no 619120 (Demonstrating Managed Aquifer Recharge as a Solution to Water Scarcity and Drought—MARSOL). Author Contributions: Joseph Guttman and Ido Negev are the hydrogeologist and hydrologist (respectively) that constructed the new drilling methodology, conceived and designed the pilots, and supervised the drilling and the pumping experiments; Genadi Rubin is the drilling engineer that designed the pumping and recharge wells and carried out the site supervision during the drilling and the pumping tests. Conﬂicts of Interest: The authors declare no conﬂict of interest.

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