If you haven’t checked out that book on how to survive Y2K yet, chances are you missed it.

The Charleston County Public Library is in the midst of its first major spring cleaning in 15 years, and officials say roughly 50,000 books are coming off the shelves. That’s between 2 percent and 3 percent of the 1.5 million volume collection.

Library officials say most of these volumes are damaged books, outdated histories or multiple copies of books that have waned in popularity.

Some of them are simply volumes that no one has checked out in years — such as “Resumes in Cyberspace,” which sounds like something helpful these days considering the economy. Until you figure out “Resumes in Cyberspace” was published in 1997.

“If they had done it as a spring cleaning every year, no one would notice,” said Douglas Henderson, executive director. “We’re not getting rid of anything of archival value.”

Henderson said part of the move is to clear shelf space for new material — the library adds 100,000 books a year. And some of it is to make way for new technology or additional space for people to sit and connect to Wi-Fi.

A letter to the editor in Saturday’s Post and Courier called the move a “great disservice” to the community that will affect its choice of books available to everyone.

Other library systems say this is just something that has to be done from time to time.

“Some tough decisions have to be made about what to keep and what to let go,” said Donna Osborne, Berkeley County Library director. “If a science book has Pluto listed as a planet, or we haven’t been to the moon yet, it’s probably time for it to go.”

In Berkeley and Dorchester counties, as in Charleston, determining whether a book stays or goes comes down to several factors: how many copies they have; whether the material is current; and if it has been checked out recently. Folks who study library science even take classes on how and when to discard books.

Lowcountry librarians say it all comes down to a library’s mission. Some are archival repositories, intent on keeping everything. But many public libraries rotate their collections to keep current.

For instance, books by Marcia Clark are not in demand because the O.J. Simpson trial happened nearly 20 years ago.

Rodger Smith, collections development manager at Charleston County Public Library, said libraries are no longer book warehouses.

He said a team of librarians evaluates books by several criteria to reshape the collection.

“You look at circulation, and if it hasn’t been used,” Smith said. “This hasn’t been done in a long time. We were concerned with filling up the shelves when we moved in here 12 years ago.”

With 100,000 new books a year coming into the 16-library system, Henderson said it is not as if the collection is on the wane. And circulation is up 11 percent, which he said means folks seem to like the material the library is replacing old stock with.

Many of the discarded books go to Charleston Friends of the Library, which sells them and donates the money to library programs and a fund to buy new material.

Emily Everett, executive director of Friends of the Library, said weeding the collection is the best way to “keep the collection current.”

“We have volunteers sorting books that come in or are discarded five days a week,” Everett said. “Anything that has any value, we sell and put the money back into the library.”

Reach Brian Hicks at 937-5561 or follow him on Twitter at @BriHicks_PandC.