Equipment and Supplies: Automatic pumping samplers--Tests of efficiency of Manning and ISCO samplers


In Reply Refer To:                             November 28, 1980
EGS-Mail Stop 412



QUALITY OF WATER BRANCH TECHNICAL MEMORANDUM NO. 81.06

Subject: Equipment and Supplies: Automatic pumping samplers--
         Tests of efficiency of Manning and ISCO samplers

Enclosed is a brief unpublished report of tests performed by the 
U.S. Forest Service, Redwood Sciences Laboratory, Arcada, 
California, of the Manning and ISCO pumping samplers. The tests 
indicate the importance of frequently checking the sampler 
efficiency of any pumping sampler that you may be using. We 
believe that sampler efficiency is reduced as the concentration of 
sandsize material increases. If the water-sediment mixture being 
sampled is mostly fine material, the sampler efficiency should be 
close to 100 percent.

We believe that you should be aware of the potential for erroneous 
samples under some circumstances if either of these two samplers 
is used. Please distribute this memo to all District and research 
personnel who are working with pumping samplers or pumping-sampler 
data.



                          R.J. Pickering
                          Chief, Quality of Water Branch

Enclosure

Superseded memoranda: None.

Key words: Water quality, sampling, samplers, pumping samplers.

WRD Distribution: A, B, FO, PO.




              Pumping Sampler Cross Contamination Test

Purpose

The purpose of this test was to determine the response of two 
commonly used portable pumping samplers to sudden changes in 
suspended sediment concentration. The two samplers tested were:

1. Manning - model S-4050 as modified by the factory in the summer 
of 1980. (Modifications included a change in the electronics which 
control a pinch valve to empty the measurement chamber, and 
changes in the "plumbing" to improve the control of pressure and 
vacuum.) This is a pressure/vacuum sampler with an intake nozzle 
at the end of a 25' long - 3/8" i.d. plastic tube. The sampler is 
operated by a 12 volt battery. It was set to collect samples of 
about 260 ml with a velocity setting of 6 (line speed of 3.3 
ft/sec) and a head of 4.2'.

2. ISCO model 2100. This sampler has a peristaltic pump, and 22' 
of 1/4" i.d. intake hose with nozzle. For the test a 110 volt 
battery charger replaced the 12 volt battery. The sample volume 
setting was 240 ml, the line speed was 5.0 ft/sec, and the suction 
head 6'.

Experimental facility

Lacking a flume, a 30 gallon plastic drum was fitted with a rack 
to support the intake of the sampler being tested. The intake was 
mounted vertically about 3 1/4 inches from the side of the drum 
with its center about 7 1/4 inches from the bottom. The drum was 
partly filled with a made-up water/sediment mixture which was kept 
in motion by a paddle mounted in a variable speed drill press. 
Immediately "in-front" of the sampler intake, a j-shaped reference 
nozzle - having the same i.d. as a DH-48 nozzle - was oriented 
into the flow, passed out through the wall of the drum, and was 
connected to a short piece of tubing outside which had a pinch 
valve to allow collecting reference samples simultaneously with 
the pumped ones. The water velocity in the drum at the nozzle 
location was about 1.8 ft/sec, as best that could be determined 
using a pigmy current meter. We are not very sure of this due to 
the velocity gradient from the center to the edge of the drum, and 
since the meter was used with its cups in a vertical plane.

The "zero sediment" samples were taken from another 15 gallon drum 
containing tap water.

The samples were, in turn, mounted at the upper end of a gently 
sloping ramp which held the hoses. Care was taken that the hoses 
led downhill all the way from the sampler to the nozzle.

Data Collection

The large drum was filled with 56.16 L of water and 56.16 g of 
sediment (less than 2 mm) taken from the stilling ponds at Caspar 
Creek. This made a nominal concentration of approximately 1000 
mg/l in the drum as a whole. The paddle was operated for one 
minute before each sequence of 4 high sediment samples was taken 
(24 bottles in each sequence). A new water/sediment mixture was 
mixed for each batch of 24 bottles. The clear water drum was 
refilled for each batch.

Two batches of 24 bottles were run for each sampler giving 48 
samples total for each machine. Sets of 4 samples each were taken 
alternately in the high sediment and zero sediment drums starting 
with the high sediment. That is, for each sampler there were 6 
sets of 8 sample patterns consisting of 4 high sediment followed 
by 4 zero sediment samples. The 4 samples at each sediment level 
were intended to show how many samples were required for a sampler 
to adjust to a new sediment level. The measurement chamber in the 
Manning sampler was rinsed before the test was begun.

For the high sediment samples only, a reference sample was taken 
simultaneously with the pumped sample. The concentration in the 
clear water drum was assumed to be zero.

Before sampling began for each batch, eleven 750 ml samples were 
removed from the high sediment drum while the paddle was rotating. 
After each pumped and concomitant reference sample (which together 
totalled about 750 ml) were taken, one of these 11 samples was 
returned to the drum to maintain the approximate volume and 
concentration.

Standard gravimetric lab analyses were done on all pumped and 
reference samples.