water Article Assessing the Impact of Recycled Water Quality and Clogging on Infiltration Rates at A Pioneering Soil Aquifer Treatment (SAT) Site in Alice Springs, Northern Territory (NT), Australia Karen E. Barry 1,*, Joanne L. Vanderzalm 1, Konrad Miotlinski 2 and Peter J. Dillon 1 1 CSIRO Land and Water, Waite Road, Urrbrae 5064, SA, Australia; [email protected] (J.L.V.); [email protected] (P.J.D.) 2 Departamento de Geologia Aplicada, Universidade Estadual Paulista (UNESP), Rio Claro 13506, SP, Brazil; [email protected] * Correspondence: [email protected]; Tel.: +61-8-8303-8725 Academic Editor: Pieter J. Stuyfzand Received: 16 December 2016; Accepted: 27 February 2017; Published: 2 March 2017 Abstract: Infiltration techniques for managed aquifer recharge (MAR), such as soil aquifer treatment (SAT) can facilitate low-cost water recycling and supplement groundwater resources. However there are still challenges in sustaining adequate infiltration rates in the presence of lower permeability sediments, especially when wastewater containing suspended solids and nutrients is used to recharge the aquifer. To gain a better insight into reductions in infiltration rates during MAR, a field investigation was carried out via soil aquifer treatment (SAT) using recharge basins located within a mixture of fine and coarse grained riverine deposits in Alice Springs, Northern Territory, Australia. A total of 2.6 Mm3 was delivered via five SAT basins over six years; this evaluation focused on three years of operation (2011–2014), recharging 1.5 Mm3 treated wastewater via an expanded recharge area of approximately 38,400 m2. Average infiltration rates per basin varied from 0.1 to 1 m/day due to heterogeneous soil characteristics and variability in recharge water quality. A treatment upgrade to include sand filtration and UV disinfection (in 2013) prior to recharge improved the average infiltration rate per basin by 40% to 100%. Keywords: soil aquifer treatment; clogging; infiltration rates; managed aquifer recharge 1. Introduction Infiltration techniques such as soil aquifer treatment (SAT) are attractive options in supporting irrigation as they are nominally lower in cost than well injection schemes [1] and they can take advantage of the potential for natural treatment through the unsaturated zone [2]. Australia has tremendous potential to increase the amount of water that is recycled via managed aquifer recharge (MAR), as a large proportion of the Australian landscape is covered in favorable sedimentary deposits of sand, gravel and limestone. However, to date there is only one operational SAT scheme in the Northern Territory, Australia, and this has a license to recharge 0.6 Mm3/year. Parsons et al. [3] reported on uncertainty regarding the feasibility of MAR schemes, owing largely to a lack of documented demonstration sites, as a key limitation to the use of MAR for water recycling in Australia. Uncertainty arises from challenges in the implementation of MAR in the presence of lower permeability sediments, such as silt and clay, and/or due to clogging processes, both of which inhibits infiltration rate. Clogging and its management remains a key operational challenge for all MAR schemes [4,5]. The clogging layer often referred to as the ‘schmutzdecke’ usually consists of a thin layer (millimeters to centimeters) thickness, which contains suspended solids, algae, microbes, dust, and salts. Houston et al. [6] defined Water 2017, 9, 179; doi:10.3390/w9030179 www.mdpi.com/journal/water Water 2017, 9, 179 2 of 12 Water 2017, 9, 179 2 of 12 and salts. Houston et al. [6] defined this clogging layer as the zone of material over which a sharp this clogging layer as the zone of material over which a sharp drop in hydraulic head occurs as water drop in hydraulic head occurs as water infiltrates into a sedimentary profile. infiltrates into a sedimentary profile. Management strategies include pre-treatment of the recharge water to minimize clogging [7,8], Management strategies include pre-treatment of the recharge water to minimize clogging [7,8], along with remediation measures such as drying and desiccation of the basin surface [9]. Operation along with remediation measures such as drying and desiccation of the basin surface [9]. Operation of SAT basins in alternating wet and dry cycles to develop anoxic and oxic conditions can optimize of SAT basins in alternating wet and dry cycles to develop anoxic and oxic conditions can optimize the potential for biological treatment processes [2]. Remediation measures are also influenced by the the potential for biological treatment processes [2]. Remediation measures are also influenced by sediment properties of the individual basins [10]. Periodic scraping of the basins is a further the sediment properties of the individual basins [10]. Periodic scraping of the basins is a further management tool [11,12] which can impact on the economic feasibility [13]. Basin floor design using management tool [11,12] which can impact on the economic feasibility [13]. Basin floor design using parallel ridges and furrows has been reported to reduce the need for maintenance [12]. parallel ridges and furrows has been reported to reduce the need for maintenance [12]. The key objectives of this paper are to assess: (i) the impact of sediment properties; and (ii) The key objectives of this paper are to assess: (i) the impact of sediment properties; recycled water pre-treatment on the infiltration rate of a SAT scheme in Alice Springs (NT), in order and (ii) recycled water pre-treatment on the infiltration rate of a SAT scheme in Alice Springs (NT), to identify improvements to the management of such schemes. in order to identify improvements to the management of such schemes. 2.2. Materials and Methods 2.1.2.1. Study Site and Operations FieldField investigationsinvestigations were were carried carried out out on on MAR MAR using using SAT SAT from from 2008 to2008 2014, to using2014, rechargeusing recharge basins locatedbasins located within awithin mixture a mixture of fine and of fine coarse and grained coarse riverinegraineddeposits riverine neardeposi Alicets near Springs, Alice Northern Springs, Territory,Northern AustraliaTerritory, [14Austra,15].lia The [14,15]. SAT scheme The SAT is operatedscheme is by operat the Northerned by the Territory Northern Power Territory and Power Water Corporationand Water Corporation (PWC) and (PWC) located and approximately located approximately 7 km south of7 km the south Alice Springsof the Alice Township Springs (Figure Township1) at the(Figure Arid 1) Zone at the Research Arid Zone Institute Research (AZRI), Institute in an (AZRI), area historically in an area referred historically to as referred the Outer to as Farm the Basin.Outer TheFarm Alice Basin. Springs The Alice area isSprings characterized area is bycharacterized desert climate by withdesert high climate evaporation with high rates evaporation (3000 mm/year) rates and(3000 an mm/year) annual average and an rainfallannual ofaverage 284 mm. rainfall of 284 mm. Figure 1. Location of soil aquifer treatment (SAT) studystudy site,site, inin thethe outerouter basinbasin [[1515].]. TheThe rechargerecharge waterwater isis producedproduced atat thethe WaterWater ReclamationReclamation PlantPlant (WRP),(WRP), whichwhich isis situatedsituated nextnext toto IlparpaIlparpa SwampSwamp adjacentadjacent to Blatherskite Park, approximatelyapproximately 5 km northwest of the site (Figure 11).). WastewaterWastewater forfor rechargerecharge hashas beenbeen treatedtreated byby stabilizationstabilization pondsponds andand DissolvedDissolved Air Flotation (DAF) sincesince 2008, and and in in 2013 2013 the the DAF DAF plant plant was was upgraded upgraded to toinclude include a sand a sand filtration filtration step step (DAFF) (DAFF) plus plus UV UVdisinfection. disinfection. Recharge water targets a palaeochannel of the Todd River (which runs in a north west to south east direction), a Quaternary alluvial aquifer consisting of coarse grained sediments overlain by finer Water 2017, 9, 179 3 of 12 Watergrained2017, clayey9, 179 silts, clays and sands [16] (Figure 2). Quinlan and Wooley [17] reviewed the hydraulic3 of 12 parameters of the Quaternary aquifers in the Town and Inner Farm Basins (Figure 1), and estimated 2 an averageRecharge hydraulic water targets conductivity a palaeochannel of 45 m/day of the (T Todd= 310 Riverm /day) (which and runsa specific in a northyield westof 0.7. to Berry’s south east[18] direction),work on the a Quaternary Inner Farm alluvial Basin indicated aquifer consisting a hydraulic of coarseconductivity grained range sediments of 1 to overlain 117 m/day, by finerwith grainedhigher values clayey evident silts, clays in the and palaeochannel. sands [16] (Figure Dual2). in Quinlanfiltration and ring Wooley and soil [ 17 permeameter] reviewed the tests hydraulic carried parametersout by Knapton of the et Quaternary al. [16] in aquifersthe Outer in Farm the Town Basi andn reported Inner Farm hydraulic Basins conductivity (Figure1), and ranging estimated from an 4 averagem/day in hydraulic the silty conductivity sandy soil ofand 45 m/dayup to 90 (T =m/day 310 m in2/day) the gravelly and a specific sands. yield The of natural 0.7. Berry’s depth [18 to] workgroundwater on the Inner in the Farm vicinity Basin of indicated the SAT scheme a hydraulic is approximately conductivity range18 m [19]. of 1 The to 117 alluvial m/day, aquifer with highersystem valuesis comprised evident of in three the palaeochannel. connected basins,