Water Retention and Hydraulic Conductivity Characteristics of Ponded Fly Ash: Fid-Bau Portal

Water Retention and Hydraulic Conductivity Characteristics of Ponded Fly Ash

Wirth, X. / Tyndale, S. M. / Shivaprakash, S. H. / Burns, S. E.

Federal regulations concerning disposal of coal combustion products (CCPs) have prompted action across the United States to cap and close older, unlined coal ash storage ponds that do not meet the new federal, state, and local regulations. During operations, dewatering is performed to increase the strength and stability of the ponded ash, so that heavy construction equipment can work on the ash surface. However, some deposits of fly ash are not easily dewaterable and exhibit significant water retention capacities. This work seeks to identify why coal fly ash has some unusual water retention characteristics. First, particulate mixes of fine sand and highly porous additives were tested for saturated hydraulic conductivity. Results indicated that including activated carbon or diatomaceous earth in the sand matrix decreased the saturated hydraulic conductivity by one to two orders of magnitude. Second, the saturated and unsaturated characteristics of samples of highly water-retentive ponded fly ash (FA) were investigated. The FA samples (treated and untreated) had a soil water characteristic curve of a silt. The high-residual water content of the ash was found to be due to the combination of water-retentive, highly porous diatoms and kaolinite. The main conclusion from this work is that the presence of porous unburned carbons, porous diatoms, and kaolinite contributed to the increased water-retentive capacities of ponded fly ash and ash/granular mixtures.