Use of the before-after control-impact (BACI) design to detect recovery of benthic macroinvertebrate communities after the dechlorination of Upper East Fork Poplar Creek

The Department of Energy's Oak Ridge Y-12 Plant, a nuclear weapons component production facility, discharges once-through cooling water, cooling water blowdown, and process wastewaters from more than 200 outfalls into upper East Fork Poplar Creek. To improve water quality and reduce instream toxicity, dechlorination systems were installed at two sites responsible for approximately 80 percent of the chlorine loading. To determine the effects of dechlorination, a colonization study of the benthic macroinvertbrate community was conducted using the Before-After Control- Impact (BACI) design. Detection of the effect of dechlorination is achieved by testing whether the differences in population density and taxonomic richness at a "control" site and an impact site change after dechlorination. This was achieved by taking samples paired in time at three sites. The sites were chosen based on their proximity to the main sources of chlorine. The analysis revealed that no change in either density or richness in the benthic community could be attributed due to dechlorination. Reasons for these results and short comings of the BACI design are discussed.