Equipment & Supplies: Water-Quality Field instrumentation

                                             December 7, 1977


QUALITY OF WATER BRANCH TECHNICAL MEMORANDUM No. 78.02

Subject: Equipment & Supplies: Water-Quality Field instrumentation

The Water Quality Advisory Committee has requested that the 
Quality of Water Branch periodically advise the Districts of 
water-quality field instruments that are recommended or considered 
reliable for field work. Quality of Water Branch Technical 
Memorandum No. 76.03 listed several instruments that were 
considered reliable at that time. In general, the instruments 
listed in that memo still are considered to be reliable, but in 
several cases newer models have been developed which represent 
improvements or refinements of the older models. On this basis, 
the following instruments are recommended by manufacturer only and 
not by model. Specific models will be recommended only when one 
model is known to be clearly superior to other models.

Dissolved oxygen         Yellow Springs Instruments

Specific Conductance Electronic Switchgear, Beckman, Hydro Lab

pH Meters                Leeds & Northrup, Orion, Beckman

pH Electrodes            Orion, Corning, Sargent-Welch

The above list does not imply that only instruments manufactured 
by these companies should be used in our field work, nor does it 
imply official endorsement by the Geological Survey. We realize 
that there probably are other instruments that can be used 
effectively in field operations. In fact most instruments 
currently available for the above measurements will meet Survey 
specifications for accuracy but insufficient data are available to 
judge their field use reliability. However, it should be kept in 
mind that the reliability of a measurement made with any 
instrument depends on proper calibration, operation, care, and 
maintenance. Without these, no instrument should be expected to 
produce proper results.

The Quality of Water Branch, through the cooperation of many 
Districts, has been conducting a continuing but limited evaluation 
of selected field instruments. A past example is the evaluation of 
the NERA Hydrolab multiparameter recording unit (QW Branch Memo 
No. 75.16). Currently we are asking for evaluation information on 
the ISCO sampler (QW Branch Memo No. 77.09).

Last March the Branch purchased four Graphics Controls combination 
pH gel electrodes (GC 51148). These were sent to four different 
field offices for experimental use, and the results of this 
limited test showed them to be unreliable. Recently we have 
purchased two multiparameter "Water Quality Checkers", Horiba 
model U-7. These will first be laboratory checked against the 
manufacturer's specifications and then sent to several Districts 
for reliability and performance evaluations.

The recent replacement of the barrel filter unit with the plate 
filter and peristaltic pump unit has resulted in inquiries about 
the proper tubing to use in the heads of the peristaltic pumps. 
For water filtrationJ medical grade silicone tubing appears to 
offer relatively long pumping life plus #reedom from contamination 
with trace metals and other inorganics. However, silicone tubing 
has only a fair pressure rating and can "ballon" under difficult 
filtration operations. "Food grade" tygon tubing has better 
pressure capacity, but is stiffer and will cause the pump motor to 
work harder. This may cause the motor to overheat under some 
conditions. Teflon tubing is not recommended because it is too 
stiff, and the new Fluron F-5500R tubing should not be used 
because it may bleed contaminants after prolonged usage.

Instrument manufactures have redesigned many pieces of equipment 
to feature digital readouts and to make the overall package 
smaller. One example is the new pocket-sized pH meter. The Alaska 
District has reported excellent success with a Digi-Sense meter 
and the Northeastern Region has recently acquired a similar type 
pH meter (X-Rite) for testing. The Branch would appreciate 
comments from other offices that had experience with similar 
units.

The Branch will be reviewing equipment recommendations 
periodically as new equipment is developed and the Division's 
needs change. You are encouraged to relay your equipment 
experiences, observations, and needs, as well as your 
recommendations for equipment evaluations, to the Quality of Water 
Branch through your Regional Water-Quality Specialist.



                         R. J. Pickering

A, B, S, FO, PO