Announcement: New contract for 3H/3He Apparent Age Determination
The USGS contract for 3H/3He dating through the Noble Gas Laboratory of Lamont-Doherty Earth Observatory of Columbia University expired September 30, 2005, but was extended for 9 months to allow time for final processing of all samples submitted prior to the expiration date.
Recently the Acquisition and Grants Branch for the United States Geological Survey awarded a new contract to the Noble Gas Laboratory of Lamont-Doherty Earth Observatory of Columbia University. The new contract became effective on November 1, 2005, and can be renewed annually up to 5 years.
Services Provided
Schedule 1033
- Total dissolved Helium in cc at STP per g water.
- Total dissolved Neon in cc at STP per g water.
- 3He/4He isotopic ratio for total dissolved Helium (corrected to date of sample collection, and also reported for the date of extraction of the Helium from the water), expressed as δ3He, where δ3He ≡ (Rs/Ra - 1)100 where Rs is the 3He/4He isotopic ratio of the sample and Ra is the 3He/4He isotopic ratio of air ≡ 1.384 x 10-6.
Lab code 2112
- Dissolved low-level tritium in tritium units (TU) corrected to value at date of collection of water sample, as submitted with water sample.
For samples in which the total dissolved Helium, total dissolved Neon, 3He/4He isotope ratio and tritium are determined, a preliminary interpretation of age will be attempted and reported for all samples in which the analytical data lead to calculated ages in the range of approximately 0 to 50 years. The age will be calculated using the recharge temperature and recharge elevation provided for each sample during submission from the project office. In such case that the recharge temperature and elevation are not provided, the contractor will provide a preliminary age calculation for assumed values of recharge temperature and recharge elevation, and state the assumed values in the report of analysis. The preliminary interpretation of age will include an estimate of age uncertainty accounting for propagation of analytical errors. The preliminary age will be reported in two ways:
- Age calculated assuming Helium sources from tritium decay, solubility equilibrium of the water sample with air, and Helium derived from excess air during recharge. This age estimate is referred to as the "uncorrected age".
- Age calculated as in (1), above, with further consideration of a terrigenic source of Helium with a 3He/4He isotope ratio assumed to be 2x10-8. This age is referred to as the "corrected age".
Delivery Schedule
Schedule 1033 and lab code 2112. Delivery within a total of 6 months from date of sample delivery to the contract lab.
- Total dissolved Helium
- Total dissolved Neon
- 3He/4He of total dissolved Helium, as δ3He
- Dissolved low-level tritium by 3He ingrowth.
Lab code 2112. Delivery within a total of 6 months from date of sample delivery to the contract lab (if only tritium by Helium in-growth is requested).
- Dissolved low-level tritium by 3He ingrowth
Schedule 1033. Delivery within a total of 4 months from date of sample delivery to the contract lab (if only Helium, Neon, and 3He/4He of total dissolved Helium, or d3He to be determined).
- Total dissolved Helium
- Total dissolved Neon
- 3He/4He of total dissolved Helium, as δ3He
Exceptions to the Delivery Schedule
The contractor will notify the USGS where there are delays in production due to laboratory instrument problems. They will also notify the USGS when normal production has resumed. The delivery schedule will be extended by the duration of laboratory down time.
Prices
- Schedule 1033 $487.50
- Lab code 2112 $487.50
What has changed between the previous contract and the new contract with Lamont-Doherty Earth Observatory?
- There was a price increase from $875 to $975. This represents an increase of $50 for Schedule 1033 and $50 for lab code 2112. The previous price had been in place for the past 5 years and the new price represents an increase of 2.3% per year if averaged over the past 5 years.
- Turn-around time was shortened from 1 year to 6 months, for lab code 2112 combined with Schedule 1033, 6 months for lab code 2112 separately, and 4 months for Schedule 1033 (without lab code 2112).
- Tritium samples will automatically be measured on relatively large volumes of degassed water sample, provided that the large-volume samples are collected and submitted to the contract lab.
- The Noble Gas Laboratory of Lamont-Doherty Earth Observatory is in the process of permitting USGS web access to their data base for tracking of sample progress.
- The Noble Gas Laboratory at Lamont-Doherty Earth Observatory has significantly raised the threshold so that many (but not all) samples with high dissolved gas pressures will not be lost in automatic processing.
Precautions and unacceptable samples
- Be careful to follow the instructions on proper collection of 3H/3He samples (see http://water.usgs.gov/lab/3h3he/sampling/).
- Never send water samples from landfills, sites that contain radioactive wastes, or any other sources that may have been contaminated with tritium. In FY 05 a serious tritium contamination event occurred at the Lamont laboratory that delayed the normal flow of USGS samples for more than 6 months.
Samples with large excess air or high terrigenic Helium content
Samples that contain large excesses of Helium may need to be split prior to injection into the mass spectrometer and will likely carry reported errors that are greater than 1 percent (2σ), and need to be identified as such. Because of unexpected concentrations of Helium, some samples may be lost during processing. If such occurs, the contract lab will report the loss to the COR and request whether the duplicate sample should be analyzed. Alternatively, the contract lab will report the sample as unable to analyze due to large excess of Helium.
In some cases, the USGS may provide the contract lab with a preliminary analysis of dissolved Helium. The Contract lab may use this preliminary analysis as a guide to modify/adjust analytical procedures so that samples that contain large excesses of dissolved Helium are not lost in extraction. If preliminary analysis of dissolved Helium is not provided by the USGS, and the sample is lost in extraction by the contact lab due to large, unanticipated excess Helium content, the contract lab will notify the COR that the sample was lost in extraction due to excess Helium. In this case the USGS will bear the full cost of the Helium extraction/analysis. The Contract lab will notify the COR and determine whether the USGS wishes the duplicate samples to be analyzed, using procedures capable of analyzing the Helium excess in the sample. If this problem is due to collection error, the USGS will pay.
If a sample cannot be analyzed due to an error on the part of the contract lab, the duplicate sample will be analyzed at no additional cost to the USGS.
If a sample cannot be analyzed due to a sampling error on the part of the USGS and this is not determined prior to sample extraction or analysis, the USGS will pay for this analysis. In this case, the contract lab will notify the COR and request permission to analyze the duplicate sample, if available, or request submission of a duplicate sample.
Recommendations
- Collect tritium samples in duplicate in plastic or plastic-coated glass 500 cc bottles with polycone seal, and, if glass, leaving a small headspace in the bottle (few ccs) for water expansion.
- Collect noble gas samples in duplicate copper tubes, with back pressure (see http://water.usgs.gov/lab/3h3he/sampling/). The analytical request form submitted to the CFC lab initiates this process and results in the contract lab shipping the sample containers directly to the Project Office. (see http://water.usgs.gov/usgs/lab/shared/request.html)
- Collect dissolved gas samples for He analysis in any cases where there may be a large He excess (old water, mixtures containing a fraction of old water, crystalline rocks). Have the He analyzed prior to submitting the tritium/helium-3 sample to Lamont. (See http://water.usgs.gov/lab/dissolved-gas/lab/helium.html) Report the measured He values when submitting the sample for noble gas analysis. Noble gas samples with large excess He can be run in a separate laboratory at Lamont-Doherty Earth Observatory where processing is controlled for individual samples with large excesses of dissolved gases.
Sample collection Procedures
Water samples for determination of total dissolved Helium, the 3He/4He isotopic ratio of total dissolved Helium, and total dissolved Neon will be collected and submitted in sample containers provided by the Lamont-Doherty Earth Observatory. Alternatively, if sample containers are obtained from a source other than the Contractor, it is the responsibility of the USGS to determine that the sample containers are suitable for Helium samples and suitable for attachment and introduction to the high-vacuum line used by the contract lab. Normally, sample containers will be approximately 3-foot lengths of 3/8 inch copper tubing sealed at each end with steel pinch-off clamps, or other suitable sample containers, with sample volume of approximately 40 cc. The water samples will be collected in the field by USGS personnel from various ground-water sources. USGS personnel will be responsible for proper collection of water samples, including (1) care in avoiding possible damage to ends of sample containers which might preclude proper connection to laboratory high-vacuum extraction lines, and (2) exclusion of gas bubbles during sample collection. (see http://water.usgs.gov/lab/3h3he/sampling/).
The contract lab will report samples that could not be extracted due to improperly sealed sample containers and/or damaged sample containers. USGS field personnel will collect samples in duplicate and provide both samples to the contract laboratory.
Water samples for determination of dissolved tritium, by 3He ingrowth, shall be collected by USGS personnel in sealed bottles of approximately 500 cc volume. The water samples shall be tightly capped in the field using bottles with polycone seal caps and, if glass bottles are used, a headspace of approximately 1 cc will be sealed in the bottle to prevent possible breakage due to expansion. If a separate water sample is not provided for 3H determination, water used in the 3He ingrowth determination of tritium shall be that water remaining from the original water sample after degassing on the high-vacuum extraction line.
Submittal Procedures
Submittal procedures are as before and given at http://water.usgs.gov/lab/3h3he/
Questions
Julian Wayland, 703-648-5847
Niel Plummer, 703-648-5841
US Geological Survey
432 National Center
12201 Sunrise Valley Drive
Reston, VA 20192
Our main telephone number is (703) 648-5847, and our fax number is (703) 648-5832. To contact us via email you may send your message to cfc@usgs.gov.
