PIVOX Corporation served as construction contractor and construction manager for remediation and MGP waste impacted soil at PG&E’s former San Luis Obispo (SLO) Manufactured Gas Plant (MGP) site. This project is one of 20 MGP remediation projects successfully completed by PIVOX for utility clients throughout California.
The former SLO MGP is located within a mixed residential and commercial neighborhood. Remediation consisted of soil excavation using two methods: slot trenching and open excavation. Slot trenching was conducted along the site perimeter to maintain stability of the excavation boundary along the edges of the site and to maintain excavation sidewall stability at deep excavation locations. Approximately 300 slot trenches with widths of 3 feet, lengths of 7 to 10 feet, and depths of 3 to 12 feet below ground surface were excavated and immediately backfilled with cement slurry to avoid sidewall collapse. Open excavation occurred after slot trenching was completed and the site had a secured perimeter. Inside the slot trenched perimeter, an approximately 12,600 square foot open excavation was completed to depths between 3 to 5 feet below ground. Open excavations were backfilled with engineered fill and aggregate base. A total of approximately 20,000 tons of impacted soil was excavated and disposed of at PG&E-approved disposal facilities.
Due to the numerous underground anomalies typically found at MGP sites, PIVOX completed a comprehensive underground utility survey and potholed approximately 70 site locations to identify existing active and inactive utilities. Remediation included excavation alongside and under a live natural gas utility pipeline. PIVOX and the project engineer coordinated closely with the utility owner to develop excavation procedures in the vicinity of the utility line; and all excavation work within 24 inches of the gas line was performed by hand tools under direct observation by utility owner personnel. In addition, a historic building at the site was located immediately adjacent to the excavation area; this building was protected and monitored during all excavation, backfill, and compaction activities.
PIVOX implemented the following safety measures: working during City-approved hours, air and vibration monitoring, dust control, sound blankets, using appropriately sized equipment, and traffic control to safely manage trucks, vehicles, and pedestrian traffic. Worker air monitoring, site perimeter air VOC and dust concentrations were measured and logged, and environmental controls were installed and maintained by PIVOX personnel during all excavation activities.