Here is a picture of Arrium's dolomite mine at...

Here is a picture of Arrium's dolomite mine at Ardrossan

http://ardrossan.sa.au/business/primary-industry/onesteel


Notice how little water is at the bottom of the pit and it is 400 metres deep.

Now if you go south about 8-10 kms along the same line of hills you will find Hillside. It is about also on a hill similar to the dolomite mine and also about the same distance from the sea.

IMO it looks to me that we are not going to get big problems from sea water seepage. There may be some as the picture shows.

Also I visited the dolomite mine in November 2012. You can drive your car up to the lookout at the top off the mine.
Only a very small pond of water at the bottom similar to whats in the picture was evident at the time.