Built atop a former landfill, the State Ports Authority's Columbus Street Terminal sinks close to an inch a year.

So every 12 years the state agency has to build it up again to keep the tide at bay.

The latest round of work will start in October on 54 acres of the 135-acre peninsular Charleston terminal. It should be completed in April at a cost of $20.57 million. About $16 million is for asphalt alone.

"If you are driving over the bridge and look down, you can see water puddling in low places at high tide," said Joe Bryant, vice president of terminal development for the SPA.

By reinforcing the subsurface and repaving the terminal, it will keep the Charleston Harbor shipping terminal about a foot above the highest water mark, he said.

Banks Construction of North Charleston won the low bid, and engineering firm S&ME of Mount Pleasant will provide quality assurance services at a cost of $216,000.

The work is not expected to interfere with port operations, said Byron Miller, the SPA's director of marketing, public relations and planning.

The SPA board also voted to spend about

$1.6 million to thicken pavement on seven acres at North Charleston Terminal in an area serving Evergreen. Banks Construction also won the bid, which was about $1 million below budget because the SPA found it did not need as much subsurface rock as was estimated.

In another move, the board voted to spend up to $3.2 million on gate modifications at SPA's Wando Welch and North Charleston terminals.

Improvements include new computers, truck scales and personnel booths.

"It's one of the most significant things we've done," said Jim Newsome, president and chief executive officer of the SPA. "It will be a big win for the port."