Nickel concentrations (ppb) at a monitoring well (eight months of samples, two samples for each sampling occasion).
A data frame with 16 observations on the following 3 variables.
a numeric vector of nickel concentrations (ppb)
a factor indicating the month of collection
a factor indicating the sample (replicate) number
USEPA. (1992c). Statistical Analysis of Ground-Water Monitoring Data at RCRA Facilities: Addendum to Interim Final Guidance. Office of Solid Waste, U.S. Environmental Protection Agency, Washington, D.C. p.78.