Surface & Ground Water Monitoring

That water is a precious commodity speaks for itself. What is perhaps a little surprising is that there appears to be a collective body of opinion from a substantial portion of European citizens to make sure that polluted water is made clean and that clean water remains clean.  This collective desire was the primary reason for the establishment, in 2000, of the European Water Framework Directive (EWFD). This has a direct impact on all water sources and it is particularly interesting in our sector that there should be a presumption that groundwater should not be polluted at all.

Regulatory directives such as the EWFD have had a huge impact on the development of better water sampling devices and water quality meters and standards are continually being improved by introductions of schemes such as MCERTS. New guidelines are continuously being published and an interesting read is: Ground-Water Sampling Guidelines for Superfund and RCRA Project Managers.

At Van Walt we spend much time, money and effort to keep up with developments. We do this through a continuous programme of staff training, regular dialogue with manufacturers for improved equipment which complies with current standards and we introduce ever increasingly stringent and auditable internal reports of equipment performance. The health and safety of our customers is paramount and we have chosen pumps which can run on low voltage DC, we supply post rental calibration certificates and are developing and offering tailored and product specific training to our customers.

In consequence of this ongoing development we have a range of pumps, water quality meters, level monitoring equipment and sampling devices available for purchase or rent which meet the up to date requirements of our customers involved in environmental research of ground and surface water.  In many cases, we are making available accessories for remote monitoring by a selection of telemetry options which offer secure transmission to your desktop.  Data security is paramount and the newer modems are ensuring that data loss is not only minimised but in some cases eliminated by the inclusion of duplicate data options.

Our equipment programme offers a wide choice so that the right tool can be chosen for the right job for uncompromised, consistent and repeatable results.

High Volume Purging
Prior to March 2011, high volume purging and sampling was mandatory for groundwater investigations on behalf of environmental research. After a well is constructed, well development should occur as soon as possible but not sooner than 48 hours after the swelling of the bentonite is completed. Thereafter groundwater sampling may take place after a 14 day wait. The well must then be purged at 3 times the wet well volume which includes the filter sand pack, prior to each sampling. During this process field parameters should be measured. Clearly, high volume purging produces much waste water which must be disposed of correctly and this can be expensive. Additionally, this technique may be risky for low recharge wells as it may draw the water level below the filter section of the well and introduce air to the sample.

Low Volume Purging
Low flow or micro purging is now an accepted method in the United States (Puls and Barcelona 1996) and in the UK following the publication of BS 10175:2011 in March 2011. With this type of sampling, a pump is hung in the well opposite the most contaminated zone in the well screen and adjusted to a very low speed. There is no need to renew (purge) the water in the blind section of the well. By using this method, the volume of the purge water can be reduced, sometimes significantly over the conventional purging method. Water quality indicator parameters are measured (pH, EC, DO and increasingly turbidity: EC and DO are the best stability indicators) until stability is achieved. After 3 successive readings of the water quality indicator parameters have stabilized (recorded after a minimum of one tubing, pump and flow-cell volume) per cycle then sampling can begin. It is customary, but not written in stone that drawdown is kept within 10 and 20cm and this should be regularly checked with a dipmeter. This technique is excellent for slow recovering wells and saves much time and purge water disposal volumes. A dedicated pumping system for each well is recommended. This ensures minimal mixing of the stagnant water above the screen.

Passive or Diffusion Sampling
No purge devices are now beyond the infancy stage in the United States and have been gaining more acceptance since their first introduction in 2006. No doubt the technique will gain popularity in the EU. The idea is to deploy a device and leave it in a well for a certain period which may vary depending on the instrument used. Diffusion samplers need to reach an osmotic equilibrium with the surrounding water. Diffusion samplers are not a “one size fits all” solution and some are good for VOC’s and SVOC’s, such as the GORE samplers whereas others might be good for inorganics such as Columbia’s RPP samplers. The common factor is that there is minimal disturbance in the water and whereas samplers such as the Hydrasleeve are an attractive low cost solution care must be taken that they do not disturb the sediment within the well which can cause excessive turbidity and perhaps cannot be implemented for sensitive analytes such as Redox, pH and Turbidity. Other systems are coming on the market and some offer a completely different solution for a buffet of compounds.

Of great interest is the Snap Sampler from Prohydro (New York State) which does not work on the principle of diffusion but rather grabs or “snaps” a sample of groundwater. Of all the samplers available at the moment this has the best proven track record of repeatability. Unlike the Hydrasleeve, it does not disturb the well water and therefore is perfectly suitable for all analytes. Where a conservation liquid needs to be used (such as metals) then that facility is catered for.

Passive, diffusion or no purge sampling has three huge benefits: They save time and money (50-80%), the logistics are simple and above all it is “green” technology.