Mining — and Land Reclaiming — Key to CEMEX’s California Success by Kelly Gates
Frontal view of the 20 CY Rohr Dredge GT1200. Note the crewmen walking alongside the floating conveyor system.
CEMEX’s Madison, CA, site was established in 1969 as a mining operation centered on Cashe Creek, a sand- and aggregate-rich waterway that provided an abundance of materials for use in concrete, asphalt and construction applications. During the mid 1990s, environmental concerns throughout the Golden State prompted material companies, including CEMEX, to alter their mining methodology. Instead of mining the sand and gravel directly from the creek, CEMEX began harvesting material off-channel, a transition that was quite elaborate, said Marc Mammola, manager of aggregates and asphalt for the company. “We had been using several CAT 633 paddle wheel scrapers, which worked well for mining directly in the creek bed,” he said. “When we moved out of the creek and into off-channel mining, we had to switch to equipment that could harvest materials at a greater depth.” CEMEX’s managers began researching various methods of harvesting, and evaluating the machinery that was used for each application. They considered a cutter section head dredge, a bucket ladder dredge, draglines and a hydraulic excavator, among other options. The capital cost of each piece of equipment was taken into account. So were operational costs, wear costs and other functional, financial and environmental concerns. Ultimately, they opted for a unit made by Cleves, OH-based Rohr Corp. “The Rohr Dredge Tech had the greatest potential for water harvesting,” said Mammola. “The timeline for construction of the dredge met our requirements, along with the capital investment and the fact that Rohr had equipment up and running in California, so we were able to see it firsthand before making a final decision.” After witnessing the Rohr unit in action, Rinker began prepping its Madison property for transition from the drag and scraper machines to a new dredge. Equipment started arriving in March of 2005 and by end of the year the machine was already being integrated into the day-to-day mining process. By April of 2006, the company was relying on the new dredge for 100 percent of its sand and aggregate supply, with all materials pulled from the site being run through a four-stage process, Mammola told NAQN. “There is a harvesting component in which the bucket closes on the material and trolleys it to a grizzly feeder,” he explained. “Then, there is a dewatering component that moves the material onto screens, separates the coarse material and sand, sends the sand to slurry where sump pumps take out the water and the sand goes into cyclones before both materials are recombined on a discharge belt.” The third step involves a conveyance system that includes more than 1.5 miles of overland conveyors and around 400 feet of floating conveyors. Once the mixture reaches CEMEX’s aggregate plant, it enters the fourth stage of processing. The material is reduced using a Excel 300 hp cone crusher and depending on the type of product being produced — there are nine finished products in all — the sand and aggregate may then go through a series of two wet screens, three dry screens, a sand classifying tank, sand screws and a coarse materials washer. Some of the finished materials are stockpiled for later use. Others go directly into the company’s on-site ready-mix plant and asphalt plant. “We produce one millions tons per year. About 500,000 is concrete aggregate, 300,000 is asphalt aggregate and the remaining 200,000 is used as base materials and for other construction purposes by our customers,” noted Mammola. The efficient four-stage production enables Rinker to unearth and process sand and aggregates quickly, with the average cycle-from ground to stockpile-taking around 45 minutes, estimated Mammola. This quick turnaround enables the company to keep a large inventory for its own use while always having enough on hand for the steady flow of customers in need of construction materials. Giving Back With such an extensive mining operation in the works, CEMEX is poised to continue excavating and producing materials for many years to come. However, the company hasn’t forgotten about the potential impact on the local environment. According to Mark Hirzy, plant manager at the Madison, CA, location, CEMEX routinely transforms its mined acreage into reusable spaces. “Some of our reclamation plans call for us to turn the land into a series of lakes with natural set-backs from Cashe Creek,” he said. “Most of the land, however, is turned into agricultural acreage.” The process of reclaiming the land begins during mining. As soil is unearthed by the company’s stripping equipment, it is stockpiled nearby so it can quickly and easily be returned to the same site. Often, native plants are brought in and planted atop the soil to create wildlife habitats. When the land is slated for agricultural use, it is simply leveled out, plowed and planted. Local farmers use the reclaimed acreage to grow sunflowers, tomatoes, winter wheat, alfalfa, grain crops, flour, corn and melons, to name a few of the crops cultivated there. “This is not a typical dredging process where there is a spoil pile. We remove the overburden to expose the aggregate and replace the rest,” stated Hirzy. “We are actually required to replace type ‘A’ soil, acre for acre, so it is a very [restorative] process.”
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