Count Los Altos leaders among those opposed to a proposal that would add a second mining pit for limestone quarry operations in the foothills near the city and Los Altos Hills.
Lehigh Southwest Cement Co.’s updated reclamation plan, released earlier this year, bids to mine in a ridgeline protection easement and adversely impact the “viewshed,” Los Altos Mayor Lynette Lee Eng wrote to Santa Clara County Supervisor Joe Simitian July 31. The Los Altos City Council approved Lee Eng’s letter at its July 30 meeting.
Santa Clara County has jurisdiction over the long-standing cement plant and quarry, located on 2,500 acres in the hills above Cupertino. Lee Eng called Lehigh’s intention to mine more than a half-mile of exposed ridgeline “unacceptable.”
Los Altos joins the city of Cupertino and the Los Altos-based Midpeninsula Regional Open Space District in opposing the current Lehigh plan. Both Cupertino and Midpen leaders also wrote protest letters to the county last month.
“Our initial review (of the application) for its Permanente Quarry raises grave concerns for the citizens of Los Altos,” Lee Eng wrote.
In addition to visual impacts, Lee Eng aired concerns over “geotechnical stability, traffic, air and water quality, and delays of the Permanente Creek restoration.”
Besides ridgeline disturbance, another major change drawing opponents’ concerns in the new plan deals with transfer of material to fill the original pit. Instead of using on-site fill from the West Materials Storage Area, Lehigh officials propose retaining the storage area and importing materials from off-site – resulting in a sharp increase in truck traffic.
In her letter, Lee Eng called the 173-acre West Materials Storage Area a “mountain of mining-waste that already mars the lower ridge.”
“The significant traffic increase of 666 trucks per day for 30 years has been underestimated,” she wrote. “A cumulative traffic analysis must consider the Stevens Creek Quarry expansion plan, which allows 1,300 trucks per day along with Lehigh’s stated objective to open a new aggregate business.”
Lee Eng also cited the proposed use of more than 1,100 tons of explosives annually that would result in dust that would “negatively affect our residents.”
“As Lehigh cement plant air emissions contribute to mercury water pollution in the adjacent Stevens Creek Reservoir and Calero Reservoir, 20 miles away, air and water pollution are also regional concerns,” Lee Eng stated.
Los Altos officials encouraged the county to retain the 2012 reclamation plan, which they said protects the ridgeline while reducing visual impacts and truck traffic through use of material from the on-site mining debris in the storage area.
Lehigh defends proposal
Lehigh officials have framed their proposed changes as environmentally friendly. In a May letter to the county planning department, the company’s environmental director Erika Guerra asserted the project “will allow Lehigh to improve the aesthetic appearance and geotechnical stability of the Permanente Ridge and North Quarry.”
Guerra indicated that the exposed ridgeline in its current condition cannot be replanted with vegetation, but the new plan would create conditions for it.
She added the project increases water quality protection to surface and groundwater by backfilling the existing quarry with imported “surplus construction soil from regional construction projects.”
“Leaving the West Materials Storage Area largely in place rather than moving it in its entirety to backfill the North Quarry will prevent exposing limestone materials and placing these materials below future groundwater levels in the quarry,” Guerra stated.
Simitian has said he does not expect county planning commissioners or supervisors to take up discussion of the plan before next year.