Thanks for a summary of the very complex legal issues.
So what happens next? Any money to reduce the deficit can only come from one place: i.e. CH2M Hill, and recent reports suggest a precariousness in the company's trading position. One outcome mooted at the Employee Roundtable Q1 2016 is a merger or a buyout by another company. So the deficit will get passed on to the next incumbent.
See the comment here (http://www.halcrowpensioners.org.uk/forum/index.php?topic=153.msg825#msg825) which, I think, also addresses this question.