Faecal pollution introduces disease-causing microorganisms into recreational water that are largely derived from human sewage or excreta from warm-blooded animals. Guidance on setting of national health-based targets for faecal pollution is covered in Chapter 2. This chapter addresses:
faecal pollution aspects in recreational water safety plans (RWSPs;
Chapter 3 –
Recommendation 2) with the following key elements
system assessment, primarily through sanitary surveys (
section 4.1.2)
combining sanitation survey and water quality results to classify beaches (
section 4.3)
ongoing operational and verification monitoring and communication that can be done in real time using predictive models (
sections 4.2.2 and
4.2.3)
management of risks though pollution abatement (
section 4.4); and
The approach is summarized in .
Flowchart for assessing recreational water environments.
4.1. System assessment
System assessment involves identifying sources and levels of faecal pollution (human and animal) as part of RWSPs.
4.1.1. Health effects of faecal pollution
Expected pathogen numbers when thousands of people contribute to raw excreta flows are given in , together with the health effects of these pathogens.
The likelihood of a pathogen causing infection or disease depends on:
the specific strain of the pathogen;
the dose – for viral and parasitic protozoan infections, the infectious dose might be very few infectious units (
Simmons et al., 2019);
the form in which the pathogen is encountered;
the conditions of exposure; and
the host’s susceptibility and immune status.
Numbers of faecal pathogens and indicator organisms in raw sewage.
4.1.2. Sanitary inspection survey
The inspection process to determine faecal pollution impacts to inform beach classification is called a sanitary survey. Comprehensive sanitary surveys can also identify other pollution sources and risks such as nutrient sources that may promote proliferation of harmful algal blooms, sources of chemical contamination and sources of other microbial hazards as part of the RWSP (refer to section 2.2.1). Sanitary surveys, together with microbial water quality analysis (section 4.1.3), leads to the beach classification (section 4.3). Although the sanitary survey may take many forms (e.g. NHMRC, 2008; USEPA, 2013; EEA, 2020), the goal is to ascertain likely faecal sources to help select beach sampling sites and outline management actions.
Recreational water can be contaminated with faecal microorganisms from animals, human sewage and faecal sludge-related effluents and leachates; the recreational population using the water (from defecation, vomiting or accidental shedding); and – in decreasing order of human health risk – livestock, farming activities, domestic animals and wildlife. Sewage and faecal sludge are normally the most likely source of human-infectious pathogens. In studies of the impact of faecal pollution on the health of recreational water users, several faecal indicator organisms (FIOs; refer to section 4.1.3.1) have been used to index water quality. These FIOs are not considered the causative agents of illness but appear to behave similarly to some faecal pathogens, and may be related to illnesses in a dose-responsive manner (Prüss, 1998; Wade et al., 2010).
Guidance on items to include in sanitary survey forms is provided in Table 3.2 and (section 3.2.1).
Human inputs
The most important sources of human faecal contamination of recreational water environments for public health purposes are typically:
sewage and faecal sludge disposed of in the recreational water area via pipes, open drains and trucks;
riverine discharges and combined sewer overflows (CSOs), where the river is receiving water from sanitation systems (e.g. sewage discharges, liquid effluent from septic tanks) and either is used directly for recreation, or discharges near or into a coastal or freshwater area used for recreation;
contamination from recreational water users (including, in decreasing order of human health risk, faecal shedding, vomitus and urine) – particularly hazardous at high density of users; and
runoff from surrounding land where open defecation and/or flooding of pits and septic tanks is prevalent.
The risks may vary with local circumstances. For example, sewage and septic tank effluent being discharged into an estuary with small tidal interchanges may present a greater risk than the same quantity of sewage and effluent discharged into an estuary with large tidal interchanges. Similarly, a river discharging into an enclosed bay presents a higher risk than one discharging directly into the open sea.
Although several contamination sources may be significant, a recreational water environment may be most readily classified using the single most significant source of pollution. Management actions, however, should consider all the contamination sources. The classification is based on a qualitative assessment of the risk of exposure under normal conditions, considering the operation of sewage and faecal sludge treatment plants, on-site septic tanks and faecal sludge management services, and hydrometeorological and oceanographic conditions.
Sheltered coastal areas and shallow lakes may accumulate fine sediments that may be associated with high faecal microbial loads – these might be resuspended by water users or rainfall events. The health risks associated with resuspended sediments are poorly understood, but the potential risk should be noted during sanitary surveys.
Animal inputs
Animal sources are generally less important to human health risk than human excreta flows. However, in some instances, animals (e.g. gulls, waterfowl) can have a significant impact on faecal indicator bacteria used to measure microbial water quality and could result in management actions that are unnecessary in terms of public health (Smith, Snyder & Owen, 2020). Pollution of recreational waters with animal excreta can sometimes lead to human health risks, because some zoonotic pathogens (e.g. Cryptosporidium parvum; Campylobacter spp.; pathogenic Escherichia coli, such as E. coli O157:H7) can be transmitted in animal faeces, particularly from intensive livestock raising near waterways (Soller et al., 2015). Thus, local knowledge of possible sources and environmental pathways of animal pathogens to humans should form part of the sanitary inspection, as is the case for shellfish-growing waters in many countries.
4.1.3. Determining recreational water quality
Guideline values for recreational water quality (section 2.1.2) are based on standard methods (e.g. International Organization for Standardization – ISO1 and American Society for Testing and Materials - ASTM2) carried out by an accredited laboratory to assess the concentration of intestinal enterococci; however, a number of other organisms and gene targets may also be used. Although laboratory accreditation for non-culture-based, quantitative polymerase chain reaction (qPCR) to assay enterococci or E. coli may be less well developed and/or available, DNA extract may also be used to assist in determining the presence of sewage or other important sources of faecal pollution.
Faecal indicators
The most commonly used FIOs are intestinal enterococci and E. coli, typically used to assess marine and fresh recreational waters, respectively.
Different methods used to assess FIO levels may target a slightly different subset of FIOs. Hence, it is critical to have a standard method or methods for analysis to be performed by an accredited laboratory within each specific jurisdiction. Recently, non-culture-based molecular methods (qPCR) have been developed for both enterococci and E. coli (Haugland et al., 2016; Shrestha et al., 2019; Sivaganesan et al., 2019). However, at the time of writing these guidelines, only qPCR for enterococci had been used in epidemiology studies addressing marine and fresh waters and shown to reflect, in a dose–response manner, gastrointestinal illness in recreational water users (Wade et al., 2010).
Enterococci
The intestinal enterococci species most predominant in faecally polluted aquatic environments are Enterococcus faecalis, E. faecium and E. durans. In fresh water, E. faecium may prevail over E. faecalis, whereas in seawater the opposite is normal (Figueras et al., 1998; Tiwari et al., 2018).
Intestinal enterococci have some potential drawbacks for assessment of recreational water quality. For example, their environmental habitats can serve as both sources and sinks. In addition, some intestinal enterococci (and E. coli) may be endogenous in sediments, in soils and within submerged aquatic vegetation (particularly in warm and tropical climates), and therefore may not indicate recent faecal contamination (Byappanahalli et al., 2012; Tiwari, Kauppinen & Pitkänen, 2019).
Escherichia coli
E. coli is abundant in human and animal faeces, comprising approximately 1% of the total bacterial biomass (Tallon et al., 2005). It is generally present in greater numbers than intestinal enterococci in fresh excreta. E. coli is usually an innocuous resident of the gastrointestinal tract; however, some strains are pathogenic, and can cause significant diarrhoeal and other illness (Croxen et al., 2013; ). These pathogenic strains generally represent less than 1% of the total E. coli in raw sewage (García-Aljaro et al., 2019).
E. coli has been isolated from tropical water systems that have no known sources of faecal contamination (Tallon et al., 2005). Environmentally naturalized E. coli populations also exist (Luo et al., 2011), as do treatment-resistant biotypes very similar to urinary-pathogenic E. coli (Zhi et al., 2020).
Coliphages and culturable human viruses
Culturable viruses (human enteric viruses and bacteriophages) are useful faecal indicators of wastewater disinfection efficacy, such as when chlorination or ultraviolet irradiation is used, or in environments with significant solar irradiation. These culturable human viruses include adenoviruses (Rodríguez et al., 2013), enteroviruses (Costán-Longares et al., 2008) and reoviruses (Betancourt, Gerba & Abd-Elmaksoud, 2018), but methods are complex and expensive, and total enteric virus presence (infectious and non-infectious) by qPCR will still provide value in identifying the risk from human excreta (Vergara, Rose & Gin, 2016).
Several bacteriophages have been suggested as candidate indicators (McMinn, Ashbolt & Korajkic, 2017), but most attention has been on coliphages (bacteriophages that infect E. coli). Coliphages are not specific to human excreta; they occur in many animal faecal sources, and have been isolated from both fresh and marine recreational waters, although generally in low numbers (Contreras-Coll et al., 2002; USEPA, 2017). However, certain genotypes of coliphages are more likely to indicate contamination by human excreta (García-Aljaro et al., 2019).
Other organisms
Some jurisdictions have considered alternative FIOs in response to specific local conditions. For example, the bacterium Clostridium perfringens has been used as an additional FIO in Hawaii. In tropical climates, enterococci are naturally present in soils, whereas the presence of C. perfringens indicates human excreta (Vierheilg et al., 2013).
Faecal source attribution
When unacceptable levels of FIOs are detected in a water body and sewage is not expected, it is important to ascertain the faecal source(s) contributing FIOs. A suite of methods can be used, including chemical approaches and microbial source tracking (MST) techniques (Harwood, 2014). MST uses genetic markers or microorganisms in excreta that are strongly associated with a specific host (e.g. humans, livestock, dogs, waterfowl) (Wiedenmann et al., 2006; Reischer et al., 2011; Harwood et al., 2014). More than 40 MST targets have been used. Some of the most common, and their associated hosts, for investigating recreational water quality are described in Li et al. (2019).
4.2. Monitoring
The aim of RWSPs (refer to Chapter 2) is to reduce the amount of costly monitoring and to proactively manage the safety of recreational water users. Monitoring corresponding to Recommendation 2.3 in RWSPs has three aspects:
initial monitoring to characterize the recreational water body using the health-based targets and the beach classification described in
section 4.3 (refer to
section 4.2.1);
ongoing verification monitoring that provides a check on meeting health-based targets (refer to
section 4.2.2); and
operational monitoring, to enable quick response and reduce overall monitoring costs (refer to
section 4.2.3).
4.2.1. Initial microbiological water quality assessment
Initial water quality assessment supports beach classification (section 4.3) and involves five stages (for further details, refer to Bartram & Rees, 2000).
Stage 1 – initial sampling to determine if significant spatial variation exists along the recreational site.
- –
Sampling at spatially separated sampling sites should be carried out at 50–100 metre intervals along the bathing area foreshore during the initial assessment on different days. Timing of samples should consider the likely period of maximum contamination from local sewage and septic tank discharges, and maximum shedding by recreational water users (e.g. the afternoon or day of peak numbers of water users).
Stage 2 – assessment of spatial data based on data from
stage 1.
- –
If spatial variation occurs, see stage 4; if no spatial variation occurs, see stage 3.
Stage 3 – intensive sampling and assessment of results.
- –
If there is no evidence of spatial variation, the initial classification (refer to section 4.3) is determined from the results of the sanitary inspection category and microbial water quality assessment (). It is suggested that microbial water quality for recreational waters is classified into four categories (A–D) using the 95th percentile (refer to section 4.2.2) of intestinal enterococci distribution, as shown in .
Stage 4 – definition, separate assessment and management of affected areas if spatial variation is evident at
stage 2.
Stage 5 – confirmatory monitoring in the following year, using a reduced sampling regime and a repeat of the sanitary inspection. If the subsequent classification () is “very good” or “very poor”, less frequent monitoring can be justified ().
The sampling programme should be representative of the range of conditions (e.g. dry, wet) and spatial patterns (e.g. close to stormwater drains) in the recreational water environment while it is being used. When determining the recreational water classification, all routinely collected samples on days when the recreational water area was open to the public should be used. For example, it is not appropriate to resample the bathing water following a high count measured when the beach was open and no advisory notice had been posted, and then to use the resample result but not the original result. However, where an advisory notice has been posted, the sample taken during the period of the posted advisory would be omitted from the percentile calculations. On the other hand, samples may be taken following an adverse event or an unexpectedly high result from a routine sample. The additional samples may be used to investigate the full impact of the event on the bathing water or to further characterize the area and the impacts of adverse events.
It is important that sufficient samples are collected to enable an appropriate estimation of the FIO densities to which recreational water users are exposed. The number of results available can be increased significantly – with no additional cost – by pooling data from multiple years. This practice is justified unless there is reason to believe that local (pollution) conditions have changed. For practical purposes, data from 100 samples from a 5-year period and a rolling 5-year dataset could be used for microbial water quality assessment.3
Overall, bathing waters with consistent classifications will require fewer samples, and bathing waters with changing classifications will require more samples. In some circumstances, fewer samples may be required – for instance, where the water quality is consistently very poor and swimming is not recommended. However, 60 samples should be the minimum considered for an analysis of the effects of an insufficient number of values for credible derivation of water quality standards for recreational waters.
4.2.2. Ongoing verification monitoring
Many agencies have chosen to base criteria for recreational water compliance on either percentage compliance levels – typically 95% compliance (i.e. 95% of the sample measurements taken must lie below a specific value to meet the standard) – or geometric mean values of water quality data collected in the water use zone. Both statistics have significant drawbacks. For example, the geometric mean provides limited information on the high values at the top end of the statistical distribution that are of greatest public health concern. The 95% compliance system, on the other hand, does reflect much of the top-end variability in the distribution of water quality data and is more easily understood. However, the 95th percentile is affected by greater statistical uncertainty than the geometric mean; this is therefore a less reliable measure of water quality, and care is required if it is to be applied in management of water quality5 (WHO, 2009).
There is no best way to calculate percentiles. It is important to know which method is being used, as each will give a different result.
Datasets that include numerous values below the limit of detection can be difficult to manage and produce non-normally distributed data. When use of such data is unavoidable, the Hazen method is a robust method for calculating the 95th percentile (Hunter, 2002; WHO, 2009). In this method, the data are ranked in ascending order, and the percentile is calculated by interpolation between the two data points on either side of the calculated rank.
In the subsequent analyses, however, appropriate dilutions should be used to ensure that nondetectable events (termed censored data) are rare or completely avoided.
Verification parameters and frequency of assessment
Verification monitoring may use a minimum of five samples per year (to ensure that no major changes go unidentified) for recreational water areas where:
no change to the sanitary inspection category from the annual sanitary survey has occurred over several years;
the sanitary inspection category is “very low” or “low”; and
the initial microbial water quality assessment is stable and based on at least 100 samples.
For areas where the sanitary inspection resulted in a “very high” categorization for susceptibility to faecal contamination (where swimming would be strongly discouraged), a similar situation applies.
For intermediate-quality recreational water environments (i.e. “moderate” and “high”), an annual verification sampling programme involving more frequent sampling is recommended, as shown in .
Recommended verification monitoring schedule.
Where a change is made in the FIOs or microbiological method used, limited data may be available in the initial years of implementation. To overcome this, historical records may be used by applying correction factors appropriate to local conditions. These factors would normally be driven by comparative studies of the results of local analyses. Another strategy is to collect both old and new data on FIOs during the transition period. Although this increases costs, it provides a break-in period.
4.2.3. Operational monitoring and communication using predictive models
Operational monitoring may use a range of parameters, including nonmicrobiological ones – for example:
warnings on release of poorly treated sewage or faecal sludge from a utility or service provider;
rainfall that may influence runoff or release excreta from flooded septic tanks and sewers;
unloading by faecal sludge trucks in coastal zones;
changes in wind speed or direction and water temperature that may change the dispersal of sewage, septic tank effluent and stormwater from outfalls; and
operational data collected by individuals associated with a recreational site, surveillance drones and citizen science.
The range of sources of operational data means that roles and responsibilities need to be defined in the RWSP (refer to Chapter 2) for operational monitoring associated with faecal pollution.
Timely response to changing recreational water quality has been a major concern in the appropriate management of the safety of recreational water users. Predictive models can be used at bathing water areas to derive microbial water quality forecasts (e.g. daily). These can be made available to the public through means such as beach signage, websites and mobile applications (refer to Chapter 3). Predictive models provide water users and other beach users with near-real-time information on likely water quality conditions that are more up to date than the historical results provided by traditional analytical methods. When the results are well communicated, they allow water users to make informed choices on whether to use the recreational water site (refer to Example 4.1).
Example 4.1The Safeswim predictive model for Auckland, New Zealand
In 2017, Auckland City launched the Safeswim website and mobile application as a joint initiative between the Auckland Council, Watercare (the city water and wastewater utility), Surf Lifesaving Northern Region and the Auckland Regional Public Health Service. This initiative was partly funded by a targeted council rates increase for water quality improvement.
Safeswim encourages users to “jump online before you jump in”, directing users to the nearest of more than 100 classified beaches in the region. The system allows users to decide when and where they swim by indicating safety using a red and green coding system. A small number of beaches are permanently closed or unclassified.
Safeswim uses a predictive model built using real-time rainfall and tide data, together with a historical time series of water quality testing results for intestinal enterococci and E. coli. The model provides real-time estimates of the likelihood of an exceedance and classifies beaches as red when the risk of illness by ingestion exceeds 5%.
All Safeswim’s water quality models are overseen by an independent panel of public health experts, which meets quarterly to evaluate performance and provide direction. An independent audit of Safeswim completed by Audit New Zealand in 2020 found that a random sample of Safeswim’s water quality predictions was 89% accurate.
Generally, water quality, especially on the north shore, is good for 95–97% of days. However, exceedances are more common in areas of the city with CSOs where rainfall of more than 15 mm occurs in a 24-hour period, particularly after extended dry periods. In areas with permanently closed beaches, exceedance can occur in dry weather or with as little as 3–4 mm of rain.
The system is a marked improvement over the previous system, which had a 48-hour delay between sample collection and public reporting of results. Transparent public reporting has also increased public awareness and scrutiny about the causes of water pollution, and willingness to pay via targeted council rates for improvement. This has increased the capacity of local authorities to address the primary sources of pollution.
A range of improvement projects are under way, including a large central sewer interceptor (designed in preparation for future growth and impacts of climate change) that will divert overflows away from the harbour to the main wastewater treatment plant. The interceptor is due for completion in 2028. In the meantime, water quality is continually being improved through detection of damaged pipes, and misconnections of sewer and stormwater; restoration of natural treatment in streams and wetlands; and sewer and pump station upgrades. These are all combined with streetscape improvement, where possible.
Source: https://www.safeswim.org.nz/
Predictive models should be validated and checked against real conditions – they may not be suitable for some beach types, and changes within beach catchments are likely to require updating of regression-based (i.e. empirical) models. In operational standards such as the European Union Bathing Water Directive (EU, 2006), accurate predictive modelling can significantly improve regulatory compliance if a regulatory sample with high concentration of FIOs caused by, for example, high antecedent rainfall is discounted (i.e. not used) for regulatory calculations of the regulatory upper percentile values. This approach is based on the Annapolis Protocol (WHO, 1999).
Assessing and acting on single and/or high analytical results
Responsible agencies should ensure that they are fully apprised of any sanitary survey information for the site and any past records of water quality, and that they have undertaken a recent visual inspection. Three main conditions might lead beach management agencies to consider posting an advisory notice of likely adverse water quality.
Climatic conditions, such as high rainfall, lead to elevation of FIOs in recreational waters. The microbial source may be agricultural runoff and/or urban surface water. This information should be communicated to the public through signage, and to tourist information centres and the news media via electronic means. The water quality levels at which such an advisory might be prudent will depend on local circumstances.
A rare or extreme event causes gross pollution of the bathing water. Often, the first evidence of such an event will be visual reports of gross pollution, indicated by high turbidity and associated sanitary wastes from sewer overflow, and/or overflow debris from rivers and drains discharging to the bathing water. A protective advisory notice informing the public of potentially adverse water quality should be posted on first observation of the evidence. Microbiological testing to confirm adverse water quality (high microbial concentrations) could provide a yardstick of a return to more normal water quality for the affected site.
Sewer debris is reported in the bathing water but is not explained by weather events. This may indicate a gross malfunction or leakage of the sewerage system. An advisory notice to inform the public of the risk should be posted. The notice should only be removed when the new source of gross pollution has been rectified.
4.3. Beach classification based on sanitary survey and water quality
Recreational water is classified by combining the sanitary inspection category (section 4.1.2) with the microbial water quality assessment category (section 4.1.3), using a matrix such as that shown in and summarized in .
The classification emphasizes faecal contamination from humans. FIOs may significantly overestimate risks if they have sources other than human excreta (Schoen, Soller & Ashbolt, 2011).
The assessment framework () enables local management to respond to sporadic or limited areas of pollution, and thereby upgrade the classification for a recreational water body, provided that appropriate and effective management action is taken to control exposure (refer to section 4.4). This form of classification (as opposed to a pass/fail approach) therefore provides incentives for both local management actions and pollution abatement. It also provides a generic statement of the level of risk, which supports informed personal choice. It helps to identify the principal management and monitoring actions that are likely to be appropriate.
Example of a classification matrix for faecal pollution of recreational water environments.
4.3.1. Initial classification
The outcome of the sanitary inspection and the microbial water quality assessment, based on and , is a five-level classification for recreational water environments: very good, good, fair, poor and very poor. In addition, there is a follow-up category or requirement where there is discrepancy between the results of the microbial water quality assessment and the sanitary survey.
If the assessment shows that higher microbial contamination levels are limited to only a part of the recreational water environment, separate assessment and management are required for these areas.
Where there are multiple sources of contamination, the single most significant source is used to determine the susceptibility to faecal influence.
4.3.2. Follow-up of initial classification
Where the sanitary inspection and water quality data inspection result in a potentially incongruent categorization in , further assessment will be required. This could include re-examining the sanitary survey (i.e. identifying further potential faecal sources in the catchment and assessing their risk) and additional analysis of water quality, with specific consideration given to the sampling protocol (spatial and temporal) and analytical methodology.
Examples of situations that may lead to potentially incongruent assessments are when:
analytical errors have been made;
the importance of non-point sources was not appreciated in the initial survey;
the sampling points are not representative of the influence of sewage, septic tank effluents and faecal sludge;
important CSOs have not been identified or are present on the beach but do not discharge during the bathing season;
the assessment is based on insufficient or unrepresentative data; and
extreme events arise from damaged infrastructure, or inappropriate practices for sewage or faecal sludge disposal (e.g. shipping damage to marine outfalls, illegal dumping of faecal sludge, connection to surface water of foul drains from domestic and other properties).
Where sanitary inspection indicates low risk, but initial microbial water quality assessment indicates water of low quality, this may indicate previously unidentified sources of diffuse pollution. In this case, specific studies demonstrating the relative levels of human and nonhuman contamination (e.g. surveys of mammal and bird numbers, MST markers) may be appropriate. Confirmation that contamination has negligible nonhuman (e.g. bovine, avian) sources (Soller et al., 2015) may allow reclassification (refer to section 4.3.4) to a more favourable grading. Care is needed here because nonhuman pollution may still be a source of important pathogens (refer to section 4.1.2.2).
Similarly, where microbial water quality assessment indicates a very low risk that is not supported by the sanitary survey, consideration should be given to the sampling design, the analytical methodology used and the possibility that the sanitary survey may be incomplete.
A worked example is provided in Example 4.2 to illustrate beach classification.
Example 4.2Beach classification worked example
Historical microbial data for the site were available; thus, the most recent 5 years of data (in this case, more than 20 samples per year) were used to provide the initial microbial water quality assessment (refer to footnote 9 on sample number and risk of misclassification).
Sanitary inspection category (following criteria described in section 4.1.2.1)
- a)
Sewage discharges (if present)
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| Outfalls | Present? (Y/N) | If present: |
|---|
| Type of treatment | Type of outfall/disposal | Risk category |
|---|
| Sewage outfalls | Y | Primary | Effective | Low |
| CSOs | N | | | |
| Faecal sludge disposal | N | | | |
| Stormwater | Y | | Direct | Very high |
- b)
Riverine discharges (if present)
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| Present? (Y/N) | If present: |
|---|
| Size of population from which sewage or septic tank effluent originates | Type of treatment | River flow during bathing season (high, medium, low) |
|---|
| N | | | |
- c)
Water user shedding
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| Water user density in bathing season (high, low) | Dilution (low if beach has restricted water flow – lakes, lagoons, enclosed inlets; otherwise high) |
|---|
| High | High |
- d)
Physical characteristics of the beach; provide a scale sketch map showing location of sampling points and swimming areas. The beach is 800 m long. There are several stormwater drains discharging to the beach.
- e)
Overall category of sanitary inspection
Very high susceptibility to faecal influence.
Initial microbial water quality assessment
- a)
Describe the current monitoring programme for assessing microbial water quality.
Sample volume = at least 250 mL (for 100 mL analysed volume)
Tested for E. coli and intestinal enterococci
Sampling schedule: approximately every 6 days
Sampling points: 1
- b)
Summarize data file(s) covering at least 5 years of monitoring (or 100 samples) for faecal indicator organisms (100 raw numbers are needed in order to calculate 95th percentiles). Preferably, these should be the most recent data available.
Combined sanitary and microbial water quality assessment, and overall classification
Sanitary inspection category: Very high susceptibility to faecal pollution
Microbial inspection category: C
Overall classification: This beach is rated as “poor”.
View in own window
| Sanitary inspection category (susceptibility to faecal pollution) | Microbial water quality assessment category (95th percentile intestinal enterococci/100 mL) |
|---|
|
A
≤40
|
B
41–200
|
C
201–500
|
D
>500
| Exceptional circumstances |
|---|
| Very low | Very good | Very good | Follow-up | Follow-up | Action |
| Low | Very good | Good | Fair | Follow-up |
| Moderate | Good | Good | Fair | Poor |
| High | Good | Fair | Poor | Very poor |
| Very high | Follow-up | Fair | Poor | Very poor |
| Exceptional circumstances | Action |
Reassessment of beach classification following management of exposures
The initial classification based on the sanitary inspection category (very high susceptibility to faecal pollution) and initial microbial water quality assessment (C) was “poor”.
However, this classification appeared to be driven principally by the presence of occasional stormwater overflows. Subsequent investigation found that the stormwater overflow events were predictable. Signage was introduced to warn water users not to swim during rain and for up to 2 days following heavy rain. The beach was posted whenever heavy rain had occurred.
Exclusion of the stormwater overflow changes the sanitary inspection category from “very high” to “low” susceptibility to faecal pollution, which results in a provisional upgrading to “fair (but unsuitable for 2 days after heavy rain)”.
Monitoring of the recreational water over a bathing season revealed that water users complied with the notices not to bathe. Water quality sampling showed that, after 2 days following heavy rain, the microbial quality returned to normal levels. Reanalysis of microbial water quality data using the water quality to which users were exposed found a 95th percentile of 185, resulting in a final classification of “good (but unsuitable for 2 days after heavy rain)”.
The local authority intends to remove the source of stormwater overflow. They expect that the advisory can then be removed, and the beach can be classified as “good”.
4.3.3. Provisional classification
There will sometimes be a pressing need to issue advice on the classification of a recreational water environment when the information required in is incomplete.
Three scenarios may be envisaged.
No data are available on the microbial water quality of the water body or its susceptibility to faecal influence (such as new developments).
The data available from the microbial water quality assessment and/or the sanitary inspection are incomplete.
There is reason to believe that the existing classification no longer accords with changed circumstances, but insufficient data are available to complete the classification.
In these circumstances, it may be necessary to issue a provisional classification (refer to Example 4.3). When such a step is taken, it should be made clear that the advice is provisional and subject to change. A provisional classification should be time limited, and there should be a commitment to obtaining the necessary data to follow the steps described in to provide definite classification as soon as possible.
Example 4.3Actions for provisional beach classification
No historical data or assessment
Examples of recreational water environments for which no sanitary inspection information and no water quality data are available are a newly used beach or a part of a long beach that becomes popular. Steps to take are as follows.
Identify the extent of the water body or beachfront requiring classification. Urgent microbial water quality assessment will be required. If sampling and analytical capacities are insufficient, the most intensively used recreational water area should be selected for initial study.
At the first opportunity, and during the bathing season, take a minimum of 8–12 samples across the selected transect, ideally at about 50 m intervals (depending on the length of the beach and possible discharges from stormwater or other outfalls), but, in any case, not more than 200 m apart.
Conduct a limited sanitary survey to identify possible pollution sources in the immediate vicinity of the area that will require further evaluation. While waiting for laboratory results, the sanitary survey should be completed as far as possible. Arrangements should be made to obtain maps, plans, information on the sewerage system and other information that may be needed for a proper interpretation of the findings.
Review the initial laboratory results as soon as they become available. If the results are extremely good or extremely bad, it may already be obvious that the water body may be provisionally placed in microbial water quality assessment categories A or D. For example, if at any time during the collection of classification data it becomes obvious that, once all 100 samples have been collected, the 95th percentile will exceed a particular classification boundary, the recreational water should be provisionally classified at the appropriate level.
If the results are less clear-cut, a second round of sampling will be needed; use of MST markers may be beneficial. This should be conducted as soon as possible, providing it is during the bathing season.
Based on the sanitary survey and the microbial water quality assessment data available after the second round of sampling, make an early assessment. If necessary, a time-limited provisional classification of the recreational water environment should be made and acted upon. At the same time, a commitment should be made to proceed with all necessary steps to permit full classification of the area in accordance with and as soon as possible.
Incomplete data
Where the data available are insufficient, the steps are as follows (also see footnote 9).
For either or both of the microbial water quality assessment or the sanitary survey, review the data carefully to see whether it is possible to reach any provisional conclusions. This may be relatively easy at the extreme ends of the classification spectrum – for example, if there is a major sewage or feacal sludge discharge point in the immediate vicinity of the recreational water area, or a set of analytical results with a strong trend towards very high or very low values.
If it is not possible to make a provisional classification, use the review to identify key deficiencies in the data and therefore the additional information that is most critically needed.
In the absence of past intestinal enterococci data, consider using historical records relating to another FIO.
Consider undertaking a complete data gathering process (as in ).
If beach classification is urgently needed, the procedure outlined above for a recreational water environment for which there are no data may be adapted accordingly.
Inappropriate existing classification
Where there is reason to believe that the existing classification no longer accords with changed circumstances, the steps are as follows.
Collect sufficient data before reassessing the beach classification, or carefully review the existing data to see whether any provisional conclusions can be reached.
If this review shows an incongruity between the sanitary survey data and the microbial water quality assessment data, take steps (as set out in
section 4.3.2) to understand this.
If both the sanitary survey data and the microbial water quality data point to a similar change in beach classification, draw a provisional conclusion, and take steps to obtain sufficient data for proper classification.
4.3.4. Upgrading classifications
As water contamination may be triggered by specific and predictable conditions (e.g. rainfall), local management actions (e.g. advisories) can be used to reduce or prevent exposure at such times. If these actions are effective, the recreational water classification may be upgraded to a more favourable level. A reclassification should, however, initially be provisional and time limited. It may be confirmed if the efficacy of management interventions is subsequently verified during the following bathing season. If the reclassification is not confirmed, the water environment will automatically revert to the original classification. This is illustrated by the last part of the worked example in Example 4.2.
4.3.5. Exceptional circumstances
Although these guidelines do not provide general guidance (e.g. guideline values) about risks during exceptional circumstances – such as sewer breaks, extreme floods and rainfall events with a return period of more than 5 years – the ability to identify and manage these types of circumstances is important. Initial identification of a problem may arise from (human) disease surveillance, authorities responsible for wastewater treatment, and management or veterinary authorities. Public health authorities should be engaged in defining water quality standards or appropriate triggers relevant to specific circumstances. This will normally require the responsibility and authority to act in response to such circumstances (refer to Chapter 3). Implementing appropriate actions will require intersectoral action, often including local government, facility operators, user groups and so on.
4.4. Management and communication
This section describes abatement and remediation measures for managing water quality improvement and ensuring the safety of recreational water users.
4.4.1. Direct point-source pollution abatement
Effective outfalls with sufficient length and diffuser discharge depth are designed to ensure a low probability of sewage-contaminated water reaching the recreational water environment. Long outfalls can be an effective means of protecting public health by separating recreational water users from contact with sewage. Pretreatment with milli-screens is the minimum treatment level.
For nearshore discharges of large urban communities, where effluent may meet recreational waters, tertiary treatment with disinfection will provide the greatest health benefits and a sanitary inspection category of “very low” susceptibility to faecal influence. However, public health risks will depend on the operation and reliability of the plant and the effectiveness of disinfection.
4.4.2. Intermittent pollution abatement
Runoff via drainage ditches and so on is predominantly event-driven pollution that may affect recreational water areas for relatively short periods after rain. CSOs – where effluent combines with rainfall – are built into many sewerage systems. Similarly, many in-site sanitation systems, such as pit latrines and septic tanks, overflow or leach via groundwater to nearby recreational water sites in heavy rain. These may expose water users to diluted untreated human excreta. Where the sanitation system does not receive surface water after rainfall, dry-weather raw sewage overflows and unmanaged septic tank effluent present a direct health risk, and contact with the overflow should be avoided.
The best option is to have separate collection systems for human excreta and rain/stormwater. Although treatment is an option for CSOs, often the treatment plant cannot cope with the quantity of sewage, or the effectiveness of the treatment is lowered as a result of a change in the load of the sewage.
Other pollution abatement options for CSOs include:
retention tanks that discharge during periods when recreational water is not being used – these are costly and may be impractical for large urban areas;
transport of sewage to locations distant from recreational areas via piped collection systems or effective outfalls; and
disinfection (ozone, chlorine, peracetic acid or ultraviolet light), which may not be effective against all hazards.
These pollution abatement alternatives usually require major capital expenditures and may not be readily justifiable, especially in low- and middle-income countries. An alternative is management programmes that minimize recreational water use during event-driven pollution incidents (refer to section 4.4.1).
Programmes to scare gulls and waterfowl away from recreational sites, or remove seaweed or other detritus that may attract them, have been effective in reducing FIO levels (Converse et al., 2012).
4.4.3. Catchment pollution abatement
Significant pollution sources that may present a challenge to pollution abatement include:
upstream diffuse pollution (e.g. poorly functioning septic tanks, local breaks in sewerage pipes);
point-source discharges (e.g. illegal faecal sludge disposal sites);
animal-derived faecal pollution, especially in livestock-raising catchments; and
pathogen accumulation in stream sediments and remobilization via riverine discharges to coastal recreational areas.
Major sources of pollution should be identified and a catchment-wide pollution abatement programme developed. This requires cooperation among health agencies, environmental control agencies, local authorities, users and polluters. The role of the agricultural sector in generation and remediation of pollution loadings is often crucial in catchments that are primarily affected by livestock pollution.
4.4.4. Enforcement of regulatory compliance
Enforcement of regulatory compliance has limitations as the principal tool for protecting and improving microbial quality of recreational waters, although the threat of closure may be a powerful driver for improvement.
Where a recreational water use location fails a regulatory standard, it may be difficult to define responsibility for this failure – in many locations, several sources will contribute to the overall pollution.
It may be appropriate to base regulatory compliance on the obligation to act. Thus, there could be a requirement to immediately consult the public health authority and to inform the public, as appropriate, when conditions are detected that are potentially hazardous to health and uncharacteristic of the location. There could also be a general requirement to strive to ensure the safest achievable bathing conditions by taking measures to improve classification of the recreational water, including pollution control.
4.5. Research needs
Empirical data from the United Kingdom and the USA suggest very high within-day variability (i.e. 2–4 log10 orders every day in the bathing season) in regulatory FIO concentrations (Fleisher, 1985; Wyer et al., 2018). This pattern has been evident at seven marine beaches sampled to date at 30-minute intervals for 12 hours over 60 bathing season days, with triplicate analyses to increase the precision of single-sample bacterial enumeration. The inherent assumption that the compliance sample set (one sample on the compliance sampling day) represents the water quality on the bathing day is therefore being questioned, and this has implications for design of predictive modelling protocols. It is important to test the hypothesis that this apparently chaotic pattern is present in other settings worldwide.
Although still relevant, the epidemiological studies underpinning recommended water quality guideline values are old, and limited in terms of activities, exposure types, geography and subpopulations studied. New, high-quality epidemiological studies in a variety of locations, with subjects from the general population as well as the subpopulation of interest (e.g. children, immunocompromised people, the elderly, elite sportspeople), as well as a variety of activities and exposure scenarios, would enable future validation and updates to recommended guideline values. Epidemiological studies are also needed to associate the levels of Clostridium perfringens (as an FIO for tropical waters) and various MST (molecular) markers with ailments after bathing in recreational areas. Although the research is compelling with regard to the value of MST markers, standardization of MST targets and methods have not reached the same maturity. Hence, research is needed on implementation aligned with progress made on portable qPCR machines and application of sequencing machines (e.g. Oxford MiniIon) for field use (Symonds et al., 2016; Liang, Goh & Gin, 2017; Zhang et al., 2019; Gitter et al., 2020).
In addition, statistical approaches to censored data are needed to resolve the inability to compare methods when waters are too clean.
Further research is also needed to understand the sanitary significance of environmental proliferation of FIOs, particularly in submerged vegetation compared with pollution derived from human and animal faeces, and its consequences for monitoring and interpretation of results.
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- 1
Relevant ISO standards include ISO 7899-1, ISO 7899-2, ISO 9308-2, ISO 9308-3, ISO 14189.
- 2
Relevant ASTM standards include ASTM D6503.
- 3
The standard error of any percentile calculation is inversely proportional to the square root of the number of data points included in the calculation, and also increases with the variance in the underlying data and the distance of the percentile from the median. This means that any beach classifications made on the basis of small numbers of microbiological test results are liable to considerable uncertainty – for example, a classification based on 10 or 20 samples will result in >20% and >14% misclassification, respectively. If compliance is estimated from 100 samples, as may be accrued over five bathing seasons with 20 samples per season, the probability of misclassification is less than 1%. Thus, estimating compliance on too few samples is unlikely to protect public health (because it will allow too many beaches to pass) or protect the interests of beach managers (because it will fail too many good-quality beaches).
