WQ1978.03 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 Theoretically, any subsample withdrawn from the churn should be equal in chemical quality and sediment concentration to any other subsample from the churn.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