In the summer of 1994, USEPA responded to an oil
release into the Housatonic River emanating from an operating hydroelectric
facility located at 140 Roosevelt Drive on the site of the former Hull Dye
facility in Derby, Connecticut. This facility housed two electricity-producing
turbines which, when operating, were powered by water from an up-gradient canal
that is fed by the Housatonic River. Oil-saturated soil and river sediment adjacent
to the facility were excavated and an interceptor trench and recovery well
system were installed close to the breakout location. In 1999, another oil
sheen emerged from the facility tailrace. After shutting down the turbines and
a thorough investigation, a second oil recovery system was installed over the suspect
source area in August 2000 and was operated until 2013.
Due to a continuing seepage of subsurface oil into
the facility tailrace, a sandbag and riprap dam that physically separates the
tailrace from the Housatonic River was constructed in 2007.
After years of study
and remediation, EPA determined in 2017 that sealing the walls and floor as
planned was not feasible and major reconstruction would be necessary to bring
the hydroelectric facility back online.
EPA discussed potential options with the National Pollution
Funds Center (NPFC) Case Officer and evaluated the estimated costs of either
renovating and bringing the facility back online or permanently shutting down the
facility. The NPFC and EPA agreed that attempting to bring the plant back
online would be cost prohibitive and the potential for oil to continue to
migrate into the river would always be present. In addition, EPA proposed to include
an oil recovery system into the permanent closure design so the potential for a
future oil breakout to the river would be further diminished.
In 2019, EPA’s technical assistance contractor was tasked
with preparing a final 100% design/cost report for sealing the tailrace and
permanent closure of the hydroelectric plant, which was completed in early
2020.
Due to funding limitations, only minor preparatory
activities were conducted in 2020. In
the spring of 2021, final facility closure began with filling of the penstocks
(subsurface pipes that carried water from the canal to the turbines to generate
power) with a flowable fill material. After extensive site preparation in the
fall and early winter, installation of the sheet pile wall was completed in
December 2021.This was followed by pressure grouting in the spring of 2022 to
seal the ends of sheet pile wall where it abuts the existing stone walls.
One of the remaining closure-related activities is filling
in of the tailrace with a flowable concrete mixture. This is being done to contain the source oil
under the building and not to allow it to migrate through the tailrace and out
to the river. The other remaining tasks
include installation of a passive oil observation/collection trench adjacent to
the sheet pile wall, and final site restoration. Due to an unavoidable delay related to ongoing
decommissioning issues, filling the tailrace and completing the remaining work
will continue through the end of the summer and is expected to conclude by late
autumn, 2022.
