SACRAMENTO – As PG&E works to cleanup a facility that was used decades ago to make gas for heating and lighting, the utility has incorporated a technology that’s being used for the first time at a project like this in California.
Last month, the director of the state’s Department of Toxic Substances Control (DTSC), which regulates such projects, toured PG&E’s job site located adjacent to the Sacramento River just south of Old Sacramento.
Manufactured gas plants (MGPs) existed in the late 1800s and early 1900s to produce gas for homes and business before natural gas could be widely transported. PG&E has been actively evaluating the locations of several of these historic plants in its service area. As part of that effort, the company is constantly looking for best practice methods for remediation of soil and ground water.
Plant opened in 1873
The Sacramento MGP operated between 1873 and 1930 and was used to supply the area with gas to light and heat local homes and businesses. After being maintained on standby through World War II and the 1950s, the MGP was permanently decommissioned and demolished in 1961.
Because MGPs operated well before the environmental standards of today, PG&E did an extensive investigation to determine whether remediation of soil and groundwater at the site was needed.
In Sacramento, PG&E and its consultant Arcadis are utilizing a technology that’s new to California, but one that has been proven effective throughout the United States – In Situ Soil Solidification/Stabilization (ISSS).
The ISSS technology involves mixing a binding material such as Portland cement into the soil using large diameter augers. Typically a cement-based mix is used to bind together the contaminants, creating semi-solid columns underground to hold and immobilize the contaminants in the soil and allow clean groundwater to move around the columns. In this remediation project, more than 850 overlapping stabilized columns will be created utilizing this process at depths ranging up to 45 feet below ground.
‘Leave a better footprint’
“We are always looking at new ways to improve our environmental remediation work and leave a better footprint for the future,” said Tom Wilson, PG&E’s director of environmental remediation. “This technology has proven successful in other areas of the country and we are excited about being the first to bring it to California and the opportunities that it will give us in the future as we continue our remediation work.”
While this is the first MGP site in California to utilize the ISSS technology for site remediation activities, it has been used successfully by other utilities on similar projects. The technology is a sustainable remediation solution in that it reduces the amount of soil that has to be excavated and removed from the site. Most of the contaminated material is handled and contained on site, within the columns, allowing PG&E to conserve landfill space and reduce the truck traffic that would be required to haul away the soil.
California DTSC Director Deborah Raphael recently visited the site to get a first-hand view of the technology at work.
After her tour, she commended PG&E on its use of innovative technologies.
“This work is an excellent example of how green and sustainable technology can be used to clean up contaminated property to safe levels so that they can be put back into productive use,” she said.
Work on the Sacramento MGP site is expected to continue through December 2012.
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