Conducting the Environmental Impact Analysis and Assessment - Environmental Impact Analysis: Process and Methods - page 178

description of the affected environment and minimize uncertainty. The final
phase consisted of collection and processing sediment samples from a range
of areas along an enrichment gradient defined by the first two phases of
the investigation for both chemical and biological characteristics (Figure 5.1).
Thus there were verifiable laboratory data to confirm conclusions from the
first two phases of the affected environment investigation. The laboratory
analysis was able to quantify the degree of enrichment as the organic carbon
content of sediments in the enriched area approached 4% as opposed to less
than 1% in other areas. The analysis also documented a different biologi-
cal assemblage in the area, indicating that although not currently stressed,
substantial additional organic and nutrient inputs to the area could result in
degraded conditions.
The approach used to describe the affected environment for the Scituate
wastewater environmental impact analysis was creative, conclusive, and effi-
cient. The major area of concern (the sediment), which was also indicative
of related enrichment conditions, was identified and the investigation was
focused on this area. The approach was phased with the early efforts providing
general observations over a large area and later phases focusing on the specific
areas of concern and providing more detailed information. The result was a
detailed description of a small well-defined subset of affected environmental
conditions (area of impact in the “credit card” Figure 4.1) that were subject to
impact. The description of the affected environmental also provided the nec-
essary input to compare alternatives and make an informed decision. In the
final analysis, based on the description of existing conditions, there was a clear
choice between advanced waste treatment and an offshore discharge with the
outfall extending well beyond the enriched area at the mouth of the North
River (Figure 5.4). The impacts of the two alternatives on water quality and the
estuarine system were similar, but they differed significantly in other areas.
The cost of the offshore outfall and diffuser were much higher than the cost of
advanced wastewater treatment because the outfall pipe had to extend beyond
the enriched area. Also there were potentially significant adverse impacts
associated with the construction of the outfall pipe, particularly in the section
through the salt marsh, barrier beach, and sand dunes. Thus the decision was
an advanced wastewater treatment plant with a discharge to the North River
system. The plant is now in place and the reduction of nutrients and organic
matter to the system has been effective in protecting the health of the estuarine
ecosystem.
5.2.5 Over-the-Horizon Radar-Affected Environment
Investigation Case Study
As part of the Cold War defense system, the U.S. Air Force committed to install-
ing an over-the-horizon (OTH) radar system providing detection capability up
to 5000 km beyond the shores of the continental United States. Four transmit-
ting and four receiving facilities located throughout the country were called for,