Sodium concentrations (ppm) collected over several years. The sample dates are recorded as the year of collection (2-digit format) plus a fractional part indicating when during the year the sample was collected.
A data frame with 10 observations on the following 2 variables.
a numeric vector indicating the year of collection (a fractional number)
a numeric vector of sodium concentrations (ppm)
USEPA. (2009). Statistical Analysis of Groundwater Monitoring Data at RCRA Facilities, Unified Guidance. EPA 530/R-09-007, March 2009. Office of Resource Conservation and Recovery Program Implementation and Information Division. U.S. Environmental Protection Agency, Washington, D.C. p.17-36.
USEPA. (2010). Errata Sheet - March 2009 Unified Guidance. EPA 530/R-09-007a, August 9, 2010. Office of Resource Conservation and Recovery, Program Information and Implementation Division. U.S. Environmental Protection Agency, Washington, D.C.