PROGRAMS AND PLANS--Data Handling, corrections to the WATSTORE Water-Quality File In Reply Refer To: June 29, 1981 EGS-Mail Stop 412 QUALITY OF WATER BRANCH TECHNICAL MEMORANDUM NO. 81.18 Subject: PROGRAMS AND PLANS--Data Handling, corrections to the WATSTORE Water-Quality File File Action Will Be Taken July 31-Aug. 3, 1981 As noted in my memorandum of April 24, 1981, on the same subject to Regional Hydrologists and District Chiefs, the Analytical Services Coordinator has identified in the WATSTORE Water-Quality File a problem that has evolved over the years as a result of changes in the precision and detection limits of the analytical procedures used in the Central Laboratories and the manner of reporting some analytical results in one of the Central Laboratories. The investigation that uncovered the problem was prompted by recent queries from the Environmental Protection Agency (EPA) and the President's Council on Environmental Quality (CEQ) on the significance of 1973-79 NASQAN trace metal data they had retrieved from STORET. The questions pertained to water-suspended sediment ("whole water") samples analyzed for total cadmium, copper, lead, mercury, and silver. For example, an examination of the data sets in question revealed that for lead at a particular site, the analytical results for 1973-1977 contained approximately equal numbers of <100 and 100 ug/L values, while the analytical results for 1978-79, after detection limits had been lowered through new methodology, contained roughly equal numbers of O and 1 ug/L values. This situation was brought about by a practice started in the Salt Lake Central Laboratory in which an analyst, when reporting analytical results at or below the detection limit by atomic- absorption methods, would enter a 100 or <100 (or a 1 or O) depending on whether the instrument reading was above or below the point on the instrument scale designated as the limit of detection, rather than rerunning the sample using a more sensitive method with a lower detection level. The investigation also revealed a problem with the existing quality of Water Branch policy concerning the convention to be used to indicate detection limits and precision of water-quality data. In 1972, the Branch adopted a policy of using a fixed number of "significant zeros" to specify both the precision and the lower limit of detection of each water-quality parameter in WATSTORE. That convention was valid as long as the detection limit for a given constituent was essentially the same for all types of samples analyzed and analytical procedures used. Due to improvements in methods and instrumentation over the last few years a variety of analytical methods, each with different detection limits, can be used for analysis of the same constituent. Moreover, the chemical matrix of the sample affects the detection limit for a number of determinations. Because of these two considerations, the use of "less thans" rather than "significant zeros" is now considered more useful and appropriate. The Automatic Data Section (ADS), working closely with the Quality of Water Branch, will correct the problems described above by a mass change of data stored in the Water-Quality File to be conducted simultaneously with the routine merge of the current file and back file on the weekend of July 30-Aug. 3, 1981. The changes to be made are based on Central Laboratories System criteria and are listed in Tables 1-3. The changes will be applied to all data for samples collected during the period October 1, 1972 through September 30, 1978, regardless of analyzing laboratory. Districts will be responsible for reentering any cooperator laboratory data changed inappropriately by the ADS procedure. Central laboratories System criteria may very well be appropriate for cooperator and District laboratory data in many cases, thus minimizing the updates to be done by the District, but the Districts should verify this and carefully document such criteria prior to updating the file. The choice of different criteria than those listed in Tables 1-3 for data from a given District or cooperator laboratory should be based on that laboratory's performance on reference samples, round-robin samples, or other quality assurance documentation. Action must be taken in the following sequence. First, Districts will identify all data from District and cooperator labs for which changes as specified in the attached tables may not apply and retrieve those data utilizing the retrieval list option (non-blank character in column 44 of the "M" card) in the retrieval deck to make a listing of the data. Use of the A534 Water Quality Tables program for this listing could be prohibitively expensive and should not be necessary. Next, ADS will make the wholesale changes as described. Finally, the Districts will make another retrieval and listing of the same data retrieved in step 1, compare the two listings, and make appropriate updates. Many people have objected to the fact that the ND, "not detected", remark will be applied to some data in the corrected file. For clarification, the ND remark is only used to indicate that an analysis was made, that the detection limit of the technique was unknown, and that the constituent was not detected. The remark provides no quantitative information and is merely holding a place in storage until definitive information on the analytical technique becomes available, at which time the remark can be replaced with a "less-than" value. District offices are requested to replace any ND remarks in the changed file with "less-than" detection limit values wherever sufficient information is available from reference samples or other inter-laboratory calibration activities of the District or cooperator laboratory to enable a determination of the detection limit of the analysis. Advice and assistance in this work will be provided by the Branch as needed. The Branch plans to pursue the detection-limit problem for the period prior to 1973. An attempt will be made to determine the detection limits from documented performance on Standard Reference Water Samples. The exercise will have to be performed on a lab-by- lab, constituent-by-constituent basis and may take considerable time to complete. District advice regarding this effort will be welcomed. R J. Pickering Chief, Quality of Water Branch Enclosure WRD Distribution: A, B, S, FO, PO Key Words: Water quality, data handling, WATSTORE, trace metal data This memorandum describes action planned as a result of responses to the memorandum of April 24, 1981 on the same subject from the Branch Chief to the Regional Hydrologists and District Chiefs.