TM03-01 Data-reporting conventions and implications for interpreting results from custom method 9060 for samples collected from March 1, 1999, to December 31, 1999

Most samples analyzed using custom laboratory code 9060 (LC9060) between March 1999 and March 18, 2000 were subject to extended holding times. This technical memorandum describes the holding time studies undertaken at the NWQL to evaluate the effects of these extended holding times and guidance for the interpretation of these results. Data recoding procedures that the NWQL will implement also are described. This recoding is undertaken so that these results are properly remarked and qualified for USGS and public use. These results are part of a multiyear LC9060 data set, and this technical memorandum provides the time history of changes to LC9060 up until the approval of the official method SH2060. Also described are the recoding procedures that the NWQL will apply to ensure (1) consistency within the LC9060 dataset and (2) compatibility with SH2060 results. The recoding to produce this consistency and compatibility was undertaken to provide the National Water-Quality Assessment Program with the ability to interpret these LC9060 and SH2060 data over the multiple years in which data were collected.