1. Ninth Amendment — Anaheim City Council, June 10, 2025

Tetra Tech BAS
21700 Copley Drive, Suite 200, Diamond Bar, CA 91765
Tel 909.860.7777 Fax 909.860.8017 www.tetratech.com

August 14, 2024

Stephen Stoewer
Housing & Community Development Department
201 South Anaheim Blvd. 10th Floor
Anaheim, Ca 92805

RE: UPDATED WESTGATE REMEDIATION COSTS FOR CITY FOR ANAHEIM JULY 1, 2024 THROUGH JUNE 30, 2025

Dear Mr. Stoewer:

At the request of the City of Anaheim (the City), Tetra Tech BAS (TT-BAS) has prepared this update to the planning level evaluation for the anticipated scope and costs for the City’s Recognized Obligation Payment Schedule (ROPS) from the California Department of Finance (DoF) for the period from July 1, 2024 through June 30, 2025 relating to the currently projected in-place closure and clean closure activities associated with the Davis Mud Pit and the Sparks, Anderson, Rains Pits Landfill. The scope and costs included herein are updates to the original estimates provided in our letter of December 15, 2023 and are intended for the City’s planning purposes. Proposals for various work items will be provided separately based on the City’s decisions regarding the appropriate path forward.

All work will be performed in accordance with the Requirements of Title 27 of the California Code of Regulations and applicable local requirements. Clean Closure of the Davis Mud Pit portion of the site has been partially completed. Completion of these activities, as well as in-place closure of the small remaining portions of that disposal area are anticipated to occur during the ROPS 2024-2025 period. In-place closure activities are associated with the phased closure of four separate portions of the Sparks, Anderson, Rains Pits Landfill. Phase I and II closure activities were completed prior to the ROPS period in question. Based on the recent developments relating to the relinquishment of Beach Blvd. from Caltrans back to the City, and in recognition of the long term technical, logistical and financial considerations associated with in-place closure, clean closure has been determined to be the preferred approach for addressing the residual Davis Mud Pit wastes beneath Beach Boulevard. Phase IV Closure planning and engineering for the remainder of the Sparks, Anderson Rains Pits are anticipated to occur during the ROPS 2024-2025 period.

The following sections detail the various activities that will need to be performed. Costs and schedule considerations are provided for each major scope.

Re: Westgate Update of Remediation Costs for City of Anaheim August 14, 2024

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COMPLETION OF CLEAN CLOSE THE DAVIS MUD PIT

Davis Mud Pit clean closure activities, were recommenced on July 1, 2024, as planned.

During implementation of these activities, a mud and waste was found to encroach nearer than expected to the north boundary of the City-owned property. In order to address this condition, specialized removal actions will likely be required and are anticipated to include the following.

• Slot cutting of alternating removal trenches perpendicular to the property boundary under supervision of a registered geotechnical engineer. • Direct loading and disposal of slot cut materials.
• Haul and dispose of excavated material
• Increased confirmation sampling frequency to allow for immediate backfilling of the slot trenches.
• Backfilling of the slot cut trenches with concrete slurry. • Based on the results of confirmation sampling, perform the following activities to remove residual impacts:
 Demolition of the two northern perimeter walls
 Design, installation and subsequent removal of shoring  Excavation of residual impacted material within the City-owned property  Direct load excavated material for disposal
 Haul and dispose of excavated material
 Backfill with clean import material
 Reconstruction of northern perimeter wall

Anticipated Time to Complete: 3 Months
Anticipated Added Cost: $3,000,000.00

PARTIAL CLEAN CLOSURE OF THE SOUTHWEST DAVIS MUD PIT

In the original December 15, 2023 projection two options were provided for this task (In- Place Closure and Clean Closure) and both encompassed engineering, coordination between the regulators and developers, permitting, and construction of the in-place closure of the extreme southwestern portions of the Davis Mud Pit, within current City- owned property. However, since development of the December 15, 2024 projection, the timeline for relinquishment of Beach Blvd. by Caltrans to the City has been accelerated and will occur in the latter part of calendar 2024. This will expand the area requiring closure and impact the long term technical, logistical and financial considerations associated with in-place closure such that, clean closure has been determined to be the preferred approach for this area. Tasks associated with clean closure of the expanded area are as follows:
• Engineering and encroachment permits from both Caltrans and the City. • Investigation of the expanded area for limits of waste. • Pre-removal confirmation sampling.
• Pre-removal protection and/or relocation of existing improvements within the expanded area.

Re: Westgate Update of Remediation Costs for City of Anaheim August 14, 2024

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• Removal of mud and waste through concentric borehole drilling • Off-site disposal of removed material
• Back filling of borings
• Replacement of paved surface
• Replacement of improvements within the expanded area

Because of the expanded closure area and in consideration of added complexity related to the relinquishment of Beach Blvd, additional costs are projected.

Anticipated Time to Complete: 3 Months
Anticipated Added Cost: $1,500,000

PHASE III CLOSURE ENGINEERING AND CONSTRUCTION
The scope and budget for this task presented in the original December 15, 2023 estimate has not changed.

Anticipated Time to Complete: 12 Months
Anticipated Added Cost: No Change

PHASE IV CLOSURE PLANNING
The scope and budget for this task presented in the original December 15, 2023 estimate has not changed.

Anticipated Time to Complete: 12 Months
Anticipated Added Cost: No Change

ROUTINE LANDFILL GAS MAINTENANCE, MONITORING, AND REPORTING The scope and budget for this task presented in the original December 15, 2023 estimate has not changed.