Gibson Generating Station Settling Pond

Project Name: Gibson Generating Station Settling Pond

Location: Owensville, Indiana

Engineer: Burns & McDonnell

Project Revenue: $7,717,023.00

The Challenge:

Dewatering was necessary as the pond was built below the groundwater level and all CCR material had to be completely removed for clean closure of the pond.

At times, the water table was higher than the bottom of the ash pond, saturating the ash and making excavation impossible. Groundwater levels needed to be controlled at a level below the bottom of the pond to allow complete excavation in a safe, stable environment. Adding to the challenge, the west border of the pond was an USACE levee and no dewatering could be installed within 60 feet (ft.) of the levee.

The Solution:

Griffin installed 47 drilled deep wells around 3 sides of the pond, varying in depth from 40-55 ft.  In addition to groundwater control, the free water in the pond was pumped and the drawdown of the free board water was limited to 1 ft. per day to prevent a rapid increase in outside pressures that could cause serious issues if there was a breach of the levee or the cooling pond. A filtration system was installed to maintain turbidity levels less than 30 NTU’s in the discharge flow; the system was sized to handle up to 10,000 GPM.

The Griffin Difference:

The in-depth preliminary analysis and modeling, coupled with field testing, allowed us to obtain

drawdown by placing wells on three (3) sides of the pond and honoring the 60 ft. USACE levee

setback. Griffin personnel were on-site 24/7 monitoring water levels and discharge to ensure compliance.