2014/16 – Stamford Hill Tank, Bacchus Marsh (Victoria) – Streptococci

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Stamford Hill Tank, Bacchus Marsh 9 Jan 2014 (Lerderderg locality)

Issue
Routine sampling at the Stamford Hill tank resulted in a faecal streptococci detection of 1 org/100ml in the presence of 0.01mg/L free chlorine and 0.06mg/L total chlorine.

Actions

As per procedure, this tank was spot dosed and resampling conducted at the tank and two reticulation sites downstream of the tank. All results were clear of any
microbiological detection.

This tank receives freshly chlorinated water from a nearby booster chlorination station. It was thought that there may be some short circuiting occurring in the tank. This was investigated through an extensive system analysis of historical chlorine residuals in the reticulation system
supplied by this tank.

Stamford Hill and Gisborne Road Tanks, 7 Feb 2014
(Lerderderg locality)

Issue

Routine sampling resulted in two detections of faecal streptococci at two separate tanks, on Stamford Hill and Gisborne Road. The results were 2 orgs/100ml and 4
orgs/100ml respectively.

Actions

Both tanks were spot dosed and resampling was then conducted over three consecutive days with all follow up results remaining clear.

At the time of the detections it was noted that the chlorine residuals were dropping away rapidly from the treatment plant. Investigation into the water quality showed an
increase in dissolved organics as well as soluble manganese.

The water being treated at the time was a blend of Merrimu water and Djerriwarrh Reservoir water. The Djerriwarrh Reservoir water was found to be the source of the organics and manganese. Blending was discontinued and 100% Merrimu water was supplied with chlorine
residuals stabilising shortly afterwards.

4/2/16: Stamford Hill Tank Bacchus Marsh

Stamford Hill Tank, 4 February 2016 (Bacchus Marsh) Issue – Routine sampling at the tank resulted in a detection of 1org/100ml of F.strep in the presence of 0.17mg/L total chlorine. Actions – The tank was isolated from supply and spotdosed with chlorine to return a residual of 0.82mg/L total chlorine. The freshly chlorinated water was pumped into the reticulation system via pump station. Resampling was conducted for three consecutive days with all results clear of F.strep. The reported routine result was declared as a false positive. The tank was inspected and some ingress at the inspection hatch was suspected as the root cause, however resampling demonstrated no contaminated water was supplied to customers. Outcome – During early 2016, the tank was assessed by external consultants for refurbishment and a booster chlorinator was installed in 2016.