The Reston Groundwater Dating Laboratory

Dissolved Gas N2 / Ar Sample Collection Procedure

(Also for Dissolved Helium Sample Collection)


Sampling Air or Unsaturated Zone Gas

The bottles and stoppers used for collection of dissolved gas N2 / Ar are supplied by the USGS. Septum Bottle Picture USGS personnel may order bottles from internal USGS only one stop shopping stock number Q615FLD - a set of two preweighed bottles with stoppers and one needle. If you are outside the USGS, please email cfc@usgs.gov or call 703-648-5847 to request bottles.

Sampling Instructions:

The N2 / Ar bottles are date coded by the first two digits of the bottle number. 18Y**** bottle number is a 2018 bottle. Do not use bottles more than two years old.
  1. Remove the stopper from the bottle. Insert a needle into the stopper until the tip slightly exits through the bottom of the stopper. (See illustrations below) and Picture Here.
  2. Fill a 2-4 liter plastic or metal beaker with raw unfiltered sample water. Sample flow rate can be between 500 ml and 2 L per minute.
  3. Place the water discharge tubing at the bottom of the 150 mL sample bottle. The tubing can be C-flex, tygon, copper, Teflon, etc. After it is filled place the bottle in the water filled beaker. The water should be flowing into the bottle when it is put in the beaker. Do not filter the sample, use raw sample.
  4. Make sure that no bubbles are adhering to the sides of the bottle. Shake the bottle or jiggle the tubing to dislodge bubbles if present. Place the stopper / needle combination under water and purge the needle of air either by flicking it until all bubbles stop appearing or by directing the discharge from the tubing into the needle until no more air appears.
  5. After at least 500 mL total have flushed through the bottle, withdraw the tubing and insert the stopper in the bottle while the bottle is submerged in the water. Make sure to push the stopper all the way down. Take duplicates of all samples, two bottles total for N2/Ar at each site.
  6. Remove the needle from the stopper while the bottle is still submerged. Properly dispose of all needles.
  7. Take duplicates of all samples at each site, two bottles total for N2/Ar.
  8. Record the (a) sample name, (b) water temperature and (c) estimated recharge altitude (elevation of the well can be substituted) on the label attached to the foam sleeve. Do not put a label on the bottle. The bottle with stopper is pre-weighed. Do not switch stoppers from bottle to bottle.
  9. Store samples on ice / refrigerated or at least as cool as the temperature of the sampled water. This will keep the stoppers from pushing out if the sample warms up. Store sample bottles upside down or on their side to keep any bubble that forms away from the stopper. A bubble may form in the sample while stored. This is normal.
  10. Ship samples on ice overnight to:
    USGS Groundwater Dating Lab
    12201 Sunrise Valley Dr. ms432 rm 5B-353
    Reston, VA 20192
    Phone: 703-648-5847
    Email: cfc@usgs.gov
    Do Not ship samples on a Friday or before a federal holiday.
  11. Include a prepaid return label if you desire to have your cooler / container return shipped.