Nitrogen and Phosphorus Treatment Can Be Sustainable During on-Site Wastewater Disposal.

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.

Nitrogen Attenuation in Septic System Plumes.

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.

Use of mature willows (Salix nigra) for hydraulic control of landfill-impacted groundwater in a temperate climate.

Phreatophytic trees such as willows and poplars have a large capacity for extracting shallow groundwater, as evidenced by diurnal water table fluctuations corresponding to intensified transpiration during the day. As a result, they have been employed for phytoremediation of shallow contaminated groundwater. In this study, the water extraction (i.e. pumping) capacity of mature willows (Salix nigra) to capture shallow polluted groundwater in Belle Park, the site of a former landfill in Kingston, Ontario (Canada), was assessed using continuous field measurements of sap flow and water table levels associated with a single willow tree, combined with a transient numerical model (FEFLOW). On an annual basis, the sapflow averaged 2.3 m3d-1, with 70% of the cumulative sap flow occurring during the active growing season (May to September). The calibration showed a good fit (0.91 < R2<0.97) between measured groundwater levels from three shallow wells installed near the willow and the calculated water table level fluctuations, thus confirming that the water extraction rate based on sap flow data for the willow was appropriate. At stand level, additional modelling suggests that 3.4-4.7 ha of mature willows (i.e. between 7.8% and 10.6% of the Park area), could compensate for the current water volumes extracted by the municipality using a conventional pump and treat system. The results of this study indicate that willows can play a significant role in capturing contaminated groundwater underlying Belle Park, and potentially at other sites where removal of contaminants from shallow aquifers is desired.

Variable persistence of artificial sweeteners during wastewater treatment: Implications for future use as tracers.

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.

Environmental fluxes of perchlorate in rural catchments, Ontario, Canada.

Quantitative information about fluxes of perchlorate in the environment is lacking. This study reports analyses of perchlorate in various environmental waters sampled from rural headwater catchments in the Thames River basin in southern Ontario (Canada) that provide evidence about the fluxes and fate of perchlorate in the environment. Concentrations in streams (16 to 1047 ng/L) were used to estimate exports from these rural catchments (228-1843 mg/(ha·year)), atmospheric deposition (1480 ± 230 mg/(ha·year)), as well as variable rates of microbial degradation of perchlorate, which appeared to be enhanced in catchments with higher percentages of wetlands. Groundwater data supported earlier evidence that degradation of perchlorate occurs in the subsurface under oxygen-depleted conditions. The stream data suggest that the rate of degradation varies strongly between catchments and ranges up to >1000 mg/(ha·year).

Detections of alkyl-phenoxy-benzenesulfonates in municipal wastewater.

This study presents the first reported detections and concentrations of alkyl phenoxy-benzenesulfonate surfactants (APBS) in municipal wastewater. A semi quantitative direct injection LC/MS/MS method was developed. Samples of raw influent and final effluent were obtained from fourteen municipal wastewater treatment plants (WWTPs) at various locations in Canada and were analyzed for APBS, including five homologues of monoalkyldiphenylether disulfonates (MADS) and one monoalkyldiphenylether sulfonate (MAMS) homologue. APBS were detected in all 42 of the wastewater raw influent samples and in 37 of the 42 wastewater final effluent samples; the other 5 final effluent samples had trace levels below the minimum detection limit. In the samples of raw influent from the fourteen municipal treatment plants, the dissolved concentrations of APBS (total) ranged from 0.9 to 13.6 µg/L. In samples of final effluent from the same plants the total APBS ranged from below detection to 4 µg/L. The APBS were more resistant to loss during wastewater treatment compared to previous studies of linear alkylbenzene sulfonates in wastewaters. The most effective wastewater treatments for removal of APBS were those that involved either secondary treatment with aeration or advanced treatment including biological nutrient removal. Available information on ecotoxicity is lacking for evaluating the impacts of APBS surfactants when released to the environment.

Review of phosphorus attenuation in groundwater plumes from 24 septic systems.

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 P at 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.

Glyphosate residues in rural groundwater, Nottawasaga River Watershed, Ontario, Canada.

BACKGROUND: The objective of this study was to investigate the occurrence of glyphosate residues (glyphosate and its metabolite AMPA) in shallow groundwater in a catchment dominated by agriculture, and to examine the potential for this groundwater to store and transmit these compounds to surface waters. RESULTS: Glyphosate residues were found in some of the groundwater samples collected in riparian (surface seeps), upland (mostly <20 m below ground) and wetland settings (<3 m below ground). Overall, glyphosate and AMPA were detected in 10.5 and 5.0%, respectively, of the groundwater samples analyzed as part of this study. All concentrations of glyphosate were well below Canadian guidelines for drinking water quality and for protection of aquatic life. Seasonal differences in concentrations in riparian seeps were possibly related to cycles of weather, herbicide application and degradation of glyphosate. Highest concentrations were at upland sites (663 ng L(-1) of glyphosate, 698 ng L(-1) of AMPA), apparently related to localized applications. Most glyphosate detections in wetlands were >0.5 km distant from possible areas of application, and, combined with other factors, suggest an atmospheric transport and deposition delivery mechanism. In both upland and wetland settings, highest glyphosate concentrations were sometimes not at the shallowest depths, indicating influence of hydrological factors. CONCLUSION: The glyphosate/AMPA detections in riparian seeps demonstrated that these compounds are persistent enough to allow groundwater to store and transmit glyphosate residues to surface waters. Detections in the wetlands support earlier evidence that atmospheric transport and deposition may lead to glyphosate contamination of environments not intended as targets of applications. This interpretation is further supported by detections of both glyphosate and AMPA in precipitation samples collected in the same watershed. © 2016 Her Majesty the Queen in Right of Canada Pest Management Science © 2016 Society of Chemical Industry.

Natural attenuation of perchlorate in denitrified groundwater.

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 35 m from the tile bed. The ClO4⁻ natural attenuation occurs at the site only when NO3⁻ -N concentrations are <0.3 mg/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.

Artificial sweeteners as potential tracers of municipal landfill leachate.

Artificial sweeteners are gaining acceptance as tracers of human wastewater in the environment. The 3 artificial sweeteners analyzed in this study were detected in leachate or leachate-impacted groundwater at levels comparable to those of untreated wastewater at 14 of 15 municipal landfill sites tested, including several closed for >50 years. Saccharin was the dominant sweetener in old (pre-1990) landfills, while newer landfills were dominated by saccharin and acesulfame (introduced 2 decades ago; dominant in wastewater). Cyclamate was also detected, but less frequently. A case study at one site illustrates the use of artificial sweeteners to identify a landfill-impacted groundwater plume discharging to a stream. The study results suggest that artificial sweeteners can be useful tracers for current and legacy landfill contamination, with relative abundances of the sweeteners potentially providing diagnostic ability to distinguish different landfills or landfill cells, including crude age-dating, and to distinguish landfill and wastewater sources.

Sulfur analyses as tracers of microbial degradation of hydrocarbons in the capillary fringe.

Analyses of solid-phase sulfur species in soil cores indicate the role of sulfur redox cycling in the fate of a BTEX-rich natural gas condensate plume in a silt-clay aquitard at a gas well site in Alberta, Canada. These analyses confirmed that sulfate reduction has been a key anaerobic electron-accepting process in the plume. The observed concentrations (microg/g sediment) of the reduced solid-phase sulfur components provided evidence regarding the quantity of sulfate that has been reduced over time, and the extent of hydrocarbon plume degradation. The spatial distribution of these phases indicates that degradation of petroleum hydrocarbons linked to sulfate reduction was focused in the capillary fringe, where sulfides and elemental sulfur were the main inorganic sulfur species produced as a result of sulfate reduction.

Microbial reduction of sulfate injected to gas condensate plumes in cold groundwater.

Despite a rapid expansion over the past decade in the reliance on intrinsic bioremediation to remediate petroleum hydrocarbon plumes in groundwater, significant research gaps remain. Although it has been demonstrated that bacterial sulfate reduction can be a key electron accepting process in many petroleum plumes, little is known about the rate of this reduction process in plumes derived from crude oil and gas condensates at cold-climate sites (mean temperature <10 degrees C), and in complex hydrogeological settings such as silt/clay aquitards. In this field study, sulfate was injected into groundwater contaminated by gas condensate plumes at two petroleum sites in Alberta, Canada to enhance in-situ bioremediation. In both cases the groundwater near the water table had low temperature (6-9 degrees C). Monitoring data had provided strong evidence that bacterial sulfate reduction was a key terminal electron accepting process (TEAP) in the natural attenuation of dissolved hydrocarbons at these sites. At each site, water with approximately 2000 mg/L sulfate and a bromide tracer was injected into a low-sulfate zone within a condensate-contaminant plume. Monitoring data collected over several months yielded conservative estimates for sulfate reduction rates based on zero-order kinetics (4-6 mg/L per day) or first-order kinetics (0.003 and 0.01 day(-1)). These results favor the applicability of in-situ bioremediation techniques in this region, under natural conditions or with enhancement via sulfate injection.