This proposed housing development site had been used as a plant yard and contained below ground fuel tanks which had been leaking for a considerable period.
It would have been possible to remove an assumed, say 500mm of soil from around the excavation left by removal of the tank and then take samples for testing at a laboratory to see if the contamination had been removed. If these showed continued presence of contamination then the operation would have to be repeated.
To avoid the expense of removing too great a quantity of potentially contaminated soil and the uncertainty and delay of removing insufficient contaminated material insitu testing was used. When the insitu results indicated that sufficient material had been removed samples were taken for confirmation in the laboratory.