This gap is driving me crazy!

At the bottom of this page conald marlow there is a gap between the final ruler line and the top of the footer.  I cannot see why this gap exists.

I have a slight suspicion it may be  something to do with my ‘sticky footer’ which I have copied from css tricks  (I am using the first of the five methods described there).  I say  this because there is a div in that gap used by the ‘sticky footer’ with a class of 'push'  but it’s only 50px but that does not account for the rest of the gap.

There are other pages in my site that do not have such a gap, take a look at  annie or harry 

I have validated the html and the three css files involved and looked at the page with Firefox Developer tools but still cannot figure out why that gap exists – help!