on reflection, my first effort at this was pretty watery. I was told to spell it out, in detail. So for example "this study advances the field of x by...' and then go through what you did. While your particular study is new it must surely be in a particular field so you have added to knowledge in this field. 'This study adds to previous studies of x. Furthermore the approach taken here advances knowledge of 'y'. It's hard to write withough knowing the field but hopefully you get the point. Originally I said my thesis added to my field and my supervisor replied 'how does it add?'. Don't be afraid to add to the field in a number of ways - your overall area, your methodology, your recommendations etc etc. Think how you go through your work experience on a CV. Break down your contribution to knowledge similarly. If you're going with the major, but essentially one untouched area, break this down into smaller bites.
My take on it...