Galena became an important mining town with numerous mines and smelters, most notably the Eagle-Picher smelter plant north of the pre-1940s Route 66 alignment, which operated from around the late 19th century until 2004 as one of the largest smelters in the U.S., processing lead, zinc, and cadmium ores and producing those metals along with zinc oxide, zinc sulfide, manganese sulfate, manganese dioxide, and sulfuric acid. "Hell's Half Acre," once known as "Hickory Flats," was a major center of activity marked by countless mine shafts, chat, and tailings left after mining ceased. Although mining brought substantial wealth to the region, it also created lasting physical and environmental hazards: shafts and tunnels could collapse, as shown in 2009 when buildings in Galena partially collapsed after a tunnel gave way, and abandoned tunnels refilled with contaminated water that seeped into springs and groundwater in the same bedrock as the area's shallow aquifer. Large piles of chat and tailings covering more than 4,000 acres contained high concentrations of lead, zinc, and cadmium that leached into surface water and groundwater and could also be blown by wind into nearby soils, helping make the area one of the most ecologically blighted in the nation during the 1980s. Cleanup efforts by the Environmental Protection Agency and the Kansas Department of Health and Environment later addressed many of these problems. After the Environmental Protection Agency placed Cherokee County on the National Priorities List in 1983, investigators identified more than 1,500 open shafts and nearly 500 collapses, with Galena becoming an early focus because it had some of the worst contamination and 599 identified mine hazards, many in "Hell's Half Acre." The Environmental Protection Agency installed water treatment units for contaminated wells, helped Galena provide safe water to more than 500 affected residences and businesses, and by 1995 had removed metal-contaminated soils from residences, filled mine collapses and shafts, collected surface mine wastes, diverted streams away from waste, and replanted sites with native vegetation. In other badly contaminated places, residential soils were removed and replaced, and residents were relocated, including about 1,600 people from Picher, Oklahoma, in 2008 and 100 from Treece, Kansas, in 2014. Overall, cleanup restored a 25-square-mile portion of the 115-square-mile Cherokee County Superfund site as wildlife habitat, reducing risks to human health as native grasses, streams, and wildlife returned, though some evidence of lead and zinc mining remains and monitoring and further work continue.