By Tim Hunt
Could new quarry operations threaten PG&E gas pipeline on Isabel Avenue?Uploaded: Dec 5, 2019
Geo-technical engineer Frank Berlogar has built a well-deserved reputation as a conservative, thoughtful professional over his more than 50-year career here in the East Bay.
A Pleasanton resident since the 1970s, he has worked on many development projects over the years, including consulting recently on a well-known tilting building. In short, he’s respected in his profession.
That’s why PG&E and government agencies should be taking seriously his concerns about the mining permit that Alameda County is processing for a gravel quarry next to Isabel Avenue (Highway 84) in Livermore. Frank’s trained eye already had detected some soils movement on the new highway last spring. He wrote that the movements could suggest “active deep seated slope instability.”
His over-riding concern is there is a 24-inch PG&E high-pressure natural gas pipeline that runs on the Isabel corridor and is right next to the lake where CEMEX is seeking to expand and deepen its mining operations. The Alameda County Community Development Dept, is processing the application and drafting the initial environmental study.
Berlogar has first-hand experience with gravel mining in the area. He was the consulting engineer on the gravel quarry across Isabel Avenue after properties along Lakeside Circle began experiencing moving soils. To solve the problem, quarrying was stopped and literally tons and tons of heavy rock were backfilled into the pit to stabilize the land and the subdivision.
In an email, Bruce Jensen from Alameda County, wrote, “The immediate Lakeside Circle neighborhood is also the only place where the offending clay layer, known as a “slickensided” clay later, has been discovered AND where proximate mining has occurred. Following the Lakeside Circle events, other prior drill holes and new drill holes have been examined – by not only CEMEX but also other quarry operators - to see whether a similar problem could happen anywhere else as a result of underground geology. In no other place has (a) a slickensided clay layer been found, or (b) other geology that would promote an inadequate factor of safety for surrounding land uses, public or private, at existing and proposed setbacks from quarry excavations.”
Berlogar became aware of the issue nearly 2 ½ years ago, he notified both PG&E and CalTrans officials of his concerns. He exchanged several emails with Bob McManus, of the PG&E geosciences group. After they met, McManus wrote, “…there appears to be a valid ground movement concern here.”
Reaching out to CalTrans and PG&E after Frank brought this to my attention earlier this year, both responded.
CalTrans engineer Bill Bornham, the division chief for construction in Division 4, wrote, “
Briefly, we investigated this location a couple years ago by installing slope inclinometers and monitoring them for a few months. At that time we did not detect any movement that would indicate an active slide.
“Since then we have completed the paving and recently noticed a slight undulation in the new pavement surface. Our geotechnical engineering staff investigated again recently and did not detect movement related to a slide. We will continue monitoring the site and repair the pavement if it becomes necessary.”
PG&E Spokeswoman Tamar Sarkissian wrote, “The safety of our customers and the communities we serve is our most important responsibility. PG&E has evaluated the pipe and determined that it is safe to operate at this time. PG&E is aware of land movement, and is working closely with CalTrans to monitor the situation. We will continue to monitor the pipe for any signs of ground movement using patrols and high tech laser testing, and will take any appropriate steps, if needed.”
Joseph Sun, a PG&E engineer, responded to Berlogar during the series of emails. His email indicated that PG&E was confident that the pipeline would remain intact based on its experiences elsewhere with ground movement.
Berlogar remains concerned, particularly about the potential for deeper quarrying in the gravel pit next to the gas pipeline.
As Jensen wrote, a similar clay layer to what caused the Lake B issues has not been found so that’s positive news. Of course, that’s no guarantee that there isn’t one. As the county moves ahead with the environmental report, given the PG&E line, continuous monitoring would be prudent.