REPORTS--Sample Collection and Analysis for Tritium In Reply Refer To: April 25, 1988 WGS-Mail Stop 412 OFFICE OF WATER QUALITY TECHNICAL MEMORANDUM NO. 88.03 Subject: REPORTS--Sample Collection and Analysis for Tritium The foIlowing information was prepared by Robert Michel to assist District personnel on the issue of tritium analysis. The "Choice of Precision" section provides guidelines as to which of the four analyses available in the Water Resources Division (WRD) Analytical Services Catalogue best fits a given geographic region and project objective. All four analyses are available through the WRD National Water Quality Laboratory--the actual analyses are done for methods 0452, 0460, and 0624 in the USGS Tritium Laboratory in Reston, and for method 1043 at the University of Miami. Bob Michel is available by phone at FTS 959-5968 to answer questions concerning sampling of water for tritium analysis, choice of laboratory method, and project-design issues concerning tritium. SAMPLE COLLECTION Polyethylene bottles are acceptabIe for most samples, particularly if storage times are short. However, for low- level samples, glass bottles are preferable. For example, a narrow-mouth flint glass bottle (#16151-107 from Van Waters and Rogers catalogue) with a 500 polyseal cap (16217-103) would be an excellent choice for a 5OO-ml sample. Although not necessary, best results for waters with low concentrations are obtained if the bottle has been flushed with dry argon or nitrogen to remove any atmospheric water vapor. Water should be drawn into the bottle unti1 it reaches near the top and then capped. The bottles should not be pre- rinsed with sample water. The cap should be taped with electrical or similar tape to prevent it from working loose during transit. Date of collection should always be given as results are age conected to time of collection. CHOICE OF PRECISION When choosing a level of precision, consideration should be given to both the tritium concentration expected and the accuracy desired. Present-day tritium concentrations in precipitation in the United States are on the order of 10 Tritium Units (TU) or less for most of the Southern and Western States and in the 3O-4OTU range in the Upper Midwestern and East Coast States. There are four levels of precision available through the National Water Quality Laboratory (NWQL) for tritium analyses. These analyses have a detection limit at the 2 sigma level of 8TU (one TU = 3.2 picocuries/liter of water), l.8TU, O.8TU and 0.2TU. As a rule, the maximum precision of a sample will be the larger of either plus or minus 5% of the sample's tritium concentration or the detection limit. 0452 8-20000TU Liquid Scintillation Counting 25 ml This method involves direct counting of the water sample without electrolytic enrichment. Its uses are limited to determining whether there are substantial amounts of post-bomb tritium in water in the Northen United States. It can also be used to study the migration of the bomb tritium peak through unsaturated-zone soils. 0460 1.8-1000TU Electrolytic Enrichment/Liquid 250 ml Scintillation Counting This method involves electrolytic enrichment and liquid scintillation counting. It is the minimum level of accuracy now required for tritium studies in the Southern and Southwestern States. In most ground-water studies, it will provide an indication as to whether post-bomb tritium has entered the system under study in a significant amount. In the Northern U.S., it is sufficient for studying tritium distribution in present-day lakes and rivers and the ground waters that are strongly affected by them. 0624 0.8-500TU Electrolytic Enrichment/Liquid 500 ml Scintillation Counting This method involves greater enrichment and liquid scintillation counting. It is suitable for studies where the gradient of the tritium concentration within the water table is important. It will be able to distinguish differences between tritium concentrations within the water table that can be used to study flow directions and rates. It is the level of accuracy presently suggested for most studies in Southern and Southwestern States. All Carbon-l4 samples should be analyzed using this method to check for contamination of recent water. 1043 O.2-5OOTU Electrolytic Enrichment/Gas Counting 1000 ml This method involves electrolytic enrichment with gas counting. It is the most sensitive method available through the NWQL. This method should be used when low tritium concentrations are expected. It can be used to determine if small amounts of bomb tritium have entered a system (i.e.