CUPERTINO — A longstanding quarry in the Cupertino hills, which has been vilified for years by nearby residents who oppose its impact on the environment and their homes, wants to significantly expand its operation.

The Lehigh Permanente Quarry will file an application to dig a second pit on the southern portion of its property and begin extracting and grading along the northern ridgeline, according to Lehigh’s environmental director, Erika Guerra.

If approved, it would be the second quarry pit on the site since Lehigh began mining the original one in 1903.

Santa Clara County planners met with representatives of Lehigh on April 2 to discuss the plan, which was disclosed in a brief staff report for a Thursday meeting of the county’s Housing, Land Use, Environment and Transportation Committee.

“We have not cut any deals behind closed doors with any applicant,” Planning Director Jacqueline Onciano said at the committee meeting, responding to concerns raised by some residents. “We have not, to date, received a formal application.”

Once an application is filed, there will be a “robust environmental review, community outreach process and formal consideration of the application,” Guerra said.

The limestone and aggregate rock mining operation includes a cement plant that has been permitted since May 1939. The quarry was granted vested rights by the county Board of Supervisors in 2011, a recognition that Lehigh’s mining operations were legally established and can continue until the use ceases.

Lehigh has discussed a second mining pit for several years and filed an application in 2011, but later withdrew it.

The current quarry pit covers an area exceeding 630 acres, Guerra said, and the company is requesting a second pit to “continue supplying the market,” she said.

The facility produces 70 percent of the cement used in Santa Clara County and more than half used in the entire Bay Area.

It’s also one of the region’s major polluters, ranking eighth in 2017 for total emissions among top Bay Area industrial sites, according to data from the U.S. Environmental Protection Agency.

In 2013, the Sierra Club won a settlement that required Lehigh to install an interim wastewater treatment system. Two years later, the company agreed to pay $7.5 million to the EPA to settle charges it dumped millions of gallons of toxic wastewater into a nearby creek.

Nearby residents have long complained about the quarry, citing concerns about pollution and dust generated by the cement plant.

“Water quality is really important to me and we all agree prevention is far more desirable than remediation,” Cupertino resident Paula Wallace said, referring to the Sierra Club lawsuit.

The quarry is governed by a document called a reclamation plan, which requires Lehigh to show how it will restore the mined property over time. Adding a second pit would involve a major amendment to the plan requiring Planning Commission approval.

Lehigh is already asking for a separate amendment to its reclamation plan to accommodate a haul road it cleared on its property without county permission to truck crushed rock to neighboring Stevens Creek Quarry.

After the county found out about the road and required the quarry to stop using it pending proper approvals, Lehigh and Stevens Creek began hauling that crushed rock on city streets. The county, responding to outrage from the city and its residents, told the quarries in February to stop trucking the materials altogether.

Cupertino’s interim city manager, Timm Borden, said the city is aware of the company’s interest but also has not seen a formal proposal.

“The City will continue to work with all parties involved, including Lehigh and Santa Clara County, to ensure the safety and quality of life of our residents,” Borden said in a statement.

Supervisor Joe Simitian, whose district includes the quarry and neighborhoods around it, said at the committee meeting that the number of changes proposed by Lehigh has generated confusion among residents.

“I do think the change in applications has made this an even tougher moving target for the community to track, and that’s going to create some angst, ” Simitian said.

County staff said it would post the quarry’s project application and other materials online once a formal proposal is received.

Contact Thy Vo at 408-200-1055 or tvo@bayareanewsgroup.com.