Low-Flow Groundwater Sampling Becoming The Norm
With a growing emphasis placed on the application of low-flow sampling techniques for groundwater sampling, equipment manufacturers have begun developing new instrumentation to meet the needs of the environmental professional. Low-flow sampling has become the standard for groundwater sampling. The major drawback to the older method of sampling was the draw down impact (stress) that was created and the large amount of waste water that had to be disposed of properly, adding additional expenses. Both of these issues are now addressed through the low-flow technique.
Low-flow sampling allows the use of a number of submersible pumps such as down hole electric pumps, bladder pumps and surface peristaltic pumps. These pumps can be adjusted through a control box to slow the purge rate to a minimum so as not to create draw down. A multi-parameter water quality instrument is typically used in conjunction with the pumps. The water quality instruments are equipped with electrodes for continuous readings of pH, temperature, specific conductance, oxidation reduction potential (ORP), dissolved oxygen and turbidity. The instrument’s probe that houses these electrodes is placed into a flow cell allowing the slowly pumped water from the monitoring well to be moved across the electrodes. By examining the real time readings obtained by the instrument, the environmental professionals are able to observe when stabilization occurs signifying that the water flowing across the electrodes is representative of the surrounding groundwater in their screened interval. Once this stabilization is observed, water samples can then be taken for lab analysis.
Horiba Instruments has recently introduced the U-50 Series multi-parameter monitoring line of products. The Horiba U-50 addresses the needs of the end user by incorporating the required electrodes for real time measurements of pH, temperature, specific conductance, oxidation reduction potential (ORP), dissolved oxygen and turbidity as well a few added features such as GPS and your choice of turbidity sensors.
Horiba has listened to the requests of end users and produced a unit with the desired features. Most notable are the large easy to read LCD screen on the control unit that displays 11 parameters simultaneously, a sturdy easy to assemble and clean flow cell chamber, an up to date dissolved oxygen sensor that allows for quick membrane replacement in the field, a patented auto-calibration feature for ease when calibrations are required and an improved data management software program. On a budgetary note, Horiba has also made the U-50s affordable in comparison to other instruments with capabilities similar to the U-50 Series. Clearly Horiba has made strides to meet needs of today’s environmental professional.
I have used Horiba, Hydrolab and YSI instruments over the years and found both Hydrolab with a flow-through cell and YSI superior to Horiba. I agree both Hydrolab and YSI and more expensive than the Horiba instrument, but after having used these instruments for over 20 years for river/lake water quality profiling and over 10 years for low-flow groundwater sampling, I found them to be superior to the Horiba instrumentation.