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The San Juan coal-fired power plant, west of Farmington, NM, was one of the first in the US to be freed from total on a holding pond for wetted fly ash, one of the by-product in the combustion process. At San Juan, a zero-discharge plant, fly ash is dewatered and eventually transported to an environmentally safe disposal area.

The plant has several back-up holding ponds, however, where some fly ash eventually settles. When fly ash filled one of the emergency holding ponds, the natural runoff that must drain into the pond had no place to go.

Because San Juan's holding pond is lined with soil cement, a dragline could not be used to remove the fly ash sludge. The dragline would have penetrated the liner. Instead, PNM leased a Mud Cat™ to pump fly ash from the pond.

The Mud Cat™ digs into the sludge with an auger at the end of a hydraulic boom. The sludge is sucked up and pumped uphill to a surge tank. There it is dewatered in a centrifuge and dumped onto a conveyor belt for transport. Sludge is then hauled by truck to the disposal site. The disposed fly ash is covered with overburden and planted with special grass seed developed for desert terrain.

The small, portable hydraulic Mud Cat™ pumps a greater percentage of solids than most dredges, according to maintenance supervisor Marvin Smith. An added plus for the dredge is the fact that it doesn't pump much water - a scarce commodity in the Southwest - so there is more left for plant reuse.

The San Juan plant is owned by Public Service Co. of New Mexico (PNM) and Tucson Electric Power. PNM is manager and operator of the plant, which supplies electricity to much of New Mexico and parts of Arizona. The plant has been operating more than six years.

Reprinted from Mining Engineering