EQUIPMENT AND SUPPLIES--Bag-Type Suspended-Sediment Sampler In Reply Refer To: March 8, 1983 EGS-Mail Stop 412 QUALITY OF WATER BRANCH TECHNICAL MEMORANDUM NO. 83.08 Subject: EQUIPMENT AND SUPPLIES--Bag-Type Suspended- Sediment Sampler Attached for your information is Report Y, entitled "Development of A Bag-Type Suspended-Sediment Sampler" by J. J. Szalona. This report describes the adaption of a U.S. D-77 sampler for use with a thin plastic food-storage bag. The advantage of a bag-type sampler over a rigid- container sampler, our normal sampler, is that the limitation on the depth at which the rigid-container sampler may be used (due to the compressibility of air within its container) is removed. A continuous depth integrated sample can therefore be collected at depths greater than 19 feet; the maximum sampling depth will depend only on the stream velocity, bag size, and the rate of transit. A solenoid-actuated valve has also been developed for the D-77 sampler which allows for the collection of point-integrated samples. Caution should be exercised when using the bag-type sampler. All the tests run so far on this sampler have been performed in a laboratory setting. No field tests have been run and, consequently, we have no feel for any unusual problems that may arise. Laboratory tests have shown that the sampling rate is strongly influenced by the bag itself. The back pressure fluctuates as the bag unfolds; therefore, the sampling rate fluctuates from one sample to the next. This fluctuation can sometimes exceed +/-8% if the mean sampling rate. Because of the limited testing and uncertainty of the sampling rates, the Quality of Water Branch suggests that the following rules be observed when using the bag-type sampler: (1) The sampler should be used only if the mean velocity in the sampling vertical exceeds 1.5 ft/s. (2) The sampler should be used only when the stream temperature is above 7 degrees C. (3) Only lightweight quilted food storage bags should be used. These are available in most grocery stores. (4) As with other samples, the transit rate in the vertical should be no more than .4 the mean velocity of the stream. The sampler is prone to undersample, due to the back pressure created by the bag. During this period of extented evaluation, possible duplicate samples should be collected at each vertical using identical transit rates. The sample with the larger volume should be kept. Bronze D-77 samplers are available from the Federal Inter- Agency Sedimentation Project at the St. Anthony Falls Hydraulic Laboratory and presently cost $850.00 each. The D-77 must be modified for use as a bag sampler. With all modifications, the unit will cost an additional $400.00. However, in most sampling applications, a value would not be required. Anyone interested in purchasing a bag-type sampler or in having their D-77 modified should contact John Skinner at the St. Anthony Falls Hydraulic Laboratory (FTS 725-2218). Because the bag-type sampler has not been field tested, the Quality of Water Branch requests anyone who is presently using or anticipates using a bag-type sampler to contact the Chief, Quality of Water Branch and provide the following information: (1) The type bag sampler being or to be used. (2) Type of bag used. (3) Temperature range of samples being collected or anticipated. (4) Range of velocities at which the sampler has been or will be used (include mode of suspension, i.e., boat, bridge, cableway, etc.) (5) Range of depths at which the sampler has been or will be used. (6) Results of any comparison tests between bag-type sampler and other depth-integrating samplers. (7) Any general comments about the bag-type sampler. Include suggestions on how the sampler may be improved and comments on problems which arose while using the sampler. Your cooperation in helping us document the effectiveness of this type of sampler will be greatly appreciated. R. J. Pickering Attachment WRD Distribution: A, FOLS, PO