Brisbane Region Environment Council
Urgent Report on Risks Posed by Extractive Industry Site - Elimbah Ck
March 2 1999
To the Caboolture Shire Council
This is the Brisbane Region Environment Council's preliminary report on the risks and rehabilitation potential of the old mining site at Toorbul. The Brisbane Region Environment Council(BREC) believes that this site represents a imminent risk of serious environmental harm. (see attached Air Photo and Diagram)
The major risks are threefold, firstly the hydraulic pressure will breach both the Western and Eastern walls of the mine pit. This will realign the stream bed of Elimbah Ck. The old creek channel to the north of the mine site will, if starved of water flow, silt up and the unique fringing vegetation will dieback. This area to the north also contains some unique inland island ecosystems which will also be destroyed.
Secondly this breach will allow accumulated precipitates to be released into the waterway and then to flow on into the Pumicestone Passage. Given that these precipitates will contain a range of metals released from the soil by acid mine water there is a strong possibility that these precipitates will cause environmental harm. The levels of iron that could be released is sufficient, in our view, to exacerbate the Lyngbya problems in the passage. Our advice has been that iron, at the very least, will be present in a bioavailable form. The other metals could either have acute or chronic effects on downstream aquatic ecosystems depending on there bio availability and concentrations.
Thirdly the disruption to the integrity of the site and possible lower water level could expose more potentially acid generating sediments or parent rock. This will create an ongoing discharge of sulphuric acid and leached heavy metals into Elimbah creek and the passage.
Because of the imminent risk of serious environmental harm to the Elimbah Ck, Pumicestone passage and to wildlife downstream, we believe that the council should apply to have a Environmental Protection Order, under section 109 Environmental Protection Act 1994, placed on the company if it fails to voluntarily enter into a Environmental Management plan as per section 101 of that Act. We believe due to the risk of modification to an existing watercourse there could also be a possible breach of Section 42 and Section 70 of the Water Resources Act 1989.
Further Investigation and Rehabilitation
Firstly we need a complete physical test to determine horizontal water flow and further investigate the hydrology (any positive gradients) that exist between the old mine pond and Elimbah Creek.
Sediment tests need to be taken within a lm radius around the old pond water monitoring points. The sediment analysis should examine the cores in 30mm intervals in the top 300mm. Further tests of the core should be done at subsequent 1m intervals till the end of the core. We suggest sediment tests be done at all of the points on attached Diagram A. This will allow the correlation of water quality and sediment precipation patterns. The cores should be down to the mining depth of 7m although operators talk of 10m, and the mining operator refers to a coffee rock base at depth. We would also require further information about mining depths and did surveyors record a general slumping of surrounding ground levels with progressive mining operations?
Information is required about the dosing regime (pH trim). In-line continuous dosing of spoil (maintaining pH within control limits) may result in a more uniform colloidal lock up. Sporadic whole of pond dosing with large fluctuations in pH ie 4- to 9+ pH would result in precipitation of liberated metals in sedimentary layers over the then upper layer of the pond sediments , particularly around the discharge point.
Was the discharge point regularly moved, was there a record kept of these movements. The old exposed (to air) waste stock pile that promoted low pH pond levels, where, was it discharged?
The percentage (pond area) of submerged mined waste material positioned to be air exposed, when a breach between the creek and pond occurs again, needs to be determined Pyrite can oxidise in low fresh water situations. Confirmation is required as to the % of return to pond spoil material ie. 35% of extracted material / year, over the miner operational period , including prior leases.
After these investigations a contaminated lands management plan can be developed. The old mine pond will require internal reinforcement., although this may not stop the break through occurring.
It may be necessary to investigate a hardened flow diversion structure on the western or upstream side of the mine pond if a breach occurs to maintain some environmental flows to the old Elimbah creek channel.
The identification of hydrological conditions and sediment sampling is urgently required to prepare an effective management plan. The council needs to be aware that the breach of the mine pond wall is imminent and emergency services and councils authorised officers under the EP Act need to be alerted and emergency plans need to be developed.
We hope that the Council will take immediate action and we also hope that this brief report proves useful in the dealing with this very serious situation.
Yours SincerelyMichael Petter