³H and ¹4C as Tracers of Ground-Water Recharge

by John A. Izbicki, U.S. Geological Survey, San Diego, United States,
Robert L. Michel, U.S. Geological Survey, San Diego, United States,
Peter Martin, U.S. Geological Survey, San Diego, United States,

Document Type: Proceeding Paper

Part of: Irrigation and Drainage: Saving a Threatened Resource—In Search of Solutions


Surface spreading of water from the Santa Clara River is used to recharge aquifers underlying the Oxnard Plain. These aquifers are divided into an upper system about 400 feet thick, and a lower system more than 1,000 feet thick. In previous studies, it has been reported that surface spreading recharged aquifers in both the upper and lower systems. Water from most wells perforated in the upper system has tritium levels consistent with decay-corrected concentrations found in water recharged after 1952 when tritium levels increased as a result of atmospheric testing of nuclear weapons. Water from most wells in the lower system does not contain measurable tritium and must have been recharged prior to 1952. Carbon-14 ages estimated for water from wells in the lower system range from recent to about 25,000 years before present. These data show that the lower system is not effectively recharged by surface spreading.

Subject Headings: Probe instruments | Groundwater recharge | Recharge wells | Surface water | Water surface | Weapons | Carbon | Rivers and streams

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