EQUIPMENT & SUPPLIES -- Churn Splitters
January 17, 1978
QUALITY OF WATER BRANCH TECHNICAL MEMORANDUM NO. 78.03
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Theoretically, any subsample withdrawn from the churn should be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
valve?
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
splitters?
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
purchased.
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