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Upgrades, expansion ensure future operation of WCSA’s second-largest water source

Earlier this year, WCSA completed a long-planned major upgrade and expansion of the Mill Creek Water Treatment Plant. Jointly owned by WCSA and the town of Chilhowie, the plant is the town’s primary source of water and is Washington County’s second-largest water source. The Mill Creek facility also serves the Wideners Valley, Friendship, Glade Spring, Meadowview and Emory areas of Washington County.

Water is supplied to the plant from three springs located near the Washington County/Smyth County line. The water travels from the springs into a water storage tank for mixing and is then pumped into the treatment plant. Since conventional water treatment is not effective for the facility’s sources, the water is sent through a pre-filtration process before it is again pumped into the headworks of the plant’s membrane filtration system.

This membrane filtration system consists of thousands of tiny hollow fiber membranes bunched together in a cartridge. The cartridges are grouped together in a structure known as a skid. The Mill Creek plant operates with three skids, and each skid contains 40 cartridges. Treatment is accomplished by forcing raw water through microscopic openings in the fiber membranes, which removes contaminants from the water.

Once water travels through the membrane filters, chlorine and fluoride are added, and the water is piped to two parallel water storage tanks located beside the water treatment plant. Water remains in the tanks until it has met the required disinfection time. Water is then pumped into Chilhowie’s and WCSA’s distribution systems.

“Because the plant was built in 1999, Mill Creek’s membrane filtration system was relying heavily on outdated instruments and equipment,” says Robbie Cornett, general manager of WCSA. “A few years ago, Chilhowie and WCSA commissioned The Lane Group architectural/engineering firm to prepare a report on the long-term operation of the plant. Their recommendation was to replace the plant’s entire membrane filtration system and make various other improvements.”

WCSA and Chilhowie were proceeding with the step-by-step course to prepare for this major project when, in March 2015, Mother Nature decided to interfere with the process. Heavy rains, combined with early spring snowmelt, suddenly rushed down from the highlands — with a devastating effect on the Mill Creek facility. Plant employees noticed an increase in sediment swirling in the lines, and discovered that a buildup of sand, dirt and other organic material had entered the system due to unusually high turbidity. As a result, the plant’s three skids of membrane filters were being stretched to the point of rupture.

“That was a situation you never want to face,” Cornett said at the time of the incident. “The filtration membranes that protect potable water supplies are at the heart of any system. They require constant monitoring and care to operate properly. In this instance, because of the heavy burden of particulate that reached the plant, all three skids of membranes were stretched and, in some cases, ruptured.”

Quick action by employees enabled WCSA to avoid any further equipment damage, and also prevented contamination from entering Chilhowie’s drinking water supply. However, it was determined that all three skids were beyond repair, and the Mill Creek facility had to be shut down until they could be replaced. Using the permanent interface system that links WCSA and the Mill Creek plant, flow from the Middle Fork Water Treatment Plant was diverted to replace Mill Creek’s lost supply until equipment could be upgraded and new skids installed. The plant was restored to full capacity in August 2015, and the cost to replace the skids was reimbursed by the Virginia Municipal League Insurance Program.

The process to replace Mill Creek’s skids accelerated the implementation of the remaining planned upgrades. By early 2017, all preparations for the plant improvements project were complete, including approximately $3.8 million in funding to pay for the project, provided by USDA Rural Development. Construction began in February 2017 and was completed in early 2019.

Improvements include a 1,200-square-foot addition to the existing building to house the new ultrafiltration water treatment system, an upgraded laboratory, and room for spare parts inventory and maintenance activities. Other improvements include associated upgrades to existing equipment, replacement of water pumps, air compressors and other plant components, and a space for a septic tank drain-field system.

“With these upgrades, Mill Creek’s functional capacity was expanded from 2.5 million gallons per day (MGD) to 3.1 MGD,” Cornett says. “This project will directly impact approximately 5,000 existing connections within WCSA’s distribution system, which include two industrial parks, one college and five county schools, in addition to many residents. These long-awaited improvements and the expansion will ensure Mill Creek’s continued operation, and provide a safe and reliable source of treated water for WCSA customers and the town of Chilhowie for many years to come.”