Former Hollister MGP Site Remediation

PIVOX Corporation served as construction contractor and construction manager for remediation of MGP waste impacted soil at PG&E’s former Hollister 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 Hollister MGP is located within a mixed residential and commercial neighborhood. Remediation consisted of underground structure removal and soil excavation using three methods: open excavation, slot trenching, and large-diameter auger open excavation. This project used a novel large-diameter auger approach; PIVOX utilized a large-diameter continuous-flight auger rig, normally used for deep foundation pile installation, to remove MGP wastes to a depth of over 60 feet below ground. A total of approximately 20,000 tons of impacted soil was excavated and disposed of at PG&E-approved disposal facilities.

PIVOX implemented the following safety measures: working during City-approved hours, air and vibration monitoring, strict exclusion zone delineation (especially at the large-diameter auger), dust control, sound blankets, using appropriately sized equipment, and traffic control to safely manage trucks and vehicles in the surrounding neighborhood. 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. 

This project was also notable due to adoption of low-impact, advanced stormwater management features during post-remediation site restoration. PIVOX worked with the project engineer, Owner, and municipality to install over 23,000 square feet of pervious concrete and asphalt paving. This project served as one of the first installations of advanced stormwater management infrastructure in this municipality. A specialty contractor and third-party quality assurance expert were brought onto the project to ensure the pervious concrete and asphalt was installed consistent with the most recent industry standards, and the performance of the installed pervious pavement was tested and confirmed through a high-rate timed water application test, where the installed pervious pavement was observed to permeate applied water at the required rate developed by the project engineer’s hydrological design.