The first thing you need to understand is that Hong Kong International "Chek Lap Kok" is built entirely on a man made island off the side of Lantau island.
Current growth estimates, again from CNN suggest that by 2030 Hong Kong's air traffic will increase from fifty million annually to nearly one hundred million annually with a matching increase in air freight. The airport pretty much has to have the runway to meet the need.
If you're looking for ground transportation info. on the airport, try here.
So what's the problem?
Being a city of seven million people on a landmass of only 426 square miles, Hong Kong places tremendous pressure on the ocean around it. There, water pollution, noise pollution, habitat destruction and a host of other issues. Put into the context of the overall human impact on the ocean around Hong Kong, the new runway doesn't seem as big a deal.
Physically, while 5000 Olympic swimming pools seems very large, compared to the size of the ocean, or even just the waters around Hong Kong, it's not much space, less that 1/2% of the total Pearl River estuary. The real questions have to do with water pollution and noise pollution and these questions remain largely unanswered at this point.
Fortunately, Hong Kong is a world leader in Environmental initiatives. Fully 40% of Hong Kong's landmass is dedicated to parks and wildlife preserves. (Maybe that's why Nathan Lane always seems so crowded.) They have a strong environmental lobby and a track record of balancing human needs with the need to preserve their beautiful heritage.
The staff of HKG recently put out the "Hong Kong International Airport Master Plan 2030" out lining their plans. You can see the video they put out on the subject here:
Can a third runway be put in at Hong Kong International Airport without sever environmental impact? That has yet to be seen, but if any city in Asia has the power and smarts to grow and grow green at the same time, it's Hong Kong. Good luck little pink dolphins! Good luck HKG!
For more information on the Hong Kong International Airport click here.