CHIPPEWA FALLS, Wis. ‚?? Largely overlooked in the national debate over hydraulic fracturing, or fracking, to unlock underground gas and oil supplies is the emerging fight in the U.S. heartland over mining ‚??frac sand.‚?Ě Mining companies say the work provides good jobs in rural areas, but some residents fear the increase in mining could harm human health and the environment. ‚??More and more people are waking up to the fact that there are difficulties with this massive explosion,‚?Ě said Pat Popple, a retired school teacher and principal and anti-sand mining activist. U.S. frac sand producers sold or used more than 6.5 million metric tons of sand worth $319 million in 2009, according to the U.S. Geological Survey. Nearly three-fourths of frac sand comes from the Midwest. Activists fear fine silica dust from the mines and plants will make people sick, spoil the landscape and contaminate ground water. Some counties in Minnesota and Wisconsin have responded to health and environmental concerns by passing mining moratoriums to buy time for more study. Others are debating whether to hit the brakes on further mine development.