Was the land flooded or at least very damp last year? If it was, it
suggests it's the site not the builder at fault. Compaction by builders
often makes sites look more flooded than before but if there's serious
deterioration, it may be they've "broken" something.

But you need proper advice on site.

Steve Harris - Cheltenham - Real address steve AT netservs DOT com
A useful bit of gardening software at http://www.netservs.com/garden/