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Case Study: Water Plant Retrofit Eliminates Dwindling Capacity
January 5, 2006
•Case Study: Water Plant Retrofit Eliminates Dwindling Capacity
The City of Danville, Virginia undertook a recent $3.3-million retrofit of the municipal water plant to replace worn out equipment and to restore the 18-MGD capacity the state permits the utility to draw from the Dan River. The water utility serves approximately 50,000 customers with a 310-mile distribution system and also operates municipal electric and natural gas utilities.
Although portions of the plant infrastructure originated nearly a century ago, a series of upgrades over the years have enabled it to consistently produce high-quality water. An earlier proposal to replace the plant was rejected as declining demand set in and made a new facility cost prohibitive. Factors contributing to the reduced consumption included industrial water conservation initiatives and the mill town's struggling textile manufacturing sector, explained Barry Dunkley, PE, director of Danville's water & wastewater utilities. Although the plant received modifications to expand the capacity of the declining rate filters to the rated 18-MGD, production never reached the intended goal. The plant delivered only about 16-MGD at the outset of the upgrades.
"We were supposed to achieve 18-MGD with the filtration modifications made in 1991 but never did," Dunkley said. "The plant hydraulics, mainly the sizing of the filter orifice plates, restricted the flow."
Retrofit Responds To A Strategic Plan...
The improvements were prioritized by a master plan developed by Environmental Engineering & Technology, Inc., located in Newport News, VA. The daily demand for the years 2000 to 2001 varied from 3- to 10.6-MGD, resulting in using 7.3-MGD as the average daily demand in planning the project.
"We examined the entire treatment process before identifying three major initiatives, Dunkley said." These included replacing worn out or obsolete equipment, improving our filters to meet existing and proposed criteria, and correcting any other shortcomings that contributed to the capacity decline," Dunkley said.
The work in 2004 was the fifth major renovation since 1950, Dunkley added. The most recent contract automated process controls, replaced the raw water and high-service pumps, installed an advanced filtration system, upgraded valves and repaired deteriorated concrete. The utility capitalized the project without enacting a rate increase.
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