Clark Jordan F, Hudson G Bryant, Davisson M Lee, Woodside Greg, Herndon Roy
Department of Geological Sciences, University of California, Santa Barbara, CA 93106, USA.
Ground Water. 2004 Mar-Apr;42(2):167-74. doi: 10.1111/j.1745-6584.2004.tb02665.x.
Critical for the management of artificial recharge operations is detailed knowledge of ground water dynamics near spreading areas. Geochemical tracer techniques including stable isotopes of water, tritium/helium-3 (T/3He) dating, and deliberate gas tracer experiments are ideally suited for these investigations. These tracers were used to evaluate flow near an artificial recharge site in northern Orange County, California, where approximately 2.5 x 10(8) m3 (200,000 acre-feet) of water are recharged annually. T/3He ages show that most of the relatively shallow ground water within 3 km of the recharge facilities have apparent ages < 2 years; further downgradient apparent ages increase, reaching > 20 years at approximately 6 km. Gas tracer experiments using sulfur hexafluoride and xenon isotopes were conducted from the Santa Ana River and two spreading basins. These tracers were followed in the ground water for more than two years, allowing subsurface flow patterns and flow times to be quantified. Results demonstrate that mean horizontal ground water velocities range from < 1 to > 4 km/year. The leading edges of the tracer patch moved at velocities about twice as fast as the center of mass. Leading edge velocities are important when considering the potential transport of microbes and other "time sensitive" contaminants and cannot be determined easily with other methods. T/3He apparent ages and tracer travel times agreed within the analytical uncertainty at 16 of 19 narrow screened monitoring wells. By combining these techniques, ground water flow was imaged with time scales on the order of weeks to decades.
人工回灌作业管理的关键在于详细了解补给区附近的地下水动态。地球化学示踪技术，包括水的稳定同位素、氚/氦-3（T/3He）测年以及专门的气体示踪实验，非常适合这些调查。这些示踪剂被用于评估加利福尼亚州橙县北部一个人工回灌场地附近的水流情况，该场地每年大约回灌2.5×10⁸立方米（20万英亩英尺）的水。T/3He年龄表明，补给设施3公里范围内大部分相对较浅的地下水的表观年龄小于2年；在下游更远的地方，表观年龄增加，在大约6公里处达到20年以上。利用六氟化硫和氙同位素进行的气体示踪实验是从圣安娜河和两个补给盆地开展的。这些示踪剂在地下水中被追踪了两年多，从而能够对地下水流模式和流动时间进行量化。结果表明，水平地下水的平均流速范围从每年小于1公里到大于4公里不等。示踪剂斑块的前沿移动速度约为质心移动速度的两倍。在考虑微生物和其他“对时间敏感”污染物的潜在迁移时，前沿速度很重要，而用其他方法不容易确定前沿速度。在19口窄筛监测井中的16口井中，T/3He表观年龄和示踪剂运移时间在分析不确定度范围内是一致的。通过结合这些技术，能够以数周至数十年的时间尺度对地下水流进行成像。
