Sulfate concentrations (ppm) at two background wells (five quarterly measures at each well).
EPA.09.Ex.6.3.sulfate.dfA data frame with 10 observations on the following 4 variables.
Montha numeric vector indicating the month the observations was taken
Yeara numeric vector indicating the year the observation was taken
Wella factor indicating the well number
Sulfate.ppma numeric vector of sulfate concentrations (ppm)