Conducting the Environmental Impact Analysis and Assessment - Environmental Impact Analysis: Process and Methods - page 221

5.4.3 DCR Management Mitigation Case Study

In the USCG DCR EIS example (background discussed in Section 10.2), the
impact prediction conceptual model (Figure 5.10) can also provide a guide
for impact mitigation evaluation. Where impacts are predicted (e.g., potential
increase in invasive zebra mussels in the DCR example) the progression of
actions which resulted in the impact can be traced in reverse to the initial action,
(i.e., loading and unloading of dry cargo in the DCR example). Each of the steps
and the connection between steps in the progression causing the impact can be
an opportunity for mitigation. Alteration of any of the actions or an interruption
in any of the connections between steps can reduce the impact. For example, the
impacts originated from the spillage of DCR, which occurred primarily in the
ship's tunnel during unloading. Thus alternatives were developed and mitiga-
tion measures evaluated that would reduce the amount of DCR accumulating in
the tunnels from unloading events. The measures considered included:

r Pumping the sweepings from the ship's hold back onto the unloading
conveyor belt
r Installing and periodically cleaning screens over the sumps which
collected the wash water from sweeping activities
r Installing and maintaining scrapers to remove accumulated DCR
from the conveyor belt at locations where it could be collected rather
than spilled in the ship's hold
r Manual collection of large deposits of DCR before they become
mixed with wash water

Consistent with the integrated and proactive mitigation approach
described in Section 5.4.2, each of these measures were incorporated into
alternatives. As part of the impact prediction step in the DCR environmental
impact analysis, the quantity of DCR generated and discharged was esti-
mated from each of these measures and the resulting impacts on the envi-
ronmental resources for each measure fully evaluated.

5.4.4 RWA Lake Whitney Mitigation Case Study

The environmental impact analysis for returning Lake Whitney to a water
supply reservoir by the South Central Connecticut Regional Water Authority
(RWA) included a successful application of the classic approach to impact
mitigation. The environmental impact analysis identified the most serious
impact of the proposed action as a lowering of dissolved oxygen (DO) if the
flow in the Mill River, controlled by releases for the Lake Whitney Dam,
was reduced. This impact was identified as critical in the impact prediction
conceptual model, so an investigation was conducted to quantify the DO
concentration reduction as a function of river flow.