WATER QUALITY - Field determinations


                                        September 11, 1972

QUALITY OF WATER BRANCH TECHNICAL MEMORANDUM NO. 73.02

Subject: WATER QUALITY - Field determinations

Water-quality characteristics selected for determination in 
the field as part of our basic data collection programs are 
those that might be expected to change significantly between 
collection of the sample and its analysis in the laboratory, 
and which cannot be fixed satisfactorily to permit later 
analysis. Characteristics that can be determined in the 
laboratory are usually not measured in the field because of 
the attendant difficulties of avoiding contamination of the 
sample and maintaining analytical quality control.

The most common characteristics determined in the field in 
preference to the laboratory are those affected by loss or 
gain of carbon dioxide by the water sample--namely, pH, 
bicarbonate and carbonate (alkalinity), and sometimes 
specific conductance--and those affected by oxidation or 
temperature--namely, dissolved oxygen, temperature, and the 
ferrous-ferric iron ratio.

Some of these characteristics are measured in the laboratory 
as a step in making other determinations, thus obtaining for 
them both a field value and a laboratory value. In such 
cases, the field measurement should logically be the result 
to be published, because it represents the composition of the 
water at the time it was sampled. If the field measurement is 
not considered compatible with the laboratory measurements, 
then there must have been other determinations that should 
have been made in the field rather than in the laboratory. If 
this is the case, and the laboratory value is believed not to 
be representative of the sample at the time of collection, it 
probably should not be reported or published.

Reporting and publication of both field and laboratory 
results should be avoided, except in studies documenting 
water-cuality changes between the time of sampling and the 
time of analysis. Exceptions to this general rule
should be discussed with and approved by the Quality of Water 
Branch.


                             R. J. Pickering
                             Chief, Quality of Water Branch

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