We have a question in from Mark, who says he doesn’t know much about the proposal, but he heard there were issues with having town water supply in a dam downstream from the Mt Marlay Treatment Plant. 

The issues with the poor state of the existing sewage treatment plant have been well covered by the local press.  There have been a number of cases where effluent has ended up in the waterways. 

Any water taken by SDRC from Emu Swamp Dam will need to be treated, and of course this is no different to Storm King Dam.  The question though is will the treatment required be roughly the same? 

An SDRC employee has advised that they do not yet know whether the existing treatment plant will be able to treat the water from Emu Swamp Dam.  This will not be known until they can do some water sampling from the dam itself, if it goes ahead.  Once they have samples SDRC can determine whether (a) the existing water treatment plant is sufficient, (b) whether they need to make alterations to the existing treatment plant or (c) whether they need a new treatment plant.  The costs of options (b) and (c) are unknown at this point.

What we do know is that there is significantly higher agricultural run-off in the Emu Swamp Dam catchment compared to the Storm King Dam catchment.  The Sinclair Knight Merz report to SDRC of 1997 describes the Storm King Dam catchment as “Much of the catchment is covered with eucalypt forests.  Relatively little of the catchment has been cleared for cultivation or pasture production.”

By comparison, The Broadwater (upstream of Emu Swamp Dam) was described in the same report as “Water quality could be a problem in The Broadwater dam.  There is extensive horticultural development within its catchment, and given the normal irrigation management methods and fertile application rates within this industry, it could be expected that significant amounts of nitrates and phosphorous could find its way into the dam.  Apart from the resulting algal blooms, this situation is best avoided if possible for an urban water supply.”  It further stated “Considering the high capital cost and likely poor water quality of a dam on The Broadwater, it is considered that this would not be a suitable water supply source for Stanthorpe.”

The EIS for Emu Swamp Dam states that the “total nitrogen and phosphorous concentrations were more than four times and three times higher respectively, than guideline values.  The elevated concentrations may be attributed to surrounding agricultural land uses, geological features or groundwater influences in the catchment area.”  It later states “The median concentrations of aluminium, zinc and copper also exceeded the ANZECC 95% protection level, whilst the median concentration of copper also exceeded the less conservative 90% protection level.  These concentrations may be reflective of the geology of the area, but may also be influenced by surrounding agricultural runoff.”

We know it’s not much of an answer Mark, because it’s a case of “who knows”?  But the issues with the Mt Marlay Treatment Plant and agricultural chemical run-off are live ones, and will need to be answered should SDRC proceed with an investment in Emu Swamp Dam.