FROM: Robert Thompson, General Manager
Originator: Mike Dorman, Director of Engineering
SUBJECT:
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DIGESTER REPLACEMENT AT PLANT NO. 2, PROJECT NO. P2-128
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GENERAL MANAGER'S RECOMMENDATION
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RECOMMENDATION: Recommend to the Board of Directors to:
Approve a Contingency increase of $6,288,000 (16%) to the existing Professional Design Services Agreement with Brown and Caldwell for the Digester Replacement at Plant No. 2, Project No. P2-128, for a new total contingency amount of $10,218,000 (26%).
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BACKGROUND
The Orange County Sanitation District (OC San) is replacing some of the digesters at Plant No. 2 due to condition and seismic vulnerability.
In 2017, OC San completed a comprehensive Biosolids Master Plan (BMP) that recommended upgrading the existing digester complex by adding Temperature Phased Anaerobic Digestion (TPAD) facilities including new thermophilic digesters, batch tanks, and replacing some existing digesters. The TPAD facilities would be capable of creating Class A biosolids, rather than the current Class B biosolids which could provide greater reuse opportunities.
In 2020, a Professional Design Services Agreement (PDSA) was awarded to Brown and Caldwell to complete the design of the TPAD digesters and associated facilities. As the project design progressed, the construction cost increased significantly, and OC San staff began evaluating cost saving options. Staff and the project team determined that the biosolids market has changed little since the BMP and the need to produce a higher grade biosolid was not needed at this time. It also makes sense to wait to see the outcome of the supercritical water oxidation research project.
In early 2024, the project team decided the best approach was to construct the TPAD facilities in two phases: Phase 1 would construct new mesophilic digesters, and if needed, Phase 2 could convert the digesters to thermophilic operation by constructing necessary support facili...
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