Monday, 17 December 2007

Result Unsatisfactory

A warning that the beaches are unsafe for surfing and swimming
is always a day late, at best.

Check out the DCC website here for up-to-date water test results

What are we being advised not to surf and swim?

Because of the presence of fecal contaminants in the water, swept along the coast from sewerage pumped out off the end of Lawyers Head from the Tahuna Waste Water Treatment Plant (WWTP).
-When there is a North-ish swell, the sewerage is washed straight back into shore to St Kilda, Middles and St Clair and Seconds beaches too.
The day the sign goes up is actually 24 hours after the contaminated water is collected to be taken away for testing.
Why the delay? because it takes 24 hours for the contaminants to grow enough of a culture to verify if it is present.
What do they test for?
Enterococci, because this bacteria lives the longest in Salt water, and is the most likely contaminant to be a health risk for swimmers and surfers.
"This is because the Lawyers Head outfall offers only minimal dilution compared to the greater level of dilution that occurs with a properly constructed outfall, such as the one at Green Island." - DCC
HISTORY of the Lawyers Head wastewater outlet.
It was commissioned in 1908. This was a huge improvement from previous methods of wastewater disposal which was dispersing the waste into the upper Otago Harbour.
So for the last 100 years almost raw sewerage has been pumped on to the beaches at Tomahawk, and Smails beaches.

The Tahuna Wastewater Treatment Plant
This facility was constructed in 1981. Since then the plant has undergone a number of improvements especially the installation of odour control biofilters.
In the short term chlorination has been chosen as the best means of disinfection.

In the longer term, the Tahuna WWTP itself will be upgraded to UV treatment. This will occur by September 2011. According to the DCC "In-depth risk analysis, using computer modeling, has shown that installing an outfall at 1100 metres off the coast, discharging chlorinated effluent, would effectively give the coastline a clean bill of health in terms of indicator bacteria for swimming and shellfish gathering."

Below: application for consent through the Otago Regional Council to discharge sewerage from Lawyers Head.



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