Conducting the Environmental Impact Analysis and Assessment - Environmental Impact Analysis: Process and Methods - page 206

discharge both revealed sediment concentration below levels of con-
cern. Also the exposure of sediment-dwelling organisms to DCR in
the laboratory did not produce an adverse response. Thus no sedi-
ment chemistry impact was predicted.
r Sediment alteration and deposition: The prediction of deposition and
resulting physical characterization of the sediment did not identify
a change in the sediment to a level of concern. However, measure-
ment of sediment in the areas of heavy DCR discharge and condi-
tions reported in the literature (Mudrock et al. 1988) did indicate a
potentially small degree of sediment alteration. As discussed below,
this led to follow-up investigations to determine the effect this might
have on invasive mussel species.
r Benthos, pelagic organisms, and water fowl: With the exception of poten-
tial sediment alteration, no change in the chemical or physical char-
acteristics of Great Lakes habitat attributes was predicted. Thus no
impact to the biological resources was expected with the possible
exception to changes in invasive mussel population that warranted
additional investigation as described in the next section.

5.3.4.2 Prediction of Invasive Mussel Impacts

The scientific investigations (Table 5.4) conducted to evaluate the potential
impacts identified in the conceptual model (Figure 5.10) revealed an interest-
ing and potentially significant ecological impact. The initial scientific results
were reviewed in light of the conceptual model by the project team and a TAC
formed for the project. The review identified a potential expansion of invasive
mussel populations in the Great Lakes resulting from the predicted alteration
of the sediment physical characteristics. This concern was based on the fact
that mussels prefer the hard substrate offered by the DCR. It then became
necessary to amend the original scope of the scientific investigations to take a
hard look at the potential for DCR management practices to cause an expan-
sion and density increase in the Great Lakes' invasive mussel population.
The nonindigenous zebra ( Dreissena polymorpha ) and quagga mussels
( D. bugensis ) have invaded freshwaters throughout the United States from
New England to California. Once introduced, they breed rapidly with a
fully mature female mussel capable of producing up to one million eggs
per season (Claxton and Mackie, 1998) and in many habitats very dense
populations can become established. One of the critical mussel habitat
characteristics is a hard substrate (Czarnoeski et al. 2004) and introduc-
tion of the hard DCR into the otherwise soft muddy bottom of the Great
Lakes could create a habitat conducive to high mussel population densi-
ties. The high density of these invasive mussels can preclude establish-
ment of native species, affect water quality, and also become so dense that
they clog water intakes for power plants and municipal water supplies.