By Matt Nauman
SANTA ROSA – In cities around the country, utilities such as PG&E are cleaning up the remnants of plants that once provided gas for cooking, light and heat.
That’s what’s happening in downtown Santa Rosa, where PG&E has been working for several years to clean up the materials leftover from a manufactured gas plant, known as a MGP. These plants existed in cities across America starting in the early 1800s, and were phased out as natural gas became available, which was in the 1930s in Northern California.
“As part of our commitment to safe environmental practices and operations, we are actively addressing the environmental legacies of our historic sites,” said Tom Wilson, PG&E’s director of environmental remediation. “In Santa Rosa, PG&E has been working steadfastly to use technology and best practices to clean up the site of the former MGP.”
This work, Wilson said, has been done in coordination with the North Coast Regional Water Control Board. PG&E’s work is very visible – a fence surrounds the project site and a large sign explains the project – and the cleanup plans have been shared with the public.
“Communication and coordination with the property owners, tenants on the property, and the surrounding neighborhood has been a crucial part of our efforts for several years,” he said.
Plant constructed nearly 140 years ago
The Santa Rosa MGP was built on what is now 111 Santa Rosa Avenue next to Santa Rosa Creek between 1876 and 1877. It was owned by the Santa Rosa Gas Light Company.
PG&E acquired the Santa Rosa plant in 1908 and ended gas-manufacturing operations there in 1924. After all related gas-manufacturing structures and equipment were removed, the property was operated as a gas-storage facility until around 1969. It first stored gas manufactured in San Rafael and then was used to store natural gas once that came into use. When the MGP site was shut down, byproducts of the historic gas-making process, which converted coal and oil into gas, were disposed of at the site, consistent with standard practices of the time and long before current environmental standards and sensibilities existed. These materials primarily consist of coal tar and lamp black.
The property was sold to the 137 Santa Rosa Group Partnership in 1987 and later to Upway Properties, the current property owner. A parking lot currently occupies the former MGP site. PG&E, 137 Santa Rosa Group Partnership and Upway Properties have been actively working to comply with the Water Board’s Cleanup and Abatement Order to investigate and remediate the site.
Based on the utility industry’s experience at former MGP sites across the country, as well as information obtained to date by PG&E at this site, MGP residues are buried underground where direct exposure is unlikely.
Using cutting-edge technology
After several years of planning, coordination with the owners of the site and an extensive tenant and community outreach program, PG&E began removing the gas-manufacturing residues in and around the bottom of a long-buried former gas holder tank at the site in January 2009. This work took place to address the most significantly impacted area of the site.
Using a cutting-edge technology known as electrical resistance heating (ERH), crews successfully removed 55,000 gallons of liquid coal tar from the site. With ERH, metal rods were installed in the ground which heated the soil up to 160 degrees Fahrenheit. The applied heat turned the coal tar into vapors and liquids that were captured in a specially designed system.
Using ERH technology offered many advantages including the fact that the coal tar did not have to be excavated, transported to, and buried in a landfill. It also allowed nearby downtown businesses to continue operating with minimal disturbance.
The ERH process proved highly effective. Once the process was completed, PG&E stabilized the treated soil with grout and is currently restoring the site for continued use as a parking lot.
The stabilization work at the site took place at night and on weekends in 2012 and 2013 to avoid inconveniencing on-site businesses. About half of the parking lot has remained open for daily use since the cleanup project began.
Further cleanup activities starting soon
PG&E and its contractors will soon begin the next phase of this project as soil and groundwater impacts at the remainder of the site are addressed. This work will concentrate on three additional areas of the former plant site, including the southern portion where there is an underground storage tank, the area near the neighboring Santa Rosa Creek, and the residual petroleum layer generally at the water table.
Groundwater monitoring at the site began in 1988 and is ongoing. The data do not indicate that impacted groundwater is migrating to Santa Rosa Creek.
In 2012, the Water Board approved a Feasibility Study that discusses plans to install an underground cut-off wall with a treatment zone along the Prince Memorial Greenway, adjacent to the Santa Rosa Creek to prevent any possible future migration of impacted groundwater.
The feasibility study identified the construction of a funnel and gate system as the preferred remedy. When the Feasibility Study was approved, it was assumed that construction of this system would take one construction season; however, additional engineering evaluations, property access concerns, and preliminary discussions with local government and resource agencies indicate that issues, including the presence of endangered species, could extend the construction schedule from one year to three years.
Seasonal rerouting of Santa Rosa Creek and partial closure of the Prince Memorial Greenway, a popular and scenic biking and walking trail, for as long as three years, makes a full re-evaluation of all options prudent before PG&E proceeds with the work.
“PG&E wants to be confident that the chosen option balances the need to provide long-term protection of the creek environment and endangered species with the needs of the property owners and the larger downtown community,” said Wilson.
PG&E is currently evaluating if there are other options that provide equivalent protection without the multi-year, large-scale, disruptive activities inherent with the funnel-and-gate construction. Options will be evaluated during 2013 and any alternate option would need to be approved by the Water Board as well as subject to permitting and a public processes.
Email Matt Nauman at email@example.com.