The present drought offers an ideal opportunity to remedy the problems that have plaguedLake Weeroona for decades. Foremost among the problems are the insufficient depth of water, the build up over many years of high nutrient sludge from the old city salesyards in
Charleston Road (now a TAFE campus) and the consequential rapid and ever occurring weed growth. Weed growth that continually causes problems to recreational and sporting boat people.
Ballarat Council have over past years had some of these problems with their much larger Lake Wendouree. They have already had heavy earth moving machinery cleaning out their lake for several weeks.
Bendigo Council on the other hand according to an article by Anthony Radford in the ‘Bendigo Weekly’ p9, March 9, ‘07, will consider: "a report to be submitted to the City of Greater Bendigo council in the next few weeks has costed the dredging plan at $3 million, a lot more than expected".
Ballarat has been decisive and taken action. Bendigo will still be considering one of their now notorious, and often laughable reports, when the wet season sets in.
Bendigo Council has on several occasions over past years hired a weed cutting dredge from Ballarat in attempts to reduce the weed problem. Many of the present council hierarchy were unaware of this recurring cost to ratepayers.
Cleaning the sludge from the bottom of the lake and deepening it to a depth of at least three metres would solve most of the lake’s present problems for many future decades.
The high nutrient sludge from the salesyards is no longer a problem and the additional depth and much increased quantity of water to be held in the lake would mean a much cleaner and less weed prone body of water. The increase of the depth of water to 3 metres would enable small sailboats to use the lake. The present depth of 1 metre prevents any boat with a keel to safely sail on the lake. Many young people would welcome this opportunity, as a small sailboat can be transported on a push bike trailer.
Despite recent claims by Bendigo Council’s CEO that the present lake when full had depths of up to two metres, others, including many of the Bendigo Rowing Club members say that when full it is barely a metre deep in most places.
The "report" to be submitted to Bendigo council should have first considered the most cost effective and practical method of cleaning up the lake and solving its many problems.
By only considering dredging and then reporting on a ridiculous amount of $3 million dollars shows a lack of understanding of the problem or a bias with a distinct hidden agenda.
The "report" expresses a concern about arsenic contaminating the sediment of the lake and therefore the high nutrient soil to be reclaimed during the clean-up and deepening work. This shows that the author(s) of the report may not be aware of the source of arsenic in the Bendigo goldfields.
Most middle aged to elderly Bendigo and Eaglehawk residents who grew up playing on or around the numerous "sand heaps" and "mullock dumps" of the old goldfields will recall ‘mundic’ or ‘fools gold’ as it was also known. This is a brass-golden mineral that occurs in the Bendigo goldfields usually in association with quartz reefs, which may also contain gold, and often in the surrounding shale. The mineral name is arsenical pyrites, also known as arseno pyrites. It is not water soluable.
Accordingly, on the Bendigo goldfield when the mined ore selected for crushing was fed into the crushing batteries it would have contained the arseno pyrite associated with the quartz and shale ores also selected. The crushed ore reduced to sand, sized to pass through the screens as a water emulsion to the vibrating, gravity separating wilfley tables which separated the crushings into gold, arseno pyrite and sand. Naturally this was not a 100% perfect separation. The arseno pyrite would have contained some gold and a little sand, the sand some arseno pyrite and a small amount of fine gold.
The gold was melted in retorts to then be poured into gold ingots. Any small amount of arsenic present as arseno pyrite at this stage would have been vaporised off through flues as arsenious oxide. The arsenious oxide was readily water soluable and therefore poisonous, but the relatively small amounts involved and the vast surrounds of the mines apparently caused very little concern in those days.
The arseno pyrite collected from the vibrating tables was collected and sent to one of the independent pyrites burners or ‘roasters’ established on the goldfields. Evidence of two of these burners still exists in Bendigo. They are easily identified by their brick red sand heaps or tailing dumps:
One just west of the intersection of Specimen Hill and Marong Roads, on the southern side of Marong Road
The other, known as Leggo’s burner in the area between White Hills and Jackass Flat. This burner was operative throughout WW 2 years andcontinued on until the early 1950’s. It treated pyrites not only from the Bendigo field, but other Victorian and interstate mines.
The arsenic from pyrites treated by these burners also vaporised off during the roasting period and was exhausted through the flues in a similar manner to the vaporising occuring during the retorting process at the individual mine stamping batteries.
However, the vaporising arsenious oxide from the roasters did have some problems. The main problems occurred on cool dewy nights when the descending dew absorbed the rising, but readily dissolvable arsenic oxide. Bees foraging next day for nectar in blossom from the surrounding yellow box - ironbark forests were poisoned, resulting in the apiarists losing their hives and income. Surrounding pastures could similarly be poisoned, so creating problems with grazing animals.
At this stage the arseno pyrites collected from the ore via the crushing process had been disposed of by retorting or roasting. The remaining arseno pyrites was then confined to two situations:
The individual mine mullock heaps. These may still be in place today or may have been carted away to privately or council operated plants to be crushed and used for road base or concrete manufacture. However, if in exposed situations, the arseno pyrite still and will remain water insoluable. Hence not dangerous.
The individual mine tailings dumps or sand heaps. The arseno pyrite here has been reduced considerably in size as explained earlier. However, it is still water insoluable and presents no dangerous problems.
Some people may raise the further concern that many sand heaps or tailings dumps were treated by cyanide plants to extract any fine gold which may have eluded treatment at the crushing batteries and so was present in the tailings sand, commonly known throughout Bendigo as ‘blue sand’. Although used many years ago they are concerned that the cyanide could still be dangerous. Factually, the cyanide as used oxidises in a short space of time and becomes totally harmless.
Over the past 130+ years hundreds of thousand of tons of this ‘blue sand’ has been distributed throughout Bendigo to home sites, before and often after the homes were built, to sports grounds, parks and gardens, as fill to loosen clay soils, and dozens of other uses.
This usage is still continuing today as council has recently authorised the sale of the sand from the Red, White and Blue mine sand heap. This sand will contain the usual amount of arseno pyrites, but once again in the water insoluable form.
Why then is there a problem from the arsenic in the lake sludge? It is very doubtful if any arsenic is present in the sludge. If water soluble it would have raised concerns years ago.
If arsenic is present where did it come from? The sales yards over many years flushed down to the lake considerable amounts of animal waste and similar organic effluent.
There would be negible arsenic from that cobblestoned source. Similarly, the few local gutters discharging storm water into the lake would have a very limited, if any supply of arsenic.
Under these circumstances it would appear to be a very positive move for council to initially arrange the collection of as much nutrient rich sludge and silt from the bottom of the lake and store it for future use on parks, gardens nature strips and similar applications.
However, this sludge/silt collection may have to wait until the water remaining at the start of the clean up is collected in a large collection pit dug by excavators in a then dry area of the lake bed situated as close as possible to the edge of the lake adjacent to the Bendigo creek. The excavators should be able to load directly into large tip truck/trailer combinations. It should not be difficult for these trucks to deliver their loads to a temporary storage site within a kilometre of the lake. This pit should be about 4 metres deep and capable of holding the bulk of the water then remaining in the lake.
A decline trench should then be dug from the water then closest to the pit, to the pit itself, through the intervening dry lake bed. The aim of this trench would be to progressively deliver the remaining water, with minimum amounts of sludge, into the water collection pit. Then, as soon as practicable, the collected water should be pumped through a suitable sized pipe (probably 150-200mm) over the lake bank and into the sewer main situated in the creek bed. This water could be treated as waste water at the sewage treatment plant and then returned to Bendigo. The decline trench could then be extended or herringboned into the remaining water and the then drying remaining sludge/silt carted away and added to the previously removed sludge/silt.
Now the real work begins. Additional large excavators and truck trailers are brought in to speedily deepen the remaining area of the lake to 3 metres. Wet weather could easily be approaching, so all inlet channels providing storm water to the lake must be diverted. A considerable amount of fill will be obtained from this exercise, but good clay rill appears to be always in demand. it can be a saleable item.
At this stage animal activists may be required to look after the birds, fish and tortoises domiciled at the lake. Many of the birds may temporarily migrate (or could be helped) to take up temporary quarters in a large dam adjoining the northern side of Powell Street in the White Hills or other dams may be available in adjacent areas. Crusoe or Spring Gully reservoirs could be suitable sites for such relocations of the lake’s wildlife. The fish are probably mostly European carp and therefore of little consequence. Most of the tortoises should be easily caught throughout the whole operation.
The approach to cleaning up and improving the quality and useability of the lake as outlined above could come in at 1/10th to 1/6th of the proposed dredging plan, initially costed at $3 million dollars. i.e. $300,000 to $500,000.
At the moment of drafting this document Bendigo still has a small window of opportunity available to implement significant and relatively low cost improvements to Lake Weeroona. Will our council quickly grasp this opportunity, or as has happened so often with our councils of recent years, will our present council still be fiddling while Rome burns?
Ray Foley
Strathfieldsaye