Conducting the Environmental Impact Analysis and Assessment - Environmental Impact Analysis: Process and Methods - page 222

The investigation took advantage of a planned lowering of the lake level
for dam maintenance. Rather than gradually refilling the reservoir after the
maintenance and maintaining a downstream release, the release was severely
curtailed and the reservoir captured all the flow. The DO concentrations in
the river were monitored at increasing distances downstream from the dam.
The investigation was very successful, in that it demonstrated the dam release
rate associated with unacceptably low DO to be below approximately 20,000
cubic meters a day. However, the enthusiasm and scientific curiosity of the
environmental analysis team did create some issues as the dam release was
throttled below the volume considered adequate to maintain acceptable DO
concentrations as a validation of the prediction. The prediction was indeed
validated, but the resulting minor fish kill was not appreciated by the down-
stream stakeholders that frequented the park adjacent to the Mill River.
With a validated impact prediction quantifying lowered DO with river
flow, mitigation measures could be investigated and evaluated. An inte-
grated approach was not applicable to this impact because years of water-
needs studies, alternative source investigations, regulatory intervention, and
litigation had clearly demonstrated that the only feasible and environmen-
tally sustainable water supply alternative to supply south central Connecticut
(centered on New Haven) was the reactivation of Lake Whitney as a water
supply reservoir. Thus, after-the-fact mitigation of the predicted DO impact
was the only option available.
The mitigation measure selected was a lake management plan. The plan
was a negotiated compromise among stakeholders and included:
r Residents and the watershed association around the lake, who were
strongly opposed to lowering the lake level because of aesthetic issues
r Users of Mill River downstream of the dam who used the adjacent
park and correctly feared that extremely reduced dam releases
would impact DO and result in aquatic biota and wildlife impacts
r State regulatory officials charged with ensuring an adequate water
supply
r State regulatory officials charged with ensuring water quality,
including DO, in the Mill River downstream of the dam
r State regulatory officials charged with ensuring fish migration
r RWA customer representatives concerned with the price of water,
particularly to economically depressed neighborhoods in central
New Haven.
A lake management plan was developed and accepted by stakeholders to
mitigate DO impacts and consisted of the following major elements:
r Pumping water from the reservoir over the dam if the lake level
dropped below the dam and river flow was below a specified level