Column Theme: Ground Water Replenishment with Recycled Water

Ground Water Replenishment with Recycled Water—AnAustralian Perspectiveby Peter Dillon

Water Recycling and Diversified Supplies, Water for a HealthyCountry Flagship Program, CSIRO Land and Water, PMB 2 GlenOsmond, South Australia, 5062, Australia; +61-8-8303-8714;fax: +61-8-8303-8750; peter.dillon@csiro.au

Extensive drought, climate change, populationgrowth, urbanization, and a historical legacy of under-investment in new water supplies has seen Australianmajor cities clamor in recent years to build 800 millionm3/year of alternative supplies (PMSEIC 2007). Sea waterdesalination is emerging as the dominant contributor, andthere are substantial advances in water recycling (Rad-cliffe 2004). A recent economic evaluation has shownthat the costs of storm water harvesting via aquifers forone Australian city, Adelaide, were one-third to one-halfthe cost of sea water desalination and consumed only 3%of the energy (Dillon et al. 2009a). In Perth, plans for

Copyright © 2009 The Author(s)Journal compilation ©2009NationalGroundWaterAssociation.doi: 10.1111/j.1745-6584.2009.00587.x

water reclamation via aquifers will augment future drink-ing water supplies based on the results of commissioningtrials currently in preparation.

In other Australian cities, the National Water Com-mission has instituted a series of studies to map the oppor-tunities for subsurface storage of storm water, reclaimedwater, and other waters to help focus efficient water sup-ply investment. For cities without aquifers, this option isclosed. Other aquifers, previously considered too brack-ish to be used for water supply, have been turned intovaluable ground water storage by recharging them withfresh water. Where new supplies are being developedfor aquifers that are fresh, shallow, or support groundwater–dependent ecosystems, aquifer replenishment is anintegral component to ensure protection of existing envi-ronmental values (including beneficial uses).

Australian GuidelinesAustralia has the benefit of a National Water Quality

Management Strategy (Figure 1), which was conceivedin the 1990s as a set of principles and has been pro-gressively implemented since then through the productionof more than 20 national guidelines. These include Aus-tralian Guidelines for Water Recycling: Managing Healthand Environmental Risks (Phase 1) (NRMMC–EPHC–AHMC 2006). These have been extended in Phase 2to address Augmentation of Drinking Water Supplies(EPHC–NHMRC–NRMMC 2008a) with draft guidelinesfor Managed Aquifer Recharge and for Stormwater Har-vesting and Reuse released for public consultation in May2008.

The draft guidelines for Managed Aquifer Recharge(EPHC–NHMRC–NRMMC 2008c) allow for stageddevelopment of managed aquifer recharge (MAR), whichis defined as recharge of an aquifer using a source ofwater (including recycled water) under controlled condi-tions to store it for later use or for defined environmentalbenefit. MAR is thus the purposeful recharge of waterto aquifers; it is not a method for waste disposal. Theguidelines allow for an attenuation zone beyond whichat all times and within which beyond a defined time, allambient environmental values (e.g., beneficial uses) ofthe aquifer are protected. This relies on information con-cerning inactivation rates of pathogens and degradation

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rates of degradable organic chemicals. The risk manage-ment framework common to drinking water and recycledwater guidelines applies. This is extended beyond waterquality issues to also address aquifer pressures, dischargesand leakages, and impacts on ground water–dependentecosystems (Dillon et al. 2009b).

These guidelines are intended to provide a confidentpathway forward for proponents, regulators, and otherstakeholders. The guidelines also reinforce the need forpublic consultation processes where others may poten-tially be affected by MAR projects.

Hazards addressed in the MAR guidelines are:

1. Pathogens2. Inorganic chemicals3. Salinity and sodicity4. Nutrients5. Organic chemicals6. Turbidity/particulates7. Radionuclides8. Pressure, flow rates, volumes, and levels9. Contaminant migration in fractured rock and karsticaquifers10. Aquifer dissolution and aquitard and well stability11. Impacts on ground water–dependent ecosystems12. Greenhouse gas emissions.

For each hazard, the guidelines describe sources orcauses, the effect on public health and environment, howit can be managed (including preventive measures), theproposed validation, verification and operational monitor-ing, and acceptance criteria for the various stages of riskassessment that parallel the stages of project development.

Reactions between Recharged Water andAquifers

A simplistic view that treating water to near drink-ing standards before recharge will protect the aquifer andrecovered water is incorrect. For example, chlorination,which removes pathogens that would have been inevitablyremoved in a warm aquifer, can result in water recov-ered from some aquifers containing persistent excessivechloroform. In some locations, drinking water injectedinto potable aquifers has resulted in excessive arsenicconcentrations on recovery due to the reactions betweeninjected water and pyrite containing arsenic. Source waterthat has been desalinated to a high purity dissolves moreminerals within the aquifer than water that has beenless treated. Similarly, reduction of nutrients to very lowlevels in recharge water can impede the co-metabolismof some trace organics, which otherwise would havebeen degraded within the aquifer. The American WaterWorks Association Research Foundation, along with Aus-tralian, European, and American partners, have supportedmuch of the research in this area. Consequently, theMAR Guidelines adopt a scientific approach that takesinto account the three ways that aquifers interact withrecharged water:

• Sustainable hazard removal. The guidelines allow forpathogen inactivation and biodegradation of someorganic contaminants during the residence time ofrecharged water in the soil and/or aquifer within anattenuation zone of finite size.

• Ineffective hazard removal. These hazards need to beremoved prior to recharge because they are either notremoved (e.g., salinity) or removal is unsustainable(e.g., adsorption of any metals and organics that arenot subsequently biodegraded, or excessive nutrients orsuspended solids).

National Water Quality Management Strategy: Policies and Principles[1]

Aust. and N.Z. Guidelinesfor Fresh and Marine Water

Quality [2]

Guidelines forGroundwater Protection

in Australia [3]

Australian Drinking Water Guidelines[5]

Australian Guidelines for Water Recycling – Phase 1Managing Health and Environmental Risks [6]

Augmentation ofdrinking water

supplies[7]

Stormwaterharvestingand reuse

[9]

Australian Guidelines forWater Quality Monitoring

and Reporting [4]

AustralianGuidelines for

Water RecyclingPhase 2

Managedaquifer

recharge[8]

Figure 1. National Water Quality Management Strategy, showing the foundations for protecting human healthand the environment, and innovation in Australian water management [1 ARMCANZ–ANZECC (1994); 2ANZECC–ARMCANZ (2000b); 3 ANZECC–ARMCANZ (1995); 4 ANZECC–ARMCANZ (2000c); 5 NHMRC–NRMMC(2004); 6 NRMMC–EPHC–AHMC (2006); 7 EPHC–NHMRC–NRMMC (2008a); 8 EPHC–NHMRC–NRMMC (2008c); 9EPHC–NHMRC–NRMMC (2008b)].

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• New hazards introduced by aquifer interaction (e.g.,metal mobilization, hydrogen sulfide, salinity, sodicity,hardness, or radionuclides). There is a need to changethe quality of recharge water to avoid these (e.g.,change acidity–alkalinity, reduction–oxidation status,or reduce nutrients).

Attenuation ZoneThe response of an aquifer to any water quality hazard

depends on specific conditions within the aquifer, includ-ing temperature, presence of oxygen, nitrate, organic car-bon and other nutrients and minerals, and prior exposureto the hazard. The guidelines indicate the state of currentknowledge on attenuation rates of pathogens and organiccompounds under a range of conditions. They also allowfor consideration of new local knowledge when assessingrisks, determining sizes of attenuation zones, and sitingof monitoring wells.

In most aquifers, with appropriate pretreatment ofwater to be recharged, the attenuation zone will besmall and generally on the order of 20 to 200 m fromthe recharge area or well (Figure 2). Water that travelsfurther has had sufficient residence time in the aquiferfor attenuation of pathogens and contaminants to belowthe relevant guideline values for native ground water andintended uses of recovered water.

The volume of an aquifer in which water quality maybe measurably affected by MAR may be larger, but inthis outer domain the water quality should continuouslysatisfy the initial environmental values of the aquifer(Figure 2). The effects of MAR operations on hydraulicheads (pressures) may be measurable over a much largerarea, especially in confined aquifers. If the aquifer isoriginally too saline for the uses of recovered water, astorage zone can be identified that contains water which,when recovered, is fit for its intended use (Figure 2).

The dotted line in Figure 2 marks the outer bound-ary of the attenuation zone. This represents the maximumseparation distance between the recharge structure andwells for verification monitoring to ensure that the ambi-ent ground water quality is protected. As the attenuation

zone is defined only for enduring attenuation processes,on cessation of the MAR operation, it will shrink anddisappear as ultimately the whole aquifer will meet allits initial environmental values. Attenuation rates undervarious aquifer conditions are summarized in the appen-dices of the guidelines and will be supplemented on theMAR Guidelines website with further attenuation rates tobe provided by studies designed to fill major gaps.

Public AcceptancePublic support for recycling via aquifers in Australia

is relatively strong. A survey of 500 people in Perth foundmore than 78% were unopposed to water recycling viaaquifers to drinking water supplies (Leviston et al. 2006).Almost half the respondents believed that if recycledwater was left underground for a number of years, it wouldbe no different than natural ground water. Clearly, publicacceptance of the treatment capacity of aquifers couldbe further enhanced by disseminating factual informationon aquifer treatment effectiveness and information onpretreatment processes used to remove hazards for whichin situ aquifer treatment is ineffective.

Water Resources Planning and ManagementA further step required for effective use of MAR is to

address the rights of rechargers to access, store, recover,trade, and use water. This is particularly important wheresurface water systems are over-allocated but rights mar-kets are yet to be established for recycled waters. It isalso important in generating incentives for replenishingover-allocated aquifers with water of an appropriate qual-ity. A position paper on this topic has been prepared forAustralian regulators with responsibility for planning andmanaging surface and ground water resource entitlementsand allocations (Ward and Dillon 2009). If MAR is toreach its full potential in urban and rural water supplies,jurisdictions will need a holistic and workable policyframework that accounts for MAR. The concept of man-aging recharge without also managing discharge restrictsthe security and equity of benefits for communities thatinvest in MAR.

Hydraulic impact zone

Water quality impact zone

Attenuation zone

Storage zone

Rechargearea

Figure 2. Schematic showing zones of influence of a MAR operation.

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Those involved in urban water supply planningneed to consider the additional environmental benefits ofrecharging aquifers with storm water and reclaimed water,such as improved urban coastal water quality, enhancedurban amenity, reduced reliance on over-allocated andstressed surface water resources, reduced urban flooding,and reduced greenhouse gas emissions. It is intended thatincreased awareness and understanding of urban hydro-geology through mapping studies improved awareness ofthe economics and technical viability of MAR with recy-cled water through demonstration projects and research,appreciation of public support for well-managed waterrecycling, new Australian guidelines for Managed AquiferRecharge and Augmentation of Drinking Water Supplies,emergent policy frameworks, and holistic water supplyplanning will enable ground water replenishment to com-pete on a level playing field with traditional and emergingalternative water supplies.

Further international guidance on MAR is avail-able from the International Association of Hydroge-ologists Commission on Managed Aquifer Recharge:http://www.iah.org/recharge.

AcknowledgmentsThe author thanks American Water Works Research

Foundation, the National Water Commission, NationalEnvironment Protection Council, our many partners inresearch projects and colleagues in CSIRO Water for aHealthy Country Flagship Program who have contributedto the knowledge base for the Australian guidelines onmanaged aquifer recharge. He is also indebted to SallyTetreault-Campbell and Sonja Mennen for reviewing adraft of this article.

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