a single wind turbine. But it requires less concrete, stands one-third as tall, and is present for just 30 days instead of 20–30 years. Between 7 and 15 weeks are spent setting up the drill pad and completing the actual hydraulic fracture. At that point, the drill pad is removed, leaving behind a single garage-sized wellhead that remains for the lifetime of the well. A study published in 2015 on the Fayetteville Shale found that a mature gas field impacted about 2% of the land area and substantially increased edge habitat creation. Average land impact per well was 3 hectares (about 7 acres) Water With coal mining, waste materials are piled at the surface of the mine, creating aboveground runoff that pollutes and alters the flow of regional streams. As rain percolates through waste piles, soluble components are dissolved in the runoff and cause elevated total dissolved solids (TDS) levels in local water bodies. Sulfates, calcium, carbonates and bicarbonates – the typical runoff products of coalmine waste materials – make water unusable for industry or agriculture and undrinkable for humans. Acid mine wastewater can drain into groundwater, causing significant contamination. Explosive blasting in a mine can cause groundwater to seep to lower-than-normal depths or connect two aquifers that were previously distinct, exposing both to contamination by mercury, lead, and other toxic heavy metals. Contamination of surface waterways and groundwater with fracking fluids is problematic. Shale gas deposits are generally several thousand feet below ground. There have been instances of methane migration, improper treatment of recovered wastewater, and pollution via reinjection wells. In most cases, the life-cycle water intensity and pollution associated with coal production and combustion far outweigh those related to shale gas production. Coal resource production requires at least twice as much water per million British thermal units compared to shale gas production. And while regions like Pennsylvania have experienced an absolute increase in water demand for energy production thanks to the shale boom, shale wells actually produce less than half the wastewater per unit of energy compared to conventional natural gas. Coal-fired power plants consume two to five times as much water as natural gas plants. Where 520–1040 gallons of water are required per MWh of coal, gas-fired combined cycle power requires 130–500 gallons per MWh. The environmental impact of water consumption at the point of power generation depends on the type of power plant: plants either use