PG&E Bakersfield MGP

Setting

From 1888 to 1910, a small plant in what is now downtown Bakersfield made gas for the city’s lamps and stoves, first from naphtha and then from coal. It stood by as a backup into the 1940s, was torn down in 1951, and the lot went on to a long life as an auto-body shop. What the plant left behind stayed in the ground: the tars, oils and residues of gas-making.

Sites like it are common. California’s utilities built manufactured gas plants (MGPs) in most towns of any size before natural gas arrived, and PG&E has identified 43 former MGP sites it owned or operated. Since the 1980s it has been investigating and cleaning them up under state oversight, and more than 30 have now been remediated. PG&E bought the Bakersfield lot back in 2019 to clean it up.

The investigation

Rounds of investigation from 2017 to 2023 put about 60 soil borings and 30 soil-vapor probes into a lot of under an acre, with more than 550 samples between them. The chemicals of concern are the classic MGP set: polycyclic aromatic hydrocarbons (PAHs) and naphthalene, the most widespread, along with benzene, petroleum hydrocarbons and lead, and some chlorinated solvents in soil vapor. Groundwater lies deep here, around 67 feet down, and was not reached.

The work runs under the Department of Toxic Substances Control (DTSC): a voluntary cleanup agreement in 2021, a human health risk assessment and a Remedial Action Plan in 2023, and a CEQA review in 2024. DTSC approved the plan in December 2024.

The cleanup

The remedy is excavation. Fieldwork began in July 2026: about 6,400 cubic yards of soil dug out to around 6 feet across most of the lot and as deep as 15 feet in one corner, where shoring holds the walls, then trucked to a permitted landfill in about 450 loads and replaced with clean fill.

Digging MGP soil downtown is as much about the neighbors as the ground. The plan sets air monitoring around the perimeter and upwind and downwind, noise and vibration monitoring, water, foam and plastic sheeting to hold down dust and odor, tarped trucks on a set route, and confirmation sampling of soil and soil vapor before the excavation is backfilled.

My role

I have worked the project from investigation to construction:

• Characterization. The investigation that defined the extent of the impacts and fed the Remedial Action Plan.
• Scope and specifications. Writing the scope of work and drafting the technical specifications that turned the plan into something a contractor could bid and build.
• Construction. Taking the job out to bid, then on site as a field engineer once the excavation began.
• Monitoring software. Building the tools that watch the perimeter.

Watching the perimeter, live

The monitoring is the neighbors’ guarantee, and on a downtown dig it runs for every hour of work. Perimeter air monitoring uses Aeroqual stations around the site, and noise and vibration are measured with Specto Technology sensors. Out of the box, that means data in several places and daily reports assembled by hand.

The Aeroqual units have an API, so I built a portal that pulls their readings as they are recorded: the whole perimeter on one screen in real time, where a rising reading shows up while there is still time to act on it, with the daily air-monitoring report generated from the same data. I built the same kind of reporting tool for noise and vibration: it takes the raw data from the sensors and produces the daily noise and vibration reports. The field team spends its time on the site instead of on spreadsheets, and every report comes from the same data, the same way, every day.

Skills demonstrated

Site characterization of a former manufactured gas plant; scopes of work and technical specifications; taking a remedy from DTSC approval through bid and construction; field engineering on an urban excavation with shoring; and building real-time monitoring and automated reporting software on sensor APIs.