FTSE 250-listed water, waste management and renewable energy company Pennon Group has announced the intended retirement of Colin Drummond, the Chief Executive Officer of its subsidiary Viridor and an Executive Director of Pennon Group. Drummond will take up the position of Non-executive Chairman of Viridor once a successor has been appointed, which is expected to be by the end of September 2013, the group stated.Ken Harvey, Chairman of Pennon Group, said: "Colin has made a tremendous contribution to the success of Viridor and Pennon over many years. His leadership of Viridor and the development of its strategy have resulted in the company becoming one of the largest and best respected recycling, renewable energy and waste management businesses in the UK."Pennon's share price was down 0.39% to 642.50p at 10:48 on Wednesday.MF