Dave
I think you need a little bit more indirect, its just the side of the building / tanks looks a tad too dark.
Also you could do with a higher res grass map. Try creating a mowed lawn effect, that should help breakup the tile of the lawn, plus you should be able to create this really easy using a gradient and blend maps.
You really need a tarmac map, some lines on the roads too. Where the tanks park are likely to be concrete panels so again it will help to brake up the flat areas. How about some of the kit next to the tanks maybe fuel barells, pallets with anumitions etc. Make it look busy.
You could add some signage, you know the sort, stop signs etc.
Just some ideas.
Regards Anthony