An approach recently developed to exploit natural gas deposits involves the hydraulic fracturing, or hydrofracking, of certain types of sedimentary rock. In short, a liquid cocktail is injected at very high pressures underground, within horizontally oriented well casings. This pressure cracks open the friable shale rock, releasing the natural gas embedded within. In this process, fracking sand (or frac sand) is used to prop the cracks open to allow the gas to enter the well after the pressure is reduced (hence the technical name “proppant”).
An Increased Demand for Frac Sand
Between 2002 and 2013, over 6,500 hydrofracking gas wells have been drilled in Pennsylvania alone, with thousands more in several states. Approximately 10,000 tons of frac sand is used per natural gas well subjected to hydraulic fracturing. In 2013 alone, 28 million tons of frac sand was sold.
This high demand has led to a mining boom in extensive sand deposits located in Minnesota and Wisconsin, and to a lesser extent in states like Illinois, Missouri, and Texas. These silica sands meet the precise specifications (in terms of size, grain shape, and hardness) needed to perform as hydrofracking proppant. In recent years dozens of new mines have been opened, and more are planned.
Environmental Issues Associated with Frac Sand Mining
- Landscape transformation. Frac sand mining generally has a large footprint on the land, often hundreds of acres, disturbing the rural character in the eye of many residents. Large sand deposits, carved-out slopes, and leveled hilltops all can have a strong visual impact and potentially negative effects on neighboring property values.
- Transportation. Moving frac sands to oil and gas well sites across the country is done by truck and railroad. This leads to a large increase in truck and train traffic, converging most noticeably in communities where the mines are located. This translates to vehicle emissions (for example diesel particulate matter), which degrade the area’s air quality. Also associated with increased traffic are noise complaints, road safety issues, and roadway damage from the use of municipal and county roads by heavy trucks.
- Air quality. Fine silica dusts produced in the mining operations can produce lung disease. The small-diameter particles enter the lungs and can create irritation and infection, leading to bronchitis. In more severe cases scarring leads to irreversible silicosis and sometimes lung cancer. Workers are most exposed, but workplace safety precautions can mitigate this hazard to a large extent. Less is known about how to protect the surrounding communities from silica dust and other airborne particulate matter. In Wisconsin, there currently is no emissions standards and acceptable limit set for fine silica emissions.
- Water quality. Holding ponds and waste piles containing sand and silt from processing can leak and spill into waterways, damaging sensitive aquatic habitats. Sand and silt can inhibit plant growth, suffocate fish eggs, and fill the gravel beds serving as trout spawning grounds. Frac sand is processed using hydrochloric acid, a very strong corrosive agent, and polyacrylamides, which are toxic and carcinogenic. In addition, large amounts of water are used to process the frac sands, in the order of hundreds of thousands of gallons a day. This could deplete sensitive groundwater supplies, dry municipal and private wells in the surrounding communities, and affect stream water levels.
Communities have attempted to block frac sand mines, with various levels of success. In Wisconsin, several bills have been proposed to effectively prevent local governments from establishing moratorium ordinances.
This growing industry is generating substantial revenue and creating local jobs. The conflict between these benefits and the environmental hazards associated with frac sand mining is a difficult challenge for many communities.
Milwaukee Journal Sentinel. Accessed 22 January, 2014. Frac Sand Mining Splits Wisconsin Communities.
Minnesota Department of Natural Resources. Accessed 22 January, 2014. Industrial Silica Sand FAQs.
Pennsylvania Department of Environmental Protection. Accessed 22 January, 2014. Wells Drilled by County.
Wall Street Journal. Accessed 22 January, 2014. In Fracking, Sand is the New Gold.
Wisconsin League of Conservation Voters. Accessed 22 January, 2014. Frac Sand Mining.