Delineating groundwater discharge to Little Bayou Creek

Little Bayou Creek is an 11-km long, first-order
stream in the lower Ohio River valley in McCracken County, Kentucky. The
creek’s ~ 24-km2 watershed includes part of the US Department of Energy’s
Paducah Gaseous Diffusion Plant (PGDP), which enriched uranium for use in
nuclear reactors; the Tennessee Valley Authority’s Shawnee Plant (a
coal-fired generating station); the state-run West Kentucky Wildlife
Management Area; and several small farms. Little Bayou Creek was originally
a tributary of the Ohio River, but between 1953 and 1971, the creek was
rerouted around ash ponds at the Shawnee Plant. Thereby, Little Bayou Creek
was channelized along its lower 2.5 km and connected to Bayou Creek, a
second-order perennial stream, 340 m southwest of the river. Flow of Little
Bayou Creek was partly sustained by discharge of process water from PGDP,
which obtained at least 498 L/s of water from the river via two pipelines.

With graduate students and other collaborators, I have conducted three
USDOE-funded studies of groundwater discharge to Little Bayou Creek
(1996-98, 1999-2003, and 2011-12). We observed focused discharge via seeps
and springs along the upper ~ 300 m of the channelized reach, where the
channel appears to have intersected preferential pathways within the
confining unit. Diffuse discharge was evident downstream where the channel
is incised into the semi-confined Regional Gravel Aquifer. During 19 days
in fall 2011, we deployed a FO cable with a CTEMPs Oryx DTS unit along the
head of the channelized reach, running the cable ~ 500 m along one bank and
then looping the cable back down the opposite bank. The DTS results
corroborated manual temperature probing and visual observations of seeps
and springs.

I am seeking to revisit these previous studies to examine changes in
groundwater discharge along the channelized reach of Little Bayou Creek
during the past 11 years. PGDP stopped uranium enrichment in 2013; the
Olmsted Lock & Dam was completed in 2018, raising Ohio River pool elevation
by 3.7 m; and TVA installed a sheet pile wall along ~ 850 m of the creek. I
envision running the DTS sequentially along three segments of ~ 1000 m for
periods of ~ 1 week each during June-July 2024, when temperature contrasts
between groundwater and stream water are likely to be pronounced. I
purchased a 1000-m FO cable from CTEMPs for our previous DTS study. We
intend to follow this new deployment with a year-long monitoring study of
groundwater discharge along the channelized reach of Little Bayou Creek.
This would involve quarterly stream gaging, tracer (dilution) tests,
sampling of stream water and seeps for solutes and stable isotopes of water
(for end-member mixing calculations), and real-time monitoring of discharge
rates at selected seeps.