Greater than the sum of its parts

Shenton Aquatic
Monday, 08 October, 2018


Greater than the sum of its parts

South Hedland Aquatic Centre in WA underwent an upgrade back in 2011. Plagued by ongoing water quality issues the facility closed and reopened a number of times, until a more permanent closure in 2015 drove the Town of Port Hedland to seek a conclusive solution.

South Hedland Aquatic Centre (SHAC) in WA’s Pilbara Region is a valuable health and leisure hub for the local community. It features a large outdoor pool for lap swimming, as well as diving and deepwater aquarobics facilities and a children’s leisure pool that incorporates slides, obstacles and water features.

Ongoing issues, including recurring Escherichia coli outbreaks and the repeated presence of Pseudomonas aeruginosa in backwash samples, left the centre with no choice but to shut the doors until a permanent solution was found.

The Town of Port Hedland (TPH) consulted experts from a range of fields for advice; several pool contractors were invited to weigh in, with more than one recommending a complete plant replacement — a cost the town was reluctant to consider. Site inspections carried out by representatives from both the State Health Department and the Leisure Institute of Western Australia were inconclusive with respect to a suitable solution. At one point, even the information technology (IT) staff from TPH were dispatched to site, as the installation incorporated programmable logic controllers (PLCs) and it was thought the IT gurus may be able to shed some light.

The issues

TPH had essentially lost faith in the commercial pool industry and basically resolved to rectify the issues without any industry input. Despite the scepticism, David Watson from Shenton Aquatic was invited to ascertain the issues. As he saw it, five key problems were at the root of TPHs dissatisfaction:

  • A series of pipe glue joints had failed and were buried under paving and/or concrete slabs.
  • There was a steady presence of E. coli in the AquaTower feature of the kids’ area.
  • Testing uncovered a constant and persistent P. aeruginosa bacteria count — primarily in backwash, but also in the water bodies themselves.
  • The facility had a non-functioning wave machine that required more staff to operate than there were total users.
  • Ongoing issues with heat pumps.

Watson is a self-proclaimed problem solver and gladly accepted the challenge, while also appreciating the TPH’s trust and support, given its concerns around the industry’s ability to resolve the problem.

A detail man, Watson assessed the situation thoroughly. He looked beyond the mechanics of the installation and factored in other details including the pool interior material, location, make-up of the water supply, the bathing populace, prevalent flora and fauna, operational behaviour and log books, as well as some expected particulars such as pump makes and models.

Watson said this approach gave him a feeling of place, expectation and an understanding of how the community uses the pool. It presented a high-level view of the main issues — and he uncovered several at SHAC.

The water

Part of the problem was the mains water make-up. Watson reviewed water quality data analysis provided by Water Corporation and noted several things.

  1. The readings for sulphate, chloride and potassium were all ion-specific, meaning the reading is not what you would see testing for these parameters using a pool test kit in the field.
  2. Water hardness shown is total hardness, not calcium hardness, as would normally be tested. Based on the reported calcium ion concentration (42–47), this equates to a calcium hardness equivalent to calcium carbonate of 105–120 mg/L.
  3. The pH result was 7.84 to 7.98. Pool professionals would normally aim for less than this (around 7.2 to 7.6). In a simplified explanation, Watson said this result meant a pH incoming main of around 8.2 would not be surprising. This likely meant that each time the balance tank was topped up the dosing systems would respond disproportionately, based on the pH being attained in the balance tank and not necessarily representing the entire pool volume.

Installation concerns

SHAC incorporates horizontal sand filters. While the Western Australian Department of Health had previously required backwash water to be tested and clear of the same bugs as the pool water once a month, this requirement has since been relaxed. According to Watson, installing the backwash lines so they completely empty after each backwash is the key to preventing bacteria growth. He thinks this simple and effective lesson has been lost in the murk of construction.

“The SHAC pool featured a filter of some two metres in height, connected to a backwash pipe rising about four metres to discharge into an above-ground tank. I’ve seen this on many sites and have noted that the pipe often contains water — it may not be full, but is potentially damp all the way back to the filters.

“This arrangement may work in locations where the climate is less aggressive, but at South Hedland it became a perfect underground petri dish environment that consequently kept back-infecting the entire system,” he said.

The perfect storm

There were other factors that contributed to continuing system failure. The make-up of Port Hedland mains water increased the tendency for the water to ‘plate’, creating a sticky surface that subsequently provides optimum conditions for a bacterial colony to emerge and thrive.

The region’s ambient temperature — which is warm even by WA standards — also contributes to the problem. Although the pipe work is underground, that temperature is likely to sit in the mid-thirties for most of summer, which is clearly not ideal as the incubation temperature for bacteria is typically 32°C.

Watson decided to research P. aeruginosa, the repeat offender in the backwash system. He found that treatment for infection in humans often required reducing iron levels which, according to several medical texts, slowed and eventually deactivated the bacteria. He figured SHAC’s proximity to Port Hedland — a major hub for iron ore exports — meant that iron egress into the pool water was highly likely. As a constant in the environment, iron is not easily treated and removed, so any rectification process would have to consider this.

Further exacerbating the issue, P. aeruginosa is chlorine resistant. Watson suggested a CT value of 15 is generally accepted, which would mean continuous exposure to chlorine at a constant value of 1.5 mg/L for 10 hours or 15 mg/L for one hour (or any other combination equalling 15) to have any effect. He pointed out that ‘continuous exposure’ was key here.

“This is important when looking at P. aeruginosa.

“To get continuous exposure, we first need to get at the bug, which can be a problem in pools. Even in the best maintained pool, this little bug likes to hide. It will find a space in the tiles, a gap in the pool shell or some dirt in a corner of pipework and hide there. This makes chemical treatment difficult, as the chemical needs to break down not just the bug, but all the dirt above and around it, while still maintaining enough strength to kill the bug once it reaches it,” he said.

Filter media is an ideal habitat for this particular bacteria, meaning it should be removed and disposed of at the first detection of P. aeruginosa.

When Watson thought about the bug’s propensity for hiding, he turned his mind to the installation’s infrastructure — specifically the pipework, which is constructed from acrylonitrile butadiene styrene (ABS). ABS has some great qualities: shatter resistance, thermal insulation and impact tolerance, for example. But Watson wondered if, like polystyrene, it also contained minute holes and crevices. Could this be the ultimate P. aeruginosa breeding ground?

He sourced some increasingly high magnification images of ABS, utilising scanning electronic, atomic force and, finally, transmission electron microscopy. The images clearly showed that ABS featured small catches, crevices and other suitable hiding spots for bacteria.

Conclusions drawn

Taking all of this information into account, Watson speculated that most likely the backwash line wasn’t clearing and that the water contained in the line (besides containing normal detritus) exhibited a plating tendency. He figured this, combined with the high ambient temperature, was providing ideal incubation conditions.

He then looked to operational activities. Chemical treatment happens post-filter so backwash water is, for the most part, raw mains. He asked to see a demonstration of the standard backwash procedure, which he found flawed by his estimation.

“The procedure went something like:

  1. Isolate filter from incoming water.
  2. Isolate filter from outgoing water.
  3. Open backwash valve.
  4. Open valve at the back of filter (a drain valve intended only for maintenance).
  5. Remove air relief/vacuum breaker.
  6. Drain the filter so water is observed just above the sand bed (observation port in lid).
  7. Run blower to agitate the sand (which simply moved the dirt about on the filter bed).
  8. Carry out some form of rinse.

“I was a bit taken aback and asked the operator where the procedure had come from. He produced written instructions that outlined almost exactly what he had done. The exception was removal of the air relief, which the centre had started doing to encourage faster emptying.

“I then demonstrated the original equipment manufacturer’s method of air-powered backwashing, which highlighted what I saw as errors in the original instructions. These were to open the backwash valve and let the filter drain off some water (the water above the top of the inlet pipe). This provides room for the aeration and agitation that occurs and pushes a small amount of water out of the filter,” he said.

Watson revisited the installation with this process in mind. As the backwash line rises above the top of the filters, he said this particular procedure was immediately identified as impractical, because the line could easily be full rather than empty. He suggested undue importance was being placed on opening the drain valve, as it was only necessary to provide space for agitation and not for any other purpose.

Rectification and recommendations

Given the breadth of problems, rectification of the issues at SHAC required a many-pronged approach.

The ABS backwash line was replaced with PVC alternative and an air gap was introduced, ensuring it drained completely on each cycle. Additional upgrades and minor improvements included replacement of some pipeworks entering the balance tank. This exposed previously hidden works, including pipes from the original pool which, rather than being removed, had been cut off and left open in the balance tank.

At one point, the 50 m pool returned a bacteria count, even after the backwash line had been replaced. It was identified as a failure to replace elbows in the line and immediately rectified by the contractor.

Watson recommended an alternate backwash routine which involved fewer steps, discounted removal of the air relief and relied on the equipment as installed. It resulted in the filters expelling dirt which was easily observable from the sight glass in the filter lid and meant the filter beds were cleaner. The process incorporated purging the backwash line (as thoroughly as possible) by opening a small valve near the backwash tank. In the weeks following, the pool water delivered satisfactory results.

Plumbing changes and a new filtration system for the AquaTower in the kids’ area completed the works.

The combination of rectification works delivered exactly what TPH was after — a permanent solution to the ongoing problems which had plagued SHAC off and on for years. By looking beyond the equipment installation and considering other potential external factors, Watson was able to deliver a functioning system without an unnecessary and costly plant replacement.

Image credit: © stock.adobe.com/au/trekandphoto

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