The pumping station contains machinery that keeps the underground saltworks free of water.
Namely pumps. Large, industrial pumps. When the mine is operating, these pumps keep water from filling the lower levels of the mine by driving water into a serious of pipes that eventually drain to a nearby reservoir. These pipes have internal pumping mechanisms, but are aided by the heavy-duty industrial pumping machines topside.
The pumping unit also served as a power station for the underground pumps.
Since the closing of the mine due to the SNS outbreak, the backup pumps have mysteriously ceased operating, allowing the water to seep inexorably into the mine shafts, flooding the lower levels of the saltworks.