Protecting Our Groundwater From Mining Contamination

Photo of Lehigh Quarry

Santa Clara County has enacted a new ordinance requiring mining operations to maintain a 50-foot protective buffer from groundwater. We’re celebrating this important step by the County to protect our groundwater resources from the potentially harmful impacts of mining. And we’re proud that the initial idea for this ordinance came from a Green Foothills Leadership Program capstone project! Kudos to Rhoda Fry who brought this idea to our Leadership Program, and to her fellow alumni Kian Nikzad and Manjeet Singh Bhamra for working together to help get it done.

Mining Can Contaminate Groundwater and Creeks

Surface mines (i.e. quarries) involve excavating huge pits that can delve hundreds of feet deep. When these pits are deep enough to come in contact with groundwater, contamination from mining operations can potentially pollute surrounding water.

An example of this occurred when Lehigh Quarry near Cupertino dug their giant pit below the groundwater table, resulting in groundwater seeping into the pit and collecting there. Lehigh pumped the pit water out into nearby Permanente Creek, where significant levels of contamination began to occur – including selenium, an element that is toxic to wildlife in high concentrations. Selenium is naturally occurring in the Lehigh Quarry limestone and leaches into water when the limestone is submerged, as happened when Lehigh excavated their quarry pit below the groundwater table. It took a lawsuit by the Sierra Club Loma Prieta Chapter and multiple citations from the Regional Water Quality Control Board to get Lehigh to take steps to control their selenium discharges.

What Does the New Ordinance Do?

The ordinance approved on May 21 by the County Supervisors prohibits mining operations from excavating closer than 50 feet to groundwater. Annual reports to the County by mining operators are required to show that the mine is complying with this requirement. The County can also require a bigger buffer than 50 feet if necessary to protect groundwater, or they can reduce the buffer if the science shows that a smaller buffer would be adequate. This requirement will apply to all new mining operations in the County, including the highly controversial proposed Sargent Ranch Quarry at Juristac, if that project were to be approved. (That quarry is still pending the County’s review of its Draft Environmental Impact Report (DEIR), with the review expected to be completed sometime in 2025.)

Thanks to the Santa Clara County Board of Supervisors for taking this action to protect our groundwater, and especially to Supervisor Otto Lee who championed the idea for the ordinance, acting on research from Green Foothills Leadership Program 2021 participants Rhoda, Kian, and Manjeet. We’re particularly pleased to have this connection to the success of this effort!

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