FROM: James D. Herberg, General Manager
Originator: Kathy Millea, Director of Engineering
SUBJECT:
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TPAD DIGESTER FACILITY 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:
A. Consider, receive, and file the Addendum to the Final Program Environmental Impact report for Biosolids Master Plan for Project No. P2-128; and
B. Approve the project modifications as identified and described in the Addendum to the Final Program Environmental Impact report for Biosolids Master Plan for Project No. P2-128 (Chapter 4.0, Table 2, pages 8-11).
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BACKGROUND
The Orange County Sanitation District (OC San) uses anaerobic digesters at both plants to stabilize sludge prior to dewatering. Anaerobic digesters are large, enclosed concrete structures that require pumping, mixing, heating, and gas handling systems. Anaerobic digesters also generate methane gas used to produce power and heat.
OC San has 18 digesters at Plant No. 2 that were built from 1959 through 1979. In 2017, OC San completed a comprehensive Biosolids Master Plan (2017 BMP), Project No. PS15-01, that provided a roadmap and framework for sustainable and cost-effective biosolids management options. The study recommended upgrading the existing digester complex by adding Temperature Phased Anerobic Digestion (TPAD) facilities, including new thermophilic digesters and batch tanks, and refurbishing some existing digesters as the most resilient, lowest lifecycle cost.
TPAD Digester Facility, Project No. P2-128, is the combination of two projects identified in the 2017 BMP: (1) TPAD Digester Facility at Plant No. 2, and (2) Perimeter Screening. OC San certified a Final Programmatic Environmental Impact Report (PEIR) in 2018 and both of these projects were analyzed in that PEIR. Modifications to these two projects have been proposed since the 2017 BMP was adopted. OC San has engaged the se...
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