PROGRAMS AND PLANS--Quality of Existing Dissolved Trace-Element Data

In Reply Refer To:                                  March 20, 1992
Mail Stop 412


Subject:  PROGRAMS AND PLANS--Quality of Existing Dissolved 
                              Trace-Element Data


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.


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 

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.

                       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.

                         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

    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).


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 

    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