Abstract
Previous investigations indicate that concentrations
of chlorinated volatile organic compounds (CVOCs) are
substantial in groundwater beneath the 9-acre former landfill
at Operable Unit 1, Naval Undersea Warfare Center, Division
Keyport, Washington. The U.S. Geological Survey has
continued to monitor groundwater geochemistry to ensure that
conditions remain favorable for contaminant biodegradation as
specified in the Record of Decision for the site.
This report presents groundwater geochemical and
selected CVOC data collected at Operable Unit 1 by the U.S.
Geological Survey during July 9–18, 2013, in support of longterm
monitoring for natural attenuation. Groundwater samples
were collected from 13 wells and 9 piezometers, as well as
from 10 shallow groundwater passive-diffusion sampling
sites in the nearby marsh. Samples from all wells and
piezometers were analyzed for oxidation-reduction (redox)
sensitive constituents and dissolved gases. Samples from all
piezometers and four wells also were analyzed for CVOCs, as
were all samples from the passive-diffusion sampling sites.
In 2013, concentrations of redox-sensitive constituents
measured at all wells and piezometers were consistent with
those measured in previous years, with dissolved oxygen
concentrations at all except an upgradient well 0.2 milligrams
per liter or less; little to no detectable nitrate; abundant
dissolved manganese, iron, and methane; and commonly
detected sulfide. In the upper aquifer of the northern plantation
in 2013, CVOC concentrations at all piezometers were similar
to those measured in previous years, and concentrations of
the reductive dechlorination byproducts ethane and ethene
were slightly lower or the same as concentrations measured
in 2012. In the upper aquifer of the southern plantation,
CVOC concentrations measured in piezometers during 2013
continued to be variable as in previous years, and often very
high, and reductive dechlorination byproducts were detected
in two of the three wells and in all but one piezometer.
Beneath the marsh adjacent to the southern plantation,
chloroethene concentrations measured in 2013 continued to
vary spatially and temporaly, and also were very high. Total
CVOC concentrations, at what have been historically the most
contaminated passive-diffusion sampler sites (S-4, S-4B, S-5,
and S-5B) remained elevated. For the intermediate aquifer in
2013, concentrations of reductive dechlorination byproducts
ethane and ethene and CVOCs were consistent with those
measured in previous years.
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First posted September 3, 2014
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