The State Ports Authority has relinquished its rights to a valuable sliver of real estate across from its Concord Street headquarters - but not without getting the city of Charleston to return the favor.

The city asked the SPA to abandon its claim to the property so the site could be sold for $6 million this week to a condominium builder. The port board agreed to the request at an emergency meeting Tuesday, capping several weeks of negotiations.

The real estate sale hit a snag about six weeks ago, when representatives of Estates Inc., the Columbia-based buyer, discovered the port authority controlled certain rights to the land under a 1981 agreement.

The narrow strip at Concord and Cumberland streets was part of a larger tract that the city acquired from the SPA to build a municipal parking garage. Under that deal, the SPA retained the option of acquiring the half-acre parcel if a maritime office wasn't built on it, said Bernard S. Groseclose Jr., president and chief executive of the ports authority.

With upscale residences proposed for the land, the SPA could have invoked its so-called reverter clause. Instead, the condo plan presented the state agency with a chance to renegotiate and "secure certain rights" that the city has over some port-owned properties, according to a resolution approved by its board this week.

The discussions resulted in several concessions.

The city will relinquish all options to acquire the SPA's existing cruise-ship passenger terminal and other properties within Union Pier. It also agreed to work with port officials to ensure that the closed-off portion of Concord Street remains closed for at least as long as BMW automobiles are loaded, unloaded and stored on that part of the peninsula.

In addition, the city will give up its right to reacquire a prime spit of SPA real estate on Charleston Harbor where, up until the mid-1990s, the Navy demagnetized minesweeper ships. The port authority, which has owned the degaussing station since 1947, no longer needs the elevated two-story structure, which juts out over the water and includes three-fifths of an acre. "We have interests in selling it," Groseclose said.

The city isn't ceding much by clearing the way for what is expected to be a quick sale of the station south of Waterfront Park. According to the original deed, the land would revert to the city only if the SPA ceases operations in Charleston.

Residents of the nearby Charlestowne neighborhood in the past have expressed concerns that the property might be developed for commercial purposes. Mayor Joe Riley said last month the city would oppose any new structures on the site.

The give-and-take stemmed from the city's decision last March to sell the Concord and Cumberland property to raise money for affordable-housing projects. Officials ultimately picked the development proposed by Estates Inc., which agreed to pay $6 million for the site. Plans show 28 one-, two-, and three- bedroom residential condos.

"We hope to start construction immediately," said Bob Mundy, president of Estates.

Charleston attorney Charlton deSaussure Jr., who represented Charleston in its talks with the port, said the city didn't anticipate any problems from the deal. Officials thought the SPA's land option on the condo site expired in 1988, he said.

DeSaussure said the city agreed to the conditions that the SPA approved this week to finalize the deal with Estates Inc. and "to clean up a lot of loose ends" that were negotiated with the port in a rash of real estate transfers 25 or more years ago. "The city and the port authority have been very good partners, and that continued in this situation," deSaussure said.

The Union Pier concessions are not expected to diminish the city's role in the eventual redevelopment of the shipping terminal, deSaussure and Groseclose said. "As we move ahead on Union Pier, we'll work closely with the city to come up with an appropriate development plan," Groseclose said.

Reach John McDermott at jmcdermott@postandcourier.com or 937-5572. David Slade of The Post and Courier contributed to this report.