Aggregate production plant noise and dust control
The primary source of noise and dust from aggregate extraction is from vehicle movements, processing equipment, and blasting. Aggregate producers are responsible for ensuring that the noise and dust emitted from the pit or quarry do not exceed regulated levels. Carefully prepared and implemented noise and dust control plans can keep emissions within the required limits. The size and design of blasts can be modified to limit generation of noise and dust. Blasting can be scheduled for certain times of the day and restricted during adverse weather conditions. Low-noise equipment and dust suppression or collection systems can significantly reduce impacts. Equipment that is noisy or generates dust can be located so that naturally vegetated areas, landscaping, earthen berms, quarry walls, stockpiles, and topographic barriers shield or absorb noise and block the wind that transports dust. Equipment that generates noise or dust can be located in sound-deadening, vacuum-equipped enclosures. Proper location and surface treatment of haul roads and careful routing of trucks can help reduce noise and dust. Conveyors can be used instead of trucks for in-pit movement of materials.
Aggregate production plant vibrations from blasting
Blasting may occur daily or as infrequently as once or twice a year, and usually is restricted to quarry operations. Most of the energy of a quarry blast is expended on breaking the rock. A small amount of energy is released as vibrations that go through and along the surface of the earth. Some energy from a quarry blast escapes into the atmosphere and causes audible noise and sub-audible noise referred to as ‘airblast’ or ‘air concussion’. Airblast is most noticeable within a structure, and frequently is mistaken for ground vibrations. Airblasts are less likely to cause damage to structures than ground vibration because the mechanics of airblast vibrations are different from vibrations that cause ground shaking. Extensive research by the former US Bureau of Mines resulted in ground vibration and airblast standards that are recognized worldwide and have become industry standards for safe blasting. Impacts from blasting can be mitigated by maintaining blast vibrations below well-documented limits on ground motion and air concussion
Aggregate production plant impacts on groundwater
The environmental impacts of aggregate operations on groundwater are highly dependent on the local geology, hydrology, and climate. In dry climates, evaporation of water from pits or quarries may lower the water table. In humid climates, precipitation may flow into a quarry and recharge groundwater. Groundwater flow in springs, gaining streams, and wells may be impacted by nearby aggregate operations that pump groundwater from the pit or quarry. Extracting rock from karst areas can have a severe impact on the groundwater, but the impact can commonly be controlled with well-designed and implemented environmental management procedures. Impacts on the water table as a result of dewatering can be monitored by use of observation wells, and recharging aquifers or augmenting flows to streams with water that has drained into the pit or quarry can maintain water levels. In highly permeable deposits, slurry walls or grouting may be necessary to isolate the operation from the water table.
Aggregate production plant impacts on surface water
Aggregate operations entail removal of vegetation, which can increase runoff. Aggregate extraction may change runoff patterns and promote erosion, which can result in increased sediment in nearby streams. Slope stability, water quality, erosion, and sedimentation are commonly controlled by sound engineering practices. Finished slopes, roads, drainage ditches, and operational areas must fit the particular site conditions. Disturbed areas can be protected with vegetation, mulch, diversions, and drainage ways. Sediment can be retained on site using retention ponds and sediment traps. Regular inspections and maintenance help ensure continued erosion control. Water from aggregate processing and storm runoff over pit or quarry sites can increase the suspended material (turbidity) in stream runoff. Turbidity is generally greatest at pit or quarry and wash-plant water discharge points and decreases downstream. Turbidity can be controlled by filtering or by containing runoff or wash water at sediment traps. Aggregate production within stream floodplains may have an impact on stream-channel morphology. Careful hydrologic studies and application of best management practices can allow aggregate to be extracted from certain parts of active stream channels with little environmental impact. However, improper aggregate extraction may cause widespread erosion and loss of riparian habitat.
Aggregate production plant impacts from transportation
Aggregate is commonly delivered from the pit or quarry to the construction site by truck, which can create problems of noise and exhaust as the trucks pass nearby dwellings. Truck traffic ultimately intermingles with automobile traffic creating potential hazards such as those caused by trucks that transport other consumer products. The environmental impacts and hazards of trucks can be minimized when the trucks are well maintained and operated, and when automobile drivers allow reasonable space for truck drivers to maneuver and stop safely. Trucks can be equipped with mud flaps and load covers to prevent loose material from being thrown from wheels and loads. Limiting the number of quarry entrances and exits, and constructing acceleration and deceleration lanes at pit or quarry entrances can allow trucks to enter and exit traffic smoothly. Delivery routes can be designed to minimize interference with neighborhood traffic.
Aggregate production plant energy consumption
Producing aggregate requires the use of energy, which in turn causes the release of greenhouse gases to the atmosphere. The energy consumption required to bring aggregate to a useful state is referred to as ‘embodied energy’. The energy consuming activities of aggregate extraction and processing include:
1.removing vegetation and soil, building the processing facilities, and otherwise
preparing the site for operation;
2.drilling, blasting (for crushed stone), and excavating the material;
3.transporting material from the excavation site to the processing facility by truck
or conveyor;
4.processing, including multiple stages of crushing, screening, dust collection,
sand classification, washing, and stockpiling;
5.load-out and transporting to market.
Embodied energy for some common building materials
Embodied energy has been calculated for a number of building materials by a number of investigators. The values vary from one investigator to another because of variations in inputs and analytical approaches. Above Table shows embodied energy values for a number of common building materials, including aggregate. All values are from one investigator to ensure conformity. The values in Table are generalized. In practice, energy consumption varies greatly from one aggregate operation to the next, and has been calculated to range from 6
to 139 kW h/tonne (0.022–0.5 MJ/kg). Actual consumption is dependent on a number of factors including: the size of the operation; plant layout and design; the type of rock or sand and gravel being mined and processed; the amount of drilling or blasting required; the type, efficiency, and maintenance of equipment being utilized; the experience and training of drillers, blasters, and other operators; and the method of transport and distance to market.
Methods to reduce the embodied energy in aggregate resources include:
1.efficient plant design;
2.proper drilling and blasting to create appropriately sized crusher feedstock;
3.selecting the right equipment (e.g. matching the crusher to the rock being processed, or matching motors to the equipment being used) and operating the equipment properly (e.g. monitoring drill rates, or matching the feed rate to the crusher);
4.properly maintaining equipment (e.g. drilling, crushing, processing, on-site power generation, dust collectors, water pumps, conveyors, excavating equipment, and trucks);
5.reducing idle time of truck, maintaining haul roads, driver education and awareness.
Generally the transportation of finished goods to the customer is not included in the embodied energy calculations for a product. However, aggregate is a high-bulk commodity and transportation can be a significant part of the put-in-place cost. For comparison, Eastman reported that the distance one liter of fuel can move one tonne of material is 23 km by truck, 78 km by train, and 198 km by barge.
