Carollo completed the Plant No. 2 Headworks Replacement Project for the Orange County Sanitation District (OCSD). The new headworks, currently in the construction phase, has a rated capacity of 340 mgd and an estimated construction cost of $192 million. Carollo began preliminary design of the project in the fall of 2001, and final commissioning of the project is expected at the end of 2009. Following commissioning, demolition of existing facilities and modifications to the existing plant will be implemented and completed in February 2011.

Carollo was selected for final design of the Plant No. 2 Headworks Replacement Project after developing the Preliminary Engineering Report. This report consisted of a series of Technical Memoranda that evaluated alternatives for each headworks process and identified best available technologies as applicable to Plant No. 2. The project also included planning and conducting pilot tests to confirm selection of key equipment before selection.

The Plant No. 2 Headworks Replacement Project will eliminate the two existing headworks facilities and combine them into a common headworks. The final project includes the following elements:

• Influent pump station and flow metering.

• Influent diversion and primary influent junction boxes.

• Bar screen facility.

• Screenings washing and screenings loading building.

• Grit basins and grit handling facility.

• Primary flow splitting and metering.

• Advanced primary treatment chemical facility.

• Odor control and chemical facilities.

• Headworks electrical and instrumentation building.

• Waste side stream pump station.

• Pilot testing of bar screens, screenings washer, and shaftless screw conveyors for confirmation of equipment selection and design criteria.

• Designed for fully automated, unattended operation.

• Extensive construction sequencing requirements/constraints.

• Detailed testing, start-up, and commissioning plan.

• Computational fluid dynamic (CFD) and physical modeling for improved hydraulics.

The commissioning process was started early in the design phase. The commissioning team included the various stakeholders and met several times during design to develop a detailed plant that was included in the Contract Documents.

Due to the necessary parallel operation of the existing and new systems during start-up and testing, a detailed construction sequence was developed during the design phase of the project. This construction-conscious effort will also allow difficult tie-ins to be completed, and abandoned facilities demolished without disruption of plant operations.