DPI Update (Issue 58)
COLIN THORNTON, General Manager Minerals and Extractive Operations, discusses critical issues with dams at quarry sites.
WATER and water management are critical issues, not only for the Earth Resources industry, but for society in general. Within a year we have seen the emphasis go from the need to manage water usage in a water constrained environment, to ensuring operations are designed and operated to cope with large rainfall events. Over the past twelve months the Operations Branch of the Earth Resources Regulation have undertaken two targeted audits in the water space, most recently focusing on embankment dams.
During the January-June period of 2010 DPI officers completed thirty six targeted audits on mines and quarries across Victoria inspecting their management of water dams on site. Each audit assessed compliance issues and the overall performance in relation to the design and operation of water dams. Tailings Storage Facilities and dams without constructed embankments (i.e. old pits & excavations) were not included.
There were sixty eight dams assessed at the thirty six sites visited. The dams inspected were used for wash plants, various processing uses, dust suppression and site runoff/sediment settling. Dam size varied from less than 500,000 litres to over 60 Megalitres.
Embankment height (at the highest point) varied from 1 metre to over 6 metres. Only five dams assessed were licenced with the applicable water authority. A further three dams were identified that required assessment by the relevant catchment authority. The remaining dams assessed did not require licencing.
OPERATION AND MANAGEMENT
Only 15% of quarry operations assessed had dam operating plans, operating procedures or other documented methodology for operating their dams, compared to 80% of mine sites. All other Work Authorities had no dam operating plans or procedures. This deficiency was mitigated by the generally smaller volume of quarry dams and the fact many dams were often only utilised for washing, dust suppression purposes, or capturing run off . Many operators were able to describe anecdotally procedures for dam control and water management.
All but four sites inspected were able to show documented dam inspections or provide details of regular visual observations undertaken. However, only half of the sites were able to show the recordings of abnormal features identified and reported to senior levels of management. Almost a third of sites did not record dam faults identified or actions taken to rectify those faults.
DESIGN AND CONSTRUCTION
All but six dams assessed on quarry sites had been approved under the current site work plans. Twenty percent of dams at quarry sites had been constructed to guidelines on the safe design and operating standards for water dams. Most dams had been constructed by previous operators, often many years before. Of these, no design documentation or construction reports were found to exist.
PUBLIC SAFETY & PUBLIC INFRASTRUCTURE
All but one tenement assessed had adequately protected their dam sites against access by unauthorised personnel. Sites were generally fully fenced. In addition many dams themselves were also further fenced. Gates and appropriate signage were in place.
CONCLUSION
Overall, only 19 of the 36 sites audited were able to provide objective evidence of good dam design, construction, operation and management of their embankment dams. However, 93% were found to comply or substantially comply with the requirements in their own work plans and/or work plan conditions.
Six tenement holders have been required to submit work plan variations to rectify identified deficiencies or to apply for a modification of conditions. A number of notices and directions were also issued and will be followed up to ensure compliance.
All quarry dam owners are legally responsible for the safety of their dams and any problems these dams may cause if they fail. Dams on quarry sites require regular inspection and maintenance to keep them in good order.
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