EQUIPMENT & SUPPLIES -- Churn Splitters

                                                January 17, 1978


Subject: EQUIPMENT & SUPPLIES -- Churn Splitters

The USGS churn splitter, first introduced in Quality of Water 
Branch Technical Memo 76.24T, has been in use by our field offices 
for about a year. Since its introduction, several questions have 
arisen about its operation. This memo is intended to answer most 
of those questions.

Question: What is the purpose of the churn splitter?

The churn splitter was designed to facilitate the withdrawal of a 
representative subsample from a large composite sample of a water-
sediment mixture. For example, samples from several verticals in a 
stream cross section, differing slightly from each other in 
chemical quality and sediment concentration, can be placed in the 
churn and be mixed into a relatively homogenous suspension. 
Theoretically, any subsample withdrawn from the churn should be 
equal in chemical quality and sediment concentration to any other 
subsample from the churn.

Question: When should the churn splitters be used?

The churn splitter was designed to be used for compositing and 
subsampling of chemical-quality samples that are to be analyzed 
for "total" or "total recoverable" inorganic constituents. 
Currently, the Central Laboratory Quality Assurance Section is 
evaluating the churn splitter to determine if it also can be used 
for organic carbon, radiochemical, or pesticide residue samples. 
The results of their evaluation will be announced in a later 
memorandum. Meanwhile, subsamples should not be taken from the 
churn splitter for determination of organic carbon, 
radiochemicals, pesticide residues, oil and grease, bacteria, or 
other constituents that require special handling.

The use of the churn splitter should not be considered to be 
limited to NASQAN stations alone. The splitter can and should be 
used at any chemical quality sampling site where subsampling of a 
composite water-sediment sample is required. In addition, the 
churn splitter can be used for subsampling composited surface-
water or ground-water samples that are to be filtered and analyzed 
for "dissolved" constituents.

Question- Are there any limitations to using the churn splitter?

Yes. Tests of the churn splitter using sand-size particles (>0.062 
mm) have indicated that when relatively high concentrations of 
such particles are present, subsamples for suspended-sediment 
concentration or particle size determinations should not be taken 
from the churn. Those samples should be collected in separate 
bottles directly from the stream. When essentially all particles 
are silt-size or smaller (<0.62 mm), sediment concentration and 
particle size subsamples may be taken directly from the churn.

Question: How critical are the operational procedures?

Tests have indicated that it is very important that a churning 
rate of about 9 inches per second be established and maintained 
during the sample withdrawal procedure. When faster or slower 
churning rates were used, maximum errors of about +/-45 to +/-65% 
were  observed, as compared with errors of about +/-8 to +/-15% 
when using the 9 in/sec rate. It is also important that the churn 
disc not break the water surface during mixing of the sample 
because this would aerate the sample and could cause chemical 
changes that would result in the sample no longer being 
representative of the water in the stream.

Question: Can subsamples for measuring pH, bicarbonate and 
carbonate, dissolved oxygen, specific conductance, and temperature 
be taken from the churn splitter?

In-stream measurements of these characteristics (except 
biocarbonate and carbonate) are preferred and recommended. If this 
is impractical, pH, specific conductance, bicarbonate and 
carbonate may be measured on a subsample taken from the churn 
before any other subsamples are withdrawn. However, the proper 
churning rate must be established before taking the subsample for 
these measurements in order to assure that a representative 
mixture remains in the churn for further sampling. Dissolved 
oxygen and temperature should never be measured on subsamples from 
the churn splitter.

Question: Is there any preferred order in which subsamples should 
be withdrawn?

1. Withdraw subsamples for "total", "total recoverable" or 
"suspended" determinations first.

2. The first subsample withdrawn should be the largest subsample 
required (usually l-liter) of the water-sediment mixture.

3. If it is absolutely necessary to use a subsample from the 
splitter to determine suspended-sediment concentration (see third 
question), that subsample should probably be withdrawn when 
about half of the volume originally collected remains, because the 
first withdrawals are normally high in suspended-sediment 
concentration and the last sithdrawals are low.

4. After all subsamples for "total", "total recoverable" and 
"suspended" determinations have been withdrawn, the remainder 
can be used for withdrawal of the required filtered samples.

5. It is recommended that subsamples for other than "dissolved" 
determinations not be withdrawn below a point about 1 1/2 inches 
(4 cm) above the spigot intake.

Question: What about cleaning the churn splitter?

Prior to taking it into the field the churn should be washed with 
a non-phosphate laboratory detergent and thoroughly rinsed with 
tap water followed by distilled water. Wash it the same way after 
a field trip. Before using it at a station, rinse the churn 
thoroughly with sample water. Cleaning between station visits 
while in the field may be accomplished by thorough rinsing with 
distilled water.

Question: Can the push-button spigot be replaced with a twist 

No. The withdrawal port is cone shaped inside with the push-button 
seat at the apex of the cone so that no space exists that will 
allow an accumulation of sediment. A twist valve would have a 
slack-water channel in which sediment could accumulate; this 
sediment would be withdrawn into the sample the next time the 
valve was opened. Replacement push-button spigots are available 
from this office.

Question: Where can I get technical information on the churn 

Any questions on the operation, design, or limitations of the 
churn splitter should be directed to the Quality of Water Branch, 
which was responsible for the design and testing of the units. 
Inquiries can be made by memorandum addressed to the Chief, 
Quality of Water Branch, MS 412, National Center, Reston, VA, or 
by telephone through FTS 928-6834. Inquiries, other than questions 
about outstanding orders, should not be made to the manufacturer.

Question: What sizes of churn splitters are available?

There are two accepted sizes available at this time. The larger is 
a 14-1iter size, which was the original splitter developed and 
distributed as part of the NASQAN program. The smaller is an 8-
liter size. Both of these sizes have been tested and approved for 
use. A 4-liter churn splitter was made and tested, but was found 
to be unacceptable. It is not recommended and should not be 

Question: Where can the churn splitters be ordered?

Both sizes of churn splitters can be ordered directly from Bel-Art 
Products, Pequannock, New Jersey 07440. Ordering information and 
prices quoted as of 7/28/77 are:

840130000  Churn Sample Splitter, Polyethylene   14-1iter size
           $95.00 ea

840150000  Churn Sample Splitter, Polyethylene    8-liter size
           $75.00 ea

New models do not have instructions inscribed on the sides.

Question- Where can I get the churns inscribed?

Decals for both the 14-1iter and 8-liter churns are being 
designed and will shortly be available from Operations Section, MS 
405, National Center, Reston. Information on the decals will 
include the name and symbol of the Survey, operating instructions, 
and volume gradations.

It is recommended that all personnel who use the churn splitter 
take time to reread the operational instructions distributed with 
Quality of Water Branch Technical Memo No. 76.24T. Additional 
information is given in Quality of Water Branch Technical Memo No. 
77.01. This office can provide copies of both memos on request.

                             R. J. Pickering
                             Chief, Quality of Water Branch

WRD Distribution: A, B,S,FO,PO