Johnston Construction Co.

Owner:

United Water Pennsylvania, Inc

General Contractor:

Johnston Construction Company

Scope Of Work

Johnston Construction Company, as a design-build subcontractor, provided construction and commissioning services under a fixed price subcontract for the $2,290,000, high-rate clarifier water treatment plant process renovation and upgrade.

The Sixth Street Water Treatment Plant has a rated capacity of 12 MGD and serves industrial and residential customers in several East Shore municipalities and the Borough of Marysville in Perry County. The facility has historically drawn raw surface water from the Stoney Creek and Susquehanna River in Harrisburg, Pennsylvania. By late 2005, United Water of Pennsylvania was required to abandon the relatively low turbidity Stoney Creek raw water source and solely use the Susquehanna River source thereafter. The new source experiences a much greater variation in flow and solids content as a result of weather events that proved to be a challenge for the existing Microfloc Trident clarification system. An Infilco Degremont, DensaDeg clarifier system was selected to accommodate a wide range of water flow rates and solids from the river water.

The new process features three 5 MGD Densadeg units and associated chemical feed and metering equipment. The system was installed in a new pre-engineered metal building that was located adjacent to the North Filter Building. The high-rate clarifiers served as the foundation and lower support structure for the new building.

Construction was started in late February 2005 and the new Densadeg process was producing high quality water several months ahead of schedule in August 2005.