Monitoring of a seasonal-use, on-site wastewater disposal system (septic system) in Canada, over a 33-year period from 1988 to 2021, showed that during recent sampling the groundwater plume had TIN (total inorganic nitrogen) averaging 12.2 mg/L that was not significantly different than early values, representing 80% removal, whereas SRP (soluble reactive phosphate), although higher than early values averaging 0.08 mg/L, was still 99% lower than the effluent concentration. Evidence suggests that the anammox reaction and possibly also denitrification contribute to TIN removal, whereas SRP removal is primarily the result of mineral precipitation. Most of the removal occurs in close proximity to the drainfield infiltration pipes (within about 1 m) demonstrating that reaction rates are relatively fast in the context of typical groundwater plume residence times. This long-term consistency demonstrates that sustainable nutrient treatment can be achieved with conventional on-site wastewater disposal systems that have low capital costs and require minimal energy input and maintenance.

Previous studies of the nutrient budgets of lakes in Precambrian Shield regions have generally ignored the role of groundwater as a source or sink (influx or efflux) of nutrients. This paper and its companion (Part 2) address this science gap by probing the role of groundwater in the nutrient balance for a restricted bay of a Precambrian Shield lake that has undergone extensive shoreline development. In Part 1, we introduce a conceptual model of the relevant processes, including the role of groundwater. A cottage study site is described, concentrations of nutrients and septic tracers (artificial sweeteners), water levels and other data are reported. This includes data from samples of the septic wastewater plume in groundwater at the cottage, and samples from the bay. The artificial sweetener data indicate seepage of septic plumes to the bay, but significant attenuation of septic-derived nutrients in the subsurface. These data are used for numerical modeling in Part 2.

For more than a decade the artificial sweeteners acesulfame (ACE) and sucralose (SUC) have been applied as tracers of the input of wastewater to environmental waters. Recently concerns have been raised that degradation of ACE during treatment may hinder or restrict its use as a wastewater tracer. In this study the value of ACE and SUC as tracers was reassessed based on samples of wastewater at 12 municipal wastewater treatment (MWWT) plants and from 7 septic systems and associated septic plumes in groundwater. The results indicated stability of SUC during MWWT at most plants, and variable removal of both sweeteners during some MWWT and in the septic wastewater systems. However, the residual concentrations of ACE and SUC in municipal effluent and in septic plumes indicate that both sweeteners remain valuable wastewater tracers. The mass ratio SUC/ACE was found to be a useful parameter for examining the relative persistence of these sweeteners.

We have established a monitoring record of phosphate (PO43-) migration in the Long Point, ON campground septic system plume that now spans 26 years. Previously, at year 16 (2006), a P plume 16 m in length was documented and provided a good fit with an analytical advection dispersion model when a P migration velocity of 0.8 m/yr was used (retardation factor of 37) and when P behaved in an otherwise conservative manner (sorption only). However, between years 16 and 26 (2016), the P plume length expanded by only 2 m (0.2 m/yr) and increased in depth by only 0.5 m. The zone of abrupt P depletion at depth occurs close to the zone where SO42- concentrations increase in response to NO3- oxidation of pyrite. Scanning electron microscope images of sand grains from the nose of the P plume reveal abundant authigenic mineral coatings of considerable thickness (similar to 5 to 20 mu m), with Fe as the dominant cation and containing 1 to 3 wt % P. This evidence suggests that P is now being attenuated along a reaction front that coincides with the zone where pyrite oxidation is occurring. P migration may now be controlled by the rate of migration of the pyrite oxidation front and this is several times slower than the previously indicated rate in the shallower, sorption-controlled portion of the plume. Monitoring at Long Point has demonstrated the danger of embracing an overly simplistic conceptual model when attempting to predict wastewater P migration in groundwater and also highlights the unique insight provided by a long-term monitoring record.

The persistence of inorganic nitrogen is assessed in a set of 21 septic system plumes located in Ontario, Canada, that were studied over a 31-year period from 1988 to 2019. In the plume zones underlying the drainfields, site mean NO3- values averaged 34 +/- 27 mg N/L and exceeded the nitrate drinking water limit (DWL) of 10 mg N/L at 16 of 21 sites. In plume zones extending up to 30 m downgradient from the drainfields, site mean NO3- values averaged 24 +/- 20 mg N/L and exceeded the DWL at 9 of 13 sites. Site mean total inorganic nitrogen (TIN; NH4+ + NO3- - N) removal averaged 34 +/- 26% in the drainfield zones and 36 +/- 44% in the downgradient plume zones, indicating that much of the removal occurred within the drainfields. Removal was much higher at nine sites where drainfield TIN included >10% NH4+ (62 +/- 25% removal). TIN removal was not correlated with wastewater loading rate, system age, or sediment carbonate mineral content, but was correlated with water table depth, where shallower water table sites had generally less complete wastewater oxidation. At many of these sites, both NO3- and NH4+ were present together in the plumes and were lost concomitantly, suggesting that the anammox reaction was making an important contribution to the observed TIN loss. When groundwater nitrate contamination is a concern, considering on-site treatment system designs that lead to a lesser degree of wastewater oxidation, could be a useful approach for enhancing N removal.

Groundwater nutrient loading to L Huron was assessed along a 1.7 km section of beach at Grand Bend, ON, Canada, where septic systems are used for wastewater disposal. The artificial sweetener acesulfame (ACE) was detected in all groundwater samples (7-842 ng/L, n = 78), revealing that the entire surficial aquifer was impacted by septic system wastewater. Nitrate concentrations (3.5 +/- 1.4 mg/L, n = 78) were correlated with ACE (r(2) = 0.54), indicating that septic systems contribute to nitrate loading in the aquifer. Chloride was also elevated (37 +/- 11 mg/L, n = 78), but was not correlated with ACE (r(2) = 0.008), indicating a non wastewater source was dominant, likely road salt. Soluble reactive phosphorus (SRP) values were low (53 +/- 9.3 mu g/L, n = 77) and were not correlated with ACE (r(2) = 0.006). Sediment profiling below two of the septic system drain-fields, showed that the sand grains had distinct secondary coatings containing P, indicating that mineral precipitation reactions played a role in limiting P concentrations present in the aquifer. Groundwater nutrient loading to the lake was estimated at 13,000 kg N/year from NO and 1.9 kg P/year from SRP. These amounts are insignificant compared to nutrient loading from a stream that drains an agricultural catchment and discharges to the lake at the north end of the study site (Parkhill Creek). This calls into question, in some cases, the rationale of decommissioning properly functioning septic systems as a mitigation measure for reducing nutrient loading to nearby water courses. (C) 2019 International Association for Great Lakes Research. Published by Elsevier B.V. All rights reserved.

Sparsely populated or peri-urban areas commonly lack access to public water supply and sewerage systems. The inhabitants must make use of excavated wells to meet their water needs and septic systems or pit latrines for domestic wastewater disposal, which can release pathogens and nutrients (nitrate and phosphate) into shallow groundwater. This study compares two on-site sanitation systems improved with permeable reactors for removal of nutrients and pathogens: a lateral flow design at Maryhill site (Canada) and a downflow design at Parelheiros site (Brazil). Both alternative latrines employed two reactive materials: BOF (Basic Oxygen Furnace) slag for pathogen removal and sawdust for nitrate removal. At Maryhill, the sawdust tank was emplaced before the BOF slag tank, and at Parelheiros, the BOF slag layer was emplaced before the sawdust layer. Maryhill latrine was able to oxidize up to 98% of ammonium to nitrate and to remove 99% of nitrate, phosphate, and E. coli from the effluent. Parelheiros latrine was more efficient in promoting nitrification, with almost complete ammonium oxidation, but nitrate removal by denitrification ranged between 13 and 57%, while phosphate and E. coli were completely removed. The BOF slag overlying sawdust layer in Parelheiros design may have negatively affected the performance in denitrifying bacteria due to the high pH created in BOF slag. The Maryhill latrine proved to be a more satisfactory design for nitrate removal. The combined use of sawdust and BOF slag in differing subsurface environments has shown considerable potential for mitigating impacts of on-site sanitation systems on groundwater.

Although sulfamate (the anion of sulfamic acid) has been in use for decades in various industrial and other applications, there is no previously published information about its occurrence and fate in environmental waters. In this study sulfamate was widely detected in environmental waters in Ontario, Canada, ranging up to 128,000ng/L. It was always detected (>100ng/L) in bulk precipitation samples and streams, it was usually detected in samples of lake water, and often detected in groundwater. Spatial and temporal variations suggest that both widespread atmospheric deposition and localized land-based anthropogenic sources of sulfamate may be important. Lower concentrations or non-detections of sulfamate in waters that had relatively low dissolved oxygen (e.g. some groundwaters) suggest that sulfamate may be degraded in the environment under suboxic or anoxic conditions. Given our findings of a wide distribution of sulfamate in environmental waters, including precipitation, it is not likely to be very useful as a wastewater tracer.

Nutrients, like nitrate and phosphate, and pathogens are the primary contaminants released into groundwater by on-site sanitation systems, which are an effluent disposal outcome for regions not covered by sanitation infrastructure, as periurban communities in developing countries. As appropriate setback distances between pit latrines and supply wells often cannot be met to avoid groundwater contamination, especially in a densely-populated situation, efficient, low-cost and accessible technologies are extremely necessary to protect water resources and surpass critical and persistent public health problems. This paper presents 1-year field-testing of an alternative latrine (AL) that incorporates two waste materials as permeable reactive barriers (PRB) in an irregular settlement at the municipality of Sao Paulo (Brazil). Basic oxygen furnace (BOF) slag in contact with wastewater effluent increases its pH level, which causes pathogens inactivation and phosphate adsorption. Sawdust under water saturation creates reducing conditions that encourage the growth of denitrifying bacteria that remove nitrate. A control latrine (CL) was constructed 90 m apart from AL with similar hydraulic characteristics and nonreactive materials for hydrochemical comparison. It was evident for AL the formation of well-defined nitrification and denitrification reaction zones, whereas CL overall presented nitrogen in its ammoniacal form, with incipient nitrate production at CL bottom, indicating that nitrification is probably boosted below that. BOF slag had attenuated microorganisms and phosphate almost completely, but nitrate removal average efficiency was 42%. The high pH effluent generated in BOF media may have also affected in the short-term the denitrifying bacteria in sawdust barrier 1 m below. The inverted position of the reactive barriers, i.e., sawdust PRB overlying BOF slag PRB, should be a more suitable design to achieve nitrate and pathogens removal. This kind of sanitation solution employing cheap and accessible waste materials have never been applied in the design proposed in this paper and also was a novelty for Brazilian context, proving to be a suitable technology to meet local needs.

Dissolved organic matter (DOM) is an important energy source for biogeochemical reactions. However, DOM is often assumed to be recalcitrant in the groundwater zone due to extensive microbial processing in the overlying soil zone and long groundwater residence times. Consequently, further heterotrophic microbial processes proceed at inherently low rates. Septic systems provide an ideal opportunity to study the evolution of groundwater DOM due to the development of confined and easily identifiable plumes of known age. Here we use measures of DOM composition (size-exclusion liquid chromatography, ultraviolet absorbance, and C:N) to quantify DOM evolution along an exceptionally well-characterized septic-impacted groundwater plume. Elevated concentrations (5 to 8 mg C/L) close to the tile bed decrease to values below 2 mg C/L with lower UV-absorbing components normalized to overall DOM concentration (specific ultraviolet absorbance) along the six-year-old plume flow path. The humic substance fraction (HSF) comprises the largest percentage of DOM and decreases in concentration along the septic plume. HSF properties also change with travel time becoming lower in molecular weight, specific ultraviolet absorbance, and C:N. Denitrification continues along the length of the plume concomitant with changes in DOM and HSF composition. Thus, HSF, typically considered recalcitrant in subsurface environments, is actively cycled by microorganisms on multiyear time frames in accordance with the recent paradigm shift for soil organic matter evolution. Lastly, measures of DOM composition indicate changes in DOM that are not evident from measures of concentration alone. Plain Language Summary On-site wastewater disposal in septic systems is a known source of groundwater pollution, including large amounts of organic matter. Dissolved organic matter (DOM), made up of thousands of different molecules, plays a number of important roles within the environment. For instance, DOM is an energy source for microbes. Generally, groundwater DOM can be difficult to use as an energy source as easily degradable components have been lost as slow groundwater transport leads to enhanced physical, chemical, and biological processing. However, recent studies find continuous reworking and recycling of DOM occurring on longer time scales. Septic plumes provide an ideal environment to study this as they provide a known source of easily degradable DOM that can be tracked. Our objective was to measure changes to the concentration and composition of DOM along an extensively studied septic-impacted plume. This allowed us to link DOM evolution with known groundwater ages and known processes. We found that as DOM degraded, most of the change over time came from the humic substance fraction. We were also able to calculate one of few rates for wastewater DOM in groundwater. Results from this study illustrate how DOM continues to change on long time scales in ways that are not observed by measuring only its concentration.

This study reviews phosphorus (P) concentrations in groundwater plumes from 24 on-site wastewater treatment systems (septic systems) in Ontario, Canada. Site investigations were undertaken over a 30-year period from 1988 to 2018 at locations throughout the province that encompass a variety of domestic wastewater types and geologic terrain. The review focuses on P behaviour in the drainfield sediments and in the proximal plume zones, within 10 m of the drainfields, where plume conditions were generally at steady state. At these sites, mean soluble reactive phosphorus (SRP) values in the septic tank effluent ranged from 1.8 to 13.8 mg/L and averaged 8.4 mg/L. Phosphorus removal in the drainfields averaged 90% at sites where sediments were non calcareous (13 sites) and 66% at sites where sediments were calcareous (11 sites). Removal considering both the drainfields and proximal plume zones, averaged 97% at the non-calcareous sites and 69% at the calcareous sites, independent of the site age or loading rate. At 17 of the 24 sites, mean SRP concentrations in the proximal groundwater plumes (within 10 m) declined to <= 1 mg/L, which is a common treatment level for Pat sewage treatment plants. Zones of P accumulation were present in almost all of the drainfields, where sand grains exhibited distinct secondary coatings containing P, demonstrating that mineral precipitation was likely the dominant cause of the P retention observed at these sites. This review confirms the often robust capacity for phosphorus removal in properly functioning septic systems. At the majority of these sites (17/24), P retention meets or exceeds removal that would normally be achieved during conventional sewage treatment. This challenges the necessity of avoiding septic system use in favor of communal sewer systems, when limiting phosphorus loading to nearby water courses is a principal or major concern. (C) 2019 Elsevier B.V. All rights reserved.

Wood particle biofilters are being used for remediation of nitrate in watercourses but so far, have received little attention for the possibility of phosphorus (P) treatment. Phosphorus export in many agriculture and urban stressed watercourses however, is dominated by particulate rather than dissolved P and particulate P is potentially treatable by physical filtration. Five low cost, highly permeable media types, including woodchips, sawdust, bark mulch, corn cob chips and peastone, were tested in eight pilot scale biofilters over a six month period for their ability to remove suspended solids (TSS) and particulate P from turbid stream water. The biofilters were operated at high loading rates, with retention times averaging 1.9-4.2 h and achieved TSS removal averaging 85-97%. Excluding a 30 day startup period, seven of the eight biofilters removed an average of 53-64% of stream total P (TP) averaging 65.6 mu g/L. The corn cob media provided lower TP removal (1%) because P leached from the media. These filters provided TP removal at hydraulic loading rates that were an order of magnitude higher than when similar media is used for nitrate remediation. These low cost filter media, with capacity for high loading rates, could offer a practical solution for P removal in urban storm water ponds, sewage lagoons and agriculturally impacted water courses.

This study reports the first comprehensive data set of characteristic concentrations of four artificial sweeteners: acesulfame (ACE), sucralose (SUC), saccharin (SAC), and cyclamate (CYC), and their ratios with nutrients, for untreated septic system wastewater. Samples were collected from the tanks of 19 different septic systems from across Ontario, Canada; these had a variety of usages, from single‐family cottages to multiple‐dwelling (campground or resort) facilities and had no additional treatment systems. The artificial sweetener concentrations and their relative proportions were highly variable in some cases, both temporally for several individual tanks and from site‐to‐site. Variability tended to be lower for multiple‐dwelling compared to single‐dwelling systems. This variability likely reflects differing use of artificial sweetener‐containing products. The median concentrations for the complete data set of all four artificial sweeteners (in a range of 10 to 60 μg/L) were of a similar order of magnitude, but slightly higher, than has generally been reported for wastewater treatment plant influent (though these vary substantially globally). Both SUC and ACE provided adequate positive linear relationships for dissolved nitrogen and phosphorus in the septic tanks, while a summation of ACE and SUC concentrations also gave a strong correlation. In contrast, CYC and SAC showed poor linear correlation with these nutrients. These reported ranges for artificial sweetener concentrations and ratios with nutrients may be used in future studies to estimate the contributions of nutrients or other wastewater constituents (e.g., pharmaceuticals, bacteria, and viruses) from domestic septic systems to groundwater, including water supply or irrigation wells, and nearby surface water bodies.

Groundwater inputs of phosphorus (P) to the Laurentian Great Lakes are poorly known, but may contribute to eutrophication and algal bloom issues. This study's objective was to assess the contribution of P to Nottawasaga Bay from the surficial sand aquifer at Wasaga Beach, representing a coastal cottage area with decommissioned septic systems, and how this might change with time. The first part of the study involved site-scale groundwater sampling beside 4 provincial park public washrooms. Legacy P plumes were detected at two of these sites, with one being >30years since decommissioning. P transport calculations including sorption onto aquifer sediments indicate the majority of P plumes from the town's decommissioned septic systems have likely not yet reached the shoreline, >50years since installation, and will likely contribute P to the bay for many decades. The second part of the study consisted of broader-scale (town-wide) surveys of shallow beach groundwater. Dissolved P concentrations were ~50μg/L for background groundwater (in town and reference area), which is similar to literature values. This P may have been sourced from degrading organic matter, bird droppings, or soil-aquifer minerals. Sporadic elevated concentrations up to 420μg/L may be from legacy septic systems and/or natural sources. A rough calculation suggests groundwater P loading along Nottawasaga Bay's eastern shore (Wasaga Beach, 10-km; adjacent similar beaches, 40-km) is a few percent at most of that from the Nottawasaga River. Thus, it more likely affects localized periphyton and macrophyte growth rather than significantly affecting the Nottawasaga Bay P budget.

Woodchip filters have received attention in recent years for their ability to sustain denitrification activity across multiyear time frames. However, in some freshwater aquatic ecosystems, P rather than N is the nutrient considered most responsible for eutrophication. Previous studies have indicated that woodchip filters have limited ability to remove dissolved P, but in agricultural terrain, P export in watercourses is often dominated by particulate P (PP). Woodchip media, because of their high porosity and permeability and the surface roughness of the particles, could be effective for PP removal. In this study, we tested a woodchip filter for its ability to remove suspended sediment and associated PP at a farm in southern Ontario, Canada, where vegetable wash water with extremely high total suspended solids (TSS) was generated. The treatment system consisted of a 12.3-m concrete sedimentation tank and a slightly larger woodchip filter (16.1 m) installed in a subsurface trench. During 7 mo of full-scale operation, treating 10.8 m d, the filter system removed 71% of influent total P (TP) averaging 8.8 mg L and 99% of TSS averaging 5800 mg L, with most of the removal occurring in the tank and a lesser amount (6-16%) occurring in the woodchip filter. Almost all of the TP removal was associated with PP (91% removal) because dissolved P, averaging 1.5 mg L in the wash water, was little changed. Woodchip filters, when coupled with a solids settling tank, have the potential to provide high-capacity, low-maintenance treatment of suspended solids and associated particulate P in turbid waters.

The artificial sweetener acesulfame (ACE) is a potentially useful tracer of waste water contamination in groundwater. In this study, ACE concentrations were measured in waste water and impacted groundwater at 12 septic system sites in Ontario, Canada. All samples of septic tank effluent (n = 37) had ACE >6 µg/L, all samples of groundwater from the proximal plume zones (n = 93) had ACE >1 µg/L and, almost all samples from the distal plume zones had ACE >2 µg/L. Mean mass ratios of total inorganic nitrogen/ACE at the 12 sites ranged from 680 to 3500 for the tank and proximal plume samples. At five sites, decreasing ratio values in the distal zones indicated nitrogen attenuation. These ratios were applied to three aquifers in Canada that are nitrate-stressed and an urban stream where septic systems are present nearby to estimate the amount of waste water nitrate contamination. At the three aquifer locations that are agricultural, low ACE values (<0.02-0.15 µg/L) indicated that waste water contributed <15% of the nitrate in most samples. In groundwater discharging to the urban stream, much higher ACE values (0.2-11 µg/L) indicated that waste water was the likely source of >50% of the nitrate in most samples. This study confirms that ACE is a powerful tracer and demonstrates its use as a diagnostic tool for establishing whether waste water is a significant contributor to groundwater contamination or not.

The artificial sweetener sucralose has been in use in Canada and the US since about 2000 and in the EU since 2003, and is now ubiquitous in sanitary wastewater in many parts of the world. It persists during sewage treatment and in surface water environments and as such, has been suggested as a powerful tracer of wastewater. In this study, longer-term persistence of sucralose was examined in groundwater by undertaking a series of three sampling snapshots of a well constrained wastewater plume in Canada (Long Point septic system) over a 6-year period from 2008 to 2014. A shrinking sucralose plume in 2014, compared to earlier sampling, during this period when sucralose use was likely increasing, provides clear evidence of degradation. However, depletion of sucralose from a mean of 40 mu g/L in the proximal plume zone, occurred at a relatively slow rate over a period of several months to several years. Furthermore, examination of septic tank effluent and impacted groundwater at six other sites in Canada, revealed that sucralose was present in all samples of septic tank effluent (6-98 mu g/L, n = 32) and in all groundwater samples (0.7-77 mu g/L, n = 64). Even though sucralose degradation is noted in the Long Point plume, its ubiquitous presence in the groundwater plumes at all seven sites implies a relatively slow rate of decay in many groundwater septic plume environments. Thus, sucralose has the potential to be used as an indicator of 'recent' wastewater contamination. The presence of sucralose identifies groundwater that was recharged after 2000 in Canada and the US and after 2003 in the EU and many Asian countries. (C) 2015 Elsevier Ltd. All rights reserved.

This study evaluates the use of ground water N2O concentration and stable isotope composition for providing insights into nitrogen cycling processes in a large septic system plume in southern Ontario, Canada. An extremely large range of dissolved N2O concentrations were measured (0.4-1071 mu g N/L) that were higher than atmospheric equilibrium values of similar to 0.3 mu g N/L, demonstrating substantial N2O production in the subsurface. The highest N2O concentrations occurred around the periphery of a mid-depth zone where NO3- attenuation, elevated DOC concentration, and NO3- stable isotope ratios provided evidence that denitrification was occurring. Broad ranges in delta N-15-N2O (-45.8% to +30.6%.) and delta O-18-N2O (1-20.4 parts per thousand to +96.0 parts per thousand.) were evident. Using literature isotopic enrichment factors, which differ for N2O produced during nitrification and denitrification, and measured ranges of plume NH4+ and NO3- isotopic ratios, zones of both nitrifier-derived N2O (shallow zone) and denitrifier-N2O (mid-depth and deeper zones) could be identified. Time series sampling showed that nitrifier N2O was present early in the summer season (June) but then denitrifier N2O was more dominant later in the season. In a mid-depth NO3- depleted zone, the production of denitrifier-N2O was evident early in the season when N-15 and O-18 enrichment of NO3- was not sufficiently advanced to be indicative of denitrification, although delta N-15 and delta O-18 values of NO3- increased later in the season. The analysis of N2O concentrations and stable isotopic composition, in conjunction with conventional chemical analyses, provides insights into N-cycling processes in the Long Point ground water septic plume. However, large ranges in the isotopic composition of N2O produced by nitrifiers and denitrifiers meant that delta N-15 and delta O-18 analysis of ground water N2O provided qualitative, rather than quantitative, information on denitrifier versus nitrifier production of N2O at this site. Crown Copyright (C) 2014 Published by Elsevier B.V. All rights reserved.

Monitoring of a well-defined septic system groundwater plume and groundwater discharging to two urban streams located in southern Ontario, Canada, provided evidence of natural attenuation of background low level (ng/L) perchlorate (ClO4-) under denitrifying conditions in the field. The septic system site at Long Point contains ClO4- from a mix of waste water, atmospheric deposition, and periodic use of fireworks, while the nitrate plume indicates active denitrification. Plume nitrate (NO3(-)-N) concentrations of up to 103 mg/L declined with depth and downgradient of the tile bed due to denitrification and anammox activity, and the plume was almost completely denitrified beyond 35m from the tile bed. The ClO4- natural attenuation occurs at the site only when NO3(-)-N concentrations are <0.3mg/L, after which ClO4- concentrations decline abruptly from 187 +/- 202 to 11 +/- 15 ng/L. A similar pattern between NO3(-)-N and ClO4- was found in groundwater discharging to the two urban streams. These findings suggest that natural attenuation (i.e., biodegradation) of ClO4- may be commonplace in denitrified aquifers with appropriate electron donors present, and thus, should be considered as a remediation option for ClO4- contaminated groundwater.

Groundwater contamination from constituents such as NO3- often occurs where multiple sources are present making source identification difficult. This study examines a suite of major ions and trace organic constituents within a well defined septic system plume in southern Ontario, Canada (Long Point site) for their potential use as wastewater tracers. The septic system has been operating for 20 years servicing a large, seasonal-use campground and tritium/helium age dating indicates that the 200 m long monitored section of the plume is about 15 years old. Four parameters are elevated along the entire length of the plume as follows; the mean electrical conductivity value (EC) in the distal plume zone is 926 mu S/cm which is 74% of the mean value below the tile bed, Na+ (14.7 mg/L) is 43%, an artificial sweetener, acesulfame (12.1 mu g/L) is 23% and Cl- (71.5 mg/L) is 137%. EC and Cl- appear to be affected by dispersive dilution with overlying background groundwater that has lower EC but has locally higher Cl- as result of the use of a dust suppressant (CaCl2) in the campground. Na+, in addition to advective dilution, could be depleted by weak adsorption. Acesulfame, in addition to the above processes could be influenced by increasing consumer use in recent years. Nonetheless, both Na+ and acesulfame remain elevated throughout the plume by factors of more than 100 and 1000 respectively compared to background levels, and are strong indicators of wastewater impact at this site. EC and Cl- are less useful because their contrast with background values is much less (EC) or because other sources are present (Cl-). Nutrients (NO3-, NH4+,PO43-, K+) and pathogens (Escherichia coli) do not persist in the distal plume zone and are less useful as wastewater indicators here. The artificial sweetener, acesulfame, has persisted at high concentrations in the Long Point plume for at least 15 years (and this timing agrees with tritium/helium-3 dating) and this compound likely occurs at uniquely high concentrations in domestic wastewater. As such, it holds considerable promise as a powerful new tracer of wastewater impact in groundwater. (C) 2012 Elsevier B.V. All rights reserved.