Ash Storage Dam Redevelopment

Alinta Energy has a large storage dam to store the waste ash material from the coal fired power station. McMahon Services were contracted by Alinta Energy to construct a second line of levee embankments, increase the height of existing levees and supply and install pipe work for new decant outlets. The new embankment works were required improve factors of safety, thus ensuring protection against potential ash overflow into the surrounding environment.

Unique Site Challenges

The challenge on this project was the unknown environment. The ash and water in the storage dam made the ground soft and subject to uneven settlement. All construction needed to take place while the storage dam remained in operation and filled with continuous inflow of the ash slurry and outflow of clean water. Pipe work needed to be installed in part of the ash storage dam floor.

Construction of the Decants

The construction of the two decants was a five week process, using a total of 560m of 630mm HDPE pipe butt-welded on site. The 2250mm diameter concrete decant structures with outlet pipes were positioned in the ash storage dam. Rock was placed beneath and around the decants to provide strength and enhance the filtration of ash.

Creation of the Levee Embankment

130,000 cubic metres of ash excavated from the southern section of the ash storage dam were moved to the northern section to create the new two kilometre long levee embankment. The embankment was two metres high and had a six metre wide crest. The embankment was lined with Elcoseal to make it watertight. Geotextile and rip rap rock material was placed on the embankment face as protection against wave action. Two emergency spillways were also constructed for any overflow of water. These were lined with a fabric mattress filled with concrete.

In the future, the levee embankments will need to be heightened and strengthened coinciding with the increase of ash and water levels over time.