(ShareCast News) - Pennon director Ian McAulay has resigned with immediate effect as he stepped down as chief executive of the FTSE 250 group's waste business.McAuley was leaving to "pursue other opportunities", though chairman John Parker said he left Viridor "on track" to meet management expectations for the current financial year.Pennon has promoted the waste unit's chief operating officer Phil Piddington as managing director with immediate effect.Piddington, a former BP Energy and RWE executive, joined Viridor in 2014 to take charger of its newly established portfolio of the energy recovery facilities.Parker said his "wealth of operational experience will be an asset to the company".A recent note from Credit Suisse highlighted the risks around Viridor's long-term municipal contracts: "These remain exposed to commodity prices and local authority counterpart risk which, in an environment of austerity and funding pressure, are not insignificant."Viridor has roughly £295m to invest in its remaining energy-from-waste facilities.Credit Suisse predicted net debt will peak at circa £3.0bn in the year to March 2018, after which Pennon begins deleveraging.