New GIS map identifies BPA-approved switchyard rock quarries

New GIS map identifies BPA-approved switchyard rock quarries

January 29, 2026

Did you know that the top three inches of every Bonneville Power Administration substation is made up of carefully sourced, current-resistant crushed rocks? BPA meticulously tests this uncompacted aggregate before using it in switchyards and tracks approved rock sources, collecting extremely valuable and extensive geological data. Now, thanks to collaboration between BPA's Diagnostics, Metrology and Labs team and Transmission Transportation Engineering, staff can display all switchyard rock data within the agency's GIS tools.

Crushed switchyard rock offers a higher level of resistivity, or opposition to electrical currents, than native soil or other fill materials. The aggregate acts as a safeguard that supports safe, reliable system operations at switchyards and helps to offset potential side effects of the high-voltage substation equipment.

BPA can't use aggregate from any source, however. The agency's chemists perform yearly tests on aggregate samples from approved rock sources throughout the region.

According to geotechnical engineer Russell Gray, potential samples undergo routine degradation and resistivity tests before they are approved for substation use. To test for degradation, chemists use a solvent known as dimethyl sulfoxide to break down samples and determine their durability. This test, designed by BPA staff in 1993, identifies a sample's minimum resistivity. BPA's scientists also test to ensure rock samples have the proper gradation and angularity to provide a suitable driving surface for vehicles moving within the substation.

Due to natural changes in geology, as well as extraction and processing methods, previously approved samples are not guaranteed to pass the same tests the following year. "We've had samples that were approved one year and failed the next," Gray said.

To track approved, potential and declined sources, the team maintains a switchyard rock database. Currently, Gray estimates the database holds upwards of 250 recorded sources, which made it difficult to navigate. Gray and his team devised a new solution: translating the database onto a GIS map.

The new map adds to the range of GIS applications BPA manages, including maps of transmission infrastructure and fish spawning areas and a tool to monitor wildfire activity.

Senior geographer Mary Hughes worked with Gray to create a digital map that users can interact with. For each rock source, users can view its address, contact information, sample test date and status.

By translating database information to the interactive map, Gray has been able to identify rock sources with consistent samples and areas with no recorded sources. The map is currently populated with around 40 sources that actively send samples to BPA and is expanding as more sources are added.

Additionally, Gray has been coordinating with BPA's Central Electrical services; Environment, Fish and Wildlife; and Commodity Investment teams to forecast switchyard rock needs for upcoming transmission projects. With the map at hand, users can identify the closest rock sources to potential project sites - saving valuable project planning time.

"I'm able to be more proactive," Gray said. "I'm reaching out to potential sites in areas where we don't have sources and filling those gaps."

Outside of BPA, Gray says the team shares map data with agency partners and customers who request BPA-approved switchyard rock sources. "We regularly help contractors and companies to find rock sources that meet BPA standards," he said.

The map has averaged around 32,000 views. Looking forward, Gray and Hughes continue to add improvements and updates with new sources and features. "There are many people that use the switchyard rock database that are not aware of the map," he said. "As more people engage with the map, I encourage them to reach out with any feedback to increase its functionality."

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