Manganese concentrations at six monitoring wells (four monthly samples for each well).
A data frame with 24 observations on the following 3 variables.
a factor indicating the month of collection
a factor indicating the well number
USEPA. (1989b). Statistical Analysis of Ground-Water Monitoring Data at RCRA Facilities, Interim Final Guidance. EPA/530-SW-89-026. Office of Solid Waste, U.S. Environmental Protection Agency, Washington, D.C. p.4-19.