Karen Barry

Fate of disinfection by-products in groundwater during aquifer storage and recovery with reclaimed water

Knowledge on the behaviour of disinfection by-products (DBPs) during aquifer storage and recovery (ASR) is limited even though this can be an important consideration where recovered waters are used for potable purposes. A reclaimed water ASR trial in an anoxic aquifer in South Australia has provided some of the first quantitative information at field-scale on the fate and transport of trihalomethanes (THMs) and haloacetic acids (HAAs). The results revealed that THM half-lives varied from <1 to 65 days, with persistence of chloroform being highest and bromoform lowest. HAA attenuation was rapid (<1 day). Rates of THM attenuation were shown to be highly dependent on the geochemical environment as evidenced by the 2-5 fold reduction in half-lives at the ASR well which became methanogenic during the storage phase of the trial, as compared to an observation well situated 4 m away, which remained nitrate-reducing. These findings agree with previous laboratory-based studies which also show persistence declining with increased bromination of THMs and reducing redox conditions. Modelling suggests that the chlorinated injectant has sufficient residual chlorine and natural organic matter for substantial increases in THMs to occur within the aquifer, however this is masked in some of the field observations due to concurrent attenuation, particularly for the more rapidly attenuated brominated compounds. The model is based on data taken from water distribution systems and may not be representative for ASR since bromide and ammonia concentrations in the injected water and the possible role of organic carbon in the aquifer were not taken into consideration. During the storage phase DBP formation potentials were reduced as a result of the removal of precursor material despite an increase in the THM formation potential per unit weight of total organic carbon. This suggests that water quality improvements with respect to THMs and HAAs can be achieved through ASR in anoxic aquifers.

Laboratory assessment of factors affecting soil clogging of soil aquifer treatment systems.

In this study the effect of soil type, level of pre-treatment, ponding depth, temperature and sunlight on clogging of soil aquifer treatment (SAT) systems was evaluated over an eight week duration in constant temperature and glasshouse environments. Of the two soil types tested, the more permeable sand media clogged more than the loam, but still retained an order of magnitude higher absolute permeability. A 6- to 8-fold difference in hydraulic loading rates was observed between the four source water types tested (one potable water and three recycled waters), with improved water quality resulting in significantly higher infiltration. Infiltration rates for ponding depths of 30 cm and 50 cm were higher than 10 cm, although for 50 cm clogging rates were higher due to greater compaction of the clogging layer. Overall, physical clogging was more significant than other forms of clogging. Microbial clogging becomes increasingly important when the particulate concentrations in the source waters are reduced through pre-treatment and for finer textured soils due to the higher specific surface area of the media. Clogging by gas binding took place in the glasshouse but not in the lab, and mechanical clogging associated with particle rearrangement was evident in the sand media but not in the loam. These results offer insight into the soil, water quality and operating conditions needed to achieve viable SAT systems.

Pathogen inactivation during passage of stormwater through a constructed reedbed and aquifer transfer, storage and recovery.

A study was undertaken to determine the potential inactivation rates of selected enteric microorganisms in captured urban stormwater within a constructed reedbed and in tertiary carbonated aquifer during an Aquifer Storage, Transfer and Recovery (ASTR) scheme. The study was undertaken in-situ in the constructed reedbed and aquifer using diffusion chambers. The results showed that all tested bacteria had one log(10) reduction time of less than 6 and 2.5 days respectively in constructed reedbeds and aquifer, which suggests that presence of enteric bacteria in the recovered water is unlikely. However, adenovirus and Cryptosporidium oocysts showed lower inactivation rates with one log(10) reduction times of more than 33 days in the constructed reedbeds. This means that the constructed reedbed with a mean residence time 10 days cannot be relied upon as an efficient treatment barrier for virus and protozoa. Storage of stormwater in aquifer with brackish water resulted in slow inactivation of enteric viruses over the 35 day incubation period with adenovirus and rotavirus showing slowest inactivation times (extrapolated T(90) of >100 days). Cryptosporidium oocysts showed similar inactivation rate in the constructed reedbed and aquifer.

Enhancement of the membrane filtration index (MFI) method for determining the clogging potential of turbid urban stormwater and reclaimed water used for aquifer storage and recovery

Abstract Well clogging is a potential impediment to the use of aquifer storage and recovery (ASR) wells. With filtration of suspended solids the most frequently reported form of clogging, methods to predict its impact serve as useful management tools. In this study, the Membrane Filtration Index (MFI), a standard test of the rate at which water clogs a membrane filter, has been extended for use with turbid and organic-rich waters, and to improve precision of MFI for all water qualities. Waters from 12 sites, including mains, urban stormwater and reclaimed water, which are or have the potential to be water sources for aquifer storage and recovery (ASR) in southern Australia, were analyzed for MFI, turbidity, total suspended solids, total organic carbon, particle size and SEM. Time-series data were collected at two of these focus sites over a 12-month period. The upgraded MFI apparatus was found to give repeatable results with coefficients of variation generally less than 10% for MFIs of up to 900 s/L2. This extends the range of utility of the apparatus from previously reported limits of

Pathogen decay during managed aquifer recharge at four sites with different geochemical characteristics and recharge water sources

Recycling of stormwater water and treated effluent via managed aquifer recharge (MAR) has often been hampered because of perceptions of low microbiological quality of recovered water and associated health risks. The goal of this study was to assess the removal of selected pathogens in four large-scale MAR schemes and to determine the influence of aquifer characteristics, geochemistry, and type of recharge water on the pathogen survival times. Bacterial pathogens tested in this study had the shortest one log removal time (, <3 d), followed by oocysts (, <120 d), with enteric viruses having the biggest variability in removal times (, 18 to >200 d). Human adenovirus and rotavirus were relatively persistent under anaerobic conditions (, >200 d). Human adenovirus survived longer than all the other enteric virus tested in the study and hence could be used as a conservative indicator for virus removal in groundwater during MAR. The results suggest that site-specific subsurface conditions such as groundwater chemistry can have considerable influence on the decay rates of enteric pathogens and that viruses are likely to be the critical pathogens from a public health perspective.

Water quality requirements for sustaining aquifer storage and recovery operations in a low permeability fractured rock aquifer

A changing climate and increasing urbanisation has driven interest in the use of aquifer storage and recovery (ASR) schemes as an environmental management tool to supplement conventional water resources. This study focuses on ASR with stormwater in a low permeability fractured rock aquifer and the selection of water treatment methods to prevent well clogging. In this study two different injection and recovery phases were trialed. In the first phase ~1380 m(3) of potable water was injected and recovered over four cycles. In the second phase ~3300 m(3) of treated stormwater was injected and ~2410 m(3) were subsequently recovered over three cycles. Due to the success of the potable water injection cycles, its water quality was used to set pre-treatment targets for harvested urban stormwater of ≤ 0.6 NTU turbidity, ≤ 1.7 mg/L dissolved organic carbon and ≤ 0.2 mg/L biodegradable dissolved organic carbon. A range of potential ASR pre-treatment options were subsequently evaluated resulting in the adoption of an ultrafiltration/granular activated carbon system to remove suspended solids and nutrients which cause physical and biological clogging. ASR cycle testing with potable water and treated stormwater demonstrated that urban stormwater containing variable turbidity (mean 5.5 NTU) and organic carbon (mean 8.3 mg/L) concentrations before treatment could be injected into a low transmissivity fractured rock aquifer and recovered for irrigation supplies. A small decline in permeability of the formation in the vicinity of the injection well was apparent even with high quality water that met turbidity and DOC but could not consistently achieve the BDOC criteria.

Application of a probabilistic modelling approach for evaluation of nitrogen, phosphorus and organic carbon removal efficiency during four successive cycles of aquifer storage and recovery (ASR) in an anoxic carbonate aquifer

Aquifer storage is increasingly being recognised in its role as a treatment process barrier within a multiple barrier approach to water reuse. Aquifers are postulated to have the ability to provide sustainable treatment for removal of nitrogen, phosphorus and organic carbon, the dominant nutrient hazards in water recycling, but, to date this treatment performance has remained difficult to validate in field studies. This study applied a statistical method, proposed for validation of the performance of advanced water treatment processes, to evaluate nutrient removal during aquifer storage and recovery (ASR) with recycled water. Analysis of observed water quality changes during four successive ASR cycles with highly variable source water quality was used to describe the removal efficiencies for selected nutrients by an anoxic carbonate aquifer. The use of this method was found to be suitable to calculate removal efficiencies for total organic carbon (TOC) and total nitrogen (TN) over four ASR cycles with temporally variable concentrations of nutrients in the tertiary treated wastewater injectant. TOC and TN removal was dominated by redox processes, aerobic respiration and denitrification. Median removal of TOC ranged from 25 to 40% and TN from 46 to 87% over the four cycles. There was no observable reduction in this removal with time, suggesting that removal of TOC and TN by redox processes can be sustained in an ASR system. Contrastingly, total phosphorous (TP) was subject to reversible removal via adsorption and desorption processes and as a result, removal efficiency could not be calculated with this method. Thus in general, results indicated that this statistical method could be used to characterise the capacity of the anoxic carbonate aquifer treatment barrier for removal of carbon and nitrogen, but not for removal of phosphorus.

Recovery of Injected Freshwater from a Brackish Aquifer with a Multiwell System

Herein we propose a multiple injection and recovery well system strategically operated for freshwater storage in a brackish aquifer. With the system we call aquifer storage transfer and recovery (ASTR) by using four injection and two production wells, we are capable of achieving both high recovery efficiency of injected freshwater and attenuation of contaminants through adequately long residence times and travel distances within the aquifer. The usual aquifer storage and recovery (ASR) scheme, in which a single well is used for injection and recovery, does not warrant consistent treatment of injected water due to the shorter minimum residence times and travel distances. We tested the design and operation of the system over 3 years in a layered heterogeneous limestone aquifer in Salisbury, South Australia. We demonstrate how a combination of detailed aquifer characterization and solute transport modeling can be used to maintain acceptable salinity of recovered water for its intended use along with natural treatment of recharge water. ASTR can be used to reduce treatment costs and take advantage of aquifers with impaired water quality that might locally not be otherwise beneficially used.

Environmental monitoring of selected pesticides and organic chemicals in urban stormwater recycling systems using passive sampling techniques.

Water recycling via aquifers has become a valuable tool to augment urban water supplies in many countries. This study reports the first use of passive samplers for monitoring of organic micropollutants in Managed Aquifer Recharge (MAR). Five different configurations of passive samplers were deployed in a stormwater treatment wetland, groundwater monitoring wells and a recovery tank to capture a range of polar and non-polar micropollutants present in the system. The passive samplers were analysed for a suite of pesticides, polycyclic aromatic hydrocarbons (PAHs) and other chemicals. As a result, 17 pesticides and pesticide degradation products, 5 PAHs and 8 other organic chemicals including flame retardants and fragrances were detected in urban stormwater recharging Aquifer Storage and Recovery (ASR) and an Aquifer Storage Transfer and Recovery (ASTR) system. Of the pesticides detected, diuron, metolachlor and chlorpyrifos were generally detected at the highest concentrations in one or more passive samplers, whereas chlorpyrifos, diuron, metolachlor, simazine, galaxolide and triallate were detected in multiple samplers. Fluorene was the PAH detected at the highest concentration and the flame retardant Tris(1-chloro-2-propyl)phosphate was the chemical detected in the greatest abundance at all sites. The passive samplers showed different efficiencies for capture of micropollutants with the Empore disc samplers giving the most reliable results. The results indicate generally low levels of organic micropollutants in the stormwater, as the contaminants detected were present at very low ng/L levels, generally two to four orders of magnitude below the drinking water guidelines (NHMRC, 2011). The efficiency of attenuation of these organic micropollutants during MAR was difficult to determine due to variations in the source water concentrations. Comparisons were made between different samplers, to give a field-based calibration where existing lab-based calibrations were unavailable.

Microbiological risks of recycling urban stormwater via aquifers for various uses in Adelaide, Australia

This study investigates the potential for an aquifer to provide treatment of stormwater in addition to engineered treatment for the safe use of recovered water for drinking and non-drinking supplies. A brackish limestone aquifer was investigated as a treatment barrier when assessing microbial health-based targets of stormwater harvesting systems. Aquifer treatment was assessed based on pathogen inactivation and attachment to the aquifer sediments. The results showed that the health-based targets for different end uses including open space irrigation, domestic and industrial non-potable uses and drinking water could be met with additional treatment. The aquifer was estimated to have potential for ~4 log10 removal based on inactivation studies and attachment to the aquifer.