Database quality-control procedures
Two types
of data quality-control procedures were performed for data in the
Health-Based Screening Level (HBSL) database: (1) verification of
toxicity information collected from U.S. Environmental Protection
Agency (USEPA) data sources and (2) verification of HBSL values and the
methodology and information used to calculate them. These two
procedures are described below.
(1) Toxicity information collected from USEPA data sources was
entered into the HBSL database. After data entry, each record was
manually re-checked against its original USEPA data source. Any
incorrect values were corrected in the database with the correction
date noted. The process was then repeated to ensure that the
corrections made were accurate (see figure). This quality-control
procedure is followed each time updates are made to the database
(approximately monthly) and it is given a high priority to minimize
data entry errors.
(2) Using toxicity information collected from USEPA data sources,
HBSL values were independently calculated by individuals from USGS and
the Oregon Health & Science University.
The independently calculated HBSL values were
compared with each other and discrepancies were iterated and resolved
before the values were entered into the database. When an HBSL differs
from an existing USEPA Lifetime Health Advisory value and the reason
for the difference is not apparent (i.e., the same USEPA Office of
Water toxicity value and calculation method are used for the HBSL and
Lifetime Health Advisory), USGS consults with USEPA's Office of Water
to identify the reason for the discrepancy. This procedure is followed
each time updates to toxicity information result in an update to an
HBSL value.