Santee Cooper filed a $40 million plan today with the South Carolina Department of Health and Environmental Control to close its two ash ponds at Grainger Generating Station in Conway by constructing a vault around the ash and reducing the ash pond footprint by about 50 percent over the next three years.

The chosen method protects human health and the environment, meets regulatory requirements, maximizes sustainability. uses technically feasible, proven engineering and construction methods, and is cost-effective, the state-owned utility said in a prepared statement.

Santee Cooper retained Arcadis, an independent environmental engineering firm, to evaluate eight closure options before deciding on the vault plan.

If approved by DHEC, it would establish a barrier wall surrounding the ash. It would use the existing Bear Bluff Formation, which is a stiff clay layer some 15 to 25 feet below ground surface that is estimated to be at least 35 feet thick. The clay would confine and isolate the ash and groundwater. The vault would be covered by a synthetic cap.

Thick cement-fortified clay walls will be installed into the Bear Bluff Formation and will completely surround Ash Pond 1, according to designs worked up by engineering firm Worley Parsons.

The contents of Ash Pond 2 will be excavated and added to Ash Pond 1, reducing the footprint of the ash ponds and taking the height of the capped vault above the 100-foot flood level to an elevation of about 46 feet above sea level.

Finally, a multi-layer engineered synthetic cap system will seal the top of the vault, which will then be covered by soil and vegetation. The area formerly occupied by Ash Pond 2 would be maintained as wetlands.

“The vault is effective, permanent and a proven method to close such ponds,” said R.M. Singletary, Santee Cooper vice president for corporate services. “It will prevent ash from migrating beyond the vault, which also ensures water quality standards, and so it is safe for the environment. Additionally, because the material remains on site, it minimizes community impact by reducing the number of trucks required to complete the closure.”

The vault is the most cost-effective solution, according to Santee Cooper. It’s $50 million less than other plans that were studied.

“Santee Cooper is charged with delivering affordable, reliable electricity to all 46 of South Carolina’s counties and we must balance that charge with being a steward of the environment,” Singletary continued.

“We examined several plans that met environmental objectives and used proven technology and sound engineering, and then chose the plan which met that criteria and was the most cost-effective method of closure,” he added. “I am confident that this closure plan addresses the best interests of those living in the community near Grainger, our customers and the state as a whole.”