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<br />TRITIUM <br />Tritium is a hydrogen atom with two additional neutrons (3H). It is rare in <br />nature with the only natural source being the upper atmospheres <br />(stratosphere) interaction with solar radiation (cosmogenic source). <br />Precipitation brings it from the upper atmosphere to the earth's surface where <br />some can recharge ground water. Since it has a short decay half-life (12.43 <br />years), only modern waters contain tritium. Five to six half-lifes give a range <br />of about 65 years (modern water). Older waters would be termed sub or pre <br />modern, recent, ancient or fossil (connate) depending on the magnitude. <br />The tritium concentrations measured for this project are shown on Figure 3 <br />with the classification system of Clark and Aravena (2002). Concentrations less <br />than 5 TU are sub or pre-modern water since the tritium has decayed away. <br />Concentrations above 5 tritium units (TU) are classified as modern water and <br />above 15 TU as having bomb tritium influence. Tritium was produced during <br />atmospheric nuclear bomb testing in the 1950's. <br />FIGURE 3- TRITIUM (3H) AGES, SAGE CK MINE <br />0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 <br /> Tritium (3H) Concentration, TU <br />The Yampa Rive r sample was measured as 9.13 TU. This was greater than 5 TU <br />so Yampa River water was modern water younger than 65 years. Both samples <br />of Monitor Well COV23 measured tritium concentrations less than 5 TU so they <br />were classified as pre-modern water that was older than 65 years. No samples <br />showed influence of bomb tritium. <br />5