Conducting the Environmental Impact Analysis and Assessment - Environmental Impact Analysis: Process and Methods - page 205

benthic habitat once the DCR has been introduced are perhaps a more
important predictor of impact to sediment-dwelling organisms.
r Chemical characterization of deposition area: The chemical composition
of the DCR is important in determining impacts, but similar to physi-
cal characteristics, the chemistry of the sediments where the DCR
has been deposited is an important factor that could impact the ben-
thos. Chemically characterizing the sediments in the DCR deposition
areas allows determination of factors such as bioavailability and thus
the actual chemical exposure and impact to the benthos.
r Toxicity tests: Actually exposing organisms to the DCR and measur-
ing their survival and other responses (growth, reproduction, etc.)
allowed assessment of the toxicological impacts to the benthos.
r Benthic community structure evaluation: Collecting sediment samples
for the DCR deposition area and examining which animals are liv-
ing in the sediment, compared with similar areas without DCR is a
classic method of determining impacts, and was very useful for the
DCR environmental analysis. However, it is not always definitive
because it is only a snapshot of a community that is naturally highly
variable in time and space, thus it was necessary to supplement the
sampling results with information reported in the literature.
An advantage of multiple studies to evaluate impacts on a single receptor
is that it affords the opportunity to apply a weight-of-evidence approach.
Since there is variability and uncertainty in the characteristics and require-
ments of natural systems, detection of an effect in one incidence is not always
assurance that it will frequently occur or have ecosystem-wide implications.
Detection of effects through multiple lines of evidence is a much more cer-
tain and accurate predictor of impacts.
Based on the multiple investigations into the various areas of potential
impact (Table 5.4) only limited impacts were predicted as summarized below:
r Water chemistry: The concentration of potentially toxic chemicals
in the DCR was found to be low and when mixing models were
applied to the DCR discharge, the concentrations in the waters of
the Great Lakes were predicted to be well below levels harmful to
aquatic organisms.
r Enrichment and nutrients: The nutrient concentrations of the DCR
were low and addition of DCR slurry to phytoplankton cultures did
not stimulate growth to a level of concern. Thus no impact to enrich-
ment was predicted.
r Sediment chemistry: The model used to predict sediment concen-
trations based on the chemical characteristics of the DCR and the
measurement of sediment chemistry in the areas of heavy DCR