South Carolina Electric & Gas Co. will shut down six coal-fired generating units, including all three at a plant near Walterboro, by the end of 2018, the Cayce-based affiliate of SCANA Corp. announced Wednesday.

The utility will close the first of three units at Canadys Plant in Colleton County by the end of the year.

Two other units will be switched from coal to natural gas by 2015 before being shut down by the end of 2017.

SCE&G will also switch Unit 3 at its Urquhart Plant near Aiken from coal to natural gas by the end of this year and close the unit by 2018.

The company also will switch the two coal-fired units at its McMeekin Plant near Irmo to natural gas by 2015 and shut down the plant by the end of 2018.

The units at all three plants range in age from 45 to 57 years old and are SCE&G’s oldest and smallest coal-fired operations.

SCE&G said the Environmental Protection Agency in recent years has issued a series of increasingly stringent regulations targeting coal-fired electric generating plants.

Since 2008, SCE&G has installed more than $600 million in environmental equipment at its largest coal-fired power plants, significantly reducing emissions of sulfur dioxide, nitrogen oxides and mercury. The company determined that adding costly environmental control equipment to these older plants to ensure compliance with the new regulations would not at this time be a good business decision.

“Since announcing our new nuclear project in 2008, we’ve said that the addition of the two new nuclear units would give us flexibility to look at reducing our reliance on coal and allow us to achieve better fuel diversity in our electric generation portfolio,” said Kevin Marsh, SCANA chairman and CEO.

“With the planned retirement of these coal units and the addition of our two new nuclear units, we anticipate that by the end of 2018, roughly one-third of our electric generation will be fueled by nuclear power, one-third by natural gas, and one-third by scrubbed coal-fired plants. These changes will help us meet the increasingly stringent environmental regulations facing our industry and should position SCE&G to be a leader in non-emitting generation well into the future.”

SCE&G employs about 170 people at the three affected plants. The retirement of Unit 1 at Canadys will affect six employees and the switching of Urquhart Unit 3 to natural gas will affect 14 positions.

Canadys employs about 85 people, according to SCE&G spokesman Robert Yanity.

The company said it will help employees look for other positions within the company.

Read more in tomorrow’s editions of The Post and Courier.

Reach Warren L. Wise at 937-5524 or twitter.com/warrenlancewise.