Industry Notebook: Quarry Operations
What is a Quarry?
A quarry is an open-pit mining process designed specifically for the removal of large deposits of rock. Quarries can be found all over the world and most are located where a particular type of rock - such as granite, marble, limestone, slate, or gypsum - occurs near the earth's surface. Quarries produce crushed stone, sand and gravel for use in the construction of residential and commercial projects as well as roads and public works projects.
How Modern Quarries Remove Rock
Drilling and blasting are methods used to remove rock from the earth. Blasts are carefully designed to free rock using the least amount of explosive possible. First, holes are drilled into the rock following a predetermined pattern. Then, explosives are placed at the bottom of each hole and covered. Each hole is detonated separately within milliseconds of one another in order to control the intensity and direction of the blast vibration. The explosives are detonated to provide the smallest release of energy for the most efficient blast. The entire blasting process occurs in just a few seconds. The blasting is monitored with instruments to record sound and vibration.
Loading and Hauling Rock from the Pit
The hole that is formed in the earth once the rock is removed becomes the quarry or pit. Large haul trucks are loaded with the freed rock and transport it to the processing plant to be crushed and divided into different sizes.
Breaking, Separating and Transporting Rock through the Plant
A primary crusher reduces the size of the blasted rock. The rock may then be further reduced in size by secondary crushers. Once crushing is complete, screens are used to separate the rock into specific sizes. Rock may be crushed and screened several times before being put in a stockpile with other rocks of the same size. Conveyor belts are used throughout this process to move the rock.
Dust and Water
Mining and moving rock around a processing plant can create fine particles of dust. Dust is typically controlled by using water spray, as needed, on the quarry road and in the mining process.
Water (process water and rainwater) is typically recycled in a closed loop water system. Recycled water is stored in a pond where the sediment is allowed to accumulate. Under certain circumstances, some wastewater or stormwater may be discharged under a wastewater discharge permit.
Rock is stored in stockpiles based on size. Stockpiles are kept a safe distance away from stormwater flows, drainage courses and inlets. Practices to control erosion of the stockpile by the wind are used as appropriate.
Weighing Rocks and Trucks
Rock is sold by the ton. Trucks arriving at the quarry are weighed before and after loading. The weight of the empty truck is subtracted from the weight of the full truck to determine how much the load weighs.
Who regulates quarry operations?
Agencies with regulatory oversight of quarries ensure compliance with federal and state environmental, health and safety standards. The United States Department of Labor - Mine Safety and Health Administration (MSHA) administers the Federal Mine Safety and Health Act to ensure compliance with mandatory safety and health standards for mine employees. The South Carolina Fire Marshal's Office oversees blasting operations at South Carolina quarries. Federal environmental protection requirements are developed by the United States Environmental Protection Agency (EPA). In general, the EPA has assigned implementation and enforcement of federal environmental requirements to individual states. In South Carolina, the S.C. Department of Health and Environmental Control (DHEC) implements and enforces EPA's requirements, as well as additional state environmental laws and regulations that apply to quarry operations. In addition to MSHA and DHEC, other state and local governing bodies may have additional requirements for quarry operations.
How are quarry operations regulated?
Permits are issued to regulate quarry operations. A permit is a legal document that details how a facility will comply with state and federal environmental regulations. Multiple permits may be needed and generally include measures for environmental protection and public safety, restoring disturbed areas, emission/discharge limitations, work-practice standards, record-keeping, monitoring and reporting requirements.