It's often too easy to assign a "safe" setback distance from a source of contamination when considering the installation of a new drinking water source. In B.C., that setback is set forth in the Sewerage System Regulation, and states that an onsite sewerage system can't be installed closer than 30m from a drinking water supply (unless a hydrogeologist is willing to say that there's no risk to reducing it). This distance of 30m, or 100', is fairly common: it's also used by Maine, Massachusetts, California, etc. In a province as diverse and large as B.C., however, this singular measure does not take into account the soil and climate differences that might prevent wastewater from being adequately treated before it makes it to somebody's tap.
After a Norovirus outbreak in Iceland, which was traced back to contaminated drinking water, a group of researchers set out to identify whether there were some considerations for setback distances that weren't being accounted for. The outbreak in question occurred in late summer at a location frequented by tourists and those who owned summer property, with the drinking water being drawn from a well. Due to a few different factors, which will be discussed further on, the minimum setback required for a 9-log reduction in viral load was nearly 900m. That's 30x the setback in the B.C. legislation!
According to this specific study, approximately 1/3 of waterborne outbreaks in affluent nations are due to sewage contamination of groundwater. We assume that a combination of deep drilled wells and relatively slow-moving soils will allow for adequate filtration of the waste water to ensure the effluent entering the aquifer is treated. However, what this doesn't account for are the aspects of soil chemistry that can affect the filtration rate. For instance, viruses travel longer distances in cold groundwater. The groundwater in the Iceland study was around 5'C, which can lead to an inactivation rate for viruses of 1 order of magnitude lower than ground water at 25'C. The researchers point out that not many studies have focused on the relationship between groundwater temperature and viral inactivation.
To properly identify a safe distance between a sewerage system and a well, it's important to consider more than just soil grain size. It's also necessary to look at groundwater temperature, seepage velocity, and soil acidity to determine how long it will take to adequately neutralize the wastewater. The researchers suggest that looking at travel times (e.g. 50 days) may be more reasonable than simply looking at setback distances.
I mentioned above that a 9-log reduction in viral load would've required a setback of 900m in this specific case study. While B.C. legislation has no requirements for reduction of viruses, the Guidelines for Canadian Drinking Water Quality speak to a minimum 4-log reduction of viruses in treatment systems. Since most groundwater systems don't have subsequent treatment (because of their inherent safety), one could attribute a 4-log reduction in soil to being adequate as well. Given all the various parameters that must be considered to determine viral inactivation, it's nearly impossible to say "this setback distance throughout B.C. will lead to a 4-log reduction in viruses".
The summary of this study was that a) the setback distance between the well and the hotel's septic system was inadequate to provide safe drinking water, and that subsequent treatment was necessary, and b) that a lot more research needs to be done to determine how various soil chemistry factors affect wastewater treatment in vivo. Simply saying "it's 30m away, so it's safe" isn't an adequate means of protecting public health, without considering what happens in those 30m.
Source: Gunnarsdottir, M.J., Gardarsson, S.M., & Andradottir, H.O. (2013). Microbial contamination in groundwater supply in a cold climate and coarse soil: case study of Norovirus outbreak at Lake Mÿvatn, Iceland. Hydrology Research, 44(6), 1114-1128.
Showing posts with label sewage. Show all posts
Showing posts with label sewage. Show all posts
4.25.2014
3.24.2014
Effects of wastewater on small streams
If there's one thing that interests me, it's the intersection between ecology and human health. There's a fascinating link between our interactions with the world in which we live, and public health outcomes. In the most straightforward sense, these interactions manifest themselves in things like drinking water quality and outdoor air quality. But there can also be considerations for things like freshwater ecology and wildlife health. Environmental health often looks at how changes to the environment can affect public health, but rarely look at how public activities can affect the environment (mostly because it's out of scope).
There's value to looking at ecology and environmental indicators without thinking directly about public health, however. In the early part of the millennium, 80% of creeks surveyed in the USA were found to be contaminated with "environmentally relevant" concentrations of compounds that were indicative of sewage contamination; I would suspect the number to be similarly high in semi-populated areas of Canada (either those within proximity to large communities, or those within proximity to a large number of onsite wastewater systems). Our sewage treatment systems are still designed to remove (mostly) contaminants of biological concern, and are unable to adequately remove contaminants of emerging concern, such as pharmaceuticals and "hormonally active compounds". While the long-term risk of these compounds to human health is relatively unknown, there is certainly an environmental impact to them making their way into lakes and streams.
A study by the North Carolina Water Science Center looked at water quality in a number of small, freshwater streams to determine how effective on-site and centralized wastewater treatment methods are, and to identify potential new indicators for sewage contamination. They looked at a number of sites, and ensured they had representative samples from areas served by municipal wastewater systems and onsite systems, and a control with no houses nearby. Using GC/MS, they looked for a total of 33 pharmaceutical compounds (in addition to normal fecal coliform analysis) to identify sewage contamination of the freshwater streams.
In general, and somewhat surprisingly, the researchers found that "properly functioning onsite wastewater" systems really had no effect on the water quality in freshwater streams. The "properly functioning" part is important, since one of the sites they looked at (which showed "effects of wastewater") was close to a "suspected" sewer line leak. Though they found that some compounds were prevalent in higher concentrations in the sites serviced by onsite wastewater, the site with the lowest concentration was actually one serviced by an onsite system.
Given the small sample size (just 7 sites) , and the relative lack of information provided on what specific "onsite" treatment methods were being utilized, I'm not sure I'd be willing to take this data to the Ministry of Environment as proof that there's no risk to freshwater streams from nearby sewerage systems. However, it is nevertheless interesting that the onsite systems were found to be equally as effective at treating wastewater as the larger, centralized systems. From experience, I know how difficult it is to link stream contamination with a specific sewerage system or event. Unless there's only one in the area, there's always a factor of doubt in your head that any contaminants you find are actually due to some other system. True background data or control sites are exceedingly difficult to find and match to your sample sites, but the researchers here did a decent job of identifying a freshwater stream with a low chance of being impacted by sewage.
Personally, I think that one of the most interesting things that came out of this research was the identification of a potential indicator for wastewater contamination. The researchers state that "optical brighteners" were strongly correlated with the presence of wastewater, and therefore have value in identifying sources of contamination. These are the compounds that you find in your laundry detergent that make your "whites whiter" (and aren't bleach). They're relatively inexpensive to test for, since they fluoresce at a specific wavelength, and could provide a quick and dirty methodology for "yes/no" contamination data. However, it's worth pointing out that other (naturally occurring) compounds fluoresce at the same wavelength, so one wouldn't want to hinge a court case on the presence of optical brighteners identified through fluorescence, unless one first removed any source of that background organic material.
While research like this isn't going to cause a sea change in the way we identify contamination from sewerage, every study helps to change the way we view the interactions between our waste disposal and our environment. It's clear that simply looking at coliform bacteria is no longer an adequate means of assessing whether our wastewater treatment is effective; we must recognize that there are new contaminants in our wastewater, and identifying their prevalence is the first step to determining how to remove them.
Ferrell, G.M., & Grimes, B.H. (2014). Effects of centralized and onsite wastewater treatment on the occurrence of traditional and emerging contaminants in streams. Journal of Environmental Health, 76(6), 18-27.
3.06.2014
How deep does the E. coli go?
The B.C. Sewerage System Regulation (B.C. Reg. 326/2004) restricts individuals from placing sewerage systems within 30m from a well supplying a domestic water system, unless a "professional" provides written confirmation that doing so would not cause a health hazard. While setting a minimum setback level gives sewage practitioners and homeowners a baseline for ensuring the safety of their water supply (and that of their neighbors), it doesn't take into account the multitude of factors that can limit or extend the transport of disease-causing bacteria from a sewage system to a water system.
While "professionals" (essentially engineers) can reduce this setback distance, it's not clear how much research and information gathering goes into doing so. In my experience, professionals will provide support for a reduced setback because of secondary or tertiary treatment methods, or because they've looked at the soils and feel that lateral transport is going to be minimal. A study in last month's issue of the Journal of Environmental Health looked at the ability of E. coli to move through sandy loam soil (specifically that from North Carolina) to a water table in situ. They looked at 30cm, 45cm, and 60cm vertical separation between ground level and the water table, and took samples daily to identify whether those individual soil separation distances were sufficient to reduce the load of E. coli prior to the effluent coming into contact with the water.
Using a 64% sand / 30% silt / 6% clay mixture of soil (that was obtained in the field by the researchers), the researchers applied 200mL of an artificial wastewater solution to each soil column daily. The artificial wastewater (which contained nutrients like potassium, sodium, and phosphate) was spiked with E. coli that was obtained from human urine. With this application, they found that 30cm and 45cm of vertical separation were inadequate to mitigate the bacterial content to acceptable levels, with 45cm reducing the levels somewhat, but not below the recommended standard of 200cfm/100mL. 60cm of vertical separation, on the other hand, was found to be most efficient at removing E. coli to levels where the water table would not be adversely affected.
While this research was done with a specific soil type, and did not include extenuating factors that could impact the amount of bacteria that was able to move through the soil, it does provide some great data on what sort of vertical separation is required when designing onsite sewerage systems. It's the type of relatively low-cost research that should be done more often by both regulators and practitioners to ensure that the best sewerage systems (and those that are most cost effective) are being installed in areas that are potentially sensitive. When "professionals" (as defined in the Regulation) are determining whether or not to reduce the minimum setback to a well, this is the type of data that should be consulted prior to making that determination. One can use mathematical models to determine rates of flow, but they might not adequately determine the actual decrease in bacterial concentrations. Having actual in situ research that shows how wastewater moves through a specific soil composition, and how effective it is at reducing bacteria, would give professionals the confidence to reduce minimum setbacks without putting themselves at any professional liability risk.
Source: Amoozegar, A., Graves, A., Lindbo, D., Rashash, D., & Stall, C. (2014). Transport of E. coli in a sandy soil as impacted by depth to water table. Journal of Environmental Health, 76(6), 92-100.
While "professionals" (essentially engineers) can reduce this setback distance, it's not clear how much research and information gathering goes into doing so. In my experience, professionals will provide support for a reduced setback because of secondary or tertiary treatment methods, or because they've looked at the soils and feel that lateral transport is going to be minimal. A study in last month's issue of the Journal of Environmental Health looked at the ability of E. coli to move through sandy loam soil (specifically that from North Carolina) to a water table in situ. They looked at 30cm, 45cm, and 60cm vertical separation between ground level and the water table, and took samples daily to identify whether those individual soil separation distances were sufficient to reduce the load of E. coli prior to the effluent coming into contact with the water.
Using a 64% sand / 30% silt / 6% clay mixture of soil (that was obtained in the field by the researchers), the researchers applied 200mL of an artificial wastewater solution to each soil column daily. The artificial wastewater (which contained nutrients like potassium, sodium, and phosphate) was spiked with E. coli that was obtained from human urine. With this application, they found that 30cm and 45cm of vertical separation were inadequate to mitigate the bacterial content to acceptable levels, with 45cm reducing the levels somewhat, but not below the recommended standard of 200cfm/100mL. 60cm of vertical separation, on the other hand, was found to be most efficient at removing E. coli to levels where the water table would not be adversely affected.
While this research was done with a specific soil type, and did not include extenuating factors that could impact the amount of bacteria that was able to move through the soil, it does provide some great data on what sort of vertical separation is required when designing onsite sewerage systems. It's the type of relatively low-cost research that should be done more often by both regulators and practitioners to ensure that the best sewerage systems (and those that are most cost effective) are being installed in areas that are potentially sensitive. When "professionals" (as defined in the Regulation) are determining whether or not to reduce the minimum setback to a well, this is the type of data that should be consulted prior to making that determination. One can use mathematical models to determine rates of flow, but they might not adequately determine the actual decrease in bacterial concentrations. Having actual in situ research that shows how wastewater moves through a specific soil composition, and how effective it is at reducing bacteria, would give professionals the confidence to reduce minimum setbacks without putting themselves at any professional liability risk.
Source: Amoozegar, A., Graves, A., Lindbo, D., Rashash, D., & Stall, C. (2014). Transport of E. coli in a sandy soil as impacted by depth to water table. Journal of Environmental Health, 76(6), 92-100.
3.03.2014
Don't flush your drugs down the toilet, please
It's fairly common knowledge that prescription medication is becoming a concern in wastewater treatment (both municipal, and on-site). The systems that are in place to treat bacteria that is common in sewage aren't set up to deal with the other metabolites that tend to make their way into wastewater. This is increasingly leading to concerns with effluent making its way into drinking water supplies (both ground water, and surface water).
What is studied less often is the impact that illicit drugs have on the quality of wastewater effluent, and how they might affect drinking water quality. These compounds in sewage effluent and influent have the ability to not only impact on public health, but also to impact on the environment. As a biologist, I can only imagine the impact that cocaine and methamphetamine would have on fish and frogs who come into contact with the contaminated water supplies!
A group of French scientists decided to look at illicit drugs in a number of sewage treatment plants to determine how efficient the systems were at reducing the levels of the drugs and their metabolites, and also to identify patterns of illicit drug use in the country. Though the patterns of drug use are certainly of public health interest, they're not really of environmental health interest (although the data could help to identify areas where better sewage treatment would be best placed). The efficacy of "normal" sewage treatment plants at removing illicit drugs from wastewater, however, is of great interest.
The scientists looked at 17 different illicit drugs and their metabolites, including cocaine, methamphetamine, opiates, and cannabis. The indicator for cannabis (THC-COOH) was found in every single influent the researchers looked at. They found morphine, major metabolites of cocaine, and methadone and its metabolites in 75% of influents, but found methamphetamine and amphetamine, heroin and its metabolites, and minor metabolites of cocaine in less than 10% of influents. The study goes on to further discuss what compounds were found in influent/effluent, and in what amounts, and how this can be related to patterns of drug usage throughout France, but as mentioned above, the environmental health concern is more about how efficient the sewage treatment plants are in removing the drug compounds.
While THC-COOH was found in all of the influent samples, it was also noted to be the easiest of the illicit drugs to remove, regardless of sewage treatment plant technology. Methadone and its metabolite EDDP, on the other hand, appeared to be very difficult to remove from the wastewater. Falling somewhere in between were cocaine and its metabolites, and morphine. Based on the data, it appeared as though low-load activated sludge was more effective at removing the drug compounds than medium-load activated sludge or biofilters (likely due to the longer retention time associated with low-load activated sludge).
The results of the study should be of interest to public health practitioners, and to those involved with making decisions surrounding wastewater treatment. Treatment methods that are common in municipal sewage treatment plants just aren't effective for a large number of illicit drugs and their metabolites. Performing similar "sewage epidemiology" studies in specific geographic regions would allow local governments to identify the compounds of concern in their specific area, and work on identifying treatment methods that may be somewhat more successful than activated sludge. From a terrestrial biology perspective, working together with public health practitioners could lead to a mutually beneficial outcome: reduction of illicit drug metabolites in sewage effluent will lead to safer drinking water, and safer habitats for aquatic and terrestrial animals alike.
Source: Nefau, T., Karolak, S., Castillo, L., Boireau, V., & Levi, Y. (2013). Presence of illicit drugs and metabolites in influents and effluents of 25 sewage water treatment plants and map of drug consumption in France. Science of the Total Environment, 461-462, p.712-722.
What is studied less often is the impact that illicit drugs have on the quality of wastewater effluent, and how they might affect drinking water quality. These compounds in sewage effluent and influent have the ability to not only impact on public health, but also to impact on the environment. As a biologist, I can only imagine the impact that cocaine and methamphetamine would have on fish and frogs who come into contact with the contaminated water supplies!
A group of French scientists decided to look at illicit drugs in a number of sewage treatment plants to determine how efficient the systems were at reducing the levels of the drugs and their metabolites, and also to identify patterns of illicit drug use in the country. Though the patterns of drug use are certainly of public health interest, they're not really of environmental health interest (although the data could help to identify areas where better sewage treatment would be best placed). The efficacy of "normal" sewage treatment plants at removing illicit drugs from wastewater, however, is of great interest.
The scientists looked at 17 different illicit drugs and their metabolites, including cocaine, methamphetamine, opiates, and cannabis. The indicator for cannabis (THC-COOH) was found in every single influent the researchers looked at. They found morphine, major metabolites of cocaine, and methadone and its metabolites in 75% of influents, but found methamphetamine and amphetamine, heroin and its metabolites, and minor metabolites of cocaine in less than 10% of influents. The study goes on to further discuss what compounds were found in influent/effluent, and in what amounts, and how this can be related to patterns of drug usage throughout France, but as mentioned above, the environmental health concern is more about how efficient the sewage treatment plants are in removing the drug compounds.
While THC-COOH was found in all of the influent samples, it was also noted to be the easiest of the illicit drugs to remove, regardless of sewage treatment plant technology. Methadone and its metabolite EDDP, on the other hand, appeared to be very difficult to remove from the wastewater. Falling somewhere in between were cocaine and its metabolites, and morphine. Based on the data, it appeared as though low-load activated sludge was more effective at removing the drug compounds than medium-load activated sludge or biofilters (likely due to the longer retention time associated with low-load activated sludge).
The results of the study should be of interest to public health practitioners, and to those involved with making decisions surrounding wastewater treatment. Treatment methods that are common in municipal sewage treatment plants just aren't effective for a large number of illicit drugs and their metabolites. Performing similar "sewage epidemiology" studies in specific geographic regions would allow local governments to identify the compounds of concern in their specific area, and work on identifying treatment methods that may be somewhat more successful than activated sludge. From a terrestrial biology perspective, working together with public health practitioners could lead to a mutually beneficial outcome: reduction of illicit drug metabolites in sewage effluent will lead to safer drinking water, and safer habitats for aquatic and terrestrial animals alike.
Source: Nefau, T., Karolak, S., Castillo, L., Boireau, V., & Levi, Y. (2013). Presence of illicit drugs and metabolites in influents and effluents of 25 sewage water treatment plants and map of drug consumption in France. Science of the Total Environment, 461-462, p.712-722.
2.27.2014
Can an inappropriate septic setback affect more than just your health?
Regardless of what your level of education is, you likely know that if your septic system isn't far enough away from your drinking water / house / swimming pool / driveway, you're going to have a bad time. There are other factors to take into consideration, of course, like soil composition, pre-discharge sewage treatment, and potential break-out areas, but in general you want to keep your septic system far away from the rest of your life.
There are certain geographic areas where a traditional on-site sewerage system just isn't going to be feasible because of high water tables, or poor soils, or just small lot sizes. In B.C., the Sewerage System Regulation is fairly outcome based: maintain a 30m setback from a well, hire an "authorized person" to do the work, and you'll be just fine. It's up to the professional expertise of the authorized person to determine appropriate setbacks and siting for the sewage systems. If you're in one of these tough geographic areas, your course of action is typically a) hire an engineer to design you a treatment plant that treats the effluent before it goes into the soil, or b) find an Onsite Wastewater Practitioner who's willing to fudge some data to get your system in the ground.
Apparently, there are considerations besides just public health when you're looking to place your septic system in a less-than-ideal location. In Ohio, only 6.4% of soils have the requisite 4' vertical separation to allow for traditional tank-and-field on-site sewerage systems. As mentioned above, there are alternatives to traditional systems, but those typically cost a fair bit more money and require some professional input (which also doesn't come cheap). A recent study has shown that costs associated with inadequate sewerage systems can include repair costs, human health costs, increased system maintenance costs, and a "loss of property valuation".
The study looked 800 on-site sewerage systems (out of a possible 22000 in Licking County, OH), of which 616 used traditional tank-and-field systems. They only looked at those for which appropriate soils data was available, leaving them with a sample size of 549 properties for the study. Using the hedonic pricing method, which "uses the different characteristics of a traded good, such as real estate, to estimate the value of a non-traded good, such as water or soil quality", the researchers were able to identify the effect that a well-functioning septic system had on property values in the county.
The researchers looked at a number of variables that could have an effect on property value (property size, number of bedrooms, etc.), but their specific hypothesis was looking at the quality of soils with regard to sewage disposal. They found that a property with soils suitable for a traditional leach field system were worth $14,062 more than a comparable property with soils unsuitable for an onsite sewerage system. Properties with soils suitable for a mound system were worth $12,897 more. This correlated to a difference of 6.8% and 6.2%, respectively. Interestingly, these price differences were actually higher than the cost in Ohio of installing a drip irrigation or mound system.
While the research outcome does a fantastic job of tying economic benefits in with good soil profiles, it's worth noting that the median value of a housing unit in the county of study was $110,700. As of January, 2014, the median value of a housing unit in the North Okanagan (where I live) is $238,750, or 2.2x higher. It would be valuable to look at similar statistics in places with higher housing costs (where onsite sewerage is prevalent, unlike Metro Vancouver) to see if similar correlations between quality soils and housing values could be found.
Source: Vedachalam, S., Hitzhusen, F.J., & Mancl, K.M. (2013) Economic analysis of poorly sited septic systems: a hedonic pricing approach. Journal of Environmental Planning and Management, 56(3), 329-344.
There are certain geographic areas where a traditional on-site sewerage system just isn't going to be feasible because of high water tables, or poor soils, or just small lot sizes. In B.C., the Sewerage System Regulation is fairly outcome based: maintain a 30m setback from a well, hire an "authorized person" to do the work, and you'll be just fine. It's up to the professional expertise of the authorized person to determine appropriate setbacks and siting for the sewage systems. If you're in one of these tough geographic areas, your course of action is typically a) hire an engineer to design you a treatment plant that treats the effluent before it goes into the soil, or b) find an Onsite Wastewater Practitioner who's willing to fudge some data to get your system in the ground.
Apparently, there are considerations besides just public health when you're looking to place your septic system in a less-than-ideal location. In Ohio, only 6.4% of soils have the requisite 4' vertical separation to allow for traditional tank-and-field on-site sewerage systems. As mentioned above, there are alternatives to traditional systems, but those typically cost a fair bit more money and require some professional input (which also doesn't come cheap). A recent study has shown that costs associated with inadequate sewerage systems can include repair costs, human health costs, increased system maintenance costs, and a "loss of property valuation".
The study looked 800 on-site sewerage systems (out of a possible 22000 in Licking County, OH), of which 616 used traditional tank-and-field systems. They only looked at those for which appropriate soils data was available, leaving them with a sample size of 549 properties for the study. Using the hedonic pricing method, which "uses the different characteristics of a traded good, such as real estate, to estimate the value of a non-traded good, such as water or soil quality", the researchers were able to identify the effect that a well-functioning septic system had on property values in the county.
The researchers looked at a number of variables that could have an effect on property value (property size, number of bedrooms, etc.), but their specific hypothesis was looking at the quality of soils with regard to sewage disposal. They found that a property with soils suitable for a traditional leach field system were worth $14,062 more than a comparable property with soils unsuitable for an onsite sewerage system. Properties with soils suitable for a mound system were worth $12,897 more. This correlated to a difference of 6.8% and 6.2%, respectively. Interestingly, these price differences were actually higher than the cost in Ohio of installing a drip irrigation or mound system.
While the research outcome does a fantastic job of tying economic benefits in with good soil profiles, it's worth noting that the median value of a housing unit in the county of study was $110,700. As of January, 2014, the median value of a housing unit in the North Okanagan (where I live) is $238,750, or 2.2x higher. It would be valuable to look at similar statistics in places with higher housing costs (where onsite sewerage is prevalent, unlike Metro Vancouver) to see if similar correlations between quality soils and housing values could be found.
Source: Vedachalam, S., Hitzhusen, F.J., & Mancl, K.M. (2013) Economic analysis of poorly sited septic systems: a hedonic pricing approach. Journal of Environmental Planning and Management, 56(3), 329-344.
Are there better methods for identifying sewage than coliforms?
Typically when health or environment officials are looking for confirmation of sewage contamination of a water source, they'll go with indicator organisms as evidence. By sampling the water and looking for fecal coliforms, you can tell whether it has been contaminated by bacteria that typically reside in the gut of warm-blooded animals. There's also fluorescein dye if you're looking to confirm that sewage isn't staying in the ground, but that's only effective if the septic failure leads to wastewater being discharged to the ground surface. In other words, if the sewage is making its way into an aquifer, you're not going to see the dye.
There are a couple of problems with fecal coliforms as indicator organisms: they're not necessarily confirmation of human sewage (i.e. just confirmation of some sort of fecal contamination) and they're not overly persistent in the soil. If you're just trying to tell a water system operator that they've got some contamination issues and need to issue a public notification, they work just fine. But if you're looking to confirm that some actual sewage is getting into the water, you're going to have a hard time in front of a judge.
Researchers from Ontario looked at a wastewater plume from a septic field serving a campground that had been in existence for around 20 years (which, incidentally, is about the life span of the average on-site sewerage system), and note that typical indicators of contamination (besides coliforms) are not necessarily unique to sewage, and therefore don't make the best indicators. Chemical compounds that are unique (ibuprofen, pseudoestrogens, carbamazapine) haven't been studied enough to give a clear indication of how long they persist in the environment. They suggest that artificial sweeteners might have value as a wastewater indicator, since they're unique to human waste, resistant to breakdown in normal sewage treatment, and persist in groundwater.
By setting up a number of piezometers and trace gas sampling points along the wastewater plume from the campground, the researchers were able to not only sample the groundwater for the contaminants of interest, but were also able to perform tritium/helium age dating to identify the age of the wastewater plume. Unsurprisingly, their study showed that once you got about 50m away from the sewage dispersal field area, nutrients and pathogens normally found in sewage were reduced to non-detectable levels. Of the sweeteners tested for persistence, they found that cyclamate and sacharrin appeared to degrade quite effectively, while acesulfame and sucralose concentrations remained relatively constant regardless of distance from the septic tank.
Since the acesulfame was detected in levels nearly 1000x higher than background concentrations in the wastewater plume, and degradation didn't occur over approximately 20 years of sewage system use, it presents itself as a potentially viable indicator for wastewater contamination. Apparently, acesulfame is also added to some animal feed, so it could be used as an indicator of groundwater contamination from manure spreading as well.
There's still some further work to be done, since this is just one study of one onsite sewerage system. However, it shows great potential for a new way of determining whether aquifers are being impacted by nearby wastewater. It's worth noting that, from a public health perspective, there is always the issue of cost when speaking to new indicators. The current culture sampling for pathogens is relatively inexpensive, and provides a "good enough" method of identifying contamination. Moving to a compound that requires some analytical chemistry for identification may just be simply too expensive for publicly funded environmental health organizations.
Source: Robertson, W.D., Van Stempvoort, D.R., Solomon, D.K., Homewood, J., Brown, S.J., Spoelstra, J., & Schiff, S.L. (2013). Persistence of artificial sweeteners in a 15-year-old septic system plume. Journal of Hydrology, 477, 43-54.
There are a couple of problems with fecal coliforms as indicator organisms: they're not necessarily confirmation of human sewage (i.e. just confirmation of some sort of fecal contamination) and they're not overly persistent in the soil. If you're just trying to tell a water system operator that they've got some contamination issues and need to issue a public notification, they work just fine. But if you're looking to confirm that some actual sewage is getting into the water, you're going to have a hard time in front of a judge.
Researchers from Ontario looked at a wastewater plume from a septic field serving a campground that had been in existence for around 20 years (which, incidentally, is about the life span of the average on-site sewerage system), and note that typical indicators of contamination (besides coliforms) are not necessarily unique to sewage, and therefore don't make the best indicators. Chemical compounds that are unique (ibuprofen, pseudoestrogens, carbamazapine) haven't been studied enough to give a clear indication of how long they persist in the environment. They suggest that artificial sweeteners might have value as a wastewater indicator, since they're unique to human waste, resistant to breakdown in normal sewage treatment, and persist in groundwater.
By setting up a number of piezometers and trace gas sampling points along the wastewater plume from the campground, the researchers were able to not only sample the groundwater for the contaminants of interest, but were also able to perform tritium/helium age dating to identify the age of the wastewater plume. Unsurprisingly, their study showed that once you got about 50m away from the sewage dispersal field area, nutrients and pathogens normally found in sewage were reduced to non-detectable levels. Of the sweeteners tested for persistence, they found that cyclamate and sacharrin appeared to degrade quite effectively, while acesulfame and sucralose concentrations remained relatively constant regardless of distance from the septic tank.
Since the acesulfame was detected in levels nearly 1000x higher than background concentrations in the wastewater plume, and degradation didn't occur over approximately 20 years of sewage system use, it presents itself as a potentially viable indicator for wastewater contamination. Apparently, acesulfame is also added to some animal feed, so it could be used as an indicator of groundwater contamination from manure spreading as well.
There's still some further work to be done, since this is just one study of one onsite sewerage system. However, it shows great potential for a new way of determining whether aquifers are being impacted by nearby wastewater. It's worth noting that, from a public health perspective, there is always the issue of cost when speaking to new indicators. The current culture sampling for pathogens is relatively inexpensive, and provides a "good enough" method of identifying contamination. Moving to a compound that requires some analytical chemistry for identification may just be simply too expensive for publicly funded environmental health organizations.
Source: Robertson, W.D., Van Stempvoort, D.R., Solomon, D.K., Homewood, J., Brown, S.J., Spoelstra, J., & Schiff, S.L. (2013). Persistence of artificial sweeteners in a 15-year-old septic system plume. Journal of Hydrology, 477, 43-54.
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