Tertiary Treatment for Turlock

Wastewater plant in Central Valley city undergoes $35.4 million expansion

The 86-year-old facility is the first in the area to convert to a higher level of treatment. Designers chose a combination of high-rate clarifier/thickener and cloth-disk filters for the tertiary system, and saved $2 million in the process. The primary treatment area will also be expanded.

By Paul Napolitano

The site looks like a "battlefield," but progress on Turlock's largest financial investment is marching along the way a construction project should, according to managers overseeing a major upgrade to the city's wastewater treatment plant.

	PHOTO COURTESY OF OVERAA CONSTRUCTION

"Everybody is focused on getting the job done instead of covering their [rear ends]," said Jeff Naff of Richmond-based Overaa Construction "It's firing on all cylinders."

The "job" is a $35.4 million upgrade to tertiary treatment standards and an expansion of the primary treatment plant for the Turlock Regional Water Quality Control Facility, a system that serves a population of about 400,000.

Designed by Phoenix-based Carollo Engineers, the project started construction in October and is scheduled for to be fully operational by May 2006.

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The 86-year-old Turlock plant, located on the city's west side, is the first wastewater treatment facility in Region 5 to undergo this kind of upgrade because its license was first in line for renewal, said Dan Madden, Turlock's water resources manager.

"This project will be the poster child to the other wastewater treatment plants that discharge into the San Joaquin River," said Mike Britten, a partner in the Walnut Creek office of Carollo Engineers.

Effluent from the existing secondary treatment process will be diverted through the new tertiary treatment plant. The main features of the tertiary plant are a new pump station, high-rate clarifier/thickener, chlorine contact basin and cloth-disk filters. Treatment capacity will be 22 million gallons a day with the ability to expand to 40 mgd by adding filter units in the future.

Two digesters, a sludge pump station and an electrical equipment building will support the expanded primary treatment section of the plant.

	Nine cast-in-place concrete structures will be built on 20 acres in Turlock, part of a 117-acre landfill site that was closed in the early 1970s. When the upgrade is completed, the enlarged treatment plant will occupy 80 acres (photo courtesy of Overaa Construction).

Britten said "trying to come up with a design that will meet really stringent requirements at a reasonable cost" was his firm's toughest task. A Carollo team of 30 associates spent "a lot of time" researching the high-rate floculation/sedimentation filtration process, he added.

Cloth media disk filters, chosen instead of more expensive sand filters, will remove metals such as iron and copper that could harm fish and marine life in the San Joaquin River. The cloth filters will also the city $2 million, Britten said.

Nine cast-in-place concrete structures -comprised of about 20,000 cu. yds. of concrete-will be built on 20 acres, part of a 117-acre landfill site that was closed in the early 1970s, Madden said. When the upgrade is completed, the enlarged treatment plant will occupy 80 acres.

"Every time we build a structure we have to dig all the way down (about 22 ft.) through a garbage pile of solid material," Overaa's Naff said.

The bulk of the work that has been taking place this year has been excavation. The installation of chemical storage tanks and electrical work began in the summer. Construction crews will be pouring concrete foundations until the fall.

Madden said that in addition to scorching summer temperatures in Turlock, which can reach 105 degrees, the most difficult aspect of the underground work is the installation of a 54-in.-diameter. by 200-lin.-ft. pipe into existing underground facilities that have been in place since the turn of the [20th] century.

"There are very few [pipes] that were marked," Madden added.

In some places, the new pipe, which will serve as the discharge pipe for one of the new tanks, will be placed 15-ft. under ground. The new pipe will carry effluent to another unit for processing.