Air Quality Criteria for Lead Volume II of II - (NEPIS)(EPA) - US ...

The NAWQA dataset was chosen over other readily available national databases (i.e. the
USEPA-maintained database for the STOrage and RETrieval [STORET] of chemical, physical,
and biological data), because the study design and methods used to assess the water quality of
each study unit are rigorous and consistent, and, as such, these data may be presented with a high
level of confidence. This is in stark contrast to the STORET database, which essentially serves
as a depot for any organization wishing to share data they have generated. This lack of a
consistent methodology or QA/QC protocol has lead to the STORET data being highly qualified
and offered with only a mild level of confidence. Furthermore, because there is no standard for
site selection within STORET, the database may be biased toward contaminated sites. Finally,
and, perhaps most importantly, the majority of the available Pb data in STORET predate the use
of clean techniques for Pb quantification.
The authors recognize the existence of several local and regional datasets that may be of
quality equal to NAWQA; however, due to the national scope of this assessment, these datasets
were not included in the following statistical analyses. However, because the NAWQA database
does not cover lakes and the marine/estuarine environment, and we were unable to identify any
monitoring data of similar quality, local and regional datasets were used in these cases to provide
general information on environmental Pb concentrations.
Data Acquisition and Analysis
The following data were downloaded for the entire United States (all states) from the
NAWQA website (http://water.usgs.gov/nawqa/index.html): site information, dissolved Pb
concentration in surface water (µg/L), total Pb concentration (µg/g) in bed sediment (