Did the NAWQA study address changes and trends during the 10-year period of study (1992-2001)?
In general, no, because the NAWQA assessment was not designed to look at changes in pesticides (trends) that may have occurred during the period of study (1992-2001). Rather, the 10-year period reflects the total time for NAWQA to sample and assess pesticides in all 51 Study Units across the Nation. In order to effectively study the large areas, given the logistical and budget constraints, Study Units were assessed on a rotational schedule, with intensive data collection for the first 20 study units from 1992-1995, 16 study units from 1996-1998, and 15 study units and the High Plains study from 1999-2001. The combined results for the 1992-2001 study-period represent a composite picture of the decade. Most analyses of pesticides in stream water in the national compilation of data are based on one year of data for each site, generally representing the single most complete year of sampling, in order to give equal influence to each stream. Data analyses for ground water were based on one s
