BARBARAELLEN KOCH FILE PHOTO | The Riverhead Charter School on Route 25 in Calverton.

The Riverhead Town Planning Board approved a proposed two-story, 49,000-square-foot building for the Riverhead Charter School Thursday.

The new school, located to the south of the 5.8-acre property on Route 25 in Calverton, will replace an existing 8,000-square-foot modular school building that the school has been using on an interim basis for several years.

The Planning Board also approved 1998 Peconic LLC’s proposal to build a 17,000-square-foot building on a lot immediately southwest of the charter school property.

At a Feb. 7 public hearing on the charter school expansion, Keith Brown, an attorney for 1998 Peconic LLC, raised concerns about children from the school wandering onto his client’s industrial property.

“We don’t want to be liable if, God forbid, any child goes from that (charter school) property to a property with industrial purposes,” Mr. Brown said at the time.

The charter school agreed to put up a fence separating the two properties. The school agreed to pay for 75 percent of the cost while 1998 Peconic pays the remaining 25 percent.

Headed by Paul Elliot and Jim Miller, 1998 Peconic — a real estate development company — also owns the property west of the charter school where a gas station and convenience store are located. It also owns the vacant property just south of the Cinco de Mayo restaurant, on which it received approval for a drive-through pharmacy and a bank last year, neither of which has been built.

The Planning Board approval also gives the charter school an extension on the use of the modular building on a temporary basis until July 15, 2015. The school had received several prior extensions for the use of the modular building, with the most recent one slated to expire on July 15, 2013.

The charter school currently goes from kindergarten to sixth grade, and it hopes to add seventh and eighth grades with the new, larger building.

The additional grades, which require approval from the state Board of Regents, would expand the school’s maximum enrollment to 400 students. It currently has about 275 now, according to officials.

tgannon@timesreview.com