Geochemical characterization of groundwater discharging from springs north of the Grand Canyon, Arizona, 2009–2016

Abstract

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Geochemical characterization of groundwater evolution south of Grand Canyon, Arizona (USA)

“…In the field blank from 2016 the following chemical analytes had a value above the reporting level concentration (in parentheses); aluminum (0.4 μg/L), nickel (0.06 μg/L), antimony (0.005 μg/L), tin (0.1 μg/L), and sulfate (0.02 mg/L). The measured concentrations in the blank for the aforementioned constituents were similar to concentrations in blanks collected by the same method reported in Beisner et al (2017). For the majority of those analytes, the environmental sample values were more than 10 times greater than the blank concentrations and likely do not bias the environmental values.…”

“…As the majority of trace elements had one or more values below a laboratory reporting level, with several elements containing multiple reporting levels, specific statistical methods (Helsel 2012) for data with values below a censoring threshold (laboratory reporting level) were used to analyze the majority of analytes presented in this study. Detailed description of the statistical tests is given in Beisner et al (2017). A p-value threshold of 0.05 (95% confidence level) was used to indicate statistical significance for all mentioned statistical tests.…”

“…Robust regression on order statistics (ROS) using the cenros function from the NADA software package in R (R Core Team 2018; Lee 2017) was applied to chemical analysis from spring samples for each element to calculate the median, mean, and standard deviation of the data. Groundwater in this study was compared to groundwater north of Grand Canyon (Beisner et al 2017), using the cendiff function from the NADA package in R (Lee 2017;Helsel and Lee 2006).…”

“…All samples were collected by the USGS using standard field methods (USGS 2006;2018), and filtered samples were passed through a 0.45-μm capsule filter. Detailed field and analytical descriptions are published in Beisner et al (2017).…”

“…Multiple standard reference samples were analyzed by the USGSTMCO during every analytical run. A detailed analysis of the standard reference sample performance for the respective laboratories is presented in Beisner et al (2017).…”