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Gainesville Regional Utilities (GRU) has resolved a problem with the frequent maintenance of the five low-pressure sump pumps on Deerhaven generating statione's Unit 2 bottom ash handling system. The old sump pumps were subjected to abrasion from pumping water entrained with hard, crystalline bottom ash. Recently, three of the pumps were replaced with submersible pumps that have abrasion-resistant components and replacement liners.

The sump water, pumped by low-pressure pumps, is used for flushing the unito's three bottom ash hoppers and for purging the bottom ash sump. These pumps are also used to enhance the operation of the high-pressure pumps. Twice per day the high-pressure pumps pump the bottom ash slurry out to the settling ponds through an 8-inch, basalt-lined pipe. Some additional water with a relatively high concentration of the gritty bottom ash reaches the sump from the overflow of the bottom ash hoppers. Since only about 60 percent of this abrasive ash normally settles out in the sump, the sluice water delivered from the sump back to the hoppers has a fairly high amount of suspended fines.

The situation was further aggravated when the hopper system underwent a reconfiguration from a wall cooling system to a notched weir system. This enabled some of the overflow from the hoppers that had high concentrations of bottom ash to reach the sump. As a result the sump required periodic cleaning to remove the ash. In addition, the residual ash also damaged and dictated repairs to the five low-pressure pumps every three to four months.

Even so, adopting a smaller submersible unit designed for wastewater applications for the power plant sump proved to be a mistake in the sump application. The first submersible pumps soon became susceptible to lower end bearing failures and impeller and casing damage from the abrasive ash water. After the first year of operation these pumps also began failing.