P2-128: Temperature Phased Anaerobic Digestion (TPAD) Digester Facility at Plant No. 2 and P2-128A: South Perimeter Wall and Soil Improvements at Plant No. 2

P2-128: Temperature Phased Anaerobic Digestion (TPAD) Digester Facility at Plant No. 2 and P2-128A: South Perimeter Wall and Soil Improvements at Plant No. 2

Orange County Sanitation District (OC San) is proposing to implement Project No. P2-128 TPAD Digester Facility at Plant No. 2, which is the combination of two projects identified in OC San’s 2017 Biosolids Master Plan (BMP 2017): P2-504/P2-504A/P2-504B Temperature Phased Anaerobic Digestion (TPAD) Digester Facility and P2-501 Perimeter Screening, which are both located at Plant No. 2 in Huntington Beach. OC San certified a Final Programmatic Environmental Impact Report (PEIR) in 2018 as lead agency pursuant to the California Environmental Quality Act (CEQA) for the BMP 2017 that identified and evaluated both projects. Since the certification of PEIR, modifications to the project have been proposed during subsequent project level design that would occur within the same approximate footprint. The Addendum outlines the specific modifications and evaluates whether they would result in the need for subsequent CEQA documentation. The project is defined in detail below. The proposed TPAD Digester Facility includes the construction of a new Digester Feed Facility (DFF) with two sludge blending tanks and odor control; five new thermophilic digesters with space dedicated for one future thermophilic digester, if needed, and associated digester control building; six new Class A batch tanks, which will allow the facility to generate Class A biosolids; new sludge cooling facilities (Cooling Tower Facility); new hot water boilers (Boiler Facility); and a new power building (Distribution Center M or DC-M). The TPAD facilities will be constructed in the southwest corner of Plant No. 2. Digested sludge from the Class A batch tanks will then be cooled and discharged to the existing mesophilic digesters prior to dewatering. In the event of a catastrophic failure of the existing mesophilic digesters (e.g., seismic event, structural failure), the thermophilic digesters will be capable of processing the full Plant No. 2 design solids flow and load capacity, thus mitigating the seismic and operational risks with the existing digesters. The project includes implementation of the first portion of a new Plant No. 2 perimeter wall from the southwest corner of the existing activated sludge (AS) plant to the corner of Brookhurst Street (approximately 1,070 linear ft). The new wall along Talbert Marsh will act in conjunction with the existing Talbert Marsh Levee to protect the Plant from a 100-year flood adjusted for the 2070 projections of sea level rise as identified in the OC San Climate Resiliency Study, Project No. SP-152 (2019). The height of the wall is not designed for flood water elevations associated with a design tsunami; however, the wall will be designed to not fail during a tsunami event. The perimeter wall height varies from approximately 8.5 to 11.3 feet above the existing ground surface and will include architectural treatments for aesthetics. The perimeter wall construction includes ground improvements, excavation, installation of buried concrete piles and pile caps, installation of the concrete wall, and structural backfill. Landscaping (coastal native shrubs, groundcover, and succulents, as well as vines) will be installed between the proposed perimeter wall and bike trail to improve overall aesthetics and provide an approximately 10-foot landscaped buffer between the bike trail and the wall. The existing bike path will be slightly re-aligned to allow more space for this landscaping. As shown on the site plan, a proposed planter area will be constructed along the northwest corner inside of the perimeter wall. The planter wall itself is not visible from outside of OC San property; however, the trees within the planter will be visible from outside.

Huntington Beach

Orange

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Orange