SURFACE-WATER-DISCHARGE AND SURFACE-WATER-QUALITY RECORDS
The following remark codes may appear with the water-quality data
in this section:
PRINT OUTPUT REMARK
E Estimated value.
> Actual value is known to be
greater than the value shown.
< Actual value is known to be
less than the value shown.
K Results based on colony
count outside the acceptance
range (non-ideal colony count).
Data generated from quality-control (QC) samples are a requisite
for evaluating the quality of the sampling and processing
techniques as well as data from the actual samples themselves.
Without QC data, environmental sample data cannot be adequately
interpreted because the errors associated with the sample data are
unknown. The various types of QC samples collected by this
District are described in the following section. Procedures have
been established for the storage of water-quality-control data
within the USGS. These procedures allow for storage of all
derived QC data and are identified so that they can be related to
corresponding environmental samples.
The dates and times of QC samples are noted in the water
quality tables, but the QA data are not displayed. The various
types of QA data are available upon request from the U.S.
Geological Survey North Dakota District office (see address on
back of the title page of this report).
Blank samples are collected and analyzed to ensure that
environmental samples have not been contaminated by the overall
data-collection process. The blank solution used to develop
specific types of blank samples is a solution that is free of the
analytes of interest. Any measured value signal in a blank sample
for an analyte (a specific component measured in a chemical
analysis) that was absent in the blank solution is believed to be
due to contamination. There are many types of blank samples
possible, each designed to segregate a different part of the
overall data-collection process. The types of blank samples
collect in this District are:
Field blank - a blank solution that is subjected to all aspects
of sample collection, field processing preservation,
transportation, and laboratory handling as an environmental
sample.
Trip blank - a blank solution that is put in the same type of
bottle used for an environmental sample and kept with the set
of sample bottles before and after sample collection.
Equipment blank - a blank solution that is processed through
all equipment used for collecting and processing an
environmental sample (similar to a field blank but normally
done in the more controlled conditions of the office).
Sampler blank - a blank solution that is poured or pumped
through the same field sampler used for collecting an
environmental sample.
Filter blank - a blank solution that is filtered in the same
manner and through the same filter apparatus used for an
environmental sample.
Splitter blank - a blank solution that is mixed and separated
using a field splitter in the same manner and through the same
apparatus used for an environmental sample.
Preservation blank - a blank solution that is treated with the
sampler preservatives used for an environmental sample.
Reference material is a solution or material prepared by a
laboratory whose composition is certified for one or more
properties so that it can be used to assess a measurement method.
Samples of reference material are submitted for analysis to ensure
that an analytical method is accurate for the known properties of
the reference material. Generally, the selected reference
material properties are similar to the environmental sample
properties.
Replicate samples are a set of environmental samples collected in
a manner such that the samples are thought to be essentially
identical in composition. Replicate is the general case for which
a duplicate is the special case consisting of two samples.
Replicate samples are collected and analyzed to establish the
amount of variability in the data contributed by some part of the
collection and analytical process. There are many types of
replicate samples possible, each of which may yield slightly
different results in a dynamic hydrologic setting, such as a
flowing stream. The types of replicate samples collected in this
District are: Sequential samples - a type of replicate sample in
which the samples are collected one after the other, typically
over a short time.
Split sample - a type of replicate sample in which a sample is
split into subsamples contemporaneous in time and space.
Spike samples are samples to which known quantities of a solution
with one or more well-established analyte concentrations have been
added. These samples are analyzed to determine the extent of
matrix interference or degradation on the analyte concentration
during sample processing and analysis.
*NOTE.-- Traditionally, dissolved trace-element
concen-trations have been reported at the microgram per liter
(mg/L) level. Recent evidence, mostly from large rivers,
indicates that actual dissolved-phase concentrations for a number
of trace elements are within the range of 10's to 100's of
nanograms per liter (ng/L). Data above the mg/L level should be
viewed with caution. Such data may actually represent elevated
environmental concentrations from natural or human causes;
however, these data could reflect contamination introduced during
sampling, processing, or analysis. To confidently produce
dissolved trace-element data with insignificant contamination, the
U.S. Geological Survey began using new trace-element protocols at
some stations in water year 1994.
*NOTE.-- Sample handling procedures at all National
Trends Network stations were changed substantially on January 11,
1994, in order to reduce contamination from the sample shipping
container. The data for samples before and after that date are
different and not directly comparable. A tabular summary of the
differences based on a special intercomparison study, is available
from the NADP/NTN Coordination Office, Colorado State University,
Fort Collins, CO 80523 (Telephone: 303-491-5643).
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