From the Associated PressThe Defense Department has pushed back its completion date for destroying a stockpile of chemical weapons in Kentucky by two years.They're now estimating the work to destroy 523 tons of munitions at Blue Grass Army Depot near Richmond may not be finished until 2023, instead of 2021.The Defense Department is also raising the estimated cost for chemical weapons destruction plants in Kentucky and Colorado. The new estimate adds about $2billion. Defense Department officials say the new estimates reflect a more conservative and realistic assessment of potential operational issues that might arise.Craig Williams, who heads a watchdog group in Kentucky, says the new predictions are a worst-case estimate. He says he doesn't expect the projects to cost that much or take so long.