Grayson sits on a liquefaction zone and when a major earthquake happens, the soil beneath the plant will liquefy and the plant will sink into the ground. The plant will be taken offline at best or destroyed at the worse in an major earthquake. Glendale Water & Power (GWP) points out that Grayson was fine after the Sylmar earthquake but Sylmar was a 6.6 magnitude earthquake. Experts say we need to be prepared for an 8.2 magnitude on the San Andreas fault. An 8.2 quake would be 250 times stronger than Sylmar.
One goal of the $500 million rebuild is to ensure power during a disaster. With the Verdugo fault like 1.4 miles away, Grayson will not do well in an earthquake. It is highly likely that ground movement would be enough to sever gas pipes, leading at worst to gas leaks, explosions, and fires, and at best to shutting down the source of power Glendale needs in just such a situation. In addition to the gas pipes there are reclaimed water pipes needed to run the plan that bridge Verdugo wash that would also be severed. This type of risk is best mitigated with a distributed solution based on a combination of solar, battery storage and micro-grid infrastructure and not one built around a single point of failure.
The map for the liquefaction hazard area can be found here.
In addition, Grayson sits in the path of any flood event that requires Hansen or Sepulveda Dams to spill water, like the recent 500-year flood event in Houston that required spilling water to save the levee. As climate change makes the weather patterns less stable we should expect to see larger rain events in Southern California. Here’s a map showing water flows near the Grayson Plant during a 100-yr flood event. While it looks safe in a 100 yr event, the hydrology study for that map did not analyse what would happen at the outflow of the Verdugo wash on the south edge of the plant. An overspill at that point would flood the plant, break the plant’s water and sewer pipes that cross the wash at that point, or submerge the Air Way electrical substation. Any of which would take Grayson off line for the duration of the storm and subsequent cleanup.
Here’s a map showing the LA River Basin. The water collected in the blue and pink sections hit the site of the power plant at the intersection of the LA River and the Verdugo Wash. See the 1949 drawing below to see the location of the damn that keep that flow in check, until they don’t as they saw in Houston last year.