Santamaria Concrete completed the construction of a cast-in-place concrete retaining wall at the former PG&E Manufactured Gas Plant (MGP) site in Napa, California. The project was part of a larger environmental remediation and restoration effort requiring coordination with engineers, environmental teams, and the general contractor.

The retaining wall was designed and constructed to support site grading, fencing, and long-term stability within an active remediation area.

Scope of work:

• Forming and placement of cast-in-place concrete retaining wall
• Reinforcing steel installation per approved shop drawings
• Installation of footing and wall reinforcement systems
• Placement of 3,000 PSI structural concrete
• Installation of embedded fence posts at top of wall
• Coordination of submittals, RFIs, and engineering revisions

Project highlights:

• Construction of approximately 246 LF of retaining wall based on approved submittals
• Work performed at former Napa MGP remediation site (OU-1 / OU-2)
• Extensive coordination with contractor and engineering team
• Integration with environmental systems including excavation, soil treatment, and site restoration
• Installation of new chain link fence embedded into retaining wall
• Tight working conditions with active remediation operations and site constraints

Engineering and coordination:

This project required significant coordination through RFIs and submittals to resolve constructability challenges.

• RFI-001 addressed lap splice requirements for reinforcing steel, which were not initially specified in the plans
• RFI-002 addressed limited space for rebar hook lengths, requiring field-adjusted solutions
• Structural drawings were revised to accommodate these conditions and ensure compliance with design requirements

The structural detail sheets show wall sections, reinforcement layout, and footing geometry, including bar spacing, lap splice requirements, and embedment conditions.

Concrete and structural details:

• Concrete strength: 3,000 PSI (28-day compressive strength)
• Reinforcing steel: ASTM A615 Grade 60
• Wall height: up to approximately 5 feet maximum per structural notes
• Reinforcement included #4, #5, #6, and #7 bars with specified spacing and lap requirements

The retaining wall section drawings illustrate footing dimensions, wall thickness, bar placement, and connection details.

Site and environmental coordination:

The project was performed within an active environmental remediation site involving:

• Excavation and soil treatment operations
• Temporary haul roads and access ramps
• Controlled work zones and safety setbacks
• Coordination with environmental engineers and specialty contractors

The construction detail sheets show staging areas, drilling operations, and material handling systems used during remediation activities.

Execution:

Construction required careful sequencing due to:

• Limited space for reinforcement placement and hook geometry
• Ongoing remediation and excavation activities
• Coordination with multiple disciplines including environmental, structural, and civil teams
• Strict inspection requirements for footing and wall reinforcement prior to concrete placement

Project information:
Location: Napa, California
Project Type: Concrete Retaining Wall / Environmental Remediation
Contractor: Santamaria Concrete