fairflyer, lengthening the existing runway will include in average a 10 m (33 ft) high landfill. Using only Google Earth as a land survey instrument, the orange area below has to filled out with compacked stone.
In addition to this three tunnels for the existing roads has to be built. The existing runway has to be widened from 23 m (75 ft) to 30 m (100 ft). 60 m (200 ft) wide safety zones to the east and west of the runway have to made (maxium slope angle for these are given by the autorities). And then there is the overrun safety zones at the ends of the runway, and for such small airports they now have to be 150 m (492 ft). The A3110 is border line to not crossing inside the overrun zone, but it has to be covered since it is angled relative to the runway centre line. In the south end (sea side) of the runway today's overrun zone isn't good enough and has to be corrected so that you don't end in the drink. These overrun zones can be shortened if EMAS (engineered materials arresting system) is used.
If there are no silt or clay and only a thin soil covering the bedrock, we are talking about between 700,000 and 800,000 metric tonnes stone masses for this landfill to fill the gully for a lengthened runway. This will mean a rather large quarry to get all that stone.