Background on Case Studies - Environmental Impact Analysis: Process and Methods - page 364

Preparation of the EIS for DCR management on the Great Lakes presented an
opportunity not typically encountered in an environmental impact analysis. The
practice of virtually uncontrolled DCR discharge within the major Great Lakes
shipping lanes had occurred for over a century, which created the possibility of
actually measuring rather than predicting the impacts resulting from the dis-
charge. Since the degree of impact was generally proportionate to the mass of
the DCR discharged, alternatives that reduced the discharge could be assumed
to have lesser impact scaled to the anticipated reduction in DCR discharge.
The DCR environmental impact analysis focused on the physical, bio-
logical, and chemical conditions in the Great Lakes shipping lanes and
represented both the affected environment and impact from historic DCR
discharges. The chemical impacts were addressed by analysis of the concen-
trations of potentially toxic components of the various cargo types, measure-
ment of sediment chemistry in areas of heavy DCR discharge, and toxicity
tests using indigenous aquatic organisms exposed to DCR. All of these tests
unambiguously demonstrated that no chemical effects on the aquatic system
were anticipated regardless of the DCR discharge rate or mass.
The combined analysis of biological and physical stressors from DCR dis-
charge indicated a potential for effects. The possible effect was on the soft
bottom invertebrate community because the addition of hard substrate pro-
vided opportunity for attachment of different species, but the impact was
not seen as significant or with consequences reaching beyond the immediate
area of discharge. However, the addition of DCR and associated changed
substrate conditions was seen as a concern for the expansion of invasive
mussel populations, and a detailed scientific investigation was initiated to
fully evaluate the effects and understand the implications (see Section 5.3.4).
The analysis demonstrated that some effects related to invasive mussels
could occur in certain locations. Specifically, Lake Superior would not be
affected because the water chemistry (e.g., low-calcium concentrations) pre-
vented establishment of mussel populations and DCR discharge would not
alter this situation. Mussel populations in Lakes Erie and Ontario were already
at maximum levels and the addition of more DCR would not result in a higher
mussel density. The populations in Lakes Michigan and Huron were not at
maximum density, at least partially due to lack of suitable substrates and the
discharge of DCR could result in an expansion of the invasive mussel popula-
tions. However the effects would not be immediate or irreversible and based
on the analysis, the USCG decided to issue an interim rule without substan-
tial changes to current practices. The analysis supported the position that no
significant environmental harm would occur while the USCG more closely
evaluated the mussel situation in relation to economic impacts on the shipping
industry resulting from more stringent DCR discharge control requirements.
The Record of Decision and interim regulation included requirements for
each Great Lake carrier to submit to the USCG information on DCR discharge.
This included estimated location and mass of DCR discharge and the mea-
sure used to minimize the spillage and discharge. The information along with