Geochemical Imaging of Flow Near an Artificial Recharge Facility, Orange County, California

Abstract

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 ∼2.5 × 108 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 ∼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.

Quantifying groundwater discharge to Cockburn River, southeastern Australia, using dissolved gas tracers 222Rn and SF6

“…Approximately 5 mL of water was collected in preweighed evacuated vials, by submerging the vial beneath the water surface, and piercing a septum with a needle. SF 6 concentrations were measured on a gas chromatograph equipped with an electron capture detector using a head space method as described by Clark et al [2004].…”

Gas Transport below Artificial Recharge Ponds: Insights from Dissolved Noble Gases and a Dual Gas (SF6 and 3He) Tracer Experiment

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Characterisation of hyporheic exchange in a losing stream using radon-222

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