skip to main content


Title: Quantifying groundwater travel time near managed recharge operations using 35S as an intrinsic tracer

By identifying groundwater retention times near managed aquifer recharge (MAR) facilities is a high priority for managing water quality, especially for operations that incorporate recycled wastewater. In order to protect public health, California guidelines for Groundwater Replenishment Reuse Projects require a minimum 2–6 month subsurface retention time for recycled water depending on the level of disinfection, which highlights the importance of quantifying groundwater travel times on short time scales. This study developed and evaluated a new intrinsic tracer method using the naturally occurring radioisotope sulfur-35 (35S). The 87.5 day half-life of 35S is ideal for investigating groundwater travel times on the <1 year timescale of interest to MAR managers. Natural concentrations of 35S found in water as dissolved sulfate (35SO4) were measured in source waters and groundwater at the Rio Hondo Spreading Grounds in Los Angeles County, CA, and Orange County Groundwater Recharge Facilities in Orange County, CA. 35SO4 travel times are comparable to travel times determined by well-established deliberate tracer studies. The study also revealed that 35SO4 in MAR source water can vary seasonally and therefore careful characterization of 35SO4 is needed to accurately quantify groundwater travel time. But, more data is needed to fully assess whether or notmore » this tracer could become a valuable tool for managers.« less
 [1] ;  [2] ;  [2] ;  [1]
  1. Univ. of California, Santa Barbara, CA (United States)
  2. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Publication Date:
Report Number(s):
Journal ID: ISSN 0022-1694
Grant/Contract Number:
Accepted Manuscript
Journal Name:
Journal of Hydrology
Additional Journal Information:
Journal Name: Journal of Hydrology; Journal ID: ISSN 0022-1694
Research Org:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org:
Country of Publication:
United States
54 ENVIRONMENTAL SCIENCES; 58 GEOSCIENCES; hydrologic tracers; travel time; retention time; sulfur-35; montebellow forebay; orange county recharge operation
OSTI Identifier:
Alternate Identifier(s):
OSTI ID: 1396551