Water quality of Onrus lagoon in Hermanus under the spotlight

Writer & Photographer Hedda Mittner

A recent report on the water quality of the Onrus lagoon has elicited much debate on social media especially relating to sampling procedures, the monitoring of those results and the prime indicators used to determine the perceived health risks to recreational users of the Onrus lagoon.

Pivotal to the report entitled Recreational water quality in the Onrus River Estuary: Issues and Appropriate Indicators by the chair of the Onrus River Estuary Forum (OREF), Dr Peter van Niekerk, is the issue of whether the guidelines pertaining to “coastal, marine waters” should be applied to the Onrus River Estuary – or whether it should rather be defined as “freshwater”.

Based on several research studies, Van Niekerk is recommending that, due to its physical characteristics, the estuary should be regarded as a “freshwater-dominated system” as it is mainly supratidal (the sandbar is higher than the tidal reach) with an average salinity that is drastically lower than that of seawater.

This would mean that a different bacteria indicator count is used to determine water quality, which results in more positive readings that classify the water quality as generally acceptable for full-contact recreation. While this might sound like good news to some, others have levelled severe criticisms against the report, with OREF, and Van Niekerk in particular, being accused of wanting to “lower standards” and “smoothing over the real issues”.

However, Van Niekerk stresses that his report does not minimise the issues or suggest there will be no risks. “The report is clear that this is not the case; it is an honest attempt to ensure that the most appropriate quality standard is applied and that we thereby have greater clarity regarding the health risks to bathers.”

Van Niekerk says the report was submitted to the Overberg District Municipality (ODM), as the responsible authority, to consider for implementation.

So what exactly are the conclusions and recommendations of the report?

Background In his report, Van Niekerk points out that Onrus River has been a sought-after family holiday destination for more than a century. Both holidaymakers and permanent residents are attracted to the area because of its natural beauty, with the Onrus beach and ‘lagoon’ (as it is commonly known) at the mouth of the Onrus River Estuary being a prime attraction.

“In recent years the quality of its water and doubts about its suitability for full contact recreation… received the greatest publicity and caused the greatest public concern, as the lagoon is especially popular with younger children due to its warmer and placid waters,” reads Van Niekerk’s report. “Warning signs, erected by the authorities, discouraged people from using it as a bathing area with consequent detrimental implications for the well-being of the users of the lagoon and the community at large.”

Although it is unfortunate that the appeal of Onrus as well as its local economy have been negatively impacted by these warnings, Van Niekerk says concerns about the water quality at the estuary mouth were not unfounded. Several studies have been undertaken over the years, including the Onrus Estuarine Management Plan, Situation Assessment Report, prepared for the Overstrand Municipality and the Lagoon Preservation Trust by Anchor Environmental Consultants (Pty) Ltd in 2016.

In this report, it is noted that, “Sewage contamination in the Onrus Estuary has been a long-standing concern. Sewage spills have occurred on occasion, and bacterial counts (indicators for faecal contamination) are frequently high. For example, in December 1999 only two pump stations were in working order and could not cope with the flows during the peak holiday season and the estuary has had to be closed to swimming at times, often during the peak summer season.”

The report also refers to a monitoring study conducted in 2007 – 2008 by Dr Vic Hamilton-Attwell at five sites on the Onrus River downstream of De Bos Dam, which “showed that faecal bacteria levels were relatively low at the dam outfall and Camphill, and increased towards the estuary. Since December 2010, the Breede-Gouritz Catchment Management Agency has been testing water quality at the estuary mouth, which shows that E. coli and Enterococci levels are very high with >185 and >500 organisms per 100 ml respectively.”

Van Niekerk says the continuous faecal contamination of the estuary has been ascribed to two sources: the Kidbrooke sewer pipeline, which was constructed in and close to the riverbed in 1996 and is in a poor condition; and leaking conservancy tanks, being earlier septic tanks reconfigured to link to a small-bore sewer system installed in the early 1990s. Both these issues were identified in a report by V3 Consulting Engineers in 2000 as having “the potential to pollute the estuary, particularly during rain events”.

According to Van Niekerk, water quality monitoring of the Onrus River and estuary is continuing; the Breede-Gouritz Catchment Management Agency (BGCMA) conducts bacteriological testing on a two-weekly basis and this is increased to weekly during the peak holiday periods. In addition, the Overberg District Municipality (ODM) in recent years also conducted its own weekly monitoring during these peak times. The BGCMA also conducts a monthly chemical analysis of the waters of the Onrus River and its estuary. This includes physical parameters such as pH and EC.

Actions taken by OREF In 2015 the Overstrand Municipality (OM) initiated the development of a management plan through a public participation process in accordance with the National Environmental Management: Integrated Coastal Management Act. Van Niekerk says the purpose of the Estuary Management Plan (EMP) is, “by means of a step-wise set of actions, to improve the estuary’s health, enhance its recreational utility and retain its sense of place”. Continues on P 4

The Onrus River Estuary Forum (OREF) was established in August 2016 to monitor and advise on the implementation of the EMP. Addressing the water quality was one of the most urgent issues for OREF to act upon. A portfolio committee was formed for this specific purpose and two actions to address obvious sources of pollution were activated: the upgrade of the Kidbrooke sewer pipeline and the replacement/upgrading of malfunctioning conservancy tanks.

In his report, Van Niekerk states that, “In 2016, environmental authorisation was granted for the upgrade of the damaged and degraded Kidbrooke pipeline. The project involved the in situ replacement of part of its lower section… the construction of two new pump stations and two rising main sewer lines to replace the rest of the old pipeline. The main pipeline replacement was completed in 2017 and the remainder of the project will be concluded in June 2019. The total cost of the upgrade will be R4.8 million.

“Two inspections of conservancy tanks were conducted – one in 2014 and the other in 2018. The first one resulted in a few tanks being replaced/upgraded. The second one, covering a larger area, found that relatively few tanks required replacement. The latter project, though, only covered some 50% of properties near the estuary. Evidence still exists of tanks in the area that are poorly managed and that could threaten the water quality in the estuary.”

Monitoring results Since its establishment the OREF has kept a close eye on the monitoring of results. Of concern were not only the frequently high levels of the indicator bacteria counts (E. coli and enterococci) but also the variability in the results and the difficulty of using the data in a coherent manner to communicate recreational safety to the public – being the responsibility of the ODM.

According to Van Niekerk, a meeting was held between ODM, OM and OREF in February 2018 to discuss and coordinate sampling procedure. “Since that meeting the record shows a marked reduction not only in the variability in the sampling results, but also the actual levels of bacteriological counts. This improvement is probably due to the attention given since to the sampling process as well as possibly the effect of the improve- ment of the infrastructure.” For this reason, says Van Niekerk, the bacteriological measurements from March 2018 onward should be used to assess the health risk for recreational users of the estuary as this data is more consistent, and therefore credible. The ODM uses the classification system of the Department of Environmental Affairs’ 2012 Guideline for Recreational Use.

According to these results, the water quality at the estuary mouth, as determined for enterococci, falls in the POOR category (90 percentile count greater than 185). On the other hand, for E. coli, the category is determined as GOOD (95 percentile count less than 500).

Appropriate indicators This 2012 guideline classification system, which was compiled for application on coastal marine waters, recommends enterococci as the most appropriate indicator to communicate perceived risk to users of the Onrus River lagoon. However, Van Niekerk points out that the Onrus Estuary is, in fact, a freshwaterdominated system. “This is confirmed by the electrical conductivity (EC) testing results over the past year. Salinity averaged over the period at 388 mS/m, or approximately

2 400 ppm. This should be compared to the salinity of seawater, typically 35 000 ppm.”

The use of enterococci as the primary indicator for the Onrus River estuary can therefore be questioned, he says. While the 2012 RSA Guideline deals only with coastal marine waters, the 2003 New Zealand guideline for recreational waters (on which the South African guidel ne of 2012 was partly based) covers both marine and freshwater situations. It is very specific about not using enterococci for freshwater conditions, as in the following extract:

The pathogens occurring in contaminated freshwater are the same as those occurring in marine waters, except that survival times in freshwater are likely to be longer, esp ecially for protozoan cysts (e.g. Giardia and Cryptosporidium) and viruses. E. coli is the preferred indicator organism for freshwaters, although there may be exceptions (e.g. in proximity to large waste stabilisation pond outfalls). Enterococci should not be used because some enterococci can multiply from natural sources, such as the decay of leaf material. This means that enterococci levels can be very high even in pristine waters, but this may not necessarily indicate high levels of pathogens.

Recommendations Van Niekerk therefore recommends that the E. coli data should be used as bacteriological indicator in the freshwater conditions of the Onrus Estuary. With the 95 percentile E. coli count of 353 per 100 ml being below 500, the category should be GOOD (according to the 2012 RSA Guideline). In both cases this would translate to acceptable conditions for fullcontact recreation. Van Niekerk therefore recommends that “the current POOR microbial classification of the Onrus River estuary should be adjusted accordingly and communicated to the public.”

However, Van Niekerk points out that there is currently no active operational management system in place for the Onrus River estuary. In his report he recommends that routine water quality monitoring should continue and that an operational management system should be developed for day-to-day management, based on the 2003 New Zealand Guideline. Sanitary inspections of all sewage infrastructure that may impact the estuary, including conservation tanks (old septic tanks) on private properties, should also be conducted programmatically.