TM05-03 Changes in reporting levels and data qualifiers for selected pesticides and degradation products in schedule 2060

An evaluation of quality-control data has shown that the absolute recoveries and variability of recoveries for many compounds in Schedule 2060 have changed temporally after the method was officially approved; most notably, a substantial change occurred after July 31, 2002. This technical memorandum describes the data analysis at the NWQL to (1) quantify the effects of this change, (2) provide guidance for interpreting results from environmental samples produced during this period of diminished method performance, (3) describe corrections made to restore method performance to conditions equal or better than conditions occurring prior to July 31, 2002, and (4) provide a quality control data summary that documents restoration of method performance. These data are part of a multiyear Schedule 2060 data set, and this technical memorandum provides the time history of changes to Schedule 2060 to the present (December 2004). Also described are the recoding procedures that the NWQL will apply to ensure consistency within the Schedule 2060 data set. The recoding to produce this consistency was undertaken to provide the National Water-Quality Assessment Program and District customers with the ability to interpret Schedule 2060 data produced by the NWQL between July 31, 2002, and September 30, 2004. This recoding also will ensure that these data are properly remarked and qualified for use by the USGS and the public. Finally, this technical memorandum describes the method audits used to identify sensitive components in the method procedure, where subtle changes may have resulted in the observed performance changes. Evaluation of these components resulted in corrective actions that have been implemented to restore method performance, which also is described. Quality-control sample results collected after these corrective actions were implemented demonstrate restoration or improvement of method performance and are included in this document.