1 In Reply Refer To: March 20, 1992 Mail Stop 412 OFFICE OF WATER QUALITY TECHNICAL MEMORANDUM 92.05 Subject: PROGRAMS AND PLANS--Quality of Existing Dissolved Trace-Element Data BACKGROUND Recent studies indicate that results for a number of dissolved trace elements reported in the Division data base include contamination. These findings were previously reported in Office of Water Quality (OWQ) Technical Memorandum 91.10. Next, a suggested caveat for inclusion in State data reports was provided in OWQ Technical Memorandum 92.03; the caveat was then revised in memorandum 92.04. The purpose of this memo is to describe: (a) some implications of OWQ Technical Memorandum 91.10, and (b) how the Division can deal with issues of uncertainty in the validity and usefulness of existing dissolved trace-element data. IMPLICATIONS OF OWQ TECHNICAL MEMORANDUM 91.10 Results of the various studies reported in OWQ Technical Memorandum 91.10 indicate that unacceptable contamination was identified in dissolved trace-element data for arsenic, boron, beryllium, cadmium, chromium, copper, lead, and zinc. Because the examined data sets were rather small, this does not imply that elements not listed are free from contamination. Nor does the finding imply that the eight trace elements can not be, or have not been, collected in specific projects in a contaminant-free manner. NASQAN data collection involves hundreds of people and sets of equipment, including many different types of sampling devices. For these reasons, collection of data for the eight trace elements cited above has been suspended in NASQAN until OWQ can: (a) certify selected sampling equipment as trace element "contaminant free" at the part-per-billion (ppb) level; (b) provide a certified sample collection and field processing protocol for trace elements at the ppb level, (c) develop and deliver associated training, and (d) provide guidelines for collecting the proper types and adequate amounts of field QC data required to support the quality of collected trace-element data. In contrast to the situation for NASQAN, present data collection efforts should continue for individual projects, provided: (a) the field methods are appropriate to the stated project objectives and to the levels of trace elements that occur in the sampled hydrologic system, and (b) adequate QC data are generated to substantiate the quality of the trace-element data and to identify problems with contamination. After suitable equipment, a proper protocol, and appropriate QC guidelines are available, NASQAN will resume production of dissolved data for the eight elements. The results reported in Memorandum 91.10 indicate that most of the contamination existing in ppb level trace-element data derives from sample collection and field processing, rather than from laboratory handling and analyses. Thus, considerable diligence will be required in sample collection and field processing to reduce trace-element contamination. The effort must cover all trace elements, not just the cited list of eight. When NAWQA begins to collect dissolved trace-element data, the program will support the field effort with appropriate QC data. In addition, at the beginning of fiscal year 1993, the OWQ will provide QC guidelines to Districts for all classes of constituents in all sample media. At that time, the OWQ will formally suggest that all Division projects substantiate the quality of collected environmental data by adding a field QC component. QUANTITATIVE CORRECTIONS CAN NOT BE MADE TO THE EXISTING DATA BASE Most dissolved trace-element data in the existing data base were collected without field equipment blanks and other collaborative QC data. Thus, we can not: (a) assure that results are contaminant free, or (b) estimate the amount of contamination based on actual data. The studies reported in Memorandum 91.10 show that depending on the specific trace element, contamination derives primarily from: (a) sampling, (b) field processing, or (c) both sampling and processing. Specific studies on sampling devices indicate that although the amount of contamination depends to a considerable degree on the type of sampler, large variability occurs between samplers of the same type. In other words, some of the contamination is systematic (sampler type), whereas some is random (variation within sampler type). This finding is important, because once identified, sources of systematic contamination can be removed, whereas random contamination can only be identified by having adequate QC data collected at the time of sampling. The Bottom Line There is no way to apply a blanket correction factor to historic data sets for dissolved trace elements, even for individual trace elements at individual sites. This inability stems from: (a) the general lack of field equipment blank data, and (b) observed variabilities in both the sources and nature of contamination for a given trace element. WHAT WE CAN SAY NOW ABOUT EXISTING DISSOLVED TRACE-ELEMENT DATA 1. Concentrations below the reporting level--all results showing less-than values are considered to be unaffected by contamination at that reporting level. 2. Concentrations at or above the reporting level-- A. If adequate field QC data (especially field blanks) are available for specific data sets, and no detections (concentrations above the reporting level) occur in the blanks, the environmental data are probably unaffected by significant contamination from sampling and field processing. Accordingly, the data are acceptable. In WATSTORE/NWIS-I, codes exist to indicate the availability and type of QC data associated with each sample. Although these QC codes exist in the present data base, they have rarely been used; consider employing these codes wherever possible. B. If adequate field QC data are available for specific data sets, and random detections occur in the blanks, some or all of the environmental data may have been contaminated by sampling and field processing. In such cases, and without additional QC information, the environmental data must be viewed as questionable, and an appropriate caveat should be added to the data base and to data reports (for reports, see OWQ Technical Memorandum 92.04). Caveats cannot be entered into WATSTORE/NWIS-I; however, NWIS-II will accomodate such comments. In addition, interpretations of such a data set must take into account the impact of potential outliers (which might result from the random contamination observed in the blanks). For example, if upon testing there is an apparent time trend, does it still occur if the potential outliers are removed? C. If adequate field QC data are available for specific data sets, and systematic detections occur in the blanks, all of the environmental data must be assumed to be contami- nated by sampling and field processing. Accordingly, the data are unacceptable, and an appropriate caveat should be added (See B above). D. If adequate QC data are unavailable, environmental results showing detectable concentrations are questionable for at least arsenic, boron, beryllium, cadmium, chromium, copper, lead, and zinc. Accordingly, an appropriate caveat should be added (See B above). HOW WE CAN BETTER DEFINE THE QUALITY OF EXISTING DISSOLVED TRACE-ELEMENT DATA As previously noted, the OWQ is developing: (a) a new protocol for producing dissolved trace-element data that are uncontaminated at the ppb level, and (b) guidelines for producing field QC data, including equipment blanks, to certify the quality of data produced by the protocol. The target date for implementation of the protocol and guidelines is October 1, 1992. Once the new protocol is available, Districts can use the following approaches to better define the quality of data produced by the present protocol: 1. Conduct a side-by-side comparison of the new and present protocols at selected sites to determine the mean levels and variability of contamination in the dissolved data for specific trace elements. 2. After an adequate number of data are generated at a site using the new protocol, statistically analyze the old and new data sets to compare means and variabilities for specific trace elements. Neither approach will enable correction of the existing data base because of the multiple sources and inherent variability of contamination for each trace element that arises through use of the present protocol. Moreover, approach 2 will not provide a clear understanding of the levels of contamination in the historic data base because of temporal variability in the actual environmental concentrations of the dissolved trace elements. However, use of either approach will enable Districts to gain some increased insight into the general level of contamination in the existing data base for specific trace elements. The OWQ will work with the Branch of Systems Analysis to define: (a) proper designs for both approaches, and (b) appropriate procedures for statistical analysis of the resulting data. David A. Rickert Chief, Office of Water Quality Key Words: Trace elements, contamination This memorandum refers to Office of Water Quality Technical Memorandums 91.10, 92.03, and 92.04. Distribution: A, B, S, FO, PO