Aggregates Manager Digital Magazine
Issue link: http://read.dmtmag.com/i/742224
AGGREGATES MANAGER / November 2016 13 C alifornia is a land of varying climate, a dense population around large cities, and continuous construction, which requires tons of aggregate. Lehigh Hanson's Mission Valley Rock Plant is in the perfect location in the Sunol Valley to provide construction aggregate, sitting on the outskirts of the small town of Sunol between Oakland and San Jose, and right across the Bay from San Francisco. The alluvial sandstone deposit came from two separate geologic events, according to Assistant Plant Manager Jon Johnstone. He explains that research shows that, during one ice age, there was an ice dam up the canyon south of the plant. When the ice age ended and the ice dam thawed and broke, water and ice carried the sand and gravel, depositing it in the Sunol Valley, while the water continued through Niles Canyon (to the north) and, ulti- mately, into San Francisco Bay, thus creating the old Livermore deposit. The new Livermore deposit was caused by another ice dam near Mount Diablo during another ice age. The same thing happened when the ice dam broke. Water and ice carried the sand and gravel down into nearby valleys with the tail end of it being deposited in Sunol Valley, and the water continued through the canyon to the bay. Johnstone explains that the two separate geologic events piled the deposits on top of each other to create two very distinct colors — brown and gray — in the Mission Valley Rock pit. Fast forward to the present century The plant was originally opened in 1952 by the Ivaldi family. They were followed by another private owner who gave the plant its current name, Mission Valley Rock. These owners ob- tained the necessary permits and approvals to open up a new pit across the highway from the current plant in 2006. "Once fi nal permits were approved, Hanson purchased the plant," says Plant Manager Dan Zacharisen. However, Johnstone explains that 90 per- cent of the land is actually leased from the San Francisco Public Utilities Commission (SFPUC, the San Francisco Water Department), which owns most of the land in the valley and much of the watershed as well. "The end use of our pit will be for water storage for the city of San Francisco," Johnstone notes. "So, in 2045, when we are projected to complete mining, it will become a reservoir. We will do our reclamation and then hand it over to the San Francisco Water Department, and they plan to make it into a water storage and recreation area with hiking trails." The heritage of the land in the area is ag- riculture, and the plant maintains this heritage as much as possible as part of its reclamation and operating permits. For example, the com- pany agreed to plant and maintain a vineyard on part of the property in keeping with the agriculture in the region. Plus, additional lands, not yet being mined, are growing hay. Before the fi rst bucket of material was moved, berms were installed around the entire pit area, with landscaping and irrigation, to create a visual barrier for neighbors and com- muters on Interstate 680. The only visible sign of the operation is the overland conveyor that carries material underneath the freeway from the pit to the processing plant. "People driving by on I-680, unless they know what a conveyor belt is, don't know there's a pit over here at all," Johnstone says. "That's the whole idea behind it." Embracing new technology Zacharisen embraces the challenges of op- erating and maintaining an older plant, but he is also excited about the new technology being used to measure stockpiles and track pit progression. Over the years, the plant had measured the stockpiles in several different ways, ranging from using a stake to measure the height of the stockpile, to an app that required someone to walk around each stockpile, to a radar truck with a laser. Whatever form was used, it was only done twice a year. But about a year ago, the plant started using a Kespry drone to mea- sure its stockpiles every month. "With the drone, we can measure the stock- piles more often and get the data back faster, and it's a lot more accurate," says Mike Moy, Lehigh Hanson's operations analyst. "It really helps us with our production splits — sand and gravel. We can assume that we're getting an X amount of natural products as a certain percentage of the raw feed. Whereas, when we fl y the drone, we can adjust our splits accord- ingly. Particular parts of the deposit give us a