in this regard is to keep the cell count in the heap in the range of from 10 6 to 10 12 cells ton of ore in another approach inoculum 72 from one or more of the reactors is directed to an inoculum pond 74 which is aerated 76 the pond is a storage and maintenance pond and as required inoculum 78 typically with a cell concentration of from 10 5 to 10 8 cells ml is directed to the irrigation system in another variation the inoculum 78 either from the pond or any of the reactors is directed into a small separate heap 80 which is operated under closed circuit conditions solution draining from the heap is collected in a pond 82 and either is directly re circulated to the heap or is stored and maintained in the inoculation pond 74 ore 84 which contains the inoculum is separated from the heap 80 and is then agglomerated with the ore in the heap 30 to help maintain the population of the consortium in the heap at an appropriate level it is also possible to direct the raffinate 58 and the intermediate leach solution 44 or a mixture thereof to the irrigation system to maintain the cell count in the heap in a different approach shown at the top right hand side of fig2 the inoculum 86 from one or more of the reactors 68.