PROGRAMS AND PLANS - Sampling and analysis of water-quality constituents associated with suspended solids



                                            March 18, 1971

QUALITY OF WATER BRANCH TECHNICAL MEMORANDUM 71.05

Subject:  PROGRAMS AND PLANS - Sampling and analysis of water-
          quality constituents associated with suspended solids

The Quality of Water Branch staff, in consultation with Division 
Research Hydrologists and others, is reviewing the state of 
knowledge of water-quality constituents associated with suspended 
solids, for the purpose of establishing guidelines for sampling 
and analysis of those constituents.  These guidelines will be 
finalized within the next few weeks and promptly distributed to 
field offices.  In the meantime, it seems appropriate to present 
the philosophy upon which the guidelines will be based, as an aid 
to District and Regional programming efforts.

It is well known that certain water-quality constituents, 
especially some of the minor elements and organic compounds, are 
transported in streams either sorbed on or attached to suspended 
solids in large part.  For such constituents, the traditional 
analysis of a "clear-water" sample only may present an erroneous 
picture of the concentration or load in the stream.  This danger 
has been taken into account in our current procedures for analysis 
of water-suspended solids mixtures for "total" phosphorus, 
nitrogen, mercury, and pesticides.  Similar procedures are 
required for the remainder of such constituents.

Our objectives in sampling constituents associated with suspended 
solids should be: (1) to define the content of the constituent in 
both the dissolved and suspended phases; (2) to assess the 
relative significance of the two phases in the water sampled; and 
ultimately, (3) to define the source, behavior, and fate of each 
constituent.  Objective 3 will be met largely through District and 
Division research projects, but an important contribution can be 
made by carefully collected basic data.  In all circumstances, 
samples for the constituents under discussion should include the 
suspended phase.  Whether it is necessary to sample all size 
fractions of suspended solids for all constituents of interest 
will be one of the questions considered in establishing sampling 
guidelines.  Appropriate methods of extraction from the sampled 
solids will be considered also.

At the present time, programming for water-quality constituents 
known to be significantly associated with suspended solids should 
be done with the following principles in mind:

  (1)  Sampling should include the suspended phase as well as
the dissolved phase.

  (2)  An assessment of the relative loads of the constituent 
transported by each of the phases is usually desirable.  For this 
purpose, the concentration of the solids in the water-solids 
mixture is needed in addition to the concentrations of the 
constituent of interest in each phase of the mixture.

  (3)  Some knowledge of the content of the constituent in bed 
sediments should be obtained.  Solids in the streambed at low 
flows contribute substantially to suspended solids at high flows.  
Furthermore, bed sediments can act as either a source or a sink 
for a number of constituents, thus exerting control on constituent 
concentrations in the water even when immobile.

Consideration of the above principles, along with the expected use 
of the data, will provide a firm basis for preliminary planning of 
data-collection activities related to constituents associated with 
suspended solids.


                                  W.H. Durum
                                 Chief, Quality of Water Branch

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