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NAWQA assessments of pesticides during Cycle I (1992-2002) followed
a nationally consistent approach in 51 of the Nation's major river
basins and aquifer systems, referred to as "Study Units,"
with 20 Study Units examined during 1992-1995; 16 during 1996-1998;
and 15 during 1998-2001. Nationally, water samples for pesticide
analysis were collected from 68 urban stream sites, bed-sediment
samples were collected from 134 urban stream sites, and fish samples
were collected from 95 urban stream sites. Ground-water samples
were collected from 856 urban wells.
Most water samples were analyzed for 75 pesticides and 8 degradates,
including 20 of the 25 most heavily used herbicides and 16 of the 25 most
heavily used insecticides. In addition, 32 organochlorine pesticide compounds
were analyzed in bed sediment and/or fish tissue, including 19 pesticides
and 13 degradates or manufacturing by-products. Most of the organochlorine
pesticides are no longer used in the United States, but organocholrine
compounds still persist in the environment.
NAWQA assessment of pesticides in Cycle 2 (2002-2012) will continue
at a subset of surface-water and ground-water sites in 32 of the
Nation's major river basins and aquifer systems.
The stream-sites maps and table include only urban fixed sites.
An urban fixed site is a surface-water site where streamflow is
measured and samples are collected and analyzed for various chemical,
physical, and biological characteristics. Combined, such sites are
used to assess broad-scale spatial and temporal variation at the
sites in relation to hydrologic conditions and environmental setting.
Maps include urban and mixed-urban sites. Mixed urban sites are
stream sampling sites located at an outlet of a drainage basin that
contains multiple land uses, including urban.
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