3 research outputs found
Toxic Groundwater Contaminants: An Overlooked Contributor to Urban Stream Syndrome?
Screening for common groundwater contaminants was performed
along
eight urban stream reaches (100s–1000s of m) at approximately
25–75 cm below the streambeds. Four sites had known or suspected
chlorinated-solvent plumes; otherwise no groundwater contamination
was known previously. At each site, between 5 and 22 contaminants
were detected at levels above guideline concentrations for the preservation
of aquatic life, while several others were detected at lower levels,
but which may still indicate some risk. Contaminants of greatest concern
include numerous metals (Cd, Zn, Al, Cu, Cr, U), arsenic, various
organics (chlorinated and petroleum), nitrate and ammonium, and chloride
(road salt likely), with multiple types occurring at each site and
often at the same sampling location. Substantial portions of the stream
reaches (from 40 to 88% of locations sampled) possessed one or more
contaminants above guidelines. These findings suggest that this diffuse
and variable-composition urban groundwater contamination is a toxicity
concern for all sites and over a large portion of each study reach.
Synergistic toxicity, both for similar and disparate compounds, may
also be important. We conclude that groundwater contaminants should
be considered a genuine risk to urban stream aquatic ecosystems, specifically
benthic organisms, and may contribute to urban stream syndrome
Elevated Dissolved Phosphorus in Riparian Groundwater along Gaining Urban Streams
Findings
of low concentrations of dissolved phosphorus in groundwater
in large surveys [e.g., United States Geological Survey’s National
Water-Quality Assessment (NAWQA) Program (Dubrovsky, N. M.; et al. The Quality of Our Nation’s
Water: Nutrients in the Nation’s Streams and Groundwater, 1992–2004. U.S. Geological Survey Circular 1350; USGS: Reston, VA, 2010.); >5000 wells] support the common perception that groundwater
is generally of little
importance for transporting phosphorus. Here, we address whether this
applies to urban riparian settings, where discharging groundwater
may potentially contribute to urban stream syndrome and downstream
eutrophication problems. This survey study includes 665 samples of
groundwater collected along gaining stream reaches at six urban sites.
Considering the combined sample set, 27% had soluble reactive phosphorus
(SRP) concentrations >0.1 mg L<sup>–1</sup>, which is more
than double that determined in the NAWQA Program (12%), while for
individual sites the range was 12–52%, excluding one site with
consistently low SRP (0%). None of the sites showed significant correlation
between SRP and the artificial sweetener acesulfame, a promising wastewater
indicator, including two with known wastewater contamination (but
the lowest SRP). Rather, high SRP concentrations were associated with
geochemically reducing conditions. This could mean that natural aquifer
or stream sediment materials were a primary contributor of the elevated
SRP observed in this study
Profiling Oil Sands Mixtures from Industrial Developments and Natural Groundwaters for Source Identification
The
objective of this study was to identify chemical components
that could distinguish chemical mixtures in oil sands process-affected
water (OSPW) that had potentially migrated to groundwater in the oil
sands development area of northern Alberta, Canada. In the first part
of the study, OSPW samples from two different tailings ponds and a
broad range of natural groundwater samples were assessed with historically
employed techniques as Level-1 analyses, including geochemistry, total
concentrations of naphthenic acids (NAs) and synchronous fluorescence spectroscopy (SFS).
While these analyses did not allow for reliable source differentiation,
they did identify samples containing significant concentrations of
oil sands acid-extractable organics (AEOs). In applying Level-2 profiling
analyses using electrospray ionization high resolution mass spectrometry (ESI-HRMS)
and comprehensive multidimensional gas chromatography time-of-flight
mass spectrometry (GC × GC-TOF/MS) to samples containing appreciable
AEO concentrations, differentiation of natural from OSPW sources was
apparent through measurements of O<sub>2</sub>:O<sub>4</sub> ion class
ratios (ESI-HRMS) and diagnostic ions for two families of suspected monoaromatic
acids (GC × GC-TOF/MS). The resemblance between the AEO profiles from OSPW and from 6 groundwater samples adjacent to two tailings ponds implies a common source, supporting the use of these complimentary analyses for source identification. These samples included two of upward flowing groundwater collected <1 m beneath the Athabasca River, suggesting OSPW-affected groundwater is reaching the river system