Department Water Resources and Drinking Water
Guidelines for external projects
If you would like to analyze noble gases or transient tracers in water samples in one of our labs, please be aware that we can handle external projects either on a commercial basis (see price list) or as a non-commercial scientific collaboration.
To propose a project or collaboration, please provide a short summary with the following information (about 1 page, contact: Matthias Brennwald, matthias.brennwald@cluttereawag.ch):
- What is the scientific background of the project?
- How many samples will be required?
- Can you provide manpower for the lab work?
- What is the anticipated output of the project, and how will we be involved in this (e.g. publications, reports, etc.)?
Sample quality is in your responsibility. Please read and follow the manual for water sampling carefully. Commercial samples that cannot be analyzed properly due to poor sample quality will be charged the full price.
Price list
Commercial Measurements of Tritium, Noble Gases, CFCs, SF6 and Radon
For further information please contact Matthias Brennwald, matthias.brennwald@cluttereawag.ch
Prices do not include VAT or shipping costs. Note that prices are subject to changes without notice. We do not accept any time constraints for gas analysis. Extended interpretation will be charged separately depending on volume of work required.
| Tracer Price per Sample | |
|---|---|
| 3H | CH 700.- |
| He - Xe [1] | CHF 2'000.- |
| 3H, He - Xe [1, 2] | CHF 2'500.- |
| CFCs (+ Ar, N2, CH4) [3] | CHF 500.- |
| SF6 (+ CFC-12) | CHF 700.- |
| 222Rn | CHF 100.- |
| Sampling [4] | CHF 1'000.- / per day |
[1] He, 3He/4He, Ne, 20Ne/22Ne, Ar, 40Ar/36Ar, Kr, Xe
[2] 3H/3He - dating
[3] CFC-11, CFC-12, CFC-113
[4] For further information about taking water samples for gas analysis see section Sampling.
Sampling procedures
Groundwater-Sampling for Noble Gases / CFCs: procedures for samples to be analysed at the ETH noble gas facility by the Environmental Isotopes Group.
Most of these steps also apply to samples from other water reservoirs, e.g. lakes.
The sample containers consist of a copper tube which is mounted on an aluminum rack (see Figure 1). On both ends, the tube is fixed by steel clamps. The clamps can be closed with a central screw by the use of a large hexagonal spanner. By closing the clamps, the copper tube is shut absolutely gas tight. The clamps have to be tightened as much as possible. It is best to fix the sampler between your legs or on your hip and close the screws as much as you can with the spanner, but without any additional tools. The washers between the two stamps of the clamps define the closed state. The clamps are correctly closed if there is no space between the stamps and the washers.
The tube should be approximately centered on the rack and stick out on both sides by 5 to 10 cm. These end-pieces are needed for the connections both in the field and in the lab. A certain bending of the end-pieces during closure of the clamps is normal. On the further transport, however, care must be taken to avoid further bending or even breaking of the end-pieces.
Well selection and preparation
Not all wells or pumps are suitable for noble gas sampling. It is very important that during sampling any contact of the water with air or any other gas phase is avoided. Closed boreholes are necessary, open wells or springs hardly work, because they allow gas exchange. The water should be kept under enough pressure to avoid any degassing. Ideal are artesian wells with sufficient pressure or wells pumped by a submersible pump. Sucking pumps should be avoided, they are most likely to induce degassing. Pressure tanks often contain a gas phase under variable pressure which may exchange with the water and induce uncorrectable gas fractionations. If pressure or storage tanks are present, the water should be taken before it enters the tanks. Sampling after chemical treatment (e.g., chlorinization) should also be avoided if possible.
Before sampling, the well should be sufficiently flushed (pump out at least once the volume of the borehole). During flushing, temperature and electrical conductivity may be checked to see if the values stabilize. After flushing, a tight connection between the well and the copper tube has to be established. Ideal sites of connection are taps immediately near the well head. If the pressure can be regulated, keep it as high as the connections allow. Try to avoid a rushing noise in the tap, as it may indicate turbulence or degassing.
Connection
The copper tube is connected to the pump, tap or other point of water withdrawal through flexible plastic tubing. Often, several hoses need to be connected in order to reduce the diameter to the size of the copper tube. We usually deliver a piece of tubing that fits tightly on the copper tube. We recommend to use this piece as the last part in the connection. In order to withstand water pressure, we use inner braided PVC tubing, and in order to allow detection of bubbles, we prefer transparent tubing. All connections, also on the copper tube, should be secured with hose clamps. The complete tubing has to be sufficiently flushed (about one minute) and checked for bubbles. Bubbles tend to stick at connections. They can be removed by squeezing and bending the hoses or knocking against the tubing. Sometimes, air is sucked in at connections of the tubing, particularly if the diameter of the tubing increases in flow direction. Try to avoid such configurations (always go from large to small diameter) and thighten all fittings to avoid leakage. Slight leaking of water out of the tubing may be tolerated. If bubbles form due to degassing of the water, an increase of pressure can often help to suppress degassing. In general, the pressure should be as high as the stability of the connec-tions allows. The stability can be checked easily by putting a thumb on the outlet. Usually, the pressure is fine when the water jet after the copper tube reaches for several meters. If the pressure is low or if it is impossible to avoid bubbles, take the sample anyway but mark it accordingly.
Once the system is rinsed, first close the outlet steel clamp completely, and then the clamp on the inlet side. If the connections break before the inlet side is closed, but the sample tube is still completely filled with water, close the inlet clamp and take the sample anyway, but mark it. However, if you have enough spare copper tubes, remove the bad sample tube, insert a new copper tube and take a new sample. Write down that the copper tube was exchanged.
Sample identification and additional data
The aluminum racks have numbers imprinted on their back or side. Use these numbers to identify the samples. Please do not put any stickers on the samplers or write on them. For each sample, note the number, location, well name, date and approximate time of sampling in your fieldbook. To interpret noble gas data, we need some additional data, such as temperature and salinity (electrical conductivity) of the water, altitude of the well, altitude of the presumed recharge area, and if possible mean annual temperature in the recharge area. At least the water temperature and the approximate elevation at the sampling site should be known.
The most important points step by step
- Pump long enough to flush the borehole completely.
- Find a suitable tap or other outlet of the well/pump for connection.
- Avoid pressure tanks, sucking pumps, and any contact with air or gas phases.
- Connect the copper tube by a tight combination of tubing.
- Check if the connections withstand the pressure when the outlet is closed.
- Flush the tubing, remove bubbles in the hoses, keep pressure high.
- Check that the Cu-tube is approximately centered on the clamp (equal ends).
- Close clamp at the outlet completely (no free space), then at the inlet .
- Identify the samples (number on the rack, location, date).
- If possible note temperature, conductivity and altitude of the well.
- Protect the ends of the copper tube from bending and breaking.