Sewer outfall ‘safe’
• Taswater’s effluent outfall pipe at Bridport’s Granite Point and (inset) a new warning sign against swimming in or drinking the sea water.
By Tony Scott,
November 03, 2021
TasWater has answered criticism over its management of the sewerage treatment plant at Bridport, saying its regular failure to meet outfall standards is nothing to worry about.
The organisation says it will accept an offer from community group Bridport Innovations to attend a public meeting early next year to explain the situation.
Bridport water advocate Leg Gillett has been on the case and recently took TasWater to task for its performance in both sewerage treatment and water supply in a presentation to a Coastwatch group.
Mr Gillett said the lagoon-based treatment system is generally the worst performing in the State, with effluent not meeting standards for discharge to a waterway more than half of the time.
“Our average compliance for the last five years has been just 47.3% of the EPA standard.
“There have only occasionally been other towns around Tasmania that have not achieved 50%, such as Port Sorell, but for them solutions have been proposed.”
He said the standard for measurement of the Bridport outfall was changed early this year from the nationally used Accepted Modern Technology system to a new Environmental Protection Notice devised by the state Environment Protection Authority.
Despite being more compliant with the more lenient standard, the plant's performance had not changed dramatically, even after installation of more aeration equipment.
Taswater’s Department Manager of System Performance and Productivity, Fran Smith, explained the changed standards saying the AMT limits were typically applied to facilities with more complex technology than lagoon style systems, and the new EPN was in line with most similar lagoon systems.
“TasWater takes a risk-based approach to managing assets to ensure communities are well serviced and to limit environmental impacts,” she said.
The annual nutrient load (the total loads of phosphorus and nitrogen released) was below the limit set by the EPA.
“The plant is 100 percent compliant with regard to oil and grease levels, the pH range, and importantly E. coli.
“The fully compliant E. coli result protects the recreational values of the receiving environment and relies on the use of chlorine.”
The natural UV process in these lagoons does not deliver the required micro-organism kill to meet the E. coli licence limits, therefore an additional disinfection process is required.
The only means available for disinfection of the effluent is chlorine, so in order to achieve the low risk E.coli levels there is a high load of chlorine.
Half of the samples tested exceeded the levels set for ammonia, and 58 per cent exceeded the maximum suspended solids and biochemical oxygen demand limits.
However, all results in 2020-21 for these parameters were still considered low risk to the environment.
“TasWater has undertaken ambient monitoring of the water around the outfall finding no adverse environmental impacts and these results are shared with the EPA,” Ms Smith said.
Mr Gillett said the Bridport system is more than 40 years old and attempting to service a very different township than what it was back then.
TasWater said the original two lagoons built in 1978 were augmented in a third in 2002 with the effluent undergoing supplementary disinfection before being discharged at Granite Point.
During summer some of the effluent is recycled and used to irrigate the Bridport golf course.
Ms Smith said as the latest ambient monitoring shows no adverse impacts on the environment, the more immediate community impact of odour was being prioritised.
“Odour occurs when the system becomes overloaded, typically when Bridport receives increased visitations over summer.
“New aerators have been installed, and the optimisation team has started a detailed sampling program to determine what further aeration may be needed.
“While the process data is being assessed, we have identified additional measures that can be completed to improve performance and effluent quality.”
These include a baffle to reduce short circuiting in lagoon one to improve treatment and a venturi pump to increase the aeration in preparation for the upcoming summer period when loads increase to the treatment plant.
“These are interim measures until the process data can be used to identify a more permanent solution,” Ms Smith said.
TasWater is also working towards a permanent solution to Bridport’s problematic water supply, with a pipeline from Scottsdale in its capital works program for 2022 – 2026.