Further to previous rumours that CH2M were looking for an external investor to ease their cash flow problems, Apollo Global Management has taken a $300M stake in CH2M Hill. More details at the Wall Street Journal (http://www.wsj.com/articles/apollo-to-buy-minority-stake-in-engineering-services-firm-ch2m-hill-1432778211).
Another news report (http://www.infrastructure-intelligence.com/article/may-2015/ch2m-secures-300m-investment-backing-strengthen-financial-position). This also includes mention of the Halcrow purchase as costing CH2M £230M. The substantial increase from the agreed purchase price presumably includes the cost of filling the financial hole that CH2M discovered after taking over.