| Chapter 1: | The Milltown Cleanup |
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extremely high levels of arsenic contamination in several of the groundwater wells serving Milltown residents (Woessner et al., 1984; Moore & Woessner, 2003). Arsenic is not immediately toxic to humans, but prolonged exposure increases incidence of cancer and premature death (see figure 4). It is estimated that people who (daily) consume water containing arsenic at a ratio of 20 parts per billion (ppb) have an increased risk––7 in 1,000––of developing bladder or lung cancer (National Research Council, 2001). Some sources regard .5 ppb as the level necessary to drop cancer risks to 1 in 10,000—the usual level of “acceptable risk” (National Resources Defense Council, 2001). In 1981 federal standards allowed for 50 ppb, but even according to those standards, the wells at Milltown contained dangerously high levels of arsenic. Several wells showed concentrations greater than 100 ppb, and notably, in 2001, the highest level in an individual well was recorded as 890 ppb (Missoula County Water Quality District, 2002).
Locals were informed of the contamination in 1981, and by 1983 Milltown was designated as a Superfund site by the Environmental Protection Agency (EPA). In 1984, under the provisions associated with the Clean Water Act, an alternative water system was completed for 33 impacted households. A tangle of regulatory scientific and legal issues emerged with regard to the contaminated wells of Milltown. Local residents and many agency officials immediately suspected that the contaminants had come from the Milltown reservoir. Subsequent studies showed that the depth of contaminated sediments in and near the reservoir ranged from 1 to 20 feet, but the average depth of water in the reservoir ranged from only 4 to 8 feet (Missoula County Water Quality District, 2005a). These depths indicated that much of the reservoir's storage capacity was compromised by the accumulated contaminated sediments. Representatives of the Atlantic Richfield Company (ARCO), who then owned the reservoir, initially denied that water wells drawing from an underground aquifer could be impacted by reservoir sediments.
Meanwhile, dams were losing public favor, and the construction of new projects had mostly halted by the 1980s. Many environmental and conservation groups were gaining momentum in efforts calling for