This dataset is a random selection of dissolved arsenic analyses taken during the U.S. Geological Survey's National Water Quality Assessment program (NAWQA).
data(NADA.As)
A list containing 50 observations with items `obs' and `censored'. `obs' is a numeric vector of all arsenic observations (both censored and uncensored). `censored' is a logical vector indicating where an element of `obs' is censored (a less-than value).
The USGS NAWQA site at http://water.usgs.gov/nawqa