The River Benthos Record for Smurfit-Stone\u27s Missoula Mill -- Nearly a Half-Century of Clark Fork River Monitoring

The Missoula Mill of Smurfit-Stone Container discharges treated process water to the Clark Fork River near Frenchtown, Montana. Annual monitoring (1956 - present) of macroinvertebrate indicated river quality, is an integral part of the Missoula Mill\u27s environmental protection effort. Quantitative riffle benthos samples from ten sites (study reach = 22 miles) are taken during August. Impact is determined using control vs experimental comparisons of community descriptors including the biometrics subsets used in the calculation of the Montana Biological Integrity Index. Study results show significant background (upstream mill) enrichment in incremental amounts over the period 1960 through the late 1980\u27s, presumably a product of growth in the Clark Fork, Blackfoot, and Bitterroot drainages. Mill related impact throughout this same period, also expressed as enrichment was limited and localized to the zone of initial dilution. Recent study results (1995 - 1999) generally show either continuation, or a slight decline, in overall enrichment of the system relative to the Missoula Mill\u27s treated effluent